Patent Application
20120182512
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device that adopts a mode in which the initial alignment of liquid crystal molecules is a vertical alignment, and which generates a transverse electric field to perform control of the liquid crystal molecules.
Liquid crystal display devices are characterized by being thin and light, and having low power consumption, and are widely used in various fields. The display performance of liquid crystal display devices has been remarkably improved over the years, and is now becoming superior to that of a CRT (cathode ray tube).
The display system of a liquid crystal display device is defined by the manner in which liquid crystals are aligned in cells. Various display systems such as a TN (twisted nematic) mode, an MVA (multi-domain vertical alignment) mode, an IPS (in-plane switching) mode, and an OCB (optically self-compensated birefringence) mode are already known as display systems of liquid crystal display devices.
Among these, the IPS mode is a system that controls the molecular alignment state of nematic liquid crystals by disposing a comb-shaped electrode pair on a substrate, arranging comb tooth portions of the comb-shaped electrode pair in a staggered configuration, and forming an electric field in a horizontal direction to the substrate between the comb tooth portions (for example, see Patent Literature 1 to 4). More particularly, according to the IPS mode, a light blocking state and a light transmitting state are controlled by providing a polarizer and forcefully changing the molecular alignment state of nematic liquid crystals to a vertical direction or a horizontal direction relative to a substrate by switching the direction of an applied electric field in accordance with an input signal. The IPS mode can obtain response speeds that are close to 100 times faster than response speeds in the TN mode. In the respective disclosures of the above described Patent Literature, various forms of arranging comb-shaped electrodes to improve characteristics in the IPS mode are described.
In general, liquid crystal display devices, and not just liquid crystal display devices that adopt the IPS mode, have various circuits for performing image display (for example, see Patent Literature 5). For example, an image signal processing circuit that converts information that is supplied from outside into signals that a liquid crystal display panel can display, a data line drive circuit for supplying an image signal to a pixel array, and a gate line drive circuit that supplies a control signal so as to select one gate line for each pixel array to display an image on a liquid crystal display panel for a period of time during one frame period are provided in a liquid crystal display device.
Regarding the above described IPS mode, recently, a display system has been proposed that adopts a mode that, using nematic liquid crystals having positive dielectric anisotropy as a liquid crystal material, controls the alignment of liquid crystal molecules by generating a transverse electric field using a pair of electrodes that include comb teeth, while vertically aligning the nematic liquid crystals and maintaining a high contrast characteristic.
According to the aforementioned mode, liquid crystal molecules are aligned in a bent shape in the transverse direction, the director distribution forms an arch shape along the transverse electric field, and there are complementary alignment characteristics between two adjacent electrodes. Hence, even when viewing the display surface from an oblique direction, the display surface can be viewed with a display quality that is the same as when viewing the display surface from the front direction. Accordingly, the problem whereby, for example, as in the VA mode, the birefringence state of light differs between the front direction and an oblique direction because liquid crystal molecules are a rod-like shape and consequently the voltage-transmittance characteristics (V-T characteristics) change depending on the viewing angle is solved.
According to this basic configuration, a bent electric field is formed by application of an electric field, and since two domains in which the director orientations are symmetric to each other are formed in a region between the pair of electrodes in the liquid crystal layer, a wide viewing angle characteristic can be obtained.
However, as a result of conducting studies in further detail regarding response speeds, the applicants of the present application found that although a change (fall) in which liquid crystal molecules align in the vertical direction from the horizontal direction relative to a substrate surface is fast, a change (rise) in which liquid crystal molecules align in the horizontal direction from the vertical direction relative to a substrate surface can not be considered to be fast, and therefore the response characteristics with respect to a response from a state in which the voltage is off to a state in which the voltage is turned on are low in comparison to response characteristics with respect to a response from a state in which the voltage is on to a state in which the voltage is turned off.
The present invention has been conceived in view of the above described circumstances, and an object of the present invention is to provide a liquid crystal display device in which the response characteristics of liquid crystal molecules are improved.
The applicants of the present application performed various studies regarding methods to improve the response characteristics of liquid crystal molecules, and focused on the electrode structure of the liquid crystal display device according to the above described mode. As a result, the applicants of the present application found that the liquid crystal display device according to the above described mode that is currently proposed controls the alignment of liquid crystal molecules by means of comb-shaped electrodes that form a pair per picture element, and conceived of providing an additional pair of comb-shaped electrodes to enable control of the alignment properties of liquid crystal molecules using the additional pair of comb-shaped electrodes also. Furthermore, the applicants of the present application found that by adjusting the arrangement relationship between the transmission axis of a polarizer and the long axis of a comb-shaped electrode pair, transmittance of light and blocking of light by the polarizer can be controlled utilizing a fact that a response from a state in which a display is on to a state in which the display is off is a change (rise) in which liquid crystal molecules align in a horizontal direction from a vertical direction when a high voltage is applied thereto, and conceived of enabling a fast response to be obtained with respect to both a response from an off state to an on state and a response from an on state to an off state of a display.
More specifically, the applicants of the present application found that, for one of the comb-shaped electrode combinations, by adjusting so that a long axis of a comb tooth portion of the comb-shaped electrodes and a transmission axis of one polarizer form an angle of substantially 45°, and for the other of the comb-shaped electrode combinations, by adjusting so that a long axis of a comb tooth portion of the comb-shaped electrodes and a transmission axis of another polarizer are parallel or orthogonal, and furthermore, by disposing the respective comb-shaped electrode combinations so as to overlap with each other when viewing the aforementioned pair of substrate surfaces from a normal line direction, for example, when the aforementioned one of the comb-shaped electrode combinations is used to apply a voltage to form a transverse electric field and generate an angle between the alignment orientation of the liquid crystal molecules and the transmission axis orientation of the polarizer, a state is entered in which light can pass through the polarizer. Further, on the other hand, when the aforementioned other of the comb-shaped electrode combinations is used to apply a voltage to form a transverse electric field to make the alignment orientation of the liquid crystal molecules and the transmission axis orientation of the polarizer orthogonal or parallel, a state is entered in which light is blocked by the polarizer. Thus, the applicants of the present application found that, with respect to turning the display off, control can be performed with fast rise characteristics by applying a high voltage in a direction that makes the alignment orientation of liquid crystal molecules parallel or vertical relative to the axis of a polarizer, and with respect to turning the display on, control can be performed by means of the fall characteristics of the liquid crystal molecules.
Thus, the applicants of the present application successfully solved the above described problem, and accomplished the present invention.
More specifically, according to the present invention there is provided a liquid crystal display device including a pair of substrates that are disposed facing each other, and a liquid crystal layer that is sandwiched between the pair of substrates, wherein: the liquid crystal layer contains liquid crystal molecules having positive dielectric anisotropy; the liquid crystal molecules align in a vertical direction relative to surfaces of the pair of substrates in a state in which a voltage is not applied thereto; the pair of substrates includes two or more sets of comb-shaped electrode pairs in which comb tooth portions of each comb-shaped electrode are alternately disposed with each other with a certain space therebetween; one substrate of the pair of substrates comprises a first polarizer; another substrate of the pair of substrates comprises a second polarizer; a long axis of a comb tooth portion of a first comb-shaped electrode pair among the two or more sets of comb-shaped electrode pairs and a transmission axis of the first polarizer form an angle of substantially 45′; a long axis of a comb tooth portion of a second comb-shaped electrode pair among the two or more sets of comb-shaped electrode pairs and a transmission axis of the second polarizer are in a parallel or orthogonal relationship with each other; the transmission axis of the first polarizer and the transmission axis of the second polarizer are orthogonal to each other; and the first comb-shaped electrode pair and the second comb-shaped electrode pair overlap with each other when the surfaces of the pair of substrates are viewed from a normal line direction.
Hereunder, the liquid crystal display device of the present invention is described in detail.
The liquid crystal display device of the present invention includes a pair of substrates that are disposed facing each other, and a liquid crystal layer that is sandwiched between the pair of substrates. Liquid crystal molecules whose alignment properties are controlled by application of a certain voltage are filled in the liquid crystal layer. By providing wiring, an electrode, a semiconductor device and the like on one or both of the pair of substrates, it is possible to apply a voltage into the liquid crystal layer and control the alignment properties of the liquid crystal molecules.
The liquid crystal layer contains liquid crystal molecules that have positive dielectric anisotropy. Consequently, when a voltage is applied into the liquid crystal layer, the liquid crystal molecules align along the direction of an electric field, and as a result, a group of liquid crystal molecules form an arch shape.
The liquid crystal molecules align in a vertical direction relative to surfaces of the pair of substrates in a state in which a voltage is not applied thereto. By regulating the initial alignment of the liquid crystal molecules in this manner, blocking of light at the time of a black display can be performed effectively. As a method of vertically aligning liquid crystal molecules in a state in which a voltage is not applied thereto, for example, a method in which a vertical alignment layer is disposed on a surface that contacts with the liquid crystal layer of one or both of the pair of substrates may be mentioned. As used herein, the term “vertical” includes not only a completely vertical state, but also a substantially vertical state. In this case, the term “vertical” preferably refers to an angle within a range of 90±2°.
The pair of substrates includes two or more sets of comb-shaped electrode pairs in which comb tooth portions of each comb-shaped electrode are alternately disposed with each other with a certain space therebetween. The term “comb tooth portion” of the comb-shaped electrodes refers to linear parts that are formed so as to protrude planarly from a part that serves as a trunk portion. An electric field that arises when a potential difference is applied between a pair of electrodes having such kind of comb tooth portions is an arch-shaped transverse electric field. Since liquid crystal molecules exhibit alignment properties in accordance with the direction of an electric field of this kind, the same display is shown regardless of whether the viewing direction is the front direction or an oblique direction relative to the substrate surface, and consequently favorable viewing angle characteristics are obtained.
One substrate of the pair of substrates comprises a first polarizer, and another substrate of the pair of substrates comprises a second polarizer. Thus, the liquid crystal layer is disposed between the first polarizer and the second polarizer, and it is possible to utilize characteristics of the liquid crystal layer that change a polarizing state of light that passes through the liquid crystal layer to control an on state and an off state of the display.
A long axis of a comb tooth portion of a first comb-shaped electrode pair among the two or more sets of comb-shaped electrode pairs and a transmission axis of the first polarizer form an angle of substantially 45°, a long axis of a comb tooth portion of a second comb-shaped electrode pair among the two or more sets of a comb-shaped electrode pairs and a transmission axis of the second polarizer are in a parallel or orthogonal relationship with each other, the transmission axis of the first polarizer and the transmission axis of the second polarizer are orthogonal to each other, and the first comb-shaped electrode pair and the second comb-shaped electrode pair overlap with each other when the surfaces of the pair of substrates are viewed from a normal line direction. Thus, as described above, it is possible to control a change in the liquid crystal molecules from a state in which the display is off to a state in which the display is on by means of fall characteristics of the liquid crystal molecules, and the overall response speed is significantly improved. As used herein, the term “parallel” includes not only a completely parallel state, but also a substantially parallel state. In this case, the term “parallel” preferably refers to a state in which an angle that the relevant axes or the like form with respect to each other is within a range of 0±2°. Further, as used herein, the term “orthogonal” includes not only a completely orthogonal state, but also a state in which axes or the like are substantially orthogonal to each other. In this case, the term “orthogonal” preferably refers to a state in which an angle that the relevant axes or the like form with respect to each other is within a range of 90±2°. Furthermore, as used herein, the term “substantially 45°” specifically refers to an angle within a range of 45±2°.
The configuration of the liquid crystal display device of the present invention is not especially limited by other components as long as it essentially includes such components.
Preferable embodiments of the liquid crystal display device of the present invention are mentioned in more detail below.
Preferably, the first and second comb-shaped electrode pairs are disposed on respectively different substrates among the pair of substrates. By forming the first and second comb-shaped electrode pairs on different substrates to each other, each substrate can individually and efficiently exert the respective functions of transmitting light and blocking light. Further, in this case, the first comb-shaped electrode pair and a polarizer having a transmission axis that forms an angle of substantially 45° with a long axis of a comb tooth portion of the first comb-shaped electrode pair are formed on the same substrate, and the second comb-shaped electrode pair and a polarizer having a transmission axis that is parallel or orthogonal to a long axis of a comb tooth portion of the second comb-shaped electrode pair are formed on the same substrate. Hence, a deviation is less likely to arise with respect to positional matching between each axis that is provided for each substrate.
Preferably, the first and second comb-shaped electrode pairs are disposed on the same substrate among the pair of substrates. By forming the first and second comb-shaped electrode pairs on the same substrate, the process of manufacturing the electrodes can be performed by repeating the same process, and hence the manufacturing process is simplified. Further, a deviation is less likely to arise with respect to positional matching between the first comb-shaped electrode pair and second comb-shaped electrode pair. In this connection, the first and second comb-shaped electrode pairs are disposed on respectively different layers through an insulator. At this time, although either one of the first and second comb-shaped electrode pairs may be disposed on a side that is closer to the liquid crystal layer, it is preferable that a comb-shaped electrode pair that is on a side that applies a larger voltage is disposed furthest from the liquid crystal layer, since this arrangement allows a voltage to be applied more efficiently to the liquid crystal layer.
Preferably, one comb-shaped electrode of the first comb-shaped electrode pair is a pixel electrode that supplies a signal voltage, and another comb-shaped electrode of the first comb-shaped electrode pair is a common electrode that supplies a common voltage. It is possible to control the voltage for respective picture elements and realize a high-definition display by supplying separate signal voltages that correspond to respective picture elements to one comb-shaped electrode of the comb-shaped electrode pair in which the long axis of comb tooth is in a direction which forms an angle of substantially 45° with the transmission axis of the polarizer, and applying a common voltage to the other comb-shaped electrode of the comb-shaped electrode pair without differentiating among the picture elements.
Preferably, a signal voltage that is supplied by a pixel electrode of the second comb-shaped electrode pair is greater than a signal voltage that is supplied by the pixel electrode of the first comb-shaped electrode pair. As a result, the response speed is improved, and a different voltage can be applied into the liquid crystal layer even from a state in which a signal voltage is being retained in the liquid crystal layer.
Preferably, a space between each comb tooth portion of the second comb-shaped electrode pair is smaller than a space between each comb tooth portion of the first comb-shaped electrode pair. By making a space between each comb tooth portion shorter, an electric field formed between each comb tooth portion becomes denser, and hence a voltage applied into the liquid crystal layer can be increased. Accordingly, the response speed is improved, and a different voltage can be applied into the liquid crystal layer even from a state in which a signal voltage is being retained in the liquid crystal layer.
Preferably, a substrate having the first comb-shaped electrode pair has a plurality of rows of scanning signal lines, and thin film transistors that are connected to each of the plurality of rows of scanning signal lines; a scanning signal line of a given row among the plurality of rows of scanning signal lines applies a scanning voltage to a thin film transistor that is connected to a scanning signal line of the given row at a timing of supplying a signal voltage to the pixel electrode of the first comb-shaped electrode pair; and a scanning signal line of a row preceding the given row among the plurality of rows of scanning signal lines applies a scanning voltage to a thin film transistor that is connected to the scanning signal line of the row preceding the given row at a timing of supplying a signal voltage to the pixel electrode of the second comb-shaped electrode pair.
By applying a voltage to the second comb-shaped electrode pair using a scanning signal line of a row (n−xth row) preceding a scanning signal line of a given nth row, a gradation display can be obtained by means of fall characteristics of liquid crystal molecules and a black display can be obtained by means of high-speed rise characteristics of liquid crystal molecules generated by application of a high voltage. Further, a black display can be controlled using a scanning voltage that is applied to a scanning signal line that controls a timing at which a signal voltage is supplied, and thus an efficient configuration can be realized. Furthermore, since a scanning voltage is normally larger than a signal voltage, it is possible to switch to a black display even from a state in which a signal voltage is being retained in the liquid crystal layer, and thus the configuration is efficient.
Preferably, the scanning signal line of the row (n−xth row) preceding the scanning signal line of the given nth row precedes the scanning signal line of the given nth row by two rows or more (x>1). This is because the response of liquid crystal molecules is longer than a writing time.
Preferably, a substrate having the first comb-shaped electrode pair has a plurality of rows of scanning signal lines, and thin film transistors that are connected to each of the plurality of rows of scanning signal lines; a scanning signal line of a given row among the plurality of rows of scanning signal lines applies a scanning voltage to a thin film transistor that is connected to a scanning signal line of the given row at a timing of supplying a signal voltage to the pixel electrode of the first comb-shaped electrode pair; and the pixel electrode of the first comb-shaped electrode pair is connected to a common electrode of the first comb-shaped electrode pair through a resetting thin film transistor that is controlled by a scanning signal line of a row that is next to the given row, or to a storage capacitor wiring that forms a capacitance between the pixel electrode of the first comb-shaped electrode pair and the storage capacitor wiring.
By placing a voltage within the liquid crystal layer that is applied by means of the first comb-shaped electrode pair in a non-application state (reset) during a period from after a signal voltage has been supplied to the second comb-shaped electrode pair by means of a scanning signal line of an nth row until a voltage is applied by means of the first comb-shaped electrode pair, compared to a state in which a certain voltage is retained in the liquid crystal layer by the first comb-shaped electrode pair, the voltage that is applied by the second comb-shaped electrode pair can be increased and the response speed of liquid crystal molecules is improved. Further, since a configuration is adopted in which, simultaneously with a signal voltage being supplied to the first comb-shaped electrode pair by a scanning signal line of an n+1th row, the voltage of a pixel electrode that is connected to a scanning signal line of the previous row (nth row) to the n+1th row is reset, the configuration can be considered efficient. In this connection, the reset timing can be adjusted in accordance with the scanning order of the rows of scanning signal lines.
According to the liquid crystal display device of the present invention, it is possible to significantly improve a response speed in a liquid crystal display device of a type that generates a transverse electric field using a pair of electrodes that have comb teeth with respect to a liquid crystal layer including nematic liquid crystal having positive dielectric anisotropy in which the initial alignment is a vertical alignment.
The present invention will be mentioned in more detail referring to the drawings in the following embodiments, but is not limited to these embodiments.
A liquid crystal display device according to Embodiment 1 is of a type that controls an image display by controlling the alignment of liquid crystal molecules whose initial alignment is a vertical alignment by generating an arch-shaped transverse electric field with respect to a liquid crystal layer by means of a pair of electrodes that are formed in the same substrate.
The liquid crystal display device according to Embodiment 1 includes a liquid crystal display panel having a pair of substrates that are arranged facing each other, and a liquid crystal layer that is sandwiched between the pair of substrates. More specifically, the liquid crystal display device of Embodiment 1 includes, in order from a back surface side to an observation surface side, a TFT substrate, a liquid crystal layer, and an opposed substrate. The liquid crystal layer contains nematic liquid crystals having positive dielectric anisotropy (Δ∈>0). The liquid crystal display device of Embodiment 1 also includes a backlight unit on a back surface side of the liquid crystal display panel. Light emitted from the backlight unit passes through the TFT substrate, the liquid crystal layer, and the opposed substrate in that order.
In the liquid crystal display device according to Embodiment 1, a display region is constituted by a plurality of picture elements (subpixels) that are formed in a matrix shape, and a configuration is adopted so that driving can be controlled for the respective picture elements. A plurality of the picture elements (for example, three picture elements including a red, a green, and a blue picture element) constitute a single pixel. In this connection, as used herein, the term “picture element” refers to an area that is surrounded by adjacent gate wirings and source wirings.
The polarizer on the lower side in
Although the respective sets constituted by a comb-shaped electrode pair are formed on respectively different plane surfaces, each of the comb-shaped electrodes constituting a comb-shaped electrode pair is formed on the same plane surface. One of the comb-shaped electrode pairs is composed of pixel electrodes 21 and 23 to which a signal voltage is supplied, and the other of the comb-shaped electrode pairs is composed of common electrodes 22 and 24 to which a common electrode is supplied. Each of the comb-shaped electrodes 21, 22, 23 and 24 has rectilinear-shaped comb tooth portions, and the long axes of the respective comb tooth portions are parallel with each other. Solid lines in
Among the two sets of comb-shaped electrode pairs, a comb-shaped electrode pair that is nearer the first polarizer 1 is a first comb-shaped electrode pair, and a comb-shaped electrode pair that is nearer the second polarizer 2 is a second comb-shaped electrode pair. As shown in
This arrangement relationship is the basic configuration of the comb-shaped electrode pairs and the polarizers, and hence the behavior of liquid crystal molecules inside the liquid crystal layer is separately controlled by the first comb-shaped electrode pair and the second comb-shaped electrode pair, respectively. In particular, with respect to liquid crystal molecules having positive dielectric anisotropy and whose initial alignment is a vertical alignment, it is possible to adjust switching of the display device using an alignment change to a faster direction (from a horizontal direction to a vertical direction), and response characteristics can be significantly improved for the overall display device.
The plane surface configuration of the display regions of the liquid crystal display device according to Embodiment 1 will now be described in further detail.
The source wiring 11 is connected to a source driver, and a source voltage (signal voltage) that serves as an image signal that is supplied from the source driver is applied to the TFT pixel electrode 21 via the TFT 71. The gate wiring 12 is connected to a gate driver. A gate voltage (scanning voltage) that serves as a scanning signal that is supplied in pulses at a predetermined timing from the gate driver is applied to the TFT 71. A common voltage that is maintained at a constant voltage is applied to the TFT common electrode 22.
Hereunder, the configuration according to Embodiment 1 is described in detail by describing each manufacturing stage of the liquid crystal display device using
First, as shown in
Next, as shown in
When forming the drain electrode 33 of the TFT, the drain electrode 33 is extended as far as the center of the picture element. Further, a rectilinear area (hereunder, also referred to as “Cs electrode”) is provided by further extending drain lead-out wiring 13 to a position that overlaps with the Cs wiring through the insulator. Thus, a storage capacitance of a constant amount is formed between the Cs wiring 13 and the Cs electrode 33, and an image signal is stably retained.
Next, as shown in
Further, a contact portion (second contact portion) 42 is provided in one portion of the gate wiring 12. The second contact portion 42 is an area that is provided to connect the gate wiring 12 on the TFT substrate side and the pixel electrode on the opposed substrate side. Thus, a scanning signal that is supplied through the gate wiring 12 on the TFT substrate side is also supplied to the pixel electrode on the opposed substrate side via the second contact portion 42.
Next, the TFT pixel electrode 21 and the TFT common electrode 22 are provided as shown in
The TFT pixel electrode 21 is provided so as to have a trunk portion and a plurality of comb tooth portions that protrude planarly from a part of the trunk portion.
The TFT common electrode 22 is formed on a different layer to the source wiring 11 and the gate wiring 12 through the insulator, and is provided so as to overlap with the source wiring 11 and the gate wiring 12, respectively. The area of the TFT common electrode 22 that overlaps with the source wiring 11 and the gate wiring 12 is the trunk portion. The trunk portion of the TFT common electrode 22 constitutes a matrix shape that corresponds to a combined shape of the source wiring 11 and the gate wiring 12 as viewed in terms of the overall display region. The TFT common electrode 22 is provided such that comb tooth portions protrude planarly from a part of the trunk portion.
The comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 each form a semi-inverted V shape in picture element units, and are provided so as to be parallel with each other. Further, the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 are disposed so as to be alternately disposed with each other with a certain space therebetween.
Thus, the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 are provided to be also parallel with the source wiring 11. Accordingly, the comb tooth portions of the TFT pixel electrode 21 are also in a parallel relation with a part of the trunk portion of the TFT common electrode 22.
Preferably, the width of the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 is set to between 1 and 6 μm, and more preferably between 2.5 and 4.0 μm. Further, a width of drain lead-out wiring 16 is preferably set to between 1 and 6 μm.
The size of the space between the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 is preferably between 2.5 and 20.0 μm, and more preferably is between 4.0 and 12.0 μm. If the size exceeds 20.0 μm or is less than 2.5 μm, the transmittance may decrease.
Examples of materials that can be used as the material of the TFT pixel electrode 21 and the TFT common electrode 22 include a metal oxide such as indium tin oxide (ITO) or indium zinc oxide (IZO), or a metal such as aluminum or chrome. From the viewpoint of improving transmittance, a translucent metal oxide is preferable. In this connection, since the TFT pixel electrode 21 and the TFT common electrode 22 that form a pair are disposed on the same layer, the manufacturing process is simplified by using the same material for these electrodes.
The common electrode 22 on the TFT substrate side and the common electrode on the opposed substrate side are connected at an area (not shown) other than a picture element. Therefore, the common electrode on the opposed substrate side shares the electric potential of the common electrode 22 on the TFT substrate side.
Thus, a TFT substrate having a basic configuration as shown in
The opposed pixel electrode 23 has a trunk portion and a plurality of comb tooth portions that extend from one part of the trunk portion. The opposed common electrode 24 also has a trunk portion and a plurality of comb tooth portions that extend from one part of the trunk portion.
The comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 are rectilinear, and are provided so as to be parallel with each other. The comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 are disposed so as to be alternately disposed with each other with a certain space therebetween.
The opposed pixel electrode 23 connects with the gate wiring 12 included in the TFT substrate through a contact portion 42.
The opposed common electrode 24 connects with the TFT common electrode 22 included in the TFT substrate at an area other than a picture element. Accordingly, the TFT common electrode 22 and the opposed common electrode 24 are equipotential.
The gate wiring of the TFT substrate as shown in
The width of the comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 can be made the same as the width of the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22.
Although the size of the space between the comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 can be made the same as the size of the space between the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22, preferably the size of the space between the comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 is smaller than the size of the space between the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22. Thus, the density of an electric field between the comb tooth portions of the opposed pixel electrode 23 and the comb tooth portions of the opposed common electrode 24 increases, and the response speed of liquid crystal molecules improves.
The same materials that are used for the TFT pixel electrode 21 and TFT common electrode 22 can be used for the opposed pixel electrode 23 and the opposed common electrode 24.
The configuration and driving method of the liquid crystal display device according to Embodiment 1 will now be described in detail.
As shown in
The TFT substrate 50 includes a transparent substrate 51 having translucency that is made of glass or resin or the like as a main constituent, and also has the first comb-shaped electrode pair on a surface on the liquid crystal layer 4 side of the transparent substrate 51, and the first polarizer 1 on a surface on the opposite side to the liquid crystal layer of the transparent substrate 51. The comb teeth of each of the pixel electrode 21 and the common electrode 22 that constitute the first comb-shaped electrode pair are alternately disposed with a certain space therebetween.
The opposed substrate 60 includes a transparent substrate 61 having translucency that is made of glass or resin or the like as a main constituent, and also has the second comb-shaped electrode pair on a surface on the liquid crystal layer 4 side of the transparent substrate 61, and the second polarizer 2 on a surface on the opposite side to the liquid crystal layer of the transparent substrate 61. The comb teeth of each of the pixel electrode 23 and the common electrode 24 that constitute the second comb-shaped electrode pair are alternately disposed with a certain space therebetween.
In Embodiment 1, a color display can be realized by providing color filters in the TFT substrate 50 or the opposed substrate 60. The color filters, for example, include three colors, namely, red, green and blue. By disposing a color filter of one color so as to correspond to a single picture element, it is possible to individually drive each color, and a desired color can be obtained in pixel units in which red, green, and blue are taken as one set. In this connection, the colors of the color filter need not necessarily be these colors, and a configuration may be adopted in which pixels are constituted by a set of color filters that include four or more colors. Further, a black matrix (BM) of a black color may be disposed between the color filters of each color, and thus color mixing and light leakage can be prevented.
The TFT substrate 50 and the opposed substrate 60 are adhered to each other by a sealing agent that is applied along the outer circumference of the display region via a columnar spacer such as a resin.
Vertical alignment layers 52 and 62 are formed on the respective surfaces that contact the liquid crystal layer 4 of the TFT substrate 50 and the opposed substrate 60. By means of the vertical alignment layers 52 and 62, the initial alignment of the liquid crystal molecules can be made a vertical alignment relative to the surface of the TFT substrate 50 and the surface of the opposed substrate 60. A resin such as polyimide may be mentioned as an example of the material of the vertical alignment layers 52 and 62.
As shown in
However, as shown in
As shown in
The opposed pixel electrode 23 is connected to the gate wiring through the second contact portion 42, and as shown in
According to Embodiment 1, since V2 is set to a larger value than V1, by application of the voltage V2, the liquid crystal molecules 5 exhibit an alignment along an arch-shaped transverse electric field formed between the comb-shaped electrode pair on the opposed substrate 60 side. That is, since the liquid crystal molecules 5 align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair, light that passes through the liquid crystal layer 4 in this state is polarized to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (second polarizer) 2 on the opposed substrate 60 side. As a result, light is blocked by the second polarizer 2 and the display enters an “off” (black display) state.
The response to enter a black display state in this case is performed by means of an alignment change in which a high voltage is applied to liquid crystal molecules that were originally aligned in a direction at an angle of 45 degrees relative to the direction of the transmission axis of the polarizer to thereby cause the liquid crystal molecules to rotate in the horizontal or vertical direction relative to the direction of the transmission axis of the polarizer. The aforementioned response compares favorably with a response performed in the conventional manner by means of an alignment change that causes liquid crystal molecules that were originally aligned in a horizontal direction relative to a substrate surface to fall in the vertical direction. Further, since a response from a black display state to a gradation display state uses fall characteristics that cause liquid crystal molecules that were aligned in the direction of the transmission axis of the polarizer by means of a high electric field to rotate while applying a lower voltage thereto, response characteristics of a change to a gradation display state are improved.
In this connection, according to Embodiment 1, the gate voltage V2 of the gate wiring of the TFT substrate 50 is used as a voltage that is applied to the opposed pixel electrode 23, and the voltage is a sufficient size with respect to the source voltage V1 that is applied to the TFT pixel electrode 21.
On the other hand, as shown in
By application of the voltage V1, the liquid crystal molecules 5 exhibit an alignment along an arch-shaped transverse electric field formed between the comb-shaped electrode pair on the TFT substrate 50. That is, since the liquid crystal molecules 5 align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair, light that passes through the liquid crystal layer in this state is polarized to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (first polarizer) 1 on the TFT substrate 50 side. As a result, light that has passed through the liquid crystal layer 4 passes through the second polarizer 2, and thus the display enters an “on” (gradation display) state. The change in alignment in this case is a change to a direction in which the voltage falls, and originally the response characteristics are favorable.
The behavior of liquid crystal molecules in the liquid crystal layer as well as changes in the polarizing state of light in the liquid crystal display device of Embodiment 1 described above will now be described in further detail for the respective timings.
First, with respect to
When light from the backlight is incident within the liquid crystal display panel, first, only light in the transmission axis direction of the polarizer is transmitted by the polarizer (first polarizer) 1 on the TFT substrate side.
Subsequently, the light passes through the comb-shaped electrodes 21 and 22 on the TFT substrate side and liquid crystal molecules (lower layer liquid crystals) 4a adjacent to the TFT substrate. However, since a voltage generated by the comb-shaped electrodes 21 and 22 of the TFT substrate is 0V, the lower layer liquid crystals 4a do not receive the influence of an electric field and remain vertically aligned, and the light passes through while retaining the vibration direction thereof in the same direction.
Next, the light passes through liquid crystal molecules (center liquid crystals) 4b located in the center region of the liquid crystal layer. At this time, the center liquid crystals 4b receive the influence of the voltage V2 generated by the comb-shaped electrodes 23 and 24 on the opposed substrate side, and tilt in a diagonal direction relative to the substrate surface. However, the orientation of the long axis of the liquid crystal molecules when viewed from a normal line direction relative to the substrate surface is orthogonal to the orientation of the long axis of the comb tooth portion of the comb-shaped electrodes 23 and 24 on the opposed substrate side, that is, is a parallel direction to the vibration direction of the light. Therefore, light that is transmitted through the center liquid crystals 4b does not receive the influence of birefringence of the liquid crystal molecules, and passes through while retaining the same vibration direction.
Subsequently, the light passes through liquid crystal molecules (upper layer liquid crystals) 4c that are adjacent to the opposed substrate, and comb-shaped electrodes 23 and 24 on the opposed substrate side. Although the size of the tilt of the upper layer liquid crystals 4c is different to that of the center liquid crystals 4b, because the upper layer liquid crystals 4c receive the influence of the voltage V2 that is generated by the comb-shaped electrodes 23 and 24 on the opposed substrate side, the tendency is the same as for the center liquid crystals 4b, and the orientation of the long axis of the liquid crystal molecule when viewed from a normal line direction relative to the substrate surface is a parallel direction to the vibration direction of the light. Consequently, light that is transmitted through the upper layer liquid crystals 4c does not receive the influence of birefringence of the liquid crystal molecules and passes through while retaining the same vibration direction.
Next, the light arrives at the polarizer (second polarizer) 2 on the opposed substrate side. Since the orientation of the transmission axis of the second polarizer 2 is orthogonal to the direction of vibration of the light that has passed through the liquid crystal layer 4, the light is blocked by the second polarizer 2.
Thus, in a state in which a voltage is being applied into the liquid crystal layer by means of the comb-shaped electrodes 23 and 24 on the opposed substrate side, the display is a black display (an off state).
Next, with respect to
When light from the backlight is incident within the liquid crystal display panel, first, only light in the transmission axis direction of the polarizer is transmitted by the polarizer (first polarizer) 1 on the TFT substrate side.
Next, the light passes through the comb-shaped electrodes 21 and 22 on the TFT substrate side and the lower layer liquid crystals 4a. At this time, since the voltage V1 is being applied into the liquid crystal layer 4 by means of the comb-shaped electrodes 21 and 22 of the TFT substrate, the lower layer liquid crystals 4a tilt in an oblique direction relative to the substrate surface, and the orientation of the long axis of the lower layer liquid crystal 4a when the substrate surface is viewed from the normal line direction is orthogonal to the long axis direction of the comb tooth portion of the comb-shaped electrodes 21 and 22 on the TFT substrate side. That is, the long axis direction of the liquid crystal molecule when the substrate surface is viewed from the normal line direction and the vibration direction of the light form an angle of substantially 45°, and light that has passed through the lower layer liquid crystals 4a forms elliptically polarized light having a long axis in a direction that forms an angle of substantially 45° with the long axis direction of the liquid crystal molecule when the substrate surface is viewed from the normal line direction.
Subsequently, the light passes through the center liquid crystals 4b. At this time, since the center liquid crystals 4b also receive the influence of the voltage V1 generated by the comb-shaped electrodes 21 and 22 on the TFT substrate side, the orientation of the long axis of the liquid crystal molecule when viewed from a normal line direction with respect to the substrate surface is orthogonal to the long axis direction of the comb tooth portion of the comb-shaped electrodes 21 and 22 on the TFT substrate side. However, since the tilt angle of the center liquid crystals 4b with respect to the substrate surface is greater than the tilt angle of the lower layer liquid crystals 4a with respect to the substrate surface, light that is transmitted through the center liquid crystals 4b is converted to elliptically polarized light in which the orientation of the long axis is rotated by 90°.
Next, the light passes through the upper layer liquid crystals 4c, and the comb-shaped electrodes 23 and 24 on the opposed substrate side. Since the voltage generated by the comb-shaped electrodes 23 and 24 on the opposed substrate side is 0V, the influence of an electric field on the upper layer liquid crystals 4c is small and the upper layer liquid crystals 4c are close to a state of vertical alignment. As a result of this alignment, light transmitted through the upper layer liquid crystals 4c is converted from elliptically polarized light to substantially linearly polarized light while retaining the long axis orientation of the light as it is. More specifically, the light is converted to light having a vibration direction in a direction that forms an angle of 90° with respect to the vibration direction of the light when the light was incident.
Subsequently, the light arrives at the polarizer (second polarizer) 2 on the opposed substrate side. Since the direction of the transmission axis of the second polarizer 2 is parallel to the direction of vibration of the light that has passed through the liquid crystal layer 4, the light can pass through the second polarizer 2.
Thus, in a state in which a voltage is being applied into the liquid crystal layer 4 by the comb-shaped electrodes 21 and 22 on the TFT substrate side, the display is a gradation display (in an “on” state), and a transmittance that is in accordance with the voltage can be obtained.
According to the liquid crystal display device of Embodiment 1, switching between off and on states is performed in this manner at separate timings and using separate pairs of comb-shaped electrodes. Further, for all gradation displays, a black display is obtained with a fast response by a rise effect that is caused by the large voltage V2 that is applied to the comb-shaped electrode pair on the opposed substrate side when selecting the previous row (n−xth row), and a gradation display is obtained with a fast response by a fall effect that is caused by the voltage V1 that is applied to the comb-shaped electrode pair on the TFT substrate side when selecting the relevant row (nth row). Hence, dramatically improved response characteristics can be obtained for the overall display device.
Note that, in the liquid crystal display device of Embodiment 1, even in a case in which light is incident from the opposite direction to that described above, the light will exhibit similar changes, and hence the tendency for light to be transmitted or blocked by a polarizer will not change. Accordingly, in Embodiment 1, as long as the arrangement relationship between each comb-shaped electrode pair and each polarizer does not change, the incident direction of light may be from the opposed substrate side. Further, in Embodiment 1, the second comb-shaped electrode pair may be disposed on the TFT substrate side, and the first comb-shaped electrode pair may be disposed on the opposed substrate side. Furthermore, the voltage V2 that is applied to the comb-shaped electrode pair on the opposed substrate side need not necessarily be a voltage that is applied through the gate wiring.
According to the present embodiment, an example has been described in which the orientations of the comb tooth portions of the TFT common electrode and the TFT pixel electrode are at an angle of 45° with respect to the row direction, respectively, and the orientations of the comb tooth portions of the opposed common electrode and the opposed pixel electrode are orthogonal to the row direction, respectively. However, as long as the positional relationship with the polarizers is the same, the orientations of the comb tooth portions of the TFT common electrode and the TFT pixel electrode may be orthogonal to the row direction, respectively, and the orientations of the comb tooth portions of the opposed common electrode and the opposed pixel electrode may be arranged so as to be at an angle of 45° with respect to the row direction, respectively. In this case, the transmission axes of the first and second polarizers are in directions that are at an angle of 45° with respect to the row direction.
A liquid crystal display device according to Embodiment 2 is the same as the liquid crystal display device according to Embodiment 1 except that the liquid crystal display device according to Embodiment 2 includes a mechanism (reset electrode) for resetting a voltage that is retained in the pixel electrode on the TFT substrate side to 0V.
Hereunder, the configuration according to Embodiment 2 is described in detail by describing each manufacturing stage of the liquid crystal display device using
First, as shown in
Next, as shown in
When forming the drain electrode 33 of the TFT, the drain electrode 33 is extended as far as the center of the picture element. A Cs electrode is provided by further extending the drain lead-out wiring 13 to a position that overlaps with the Cs wiring through the insulator. Thus, a storage capacitance of a constant amount is formed between the Cs wiring 13 and the Cs electrode 33, and an image signal is stably retained.
Further, in Embodiment 2, the drain electrode 33 is extended as far as the vicinity of the gate electrode 32 that constitutes the second TFT, and is connected with the reset electrode 36 through the semiconductor layer 35.
Next, as shown in
The first contact portion 41 is an area provided in the insulator that is formed between the drain electrode 33 and the TFT pixel electrode 21 to connect the drain electrode 33 and the TFT pixel electrode 21. Thus, the TFT 71 is connected to the TFT pixel electrode 21 through the drain electrode 33 and the first contact portion 41, and an image signal from the source wiring 11 is supplied at a predetermined timing to the TFT pixel electrode 21 through the TFT 71 that has been placed in an “on” state for a certain time period by input of a scanning signal.
The third contact portion 43 is provided to connect the TFT common electrode 22 and the reset electrode 36. As a result, the TFT common electrode 22 and the drain electrode 33 are connected through the second TFT, and by switching a gate voltage that is applied to data wiring of an adjacent row, the gate voltage of the adjacent row is applied to the second TFT, and the TFT pixel electrode 21 and the TFT common electrode 22 become equipotential and are reset.
A contact portion (second contact portion) 42 is also provided at a portion of the gate wiring. The second contact portion 42 is an area that is provided for connecting the gate wiring 12 on the TFT substrate side and the pixel electrode on the opposed substrate side. Thus, a scanning signal that is supplied through the gate wiring 12 on the TFT substrate side is also supplied to the pixel electrode on the opposed substrate side through the second contact portion 42.
Next, the TFT pixel electrode 21 and the TFT common electrode 22 are provided as shown in
The TFT pixel electrode 21 is provided so as to have a trunk portion and a plurality of comb tooth portions that protrude planarly from a part of the trunk portion.
The TFT common electrode 22 is formed on a different layer to the source wiring 11 and the gate wiring 12 through the insulator, and is provided so as to overlap with the source wiring 11 and the gate wiring 12, respectively. The area of the TFT common electrode 22 that overlaps with the source wiring 11 and the gate wiring 12 is a trunk portion 22a. The trunk portion 22a of the TFT common electrode constitutes a matrix shape that corresponds to a combined shape of the source wiring 11 and the gate wiring 12 as viewed in terms of the overall display region. The TFT common electrode 22 is provided such that comb tooth portions 21b protrude planarly from a part of the trunk portion 21a.
The comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 each form a semi-inverted V shape in picture element units, and are provided so as to be parallel with each other. Further, the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 are disposed so as to be alternately disposed with each other with a certain space therebetween.
Thus, the comb tooth portions of the TFT pixel electrode 21 and the comb tooth portions of the TFT common electrode 22 are provided so as to be also parallel with the source wiring 11. Accordingly, the comb tooth portions of the TFT pixel electrode 21 are also in a parallel relation with a part of the trunk portion of the TFT common electrode 22.
The design profile such as the shape, size, and material of the TFT pixel electrode 21 and the TFT common electrode 22 as well as the opposed pixel electrode 23 and the opposed common electrode 24 are the same as in Embodiment 1.
Thus, a TFT substrate having a basic configuration as shown in
As shown in
The opposed Cs electrode 81 is connected to the gate wiring 12a through a third TFT 73. More specifically, the gate wiring 12a is connected to a gate pad 37 through a contact portion (fifth contact portion) 45, and the gate pad 37 and the opposed Cs electrode 81 are connected to each other through the semiconductor layer 35 of the third TFT 73.
According to this configuration, when a gate voltage is transmitted through the gate wiring 12a and is applied to the gate electrode of the third TFT 73, by a switching operation of the third TFT 73, the gate voltage flows into the opposed Cs electrode 81 and thus a scanning signal can be supplied to the opposed pixel electrode.
The opposed Cs electrode 81 is also connected to the Cs wiring 82 through a fourth TFT 74. More specifically, the Cs wiring 82 is connected to a Cs pad 38 that has been lead out from the Cs wiring 82 through a contact portion (fifth contact portion) 45, and the Cs pad 38 and the opposed Cs electrode 81 are connected to each other through the semiconductor layer 35 of the fourth TFT 74.
According to this configuration, when the gate voltage is transmitted through the gate wiring 12b and applied to the gate electrode of the fourth TFT 74, by a switching operation of the fourth TFT 74, a pixel voltage that has been retained flows into the Cs wiring 82, and the opposed pixel electrode and the opposed Cs electrode 81 become equipotential and are reset. That is, the Cs pad 38 also functions as a reset electrode.
The gate wiring of the TFT substrate or gate wiring that is formed separately and independently on the opposed substrate may be utilized as gate wiring that applies a gate voltage to the comb-shaped electrode pair of the opposed substrate. Further, a TFT may be separately formed on the opposed substrate. When utilizing the gate wiring of the TFT substrate, it is necessary to route a wiring thorough a columnar spacer or the like that is provided between the TFT substrate and the opposed substrate at a position that is outside a display region of the TFT substrate. When drawing in the gate wiring using a columnar spacer, since the liquid crystal molecules may be disturbed around the columnar spacer, it is preferable to provide a light shielding portion at a region that overlaps with the columnar spacer.
The configuration and driving method of the liquid crystal display device according to Embodiment 2 will now be described in detail.
As shown in
The design profile such as the shape, size, and material of each member of the TFT substrate 11 and the opposed substrate are the same as in Embodiment 1.
As shown in
As shown in
However, as shown in
As shown in
When a gate voltage is applied to the gate wiring of the n−xth to n−1th rows shown in
The liquid crystal molecules in the n−xth row to which the voltage V2 is applied align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair. Hence, light that passes through the liquid crystal layer 4 in this state is polarized to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (second polarizer) 2 on the opposed substrate 60 side. As a result, the light is blocked by the second polarizer and the display enters an “off” (black display) state.
The response to enter a black display state in this case is performed by means of an alignment change in which a high voltage is applied to liquid crystal molecules that were originally aligned in a direction at an angle of 45 degrees relative to the direction of the transmission axis of the polarizer to thereby cause the liquid crystal molecules to rotate in the horizontal or vertical direction relative to the direction of the transmission axis of the polarizer. The aforementioned response compares favorably with a response performed in the conventional manner by means of an alignment change that causes liquid crystal molecules that were originally aligned in a horizontal direction relative to a substrate surface to fall in the vertical direction. Further, since a response from a black display state to a gradation display state uses fall characteristics that cause liquid crystal molecules that were aligned in the direction of the transmission axis of the polarizer by means of a high electric field to rotate while applying a lower voltage thereto, response characteristics of a change to a gradation display state are improved.
In this connection, according to Embodiment 2, the gate voltage V2 of the gate wiring of the TFT substrate 50 is used as a voltage that is applied to the opposed pixel electrode 23, and the voltage is a sufficient size with respect to the source voltage V1 that is applied to the TFT pixel electrode.
As shown in
The liquid crystal molecules 5 of the nth row to, and 1st row to the n−x−1th row to which the voltage V1 is applied exhibit an alignment along an arch-shaped transverse electric field formed between the comb-shaped electrode pair on the TFT substrate 50 side. More specifically, since the liquid crystal molecules 5 align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair, light that passes through the liquid crystal layer in this state is polarized to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (first polarizer) 1 on the TFT substrate 50 side. As a result, light that has passed through the liquid crystal layer 4 is transmitted through the second polarizer 2 and the display enters an “on” (gradation display) state.
The details of the behavior of liquid crystal molecules and changes in the polarizing state of light in the liquid crystal layer of the liquid crystal display device of Embodiment 2 that is described above are the same as in Embodiment 1, and are as illustrated in
According to the liquid crystal display device of Embodiment 2, switching between off and on states is performed in this manner at separate timings and with separate pairs of comb-shaped electrodes. Further, for all gradation displays, a black display is obtained with a fast response by a rise effect that is caused by the large voltage V2 that is applied to the comb-shaped electrode pair on the opposed substrate side when selecting the previous row (n−xth row), and a gradation display is obtained with a fast response by a fall effect that is caused by the voltage V1 that is applied to the comb-shaped electrode pair on the TFT substrate side when selecting the relevant row (nth row). Hence, dramatically improved response characteristics can be obtained for the overall display device.
Further, since the liquid crystal display device according to Embodiment 2 is designed so that a potential of either V1 or V2 is always retained in the liquid crystal layer by resetting, through a reset electrode, the opposed pixel electrode when the voltage V1 is applied to the comb-shaped electrode pair of the TFT substrate or the TFT pixel electrode when the voltage V2 is applied to the comb-shaped electrode pair of the opposed substrate, the effect of a fast response can be obtained more stably. Further, it can be said that utilizing the timings for applying gate voltages of each row to set states in which the aforementioned voltages are retained is also a feature of the present embodiment.
Note that, in the liquid crystal display device of Embodiment 2, even in a case in which light is incident from the opposite direction to that described above, the light will exhibit similar changes, and hence the tendency for light to be transmitted or blocked by a polarizer will not change. Accordingly, in Embodiment 2, as long as the arrangement relationship between each comb-shaped electrode pair and each polarizer does not change, the incident direction of light may be from the opposed substrate side. Further, in Embodiment 1, the second comb-shaped electrode pair may be disposed on the TFT substrate side, and the first comb-shaped electrode pair may be disposed on the opposed substrate side. Furthermore, the voltage V2 that is applied to the comb-shaped electrode pair on the opposed substrate side need not necessarily be a voltage that is applied through the gate wiring.
A liquid crystal display device of Embodiment 3 is the same as the liquid crystal display device of Embodiment 2, except that locations at which the two sets of comb-shaped electrode pairs are disposed are different from the liquid crystal display device of Embodiment 2. More specifically, according to the liquid crystal display device of Embodiment 3, a comb-shaped electrode pair (hereunder, referred to as “TFT comb-shaped electrode pair”) constituted by a TFT pixel electrode and a TFT common electrode, and a comb-shaped electrode pair (hereunder, referred to as “opposed comb-shaped electrode pair”) constituted by an opposed pixel electrode and an opposed common electrode are disposed on a TFT substrate. In other words, relative to the liquid crystal display device according to Embodiment 2, in the liquid crystal display device according to Embodiment 3 the opposed comb-shaped electrode pair are moved to the TFT substrate side.
According to Embodiment 3, the TFT comb-shaped electrode pair and the opposed comb-shaped electrode pair are disposed on respectively different layers through an insulator having translucency inside the same TFT substrate. Examples of the material of the insulator include an organic insulator such as acryl and polyimide and the like.
The configuration and driving method of the liquid crystal display device according to Embodiment 3 will now be described in detail.
As shown in
More specifically, as shown in
Further, as shown in
The comb teeth of each of the pixel electrode 21 and the common electrode 22, respectively, that constitute the TFT comb-shaped electrode pair (first comb-shaped electrode pair) are alternately disposed with a certain space therebetween. Further, the comb teeth of each of the pixel electrode 23 and the common electrode 24 that constitute the opposed comb-shaped electrode pair (second comb-shaped electrode pair) are alternately disposed with a certain space therebetween.
The design profile such as the shape, size, and material of each member of the TFT substrate 50 and the opposed substrate 60 are the same as in Embodiment 1, and the thickness of the insulator provided between the TFT comb-shaped electrode pair and the opposed comb-shaped electrode pair is preferably between 100 and 1000 nm.
As shown in
As shown in
However, as shown in
As shown in
When a gate voltage is applied to the gate wiring of the n−xth to n−1th rows that are shown in
The liquid crystal molecules 5 in the n−xth to n−1th rows to which the voltage V2 is applied align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair. Hence, light that passes through the liquid crystal layer 4 in this state is transformed to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (second polarizer) 2 on the opposed substrate 60 side. As a result, the light is blocked by the second polarizer and the display enters an “off” (black display) state.
The response to enter a black display state in this case is performed by means of an alignment change in which a high voltage is applied to liquid crystal molecules that were originally aligned in a direction at an angle of 45 degrees relative to the direction of the transmission axis of the polarizer to thereby cause the liquid crystal molecules to rotate in the horizontal or vertical direction relative to the direction of the transmission axis of the polarizer. The aforementioned response compares favorably with a response performed in the conventional manner by means of an alignment change that causes liquid crystal molecules that were originally aligned in a horizontal direction relative to a substrate surface to fall in the vertical direction. Further, since a response from a black display state to a gradation display state uses fall characteristics that cause liquid crystal molecules that were aligned in the direction of the transmission axis of the polarizer by means of a high electric field to rotate while applying a lower voltage thereto, response characteristics of a change to a gradation display state are improved.
In this connection, according to Embodiment 3, the gate voltage V2 of the gate wiring of the TFT substrate 50 is used as a voltage that is applied to the opposed pixel electrode 23, and the voltage is a sufficient size with respect to the source voltage V1 that is applied to the TFT pixel electrode.
As shown in
The liquid crystal molecules 5 of the nth row to, and 1st row to the n−x−1th row to which the voltage V1 is applied exhibit an alignment along an arch-shaped transverse electric field formed between the TFT comb-shaped electrode pair. More specifically, since the liquid crystal molecules 5 align in a direction that is orthogonal to the long axis of the comb-shaped electrode pair, light that passes through the liquid crystal layer in this state is polarized to polarized light having an axis in a direction that is orthogonal to the transmission axis of the polarizer (first polarizer) 1 on the TFT substrate 50 side. As a result, light that has passed through the liquid crystal layer 4 is transmitted through the second polarizer 2 and the display enters an “on” (gradation display) state.
The behavior of liquid crystal molecules in the liquid crystal layer as well as changes in the polarizing state of light in the liquid crystal display device of Embodiment 3 described above will now be described in further detail for the respective timings.
First, with respect to
When light from the backlight is incident within the liquid crystal display panel, first, only light in the transmission axis direction of the polarizer is transmitted by the polarizer (first polarizer) 1 on the TFT substrate side.
Subsequently, the light passes through the opposed comb-shaped electrodes 23 and 24, the TFT comb-shaped electrodes 21 and 22, and liquid crystal molecules (lower layer liquid crystals) 4a that are adjacent to the TFT substrate. At this time, the lower layer liquid crystals 4a receive the influence of the voltage V2 generated by the opposed comb-shaped electrodes 23 and 24, and tilt in a diagonal direction relative to the substrate surface. However, the orientation of the long axis of the liquid crystal molecule when viewed from a normal line direction relative to the substrate surface is orthogonal to the orientation of the long axis of the comb tooth portion of the opposed comb-shaped electrodes 23 and 24, that is, is a parallel direction to the vibration direction of the light. Therefore, light that is transmitted through the lower layer liquid crystal 4a does not receive the influence of birefringence of the liquid crystal molecules, and passes through while retaining the same vibration direction.
Next, the light passes through the liquid crystal molecules (center liquid crystals) 4b that are positioned in the central region of the liquid crystal layer. Although the size of the tilt of the center liquid crystals 4b is different to that of the lower layer liquid crystals 4a, because the center liquid crystals 4b receive the influence of the voltage V2 that is generated by the opposed comb-shaped electrodes 23 and 24, the tendency is the same as for the lower layer liquid crystals 4a, and the orientation of the long axis of the liquid crystal molecule when viewed from a normal line direction relative to the substrate surface is a parallel direction to the vibration direction of the light. Consequently, light that is transmitted through the center liquid crystals 4b does not receive the influence of birefringence of the liquid crystal molecules and passes through while retaining the same vibration direction.
Subsequently, the light passes through the liquid crystal molecules (upper layer liquid crystals) 4c that are adjacent to the opposed substrate. Since the upper layer liquid crystals 4c do not receive the influence of the electric field and vertical alignment of the upper layer liquid crystals 4c is maintained, the light passes through in a state in which the vibration direction of the light remains in the same direction.
Next, the light arrives at the polarizer (second polarizer) 2 on the opposed substrate side. Since the direction of the transmission axis of the second polarizer 2 is orthogonal to the direction of vibration of the light that has passed through the liquid crystal layer 4, the light is blocked by the second polarizer 2.
Thus, in a state in which a voltage is being applied into the liquid crystal layer by means of the opposed substrate side 23 and 24, the display is a black display (an off state).
Next, with respect to
When light from the backlight is incident within the liquid crystal display panel, first, only light in the transmission axis direction of the polarizer is transmitted by the polarizer (first polarizer) 1 on the TFT substrate side.
Next, the light passes through the opposed comb-shaped electrodes 23 and 24, the TFT comb-shaped electrodes 21 and 22, and the lower layer liquid crystals 4a. At this time, since the voltage V1 is being applied into the liquid crystal layer 4 by the TFT comb-shaped electrodes 21 and 22, the lower layer liquid crystals 4a tilt in a diagonal direction relative to the substrate surface, and the orientation of the long axis of the lower layer liquid crystal 4a when the substrate surface is viewed from a normal line direction is orthogonal to the long axis direction of the comb tooth portion of the TFT comb-shaped electrodes 21 and 22. That is, the long axis direction of the liquid crystal molecule when the substrate surface is viewed from the normal line direction and the vibration direction of the light form an angle of substantially 45°, and light that passes through the lower layer liquid crystal 4a forms elliptically polarized light having a long axis in a direction that forms an angle of substantially 45° with the long axis direction of the liquid crystal molecule when the substrate surface is viewed from the normal line direction.
Subsequently, the light passes through the center liquid crystals 4b. At this time, since the center liquid crystals 4b also receive the influence of the voltage V1 that is generated by the TFT comb-shaped electrodes 21 and 22, the orientation of the long axis of the liquid crystal molecule when viewed from a normal line direction with respect to the substrate surface is orthogonal to the long axis direction of the comb tooth portion of the TFT comb-shaped electrodes 21 and 22. However, since the tilt angle of the center liquid crystals 4b with respect to the substrate surface is greater than the tilt angle of the lower layer liquid crystals 4a with respect to the substrate surface, light that is transmitted through the center liquid crystals 4b is converted to elliptically polarized light in which the direction of the long axis is rotated by 90°.
Next, the light passes through the upper layer liquid crystals 4c. Since the upper layer liquid crystals 4c do not receive the influence of the electric field and are maintained in a state of vertical alignment, light that passes through the upper layer liquid crystals 4c is converted from elliptically polarized light to substantially linearly polarized light while retaining the long axis orientation of the light as it is. More specifically, the light is converted to light having a vibration direction in a direction that forms an angle of 90° with respect to the vibration direction of the light when the light was incident.
Subsequently, the light arrives at the polarizer (second polarizer) 2 on the opposed substrate side. Since the direction of the transmission axis of the second polarizer 2 is parallel to the direction of vibration of light that has passed through the liquid crystal layer 4, the light can pass through the second polarizer 2.
Thus, in a state in which a voltage is being applied into the liquid crystal layer by the comb-shaped electrodes 21 and 22 on the TFT substrate side, the display is a gradation display (in an “on” state), and a transmittance that is in accordance with the voltage can be obtained.
According to the liquid crystal display device of Embodiment 3, switching between off and on states is performed in this manner at separate timings and with separate pairs of comb-shaped electrodes. Further, for all gradation displays, a black display is obtained with a fast response by a rise effect that is caused by the large voltage V2 that is applied to the opposed comb-shaped electrode pair when selecting the previous row (n−xth row), and a gradation display is obtained with a fast response by a fall effect that is caused by the voltage V1 that is applied to the TFT comb-shaped electrode pair when selecting the relevant row (nth row to, and 1st row to an n−xth row). Hence, dramatically improved response characteristics can be obtained for the overall display device.
The behavior of the liquid crystal molecules according to Embodiment 3 as illustrated in
Note that, in the liquid crystal display device of Embodiment 3, even in a case where light is incident from the opposite direction to that described above, the light will exhibit similar changes, and hence the tendency for light to be transmitted or blocked by a polarizer will not change. Accordingly, in Embodiment 3, as long as the arrangement relationship between each comb-shaped electrode pair and each polarizer does not change, the incident direction of light may be from the opposed substrate side. In addition, in the liquid crystal display device of Embodiment 3, the first comb-shaped electrode pair and the second comb-shaped electrode pair may also be disposed on the opposed substrate side. Further, the voltage V2 that is applied to the opposed comb-shaped electrode pair need not necessarily be a voltage that is applied through the gate wiring.
Although either of the TFT comb-shaped electrode pair and the opposed comb-shaped electrode pair may be disposed nearer to the liquid crystal layer side, when a large voltage that is greater than or equal to the maximum driving voltage can be applied to the opposed comb-shaped electrode pair, it is preferable to dispose the TFT comb-shaped electrode pair nearer to the liquid crystal layer side than the opposed comb-shaped electrode pair. As a result a voltage can be applied more efficiently into the liquid crystal layer.
By further disposing a transparent electrode over the entire area on the opposed substrate side on which a comb-shaped electrode pair is not formed, it is possible to prevent charge-up from outside the cell, and the display can be stabilized.
The present application claims priority to Patent Application No. 2009-184818 filed in Japan on Aug. 7, 2009 under the Paris Convention and provisions of national law in a designated State, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-184818 | Aug 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/053870 | 3/9/2010 | WO | 00 | 3/29/2012 |
