Patent Application
20070216290
Notice: [Four Digits in a bracket] denote numbers of respective paragraph in the Japanese Specification of the Japanese application JP2003-170228.
The present invention relates to an organic EL light emitting display device of the type which is provided with a region formed of an organic material which emits light due to an electroluminescence phenomenon in each pixel; and, more particularly, the invention relates to an organic EL light emitting display device having a pixel structure that is suitable for an organic EL light emitting display device which displays an image by active matrix driving using a switching element provided to each pixel.
An organic EL light emitting display device (organic electroluminescence display device), which is driven by an active matrix method (also referred to as a TFT type), is expected to be offered as a next-generation flat panel display device, which can replace the current liquid crystal display device.
The pixel constitution and a pixel circuit of the conventional organic EL light emitting display device are disclosed in the following Patent Documents 1 to 5, for example.
[Patent Document 1]
Japanese Unexamined Patent Publication Hei 11-329715.
[Patent Document 2]
National Publication of Translated Version of PCT Application Hei 11-503868.
[Patent Document 3]
National Publication of Translated Version of PCT Application Hei 11-503869.
[Patent Document 4]
U.S. Pat. No. 6,157,356
[Patent Document 5]
U.S. Pat. No. 5,561,440
The conventional organic EL light emitting display device has the following structure. On one electrode (for example, an anode electrode, hereinafter the explanation will refer to the anode electrode as the one electrode), using a thick-film bank formed of an organic insulation material (the bank-like structure or the insulation structure between neighboring pixels which forms light emitting portions (also referred to as light emitting regions or light emitting areas) which expose portions of the above-mentioned one electrode), the above-mentioned light emitting areas of the organic EL elements (light emitting layers) which constitute respective pixels are defined. Then, in the inside of the bank, light emitting layers of the organic EL elements are formed, and, at the same time, the light emitting layers are covered with another electrode (for example, a cathode electrode, hereinafter the explanation will refer to the cathode electrode as the other electrode). The anode electrode and the cathode electrode are insulated from each other by an outer periphery of the light emitting area.
It is believe that an unpredicted problem caused by light from the above-mentioned organic EL element is also attributed to the fact that light which is generated in a certain pixel leaks into other neighboring pixels as a stray light through the insulation film (the so-called bank layer) which partitions the light emitting regions (organic material layers) of the organic EL light emitting display device between the pixels. Such leaking of light is recognized by a user of the organic EL light emitting display device as smear or a contrast defect.
Further, from a viewpoint of the contrast of an image displayed by the organic EL light emitting display device, it is extremely important to increase the degree of blackness of the pixel in a non-light-emitting state. In the organic EL light emitting display device, the influence that the leaking of light generated by the reflection of light in the inside of the substrate gives to the black display becomes larger than the corresponding influence in the liquid crystal display device. Accordingly, the high brightness of the pixel in the white display state is also offset by the leaking of light which is generated when the pixel is in the black display state, and, hence, the contrast of the display image is still held at a low level. As a result, it is unavoidable that the displayed image produced by such a device is more deteriorated compared to the display image of a liquid crystal display device.
Further, with respect to an organic EL light emitting display device which uses an organic material as the above-mentioned so-called bank material, in the manufacturing step, when the so-called polymer-based organic EL material is supplied to the respective pixels in a solution state, it is necessary to form openings which have a depth to temporarily store the solution of the organic EL material therein in the bank. Accordingly, in the bottom emission type organic EL light emitting display device which emits light to the TFT substrate side, it is also necessary to take the shrinkage of light emitting regions, which is caused by narrowing of the openings of the bank at the TFT substrate side, into consideration. Accordingly, regions formed on an upper surface of the bank, which are allocated to the formation of the openings, cannot be made significantly small. On the other hand, to each pixel, a pixel circuit which controls an organic EL element formed on the pixel is also provided. Accordingly, in each pixel, it is necessary to ensure that there is a region which can be used for a switching element and a capacitive element included in the pixel circuit. Under such a circumstance, for each pixel, it is required to skillfully arrange the above-mentioned two regions in a plane inside the pixel.
Compared to the above-mentioned organic EL material of high molecular weight, with respect to the so-called organic EL material of low molecular weight which can be supplied to each pixel in a sublimated state, it is possible to make the openings of the bank shallow. However, also in the organic EL light emitting display device provided with the organic EL elements formed of the organic EL material of low molecular weight, in the above-mentioned manner, it is required to arrange the light emitting region and the pixel circuit region in each pixel in a plane.
While such an organic EL light emitting display device has an advantage in that a bright image display of high brightness can be produced, a degradation phenomenon has been observed, which is referred to as an edge growth in which, with respect to a light emitting portion (a light emitting area) of the organic EL element provided to every pixel, a region which becomes non-light-emitting grows from a peripheral portion thereof, and, eventually, the brightness of the whole screen is lowered. As a cause of the generation of edge growth, it has been pointed out that there is a possibility of diffusion of a certain substance, such as moisture, oxygen or the like, which degenerates the organic EL material from the bank, which is formed of the organic thin film for defining the light emitting areas, to the inside of the organic EL elements. When the edge growth is generated, the so-called numerical aperture is decreased, and, hence, the brightness of the above-mentioned screen is lowered as a whole.
It is also observed that the contrast ratio (an ANSI contrast), which is obtained when an ANSI pattern used in the inspection of the display device is displayed on an organic EL light emitting display device that has been manufactured on a trial basis, is held as a low value of approximately 50. It is confirmed that this is attributed to the fact that stray light from the pixel of the white display portion (light emitting portion) reaches the pixel of the black display portion, and this stray light is reflected on the tapered portion of the bank opening of the pixel; and, hence, the brightness of the black display portion cannot be made sufficiently small. Further, when stray light is continuously irradiated onto the screen, this gives rise to smear, thus deteriorating the image quality.
Further, an organic EL element is applied to the thick-film bank which defines the light emitting areas, and the cathode electrode is formed such that the cathode electrode covers the organic EL element and also covers the whole surface of the bank; and, hence, there may be a case in which short-circuiting arises between the cathode electrode and the anode electrode at a stepped portion formed on the opening end portion of the bank.
Accordingly, it is an object of the present invention to provide an organic EL light emitting display device which can overcome the above-mentioned various drawbacks, can enhance the numerical aperture by preventing edge growth, can obviate short-circuiting between an anode and a cathode, and can suppress the generation of smear, thus realizing a high-brightness and high-quality display.
Typical examples of an organic EL light emitting display device to which the present invention is applied will be described hereinafter.
(1) The first example of an organic EL light emitting display device according to the present invention includes a substrate having a main surface, a plurality of pixels arranged two-dimensionally on the main surface of the substrate, a plurality of scanning signal lines arranged in parallel in a first direction on the main surface of the substrate, a plurality of data signal lines arranged in parallel in a second direction which intersects the first direction on the main surface of the substrate, and a plurality of current supply lines arranged on the main surface of the substrate. Each one of the plurality of pixels includes a plurality of active elements, which include a first active element which acquires a data signal transmitted from one of the plurality of data signal lines in response to a voltage signal applied through one of the plurality of scanning signal lines, and a second active element which adjusts a current supplied from one of the plurality of current supply lines in response to the data signal, a data holding element for holding the data signal acquired by the first active element, and an organic electroluminescence element (organic EL element) which emits light in response to the supply of the current which is adjusted by the second active element. Further, light emitting areas of the organic EL elements of neighboring pixels are separated by an inorganic insulation film, which is formed of any one fiber selected from a group consisting of a silicon oxide film, a silicon nitride film, and a silicon oxide nitride film.
(2) The second example of an organic EL light emitting display device according to the present invention includes a substrate having a main surface, a plurality of pixels arranged two-dimensionally on the main surface of the substrate, a plurality of scanning signal lines arranged in parallel in the first direction on the main surface of the substrate, a plurality of data signal lines arranged in parallel in the second direction which intersects the first direction on the main surface of the substrate, and a plurality of current supply lines arranged on the main surface of the substrate. Each one of the plurality of pixels includes a plurality of active elements, which include a first active element which acquires a data signal transmitted from one of the plurality of data signal lines in response to a voltage signal applied through one of the plurality of scanning signal lines, and a second active element which adjusts a current supplied from one of the plurality of current supply lines in response to the data signal, a data holding element for holding the data signal acquired by the first active element, and an organic electroluminescence element (organic EL element) which emits light in response to the supply of the current which is adjusted by the second active element. Further, one electrode of the organic EL light emitting element is formed on the same layer on which a gate electrode of the active element which is connected to the scanning signal line is formed, and light emitting areas of the organic EL elements of neighboring pixels are separated by an interlayer insulation film of the active element.
Further, one electrode of the data holding element is formed of a material equal to a material of one electrode of the organic EL light emitting element and is arranged on the same layer as the gate electrode of the active element, another electrode of the data holding element is formed of the same material as the material of a semiconductor layer of the active element, and the data holding element is constituted of the pair of electrodes and an insulation film which is sandwiched by the pair of electrodes and is formed of the same material as the material of a gate insulation film of the active element.
(3) The third example of the organic EL light emitting display device according to the present invention includes a substrate having a main surface, a plurality of pixels arranged two-dimensionally on the main surface of the substrate, a plurality of scanning signal lines arranged in parallel in the first direction on the main surface of the substrate, a plurality of data signal lines arranged in parallel in the second direction which intersects the first direction on the main surface of the substrate, and a plurality of current supply lines arranged on the main surface of the substrate. Each one of the plurality of pixels includes a plurality of active elements, which include a first active element which acquires a data signal transmitted from one of the plurality of data signal lines in response to a voltage signal applied through one of the plurality of scanning signal lines, and a second active element which adjusts a current supplied from one of the plurality of current supply lines in response to the data signal, a data holding element for holding the data signal acquired by the first active element, and an organic electroluminescence element (organic EL element) which emits light in response to the supply of the current which is adjusted by the second active element. Further, one electrode of the organic EL element is embedded in the inside of an insulation film which surrounds the electrode, and the height of a surface of one electrode is substantially equal to the height of a surface of the insulation film which surrounds the electrode, and a side surface of a pattern end portion of one electrode is insulated from a material which forms the organic EL element.
Further, other specific constitutional examples of the above-mentioned organic EL light emitting display device according to the present invention will be described as follows.
(4) The organic EL light emitting display device is further provided with a first light shielding member which is arranged at a position at which light which is irradiated from the organic EL element arranged at one of the plurality of pixels to the plurality of active elements arranged in one of the plurality of pixels or another one of the plurality of neighboring pixels, and a second light shielding member which is arranged at a boundary between a pair of pixels arranged adjacent to each other among the plurality of pixels and blocks leaking of light occurring between the pair of pixels arranged adjacent to each other among the plurality of pixels at a boundary.
(5) In the organic EL light emitting display device, the plurality of active elements are provided as switching elements such as thin film transistors having channel layers made of polycrystals or pseudo-single crystals of semiconductor, for example. One example of the above-mentioned organic EL element provided to the organic EL light emitting display device includes a transparent electrode which receives a current supplied from the above-mentioned second active element, an insulation film (the above-mentioned bank) which is formed on the transparent electrode and has an opening which exposes a portion of an upper surface of the transparent electrode, and an organic material layer which is formed on a portion of the upper surface of the transparent electrode. The insulation film is formed of a dark (black) material or an inorganic material. The insulation film may be formed of a polyimide-based material. Further, a cross section of the opening of the insulation film may be tapered toward the upper surface of the transparent electrode.
(6) When the above-mentioned organic EL element includes the transparent electrode which receives the current supplied from the above-mentioned second active element, the insulation film (the above-mentioned bank) which is formed on the transparent electrode and has the opening which exposes the portion of the upper surface of the transparent electrode, and the organic material layer which covers the opening of the insulation film and a portion which is formed along the opening of the insulation film and to which the current is supplied through the portion of the upper surface of the transparent electrode, a boundary which is defined between the portion of the insulation film and the organic material layer is covered with the light shielding member as viewed from a main surface of the substrate.
(7) As the light shielding member, at least one of a portion of the scanning signal line and a conductive layer which is formed as one of electrodes of the data holding element is provided.
(8) As the light shielding member, a conductive layer which is formed on the same layer on which the scanning signal line is formed and which is formed on a light emitting region of a periphery of the organic electroluminescence element in a ring shape, an L shape or a U shape as viewed from the main surface of the substrate.
(9) the light shielding member constitutes a portion of a line which is formed on the same layer on which at least one of the data signal line and the current supply line is formed and supplies a current to the organic EL element. For example, the light shielding member is electrically connected with the transparent electrode of the organic EL element which receives the supply of the current from the second active element.
(10) The light shielding member includes an aluminum layer.
(11) The light shielding member is arranged on the plurality of respective pixels and, in each one of the plurality of pixels, the plurality of active elements and the organic EL element are separated along the main surface of the substrate by the light shielding member.
(12) When the above-mentioned organic EL element includes the transparent electrode which receives the current supplied from the above-mentioned second active element, the insulation film which is formed on the transparent electrode and has the opening which exposes the portion of the upper surface of the transparent electrode, and the organic material layer which covers the opening of the insulation film and a portion which is formed along the opening of the insulation film and to which the current is supplied through the portion of the upper surface of the transparent electrode, the first light shielding member and the second light shielding member are formed between the main surface of the substrate and the transparent electrode, and at least one of the first light shielding member and the second shielding member extends toward a lower side of the opening of the insulation film from the lower side of the insulation film.
(13) The first light shielding member is formed of at least one of a portion of the scanning signal line and a conductive layer which is formed as one of electrodes of the data holding element, and the second light shielding member is formed of at least one of a conductive layer which is formed as one electrode of the data holding element and a conductive layer which is connected to the current supply line.
(14) One of the first light shielding member and the second light shielding member is formed of a portion of the scanning signal line and another of the first light shielding member and the second light shielding member is formed of a conductive layer which is formed on the same layer on which the scanning signal line is formed and is formed in a ring shape, an L shape or a U shape on a periphery of a light emitting region of the organic EL element as viewed form the main surface of the substrate.
(15) At least one of the first light shielding member and the second light shielding member is formed of a portion of at least one of the data signal line or the current supply line, or a portion of a line which is formed on the same layer on which at least one of the data signal line and the current supply line is formed and which supplies a current to the organic EL element (for example, being electrically connected to the transparent electrode of the organic EL element which receives the current supplied from the second active element).
(16) The first light shielding member and the second light shielding member include an aluminum layer.
(17) Each one of the plurality of respective pixels is divided along the main surface of the substrate into a region where the plurality of active elements are formed and another region where the organic EL element is formed.
Here, the present invention is not limited to the above-mentioned constitution and various modifications can be made without departing from the technical concept of the present invention.
Hereinafter, a mode for carrying out the present invention will be explained in detail in conjunction with the drawings.
Reference symbol AL indicates a line between the switching elements, which constitutes a drain electrode of the switching element (a line between switches, a signal line, a drain line), and reference symbol ALS indicates a source electrode which also functions as a line between switching elements and as a shielding member (a line between switches and a shielding member) and is connected to a first gate FG through a contact hole which penetrates the insulation film IB and the gate insulation film GI. An insulation film IC is formed to cover the line AL between switches and the shielding member ALS. One electrode ITO, which is connected to the shielding member ALS through a contact hole formed in the insulation film IC, extends to a light emitting area. Here, the one electrode ITO is an anode electrode.
On the one electrode ITO, a bank BMP is formed of an inorganic insulation material and has an opening portion (a bank opening, indicated by reference symbol OPEN in
In the organic EL light emitting display device according to this embodiment, the light emitting areas of the organic EL elements of the above-mentioned pixels which are arranged adjacent to each other are formed of any one of a silicon oxide film, a silicon nitride film or a silicon oxide nitride film, and they are separated from each other by a bank made of an inorganic insulation film. Accordingly, there is no possibility that water moisture or oxygen will be diffused into the organic EL layer from the bank material, and, hence, the generation of the above-mentioned edge growth is suppressed and an image display having high brightness can be obtained without lowering the numerical aperture.
Further, the bank BMP is formed to have a thickness that is smaller than the thickness of the electrode CM, and the depth of the recess of the electrode CM formed in the bank opening is set to be smaller than the thickness of the electrode CM. Accordingly, the stepped portion of the inner periphery of the bank BMP becomes small, and the reflection of a stray light from a tapered portion of the bank opening is suppressed, and, hence, the lowering of brightness is prevented. As a result, the generation of smear is suppressed. Further, since the stepped portion at the opening end portion of the bank is small, pinholes or cracks are hardly generated in the bank, and short-circuiting between the cathode electrode and the anode electrode, which have occurred conventionally, can be prevented.
Further, one electrode of the organic EL light emitting element is formed on the same level as the gate electrode of the active element, which is connected to the above-mentioned scanning signal line, while the light emitting areas of the organic EL element of adjacent pixels are separated by the interlayer insulation film of the above-mentioned active element. One of the electrodes of the data holding element is formed of the same material as one of the electrodes of the organic EL light emitting element and is arranged on the same layer as the gate electrode of the active element. Another of the electrodes of the data holding element is formed of the same material as the semiconductor layer of the active element. The above-mentioned data holding element is constituted of a pair of electrodes and an insulation film, which is sandwiched between the pair of electrodes, and it is made of the same material as the gate insulation film of the above-mentioned active element.
Further, one electrode of the organic EL element is embedded in the insulation film which surrounds the electrode, the height of the front surface of the above-mentioned one electrode is substantially equal to the height of the front surface of the insulation film which surrounds the electrode, while the side surface of a pattern end portion of the above-mentioned one electrode is isolated from the material forming the organic EL element.
In this manner, it is possible to provide an organic EL light emitting display device which can enhance the numerical aperture by preventing edge growth, which can obviate the short-circuiting between the anode/cathode, and which can suppress the generation of smears, thus realizing a display having high brightness and high quality.
Here, the substrate SUB which forms the stacked film structure on the main surface thereof has a main surface side thereof sealed with a cover glass CG, and a desiccant (not shown in the drawing) is filled into or an inert gas is charged into a gap BG defined by the sealed structure, and, thus, the organic EL light emitting display device is completed.
Further, in the plan view shown in
Respective conductive layers C1, C2 which constitute capacitive elements are specified by reference symbols which are shown as pairs between the semiconductor layers CSi, which are provided as the pair of electrodes which sandwich an insulation material layer (a dielectric layer) and the conductive layer C1 or C2 which is laid above the semiconductor layers CSi. Although an organic EL element (a light emitting element) LED which is provided for every pixel is included in the equivalent circuit, the organic EL element LED is not completely shown in
In
On the other hand, in this embodiment, the above-mentioned electrode layer (described later as the member CM in conjunction with
The injection of the current to the organic EL element LED in each pixel of this embodiment shown in
On the other hand, the brightness of the organic EL element LED is controlled by the drive transistor DT, which is provided to the current path which supplies the current to the organic EL element LED. Accordingly, this switching element is referred to as the drive transistor. As shown in
Here, although the scanning signal lines GL are formed in a zigzag shape to avoid the contact holes (indicated by a duplicate quadrangular shape in
As shown in
Further, by a method which performs modulation of the brightness in response to control of a time-sequential axis using a linear region of the characteristics of the drive transistor DT, it is possible to put the organic EL light emitting display device into practical use. However, when the channel layer of the drive transistor DT is formed of polycrystal or pseudo-single crystal of a semiconductor material such as silicon or the like, it is not deniable that the condition for crystallization (for example, annealing by laser irradiation) differs between the pixels. The difference in the condition for crystallization allows the coexistence of pixels which differ in the characteristics of the drive transistor DT in the inside of the image display region of one organic EL light emitting display device. As a result, for example, in the inside of the image display region of the organic EL light emitting display device to which the image data, which produces a display using the same gray scale over the whole screen, is inputted, a difference in brightness (brightness irregularities) arises.
In this embodiment, one of the motivations to provide two control signal lines CL1, CL2 and the switching elements SW2, SW3 which are respectively controlled by the control signal lines CL1, CL2 shown in
To be more specific, first of all, in response to the control signal transmitted through the control signal line CL1, the switching element (first input switch) SW2 is turned on. Here, although the drive transistor DT is not turned on, a node CH2 side of the drive transistor DT is connected to the reference potential through the organic EL element LED from a floating state and the potential is elevated to a given value or more. Next, a control signal which is transmitted through the control signal line CL2 turns on the switching element (the second input switch) SW3 corresponding to the control signal. Accordingly, one electrode CSi of the capacitive element CSi-C2, which is in a floating state, is connected to the node CH2 side of the drive transistor DT through the switching element SW3, and the potential thereof is elevated to a is given value. Here, since the gate potential (the potential of the node CH1) of the drive transistor DT is equal to the potential of the output side (node CH2 side) of the drive transistor DT, the channel layer of the drive transistor DT interrupts the flow of charge.
Since a given current flows into the current supply line PL irrespective of the video signal transmitted through the drain line DL, the potential of the current supply line PL is substantially fixed. Accordingly, by sequentially turning on and off two switching elements SW2, SW3 (by sequentially placing the channel layers of respective switching elements in a conductive state), a substantially equal quantity of charge is stored in the capacitive elements CSi-C2 of any pixels. In such a state, when the channel layer of the switching element SW3 is closed and, subsequently, the switching element (control transistor) SW1 is turned on, in response to a voltage (a video signal) applied to one electrode C1 of the capacitive element C1-CSi, the capacitance of the capacitive element C1-CSi is also changed; and, in response to the change of the capacitance of the capacitive element C1-CSi, a difference arises between the potential of the node CH1 (the gate potential of the drive transistor DT) and the potential of the output side (node CH2 side). Due to this potential difference, with respect to the pixel of this embodiment, the drive transistor DT is turned on or a charge quantity which flows into the turned-on channel is controlled so as to allow the organic EL element LED to emit light at the desired brightness.
Although the channel layer of the drive transistor DT is turned on with respect to a given usual gate potential (a threshold voltage Vth), when the channel layer is, for example, formed as a polycrystalline layer or a pseudo-single crystal layer of a semiconductor material, as described previously, the threshold voltage Vth differs in response to the pixel. In this embodiment, an operational point of the drive transistor DT which is dependent on such a threshold voltage Vth is set using the potential of the node CH1 given by the capacitive element CS1-C2 as a reference, and the ON/OFF operation of the drive transistor DT is controlled based on the capacitive balance between the capacitive element CS1-C2 and the capacitive element C1-CSi, whereby the operation of the drive transistor DT is stabilized and the correction of irregularities of the threshold voltage Vth which is generated between the pixels can be performed. The details of the respective manners of operation of the switching elements SW1, SW2, SW3, DT are as follows.
The switching element SW1, which is also referred to as the control transistor, is a switch which inputs a video signal voltage for every pixel and is provided not only to the pixel of this embodiment, but also to a pixel of an organic EL light emitting display device which controls a conductive state of a channel layer of the drive transistor DT based on a threshold voltage Vth. The switching element SW1 is turned on/off in response to the scanning signal transmitted to the scanning signal line GL, which intersects the channel layer (the semiconductor layer) and writes the video signal voltage inputted from the drain line DL into the capacitive element (the capacitor) of the so-called pixel circuit provided for every pixel.
When the image data is written, for example, one time for every frame period (vertical scanning period), into the image display region of the organic EL light emitting display device which drives the organic EL element provided to each pixel by current injection, the period in which the switching element SW1 provided to each pixel is turned on is limited to the horizontal scanning period which is allocated for the scanning signal line GL. Accordingly, the current injection quantity (a charge injection quantity) to the organic EL elements which are included in the pixel row corresponding to each scanning signal line GL is also limited. In such a current-driven type organic EL display device, in contrast to a voltage-driven type display device, such as a TN type liquid crystal display device, it is difficult to hold the brightness of the pixel for a given period using the switching element SW1 which is used for acquiring the image data (the video signal). Accordingly, as described previously, another switching element, which is also referred to as the drive transistor DT, and the current supply line PL are provided for every pixel, and the conductive state of the channel layer of the drive transistor DT is held for a given period, whereby the brightness of each pixel is ensured. The capacitive element which is connected to the output side of the switching element (the control transistor) SW1 holds the gate potential of the above-mentioned drive transistor DT at a desired value for a predetermined period, so as to maintain the current injection to the organic EL element LED. Accordingly, even when the conductive state of the drive transistor DT is controlled using the threshold voltage Vth as a reference, as well as, when the conductive state of the drive transistor DT is controlled substantially in accordance with this embodiment, it is recommended to provide the capacitive element at the output side of the switching element SW1.
In the switching element SW1 of this embodiment, as shown in
The switching element SW2 performs not only the above-mentioned function of controlling the storing of a charge to one electrode (semiconductor layer) CSi of the capacitive element CS1-C2, but also has the function of a current supply switch from the drive transistor DT to the organic EL element LED. The latter function is used for writing the current which is supplied from the current supply line PL and is adjusted in response to the video signal inputted from the drain line at the drive transistor DT into the organic EL element LED when the switching element SW2 is turned on. The latter function is used not only in this embodiment, but also in a case in which a conductive state of the drive transistor DT is controlled using the threshold voltage Vth as a reference. Such a switching element (the current supply switch SW2) is subjected to ON/OFF control at the timing of the control signal line CL1.
The switching element SW3 is a switch for storing the threshold voltage Vth of the drive transistor DT in the capacitor CS1-C2 and is a switching element peculiar to the pixel circuit of the embodiment shown in
The drive transistor DT has, as shown in
One electrode (semiconductor layer) CSi which is provided to the respective capacitive elements (capacitors) C1-CS1, CS1-C2 included in the equivalent circuit of one pixel shown in
At the respective capacitive elements C1-CS1, CS1-C2, the charge is supplied to the semiconductor layer CSi which constitutes one electrode through the switching elements SW2, SW3. The charge is supplied to another electrode C1 (indicated by a thinner line than that indicating the semiconductor layer CSi) of the capacitive element C1-CSi from the drain line DL provided at the left end of the pixel region PIX through the contact hole Cont-DL and the switching element SW1. The charge is supplied to another electrode C2 (indicated by thinner line than that indicating the semiconductor layer CSi) of the capacitive element CS1-C2 from the current supply line PL formed at the right end of the pixel region PIX through the contact hole Cont-PL.
More specifically, portions of the respective semiconductor layer CSi and the conductive layers C1, C2 corresponding to the pixel region PIX shown in
As described above, in the organic EL light emitting display device of this embodiment, the charges which are stored in the respective semiconductor layer CSi and conductive layers C1, C2 which constitute two capacitive elements (capacitors) provided corresponding to the pixel region PIX determine a current quantity which is written in the light emitting region of the organic EL element (the organic material layer OCT formed on the bank opening OPN) from the branch line of the current supply line PL, which extends toward the upper end of the pixel region PIX through the contact hole CH3, the switching element DT, which is referred to as the drive transistor, and the contact hole Cont-ITO. Here, in the pixel region PIX shown in
In the organic EL light emitting display device of this embodiment, as the switching elements SW1, SW2, SW3 and the drive transistor DT, which are provided for every pixel, a field effect type transistor (also described as a thin film transistor or a poly-Si TFT) made of polycrystalline silicon (also referred to as poly-Si) and having a channel layer is used. In the display device which drives a plurality of respective pixels which are arranged on the image display region using switching elements (poly-Si TFTs) of this type, due to a photovoltaic effect which is generated when light is irradiated to the channel layers (polycrystalline layers) of the switching elements provided for every pixel, the conductive states of the channel layers are liable to be easily changed, and, hence, there exists a possibility that the brightness of the pixel which is driven by the switching element (TFT) goes beyond a desired value, thus giving rise to degradation of the image quality of the image display region.
Particularly, with respect to the pixel of the active matrix type organic EL light emitting display device, since the organic EL element (the light emitting portion) and the active element (the switching element) which controls the organic EL element are arranged close to each other, light having an intensity reaching several hundred thousand luxes is irradiated to the channel layer of the switching element from the oblique direction. For example, even when a light shielding structure similar to the light shielding structure of the conventional TFT type liquid crystal display device described in U.S. Pat. No. 5,561,440 is applied to the pixel of the organic EL light emitting display device, it is impossible to shield the channel layer of the switching element from this strong light. Accordingly, in the present invention, as illustrated in this embodiment, the electrode layer of the capacitive element (the capacitor) of the circuit (pixel circuit) which is formed for every pixel is, as the light shielding material, arranged between the channel layer of the switching element made of polycrystalline silicon (poly-Si) and the light emitting portion of the organic EL element LED, thus preventing degradation of the image displayed on the organic EL light emitting display device.
In one pixel region PIX, indicated by being surrounded by a bold broken line in
As shown in
Here, the capacitive elements C1-CS1, CS1-C2 in this embodiment are not limited to the structure in which the capacitive elements C1-CS1, CS1-C2 are overlapped to both the current supply line PL and the drain line DL which are arranged in parallel between the neighboring pixels. That is, the capacitive elements C1-CS1, CS1-C2 may be overlapped to either one of the current supply line PL and the drain line DL in accordance with areas of the capacitor regions corresponding to the respective required capacitances. In both cases, the capacitive element C1-CSi (a portion) and the capacitive element CS1-C2, which extend along the current supply line PL and the drain line DL, interrupt any leaking of light which is generated between the neighboring pixels along the extending direction of the scanning signal line GL. In the organic EL light emitting display device, the capacitive element C1-CSi which is provided for every pixel is necessary to hold the signal voltage (the video signal) from the drain line DL. However, it is not necessary to make the capacitive element C1-CSi extend below at least one of the current supply line PL and the drain line DL to also work as a shielding member for blocking light between the above-mentioned pixels. In other words, the leaking of light between the neighboring pixels along the scanning signal line GL can be suppressed by at least one of the capacitive element C1-CSi and the capacitive element CS1-C2. Here, it is not always necessary that one electrode C2 of the capacitive element CS1-C2 is connected to the current supply line PL at the contact hole Cont-PL, as shown in
In the embodiment shown in
As shown in
As described above, in the organic EL light emitting display device, the organic EL element which is arranged for every pixel region PIX has the possibility of generating strong light. When such strong light is irradiated to the switching elements (SW1, SW2, SW3, DT in this embodiment) provided with the channels made of polycrystalline silicon (poly-Si), the silicon layers (the Si layers) which constitute the channels generate a photovoltaic effect corresponding to the intensities of the electric fields. Accordingly, an electric field generated in the channel (Si layer), in spite of the fact that the switching element applies an electric field in a turn-off state to the channel, for example, generates a positive hole electron pair in the inside thereof, and, hence, the charge holding characteristics of the switching element are deteriorated. For example, the charge (determining a control voltage of the drive transistor DT) stored in the capacitive element C1-CSi leaks to the drain line DL through the channel of the switching element (the control transistor) SW1 in a turn-off state. As a result, the current which is supplied to the organic EL element through the drive transistor DT is reduced.
Such a drawback does not appear in an outstanding manner in the conventional TFT type liquid crystal display device, and, hence, it is impossible for the light shielding structure adopted by the liquid crystal display device to shield the switching element from the strong light received from the organic EL element. Particularly, in the bottom emission type organic EL light emitting display device of this embodiment, in which the organic EL element LED is formed by sequentially stacking the transparent electrode ITO, the organic material layer OCT and the electrode layer from the substrate main surface side, (TFT substrate side) and in which light generated by the organic material layer OCT is emitted to the TFT substrate side, light emitted from the pixel region PIX is liable to easily irradiate the channel of the switching element formed on the pixel region PIX, and, hence, the image quality of a display image obtained by the control of the switching element (so-called TFT driving) is liable to be easily degraded.
Accordingly, in the organic EL light emitting display device according to this embodiment, the electrodes (conductive layers) C1, C2 of the above-mentioned respective capacitive elements C1-CS1, CS1-C2 are designed to function also as light shielding layers. To be more specific, as illustrated in
Further, as shown in
Further, in this embodiment, for performing the light shielding of the lower side of the pixel region PIX (the end portion of the pixel region PIX arranged adjacent to another pixel region along the current supply line PL or the drain line DL), a portion GLS of the scanning signal line which contributes to the driving of another pixel region is arranged at an upper end of another pixel region as a light shielding layer. To observe the inside of the pixel region PIX, the above-mentioned portion GLS of the scanning signal line shields the switching element SW1 arranged below the portion GLS from the light emitting region of another pixel region arranged above and adjacent to the pixel region PIX.
As described above, in the organic EL light emitting display device according to the present invention, as described in connection with this embodiment, the bank arranged between neighboring pixels is formed of the inorganic material, and the thickness of the bank is made smaller than the thickness of the electrode above the bank, and, hence, the generation of edge growth is prevented whereby lowering of the numerical aperture can be prevented and lowering of the brightness is obviated. Further, with use of a thin bank made of an inorganic material, the slope which is formed on an inner periphery of the bank can be set to a value which can be almost ignored; and, hence, lowering of the brightness attributed to the reflection of a stray light from the neighboring pixel on the slope of the bank can be suppressed, and, at the same time, since there is substantially no stepped portion, the generation of short circuiting between the electrodes which sandwich the organic EL layer can be prevented.
Further, this embodiment adopts a structure in which the capacitive elements (capacitors) and the scanning signal line which are provided for every pixel region are respectively arranged at the upper side, the lower side, the left side and the right side of the light emitting region (the organic material layer OCT) so as to prevent light from the organic material layer OCT from being irradiated to the switching elements SW1, SW2, SW3. The above-mentioned photovoltaic effect, which appears in the channel layers of the switching elements, is not so large as to influence the respective functions of the switching elements SW1, SW2, SW3 with respect to the function of the drive transistor DT (the drive transistor DT being turned on during the light emitting period of the light emitting region). Accordingly, with respect to four switching elements which are arranged in the pixel region PIX, although the drive transistor DT can be arranged closer to the light emitting region compared to three other switching elements, as shown in
The pixel array (the portion of the image display region) which is provided to the organic EL light emitting display device of this embodiment shown in
Further,
In
In the first photo pattern shown in
As described above, the scanning signal line GL has both the function of controlling the acquiring of the video signal in the channel region of the of switching element SW1 into the pixel region and the function of blocking light which leaks from the separate pixel region arranged close to the pixel region toward the group of switching elements of the pixel region. Accordingly, as shown in
Further, the upper electrodes (the conductive layers) C1, C2 of the capacitive elements C1-CSi, CSi-C2 are also requested to have a light shielding function together with the scanning signal line GL, as previously explained. Accordingly, the conductive layers which are formed using the second photo pattern are formed using a material and thickness suitable for suppressing the optical transmissivity. The material of the conductive layer is selected by focusing on the absorbance and the reflectance. For example, by focusing on the former viewpoint, a refractory material which is exemplified by molybdenum (Mo), tungsten (W), titanium (Ti), chromium (Cr), an alloy thereof or a silicide thereof are recommended. Further, by focusing on the latter viewpoint, aluminum (Al) and an alloy thereof are recommended. These materials may be stacked in plural layers.
Here, in
The functions of the contact holes shown in
On the other hand, the contact holes Cont-DL is formed using the first photo pattern, and it connects one end (also referred to as the drain region) of the channel layer FG(SW1) of the switching element (the control transistor) SW1 which is covered with the above-mentioned first insulation film and the drain line DL which is formed on the second insulation film using the fourth photo pattern through the first and second insulation films. When the channel layer FG(SW1) of the switching element (the control transistor) SW1 is turned on in response to the application of the control signal from the scanning signal line GL, the video signal (the voltage signal) from the drain line DL is applied to the upper electrode C1 of the capacitive element C1-Csi through the contact hole Cont-DL and the channel layer FG(SW1). The charge quantity stored in the capacitive element C1-Csi controls, together with the charge quantity stored in the capacitive element CS1-C2, the voltage applied to the control electrode SG(DT) of the drive transistor DT. Accordingly, at the time the switching element SW1 is turned on, the current corresponding to the video signal flows into the channel FG(DT) of the drive transistor DT. The current corresponding to the video signal is written into the transparent electrode ITO through the switching element SW2, the line M1 and the contact hole Cont-ITO. The current corresponding to the video signal written into the transparent electrode ITO flows through the organic material layer OCT formed on the transparent electrode ITO into another electrode CM (described later in conjunction with
The line M1 is formed as a current path provided between the output side of the switching element SW2 and the node (contact hole) Cont-ITO which is connected to the transparent electrode ITO of the organic EL element LED. The line M2 is formed as a charge path provided between one end of the drive transistor DT and one end of the switching element SW3. The line M3 electrically connects another end of the switching element Sw3, the semiconductor layers CSi which constitute the lower electrodes of the capacitive element C1-CSi and the capacitive element CSi-C2 and the control electrode SG(DT) of the drive transistor DT with each other and functions as a charge path which starts from another end of the switching element SW3 and reaches the semiconductor layer CSi and a voltage signal path which starts from the node (the contact hole) CH1 and reaches the control electrode SG(DT) of the drive transistor. The line M4 is formed as a voltage signal path which is provided between the output side (also referred to as a source) of the switching element SW1 and the upper electrode C1 of the capacitive element C1-CSi.
Since the current supply line PL is also included in the conductive layers formed using the fourth photo pattern, it is desirable to set the resistance of the conductive material formed in the photolithography step using this mask to be lower than the resistance of the conductive material in the photolithography step using the mask having the second photo pattern. For example, aluminum or an alloy thereof or silicide is recommended as the conductive material formed using the fourth photo pattern.
In this embodiment, using aluminum as the conductive material, the current supply line PL and the branch line PLB thereof, the drain line DL and the group of lines M1, M2, M3, M4 are formed on the second insulation film. Further, using aluminum, the current path, the charge path and the voltage signal path which reach any one of the semiconductor layers CSi, FG and the conductive layers C1, C2, SG(DT) which are laid below the second insulation film through the contact holes formed using the third photo pattern are respectively formed. Accordingly, in the explanation of the embodiment made hereinafter, there may be a case in which the above-mentioned conductive layers PL, PLB, DL, M1, M2, M3, M4 which are formed in the photolithography step using the mask on which the fourth photo pattern is formed are indicated by reference symbols AL, ALS.
The fifth photo pattern only has a pattern represented by a rectangular frame ITO shown in
The sixth photo pattern has only a pattern shown by an octagonal frame BMP in
In the organic EL light emitting display device according to the present invention, the above-mentioned fourth insulation film which constitutes the bank BMP is formed using any one of inorganic materials such as SiO2 or SiNx or the like and a black material, wherein the thickness of the fourth insulation film is smaller than the thickness of another electrode which is formed above the fourth insulation film. The bank BMP which is formed of the latter material is referred to as the black bank hereinafter. The black bank BMP is, for example, formed of a positive type photosensitive black polyimide. As a material of this type, in this embodiment, JR 3120P, a product of Nitto Denko Ltd. is exemplified. As described above, since the organic material layer OCT is formed in the opening of the bank BMP, the light emitting region which is included in the organic material layer OCT and the bank BMP are optically coupled. Accordingly, when the bank BMP is transparent or semi-transparent with respect to light from the organic material layer OCT, there exists a possibility that the light from the organic EL element LED formed in a pixel propagates to the inside of the bank BMP and is leaked as a stray light to the other pixels arranged close to this pixel. This leaking of the light between the pixels is recognized as smears by an observer. However, as in the case of this embodiment, by forming the fourth insulation film having a thickness smaller than the thickness of the other electrode which is formed above the fourth insulation film, such leaking of the light can be suppressed, and, hence, the current flowing in the light emitting region is assuredly separated for each pixel whereby the definition of the display image of the organic EL light emitting display device is enhanced and the deterioration of the display quality of the display image attributed to the light from the light emitting region which propagates within the display device can be prevented.
Next, on the first gate FG other than the light emitting area and the active element forming region, a transparent conductive film ITO is formed (
After forming the line AL which connects between switches and the line ALS which connects between switches and constitutes the shielding member, an insulation layer IC is formed (
In the organic EL light emitting display device according to this embodiment, in the same manner as the above-mentioned embodiment, by forming the bank which is arranged between the neighboring pixels using an inorganic material and setting the thickness of the bank to be smaller than the thickness of the electrode above the bank, edge growth is not generated, and, hence, a lowering of the numerical aperture is prevented. Further, the lowering of the brightness attributed to the reflection of stray light emitted from the neighboring pixels on the slope of the bank can be also suppressed. Further, the generation of short-circuiting between the electrodes which sandwich the organic EL layer therebetween is prevented.
To an upper surface of the insulation layer IC, using an adhesive agent GRU, the substrate SUB which is favorably formed of a transparent glass is adhered (
Thereafter, on the transparent conductive film ITO, a hole transporting layer HTL, an organic light emitting layer OCT, and an other electrode (cathode electrode) CM are formed (
Since the organic EL light emitting display device according to this embodiment has no so-called bank, there is no possibility that moisture or oxygen intrudes into the organic light emitting layer and causes the deterioration of the organic light emitting layer. The deterioration of the brightness attributed to the lowering of the numerical aperture is obviated. Further, the intrusion of stray light from the neighboring pixels can be prevented. Further, there is no stepped portions around the pixel area, and, hence, the generation of so-called broken steps is avoided and short-circuiting between one electrode ITO and another electrode CM can be prevented.
The data driving circuit DDR includes a complementary circuit which is provided with a TFT (thin film transistor) having an N type channel and a TFT which is provided with a P type channel, or a shift register circuit which is provided with only a TFT having an N type channel or only a TFT having an P type channel, a level shifter circuit, an analogue switch circuit and the like. In the pixel PX surrounded by the data lines DL and the gate lines DL, a switching element (control transistor) SW1, a current supply transistor (drive transistor) DT, a capacitor C and an organic EL element OCT are arranged. The control electrode (gate) of the switching element SW1 is connected to the gate line GL, while one end (drain) of the channel is connected to the data line DL. The gate of the current supply transistor DT is connected to the other end (source) of the channel of the switching element SW1 and, to the connection point, the other electrode (+pole) of the capacitor C is connected. One end (drain) of the channel of the current supply transistor DT is connected to the current supply line PL and the other end (source) is connected to the anode of the organic EL element LED. The data line DL is driven by the data driving circuit DDR and the scanning line (gate line) GL is driven by the scanning driving circuit DDG. Further, the current supply line PL is connected to the current supply circuit PW via the common potential supply bus line PLA.
In
In the pixel structure shown in
The organic EL light emitting display device according to the present invention emits light with a brightness which is substantially proportional to the amount of current supplied to the organic EL light emitting display device and with a color corresponding to the organic light emitting material (electroluminescence material) which forms the light emitting layer provided to the organic light emitting element. In the organic EL light emitting display device which can produce a color display, in many cases, the organic light emitting layer materials which are used for the light emitting layers are changed for respective pixels for red, green, blue. Further, there also exists a case in which the color display is produced by the organic EL light emitting display device which forms the light emitting layers of respective pixels using an organic light emitting layer material which radiates a so-called white light and combines color filters used in a liquid crystal display device with these light emitting layers.
Here, in any one of the above-mentioned organic EL light emitting display devices, the video signals (data signals) can be transmitted in a form of either analogue quantity or time division digital quantity. Further, an area grayscale method which divides a light emitting area to light emitting areas of respective pixels of red, green, blue may be combined with a gray scale control of the organic EL light emitting display device.
As has been explained heretofore, according to the present invention, in the organic EL light emitting display device which produces an image display by active matrix driving (TFT driving), the degradation of the image quality and the generation of smears can be prevented. Further, the contrast ratio and the brightness of the display image is enhanced. Accordingly, it is possible to obtain an organic EL light emitting display device which can produce a high-quality image display.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-170228 | Jun 2003 | JP | national |
This application is a continuation of U.S. application Ser. No. 10/867,653, filed Jun. 16, 2004; and which application claims priority from Japanese application JP2003-170228, filed on Jun. 16, 2003, the entire contents of which are hereby incorporated by reference into this application.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10867653 | Jun 2004 | US |
| Child | 11798527 | May 2007 | US |
