JP2007115944A - Organic thin film transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film transistor which has high mobility of, for example, 0.3 cm<SP>2</SP>/V s or above. <P>SOLUTION: The organic thin film transistor is equipped with an insulating substrate 1, a gate electrode 2 formed in a prescribed region on the surface of the substrate 1, a gate insulating film 3 formed on the surface of the substrate 1 covering the gate electrode 2, a source electrode 7 and a drain electrode 8 which are formed near to the gate electrode 2 on the gate insulating film 3 separating from each other, and an organic semiconductor film 10 which is formed on the gate insulating film 3 making partial contact with the surfaces of the source electrode 7 and the drain electrode 8. At least, the certain surface areas of the source electrode 7 and the drain region 8 have a mean square surface roughness of 0.1 to 2 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic thin film transistor which is one form of a field effect transistor.

Field effect transistors are widely used as switches and amplifying elements along with bipolar transistors.
Field effect transistors are broadly classified into those using inorganic semiconductor materials and those using organic semiconductor materials. In general, a field effect transistor using an organic semiconductor material, that is, an organic thin film transistor, can be formed at a low temperature and have a large area, and can be manufactured at a lower cost than an organic semiconductor material. It is advantageous to make.

Here, for example, a bottom contact type organic thin film transistor as described in Patent Document 1 and a manufacturing method thereof will be described with reference to FIGS. FIG. 13 is a schematic cross-sectional view for explaining a conventional organic thin film transistor.
As shown in FIG. 13, the gate electrode 52 is formed on the surface of the insulating substrate 51, and the gate insulating layer 53 is formed on the surfaces of the insulating substrate 51 and the gate electrode 52. Next, a source electrode 54 and a drain electrode 55 are formed on the surface of the gate insulating layer 53. Further, an organic semiconductor film 56 is formed on the surface of the gate insulating layer 53 in contact with the source electrode 54 and the drain electrode 55, whereby the organic thin film transistor 60 is obtained.
The organic thin film transistor 60 controls the voltage applied to the gate electrode 52, thereby changing the carrier density of the organic semiconductor film 56 in the vicinity of the interface between the organic semiconductor film 56 and the gate insulating layer 53. , 55 is controlled.

In addition, according to the description in Patent Document 1, higher mobility can be obtained by setting the average roughness of the interface between the gate insulating layer 53 and the organic semiconductor film 56 to 50 nm or less.
JP 2004-63975 A

Generally, in order to control a large current for driving an element such as an organic EL with respect to a field effect transistor, an organic semiconductor film having a large mobility is required. For example, when driving a 40-inch XGA display, the on-current is required to be 3 × 10 ⁻⁵ A or more for 500 candela light emission. To control this on-current, the movement of the organic semiconductor film is required. The degree should be 0.3 cm ² / V · s or more.
However, the organic semiconductor film has a lower mobility than the inorganic semiconductor film, and the organic thin film transistor using the organic semiconductor film has a smaller controllable current than that using the inorganic semiconductor film.
Therefore, there is a demand for an organic thin film transistor that has a higher mobility than the above-described conventional organic thin film transistor and can flow a larger current.

Therefore, the problem to be solved by the present invention is to provide an organic thin film transistor capable of obtaining a high mobility, for example, a mobility of 0.3 cm ² / V · s or more.

In order to solve the above problems, each invention of the present application has the following means.
1) an insulating substrate (1), a gate electrode (2) formed in a predetermined range on the surface of the substrate (1), and a surface of the substrate (1) covering the gate electrode (2) A source electrode (7) and a drain electrode (8) formed on the gate insulating film (3) formed on the gate insulating film (3) in the vicinity of the gate electrode (2) and spaced apart from each other. And an organic semiconductor film (10) formed on the gate insulating film (3) in contact with a part of each surface of the source electrode (7) and the drain electrode (8), and the source An organic semiconductor transistor (20) characterized in that a mean square surface roughness of at least a part of each surface of the electrode (7) and the drain electrode (8) is in a range of 0.1 to 2 nm. .
2) An insulating substrate (1), a gate electrode (2) formed on the surface of the substrate (1), and formed on the surface of the substrate (1) so as to cover the gate electrode (2). A source electrode (7) and a drain electrode (8) formed on the gate insulating film (3) in the vicinity of the gate electrode (2) and spaced apart from each other; An organic semiconductor film (10) formed on the gate insulating film (3) in contact with a part of each surface of the source electrode (7) and the drain electrode (8), and at least the organic semiconductor film (10), the source electrode (7), and the drain electrode (8) are in contact with each other, and each of the source electrode (7) and the drain electrode (8) with respect to the surface of the gate insulating film (3) Each end face angle is in the range of 30-80 ° An organic semiconductor transistor (20), characterized in that.

According to the present invention, an insulating substrate 1, a gate electrode 2 formed in a predetermined range on the surface of the substrate 1, and a gate insulation formed on the surface of the substrate 1 so as to cover the gate electrode 2 Gate 3 is in contact with part of each surface of film 3, source electrode 7 and drain electrode 8 formed on gate insulating film 3 in the vicinity of gate electrode 2 and spaced apart from each other. And an organic semiconductor film 10 formed on the insulating film 3, and has a configuration in which a root mean square roughness of a part of each surface of the source electrode 7 and the drain electrode 8 is in a range of 0.1 to 2 nm. Since it did in this way, there exists an effect that a big mobility, for example, the mobility of 0.3 cm < ² > / V * s or more is obtained.

  In addition, according to the present invention, the insulating substrate 1, the gate electrode 2 formed in a predetermined range on the surface of the substrate 1, and the gate electrode 2 covering the gate electrode 2 are formed on the surface of the substrate 1. The gate insulating film 3, the source electrode 7 and the drain electrode 8 formed on the gate insulating film 3 in the vicinity of the gate electrode 2, and a part of each surface of the source electrode 7 and the drain electrode 8 are in contact with each other. The organic semiconductor film 10 formed on the gate insulating film 3, and the source electrode 7 with respect to the surface of the gate insulating film 3 in a range where at least the organic semiconductor film 10 is in contact with the source electrode 7 and the drain electrode 8. In addition, since the angle of each end face of the drain electrode 8 is in the range of 30 to 80 °, the organic semiconductor film can be formed without being divided.

The preferred embodiments of the present invention will be described with reference to FIGS.
Hereinafter, the first embodiment and the second embodiment will be described in order.
In order to distinguish each process of each example in an easy-to-understand manner, each process name is given A in the first example and B in the second example.
FIG. 1 is a diagram showing the relationship between the surface roughness of the source and drain electrodes and the mobility of the organic semiconductor film formed on the surfaces of the source and drain electrodes.
FIGS. 2-7 is typical sectional drawing for demonstrating each of A1 process-A6 process in 1st Example of the organic-semiconductor transistor of this invention.
FIGS. 8-11 is typical sectional drawing for demonstrating the B1 process-B4 process in 2nd Example of the organic-semiconductor transistor of this invention, respectively.

The inventor first paid attention to the surface roughness of the surfaces of the source electrode and the drain electrode and the surface of the gate insulating layer, which are surfaces in contact with the organic semiconductor film.
Accordingly, an organic thin film transistor as shown in FIG. 13 was prepared, and the surface roughness of the surface of the source electrode and the drain electrode and the surface of the gate insulating layer were measured. The root mean square roughness was about 5 nm, and the surface roughness (RMS) of the gate insulating layer was about 0.4 nm. That is, it was confirmed that the surface of the source electrode and the drain electrode had a larger surface roughness than the surface of the gate insulating layer.

  Therefore, the inventor examined the relationship between the surface roughness of the source electrode and the drain electrode and the mobility of the organic semiconductor film formed on the surface of the source electrode and the drain electrode. The result is shown in FIG. FIG. 1 is a diagram showing the relationship between the surface roughness of each surface of the source electrode and the drain electrode and the mobility of the organic semiconductor film formed on the surface of the source electrode and the drain electrode.

From FIG. 1, it was confirmed that each surface roughness (RMS) of the source electrode and the drain electrode should be 2 nm or less in order to make the mobility of the organic semiconductor film 0.3 cm ² / V · s or more. .
In addition, it is difficult for the surface roughness (RMS) of the source electrode and the drain electrode to be 0.1 nm or less because of performance of the film forming apparatus and production management.
For the above reasons, in order to set the mobility of the organic semiconductor film to 0.3 cm ² / V · s or more, each surface roughness (RMS) of the source electrode and the drain electrode is set in the range of 0.1 to 2 nm. It is necessary to.

Here, the reason why the mobility of the organic semiconductor film formed on the source electrode and the drain electrode is reduced as the surface roughness of the source electrode and the drain electrode is increased will be described.
Generally, a film to be formed is affected by a base film. That is, if the surface roughness of the underlying film is large, the arrangement of organic semiconductor molecules on the surface is disturbed, and the contact resistance between the source and drain electrodes and the organic semiconductor film increases. Is considered to be the cause.

Next, a method for forming source and drain electrodes having different surface roughness will be described.
As a result of inventor's diligent experiments, it has been found that when the source electrode and the drain electrode are formed, a dense film having a smaller surface roughness can be obtained as the heating temperature of the substrate is lower or the deposition pressure is lower. It was.
Accordingly, in the experiment shown in FIG. 1, the source electrode and the drain electrode were formed by changing the deposition pressure while keeping the substrate temperature constant at room temperature. That is, the surface roughness of each of the formed source and drain electrodes can be reduced as the film forming pressure is lowered, and the surface roughness can be increased as the film forming pressure is increased.

Based on the above-described results, organic thin film transistors are fabricated as the first and second embodiments.
Hereinafter, the first embodiment and the second embodiment will be described in order.

<First embodiment>
(Step A1) [Refer to FIG. 2]
First, tantalum (Ta) is formed on the surface of the glass substrate 1 that is an insulating substrate so as to have a thickness of about 200 nm by sputtering.
Next, the deposited tantalum is selectively etched using a photolithographic method to obtain the gate electrode 2 made of tantalum.

(Step A2) [Refer to FIG. 3]
A gate insulating film 3 made of silicon oxide (SiO ₂ ) is formed on the surfaces of the glass substrate 1 and the gate electrode 2 by sputtering so as to have a thickness of about 200 nm. The surface roughness (RMS) of the gate insulating film 3 is about 0.4 nm.

(Step A3) [Refer to FIG. 4]
A resist mask 5 having an opening 4 with a predetermined pattern and a thickness of about 300 nm is formed on the gate insulating film 3 by photolithography.

(Step A4) [Refer to FIG. 5]
A metal film 6 made of, for example, gold (Au) is formed on the gate insulating film 3 and the resist mask 5 using a sputtering method so as to have a thickness of about 100 nm. This metal film 6 becomes a source electrode 7 and a drain electrode 8 described later.
As sputtering conditions, a DC magnetron sputtering apparatus was used, and argon (Ar) gas was introduced, the film formation pressure was about 1 Pa, the applied power was about 100 W, and the film formation time was about 2 minutes.

(Step A5) [Refer to FIG. 6]
The resist mask 5 is removed. At this time, the metal film 6 part on the resist mask 5 is also removed together with the resist mask 5, and only the metal film 6 part formed in the opening 4 of the resist mask 5 remains. The metal film 6 formed in the opening 4 becomes the source electrode 7 and the drain electrode 8.
The surface roughness (RMS) of the source electrode 7 and the drain electrode 8 is about 0.5 nm.
Further, after forming a resist mask having a predetermined pattern in advance as in steps A3 to A5, for example, a film such as an organic semiconductor film is formed, and the resist mask and the film formed on the resist mask are removed. This method is called lift-off method.

(Step A6) [Refer to FIG. 7]
An organic semiconductor film 10 made of, for example, pentacene is formed on the gate insulating film 3 in contact with a part of each surface of the source electrode 7 and the drain electrode 8 by vapor deposition. The organic semiconductor film 10 is selectively formed in a range corresponding to the predetermined opening by using a vapor deposition mask (not shown) having a predetermined opening during vapor deposition.

The organic thin film transistor 20 is obtained by the above-described steps A1 to A6.
When the mobility of the organic semiconductor film 10 of the organic thin film transistor 20 was measured, a favorable result of about 0.55 cm ² / V · s was obtained.

<Second embodiment>
(Step B1) [Refer to FIG. 8]
First, a liquid conductive polymer material 22 is applied to a predetermined position of a glass substrate 21 that is an insulating substrate using an ink jet apparatus or a precision dispenser. Then, the conductive polymer material 22 is cured and solidified to form the gate electrode 23. The surface roughness (RMS) of the gate electrode 23 is about 0.5 nm.
The curing conditions for the conductive polymer material 22 were a curing temperature of 120 ° C. and a curing time of 30 minutes, and the curing was performed in a nitrogen atmosphere.

(Step B2) [Refer to FIG. 9]
A gate insulating film 24 made of tantalum pentoxide (Ta ₂ O ₅ ) is formed on the glass substrate 21 and the gate electrode 23 by a sputtering method so as to have a thickness of about 200 nm. The surface roughness (RMS) of the gate insulating film 24 is about 0.8 nm.

(Step B3) [Refer to FIG. 10]
The liquid conductive polymer material 22 is applied to two predetermined locations on the gate insulating film 24 in the vicinity of the gate electrode 23 using an inkjet device or a precision dispenser. Then, the conductive polymer material 22 is cured and solidified to form a source electrode 25 and a drain electrode 26, respectively. The surface roughness (RMS) of the source electrode 25 and the drain electrode 26 is about 0.5 nm.
The conductive polymer material used in step B3 is the same as the conductive polymer material used in step B1.
The curing conditions for the conductive polymer material 22 were a curing temperature of 120 ° C. and a curing time of 30 minutes, and the curing was performed in a nitrogen atmosphere.

(Step B4) [Refer to FIG. 11]
An organic semiconductor film 30 made of, for example, pentacene is formed on the gate insulating film 24 in contact with a part of each surface of the source electrode 25 and the drain electrode 26 by vapor deposition. The organic semiconductor film 30 is selectively formed in a range corresponding to the predetermined opening by using a vapor deposition mask (not shown) having a predetermined opening during vapor deposition.

The organic thin film transistor 40 is obtained by the above-described steps B1 to B4.
When the mobility of the organic semiconductor film 30 of the organic thin film transistor 40 was measured, a favorable result of about 0.50 cm ² / V · s was obtained.

  Here, the angle of each end face of the source electrode and the drain electrode with respect to the surface of the gate insulating film in the organic thin film transistors 20 and 40 of the first and second embodiments will be described with reference to FIG. FIG. 12 is a schematic cross-sectional view for explaining the angles of the end faces of the source electrode and the drain electrode with respect to the surface of the gate insulating film.

As shown in FIG. 12A, when the organic semiconductor film 41 is formed on the gate insulating film 42 in contact with the source electrode 43 and the drain electrode 44, the source electrode 43 and the drain electrode 44 with respect to the surface of the gate insulating film 42 are formed. When the angle θ of each end face is 90 °, depending on the thickness ratio between the organic semiconductor film 41 and the source electrode 43 and the drain electrode 44 and the distance between the source electrode 43 and the drain electrode 44, There is a possibility that the gate insulating film 42, the source electrode 43, and the drain electrode 44 are respectively divided and formed.
An organic thin film transistor in which the organic semiconductor film is divided cannot provide sufficient mobility.

Therefore, as a result of intensive experiments by the inventors, the organic semiconductor film 41 is formed without being divided by setting the angle θ of each end face of the source electrode 43 and the drain electrode 44 to 80 ° or less with respect to the surface of the gate insulating film 42. I knew it was possible.
Further, when the angle θ is less than 30 °, the thickness of the source electrode 43 and the drain electrode 44 in contact with the gate insulating film 42 is reduced and the resistance value in this portion is increased, so that a sufficient current flows. Becomes difficult.

  For the above reasons, it is desirable that the angle θ of each end face of the source electrode and the drain electrode with respect to the surface of the gate insulating film be in the range of 30 to 80 °.

A method for setting the angle θ of each end face of the source electrode and the drain electrode with respect to the surface of the gate insulating film in the range of 30 to 80 ° will be described with reference to FIG.
For example, when the lift-off method is used as in the first embodiment, a metal film 46 to be the source electrode 43 and the drain electrode 44 is formed on the gate insulating film 42 and the resist mask 45 as shown in FIG. When the film is formed, the resist mask 45 is formed in an inverted trapezoidal shape (also referred to as an inversely tapered shape) whose bottom surface is smaller than the upper surface, whereby the angle θ of each end surface of the source electrode 43 and the drain electrode 44 with respect to the surface of the gate insulating film 42. Can be in the range of 30-80 °.

  Further, when the conductive polymer material is used as in the second embodiment, the formed source electrode 25 and drain electrode 26 are substantially hemispherical, so that the source electrode 25 and drain electrode 26 with respect to the surface of the gate insulating film 24 are formed. The angle θ of each end face can be in the range of 30 to 80 °.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

  For example, in the first embodiment, gold (Au) is used as the material of the metal film 6, but the material is not limited to this. As other materials, nickel (Ni), chromium (Cr) or the like having substantially the same work function as gold can be used.

  The gate insulating film in the first and second embodiments can also be formed by oxidizing the vicinity of the surface of the gate electrode using an anodic oxidation method.

It is a figure which shows the relationship between the surface roughness of the surface of a source electrode and a drain electrode, and the mobility of the organic-semiconductor film formed in the surface of this source electrode and drain electrode. It is typical sectional drawing for demonstrating each A1 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each A2 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each A3 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each A4 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each A5 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each A6 process in 1st Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each B1 process in 2nd Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each B2 process in 2nd Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each B3 process in 2nd Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating each B4 process in 2nd Example of the organic-semiconductor transistor of this invention. It is typical sectional drawing for demonstrating the angle of each end surface of the source electrode and drain electrode with respect to the surface of a gate insulating film. It is typical sectional drawing for demonstrating the organic thin-film transistor of a prior art example.

Explanation of symbols

1,21 glass substrate, 2,23 gate electrode, 3,24,42 gate insulating film, 4 opening, 5,45 resist mask, 6,46 metal film, 7,25,43 source electrode, 8,26,44 Drain electrode, 10, 30, 41 Organic semiconductor film, 20, 40 Organic thin film transistor, 22 Conductive polymer material, θ angle

Claims (2)

An insulating substrate;
A gate electrode formed in a predetermined range on the surface of the substrate;
A gate insulating film formed on the surface of the substrate to cover the gate electrode;
A source electrode and a drain electrode formed on the gate insulating film in the vicinity of the gate electrode and spaced apart from each other;
An organic semiconductor film formed on the gate insulating film in contact with a part of each surface of the source electrode and the drain electrode;
Have
An organic semiconductor transistor having a root mean square roughness of at least a part of each surface of the source electrode and the drain electrode in a range of 0.1 to 2 nm. An insulating substrate;
A gate electrode formed in a predetermined range on the surface of the substrate;
A gate insulating film formed on the surface of the substrate to cover the gate electrode;
A source electrode and a drain electrode formed on the gate insulating film in the vicinity of the gate electrode and spaced apart from each other;
An organic semiconductor film formed on the gate insulating film in contact with a part of each surface of the source electrode and the drain electrode;
Have
At least a range where the organic semiconductor film is in contact with the source electrode and the drain electrode, and an angle of each end face of the source electrode and the drain electrode with respect to a surface of the gate insulating film is within a range of 30 to 80 ° An organic semiconductor transistor.

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