JPS6231174A - Field effect transistor - Google Patents

Abstract

PURPOSE:To obtain an element with a low cost, a long life and excellent electrical characteristics by employing a pi-conjugated system polymer film which has a composition shown by formula I (wherein R and R' denote radicals such as H or CH3 and R'' denotes a radical such as H or phenyl). CONSTITUTION:A pi-conjugated system polymer film 4, which has a composition shown by formula I (wherein R and R' denote H, CH3, OCH3, C2H5 or OC2H5 and R'' denotes H, CH3, C2H5 or phenyl radical), and which has ohmic contact with both of a source electrode 5 and a drain electrode 6, is formed on an insulation film 3 and the source electrode 5 and the drain electrode 6. As this polymer film 4 is economical as an organic semiconductor and has excellent stability in the air, an FET with excellent electrical characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a field effect transistor (hereinafter abbreviated as FET element), and particularly to an organic semiconductor element that utilizes the electric field effect.

[Conventional technology]

Conventional FET elements generally use an inorganic semiconductor such as 5iSGe or an inorganic compound semiconductor such as GaAs or InP as a main constituent material.

However, since these are expensive, other FET devices have been reported that use cheaper organic semiconductors, that is, organic substances that have semiconductor-like electrical characteristics, specifically polyacetylene. There is.

Figure 3 is Ebisawa et al., Journal of Applied
Physics Volume 54 N116 Page 3255-3
Page 259 (F-Ebisawa et al, Jou
rnal of Applied Physics
VOl, 54 N116 pp 3255-3259)
Conventional FET using polyacetylene shown in the paper of
FIG. 3 is a cross-sectional view showing the structure of the element. In the figure, 1 is a glass substrate, 2 is an aluminum film serving as a gate electrode, 3 is a polysiloxane film serving as an insulating film, 10 is a polyacetylene film, and 5 and 6 are gold films serving as a source electrode and a drain electrode, respectively.

Next, the operation will be explained.

When a voltage is applied between the source electrode 5 and the drain electrode 6, a current flows between the source electrode 5 and the drain electrode 6 through the polyacetylene film 10. At this time, glass substrate 1
A polyacetylene film 10 is formed on the insulating film 3.
When a voltage is applied to the gate electrode 2 separated from the gate electrode 2, the electrical conductivity of the polyacetylene film 10 can be changed by the electric field effect, and therefore the current between the source and drain can be controlled. This is thought to be because the width of the depletion layer in the polyacetylene 111!10 adjacent to the insulating film 3 changes depending on the voltage applied to the gate electrode 2, and the effective hole channel cross-sectional area changes. There is. In this case, the polyacetylene film 10 must have semiconductor-like electrical characteristics, and it must have ohmic contact with the source electrode 5 and drain electrode 6. Furthermore, it is necessary that the polyacetylene film 10 and the gate electrode 2 form an MIS junction with the insulating film 3 sandwiched therebetween.

In the conventional FET device using this polyacetylene, the polyacetylene film 10 is
HIRAKAWA et al, Polymer J
ournalVol, 2 FJa2 pp 231-2
It is formed by the method shown in the paper of 44), that is, the method of polymerizing acetylene gas with a Ziegler-Natsuta catalyst.

[Problem that the invention seeks to solve]

Conventional FET devices using organic semiconductors such as those mentioned above use polyacetylene, so if left in the air, the polyacetylene, which has many unsaturated bonds, is easily attacked by oxygen and water and deteriorates relatively quickly. . Therefore, FET elements using polyacetylene have poor stability,
Moreover, it has the problems of short life and poor electrical characteristics.

In addition, from the viewpoint of the manufacturing method, the method of polymerizing acetylene gas with a Ziegler-Natsuta catalyst to form a polyacetylene film is relatively complicated, and many problems remain to be solved before it can be put into practical use.

The present invention was made to solve the above-mentioned problems, and aims to provide an FET element that uses inexpensive materials, is stable, has a long life, and has excellent electrical characteristics.

[Means for solving problems]

The FET element according to the present invention uses 2H5 or a phenyl group as an organic semiconductor. ) using a π-conjugated polymer having the following structure.

[Effect]

In the present invention, R,R-
is H, CH3, OCH3, C2H5 or OC2H5,
R is H, CH3, C2H5 or phenyl group. )
Since the π-conjugated polymer having the structure is used, it is possible to obtain an FET element that is stable, has a long life, and has excellent electrical characteristics.

〔Example〕

FIG. 1 is a cross-sectional view showing the structure of an FET element according to an embodiment of the present invention. In the figure, 1 is a substrate, and 2 is the substrate 1.
3 is an insulating film provided on the substrate 1 and the gate electrode 2, 5 is a source electrode provided on the insulating film 3, and 6 is the source electrode provided on the insulating film 3. A drain electrode 4 provided separately from the electrode 5 is the insulating film 3. provided on the source electrode 5 and the drain electrode 6;
CH3, OCH3, C2H5 or OC2H5, R is H
, CH3, C2H5 or phenyl group. ) is a π-conjugated polymer film having the following structure.

Here, the following materials are used for the device of this example.

Although glass is generally used as the substrate 1, a polymer film such as a polyester film can also be used.

As the gate electrode 2, metals such as gold, platinum, chromium, palladium, aluminum, and indium, tin oxide, indium oxide, indium-tin oxide (ITO), etc. are generally used. Two or more may be used in combination. Furthermore, p-type silicon, n-type silicon, or organic polymer may be used. When these are used, the substrate 1 can be omitted. As the insulating film 3, silicon oxide (S i 02 ) is generally used, but silicon nitride or aluminum oxide may also be used. Insulating polymers such as polyethylene, polyvinylcarbazole, polyphenylene sulfide, and polyparaxylene may also be used. The source electrode 5 and the drain electrode 6 are made of a metal with a high work function that can make ohmic contact with the π-conjugated polymer film 4, such as gold or platinum.
Chromium, palladium, etc. are used.

The π-conjugated polymer film 4 itself is normally an insulator, but it can be made into a p-type semiconductor by doping with a suitable electron acceptor, such as perchlorate ion, tetrafluoroborate ion, or sulfonate ion. It is possible,
The conductivity can also be controlled over a wide range from an insulator region to a metal region. The device of this example is used by doping a very small amount of π-conjugated polymer film to impart p-type semiconductor properties.

The thin film of the above π-conjugated polymer is used as the gate electrode 2゜insulating film 3
, an electrochemical polymerization method (electrolytic polymerization method) is used as a method for forming the intermediate member constituted by the source electrode 5 and the drain electrode 6.

For example, a monomer corresponding to a π-conjugated polymer and a supporting electrolyte are dissolved in an organic solvent or water and used as a reaction solution, the source electrode 5 and the drain electrode 6 are used as working electrodes, and a current is generated between a countermeasure such as platinum, etc. The desired π-conjugated polymer is deposited on the vicinity of the working electrode by causing a polymerization reaction, and the deposited π-conjugated polymer film is washed and then dried in a nitrogen atmosphere. .

In this case, the deposited π-conjugated polymer film is doped with the anion of the supporting electrolyte during the reaction and becomes a p-type organic semiconductor, and since the distance between the source electrode 5 and the drain electrode 6 is sufficiently short, the distance between the two electrodes is The insulating film is also completely covered with the π-conjugated polymer film, and both electrodes are electrically short-circuited by the p-type organic semiconductor film. Furthermore, this p-type organic semiconductor film can be suitably dedoped after electropolymerization to change the electrical conductivity to pass through an FET element. Here, the organic solvent may be any solvent that can dissolve the supporting electrolyte and the above monomers, such as acetonitrile, nitrobenzene, nitromethane, N,N-dimethylformamide (
Polar solvents such as DMF), dimethyl sulfoxide (DMSO), dichloromethane, tetrahydrofuran, ethyl alcohol, and methyl alcohol may be used alone or as a mixed solvent of two or more. Moreover, a mixed solvent with water can also be used. The supporting electrolyte is a substance that has a high oxidation potential and reduction potential, does not itself undergo oxidation or reduction reactions during electrolytic polymerization, and can impart conductivity to a solution by dissolving it in a solvent. For example, Perchloric acid tetraalkylammonium salts, tetraalkylammonium, tetrafluoroborate salts, tetraalkylammonium, hexafluorophosphate salts, TeI-raalkylammonium, valatoluenesulfonate salts, sodium hydroxide, etc. are used,
Of course, two or more types may be used in combination.

In the FET element configured as described above, the π-conjugated polymer film 4 and the insulation II! π-conjugated polymer II at the interface of J3! The width of the depletion layer formed on the J4 side is controlled by the voltage applied between the gate electrode 2 and the source electrode 5,
It is considered that the current flowing between the source electrode 5 and the drain electrode 6 changes because the effective hole channel cross-sectional area changes. At this time, since the π-conjugated polymer film 4 has only p-type semiconductor properties with low conductivity, the gate electrode 2 may be made of p-type silicon, n-type silicon, or an organic polymer in addition to the metal electrode. It is thought that even if the π-conjugated polymer film 4 is used, a depletion layer with a sufficiently large width is formed in the π-conjugated polymer film 4, and an electric field effect appears.

In FIG. 1, the gate electrode 2 is provided on the substrate 1, but conversely, a π-conjugated polymer film is provided on the substrate, and a source electrode and a drain separated from the source electrode are provided on the substrate. An electrode may be provided, and a gate electrode may be provided with an insulating film interposed between the source electrode and the drain electrode.

Examples of the present invention will be described in more detail below.

Example 1 A 1,000-layer thick chromium film was provided in a ribbon shape near the center of a 3.0c111×3.0cffi glass substrate by vacuum evaporation, and a gold film was further vacuum-deposited on top of this to a 2,000-layer thickness. This was used as a gate electrode (effective gate electrode area: 5n×2 μm). Furthermore, a silicon oxide film was formed on the substrate to a thickness of 3,000 mm using the CVD method, and this was used as an insulating film. Furthermore, a gold film with a thickness of 2000 μm was deposited on it at two locations sandwiching the gate electrode by vacuum evaporation so that the channel length was 2 μm, and these were used as the source and drain electrodes (the effective area of both 5wXIQm).

100n+7! of N-methylpyrrole (0.8 g), tetraethyl perchlorate (
A solution in which 0.7 g) was dissolved was used as a reaction solution. The source and drain electrodes on the glass substrate were used as working electrodes, a platinum (Pt) electrode was used as a counter electrode, and a saturated calomel electrode (SCE) was used as a reference electrode, and they were immersed together in a reaction solution and nitrogen gas was used. A constant current (20 μA-cII+) is passed between the working electrode as the anode and the counter electrode in an atmosphere for 90 minutes to deposit a π-conjugated polymer near the working electrode, that is, near the source electrode and near the drain electrode. so that the insulating film between both electrodes is completely covered with the π-conjugated polymer film, and the source and drain electrodes are
An electrical short circuit is created using a π-conjugated polymer film having type semiconductor properties. Next, the potential of the working electrode is set to 0.0 with respect to SCE using a potentiostat. OV for 180 minutes, and after washing twice with acetonitrile, it was dried in a nitrogen gas atmosphere to obtain an FET sample (1).

Example 2 A silicon oxide film with a thickness of 300 OA was provided on both sides of a 500 μm thick p-type silicon plate (3.0 Clll x 3.0 country) having an electrical conductivity of 10 S/e11 or higher by a thermal acid method. Next, only one side is subjected to plasma etching to expose the silicon surface, and a 2,000-layer gold film is applied here by vacuum evaporation to establish ohmic contact. The p-type silicon substrate itself acts as a gate electrode, and the silicon oxide The film was made to serve as an insulating film. Furthermore, on this silicon oxide film, a chromium film with a thickness of 1,000 μm was provided at two locations using a vacuum evaporation method so that the channel length was 2 μm, and a gold film was further applied on top of the chromium film with a thickness of 2,000 μm using a vacuum evaporation method. The above source electrode, drain electrode, and insulating film between the two electrodes were formed using the electrolytic polymerization method as in Example 1. was coated with a π-conjugated polymer film having p-type semiconductor properties with appropriate conductivity, and this was used as an FET sample (■).

Figure 2 shows the FET sample (II) manufactured according to Example 2.
FIG. 3 is a characteristic diagram showing a change in drain current (ID)-source-drain voltage (V SD ) when the gate voltage (VC) of the semiconductor device is changed. Measurements were performed in vacuum in the dark.

In the figure, the vertical axis represents drain current (ID), and the horizontal axis represents source-drain voltage (V SD). Note that the gate voltage is applied to the source electrode.

According to FIG. 2, in the FET sample (n), ID flows even in the state where VG=OV, but it can be seen that a small change in VG causes a change in ID and a good electric field effect can be obtained. Moreover, it consumes less electricity.

FET sample (1) also showed almost similar characteristics. In addition, in terms of stability, the FET device according to the present invention showed no change in characteristics even after one month or more.

In Example 2, the substrate itself was used as the gate electrode, but it is also possible to operate with the gate electrode provided only between the channels, and the same or better effects as in Example 2 can be obtained.

The device substrate, gate electrode, insulating film, source electrode, drain electrode, lead wires connected to the source electrode, etc. of the FET device according to the present invention can all be made of polymer materials. In this case, the FET element according to the invention has a completely flexible structure. Furthermore, if these polymeric materials are transparent or semitransparent, the π-conjugated polymer film has considerable transparency, so FE is completely transparent or semitransparent.
A T element can be obtained.

By the way, the present invention can also be applied to a large-area substrate having a large number of electrodes. Therefore, the FE according to the present invention
It is possible to use the T-device as a thin film transistor (TPT) that serves as a substrate for a large area liquid crystal display.

〔Effect of the invention〕

As described above, according to the present invention, an organic semiconductor and 3, C2
H5 or phenyl group. ) has the structure π-
Since a conjugated polymer is used, it is possible to obtain an FET element that is inexpensive and has excellent stability, longevity, and electrical characteristics.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an FET element according to an embodiment of the present invention, and FIG. 2 is a diagram showing the drain current-source ratio when the gate voltage of the FET sample (n) manufactured according to embodiment 2 is changed. A characteristic diagram showing the change in the voltage between the drains using the vertical axis as the drain current and the horizontal axis as the source-drain voltage. FIG. 3 is a cross-sectional view showing the structure of a conventional 6FET. In the figure, 2... gate electrode, 3... insulating film, 4
...π-conjugated polymer film, 5...source electrode, ID
...Drain current, VSD...source-drain voltage, VC...gate voltage. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (4)

[Claims] (1) A gate electrode, a source electrode provided opposite to the gate electrode with an insulating film interposed between the gate electrode, and a drain electrode provided separately from the source electrode, and the source electrode and the drain electrode. There are ▲mathematical formulas, chemical formulas, tables, etc. that are placed on the above insulating film in ohmic contact with the
However, R, R' are H, CH_3, OCH_3, C_2H
_5 or OC_2H_5, R is H, CH_3, C_2
H_5 or phenyl group. ) has the structure π
- A field effect transistor characterized by comprising a conjugated polymer film. (2) The field effect transistor according to claim 1, wherein the gate electrode is composed of either p-type silicon or n-type silicon. (3) The field effect transistor according to claim 1, wherein the gate electrode is composed of an organic polymer. (4) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, R,
R' is H, CH_3, OCH_3, C_2H_5, or OC_2H_5; R is H, CH_3, C_2H_5, or a phenyl group. 2. The field-effect transistor according to claim 1, wherein the π-conjugated polymer film having the following structure is obtained by an electrochemical polymerization method (electrolytic polymerization method).