JP2005259852A - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor that does not have such a limitation that a semiconductor layer has to be comprised of a π conjugated polymer having a substituent that has large dipole moment and moves freely around main chain structure in accordance with an external electric field. <P>SOLUTION: The field effect transistor is provided with a gate electrode, a gate insulating film, a channel formation area formed of an organic semiconductor thin film made of a π conjugated polymer, and a source/drain electrode. Electrons in the π conjugated polymer are moved to the gate insulating film because of an electric field formed by applying a voltage to the gate electrode. When the application of the voltage to the gate electrode is stopped, the electrons in the gate insulating film return to the π conjugated polymer. Thus, the electric conductivity of the channel formation area formed of the organic semiconductor thin film can be controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a field effect transistor, and more particularly to a so-called organic field effect transistor in which a channel formation region is formed of an organic semiconductor thin film.

  The principle of operation of a conventional field effect transistor (hereinafter sometimes abbreviated as a silicon-based FET) using a silicon layer as a channel formation region is that a semiconductor layer constituting the channel formation region is applied by applying a voltage to the gate electrode. In this mechanism, the electric conductivity is controlled by bending the energy band and controlling the carrier concentration. In this case, even if no conduction channel is formed, current flows through a small number of carriers existing in the semiconductor layer, which hinders the improvement of the on / off ratio of the silicon-based FET.

  An organic semiconductor thin film composed of conjugated molecules is formed between the source / drain electrodes, and a voltage is applied to the gate electrode to apply an electric field in a direction perpendicular to the main chain skeleton of the molecules constituting the organic semiconductor thin film. A method for controlling the drain current is proposed, for example, in JH Schon et al, SCIENCE 294, 2138. This method is a system in which the electronic state of a certain molecular structure is changed based on an electric field generated by applying a voltage to the gate electrode, and the source-drain current is modulated by the resonant tunneling effect. Such a phenomenon is observed at an extremely low temperature of about several degrees K. At room temperature, the carrier responsible for intramolecular conduction always scatters greatly due to molecular vibrations of the molecules constituting the organic semiconductor thin film. receive. Therefore, an FET having such a structure that operates at room temperature has not been realized yet.

A field effect transistor in which a semiconductor layer constituting a channel formation region includes a π-conjugated polymer containing a substituent of any one of —CHO, —COCH ₃ , —NO ₂ , and —CN as a main component is disclosed in It is disclosed in Japanese Patent Application Publication No. 7-249775. Here, as the π-conjugated polymer, a hetero five-membered ring, more specifically, polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, polythienylene vinylene, polyparaphenylene vinylene, polypyridazine, polynaphthylene, polyazulene, Polyisothianaphthene is mentioned.

  In the field effect transistor disclosed in Japanese Patent Application Laid-Open No. 7-249775, when no voltage is applied to the gate electrode, a lateral electric field (generated by source / drain voltage) is applied by π electron conjugation of the polymer chain. On the other hand, when a voltage is applied to the gate electrode, an electric field is generated in a direction perpendicular to the gate electrode surface, and a force is applied to a substituent having a dipole moment. The formation is changed, the π-electron conjugation is lost, and the electrical conductivity of the polymer is remarkably lowered, so that no current flows between the source / drain electrodes.

JP-A-7-249775 J. H. Schon et al, SCIENCE 294, 2138

  By the way, in the field effect transistor disclosed in Japanese Patent Application Laid-Open No. 7-249775, a π-conjugated polymer having a specific substituent having a large dipole moment is used as a semiconductor layer. By applying an electric field to the moment from the outside, the conformation of the polymer is changed to change the conductivity. However, there is a problem that it is difficult to select a substituent having a large dipole moment that causes such a conformational change, and such a substituent is π-conjugated system depending on an external electric field. In order to move freely around the main chain skeleton of the polymer, a free space is required in the vicinity of the polymer, and there is a problem that it is expected to be difficult to manufacture a field effect transistor.

  Accordingly, an object of the present invention is to form a semiconductor layer from a π-conjugated polymer having a large dipole moment and having a substituent that freely moves around the main chain skeleton in response to an external electric field. An object of the present invention is to provide a field-effect transistor that does not have such a restriction.

In order to achieve the above object, the field effect transistor of the present invention provides:
(A) a gate electrode,
(B) a gate insulating film,
(C) a channel forming region composed of an organic semiconductor thin film composed of a π-conjugated polymer, and
(D) source / drain electrodes,
A field effect transistor comprising:
Due to the electric field formed based on the voltage application to the gate electrode, the electrons in the π-conjugated polymer are moved to the gate insulating film, and when the voltage application to the gate electrode is stopped, the electrons are transferred to the gate insulating film. The transferred electrons are returned to the π-conjugated polymer, whereby the electrical conductivity of the channel formation region formed of the organic semiconductor thin film is controlled.

In the field effect transistor of the present invention,
As a result of the electrons in the π-conjugated polymer being transferred to the gate insulating film due to the electric field formed by applying a voltage to the gate electrode, the π-conjugated polymer is changed from an aromatic structure to a quinoid structure. Change,
By stopping the application of voltage to the gate electrode, the electrons transferred to the gate insulating film are returned to the π-conjugated polymer, so that the π-conjugated polymer returns from the quinoid structure to the aromatic structure. It is preferable.

  More specifically, a π-conjugated polymer having an aromatic structure means that a bond between monomers constituting the π-conjugated polymer is a single bond, and a π-conjugated system. More specifically, the polymer having a quinoid structure means that a bond between monomers constituting the π-conjugated polymer is a double bond.

  In the field effect transistor of the present invention, electrons in the π-conjugated polymer are easily transferred to the gate insulating film due to the electric field formed based on the gate voltage applied to the gate electrode. Therefore, the level of the lowest unoccupied molecular orbital (LUMO) of the material constituting the gate insulating film is preferably higher than the level of the highest occupied molecular orbital (HOMO) of the π-conjugated polymer.

In the field effect transistor of the present invention, the π-conjugated polymer is preferably a complex five-membered ring. Specifically, the combination of (π conjugated polymer) / (material constituting the gate insulating film) is (π conjugated polymer consisting of a complex five-membered ring) / (material consisting of acceptor molecules). More specifically, the combination of (π-conjugated polymer) / (material constituting the gate insulating film) is (polythiophene) / (tetracyanoquinodimethane [TCNQ]), (polythiophene) / dithiolene. Mention may be made of metal complexes. Here, the dithiolene metal complex can be represented by M (dmit) ₂ , and examples of “M” include Ni, Pd, and Pt.

  The following four types of structures can be illustrated as specific structures of the field effect transistor of the present invention.

That is, the field effect transistor having the first structure is a so-called bottom gate type and a bottom contact type.
(A) a gate electrode formed on the substrate;
(B) a gate insulating film formed on the gate electrode;
(C) source / drain electrodes formed on the gate insulating film, and
(D) a channel forming region comprising an organic semiconductor thin film formed between the source / drain electrodes and on the gate insulating film;
It has.

The field effect transistor having the second structure is a so-called bottom gate type and a top contact type.
(A) a gate electrode formed on the substrate;
(B) a gate insulating film formed on the gate electrode;
(C) a channel formation region made of an organic semiconductor thin film formed on the gate insulating film, and
(D) source / drain electrodes formed on the organic semiconductor thin film;
It has.

Further, the field effect transistor having the third structure is a so-called top gate type and a top contact type.
(A) a channel forming region comprising an organic semiconductor thin film formed on a substrate;
(B) source / drain electrodes formed on the organic semiconductor thin film;
(C) a gate insulating film formed on the source / drain electrodes and the organic semiconductor thin film, and
(D) a gate electrode formed on the gate insulating film,
It has.

The field effect transistor having the fourth structure is a so-called top gate type and a bottom contact type.
(A) source / drain electrodes formed on the substrate;
(B) a channel forming region comprising a source / drain electrode and an organic semiconductor thin film formed on the substrate;
(C) a gate insulating film formed on the organic semiconductor thin film, and
(D) a gate electrode formed on the gate insulating film,
It has.

  As materials constituting the gate electrode, source / drain electrode, and various wirings in the field effect transistor of the present invention, platinum (Pt), gold (Au), palladium (Pd), chromium (Cr), nickel (Ni), Aluminum (Al), Silver (Ag), Tantalum (Ta), Tungsten (W), Copper (Cu), Titanium (Ti), Indium (In), Tin (Sn), Iron (Fe), Zinc (Zn), Metals such as magnesium (Mg), conductive metal oxides such as indium tin oxide (ITO), alloys containing these metal elements, conductive particles made of these metals, alloys containing these metals Examples thereof include conductive particles, and a stacked structure of layers containing these elements can also be used. Alternatively, an inorganic material whose conductivity is improved by doping or the like, for example, silicon single crystal, polysilicon, amorphous silicon, germanium, graphite, or the like can be used. Furthermore, an organic material such as poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid [PEDOT / PSS] can also be used as a material constituting the gate electrode and the source / drain electrode.

  Depending on the material constituting the gate electrode, source / drain electrode, and wiring, the physical vapor deposition method (PVD method) exemplified by vacuum deposition method and sputtering method; various types including MOCVD method Chemical vapor deposition method (CVD method); Spin coating method; Printing method such as screen printing method and inkjet printing method; Air doctor coater method, blade coater method, rod coater method, knife coater method, squeeze coater method, reverse roll Various coating methods such as coater method, transfer roll coater method, gravure coater method, kiss coater method, cast coater method, spray coater method, slit orifice coater method, calendar coater method, dipping method; stamp method; lift-off method; shadow mask method; Plating method or electroless method · The method or plating method such as those combinations; and can include any of a spraying method, a combination of a patterning technique as necessary. In addition, as physical vapor deposition methods, (a) various vacuum deposition methods such as electron beam heating method, resistance heating method, flash deposition, (b) plasma deposition method, (c) bipolar sputtering method, direct current sputtering method, Various sputtering methods such as DC magnetron sputtering method, high frequency sputtering method, magnetron sputtering method, ion beam sputtering method, bias sputtering method, (d) DC (direct current) method, RF method, multi-cathode method, activation reaction method, electric field Various ion plating methods, such as a vapor deposition method, a high frequency ion plating method, and a reactive ion plating method, can be mentioned.

  Depending on the material constituting the organic semiconductor thin film as a method for forming the organic semiconductor thin film, PVD methods exemplified by vacuum deposition methods and sputtering methods; various CVD methods; spin coating methods; screen printing methods and inkjet printing methods, etc. One of the printing method, the various coating methods described above, the stamp method, the lift-off method, the shadow mask method, and the spray method can be used.

  As a method for forming the gate insulating film, although depending on the material constituting the gate insulating film, PVD method exemplified by vacuum deposition method and sputtering method; various CVD methods; spin coating method; screen printing method and inkjet printing method Any of the printing method; the various coating methods described above; the dipping method; the casting method; and the spray method can be used.

  Examples of the substrate include various glass substrates, various glass substrates having an insulating layer formed on the surface, a quartz substrate, a quartz substrate having an insulating layer formed on the surface, and a silicon semiconductor substrate having an insulating layer formed on the surface. Can do. Furthermore, examples of the substrate include a plastic film, a plastic sheet, and a plastic substrate made of a polymer material exemplified by polyethersulfone (PES), polyimide, polycarbonate, and polyethylene terephthalate (PET). If a substrate made of such a flexible polymer material is used, for example, a field effect transistor can be incorporated or integrated into a display device or electronic device having a curved shape. When manufacturing a field effect transistor, if it is difficult to manufacture a field effect transistor with a flexible plastic film or plastic sheet, the plastic film or plastic sheet is made of a rigid support (for example, glass A field effect transistor may be manufactured by attaching to a plate, a semiconductor substrate, a metal plate, or the like.

  Hereinafter, the operation principle of the field effect transistor of the present invention will be described.

  π-conjugated polymers are known to have a great influence on the electrical conductivity of conformation because π-conjugation is broken if the main chain skeleton is twisted or bent. The electrical conductivity is good when the molecular surfaces of the monomers constituting the are parallel, and the electrical conductivity is deteriorated when twist is present.

  Here, the problem is the structural stability of the π-conjugated polymer at room temperature. In a system having no steric hindrance, most of π-conjugated polymers are stabilized by taking a cis structure or a trans structure. When the π-conjugated polymer is in an electrically neutral state, for example, an aromatic structure is formed in which each monomer constituting the π-conjugated polymer is connected by a single bond. On the other hand, when a voltage is applied to the gate electrode, electrons in the π-conjugated polymer are moved to the gate insulating film due to the electric field formed based on this voltage, and the π-conjugated polymer is cationized. , Recombination of the bonds of the π-conjugated polymer occurs. That is, for example, the bond between the monomers changes from a single bond to a double bond, resulting in a quinoid structure. It is known that a double bond generally has a stronger binding force than a single bond and is strong against an external force that causes twisting. On the other hand, by stopping the voltage application to the gate electrode, the electrons transferred to the gate insulating film are returned to the π-conjugated polymer. For example, the π-conjugated polymer is changed from a quinoid structure to an aromatic structure. Return to. That is, from the π-conjugated polymer to the gate insulating film accompanying the generation of the dipole moment between the gate insulating film and the π-conjugated polymer due to the electric field formed based on the voltage application to the gate electrode. Electrons moved to the gate insulating film because the dipole moment between the gate insulating film and the π-conjugated polymer disappears due to the movement of the electrons or due to the voltage application to the gate electrode being stopped. Is returned to the π-conjugated polymer, and as a result, the conformation (molecular hardness) of the π-conjugated polymer, which is an organic semiconductor thin film constituting the channel-forming region, changes. The electrical conductivity of the is controlled.

  In polythiophene which is a kind of π-conjugated polymer, the total energy change when the dihedral angle between the monomers is changed is plotted with the dihedral angle of 0 ° (trans structure) as a reference. Shown in (A). In addition, a graph showing an energy band when the dihedral angle is 0 degree and 90 degrees in the polythiophene having an aromatic structure is shown in FIG. 2A. In the polythiophene having a quinoid structure, the dihedral angle is 0 degree. The energy band at 90 degrees and 90 degrees is shown in FIG. Moreover, the schematic diagram of the molecular structure of polythiophene when the dihedral angle is 0 degree and 90 degrees is shown in FIGS. 2B and 2C, respectively. In FIG. 1A, the solid line indicates the energy change in the neutral state (the state in which an aromatic structure is formed in which each monomer is connected by a single bond), and the broken line indicates the cation state (in which each monomer has two gaps). It shows the energy change in a state in which a quinoid structure linked by a double bond is formed. From (A) of FIG. 1, in the cationic state, the valley of energy is deeply stabilized in the state in which the surfaces of the monomers constituting the π-conjugated polymer are parallel to the neutral state, compared to the neutral state. It can be seen that it can exist stably in a state where the π conjugation is strong.

  In other words, the state in which a quinoid structure in which each monomer is connected by a double bond is more π-conjugated than the state in which an aromatic structure in which each monomer is connected by a single bond is formed. The main chain skeleton in the polymer is hardly twisted, and the molecular surfaces of the monomers constituting the π-conjugated polymer are stable in a parallel state. Therefore, the π-conjugated polymer has higher electrical conductivity in the state where the quinoid structure is formed than in the state where the aromatic structure is formed.

  In general, since the double bond has stronger bond strength than the single bond, assuming that the monomers are connected to each other by a spring having a spring constant k, the spring constant k is applied by applying a voltage to the gate electrode. The value of increases in the direction of increasing. In general, since the carrier scattering probability is inversely proportional to the spring constant k, the electrical conductivity is improved in the cationic state from the viewpoint of the scattering probability.

  As described above, the movement of electrons in the π-conjugated polymer constituting the organic semiconductor thin film to the gate insulating film is controlled by the presence or absence of voltage application to the gate electrode. Conductivity is controlled.

  In the field-effect transistor of the present invention, in the state where no voltage is applied to the gate electrode, as schematically shown in FIG. 1B, the π conjugate of the π conjugated polymer constituting the channel formation region. The nature is weakened by molecular vibration, and carrier scattering is significant in intramolecular conduction. On the other hand, in a state where a voltage is applied to the gate electrode, as schematically shown in FIG. 1C, the π conjugation property of the π conjugated polymer constituting the channel formation region is increased, and the carrier in intramolecular conduction is increased. Is suppressed. In this way, the control of π conjugation and the control of the scattering probability are simultaneously controlled by an electric field according to the voltage applied to the gate electrode, and particularly in an organic field effect transistor in which carrier transport is governed by intramolecular conduction. An on / off ratio can be realized. That is, according to the present invention, the semiconductor layer must be composed of a π-conjugated polymer having a large dipole moment and having a substituent that freely moves around the main chain skeleton in response to an external electric field. There can be provided a field-effect transistor without limitation.

  Hereinafter, the present invention will be described based on examples with reference to the drawings.

Example 1 relates to a field effect transistor (hereinafter sometimes abbreviated as FET) of the present invention. The FET of Example 1 is
(A) Gate electrode 12,
(B) Gate insulating film 13,
(C) a channel forming region 16 composed of an organic semiconductor thin film 15 composed of a π-conjugated polymer, and
(D) source / drain electrode 14,
It has.

More specifically, as shown in a schematic partial sectional view of FIG. 6B, the FET of Example 1 is a so-called bottom gate type and bottom contact type thin film transistor (TFT). Yes,
(A) a gate electrode 12 formed on the substrate 11,
(B) a gate insulating film 13 formed on the gate electrode 12;
(C) a source / drain electrode 14 formed on the gate insulating film 13, and
(D) a channel forming region 16 comprising an organic semiconductor thin film 15 formed between the source / drain electrodes 14 and on the gate insulating film 13;
It has.

  The organic semiconductor thin film 15 extends also on the source / drain electrode 14. In addition, polythiophene was used as the π-conjugated polymer constituting the organic semiconductor thin film 15, and TCNQ (tetracyanoquinodimethane) was used as the material constituting the gate insulating film 13. The level of the lowest unoccupied molecular orbital of the material constituting the gate insulating film 13 is higher than the level of the highest occupied molecular orbital of the π-conjugated polymer. Further, the substrate 11 is composed of polyethersulfone (PES), and the gate electrode 12 and the source / drain electrode 14 are composed of two layers of gold (Au) layer / Ti layer.

  In the FET of Example 1, the electrons in the π-conjugated polymer are moved to the gate insulating film 13 due to the electric field formed based on the voltage application to the gate electrode 12, and the gate electrode 12 By stopping the voltage application, the electrons transferred to the gate insulating film 13 are returned to the π-conjugated polymer, thereby controlling the electrical conductivity of the channel forming region 16 composed of the organic semiconductor thin film 15. The More specifically, before the voltage application to the gate electrode 12, the polythiophene that is a π-conjugated polymer is in a state schematically shown in FIG. Then, due to the electric field formed based on the voltage application to the gate electrode 12, the electrons in the polythiophene that is a π-conjugated polymer are moved to the gate insulating film 13, resulting in the π-conjugated polymer. Polythiophene changes from an aromatic structure to a quinoid structure, and is in a state schematically shown in FIG. On the other hand, as a result of the voltage application to the gate electrode 12 being stopped, the electrons transferred to the gate insulating film 13 are returned to the polythiophene, which is a π-conjugated polymer. Returning to the structure, it returns to the state schematically shown in FIG.

  4 (A) to (D), FIGS. 5 (A) to (C), and FIGS. 6 (A) to (B), which are schematic partial sectional views of the substrate and the like. Then, the outline of the manufacturing method of the FET of Example 1 will be described.

[Step-100]
First, the gate electrode 12 is formed on the substrate 11. Specifically, a pattern for forming a gate electrode is formed on the base 11 made of polyethersulfone (PES) based on the resist layer 31 (see FIG. 4A). Next, a Ti layer as an adhesion layer and an Au layer / Ti layer as a gate electrode 12 are formed on the substrate 11 and the resist layer 31 by vacuum deposition (see FIG. 4B). In the drawings, the adhesion layer is not shown. Thereafter, the resist layer 31 is removed by a lift-off method, whereby the gate electrode 12 can be obtained (see FIG. 4C).

[Step-110]
Next, the gate insulating film 13 is formed on the base 11 including the gate electrode 12. Specifically, a gate insulating film 13 made of TCNQ (tetracyanoquinodimethane) is formed on the gate electrode 12 and the substrate 11 based on a vacuum deposition method.

[Step-120]
Thereafter, source / drain electrodes 14 are formed on the gate insulating film 13. Specifically, a pattern for forming source / drain electrodes is formed on the entire surface based on the resist layer 32 (see FIG. 4D). Next, a Ti layer as an adhesion layer and an Au layer / Ti layer as a source / drain electrode 14 are formed on the gate insulating film 13 and the resist layer 32 by a vacuum deposition method (see FIG. 5A). In the drawings, the adhesion layer is not shown. Thereafter, the resist layer 32 is removed by a lift-off method, whereby the source / drain electrode 14 can be obtained (see FIG. 5B).

[Step-130]
Next, the organic semiconductor thin film 15 is formed on the entire surface (see FIG. 5C). Specifically, an organic semiconductor thin film 15 made of polythiophene is formed on the source / drain electrodes 14 and the gate insulating film 13 based on a spin coating method. Then, the structure shown to (A) of FIG. 6 can be obtained by patterning the organic-semiconductor thin film 15 by a well-known method.

[Step-140]
Next, after an insulating layer 20 made of SiO ₂ is formed on the entire surface, an opening is formed in the portion of the insulating layer 20 above the gate electrode 12 and the source / drain electrode 14, and the insulating layer 20 including the inside of these openings is formed. A wiring material layer is formed on this, and this wiring material layer is patterned to form a wiring (not shown) connected to the gate electrode 12 and a wiring 21 connected to the source / drain electrode 14. Yes (see FIG. 6B). Thus, the FET of Example 1 can be obtained.

  As mentioned above, although this invention was demonstrated based on the preferable Example, this invention is not limited to these Examples. The structure and manufacturing conditions of the FET are merely examples, and can be changed as appropriate. When the FET of the present invention is applied to and used in display devices and various electronic devices, it may be a monolithic integrated circuit in which a large number of FETs are integrated on a substrate, or individualized by cutting each FET into discrete components. May be used.

As another structure of the FET, a so-called bottom gate type and top contact type TFT as shown in FIG. That is, this FET
(A) a gate electrode 12 formed on the substrate 11,
(B) a gate insulating film 13 formed on the gate electrode 12;
(C) a channel forming region 16 made of an organic semiconductor thin film 15 formed on the gate insulating film 13, and
(D) source / drain electrodes 14 formed on the organic semiconductor thin film 15;
It has.

Alternatively, a so-called top gate type and top contact type TFT as shown in FIG. That is, this FET
(A) a channel forming region 16 made of an organic semiconductor thin film 15 formed on the substrate 11;
(B) source / drain electrodes 14 formed on the organic semiconductor thin film 15;
(C) a gate insulating film 13 formed on the source / drain electrode 14 and the organic semiconductor thin film 15, and
(D) a gate electrode 12 formed on the gate insulating film 13;
It has.

Alternatively, a so-called top gate type and bottom contact type TFT as shown in FIG. That is, this FET
(A) source / drain electrodes 14 formed on the substrate 11;
(B) a channel forming region 16 made of an organic semiconductor thin film 15 formed on the source / drain electrode 14 and the substrate 11;
(C) a gate insulating film 13 formed on the organic semiconductor thin film 15, and
(D) a gate electrode 12 formed on the gate insulating film 13;
It has.

FIG. 1A shows the total energy change when the dihedral angle between monomers is changed in polythiophene, which is a kind of π-conjugated polymer, with the dihedral angle being 0 ° (transformer structure) as a reference. FIG. 1 (B) is a graph schematically showing the state of the π-conjugated polymer in a state where no voltage is applied to the gate electrode, and FIG. It is a figure which shows typically the state of (pi) conjugated polymer in the state in which the voltage was applied to the electrode. 2A is a graph showing energy bands when the dihedral angle is 0 degree and 90 degrees in polythiophene having an aromatic structure, and FIGS. 2B and 2C are respectively It is a schematic diagram of the molecular structure of polythiophene when the dihedral angle is 0 degree and 90 degrees. FIG. 3 is a graph showing energy bands when the dihedral angle is 0 degree and 90 degrees in polythiophene having a quinoid structure. 4A to 4D are schematic partial cross-sectional views of a substrate and the like for explaining the method for manufacturing the field effect transistor of Example 1. FIG. 5A to 5C are schematic partial cross-sectional views of a substrate and the like for explaining the method for manufacturing the field-effect transistor of Example 1 following FIG. 4D. 6A to 6B are schematic partial cross-sectional views of a substrate and the like for explaining the method for manufacturing the field effect transistor of Example 1 following FIG. 5C. 7A to 7C are schematic partial cross-sectional views of three types of modifications of the field effect transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Base | substrate, 12 ... Gate electrode, 13 ... Gate insulating film, 14 ... Source / drain electrode, 15 ... Organic-semiconductor thin film, 16 ... Channel formation area, 20 ... Insulating layer, 21... Wiring, 31, 32... Resist layer

Claims (4)

(A) a gate electrode,
(B) a gate insulating film,
(C) a channel forming region composed of an organic semiconductor thin film composed of a π-conjugated polymer, and
(D) source / drain electrodes,
A field effect transistor comprising:
Due to the electric field formed based on the voltage application to the gate electrode, the electrons in the π-conjugated polymer are moved to the gate insulating film, and when the voltage application to the gate electrode is stopped, the electrons are transferred to the gate insulating film. A field-effect transistor characterized in that the transferred electrons are returned to the π-conjugated polymer, whereby the electrical conductivity of the channel formation region formed of the organic semiconductor thin film is controlled. Due to the electric field formed by applying voltage to the gate electrode, electrons in the π-conjugated polymer are transferred to the gate insulating film. As a result, the π-conjugated polymer changes from an aromatic structure to a quinoid structure. Change,
By stopping the application of voltage to the gate electrode, the electrons transferred to the gate insulating film are returned to the π-conjugated polymer. As a result, the π-conjugated polymer returns from the quinoid structure to the aromatic structure. The field effect transistor according to claim 1. The field effect transistor according to claim 1, wherein the level of the lowest unoccupied molecular orbital of the material constituting the gate insulating film is higher than the level of the highest occupied molecular orbital of the π-conjugated polymer. The π-conjugated polymer is polythiophene,
2. The field effect transistor according to claim 1, wherein the material constituting the gate insulating film is tetracyanoquinodimethane or a dithiolene metal complex.

Images