JP2007088001A - THIN FILM TRANSISTOR, IMAGE DISPLAY DEVICE USING SAME, AND METHOD FOR PRODUCING THIN FILM TRANSISTOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive thin film transistor in which transistor OFF current is small and transistor ON current variation is small.
A thin film transistor according to the present invention includes a gate electrode, a source electrode, a drain electrode, and a channel portion, and a semiconductor layer for allowing a current to flow through the channel portion exists in an isolated region, and The semiconductor layer 4 is formed such that the droplets are discrete in time in the direction orthogonal to the channel direction of the transistor, and the droplets are continuously formed in time in the direction parallel to the channel direction of the transistor. It is characterized by.
[Selection] Figure 2

Description

  The present invention relates to a thin film transistor, an image display device using the same, and a method for manufacturing the thin film transistor, and more particularly to a thin film transistor using an organic semiconductor layer as a semiconductor layer.

  Electronic books that use liquid crystal as display elements and electronic books that use electrophoresis as display elements have been released as products, and are attracting attention as display media that can replace paper. Also, with the increase in paper consumption in offices, electronic paper is expected to be put to practical use as a medium that replaces paper.

  In an electronic book, an amorphous silicon semiconductor formed on a glass substrate as an active matrix thin film transistor for driving a liquid crystal or an electrophoretic element is used as a semiconductor material. However, in electronic paper, since it is necessary to use a film substrate as a substrate, a high temperature process of 200 ° C. or higher cannot be used. From that point of view, a thin film transistor using an organic semiconductor capable of forming a thin film transistor on a film substrate by a low temperature process has attracted attention as an active matrix thin film transistor used for electronic paper.

  In the case where thin film transistors are formed in a matrix, it is necessary to electrically isolate adjacent transistors, and thus it is necessary to pattern a semiconductor layer. As a method for patterning the organic semiconductor layer, a method using laser irradiation as disclosed in Patent Document 1, a method using ink jet printing as disclosed in Patent Document 2, and a method disclosed in Patent Document 3 are disclosed. There is a method of ejecting droplets of a solution containing such a material.

  Further, not only an organic semiconductor layer but also a general method for patterning a functional material includes a method using a photolithography method as disclosed in Patent Document 4.

  Among the above-described conventional techniques, the technique using the photolithography method has an advantage that a fine pattern can be formed. However, the number of processes such as resist removal from application of the resist through etching is large, and damage due to the process is also caused. Therefore, there are many problems in terms of cost and performance in forming an active matrix thin film transistor using an organic semiconductor.

  In addition, the method using laser irradiation has many problems in terms of performance when forming an active matrix thin film transistor using an organic semiconductor because there is much damage due to the process.

On the other hand, inkjet printing and droplet ejection methods require fewer steps, have less damage to the organic semiconductor layer, and are advantageous in terms of cost and performance. However, droplets in which the organic semiconductor is dissolved or melted are dropped. Because of this method, the area of the organic semiconductor layer formed by dropping due to variations in the volume of the droplets, variations in the dropping speed, variations in the dropping position accuracy of the dropping droplets, surface properties of the dropping surface, etc. There is a problem that varies.
JP-T-2005-500558 Japanese translation of PCT publication No. 2003-518332 JP 2004-133050 A JP 2004-064059 A

  An object of the present invention is to provide an inexpensive thin film transistor which has been made in order to solve the above-described problems and has a small transistor OFF current and a small variation in the transistor ON current.

  According to a first aspect of the present invention, the semiconductor device includes a gate electrode portion, a source electrode portion, a drain electrode portion, and a channel portion, and the channel portion exists in an isolated region in which current flows. In addition, the semiconductor layer is formed such that the droplets are discrete in time in a direction perpendicular to the channel direction of the transistor, and the droplets are continuously formed in time parallel to the channel direction of the transistor. It is characterized by being.

  According to a second aspect of the present invention, in addition to the first aspect, the semiconductor layer is formed in electrical contact with the source electrode portion and the drain electrode portion. It is characterized by that.

  According to a third aspect of the present invention, in addition to the first or second aspect, the semiconductor layer is an organic semiconductor.

  According to a fourth aspect of the present invention, in addition to the third aspect of the invention, the organic semiconductor layer is a polymer organic semiconductor.

  According to a fifth aspect of the present invention, in the method of manufacturing a thin film transistor having a gate electrode portion, a gate insulating film portion, a channel portion, a source electrode portion, and a drain electrode portion as constituent elements, the source electrode portion and the drain electrode After forming the portion, when the droplet containing the semiconductor material is dropped, the droplet is temporally dispersed in a direction orthogonal to the channel direction of the transistor and in a direction parallel to the channel direction of the transistor. It is characterized in that droplets are continuously formed in time and a semiconductor layer for supplying current is formed in an isolated region.

  According to a sixth aspect of the present invention, in addition to the fifth aspect of the present invention, a dispenser is used as a method of forming the liquid droplets by dropping.

  According to a seventh aspect of the present invention, in addition to the fifth aspect, an ink jet apparatus is further used as a method of forming the liquid droplets by dropping.

  According to an eighth aspect of the present invention, there is provided an image display device using the thin film transistor described above as an active element.

  According to the present invention, the variation in the width of the transistor semiconductor layer in the channel direction is made smaller than the variation in the width perpendicular to the channel direction of the transistor semiconductor layer, thereby suppressing the variation in the ON current of the transistor between the transistor elements. Is possible.

  In addition, since the semiconductor layer is formed in electrical contact with the source electrode portion and the drain electrode portion, a transistor with excellent electrical characteristics can be formed.

  In addition, by using an organic semiconductor as a semiconductor material, it is easy to form a semiconductor layer by dropping droplets.

  Further, by using a polymer organic semiconductor as the organic semiconductor material, it becomes easy to dissolve the semiconductor in a solvent to form a semiconductor layer.

  Further, in the manufacturing method of the present invention, the step of forming the droplet containing the semiconductor material by dropping is performed in the step after forming the source electrode portion and the drain electrode portion, so that the semiconductor layer is not damaged. Electrical conduction between the semiconductor layer and the source and drain electrode portions can be easily achieved.

  In addition, the semiconductor layer can be easily formed by dropping by using a dispenser as a method for forming the droplet by dropping.

  In addition, by using an inkjet apparatus as a method for forming droplets by dropping, a semiconductor layer having excellent mass productivity can be formed.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated in order to avoid duplication of description.

  1 is a schematic cross-sectional view showing the configuration of an organic thin film transistor to which the present invention is applied, FIG. 2 is a plan view showing the configuration of an organic thin film transistor according to an embodiment of the present invention, and FIG. It is a top view which shows the structure of the organic thin-film transistor of a comparative example.

  The organic thin film transistor shown in FIG. 1 is a bottom gate bottom contact type. The organic thin film transistor has a structure in which a gate electrode 2 is provided on a substrate 1 and a gate insulating film 3 is formed so as to cover the gate electrode 2. The A source electrode 5 and a drain electrode 6 are provided on the gate insulating film 3, and an organic semiconductor layer 4 is provided between and on the source electrode 5 and the drain electrode 6.

  The length of the channel portion in this type of thin film transistor is defined by the distance between the source electrode 5 and the drain electrode 6, and there are two methods for defining the width of the channel portion.

  One method is to define the width of the channel portion by defining the width of the source electrode (or drain electrode 6). On the other hand, as another method, there is a method of defining the width of the channel portion by defining the width of the semiconductor layer 4.

  When the width of the channel portion is defined by defining the width of the source electrode (or drain electrode 6), the width of the channel is defined by the width of the source electrode 5 (or drain electrode 6). Even if the area of 4 varies, there is an advantage that the channel width does not vary. However, the semiconductor layer 4 formed so as to protrude from the source electrode 5 (or the drain electrode 6) does not contribute as a channel portion even when the transistor is shut off by the gate electrode 2, but contributes as a resistance component instead. However, there is a drawback that the off-current of the transistor increases.

  On the other hand, when the width of the channel portion is defined by defining the width of the semiconductor layer 4, the width of the channel portion is defined by the width of the semiconductor layer 4, so that the semiconductor other than the portion that contributes to the channel Since there is no layer, there is no fear of causing an unnecessary increase in the OFF current of the transistor. However, since the width of the channel portion depends on variations in the width of the semiconductor layer, when the semiconductor layer is formed by a method of dropping droplets, the on-current of the transistor varies.

  According to the present invention, by defining the width of the semiconductor layer 4, in the structure defining the width of the channel portion, variation in transistor characteristics is reduced by suppressing variation in the channel width of the semiconductor layer that is a component of the transistor. It is a thing.

  Specifically, a semiconductor layer 4 formed by dropping droplets by an ink jet method or a dispenser method, that is, a semiconductor layer 4 formed by overstripping droplets including a plurality of semiconductor layers is formed on a transistor. The transistors are discrete in time in a direction orthogonal to the channel direction and continuously in time in a direction parallel to the channel direction of the transistor. As described above, the channel portion is formed by the semiconductor layer 4 through which current flows flowing in an isolated region, and variation in the width of the semiconductor layer 4 in the direction orthogonal to the channel direction of the transistor is caused by the channel direction of the transistor. It can be made smaller than the variation in the width of the semiconductor layer 4 in the direction parallel to.

  The advantages of the present invention can be understood by comparing FIG. 2 with FIG. The semiconductor layer 4 shown in FIG. 2 and FIG. 3 is formed by repeatedly hitting droplets including a plurality of semiconductor layers 4 using an ink jet method or a dispenser method. FIG. 2 is a plan view showing a configuration of an organic thin film transistor according to an embodiment of the present invention, and FIG. 3 is a plan view showing a configuration of an organic thin film transistor of a comparative example of the present invention.

  FIG. 2 shows that a droplet 41 including a semiconductor layer is temporally continuous between the source electrode 5 and the drain electrode 6 in a scanning direction (A direction in the drawing) parallel to the channel direction of the transistor. Thus, the semiconductor layer 4 is formed. Then, they are discretely formed in the direction perpendicular to the channel direction of the transistor.

  FIG. 3 shows a case where droplets 41 including a semiconductor layer are continuously overprinted in time in a scanning direction (B direction in the figure) perpendicular to the channel direction of the transistor. Then, they are discretely formed in time in a direction parallel to the channel direction of the transistor.

  As is apparent from FIGS. 2 and 3, when the interval between droplet formation perpendicular to the scanning direction is constant, when droplets including a semiconductor layer are overstruck in the scanning direction parallel to the channel direction of the transistor, It can be seen that, although the variation in channel width is small, the variation in channel width increases when a droplet including a semiconductor layer is overstruck in the scanning direction orthogonal to the channel direction of the transistor.

  Therefore, the configuration of FIG. 2 can suppress variations in transistor characteristics to a smaller extent than the configuration of FIG.

  As the gate electrode material / source electrode material / drain electrode material used in the present invention, an Au film, an Al film, a Cr film, a silver film formed by a screen printing method, an inkjet method or a dispenser are used. The silver and gold nanometal films that are formed are raised.

  Further, the material of the semiconductor layer 4 used in the present invention includes an inorganic material such as an amorphous silicon material, but a particularly effective material in the present invention is an organic semiconductor material, and a low molecular material such as pentacene or a low molecular material. And the like, precursors made to be soluble, thiophene-based polymer organic semiconductor materials, triarylylamine-based polymer organic semiconductor materials, and the like. In particular, the polymer organic semiconductor material is suitable for the present invention because it is soluble in an organic solvent.

  Then, the step of forming the droplet containing the semiconductor material by dropping is performed in the step after forming the source electrode and the drain electrode, so that the semiconductor layer, the source electrode, and the drain can be easily formed without damaging the semiconductor layer. Electrical continuity with the electrode becomes possible.

  Next, the present invention will be described based on specific examples. A comparative example was also created for comparison.

(Example)
An Al film having a thickness of 100 nm was formed on the optically polished glass substrate 1 by vacuum deposition, and photolithography and etching were performed to form the gate electrode 2.

  After forming the gate electrode 2, a cyanoethyl pullulan insulating film (trade name “Cyanoresin CR-S” manufactured by Shin-Etsu Chemical Co., Ltd.) is spin-coated and dried at 100 ° C. for 30 minutes using a hot plate to form the gate insulating film 3. Formed. The film thickness was 200 nm.

  Next, an Au film having a thickness of 50 nm was formed on the gate insulating film 3 by a vacuum vapor deposition method using a shadow mask to form a source electrode 5 and a drain electrode 6. The distance between the source electrode 5 and the drain electrode 6 was 5 μm, and the width of the source electrode was 1000 μm.

  Subsequently, an isolated semiconductor layer 4 is formed on the source electrode 5 and the drain electrode 6 using a triarylamine polymer dissolved in an organic solvent as an organic semiconductor material. The semiconductor layer 4 was formed by dropping a triarylamine polymer dissolved in an organic solvent using an inkjet method. As for the amount of droplets, the diameter of the semiconductor layer 41 formed by dropping is 100 μm, the interval between the droplet center positions where droplets are dropped by scanning continuously in time is 10 μm, and the interval between droplet drops perpendicular to the scanning direction. Was adjusted to 50 μm. In this sample, the scanning direction of dropping was set to be parallel to the channel direction of the transistor, and the semiconductor layer was formed so that the channel width of the transistor was 500 μm. After dripping, it was dried at 80 ° C. for 30 minutes. Ten samples were prepared by the manufacturing method of the example. These samples are designated as Sample No. 1 to sample no. 10 is assumed. These samples correspond to FIG.

(Comparative example)
As in the above example, an Al film having a thickness of 100 nm was formed on the optically polished glass substrate 1 by a vacuum deposition method, and photolithography and etching were performed to form the gate electrode 2.

  After forming the gate electrode 2, a cyanoethyl pullulan insulating film (trade name “Cyanoresin CR-S” manufactured by Shin-Etsu Chemical Co., Ltd.) is spin-coated and dried at 100 ° C. for 30 minutes using a hot plate to form the gate insulating film 3. Formed. The film thickness was 200 nm.

  Next, an Au film having a thickness of 50 nm was formed on the gate insulating film 3 by a vacuum vapor deposition method using a shadow mask to form a source electrode 5 and a drain electrode 6. The distance between the source electrode 5 and the drain electrode 6 was 5 μm, and the width of the source electrode was 1000 μm.

  Subsequently, an isolated semiconductor layer 4 is formed on the source electrode 5 and the drain electrode 6 using a triarylamine polymer dissolved in an organic solvent as an organic semiconductor material. The semiconductor layer 4 was formed by dropping a triarylylamine polymer dissolved in an organic solvent using an inkjet method. As for the amount of droplets, the diameter of the semiconductor layer 41 formed by dropping is 100 μm, the interval between the droplet center positions where droplets are dropped by scanning continuously in time is 10 μm, and the interval between droplet drops perpendicular to the scanning direction. Was adjusted to 50 μm. In this sample, the scanning direction of dropping was set to be orthogonal to the channel direction of the transistor, and the semiconductor layer was formed so that the channel width of the transistor was 500 μm. After dripping, it was dried at 80 ° C. for 30 minutes. Ten samples were prepared by the manufacturing method of the comparative example. These samples are designated as Sample No. 11 to sample no. 20 These samples correspond to FIG.

  Sample sample No. prepared in the example. 1 to sample no. 10 and the sample No. prepared in the comparative example. 11 to sample no. The transistor ON current was measured for 20 samples. The measurement results are shown in Table 1.

  As can be seen from Table 1, when the example and the comparative example are compared, it can be seen that the variation in the ON current sample is smaller in the example than in the comparative example. Therefore, according to the organic thin film transistor according to the present invention, it is possible to suppress variations in the ON current between the transistor elements.

  Next, an embodiment in which the thin film transistor of the present invention is used for an active matrix element of an image display device will be described. 4 is a plan view showing an example in which the thin film transistor of the present invention is used for an active matrix substrate of an image display device, and FIG. 5 is a longitudinal sectional view of the image display device using the active matrix substrate of the present invention. An active matrix display device can be configured by combining an active matrix substrate with an image display device such as liquid crystal, electrophoresis, or organic EL.

  As shown in FIG. 4, a Cr film having a thickness of 70 nm is formed on an insulating substrate 1 such as a glass substrate by a sputtering method, and a scanning line 20 and a gate electrode 2 are formed by a photolithography etching process. An insulating film is formed as an interlayer insulating film between the gate insulating film 3 and the scanning line 20 and the signal wiring.

  Subsequently, an Au film having a thickness of 50 nm is formed in a predetermined region on the gate insulating film 3 by a vacuum deposition method using a shadow mask, and the signal wiring 21 connected to the source electrode 5, the drain electrode 6, and the drain electrode 6. The pixel electrode 22 connected to the source electrode 5 is formed.

  Then, a triarylamine polymer dissolved in an organic solvent was dropped between and on the source electrode 5 and the drain electrode 6 using a dispenser to form a semiconductor layer 4 composed of an organic semiconductor layer divided into three. .

  Subsequently, the active matrix substrate 31 is formed by providing the passivation protection layer 7 on the organic semiconductor layer 4 including the source electrode 5 and the drain electrode 6, the signal wiring 21, and the pixel electrode 22 connected to the source electrode 5.

  As shown in FIG. 5, the image display device 30 includes a display element provided between the above active matrix substrate 31 and the transparent conductive film 32 and the second substrate 33, and is on the source electrode 5 connected to the pixel electrode 22. The display elements are switched. As the second substrate 33, plastic such as glass, polyester, polycarbonate, polyarylate, polyether sulfone, or the like can be used. As the display element 34, methods such as liquid crystal, electrophoresis, and organic EL can be used.

  In the case of configuring a liquid crystal panel, for example, an alignment film is formed on the substrate of the active matrix substrate 31 and the second substrate 33 by spin coating and subjected to alignment treatment. A silica spacer is disposed and bonded between the substrates 1 and 33, and a liquid crystal material is sealed between the gaps to form a liquid crystal panel.

  In addition, the electrophoretic display panel can be formed by forming a transparent conductive film, placing a silica spacer on a counter substrate and joining the same, and encapsulating a microcapsule type electrophoretic element between the gaps.

  In the above-described embodiment, the bottom contact type transistor is described as an example of the thin film transistor. However, the present invention can also be applied to the top contact type transistor.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  The present invention can be applied to an active thin film transistor using an organic thin film transistor such as a liquid crystal display, an electrophoretic display, and electronic paper.

  The embodiments disclosed herein are illustrative and non-restrictive in every respect.

It is a typical sectional view showing a bottom gate bottom contact type thin film transistor to which the present invention is applied. It is a top view which shows the structure of the organic thin-film transistor concerning embodiment of this invention. It is a top view which shows the structure of the organic thin-film transistor of the comparative example of this invention. It is a top view which shows the example which used the thin-film transistor of this invention for the active-matrix board | substrate of an image display apparatus. It is a longitudinal cross-sectional view of the image display apparatus using the active matrix substrate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 5 Source electrode 6 Drain electrode 41 Semiconductor layer

Claims (8)

The semiconductor device includes a gate electrode portion, a source electrode portion, a drain electrode portion, and a channel portion, and the channel portion is present in an isolated region where a current flows, and the semiconductor layer has a channel direction of the transistor. A thin film transistor, wherein droplets are discrete in time in a direction perpendicular to each other and continuous in terms of time in a direction parallel to the channel direction of the transistor.   2. The thin film transistor according to claim 1, wherein the semiconductor layer is formed in electrical contact with the source electrode portion and the drain electrode portion.   The thin film transistor according to claim 1, wherein the semiconductor layer is an organic semiconductor.   The thin film transistor according to claim 3, wherein the organic semiconductor layer is a polymer organic semiconductor.   In the method for manufacturing a thin film transistor including a gate electrode portion, a gate insulating film portion, a channel portion, a source electrode portion, and a drain electrode portion as constituent elements, a liquid containing the semiconductor material after forming the source electrode portion and the drain electrode portion When droplets are dropped, the droplets are discrete in time in the direction perpendicular to the channel direction of the transistor, and the droplets are continuously formed in time parallel to the channel direction of the transistor. A method for manufacturing a thin film transistor, characterized in that a semiconductor layer for passing a current is formed in an isolated region.   6. The method of manufacturing a thin film transistor according to claim 5, wherein a dispenser is used as a method of forming the droplet by dropping.   6. The method of manufacturing a thin film transistor according to claim 5, wherein an ink jet device is used as a method of forming the droplet by dropping. 5. An image display device using the thin film transistor according to claim 1 as an active element.

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