JP5135891B2 - Organic TFT element and organic EL display panel using the same - Google Patents

Description

  The present invention relates to an organic TFT element and an organic EL display panel using the same, and particularly has a feature in the structure of a TFT element (a driving transistor and a switching transistor).

  An organic EL element which is a constituent element of an organic EL (Electroluminescence) display generally has an organic EL light emitting element and a transistor (TFT / Thin Film Transistor) for driving the organic EL light emitting element. A general transistor has a “driving transistor” for driving the light emitting element and a “switching transistor” for turning on / off the driving transistor.

  As an example of a typical structure of an organic EL element, a driving transistor and an organic EL light emitting element are arranged on the same plane (for example, a substrate surface), and the source electrode of the driving transistor (hereinafter referred to as “S electrode”). ) Or a drain electrode (hereinafter referred to as “D electrode”) and a pixel electrode of an organic EL light emitting element are connected on the same plane (see Patent Document 1). Such an organic EL element is usually referred to as a “bottom emission organic EL element” and takes out light from the light emitting layer through a substrate.

  As another structural example of the organic EL element, a driving transistor and an organic EL light emitting element are stacked, and the S electrode or D electrode of the driving transistor and the pixel electrode of the organic EL light emitting element are connected via a contact hole. Are also known (see Patent Document 2). Such an organic EL element is usually referred to as a “top emission organic EL element” and takes out light from the light emitting layer through a sealing film on the side opposite to the substrate.

  In addition, in the case of a low molecular organic EL material, an organic EL element using an organic substance as a light emitting material is often formed by “evaporation”, and in the case of a polymer organic EL material, “inkjet” is used. It is often formed by “method”. In particular, the inkjet method is attracting attention as a technique that enables high-definition patterning of organic EL materials because droplets having a diameter of the order of μm can be discharged / coated with high resolution (for example, Patent Document 2). And Patent Document 3). In addition, in recent years, it has been reported that the technique called “roll printing method” also enables high-definition patterning.

  For example, when fine patterning is performed using an ink jet method, drying of the micro liquid applied on the substrate is extremely fast, and at the end (upper end, lower end, left end, right end) of the application region on the substrate, the pixel region Since the molecular pressure of the solvent evaporated from the micro liquid formed on the liquid crystal is low, it generally starts to dry quickly, and the difference in the drying time of the micro liquid causes film thickness unevenness within the pixel or between pixels, resulting in uneven brightness and emission color. It may cause display unevenness such as unevenness.

To solve this problem, for example, in the invention described in Patent Document 3, the display includes “an effective optical region in which a plurality of display pixels related to display are arranged, and a dummy region in which dummy pixels not related to display are arranged. By providing the first electrode on the pixel and the second electrode on the dummy pixel and arranging the organic EL material on the first electrode and the second electrode, it can be solved.
JP 2002-082632 A JP 2003-249375 A JP 2005-259716 A

  Certainly, even in the invention described in Patent Document 3, display unevenness such as brightness unevenness and light emission color unevenness due to the difference in drying time of the micro liquid in the coating region on the substrate may be reduced as compared with the prior art. .

  However, when active driving by an organic TFT element is performed using a driving transistor (hereinafter referred to as “DrT”) and a switching transistor (hereinafter referred to as “SwT”), drying of a micro liquid in the pixel region is performed. Each transistor of DrT and SwT is caused by the difference in drying time of the micro liquid in the coating region on the substrate unless considering not only the film thickness unevenness due to the time difference but also the respective structures of DrT and SwT. As a result, it is difficult to reduce display unevenness such as brightness unevenness and light emission color unevenness. That is, when the shape of the organic semiconductor layer constituting DrT and SwT and the interval between adjacent organic semiconductor layers are different, even if the organic semiconductor layer has the same shape due to the relationship with the surrounding organic semiconductor layers (for example, humidity). The evaporation rate of the organic semiconductor may differ depending on the location where the organic semiconductor layer is disposed.

  The present invention solves the above-mentioned conventional problems, and the degree of crystallization of the organic semiconductor material solution by making the drying rate of the organic semiconductor material solution (organic semiconductor layer) applied to the organic TFT element region uniform. It is an object of the present invention to provide an organic TFT element and an organic EL display panel using the same, in which the functional characteristics of the organic TFT element are stabilized, the functional characteristics of the organic TFT element are stabilized, and the luminance and emission color unevenness in the pixel region are small.

In order to achieve the above object organic TFT device of the present invention, the source electrode and the drain electrode, and a single respectively constituted by the organic semiconductor layer for electrically connecting between the drain electrode and the source electrode It possesses a switching transistor and a plurality of driving transistors, and an organic TFT device formed by arranging the single switching transistor and the plurality of driving transistors in the plurality of sets matrix, the source electrode and the drain Each of the electrodes has a shape having a long side and a short side. In the single switching organic TFT element, each of the source electrode and the drain electrode has a shape having a long side and a short side. the source of each one of the switching transistors and the plurality of driving transistors The source electrode and between the drain electrode and the source electrode and the cell before a realm Symbol organic semiconductor layer is disposed surrounded by the long side of the drain electrode are all the same shape, and, adjacent The intervals between the cells are all constant.

At this time, it is preferable that the edge portions at the four corners of the cell have an R shape. At this time, the radius of curvature of the shape is further preferably 5 to 20 μm. Further, it is desirable that the region D of the plurality of driving transistors is n times (n = 1, 2,..., 6) the region S of the single switching transistor .

In addition, when the direction perpendicular to the long sides of the source electrode and the drain electrode is the X direction and the direction perpendicular to the X direction is the Y direction, the intervals in the X direction and the Y direction of the cells are all equal. It is preferable that At this time, it is more preferable that the distance between adjacent cells is constant within a range of 10 μm to 100 μm.

  Further, the organic TFT element may be connected to an organic EL light emitting element including a pixel electrode, and a display may be obtained by combining the organic TFT element and the organic EL light emitting element. At this time, in the organic EL light emitting element, the light emitting element cell in which the light emitting material is formed has the same shape as the cell in which the organic semiconductor layer is disposed, and the interval between all adjacent cells in the display is constant. Further preferred.

  As described above, according to the present invention, the organic semiconductor layers connecting the source electrode and the drain electrode over the entire surface of the substrate are arranged at the same pitch and the same size, using an ink jet method or a roll printing method, When a DrT or SwT transistor is formed, it is unlikely that the drying rate in each cell (space where the organic semiconductor layer is formed) is different, and the degree of crystallization of the organic semiconductor layer may be uniform over the entire surface of the substrate. It is possible to provide an organic TFT element capable of stabilizing the functional characteristics of the TFT element, and to provide an organic EL display panel using the organic TFT element with less luminance and emission color unevenness in the pixel region. It becomes possible.

  An organic TFT element and an organic EL display according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  In the drawings, substantially the same members are denoted by the same reference numerals.

(Embodiment 1)
<Configuration of transistor element>
1A is a plan view showing the structure of the transistor element 10 according to the first embodiment of the present invention, and FIG. 1B is a schematic cross section taken along the line AA in FIG. FIG.

  The transistor element 10 is a bottom-gate transistor having a gate electrode (hereinafter referred to as “G electrode”) in the lower layer. The transistor element 10 includes a G electrode 2 provided on the substrate 1, a gate insulating layer 3 provided so as to cover the G electrode 2, an S electrode 4 provided on the gate insulating layer 3, On the same plane as the S electrode 4, the D electrode 6, which is spaced apart by a gap 5, on the gate insulating layer 3, on the gap 5 between the S electrode 4 and the D electrode 6, the S electrode 4 And an organic semiconductor layer 8 electrically connected across the D electrode 6.

  In the present embodiment, the driving transistor is divided into three parts for one element (for example, R organic EL material). That is, FIG. 1 shows a configuration including one SwT and three DrTs for one element. In addition, FIG. 1 is a schematic diagram that is specially specified for one element. In an actual organic EL element, the direction perpendicular to the longitudinal direction of the S electrode 4 and the D electrode 6 is defined as the “X direction”, and is perpendicular to the X direction. When the direction is “Y direction”, it goes without saying that a plurality of SwT and DrT are regularly and continuously provided in both the X and Y directions.

  Further, since DrT uses a larger voltage than SwT, the area D of DrT is necessarily larger than the area S of SwT as shown in FIG. n is a natural number). Here, the upper limit of n is at most n = 6 from the relationship between the size of the substrate 1 and the DrT region D or SwT region S.

  In this transistor element 10, a gap 5 is defined between the inner edge of the S electrode 4 and the inner edge of the D electrode 6, and an organic semiconductor layer 8 is formed across the S electrode 4 and the D electrode 6. The S electrode 4 and the D electrode 6 are electrically connected by the organic semiconductor layer 8. The organic semiconductor layer 8 is provided on the gap 5 between the S electrode 4 and the D electrode 6, is made of a polycrystal of an organic semiconductor material, and has excellent electrical characteristics from the S electrode 4 to the D electrode 6.

  At this time, the distance (d1 in FIG. 1) between the organic semiconductor layers 8 arranged in the direction (X direction) perpendicular to the longitudinal direction of the S electrode 4 and the D electrode 6 is constant in the X direction. 4 and the direction parallel to the longitudinal direction of the D electrode 6 (Y direction) are constant (d2 in FIG. 1). Note that d1 and d2 may be the same, but d1 and d2 may be different (in other words, the necessity of d1 = d2 is not necessarily required, and what is important is that the organic semiconductor layer 8 is in the X direction). The distance is constant in the X direction, and the distance in the Y direction of the organic semiconductor layer 8 is also constant in the Y direction. D1 and d2 are preferably 10 μ ≦ d1 and d2 ≦ 100 μm.

  Hereinafter, constituent members of the transistor element 10 will be described.

<Board>
As the substrate 1, a glass substrate, a plastic substrate, or the like can be used. Further, a flexible substrate may be used. When this transistor element is used for an organic EL display, a flexible substrate is preferable.

<Gate electrode (G electrode)>
The G electrode 2 is provided on the substrate 1. As shown in FIG. 1B, the transistor element 10 according to the first embodiment is called “bottom gate type” because the G electrode 2 is provided in the lowermost layer. On the contrary, a “top gate type” in which the G electrode 2 is provided in the uppermost layer as in a transistor element according to a second embodiment to be described later may be used. The material of the G electrode 2 is not particularly limited. For example, the G electrode 2 includes a laminated film of a Cr film (5 nm or less) and an Au film (about 100 nm) or a laminated film of a Ti film (5 nm or less) and an Au film (about 100 nm) Is done. Although the Cr film and the Ti film mainly act as an adhesive film, it may be more preferable to use a Ti film that hardly oxidizes.

<Gate insulation layer>
The gate insulating layer 3 is provided between the G electrode 2, the S electrode 4, and the plane on which the D electrode 6 is disposed. The gate insulating layer 3 can be formed of a commonly used insulating layer, such as a polymer insulating layer.

<Source electrode (S electrode) and drain electrode (D electrode)>
The S electrode 4 and the D electrode 6 are disposed on the upper surface of the gate insulating layer 3 formed on the substrate 1 and are separated from each other by a gap 5. FIG. 1 shows an embodiment in which the SwT D electrode 6 and the DrT G electrode 2 are connected via a contact hole.

  As the S electrode 4 and the D electrode 6, a conductive metal such as aluminum, chromium, molybdenum chromium, titanium, gold, silver, or copper, or an organic conductor such as a polythiophene derivative can be used. In particular, it is preferable to use silver having a characteristic of high light reflectance.

<Organic semiconductor layer>
The organic semiconductor layer 8 is formed between the S electrode 4 and the D electrode 6, and electrically connects the S electrode 4 and the D electrode 6. The organic semiconductor layer 8 is made of a polycrystalline material, is formed on the gap 5 between the S electrode 4 and the D electrode 6, and has excellent electrical characteristics from the S electrode 4 to the D electrode 6. Moreover, FIG.1 (c) is an enlarged view of the organic-semiconductor layer 8 in Fig.1 (a), but the edge parts of the four corners of the space (cell) in which the organic-semiconductor layer 8 is formed are R shape. preferable. This is because, for example, when an organic semiconductor material (a material that later becomes an organic semiconductor layer) is applied to the cell using an inkjet method or a dispenser method, the organic semiconductor material (ink) is concentrically formed in the cell from the applied point. If the edges of the four corners of the cell are rounded (preferably with a radius of curvature of 5 to 20 μm), the ink flow in the cell will be smooth, resulting in uniform ink in the cell. It is because it is formed.

  As the organic semiconductor material constituting the organic semiconductor layer 8, fluorene-thiophene copolymer (F8T2), tetrabenzoporphyrin, oligothiophene, pentacene, rubrene, etc. may be used. it can. In particular, when the G electrode is a top gate electrode (a gate electrode disposed above the channel when the substrate on which the channel is formed is located below), it is preferable to use F8T2, and the bottom gate electrode (channel In the case of a gate electrode disposed on the lower side of the channel when the substrate on which is formed is the lower side, tetrabenzoporphyrin is preferably used.

  The organic semiconductor layer 8 can be formed by applying a non-aqueous solution 7 containing an organic semiconductor material to a non-aqueous solvent such as ethyl benzoate and then drying it. In this case, by drying the organic semiconductor solution 7 in the form of convex droplets, the outer solvent dries more quickly, and the organic semiconductor material can easily flow from the center toward the outer side.

<Manufacturing method of transistor element>
Next, a method for manufacturing the bottom gate transistor element 10 according to the first embodiment will be described with reference to FIG.
(A) As the substrate 1, a glass substrate, a plastic substrate, or a flexible substrate is prepared.
(B) The G electrode 2 is formed on the substrate 1 using Cr or Au material (FIG. 2A).
(C) A gate insulating layer 3 is formed to cover the G electrode 2 (FIG. 2B). As the gate insulating layer 3, for example, an insulating polymer is used.
(D) Next, the S electrode 4 is provided on the gate insulating layer 3, and the D electrode 6 is disposed in the same plane as the S electrode 4 with the S electrode 4 being separated by a gap 5 (FIG. 2C). The S electrode 4 and the D electrode 6 may be formed using Cr or Au material.
(E) An organic semiconductor solution 7 of convex droplets containing an organic semiconductor material in a non-aqueous solvent so as to cover the entire surface of the S electrode 4 and the gap 5 between the S electrode 4 and the D electrode 6 Apply (FIG. 2 (d)). In addition, application | coating can be performed using the dispenser method, the inkjet method, etc., for example. Moreover, there is no problem even if it uses a roll printing method.
(F) The organic semiconductor solution 7 is dried, and the organic semiconductor material is crystallized on the gap 5 between the S electrode 4 and the D electrode 6 to obtain the organic semiconductor layer 8 (FIG. 2E). The organic semiconductor layer 8 makes it possible to electrically connect the S electrode 4 and the D electrode 6.

  As described above, the bottom-gate transistor element 10 according to the first embodiment can be formed.

(Embodiment 2)
<Configuration of transistor element>
FIG. 5A is a plan view showing a configuration of a top-gate transistor element 10a according to Embodiment 2 of the present invention, and FIG. 5B is a schematic cross-sectional view taken along line BB in FIG. It is. Compared with the bottom gate type transistor element 10 according to the first embodiment, the transistor element 10a has a gate insulating layer 3 formed on the S electrode 4 and the D electrode 6, and a G electrode 2 provided thereon. It is a top gate type transistor element. Other parts similar to those described in (Embodiment 1) will not be described.

<Manufacturing method of transistor element>
Next, a method for manufacturing the top-gate transistor element 10a according to the second embodiment will be described with reference to FIG.
(A) As the substrate 1, a glass substrate, a plastic substrate, or a flexible substrate is prepared.
(B) The S electrode 4 is provided on the substrate 1, and the D electrode 6 is disposed on the inside and outside of the same plane as the S electrode 4 so as to surround the S electrode 4 and separated by a gap 5 (FIG. 3A). The S electrode 4 and the D electrode 6 are formed using a Cr or Au material.
(C) An organic semiconductor solution 7 of convex droplets containing an organic semiconductor material in a non-aqueous solvent so as to cover the entire surface of the S electrode 4 and the gap 5 between the S electrode 4 and the D electrode 6 Apply (FIG. 3B).
(D) The organic semiconductor solution 7 is dried, and the organic semiconductor material is crystallized on the gap 5 between the S electrode 4 and the D electrode 6 to obtain the organic semiconductor layer 8 (FIG. 3C). The organic semiconductor layer 8 electrically connects the S electrode 4 and the D electrode 6.
(E) The gate insulating film 3 is formed so as to cover the S electrode 4, the D electrode 6, and the organic semiconductor layer 8 (FIG. 3D). As the gate insulating layer 3, for example, an insulating polymer is used.
(F) Next, the G electrode 2 is formed on the gate insulating layer 3 using Cr or Au material (FIG. 3E).

  As described above, the top-gate transistor element 10a according to the second embodiment can be formed.

(Organic EL display)
Hereinafter, three typical structures of the organic EL display using the transistor elements 10 and 10a described in the first and second embodiments will be described.

<< First organic EL display structure >>
FIG. 4 shows the structure of the first organic EL display, FIG. 4 (a) is a top view of the organic EL display, and FIG. 4 (b) is a part of the organic EL display (subpixel / RGB). 4 (c) is a diagram showing an equivalent circuit of a transistor.

  First, as shown in FIG. 4A, R, G, and B light emitting elements are continuously formed in the X direction of the figure, and each light emitting element includes a respective organic TFT element (a driving TFT element and a driving TFT element). Switching TFT elements) are electrically connected. By driving the organic TFT element, light emission of the light emitting element can be controlled. In the organic EL display in FIG. 4, the organic TFT element and the organic EL light emitting element are disposed on the same plane, and the source electrode or drain electrode of the driving TFT and the pixel electrode of the organic EL light emitting element are disposed on the same plane. Therefore, a bottom emission type organic EL display is shown.

  Further, as shown in FIG. 4B, the space (cell / dotted line portion) in which the organic semiconductor layer 8 is formed has the same shape on the entire surface of the substrate 1, and the cells are spaced at a constant distance d1 in the X direction. Is arranged in. Although not shown in FIG. 4, the space (cell) in which the organic semiconductor layer 8 is formed is a constant interval d1 in the X direction as described in <Configuration of transistor element> in (Embodiment 1) described above. And continuously arranged at a constant interval d2 in the Y direction. Therefore, even when an organic TFT element is formed using a so-called “printing method” such as an inkjet method, a dispenser method, or a roll printing method, the atmosphere (eg, humidity) with the surrounding cells is constant. Therefore, the drying speed of the organic semiconductor material (the material that will later become an organic semiconductor layer) in each cell can be made uniform, and the degree of crystallization of the organic semiconductor material can be made constant. Note that an equivalent circuit of a transistor in the first organic EL display structure is as shown in FIG. 4C, where 40 is a gate line, 41 is a power supply line, and 42 is a source line.

<< Second organic EL display structure >>
The organic EL display shown in FIG. 5 is a bottom emission type organic EL display similar to the organic EL display shown in FIG. 4. However, the difference from the organic EL display shown in FIG. The space (cell) in which the organic semiconductor layer 8 is formed has the same shape, and the interval between the cells in which the organic semiconductor layer 8 is formed is constant. That is, in the first organic EL display shown in FIG. 4, the space (cell) in which the organic semiconductor layer 8 in the organic TFT element is formed has the same shape, and the cell spacing remains constant in the XY direction. However, the second organic EL display shown in FIG. 5 is a mode in which the region where the light emitting material is formed is subdivided (celled) in the light emitting element.

  In this way, even the region where the light emitting material is formed in the light emitting element is made into a cell, and the space (cell) in which the organic semiconductor material and the light emitting material are formed over the entire surface of the substrate has the same shape and the same pitch. The degree of crystallization of each of the material and the light emitting material can be made constant, and an organic EL display having high performance (high luminance, low emission color unevenness) can be provided.

<< Third organic EL display structure >>
FIG. 6 shows the structure of the third organic EL display, FIG. 6 (a) is a top view of the organic EL display, and FIG. 6 (b) is a part of the organic EL display (subpixel / RGB). FIG. 6 (c) is a diagram showing an equivalent circuit of the transistor.

  The organic TFT element in this organic EL display is formed by stacking a driving transistor and an organic EL light emitting element, and connecting a source electrode or a drain electrode of the driving transistor and a pixel electrode of the organic EL light emitting element through a contact hole. This is a top emission type structure. The organic TFT element as shown in FIG. 6 may be generally referred to as “current copier”.

  In the case of the organic TFT elements in the first and second organic EL displays, a data signal is output by the gate signal of the switching TFT and the driving TFT is driven, so that the transistor itself is very susceptible to variations. It can be said that. On the other hand, in the case of the organic TFT element in the third organic EL display, the current to be output is directly supplied to the transistor itself that outputs current, and then between the gate electrode and the source electrode stored at that time. Since the circuit outputs current based on voltage, it can be said that the transistor has a very small variation in characteristics of a single transistor.

  In FIG. 6C, reference numeral 61 denotes a first control line, and 62 denotes a control line.

  The organic TFT element and the organic EL display of the present invention can be used not only as an organic EL television, for example, but also as a display unit in various electronic devices such as portable information processing devices such as word processors and personal computers and wristwatch type electronic devices. Can be used.

(A) Schematic diagram (top view) of the organic TFT element according to the present invention, (b) Schematic diagram (cross-sectional view) of the organic TFT element according to the present invention, (c) Organic semiconductor layer in the organic TFT element according to the present invention Diagram showing (cell) The figure which shows the manufacturing process of the bottom gate type transistor element which concerns on Embodiment 1 of this invention. The figure which shows the manufacturing process of the top gate type transistor element which concerns on Embodiment 1 of this invention. (A) Schematic diagram (top view) of the organic EL display according to the first aspect of the present invention, (b) Schematic diagram (top view) showing the subpixels of the organic EL display according to the present invention, (c) Transistor Diagram showing equivalent circuit (A) Schematic diagram (top view) of an organic EL display according to the second aspect of the present invention, (b) Schematic diagram (top view) showing subpixels of the organic EL display according to the present invention, (c) Transistor Diagram showing equivalent circuit (A) Schematic diagram (top view) of an organic EL display according to the third aspect of the present invention, (b) Schematic diagram (top view) showing subpixels of the organic EL display according to the present invention, (c) Transistor Diagram showing equivalent circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating layer 4 Source electrode 5 Gap 6 Drain electrode 8 Organic semiconductor layer 10 Transistor element

Claims (8)

Source and drain electrodes, and have a, a single switching transistor and a plurality of driving transistors respectively constituted by the organic semiconductor layer for electrically connecting between the drain electrode and the source electrode,
In the organic TFT element in which the single switching transistor and the plurality of driving transistors are arranged in a matrix of a plurality of sets ,
The source electrode and the drain electrode each have a shape having a long side and a short side,
Said single in between the source electrode and the drain electrode in each switching transistor and the plurality of driving transistors, and the source electrode and the realm in and before Symbol organic semiconductor surrounded by the long side of the drain electrode An organic TFT element characterized in that the cells in which the layers are arranged have the same shape, and all the intervals between adjacent cells are constant. The organic TFT element according to claim 1, wherein the edge portions at the four corners of the cell have an R shape. The organic TFT element according to claim 2, wherein the radius of curvature of the R shape is 5 to 20 μm. 3. The organic TFT element according to claim 1, wherein a region D of the plurality of driving transistors is n times (n = 1, 2,..., 6) of a region S of the single switching transistor . When the direction perpendicular to the long side of the source electrode and the drain electrode is the X direction and the direction perpendicular to the X direction is the Y direction, the intervals in the X direction and the Y direction of the cells are all equal. Item 5. The organic TFT element according to any one of Items 1 to 4. The organic TFT element according to any one of claims 1 to 5, wherein an interval between adjacent cells is all constant within a range of 10 µm to 100 µm. The organic TFT element according to any one of claims 1 to 6 is connected to an organic EL light emitting element including a pixel electrode, and the organic EL element is formed by combining the organic TFT element and the organic EL light emitting element. display. In the organic EL light emitting device, the light emitting device cell in which the light emitting material is formed has the same shape as the cell in which the organic semiconductor layer is disposed, and
8. The organic EL display according to claim 7, wherein the distance between all adjacent cells in the display is constant.

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