Patent Application
20130128206
1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for manufacturing the same.
2. Description of the Related Art
In recent years, liquid crystal has been used for a variety of devices; in particular, a liquid crystal display device (liquid crystal display) having advantages of thinness and lightness has been used for displays in a wide range of fields.
For a larger and higher-resolution display screen, shorter response time of liquid crystal has been required, and development thereof has been advanced.
As a display mode of liquid crystal capable of high-speed response, a display mode using liquid crystal exhibiting a blue phase is given. The mode using liquid crystal exhibiting a blue phase achieves quick response, does not require an alignment film, and provides a wide viewing angle, and thus has been developed more actively for practical use (for example, see Patent Document 1).
Liquid crystal display devices are favorably used for a touch panel which is operated by touching a display screen, a mobile device, and a large outdoor display screen. In the use of such devices, physical impact is applied to the liquid crystal display devices in many cases, and accordingly, the liquid crystal display devices are required to have high resistance to physical impact.
An object is to provide a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics.
An object is to provide a liquid crystal display device with high reliability and high performance.
In a liquid crystal display device in which a liquid crystal composition is interposed between a pair of substrates, a spacer which keeps a gap between the substrates is formed in a self-aligned manner by back exposure using, as a mask, a light-blocking film provided under the spacer. The spacer is provided for a light-transmitting substrate provided with a semiconductor element and an electrode layer of a liquid crystal element. Note that in this specification, a substrate provided with an element layer may be referred to as an element substrate and a substrate facing the element substrate may be referred to as a counter substrate.
In the liquid crystal display device, the spacer has a function of controlling a height of a space which is sandwiched between the facing substrates and filled with the liquid crystal composition (the space is also referred to as a cell gap), and a function of keeping the height against external impact such as pressure.
In the invention disclosed in this specification, part of a photosensitive resin layer, which is provided over a region other than a light-blocking film serving as a mask, is removed in a step of forming a spacer; thus, the spacer is provided only over the light-blocking film. The light-blocking film is one continuous film; accordingly, regions of the surface thereof have substantially the same height and the spacer can be stably provided.
Further, since the spacer is provided for the element substrate, the photosensitive resin layer can be formed by a coating method offering good coverage or the like so that unevenness caused by the element layer in a region for forming the spacer is planarized. Therefore, the spacer can be stably provided with good adhesion even in a region with some unevenness.
According to the invention disclosed in this specification, the spacer can be stably provided in a substantially flat region with less steep unevenness and fewer steep steps in the liquid crystal display device; thus, damage and a shape defect of the spacer due to physical impact can be reduced and the liquid crystal display device can have high resistance to physical impact.
Accordingly, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided. Further, a liquid crystal display device with high reliability and high performance can be provided.
As the liquid crystal composition, a liquid crystal composition exhibiting a blue phase can be favorably used.
A blue phase is exhibited in a liquid crystal composition having strong twisting power and the liquid crystal composition has a double twist structure. The liquid crystal composition shows a cholesteric phase, a cholesteric blue phase, an isotropic phase, or the like depending on conditions.
A cholesteric blue phase which is a blue phase includes three structures of blue phase I, blue phase II, and blue phase III from the low temperature side. A cholesteric blue phase which is a blue phase is optically isotropic, and blue phase I and blue phase II have body-centered cubic symmetry and simple cubic symmetry, respectively. In the cases of blue phase I and blue phase II, Bragg diffraction is seen in the range from ultraviolet light to visible light.
A chiral material is used to induce twisting of the liquid crystal composition, align the liquid crystal composition in a helical structure, and make the liquid crystal composition exhibit a blue phase. For the chiral material, a compound which has an asymmetric center, high compatibility with the liquid crystal composition, and strong twisting power is used. In addition, the chiral material is an optically active substance; a higher optical purity is better and the most preferable optical purity is 99% or higher.
An embodiment of a structure of the invention disclosed in this specification is a liquid crystal display device including a first substrate and a second substrate each having a light-transmitting property with a liquid crystal composition including nematic liquid crystal and a chiral material and exhibiting a blue phase interposed therebetween; and a first electrode layer, a second electrode layer, a light-blocking film, and a spacer which are provided between the first substrate and the liquid crystal composition. The spacer is provided over the light-blocking film. An entire bottom surface of the spacer overlaps with an upper surface of the light-blocking film.
Another embodiment of a structure of the invention disclosed in this specification is a liquid crystal display device including a first substrate and a second substrate each having a light-transmitting property with a liquid crystal composition including nematic liquid crystal and a chiral material and exhibiting a blue phase interposed therebetween; an element layer including a light-blocking conductive film, and an insulating film which are provided between the first substrate and the liquid crystal composition in this order from the first substrate side; and a first electrode layer, a second electrode layer, and a spacer over the insulating film. The spacer is provided over the light-blocking conductive film. An entire bottom surface of the spacer overlaps with an upper surface of the light-blocking conductive film.
Another embodiment of a structure of the invention disclosed in this specification is a method for manufacturing a liquid crystal display device, including the steps of forming a first electrode layer, a second electrode layer, and a light-blocking film in contact with an insulating film provided for a first substrate having a light-transmitting property; selectively forming a photosensitive resin layer over the insulating film and the light-blocking film; selectively irradiating the photosensitive resin layer with light passing through the first substrate with the use of the light-blocking film as a mask; removing a region of the photosensitive resin layer, which is irradiated with the light, to form a spacer; forming a sealant over the insulating film so as to surround the first electrode layer, the second electrode layer, and the spacer; filling the inside of the sealant with a liquid crystal composition exhibiting a blue phase so as to be in contact with the first electrode layer, the second electrode layer, and the spacer; and providing a second substrate in contact with the sealant and the spacer so as to encapsulate the liquid crystal composition.
Another embodiment of a structure of the invention disclosed in this specification is a method for manufacturing a liquid crystal display device, including the steps of forming an element layer including a light-blocking conductive film over a first substrate having a light-transmitting property; forming an insulating film over the element layer; forming a first electrode layer and a second electrode layer in contact with the insulating film; selectively forming a photosensitive resin layer over the insulating film so as to overlap with the light-blocking conductive film; selectively irradiating the photosensitive resin layer with light passing through the first substrate with the use of the light-blocking conductive film as a mask; removing a region of the photosensitive resin layer, which is irradiated with the light, to form a spacer; forming a sealant over the insulating film so as to surround the first electrode layer, the second electrode layer, and the spacer; filling the inside of the sealant with a liquid crystal composition including nematic liquid crystal and a chiral material and exhibiting a blue phase so as to be in contact with the first electrode layer, the second electrode layer, and the spacer; and providing a second substrate in contact with the sealant and the spacer so as to encapsulate the liquid crystal composition.
The light-blocking film may be formed in the same step and using the same material as those of the first electrode layer, the second electrode layer, or the light-blocking conductive film (e.g., an electrode layer of a transistor or a wiring layer) included in the element layer. Further, part of the light-blocking conductive film (e.g., an electrode layer of a transistor or a wiring layer) included in the element layer may be used as the light-blocking film.
The light-blocking film may be a single film or may include a plurality of films. In the case where the light-blocking film includes a plurality of films, a light-blocking region can be controlled by shapes of the films or a stacking structure.
The photosensitive resin layer covering at least part of the light-blocking film may be selectively formed by an inkjet method or a printing method. Alternatively, the photosensitive resin layer may be selectively formed in such a manner that a photosensitive resin layer is formed by a coating method or the like over the entire surface of the element substrate and then part thereof is removed with the use of a mask.
When the liquid crystal composition is polymerized to be a high molecular compound, the liquid crystal composition is stabilized and the temperature range in which a blue phase is exhibited can be extended. Treatment in which a liquid crystal composition is polymerized to be a high molecular compound is referred to as polymer stabilization treatment. As a liquid crystal composition exhibiting a blue phase, a liquid crystal composition including nematic liquid crystal and a chiral material is used. In the case where polymer stabilization treatment is performed, a polymerizable monomer and a polymerization initiator are further included in the liquid crystal composition. Note that polymer stabilization treatment can be performed in such a manner that a liquid crystal composition is irradiated with light to be a high molecular compound with the use of a photopolymerizable monomer and a photopolymerization initiator, for example.
The liquid crystal compound subjected to polymer stabilization treatment loses (or has lower) fluidity and becomes a solid with a low impact-absorbing property (or becomes almost a solid). In a liquid crystal composition with a low impact-absorbing property, impact caused by movement of a spacer more adversely affects display quality to cause a display defect; therefore, a stable spacer resistant to physical impact, such as the spacer disclosed in this specification, is effective.
According to an embodiment of the present invention, a technique by which a liquid crystal display device is more resistant to physical impact and can retain high-quality display characteristics can be provided.
According to an embodiment of the present invention, a liquid crystal display device can obtain high reliability and high performance.
In the accompanying drawings:
FIGS. 4A1, 4A2, and 4B illustrate an embodiment of a liquid crystal display device;
FIGS. 5A1, 5A2, 5A3, 5B1, 5B2, and 5B3 illustrate structures of a spacer of a liquid crystal display device; and
Embodiments will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the following description of the embodiments. In the structures to be given below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and explanation thereof will not be repeated.
Note that the ordinal numbers such as “first”, “second”, and “third” in this specification are used for convenience and do not denote the order of steps and the stacking order of layers. In addition, the ordinal numbers in this specification do not denote particular names which specify the present invention.
A liquid crystal composition and a liquid crystal display device including the liquid crystal composition, which are embodiments of the present invention, will be described with reference to
In a liquid crystal display device, a spacer has a function of controlling a height of a space which is sandwiched between facing substrates and filled with a liquid crystal composition (the space is also referred to as a cell gap), and a function of keeping the height against external impact such as pressure.
A spacer is generally provided for a counter substrate, and then an element substrate and the counter substrate are attached to each other so that the spacer is placed in a space between the substrates; thus, the spacer can be placed inside the liquid crystal display device.
However, since an element layer is provided under an insulating film over which the spacer is provided, a surface of the insulating film has unevenness or a step due to a transistor, a conductive film, a component for adjusting a cell gap, or the like included in the element layer. When physical impact is externally applied to the spacer provided in an unstable region due to unevenness or a step, the spacer might be damaged or moved because of local concentration of the force or the like, leading to alignment disorder of a liquid crystal composition and a display defect due to the alignment disorder.
Therefore, it is important that the spacer has high resistance to physical impact and is stably provided over a flat region in the liquid crystal display device in order to prevent damage and a shape defect due to physical impact.
In the method in which a spacer provided for a counter substrate is provided over an element layer by attaching an element substrate and the counter substrate, it is difficult to control alignment in an attaching step, and misalignment of the spacer easily occurs. As a result, the spacer is provided over an unstable region and the reliability of the liquid crystal display device is lowered. Further, a yield in the manufacturing process of the liquid crystal display device is decreased, and thus productivity is lowered.
In the liquid crystal display device of this embodiment, an element layer 210, a pixel electrode layer, a common electrode layer, and a liquid crystal composition 208 exhibiting a blue phase are provided between an element substrate 200 and a counter substrate 204. Further, between the element substrate 200 and the counter substrate 204, a spacer 245a, a spacer 245b and a spacer 245c, which keep the gap in which the liquid crystal composition 208 is provided, are provided over a light-blocking film 240a, a light-blocking film 240b, and a light-blocking film 240c, respectively. Although the pixel electrode layer and the common electrode layer are not illustrated in
The light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c are formed over the element substrate 200 provided with the element layer 210 (see
The element layer 210 includes a semiconductor element such as a transistor, a conductive film, and an insulating film as appropriate, and the common electrode layer and the pixel electrode layer electrically connected to the element layer are provided over the element layer.
The light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c are formed using a light-blocking material which reflects or absorbs at least light having a wavelength which is used for processing a photosensitive resin layer to be the spacers. For example, a black organic resin can be used, which can be formed by mixing a black resin of a pigment material, carbon black, titanium black, or the like into a resin material such as photosensitive or non-photosensitive polyimide. Alternatively, a light-blocking metal film can be used, which may be formed using chromium, molybdenum, nickel, titanium, cobalt, copper, tungsten, aluminum, or the like, for example.
There is no particular limitation on the formation method of the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c, and a dry method such as an evaporation method, a sputtering method, or a CVD method, or a wet method such as spin coating, dip coating, spray coating, a droplet discharging method (inkjet method), screen printing, or offset printing may be used depending on a material used. If needed, an etching method (dry etching or wet etching) may be employed to form a desired pattern.
The light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c may be formed in the same step and using the same material as those of the pixel electrode layer, a counter electrode layer, or the light-blocking conductive film (e.g., an electrode layer of a transistor or a wiring layer) included in the element layer 210.
Next, a photosensitive resin layer 241a, a photosensitive resin layer 241b, and a photosensitive resin layer 241c are formed to overlap with the light-blocking film 240a and the vicinity thereof, the light-blocking film 240b and the vicinity thereof, and the light-blocking film 240c and the vicinity thereof, respectively (see
At this time, the photosensitive resin layer 241a, the photosensitive resin layer 241b, and the photosensitive resin layer 241c are also formed in regions where the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c are not formed.
Further, like the photosensitive resin layer 241a, a photosensitive resin layer may be formed to cover part of a light-blocking film.
The photosensitive resin layer 241a, the photosensitive resin layer 241b, and the photosensitive resin layer 241c may be formed by an inkjet method or a printing method, or may be selectively formed in such a manner that a photosensitive resin layer is formed over the entire surface of the element substrate 200 and then part thereof is removed with the use of a mask.
The photosensitive resin layer 241a, the photosensitive resin layer 241b, and the photosensitive resin layer 241c are formed using a photosensitive material (positive photosensitive material). An exposed region of the photosensitive material is reacted and dissolved in a development step. For example, a photosensitive acrylic resin, a photosensitive epoxy resin, a photosensitive amine resin, or the like can be used. In this embodiment, photosensitive polyimide is used.
Next, the photosensitive resin layer 241a, the photosensitive resin layer 241b, and the photosensitive resin layer 241c are irradiated with light 243 from the element substrate 200 side with the use of the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c as masks. Part of the photosensitive resin layer 241a, part of the photosensitive resin layer 241b, and part of the photosensitive resin layer 241c are exposed to light by irradiation with the light 243 to be an exposed region 242a, an exposed region 242b, and an exposed region 242c (see
Next, the exposed region 242a, the exposed region 242b, and the exposed region 242c are removed in a development step; thus, the spacer 245a, the spacer 245b, and the spacer 245c can be formed (see
As described above, in this embodiment, the spacer 245a, the spacer 245b, and the spacer 245c are formed in a self-aligned manner by back exposure from the element substrate 200 side with the use of the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c as masks.
Part of the photosensitive resin layer 241a, part of the photosensitive resin layer 241b, and part of the photosensitive resin layer 241c, which are not provided over the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c serving as masks, are removed; accordingly, the spacer 245a, the spacer 245b, and the spacer 245c are formed only over the light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c. Since each of the light-blocking films 240a to 240c is one continuous film, the surface thereof does not include steep unevenness or a step, and regions of the surface thereof have substantially the same height. Thus, the spacer 245a, the spacer 245b, and the spacer 245c can be stably formed.
Further, the spacer 245a, the spacer 245b, and the spacer 245c are provided for the element substrate 200. In this case, the photosensitive resin layer 241a, the photosensitive resin layer 241b, and the photosensitive resin layer 241c can be formed with good coverage so as to planarize unevenness generated by the element layer 210 in the regions where the spacer 245a, the spacer 245b, and the spacer 245c are to be formed. Accordingly, the spacer 245a, the spacer 245b, and the spacer 245c can be stably provided with good adhesion even in regions with some unevenness.
Next, the liquid crystal composition 208 and the counter substrate 204 are provided in contact with the spacer 245a, the spacer 245b, and the spacer 245c; thus, the liquid crystal display device is manufactured (see
The liquid crystal composition 208 can be formed by a dispenser method (dropping method), or an injection method in which liquid crystal is injected using capillary action or the like after the element substrate 200 and the counter substrate 201 are attached to each other.
In this embodiment, a liquid crystal composition including nematic liquid crystal and a chiral material and exhibiting a blue phase is used as the liquid crystal composition 208.
Examples of the nematic liquid crystal include a biphenyl-based compound, a terphenyl-based compound, a phenylcyclohexyl-based compound, a biphenylcyclohexyl-based compound, a phenylbicyclohexyl-based compound, a benzoic acid phenyl-based compound, a cyclohexyl benzoic acid phenyl-based compound, a phenyl benzoic acid phenyl-based compound, a bicyclohexyl carboxylic acid phenyl-based compound, an azomethine-based compound, an azo-based compound, an azoxy-based compound, a stilbene-based compound, a bicyclohexyl-based compound, a phenylpyrimidine-based compound, a biphenylpyrimidine-based compound, a pyrimidine-based compound, and a biphenyl ethyne-based compound.
The chiral material is used to induce twisting of the liquid crystal composition, align the liquid crystal composition in a helical structure, and make the liquid crystal composition exhibit a blue phase. For the chiral material, a compound which has an asymmetric center, high compatibility with the liquid crystal composition, and strong twisting power is used. In addition, the chiral material is an optically active substance; a higher optical purity is better and the most preferable optical purity is 99% or higher.
In a liquid crystal display device, it is preferable that a polymerizable monomer be added to a liquid crystal composition and polymer stabilization treatment be performed in order to broaden the temperature range within which a blue phase is exhibited. As the polymerizable monomer, for example, a thermopolymerizable (thermosetting) monomer which can be polymerized by heat, a photopolymerizable (photocurable) monomer which can be polymerized by light, or a polymerizable monomer which can be polymerized by heat and light can be used. Further, a polymerization initiator may be added to the liquid crystal composition.
The polymerizable monomer may be a monofunctional monomer such as acrylate or methacrylate; a polyfunctional monomer such as diacrylate, triacrylate, dimethacrylate, or trimethacrylate; or a mixture thereof. Further, the polymerizable monomer may have liquid crystallinity, non-liquid crystallinity, or both of them.
As the polymerization initiator, a radical polymerization initiator which generates radicals by light irradiation, an acid generator which generates an acid by light irradiation, or a base generator which generates a base by light irradiation may be used.
For example, polymer stabilization treatment can be performed in such a manner that a photopolymerizable monomer and a photopolymerization initiator are added to the liquid crystal composition and the liquid crystal composition is irradiated with light having a wavelength at which the photopolymerizable monomer and the photopolymerization initiator react with each other. As the photopolymerizable monomer, typically, a UV polymerizable monomer can be used. When a UV polymerizable monomer is used as a photopolymerizable monomer, the liquid crystal composition may be irradiated with ultraviolet light.
This polymer stabilization treatment may be performed on a liquid crystal composition exhibiting an isotropic phase or a liquid crystal composition exhibiting a blue phase under the control of the temperature. A temperature at which the phase changes from a blue phase to an isotropic phase when the temperature rises, or a temperature at which the phase changes from an isotropic phase to a blue phase when the temperature falls is referred to as the phase transition temperature between a blue phase and an isotropic phase. For example, the polymer stabilization treatment can be performed in the following manner: after a liquid crystal composition to which a photopolymerizable monomer is added is heated to exhibit an isotropic phase, the temperature of the liquid crystal composition is gradually lowered so that the phase changes to a blue phase, and then, light irradiation is performed while the temperature at which a blue phase is exhibited is kept.
With the structure in which a pixel electrode layer and a common electrode layer are provided adjacent to each other between the element substrate 200 and the liquid crystal composition 208, a method can be used in which gradation is controlled by generating an electric field substantially parallel (i.e., in the lateral direction) to a substrate to move liquid crystal molecules in a plane parallel to the substrate. With an electric field formed between the pixel electrode layer and the common electrode layer, liquid crystal is controlled. An electric field in a lateral direction is formed for the liquid crystal, so that liquid crystal molecules can be controlled using the electric field. The liquid crystal composition exhibiting a blue phase is capable of high-speed response. Thus, a high-performance liquid crystal element and a high-performance liquid crystal display device can be achieved. Since the liquid crystal molecules aligned to exhibit a blue phase can be controlled in a direction parallel to the substrate, a wide viewing angle is obtained.
Alternatively, a structure body may be provided under each of the pixel electrode layer and the common electrode layer so that the pixel electrode layer and the common electrode layer project into the liquid crystal composition 208. For example, the pixel electrode layer and the common electrode layer may each be provided over a rib-shaped structure body.
The liquid crystal display device of this embodiment, which is capable of high-speed response, can be favorably used for a successive additive color mixing method (field sequential method) in which light-emitting diodes (LEDs) of RGB or the like are arranged in a backlight unit and color display is performed by time division, or a three-dimensional display method using a shutter glasses system in which images for the right eye and images for the left eye are alternately viewed by time division.
Further, a blue phase is optically isotropic and thus has no viewing angle dependence. Consequently, an alignment film is not necessarily formed; thus, display image quality can be improved and cost can be reduced.
The distance between the pixel electrode layer and the common electrode layer, which are adjacent to each other with the liquid crystal composition 208 interposed therebetween, is a distance at which liquid crystal in the liquid crystal composition 208 between the pixel electrode layer and the common electrode layer responds to predetermined voltage which is applied to the pixel electrode layer and the common electrode layer. The voltage applied is controlled depending on the distance as appropriate.
The maximum thickness (film thickness) of the liquid crystal composition 208 is preferably greater than or equal to 1 μm and less than or equal to 20 μm. The thickness of the liquid crystal composition 208 can be controlled by the spacers 245a, 245b, and 245c.
The light-blocking film 240a, the light-blocking film 240b, and the light-blocking film 240c may overlap with the spacer 245a, the spacer 245b, and the spacer 245c, respectively, with an insulating film provided therebetween. In
Since the shapes of the photosensitive resin layers selectively formed and the shapes of the light-blocking films are reflected in the shapes of the spacers, the shapes of the spacers can be controlled by control of the shapes of the photosensitive resin layers and the light-blocking films.
Examples of formation of a spacer are illustrated in FIGS. 5A1 to 5B3. FIG. 5A1 is a plan view of a region where a spacer is formed, FIG. 5A2 is a cross-sectional view taken along line Z1-Z2 in FIG. 5A1, and FIG. 5A3 is a cross-sectional view taken along line Z3-Z4 in FIG. 5A1. A spacer 245d is formed in a region where a light-blocking film 240d overlaps with a photosensitive resin layer 247a. The spacer 245d overlaps with part of the light-blocking film 240d.
The light-blocking film may be a single film or may include a plurality of films. In the case where the light-blocking film includes a plurality of films, a light-blocking region can be further controlled by shapes of the films and a stacking structure. FIG. 5B1 is a plan view of a region where a spacer is formed, FIG. 5B2 is a cross-sectional view taken along line Z5-Z6 in FIG. 5B1, and FIG. 5B3 is a cross-sectional view taken along line Z7-Z8 in FIG. 5B1. In FIGS. 5B1 to 5B3, a plurality of light-blocking films is used, and an insulating film 244a, a light-blocking film 246, an insulating film 244b, a light-blocking film 240e, and a spacer 245e are stacked in this order over the element substrate 200. The spacer 245e is provided in a region where the light-blocking film 246 or the light-blocking film 240e overlaps with a photosensitive resin layer 247b. The spacer 245e overlaps with part of the light-blocking film 246 or part of the light-blocking film 240e.
When a light-blocking conductive film included in an element layer is used as a light-blocking film, an additional light-blocking film does not need to be formed. This is preferable because the number of steps is not increased and the aperture ratio is not decreased.
Although the spacer seems to be a columnar spacer in a cross-sectional view, the shape of the spacer is a quadrilateral shape, a polygonal shape, a shape including a curve portion such as a circle, a cross shape as illustrated in FIG. 5B1, or the like in a plan view.
Although not illustrated in
As a liquid crystal display device, a transmissive liquid crystal display device in which display is performed by transmission of light from a light source, a reflective liquid crystal display device in which display is performed by reflection of incident light, or a transflective liquid crystal display device in which a transmissive type and a reflective type are combined can be provided.
In the case of a transmissive liquid crystal display device, a pixel electrode layer, a common electrode layer, a counter substrate, an insulating film, a conductive film, and the like, which are provided in a pixel region through which light is transmitted, preferably have a light-transmitting property with respect to light in the visible wavelength range; however, if an opening pattern is provided, a non-light-transmitting material such as a metal film may be used depending on the shape.
On the other hand, in the case of a reflective liquid crystal display device, a reflective component which reflects light transmitted through a liquid crystal composition (e.g., a reflective film or a reflective substrate) may be provided on the side opposite to the viewing side of the liquid crystal composition. Therefore, a substrate, an insulating film, and a conductive film which are provided between the viewing side and the reflective component and through which light is transmitted have a light-transmitting property with respect to light in the visible wavelength range. Note that in this specification, a light-transmitting property refers to a property of transmitting at least light in the visible wavelength range unless otherwise specified.
The pixel electrode layer and the common electrode layer may be formed using one or more of the following: indium tin oxide, a conductive material in which zinc oxide (ZnO) is mixed into indium oxide, a conductive material in which silicon oxide (SiO2) is mixed into indium oxide, organoindium, organotin, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, graphene, metals such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), and silver (Ag), alloys thereof, and nitrides thereof.
In the liquid crystal display device disclosed in the present invention, the element substrate 200 is a light-transmitting substrate which transmits at least the light 243.
As the element substrate 200 and the counter substrate 201, a glass substrate of barium borosilicate glass, aluminoborosilicate glass, or the like, a quartz substrate, a plastic substrate, or the like can be used. Note that in the case of a reflective liquid crystal display device, since the element substrate 200 is on the viewing side, the counter substrate 201, which is on the side opposite to the element substrate 200, may be a metal substrate such as an aluminum substrate or a stainless steel substrate.
As described above, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided.
A liquid crystal display device with high reliability and high performance can be provided.
This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.
As a liquid crystal display device according to an embodiment of the present invention, a passive matrix liquid crystal display device and an active matrix liquid crystal display device can be provided. In this embodiment, an example of an active matrix liquid crystal display device according to an embodiment of the present invention will be described with reference to
In
In the liquid crystal display device in
A method can be used in which gradation is controlled by generating an electric field substantially parallel (i.e., in the lateral direction) to a substrate to move liquid crystal molecules in a plane parallel to the substrate. For such a method, electrode structures used in an IPS mode as illustrated in
In a lateral electric field mode such as an IPS mode, a first electrode layer (e.g., a pixel electrode layer with which voltage is controlled in each pixel) and a second electrode layer (e.g., a common electrode layer with which common voltage is applied to all pixels), each of which has an opening pattern, are located below a liquid crystal composition. Therefore, the first electrode layer 447 and the second electrode layer 446, one of which is a pixel electrode layer and the other of which is a common electrode layer, are formed over a first substrate 441, and at least one of the first electrode layer and the second electrode layer is formed over an insulating film. The first electrode layer 447 and the second electrode layer 446 have not a flat shape but various opening patterns including a bent portion or a branched comb-like portion. An arrangement of the first electrode layer 447 and the second electrode layer 446, which complies with both conditions that they have the same shape and they completely overlap with each other, is avoided in order to generate an electric field between the electrodes.
The first electrode layer 447 and the second electrode layer 446 may have an electrode structure used in an FFS mode. In a lateral electric field mode such as an FFS mode, a first electrode layer (e.g., a pixel electrode layer with which voltage is controlled in each pixel) having an opening pattern is located below a liquid crystal composition, and further, a second electrode layer (e.g., a common electrode layer with which common voltage is applied to all pixels) having a flat shape is located below the opening pattern. In this case, the first electrode layer and the second electrode layer, one of which is a pixel electrode layer and the other of which is a common electrode layer, are formed over the first substrate 441, and the pixel electrode layer and the common electrode layer are stacked with an insulating film (or an interlayer insulating layer) interposed therebetween. One of the pixel electrode layer and the common electrode layer is formed below the insulating film (or the interlayer insulating layer) and has a flat shape, whereas the other is formed above the insulating film (or the interlayer insulating layer) and has various opening patterns including a bent portion or a branched comb-like portion. An arrangement of the first electrode layer 447 and the second electrode layer 446, which complies with both conditions that they have the same shape and they completely overlap with each other, is avoided in order to generate an electric field between the electrodes.
In this embodiment, a liquid crystal composition including nematic liquid crystal, a chiral material, a polymerizable monomer, and a polymerization initiator and exhibiting a blue phase is used as a liquid crystal composition 444. The liquid crystal composition 444 is provided in a liquid crystal display device with a blue phase exhibited (with a blue phase shown) by being subjected to polymer stabilization treatment. The liquid crystal composition 444 further includes a high molecular compound.
With an electric field generated between the first electrode layer 447 as the pixel electrode layer and the second electrode layer 446 as the common electrode layer, liquid crystal of the liquid crystal composition 444 is controlled. An electric field in a lateral direction is formed for the liquid crystal, so that liquid crystal molecules can be controlled using the electric field. Since the liquid crystal molecules aligned to exhibit a blue phase can be controlled in the direction parallel to the substrate, a wide viewing angle is obtained.
Since the first electrode layer 447 and the second electrode layer 446 have an opening pattern, they are illustrated as divided plural electrode layers in the cross-sectional view of
In this embodiment, the common wiring layer 408 and the wiring layer 405b are each formed using a light-blocking conductive film. The common wiring layer 408 and the wiring layer 405b each formed using a light-blocking conductive film function as masks when the spacer 450 is formed.
The spacer 450 is formed in such a manner that a photosensitive resin layer is selectively formed over the common wiring layer 408 and the wiring layer 405b and the photosensitive resin layer is subjected to back exposure with the use of the common wiring layer 408 and the wiring layer 405b as masks. Since the photosensitive resin layer is selectively formed by an inkjet method in this embodiment, a shape of a droplet having a curve is reflected in the shape of the spacer 450.
In the manufacturing step of the spacer 450, part of the photosensitive resin layer, which is provided neither over the common wiring layer 408 nor over the wiring layer 405b, is removed with the use of the light-blocking common wiring layer 408 and the light-blocking wiring layer 405b, so that the spacer is provided only over the common wiring layer 408 or the wiring layer 405b. Since the common wiring layer 408 and the wiring layer 405b are each one continuous film, the height of the surface of each layer is substantially uniform over the layer and thus the spacer 450 can be stably provided.
Further, since the spacer 450 is provided for the first substrate 441 which is an element substrate, the photosensitive resin layer can be formed by a coating method offering good coverage or the like so that unevenness caused by the element layer in a region for forming the spacer 450 is planarized. Therefore, the spacer 450 can be stably provided with good adhesion even in a region with some unevenness.
The spacer 450 can be stably provided in a substantially flat region with less steep unevenness and fewer steep steps in the liquid crystal display device; thus, damage and a shape defect of the spacer 450 due to physical impact can be reduced and the liquid crystal display device can have high resistance to physical impact.
Accordingly, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided. Further, a liquid crystal display device with high reliability and high performance can be provided.
The transistor 420 is an inverted staggered thin film transistor formed over the first substrate 441 having an insulating surface. The transistor 420 includes the gate electrode layer 401, a gate insulating layer 402, a semiconductor layer 403, and the wiring layers 405a and 405b which function as a source electrode layer and a drain electrode layer.
There is no particular limitation on the structure of a transistor which can be used for the liquid crystal display device disclosed in this specification. For example, a staggered type or a planar type having a top-gate structure or a bottom-gate structure can be employed. The transistor may have a single-gate structure in which one channel formation region is formed, a double-gate structure in which two channel formation regions are formed, or a triple-gate structure in which three channel formation regions are formed. Alternatively, the transistor may have a dual gate structure including two gate electrode layers positioned over and below a channel region with a gate insulating layer provided therebetween.
An insulating film 407 which is in contact with the semiconductor layer 403 is provided to cover the transistor 420. An interlayer film 413 is stacked over the insulating film 407.
There is no particular limitation on the method for forming the interlayer film 413, and the following method can be employed depending on the material: spin coating, dip coating, spray coating, a droplet discharging method (inkjet method), screen printing, offset printing, roll coating, curtain coating, knife coating, or the like.
The first substrate 441 and a second substrate 442 which is a counter substrate are firmly attached to each other with a sealant with the liquid crystal composition 444 provided therebetween. The liquid crystal composition 444 can be formed by a dispenser method (dropping method), or an injection method by which liquid crystal is injected using capillary action or the like after the first substrate 441 is attached to the second substrate 442.
As the sealant, typically, a visible light curable resin, a UV curable resin, or a thermosetting resin is preferably used. Typically, an acrylic resin, an epoxy resin, an amine resin, or the like can be used. Further, a photopolymerization initiator (typically, a UV polymerization initiator), a thermosetting agent, a filler, or a coupling agent may be included in the sealant.
In the case where a photocurable resin such as a UV curable resin is used as a sealant and a liquid crystal composition is formed by a dropping method, for example, the sealant may be cured in the light irradiation step of the polymer stabilization treatment.
In this embodiment, a polarizing plate 443a is provided on the outer side (on the side opposite to the liquid crystal composition 444) of the first substrate 441, and a polarizing plate 443b is provided on the outer side (on the side opposite to the liquid crystal composition 444) of the second substrate 442. In addition to the polarizing plates, an optical film such as a retardation plate or an anti-reflection film may be provided. For example, circular polarization by a polarizing plate and a retardation plate may be used. Through the above-described process, a liquid crystal display device can be completed.
In the case of manufacturing a plurality of liquid crystal display devices using a large-sized substrate (a so-called multiple panel method), a division step can be performed before the polymer stabilization treatment or before provision of the polarizing plates. In consideration of the influence of the division step on the liquid crystal composition (such as alignment disorder due to force applied in the division step), it is preferable that the division step be performed after attaching the first substrate and the second substrate to each other before performing the polymer stabilization treatment.
Although not illustrated, a backlight, a sidelight, or the like may be used as a light source. Light from the light source is emitted from the side of the first substrate 441 which is an element substrate so as to pass through the second substrate 442 on the viewing side.
The first electrode layer 447 and the second electrode layer 446 can be formed using a light-transmitting conductive material such as indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide, indium zinc oxide, indium tin oxide to which silicon oxide is added, or graphene.
Alternatively, the first electrode layer 447 and the second electrode layer 446 can be formed using one or more materials selected from metals such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), and silver (Ag); an alloy of any of these metals; and a nitride of any of these metals.
The first electrode layer 447 and the second electrode layer 446 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). The pixel electrode formed using a conductive composition preferably has a sheet resistance of less than or equal to 10000 ohms per square and a transmittance of greater than or equal to 70% at a wavelength of 550 nm. Further, the resistivity of the conductive high molecule included in the conductive composition is preferably less than or equal to 0.1 Ω·cm.
As the conductive high molecule, a so-called it-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof can be given.
An insulating film serving as a base film may be provided between the first substrate 441 and the gate electrode layer 401. The base film has a function of preventing diffusion of an impurity element from the first substrate 441, and can be formed to have a single-layer structure or a stacked-layer structure using one or more of a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, a silicon oxynitride film, and an aluminum oxide film. The gate electrode layer 401 and the common wiring layer 408 can be formed to have a single-layer or stacked-layer structure using any of metal materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, and an alloy material which contains any of these materials as its main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus, or a silicide film such as a nickel silicide film may be used as the gate electrode layer 401 and the common wiring layer 408.
The gate electrode layer 401 and the common wiring layer 408 can also be formed using a conductive material such as indium oxide-tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium oxide-zinc oxide, or indium tin oxide to which silicon oxide is added. It is also possible that the gate electrode layer 401 and the common wiring layer 408 have a stacked structure of the above conductive material and the above metal material.
As the gate electrode layer 401 and the common wiring layer 408, a metal oxide film containing nitrogen, specifically, an In—Ga—Zn—O film containing nitrogen, an In—Sn—O film containing nitrogen, an In—Ga—O film containing nitrogen, an In—Zn—O film containing nitrogen, a Sn—O film containing nitrogen, an In—O film containing nitrogen, or a metal nitride (e.g., InN or SnN) film can be used.
For example, as a two-layer structure of the gate electrode layer 401 and the common wiring layer 408, any of the following structures is preferable: a two-layer structure in which a molybdenum layer is stacked over an aluminum layer, a two-layer structure in which a molybdenum layer is stacked over a copper layer, a two-layer structure in which a titanium nitride layer or a tantalum nitride layer is stacked over a copper layer, and a two-layer structure of a titanium nitride layer and a molybdenum layer. As a three-layer structure, a stacked-layer structure in which a tungsten layer or a tungsten nitride layer, an alloy layer of aluminum and silicon or an alloy layer of aluminum and titanium, and a titanium nitride layer or a titanium layer are stacked is preferable.
In this embodiment, the gate electrode layer 401 and the common wiring layer 408 are formed using a tungsten film which is a light-blocking conductive film. The common wiring layer 408 formed using a light-blocking conductive film functions as a mask when the spacer 450 is formed. Further, by using a light-blocking conductive film as the gate electrode layer 401, light from a backlight (light emitted through the first substrate 441) can be prevented from entering the semiconductor layer 403.
The gate insulating layer 402 can be formed by a plasma CVD method, a sputtering method, or the like with the use of a silicon oxide film, a gallium oxide film, an aluminum oxide film, a silicon nitride film, a silicon oxynitride film, an aluminum oxynitride film, a silicon nitride oxide film, or the like. Alternatively, a high-k material such as hafnium oxide, yttrium oxide, lanthanum oxide, hafnium silicate (HfSixOy (x>0, y>0)), hafnium aluminate (HfAlxOy (x>0, y>0)), hafnium silicate to which nitrogen is added, or hafnium aluminate to which nitrogen is added may be used as a material for the gate insulating layer 402. The use of such a high-k material enables a reduction in gate leakage current.
Alternatively, the gate insulating layer 402 can be formed using a silicon oxide layer by a CVD method in which an organosilane gas is used. As an organosilane gas, a silicon-containing compound such as tetraethoxysilane (TEOS) (chemical formula: Si(OC2H5)4), tetramethylsilane (TMS) (chemical formula: Si(CH3)4), tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC2H5)3), or trisdimethylaminosilane (SiH(N(CH3)2)3) can be used. Note that the gate insulating layer 402 may have a single layer structure or a stacked-layer structure.
A material of the semiconductor layer 403 is not limited to a particular material and may be determined in accordance with characteristics needed for the transistor 420, as appropriate. Examples of a material which can be used for the semiconductor layer 403 will be described.
The semiconductor layer 403 can be formed using the following material: an amorphous semiconductor formed by a chemical vapor deposition method using a semiconductor source gas typified by silane or germane or by a physical vapor deposition method such as a sputtering method; a polycrystalline semiconductor formed by crystallizing the amorphous semiconductor with the use of light energy or thermal energy; a microcrystalline semiconductor in which a minute crystalline phase and an amorphous phase coexist; or the like. The semiconductor layer can be formed by a sputtering method, an LPCVD method, a plasma CVD method, or the like.
A typical example of an amorphous semiconductor is hydrogenated amorphous silicon, while a typical example of a crystalline semiconductor is polysilicon. Examples of polysilicon (polycrystalline silicon) are as follows: so-called high-temperature polysilicon which contains polysilicon formed at a process temperature of 800° C. or higher as its main component, so-called low-temperature polysilicon which contains polysilicon formed at a process temperature of 600° C. or lower as its main component, and polysilicon obtained by crystallizing amorphous silicon with the use of an element that promotes crystallization, or the like. It is needless to say that a microcrystalline semiconductor or a semiconductor partly containing a crystal phase can be used as described above.
An oxide semiconductor film may also be used as the semiconductor layer 403. The oxide semiconductor preferably contains at least indium (In), particularly In and zinc (Zn). In addition, as a stabilizer for reducing the variation in electric characteristics of transistors using the oxide semiconductor, gallium (Ga) is preferably contained in addition to In and Zn. Tin (Sn) is preferably contained as a stabilizer. Hafnium (Hf) is preferably contained as a stabilizer. Aluminum (Al) is preferably contained as a stabilizer. Zirconium (Zr) is preferably contained as a stabilizer.
As another stabilizer, one or plural kinds of lanthanoid such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) may be contained.
As the oxide semiconductor, for example, any of the following can be used: indium oxide, tin oxide, zinc oxide, a two-component metal oxide such as an In—Zn-based oxide, an In—Mg-based oxide, or an In—Ga-based oxide, a three-component metal oxide such as an In—Ga—Zn-based oxide (also referred to as IGZO), an In—Al—Zn-based oxide, an In—Sn-Zn-based oxide, an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, or an In—Lu—Zn-based oxide, or a four-component metal oxide such as an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide.
Note that here, for example, an “In—Ga—Zn-based oxide” means an oxide containing In, Ga, and Zn as its main component and there is no particular limitation on the ratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain a metal element other than In, Ga, and Zn.
Alternatively, a material represented by InMO3(ZnO)m (m>0, m is not an integer) may be used as the oxide semiconductor. Note that M represents one or more metal elements selected from Ga, Fe, Mn, and Co. Alternatively, as the oxide semiconductor, a material represented by In2SnO5(ZnO)n (n>0, n is an integer) may be used.
For example, an In—Ga—Zn-based oxide with an atomic ratio of In:Ga:Zn=1:1:1 (=1/3:1/3:1/3), In:Ga:Zn=2:2:1 (=2/5:2/5:1/5), or In:Ga:Zn=3:1:2 (=1/2:1/6:1/3), or an oxide with an atomic ratio close to the above atomic ratios can be used. Alternatively, an In—Sn—Zn-based oxide with an atomic ratio of In:Sn:Zn=1:1:1 (=1/3:1/3:1/3), In:Sn:Zn=2:1:3 (=1/3:1/6:1/2), or In:Sn:Zn=2:1:5 (=1/4:1/8:5/8), or an oxide with an atomic ratio close to the above atomic ratios may be used.
However, without limitation to the materials given above, a material with an appropriate composition may be used as the oxide semiconductor depending on necessary semiconductor characteristics (e.g., mobility, threshold voltage, and variation). In order to obtain necessary semiconductor characteristics, it is preferable that the carrier density, the impurity concentration, the defect density, the atomic ratio between a metal element and oxygen, the interatomic distance, the density, and the like be set to appropriate values.
For example, high mobility can be obtained relatively easily in the case of using an In—Sn—Zn-based oxide. However, mobility can be increased by reducing the defect density in a bulk also in the case of using an In—Ga—Zn-based oxide.
Note that, for example, the expression “the composition of an oxide containing In, Ga, and Zn at an atomic ratio of In:Ga:Zn=a:b:c (a+b+c=1) is close to the composition of an oxide containing In, Ga, and Zn at an atomic ratio of In:Ga:Zn=A:B:C (A+B+C=1)” means that a, b, and c satisfy the following relation: (a−A)2+(b−B)2+(c−C)2≦r2, and r may be 0.05, for example. The same applies to other oxides.
An oxide semiconductor film is in a single crystal state, a polycrystalline (also referred to as polycrystal) state, an amorphous state, or the like.
The oxide semiconductor film is preferably a CAAC-OS (c-axis aligned crystalline oxide semiconductor) film.
The CAAC-OS film is not completely single crystal nor completely amorphous. The CAAC-OS film is an oxide semiconductor film with a crystal-amorphous mixed phase structure where crystal portions are included in an amorphous phase. Note that in most cases, the crystal portion fits inside a cube whose one side is less than 100 nm. From an observation image obtained with a transmission electron microscope (TEM), a boundary between an amorphous portion and a crystal portion in the CAAC-OS film is not clear. Further, with the TEM, a grain boundary in the CAAC-OS film is not found. Thus, in the CAAC-OS film, a reduction in electron mobility, due to the grain boundary, is suppressed.
In each of the crystal portions included in the CAAC-OS film, a c-axis is aligned in a direction parallel to a normal vector of a surface where the CAAC-OS film is formed or a normal vector of a surface of the CAAC-OS film, triangular or hexagonal atomic arrangement which is seen from the direction perpendicular to the a-b plane is formed, and metal atoms are arranged in a layered manner or metal atoms and oxygen atoms are arranged in a layered manner when seen from the direction perpendicular to the c-axis. Note that, among crystal portions, the directions of the a-axis and the b-axis of one crystal portion may be different from those of another crystal portion. In this specification, a simple term “perpendicular” includes a range from 85° to 95°. In addition, a simple term “parallel” includes a range from −5° to 5°.
In the CAAC-OS film, distribution of crystal portions is not necessarily uniform. For example, in the formation process of the CAAC-OS film, in the case where crystal growth occurs from a surface side of the oxide semiconductor film, the proportion of crystal portions in the vicinity of the surface of the oxide semiconductor film is higher than that in the vicinity of the surface where the oxide semiconductor film is formed in some cases. Further, when an impurity is added to the CAAC-OS film, the crystal portion in a region to which the impurity is added becomes amorphous in some cases.
Since the c-axes of the crystal portions included in the CAAC-OS film are aligned in the direction parallel to a normal vector of a surface where the CAAC-OS film is formed or a normal vector of a surface of the CAAC-OS film, the directions of the c-axes may be different from each other depending on the shape of the CAAC-OS film (the cross-sectional shape of the surface where the CAAC-OS film is formed or the cross-sectional shape of the surface of the CAAC-OS film). Note that when the CAAC-OS film is formed, the direction of c-axis of the crystal portion is the direction parallel to a normal vector of the surface where the CAAC-OS film is formed or a normal vector of the surface of the CAAC-OS film. The crystal portion is formed by film formation or by performing treatment for crystallization such as heat treatment after film formation.
With the use of the CAAC-OS film in a transistor, change in electric characteristics of the transistor due to irradiation with visible light or ultraviolet light is small. Thus, the transistor has high reliability.
Note that part of oxygen included in the oxide semiconductor film may be substituted with nitrogen.
In an oxide semiconductor having a crystal portion such as the CAAC-OS, defects in the bulk can be further reduced and when the surface flatness of the oxide semiconductor is improved, mobility higher than that of an oxide semiconductor in an amorphous state can be obtained. In order to improve the surface flatness, the oxide semiconductor is preferably formed over a flat surface. Specifically, the oxide semiconductor may be formed over a surface with the average surface roughness (Ra) of less than or equal to 1 nm, preferably less than or equal to 0.3 nm, more preferably less than or equal to 0.1 nm.
In a process of forming the semiconductor layer and the wiring layer, an etching step is used to process thin films into desired shapes. Dry etching or wet etching can be used for the etching step.
The etching conditions (such as an etchant, etching time, and temperature) are adjusted as appropriate depending on the material so that the material can be etched to have a desired shape.
As a material of the wiring layers 405a and 405b serving as a source electrode layer and a drain electrode layer, an element selected from Al, Cr, Ta, Ti, Mo, and W, an alloy containing any of the above elements as its component, an alloy film containing a combination of any of these elements, and the like can be given. Further, in the case where heat treatment is performed, the conductive film preferably has heat resistance against the heat treatment. Since use of Al alone brings disadvantages such as low heat resistance and a tendency to corrosion, aluminum is used in combination with a conductive material having heat resistance. As the conductive material having heat resistance, which is combined with aluminum, it is possible to use an element selected from titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc); an alloy containing any of these elements as its component; an alloy containing a combination of any of these elements; or a nitride containing any of these elements as its component.
In this embodiment, the wiring layers 405a and 405b are formed using a stack of a titanium film, an aluminum film, and a titanium film. The wiring layers 405a and 405b each have a light-blocking property. The wiring layer 405b formed using a light-blocking conductive film can function as a mask when the spacer 450 is formed.
As described in this embodiment, in the case where the common wiring layer 408 or the wiring layer 405b, which is formed under the spacer 450, is formed using a light-blocking conductive film, the common wiring layer 408 or the wiring layer 405b functions as a mask when the spacer 450 is formed; accordingly, another light-blocking conductive film does not need to be formed under the spacer 450.
Needless to say, another light-blocking film may be provided under the spacer 450, and the spacer 450 can be formed using a plurality of light-blocking films as masks.
The gate insulating layer 402, the semiconductor layer 403, and the wiring layers 405a and 405b serving as a source electrode layer and a drain electrode layer may be successively formed without being exposed to air. Successive film formation without exposure to air makes it possible to obtain each interface between stacked layers, which is not contaminated by atmospheric components or impurity elements in the air. Thus, variation in characteristics of the transistors can be reduced.
Note that the semiconductor layer 403 is partly etched so as to have a groove (depressed portion).
An inorganic insulating film or an organic insulating film formed by a dry method or a wet method can be used as the insulating film 407 which covers the transistor 420 and the interlayer film 413. For example, it is possible to use a silicon nitride film, a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, or a tantalum oxide film, which is formed by a CVD method, a sputtering method, or the like. Alternatively, an organic material such as polyimide, acrylic, a benzocyclobutene-based resin, polyamide, or epoxy can be used. As an alternative to such organic materials, it is possible to use a low-dielectric constant material (low-k material), a siloxane-based resin, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or the like. A gallium oxide film can also be used as the insulating film 407.
Note that the siloxane-based resin corresponds to a resin including a Si—O—Si bond formed using a siloxane-based material as a starting material. The siloxane-based resin may include an organic group (e.g., an alkyl group or an aryl group) or a fluoro group as a substituent. Moreover, the organic group may include a fluoro group. A siloxane-based resin is applied by a coating method and baked; thus, the insulating film 407 can be formed.
Alternatively, the insulating film 407 and the interlayer film 413 may each be formed by stacking a plurality of insulating films formed using any of these materials. For example, a structure may be employed in which an organic resin film is stacked over an inorganic insulating film.
Further, with the use of a resist mask having regions with plural thicknesses (typically, two different thicknesses) which is formed using a multi-tone mask, the number of steps in a photolithography process can be reduced, resulting in a simplified process and lower cost.
As described above, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided.
A liquid crystal display device with high reliability and high performance can be provided.
This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.
A transistor is manufactured, and a liquid crystal display device having a display function can be manufactured using the transistor in a pixel portion and further in a driver circuit. Further, part or the whole of the driver circuit can be formed over the same substrate as the pixel portion, using the transistor, whereby a system-on-panel can be obtained.
The liquid crystal display device includes a liquid crystal element (also referred to as a liquid crystal display element) as a display element.
Further, a liquid crystal display device includes a panel in which a display element is sealed, and a module in which an IC or the like including a controller is mounted to the panel. An embodiment of the present invention also relates to an element substrate, which corresponds to one mode before the display element is completed in a manufacturing process of the liquid crystal display device, and the element substrate is provided with means for supplying current to the display element in each of a plurality of pixels. Specifically, the element substrate may be in a state in which only a pixel electrode of the display element is formed, a state in which a conductive film to be a pixel electrode is formed but is not etched yet to form the pixel electrode, or in any other states.
Note that a liquid crystal display device in this specification means an image display device, a display device, or a light source (including a lighting device). Further, a liquid crystal display device also refers to all the following modules: a module to which a connector, for example, a flexible printed circuit (FPC), a tape automated bonding (TAB) tape, or a tape carrier package (TCP) is attached, a module in which a printed wiring board is provided at an end of a TAB tape or a TCP, and a module in which an integrated circuit (IC) is directly mounted on a display element by a chip on glass (COG) method.
The appearance and a cross section of a liquid crystal display panel which corresponds to a liquid crystal display device of an embodiment of the present invention is described with reference to FIGS. 4A1, 4A2, and 4B. FIGS. 4A1 and 4A2 are each a top view of a panel in which transistors 4010 and 4011 formed over a first substrate 4001 and a liquid crystal element 4013 are sealed between the first substrate 4001 and a second substrate 4006 with a sealant 4005.
The sealant 4005 is provided so as to surround a pixel portion 4002 and a scan line driver circuit 4004 which are provided over the first substrate 4001. The second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Thus, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with a liquid crystal composition 4008 by the first substrate 4001, the sealant 4005, and the second substrate 4006.
In FIG. 4A1, a signal line driver circuit 4003 that is formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a substrate separately prepared is mounted in a region that is different from the region surrounded by the sealant 4005 over the first substrate 4001. FIG. 4A2 illustrates an example in which part of a signal line driver circuit is formed with the use of a transistor which is provided over the first substrate 4001. A signal line driver circuit 4003b is formed over the first substrate 4001, and a signal line driver circuit 4003a that is formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a substrate separately prepared is mounted.
Note that the connection method of a driver circuit which is separately formed is not particularly limited, and a COG method, a wire bonding method, a TAB method, or the like can be used. FIG. 4A1 illustrates an example of mounting the signal line driver circuit 4003 by a COG method, and FIG. 4A2 illustrates an example of mounting the signal line driver circuit 4003a by a TAB method.
The pixel portion 4002 and the scan line driver circuit 4004 provided over the first substrate 4001 include a plurality of transistors.
The transistor which is described in Embodiment 2 can be used as the transistors 4010 and 4011.
Further, a conductive layer may be provided over the interlayer film 4021 or the insulating layer 4020 so as to overlap with a channel formation region of a semiconductor layer of the transistor 4011 for the driver circuit. The conductive layer may have the same potential as or a potential different from that of a gate electrode layer of the transistor 4011 and can function as a second gate electrode layer. Further, the potential of the conductive layer may be GND or the conductive layer may be in a floating state.
A pixel electrode layer 4030 and a common electrode layer 4031 are provided over the interlayer film 4021, and the pixel electrode layer 4030 is electrically connected to the transistor 4010. The liquid crystal element 4013 includes the pixel electrode layer 4030, the common electrode layer 4031, and the liquid crystal composition 4008. Note that a polarizing plate 4032a and a polarizing plate 4032b are provided on the outer sides of the first substrate 4001 and the second substrate 4006, respectively.
In this embodiment, a liquid crystal composition including nematic liquid crystal, a chiral material, a polymerizable monomer, and a polymerization initiator and exhibiting a blue phase is used as the liquid crystal composition 4008. The liquid crystal composition 4008 is provided in the liquid crystal display device with a blue phase exhibited (with a blue phase shown) by being subjected to polymer stabilization treatment. The liquid crystal composition 4008 further includes an organic compound.
The structures of the pixel electrode layer and the common electrode layer described in Embodiment 2 can be used for the pixel electrode layer 4030 and the common electrode layer 4031. The pixel electrode layer 4030 and the common electrode layer 4031 have opening patterns.
With an electric field generated between the pixel electrode layer 4030 and the common electrode layer 4031, liquid crystal of the liquid crystal composition 4008 is controlled. An electric field in a lateral direction is formed for the liquid crystal, so that liquid crystal molecules can be controlled using the electric field. Since the liquid crystal molecules aligned to exhibit a blue phase can be controlled in the direction parallel to the substrate, a wide viewing angle is obtained.
For the first substrate 4001 and the second substrate 4006, glass, plastic, or the like having a light-transmitting property can be used. As plastic, a polyvinyl fluoride (PVF) film, a polyester film, or an acrylic resin film can be used. A sheet with a structure in which an aluminum foil is sandwiched between PVF films or polyester films, or a fiberglass-reinforced plastics (FRP) plate can also be used.
The spacer 4035 provided over a light-blocking film 4036 is provided to control the thickness of the liquid crystal composition 4008 (cell gap). In the liquid crystal display device including the liquid crystal composition 4008, the cell gap which is the thickness of the liquid crystal composition is preferably greater than or equal to 1 μm and less than or equal to 20 μm. In this specification, the thickness of a cell gap refers to the maximum thickness (film thickness) of the liquid crystal composition.
The spacer 4035 is formed in such a manner that a photosensitive resin layer is selectively formed over the light-blocking film 4036 and the photosensitive resin layer is subjected to back exposure with the use of the light-blocking film 4036 as a mask.
Part of the photosensitive resin layer, which is provided over a region other than the light-blocking film 4036 serving as a mask, is removed in a step of forming the spacer 4035; thus, the spacer 4035 is provided only over the light-blocking film 4036. The light-blocking film 4036 is one continuous film; accordingly, regions of the surface thereof have substantially the same height and the spacer 4035 can be stably provided.
Further, since the spacer 4035 is provided for the first substrate 4001 which is an element substrate, the photosensitive resin layer can be formed by a coating method offering good coverage or the like so that unevenness caused by the element layer in a region for forming the spacer 4035 is planarized. Therefore, the spacer 4035 can be stably provided with good adhesion even in a region with some unevenness.
The spacer 4035 can be stably provided in a substantially flat region with less steep unevenness and fewer steep steps in the liquid crystal display device; thus, damage and a shape defect of the spacer 4035 due to physical impact can be reduced and the liquid crystal display device can have high resistance to physical impact.
Accordingly, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided. Further, a liquid crystal display device with high reliability and high performance can be provided.
Although FIGS. 4A1, 4A2, and 4B illustrate an example of a transmissive liquid crystal display device, an embodiment of the present invention can also be applied to a transflective liquid crystal display device and a reflective liquid crystal display device.
FIGS. 4A1, 4A2, and 4B illustrate an example in which a polarizing plate is provided on the outer side (the viewing side) of the substrate; however, the polarizing plate may be provided on the inner side of the substrate. The position of the polarizing plate may be determined as appropriate depending on the material of the polarizing plate and conditions of the manufacturing process. Furthermore, a light-blocking layer serving as a black matrix may be provided.
A color filter layer or a light-blocking layer may be formed as part of the interlayer film 4021. In FIGS. 4A1, 4A2, and 4B, a light-blocking layer 4034 is provided on the second substrate 4006 side so as to cover the transistors 4010 and 4011. With the provision of the light-blocking layer 4034, the contrast can be increased and the transistors can be stabilized more.
In the case where a light-blocking layer or a color filter layer which functions as a black matrix is provided, a position and a formation step of the light-blocking layer or the color filter layer need to be considered so that light irradiation of the photosensitive resin layer in the formation step of the spacer is not prevented.
The transistor may be covered with the insulating layer 4020 functioning as a protective film; however, the present invention is not particularly limited thereto.
Note that the protective film is provided to prevent entry of contaminant impurities such as an organic substance, metal, and moisture in the air and is preferably a dense film. The protective film may be formed by a sputtering method to have a single-layer structure or a stacked-layer structure including any of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and an aluminum nitride oxide film.
In the case of further forming a light-transmitting insulating layer as a planarizing insulating film, the light-transmitting insulating layer can be formed using an organic material having heat resistance, such as polyimide, acrylic, a benzocyclobutene-based resin, polyamide, or epoxy. As an alternative to such organic materials, it is possible to use a low-dielectric constant material (low-k material), a siloxane-based resin, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or the like. The insulating layer may be formed by stacking a plurality of insulating films formed of these materials.
There is no particular limitation on the method for forming the insulating layer having a stacked structure, and the following method can be employed depending on the material: a sputtering method, spin coating, a dip coating method, a spray coating method, a droplet discharging method (inkjet method), screen printing, offset printing, roll coating, curtain coating, knife coating, or the like.
The pixel electrode layer 4030 and the common electrode layer 4031 can be formed using a light-transmitting conductive material such as indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide, indium zinc oxide, indium tin oxide to which silicon oxide is added, or graphene.
The pixel electrode layer 4030 and the common electrode layer 4031 can also be formed using one or more materials selected from metals such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), and silver (Ag); an alloy of any of these metals; and a nitride of any of these metals.
In this embodiment, the pixel electrode layer 4030 and the common electrode layer 4031 are formed using a reflective conductive film. Further, the light-blocking film 4036 is formed in the same process as the pixel electrode layer 4030 and the common electrode layer 4031.
Alternatively, the pixel electrode layer 4030 and the common electrode layer 4031 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer).
Further, a variety of signals and potentials are supplied to the signal line driver circuit 4003 which is separately formed, the scan line driver circuit 4004, or the pixel portion 4002 from an FPC 4018.
Further, since a transistor is easily broken by static electricity or the like, a protection circuit for protecting the driver circuit is preferably provided over the same substrate as a gate line or a source line. The protection circuit is preferably formed using a nonlinear element.
In FIGS. 4A1, 4A2, and 4B, a connection terminal electrode 4015 is formed using the same conductive film as that of the pixel electrode layer 4030, and a terminal electrode 4016 is formed using the same conductive film as that of source and drain electrode layers of the transistors 4010 and 4011.
The connection terminal electrode 4015 is electrically connected to a terminal included in the FPC 4018 via an anisotropic conductive film 4019.
Although FIGS. 4A1, 4A2, and 4B illustrate an example in which the signal line driver circuit 4003 is formed separately and mounted on the first substrate 4001, an embodiment of the present invention is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.
As described above, a liquid crystal display device which is resistant to physical impact and can retain high-quality display characteristics can be provided.
A liquid crystal display device with high reliability and high performance can be provided.
This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.
In this embodiment, electronic devices according to an embodiment of the present invention will be described. Specifically, electronic devices in each of which the liquid crystal display device described in any of the above embodiments is used are described below with reference to
Examples of the electronic devices to which the liquid crystal display device is applied are television sets (also referred to as televisions or television receivers), monitors of computers or the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also referred to as cell phones or cellular phones), portable game machines, portable information terminals, audio reproducing devices, and large-sized game machines such as pachinko machines. Specific examples of these electronic devices are shown in
The television device 7100 can be operated by an operation switch of the housing 7101 or a separate remote controller 7110. With operation keys 7109 of the remote controller 7110, channels and volume can be controlled and images displayed on the display portion 7103 can be controlled. Furthermore, the remote controller 7110 may be provided with a display portion 7107 for displaying data output from the remote controller 7110.
Note that the television device 7100 is provided with a receiver, a modem, and the like. With the receiver, a general television broadcast can be received. Moreover, when the television device 7100 is connected to a communication network with or without wires via the modem, one-way (from a sender to a receiver) or two-way (between a sender and a receiver or between receivers) information communication can be performed.
When the display portion 7402 of the mobile phone 7400 illustrated in
There are mainly three screen modes of the display portion 7402. The first mode is a display mode mainly for displaying images. The second mode is an input mode mainly for inputting data such as text. The third mode is a display-and-input mode in which two modes of the display mode and the input mode are combined.
For example, in the case of making a call or creating an e-mail, a text input mode mainly for inputting text is selected for the display portion 7402 so that text displayed on a screen can be input. In that case, it is preferable to display a keyboard or number buttons on almost all the area of the screen of the display portion 7402.
When a detection device including a sensor for detecting inclination, such as a gyroscope or an acceleration sensor, is provided inside the mobile phone 7400, display on the screen of the display portion 7402 can be automatically changed by determining the orientation of the mobile phone 7400 (whether the mobile phone is placed horizontally or vertically for a landscape mode or a portrait mode).
The screen modes are switched by touching the display portion 7402 or operating the operation buttons 7403 of the housing 7401. Alternatively, the screen modes can be switched depending on kinds of images displayed on the display portion 7402. For example, when a signal of an image displayed on the display portion is a signal of moving image data, the screen mode is switched to the display mode. When the signal is a signal of text data, the screen mode is switched to the input mode.
Moreover, in the input mode, when input by touching the display portion 7402 is not performed within a specified period while a signal is detected by an optical sensor in the display portion 7402, the screen mode may be controlled so as to be switched from the input mode to the display mode.
The display portion 7402 may function as an image sensor. For example, an image of a palm print, a fingerprint, or the like is taken by touch on the display portion 7402 with the palm or the finger, whereby personal authentication can be performed. Further, by providing a backlight or a sensing light source which emits a near-infrared light in the display portion, an image of a finger vein, a palm vein, or the like can be taken.
Each of the display portions 7452L and 7452R is a component which can display images and to which information can be input by touch with a finger or the like. For example, when the icon for the installed program is selected by touch with a finger, the program can be started. Further, changing the distance between fingers touching two positions of the displayed image enables zooming in or out on the image. Drag of a finger touching one position of the displayed image enables drag and drop of the image. Moreover, selection of the displayed character or symbol on the displayed image of a keyboard by touch with a finger enables information input. The liquid crystal display device described in any of the above embodiments can be used for each of the display portions 7452L and 7452R of the flat computer 7450. Since the liquid crystal display device described in any of the above embodiments has high physical strength, a display defect does not occur in the display portions even when the display portions are touched; thus, the flat computer can be highly reliable.
Further, the flat computer 7450 can also include a gyroscope, an acceleration sensor, a global positioning system (GPS) receiver, a fingerprint sensor, or a video camera. For example, when a detection device including a sensor for detecting inclination, such as a gyroscope or an acceleration sensor, is provided, display on the screen can be automatically changed by determining the orientation of the flat computer 7450 (whether the computer is placed horizontally or vertically for a landscape mode or a portrait mode).
Furthermore, the flat computer 7450 can be connected to a network. The flat computer 7450 not only can display information on the Internet but also can be used as a terminal which controls another electronic device connected to the network from a distant place.
This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.
This application is based on Japanese Patent Application serial no. 2011-255164 filed with Japan Patent Office on Nov. 22, 2011, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-255164 | Nov 2011 | JP | national |
