JP2006261498A - Organic thin film transistor, image display comprising it, and process for fabricating organic thin film transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film transistor having such a structure as alignment of a shadow mask for electrode is facilitated. <P>SOLUTION: The organic thin film transistor 10 comprises a substrate 1, a gate electrode 2, a gate insulation film 3, an organic semiconductor film 4, a source electrode 5, and a drain electrode 6. The substrate 1 is provided with protrusions and recesses on the surface and has planes 1A and 1B. The planes 1A and 1B are arranged at positions different from each other in the direction normal to the substrate 1. The gate electrode 2 is formed on the rear surface of the substrate 1. The gate insulation film 3 is formed on the planes 1A and 1B of the substrate 1. The source electrode 5 is formed on the plane 1A of the substrate 1 through the gate insulation film 3. The drain electrode 6 is formed on the plane 1B of the substrate 1 through the gate insulation film 3. The source electrode 5 and the drain electrode 6 are composed of materials different from each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic thin film transistor, a display device including the organic thin film transistor, and a method for manufacturing the organic thin film transistor.

  Organic semiconductors are attracting attention as low-cost materials for transistors because they are easier to form at low temperature and have a larger area than inorganic semiconductors. A CMOS (Cpplementary MOS) transistor using an ambipolar organic semiconductor as an active layer is known (Patent Document 1).

  When an ambipolar organic semiconductor is used for a CMOS transistor, it has the following advantages. In general, a CMOS circuit includes both P-type and N-type channels, and when a short-polar material is used, each needs to be patterned separately.

However, when an ambipolar organic semiconductor is used, the CMOS circuit can be operated with one kind of material. Thereby, a manufacturing process is simplified and cost can be reduced significantly.
JP 2001-177109 A

  However, in a conventional CMOS transistor using an ambipolar organic semiconductor, since the source electrode and the drain electrode are formed on the same plane, when the source electrode and the drain electrode are formed of different materials, integration is not possible. There is a problem that it is difficult.

  Accordingly, the present invention has been made to solve such a problem, and an object thereof is to provide an organic thin film transistor having a structure in which alignment of a shadow mask for an electrode is easy.

  Another object of the present invention is to provide a display device including an organic thin film transistor having a structure in which alignment of a shadow mask for electrodes is easy.

  Furthermore, another object of the present invention is to provide a method of manufacturing an organic thin film transistor having a structure in which alignment of a shadow mask for an electrode is easy.

  According to this invention, the organic thin film transistor includes an organic semiconductor film, first to third electrodes, and an insulating film. The organic semiconductor film is formed on the substrate. The first and second electrodes are electrodes for flowing current through the organic semiconductor film. The insulating film is formed in contact with the organic semiconductor film. The third electrode is an electrode for applying a voltage for generating an electric field in the film thickness direction of the organic semiconductor film through the insulating film. The first and second electrodes are arranged on different planes and are made of different materials.

  Preferably, one of the first and second electrodes is made of a first electrode material that is easy to inject electrons, and the other of the first and second electrodes is a second electrode that is easy to inject holes. Made of material.

  Preferably, the first electrode material is selected from a material group having a work function of 4.0 eV or less, and the second electrode material is selected from a material group having a work function of 4.5 eV or more.

  Moreover, according to this invention, a display apparatus is provided with the organic thin-film transistor of any one of Claims 1-3.

  Furthermore, according to this invention, the organic thin film transistor manufacturing method includes a first step of making the surface of the substrate uneven, a second step of forming the gate electrode and the gate insulating film on the uneven substrate, A third step of forming a source electrode in the recess of the substrate; a fourth step of forming an organic semiconductor film on the source electrode and the substrate after the third step; and a drain electrode on the organic semiconductor film And a fifth step of manufacturing the organic thin film transistor.

  In the organic thin film transistor according to the present invention, the first electrode is made of a material different from that of the second electrode and is arranged on a different plane.

  Therefore, according to the present invention, alignment of the shadow masks for the first and second electrodes can be easily performed.

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

  FIG. 1 is a cross-sectional structure diagram of an organic thin film transistor according to an embodiment of the present invention. Referring to FIG. 1, an organic thin film transistor 10 according to an embodiment of the present invention includes a substrate 1, a gate electrode 2, a gate insulating film 3, an organic semiconductor film 4, a source electrode 5, and a drain electrode 6. Prepare.

  The substrate 1 has an uneven surface and has planes 1A and 1B. The planes 1A and 1B are arranged at different positions in the normal direction of the substrate 1. The gate electrode 2 is formed on the back surface of the substrate 1. The gate electrode 2 is an electrode for applying a voltage for generating an electric field in the film thickness direction of the organic semiconductor film 4 through the gate insulating film 3. The gate insulating film 3 is formed on the planes 1A and 1B of the substrate 1.

  The source electrode 5 is formed on the plane 1A of the substrate 1 with the gate insulating film 3 interposed therebetween. The drain electrode 6 is formed on the plane 1B of the substrate 1 with the gate insulating film 3 interposed therebetween.

The substrate 1 is made of single crystal silicon. The gate electrode 2 is made of aluminum (Al) and is formed by vacuum deposition. The gate insulating film 3 is made of a thermal oxide film (SiO ₂ ), a polyparaxylylene derivative, a polymer material, and the like. More specifically, the gate insulating film 3 is made of an acrylic resin such as polymethyl methacrylate, a polymer such as polystyrene, polyvinylphenol, polyimide, polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, epoxy resin, or phenol resin. And a combination of these.

  These materials are formed by spin coating, dip coating, ink jet printing, or the like.

  The organic semiconductor film 4 is made of an ambipolar organic semiconductor. More specifically, the organic semiconductor film 4 is made of a known ambipolar organic semiconductor material. And in this invention, the organic-semiconductor film 4 may consist of a laminated structure of the organic-semiconductor layer which shows P-type conduction, and the organic-semiconductor layer which shows N-type conduction. Examples of organic semiconductors suitable for this stacked structure include pentacene and fluorinated pentacene, which are formed by vacuum deposition.

  In addition, the organic semiconductor film 4 includes a laminated structure of polymer materials of each polarity, a single layer structure in which other polar polymer materials are mixed, and a low molecule exhibiting N-type conduction mixed with a P-type conductive polymer material. It may be made of any of the organic semiconductor materials.

  One of the source electrode 5 and the drain electrode 6 is made of a metal that is easy to inject electrons, and the other of the source electrode 5 and the drain electrode 6 is made of a metal that is easy to inject holes.

  Metals that are easy to inject electrons are simple metals such as barium, calcium, lithium, and rubidium, magnesium alloys such as MgAg, MgIn, MgCu, and MgAu, and lithium alloys. These metals have a work function of 4.0 eV or less. Therefore, one of the source electrode 5 and the drain electrode 6 is made of a material selected from a material group having a work function of 4.0 eV or less.

Further, metals that are easy to inject holes include metals such as platinum, gold, chromium, nickel, and copper, indium oxide (InO ₂ ), tin oxide (SnO ₂ ), and indium tin oxide (ITO: Indium, Tin Oxide). It consists of any one of conductive oxides, polyaniline doped with camphorsulfonic acid, and conductive polymers such as polyethylenedioxythiophene doped with paratoluenesulfonic acid. These materials have a work function of 4.5 eV or more. Therefore, one of the source electrode 5 and the drain electrode 6 is made of a material selected from a material group having a work function of 4.5 eV or more.

  Each of the above-described metal that is easy to inject electrons and metal that is easy to inject holes is formed by any method such as a vacuum deposition method, a sputtering method, a coating method, or a sol-gel method. A patterning method for metal or the like formed by these methods includes a photolithography method combining photoresist patterning and an etching solution or plasma etching, ink jet printing, and the like. Further, metal or the like may be patterned by irradiating energy beams such as a laser and an electron beam.

  As described above, in the organic thin film transistor 10, the source electrode 5 and the drain electrode 6 are formed on the different planes 1 </ b> A and 1 </ b> B existing at different positions from the substrate 1 through the gate insulating film 3 in the normal direction of the substrate 1. Therefore, the shadow masks for the source electrode 5 and the drain electrode 6 can be easily aligned.

A method for manufacturing the organic thin film transistor 10 will be described. A silicon (Si) wafer having a low resistance (100) surface is thermally oxidized to form an oxide film (SiO ₂ ) on both surfaces. Thereafter, a photoresist is coated on a portion other than the portion to be etched by photolithography, and the thermal oxide film is etched with buffered hydrofluoric acid.

  Using a heated aqueous solution of tetramethylammonium aqueous solution, the silicon wafer is etched using the thermal oxide film as a mask to form a 20 μm trench. Thereby, the surface of the silicon wafer is roughened.

  After removing the thermal oxide film used for the Si trenching process with buffered hydrofluoric acid and removing organic substances and heavy metals with various solutions containing hydrogen peroxide, a 200 nm thermal oxide film is formed by a muffle furnace. Thereby, the gate insulating film 3 is formed.

  Aluminum is deposited on the back surface of the silicon wafer to form the gate electrode 2. Then, MgAu for the source electrode 5 is formed on the gate insulating film 3 by vacuum deposition, and a photoresist is spin-coated to perform exposure and development. In this case, since the photoresist arranged in the moat is deposited thicker than the outermost surface portion, in a normal exposure process, the photoresist existing in the upper portion of the moat is underexposed. By developing this, the photoresist remains only at the bottom of the trench, and processing is possible without using a photomask.

  Thereafter, the MgAu film is etched with a mixed solution of iodine and ammonium iodide solution to form the source electrode 5.

Then, a triarylamine and a phenylene vinylene copolymer are mixed with a perylene derivative (N, N′-dihexyl-3,4,9,10-perylenetetracarboxylic acid diimide: C ₆ -PTC) in a weight ratio of 6: 4. A 1 wt% dispersion solution is prepared, formed into a film by spin coating, and dried at 150 ° C. Thereby, the organic semiconductor film 4 is formed.

  Thereafter, silver (Ag) nanometal ink was printed only on the outermost surface with a reverse coater, and a drying treatment was performed at 150 ° C. for 30 minutes to form the drain electrode 6.

  In the organic thin film transistor manufactured by the above-described method, there is no conduction between the source electrode 5 and the drain electrode 6, and the organic thin film transistor exhibits transistor characteristics.

  The organic thin film transistor 10 is used as a drive device for a display device.

  Next, an embodiment in which the organic thin film transistor 10 according to the present invention is used as an active matrix element of an image display device will be described. FIG. 2 is a plan view showing an example in which the organic thin film transistor according to the present invention is used for an active matrix substrate of an image display device, and FIG. 3 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, and organic EL.

  As shown in FIG. 2, 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 epoxy resin having a thickness of 200 nm is formed as an insulating film to be an interlayer insulating film between the gate insulating film 3 and the scanning line 20 and the signal wiring.

  Then, an organic semiconductor film represented by the above general formula (I) is used as a semiconductor material on this epoxy resin, and is formed by spin coating to provide an organic semiconductor layer 4 having a thickness of 30 nm.

  Subsequently, an Au film having a thickness of 50 nm is formed in a predetermined region on the organic semiconductor layer 4 by a vacuum deposition method using a shadow mask, and the source electrode 5 and the drain electrode 6, the signal wiring 21 and the drain electrode 6, A continuous pixel wiring 22 is formed.

  Subsequently, a divided patterned film (not shown) is formed. Note that a protective film made of a polymonochloroparaxylylene film may be formed before the divided patterned film is formed so as not to damage the organic semiconductor layer 4.

  Then, by using the divided patterned layer as a mask, the organic semiconductor layer 4 and the gate insulating film 3 located under the dividing line are removed by dry etching with oxygen gas, and the TFT elements are separated. In this embodiment, an active matrix substrate 31 is formed by further providing a passivation film 23 made of a polymonochloroparaxylylene film on these elements.

  As shown in FIG. 3, the image display device 30 includes a display element provided between the above-described active matrix substrate 31 and the transparent conductive film 32 and the second substrate 33, and is on the drain 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, 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.

  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 is applied to an organic thin film transistor having a structure that facilitates alignment of a shadow mask for an electrode. In addition, the present invention is applied to a display device including an organic thin film transistor having a structure that facilitates alignment of a shadow mask for an electrode. Furthermore, the present invention is applied to a method for manufacturing an organic thin film transistor having a structure in which alignment of a shadow mask for an electrode is easy.

1 is a cross-sectional structure diagram of an organic thin film transistor according to an embodiment of the present invention. It is a top view which shows the example which used the organic thin-film transistor by 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

  1, 33 substrate, 1A plane, 2 gate electrode, 3 gate insulating film, 4 organic semiconductor film, 5 source electrode, 6 drain electrode, 10 organic thin film transistor, 21 signal wiring, 22 pixel electrode, 23 passivation film, 30 image display device 31 Active matrix substrate, 32 Transparent conductive film.

Claims (5)

An organic semiconductor film formed on the substrate;
First and second electrodes for passing current through the organic semiconductor film;
An insulating film formed in contact with the organic semiconductor film;
A third electrode for applying a voltage for generating an electric field in the film thickness direction of the organic semiconductor film through the insulating film;
The first and second electrodes are organic thin film transistors which are arranged on different planes and are made of different materials. Either one of the first and second electrodes is made of a first electrode material that is easy to inject electrons,
2. The organic thin film transistor according to claim 1, wherein either one of the first electrode and the second electrode is made of a second electrode material that facilitates hole injection. The first electrode material is selected from a material group having a work function of 4.0 eV or less,
The organic thin film transistor according to claim 2, wherein the second electrode material is selected from a material group having a work function of 4.5 eV or more.   A display apparatus provided with the organic thin-film transistor of any one of Claims 1-3. A first step of roughening the surface of the substrate;
A second step of forming a gate electrode and a gate insulating film on the uneven substrate;
A third step of forming a source electrode in the recess of the substrate;
After the third step, a fourth step of forming an organic semiconductor film on the source electrode and the substrate;
And a fifth step of forming a drain electrode on the organic semiconductor film.

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