JP2013258223A - Phototransistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo detector, specifically a phototransistor, having excellent electrical characteristics and atmospheric stability and capable of obtaining a high on/off ratio with a low application voltage, and a method for manufacturing the phototransistor.SOLUTION: A phototransistor includes a first electrode 5, a second electrode 6, an organic semiconductor layer 1, an insulation film layer 4, and a gate electrode 3. The insulation film layer 4 is located between the gate electrode 3 and the organic semiconductor layer 1. The organic semiconductor layer 1 is in contact with the first electrode 5 and the second electrode 6, and has a transition metal oxide layer 7 at a part of a light receiving surface. A contact interface between the organic semiconductor layer 1 and the transition metal oxide layer 7 is not continuous over the first electrode 5 and the second electrode 6.

Description

  The present invention relates to a phototransistor, a phototransistor array using the phototransistor, and an imaging apparatus.

  In recent years, organic semiconductor materials have attracted a great deal of attention as optoelectronic materials due to their various optical and electrical properties, and are actively researched and developed. In particular, an organic EL element, which is a light-emitting device using an organic semiconductor, generates excitons by recombination of holes and electrons injected by applying an electric field to an organic substance on an organic molecule. It is a device that uses a very interesting phenomenon of light emission due to live, and has reached the stage of practical application as a display device.

In addition, research and development on organic transistors using an organic semiconductor as an active layer has been actively conducted. An organic transistor is an element that switches the amount of current flowing in an organic semiconductor layer by a voltage applied to a source / drain / gate electrode.

Organic thin-film transistors made of organic semiconductor materials and organic insulating film materials can be manufactured by a wet process with excellent productivity, such as printing and coating methods, reducing manufacturing costs compared to conventional silicon transistors using vacuum processes And can be expected to expand to large-area electronic devices. Furthermore, since the manufacturing process temperature can be lowered, a flexible electronic device that is lightweight and hard to break using a plastic substrate with low heat resistance can be manufactured.

In addition, research on organic thin-film solar cells and organic photodiodes using an organic semiconductor as an active layer has been actively conducted. Unlike an organic EL element, an organic thin film solar cell is a light receiving element in which excitons excited by irradiating light on an organic semiconductor thin film are dissociated by an internal electric field and taken out as a charge into a circuit.

In an organic thin film solar cell, a p-type or n-type low-molecular organic semiconductor material or a conductive polymer laminated structure or a mixed film is used to generate light at the p-type semiconductor / n-type semiconductor junction interface upon light irradiation. Carriers are taken out to an external circuit by charge separation of the excitons.

On the other hand, a phototransistor is an element that detects a change in current between electrodes in response to light irradiation on a semiconductor layer, and is used as a light detection device. Here, it is possible to produce an organic phototransistor capable of modulating the current value by light irradiation by replacing the semiconductor material in the organic thin film transistor with a semiconductor material used in an organic thin film solar cell or an organic photodiode. It becomes.

In the conventional organic photodiode, it is difficult to suppress the dark current. However, in the phototransistor structure, since the dark current value can be suppressed by the applied gate voltage, a high on / off ratio (bright current / dark Current).
In addition, a conventional photodiode requires a junction interface between a p-type semiconductor and an n-type semiconductor, whereas an organic phototransistor provides a high photocurrent even with a single material of either p-type or n-type. It is done.

However, in a conventional phototransistor using a silicon-based semiconductor or an organic semiconductor, the dark current value is not yet sufficiently suppressed, and the on / off ratio remains at about 10 ³ to 10 ⁴ . Therefore, further improvement of the on / off ratio is indispensable for realizing an ultra-sensitive optical sensor having high light receiving sensitivity.

In Patent Document 1 (Japanese Patent Laid-Open No. 2009-176985), an on / off ratio (bright current / dark current) = about by using a tetracene derivative thin film formed by vacuum deposition as an organic semiconductor material. it is disclosed that the resulting organic phototransistors showing a 10 ^6.

However, in the phototransistor disclosed in Patent Document 1, in order to obtain an on / off ratio (bright current / dark current) = about 10 ⁶ , a high source / drain voltage of −60 V is necessary, and a practical operating voltage is required. is not.
Further, the disclosed tetracene derivative thin film is formed using a vacuum deposition method, and does not meet the expectation for an organic semiconductor material that a thin film can be formed by a simple process such as a coating method or a printing method. .

In addition, many phototransistors using a polymer organic semiconductor material that can form a thin film by a simple process such as a coating method or a printing method have been reported.

For example, Non-Patent Document 1 discloses a method of manufacturing a phototransistor using a high molecular organic semiconductor material, but the field effect mobility of a high molecular organic semiconductor material is generally lower than that of a low molecular organic semiconductor material. It is very difficult to obtain a high on / off ratio (bright current / dark current).

In addition, in order to provide a highly efficient photodetection device, how to reduce the dark current that causes false signals and crosstalk is a major issue.
For example, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2007-88033) discloses that a blocking layer having an electron-accepting organic material or an electron-donating organic material is provided between an electrode layer and a semiconductor layer. Document 3 (Japanese Unexamined Patent Application Publication No. 2010-80845) discloses that a thin film layer made of a transition metal oxide is provided between an electrode layer and a semiconductor layer. These are intended to provide a potential barrier between the electrode layer and the semiconductor layer to suppress charge injection efficiency and suppress dark current.

However, if there is a potential barrier between the electrode layer and the semiconductor layer, it causes a decrease in the drain current value in driving the transistor, resulting in a decrease in the bright current value. It is difficult to provide an organic phototransistor having an on / off ratio (bright current / dark current).

Patent Document 3 discloses that the driving voltage of the element is lowered by the thin film layer made of the transition metal oxide.
However, it is necessary to form a thin film layer made of the transition metal oxide with a film thickness of 2 nm or less. In order to form such an ultrathin film, an advanced film forming apparatus is required, which increases the manufacturing cost. Therefore, these methods do not meet the expectation for an organic semiconductor device that the device can be manufactured by a simple and low-cost process.

Patent Document 4 (Japanese Patent Laid-Open No. 2005-268550) discloses a method for manufacturing a phototransistor having a structure in which a p-type organic semiconductor layer and an n-type organic semiconductor layer are stacked.
In a structure in which a p-type organic semiconductor layer and an n-type organic semiconductor layer are stacked, efficient charge separation occurs at the p / n stacked interface, and a large bright current can be obtained.

However, since the p-type organic semiconductor layer and the n-type organic semiconductor layer are used, when the transistor is driven, as a result of showing bipolar driving, the dark current value increases, and a high on / off ratio (bright current / An organic phototransistor having a dark current) cannot be provided.
In addition, an n-type organic semiconductor is generally easily affected by oxygen, water, and the like, and is easily deteriorated. Therefore, it is difficult to provide an air-stable phototransistor.

In order to obtain a high bright current value, it is considered that carrier doping is performed on the organic semiconductor layer to increase the field effect mobility.

In Patent Document 5 (Japanese Patent Laid-Open No. 2007-19291) and Non-Patent Document 2, both layers are formed by depositing tetrafluor-tetracyanoquinodimethane (F4-TCNQ), which is a strong acceptor material, on a p-type organic semiconductor layer. It is disclosed that an interfacial charge transfer layer having a high conductivity is formed at the interface of the above.

Although carrier doping based on the charge transfer phenomenon at the interface of the thin film layer is a simple and effective technique, the organic acceptor material represented by F4-TCNQ used in Non-Patent Document 2 is uneasy, and oxygen and It is very difficult to provide an atmospherically stable phototransistor because it deteriorates rapidly under the influence of water or the like.

The present invention has been made in view of the current state of the prior art, and has a superior electrical property and atmospheric stability, and can obtain a high on / off ratio with a low applied voltage, in particular, It is an object of the present invention to provide a phototransistor and a manufacturing method thereof.

As a result of intensive studies to achieve the above object, the inventors of the present invention have the organic semiconductor layer of the phototransistor in contact with the first electrode and the second electrode, and a transition metal oxide layer on a part of the light receiving surface, Since the contact interface between the organic semiconductor layer and the transition metal oxide layer is not continuous across the first electrode and the second electrode, the conductivity at the contact interface increases based on a charge transfer phenomenon. And it has been found that the dark current value can be suppressed and a high on / off ratio can be obtained because only a part of the transistor channel has high conductivity, and the present invention has been completed.

That is, the said subject is solved by following (1)-(4) of this invention.
(1) “a phototransistor having a first electrode, a second electrode, an organic semiconductor layer, an insulating film layer, and a gate electrode, wherein the insulating film layer is located between the gate electrode and the organic semiconductor layer, The organic semiconductor layer is in contact with the first electrode and the second electrode, and has a transition metal oxide layer on a part of the light receiving surface, and a contact interface between the organic semiconductor layer and the transition metal oxide layer Is not continuous across the first electrode and the second electrode ",
(2) “The phototransistor according to (1) above, wherein the transition metal oxide layer includes an oxide of a metal selected from tungsten, molybdenum, and vanadium”.
(3) "Phototransistor array in which a plurality of phototransistors according to (1) or (2) are arranged",
(4) “An imaging device having the phototransistor array according to the item (3)”.

As will be understood from the following detailed and specific description, according to the present invention, a photo that has excellent electrical characteristics and atmospheric stability, and can obtain a high on / off ratio at a low applied voltage. A transistor is provided.

It is the schematic of the organic phototransistor of this invention. It is the upper surface schematic of the organic phototransistor of this invention. 2 is an observation photograph of an organic phototransistor produced in Example 1. It is the transfer characteristic in the dark state or light state of the organic phototransistor measured in Example 1. FIG. It is the absorption spectrum of the organic-semiconductor layer used in Example 1 and the comparative example 1, and the emission spectrum of the used light source. It is a transfer characteristic in the dark state or the bright state of the organic phototransistor measured in Comparative Example 1. It is the comparison of the transfer characteristic in the bright state of the organic phototransistor measured in Example 1 and the comparative example 1. FIG. It is a transfer characteristic with respect to different incident light intensity | strength of the organic phototransistor measured in Example 3. FIG.

  Hereinafter, the present invention will be described with reference to embodiments. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist thereof.

  The phototransistor obtained by the present invention can be manufactured by a wet process, has good electrical characteristics and atmospheric stability, and can obtain a high on / off ratio with a low applied voltage.

As described above, in order to obtain a phototransistor having a high on / off ratio (bright current / dark current), it is necessary to suppress the dark current and obtain a high bright current.
Usually, the bright current value is limited by the field effect mobility of the organic semiconductor layer used as the channel of the transistor. In a phototransistor, excitons are generated by absorbing light irradiated by an organic semiconductor, and a bright current is obtained by separating the excitons by an applied electric field.

Here, when the organic semiconductor layer serves as the channel layer in the transistor and the light receiving layer in the phototransistor, there are many required performances for the organic semiconductor layer, and it is very difficult to select an organic semiconductor layer that satisfies all the characteristics.
Further, as described above, by laminating the p-type organic semiconductor layer and the n-type organic semiconductor layer, the carrier conductive layer and the light receiving layer can be separated.

However, in this structure, the dark current value increases remarkably. Therefore, it is considered effective to increase the carrier mobility of the organic semiconductor layer that is the light receiving layer by increasing the conductivity of a part of the organic semiconductor layer.
By optimizing part of the organic semiconductor layer that is the light receiving layer and increasing the mobility, it is possible to select the most suitable organic semiconductor material from the viewpoint of the light receiving material such as high wavelength selectivity and photocurrent generation characteristics. Become.

Therefore, as a result of intensive studies on a phototransistor structure that satisfies the above-described characteristics, the organic semiconductor layer is in contact with the first electrode and the second electrode, and has a transition metal oxide layer on a part of the light receiving surface. It has been found that a transistor structure in which the contact interface between the organic semiconductor layer and the transition metal oxide layer is not continuous across the first electrode and the second electrode is suitable.

According to the present invention, the electrical conductivity in the organic semiconductor layer increases based on the charge transfer phenomenon only at the interface of the transition metal thin film layer that is in contact with a part of the organic semiconductor layer.
In the phototransistor, excitons are generated in the organic semiconductor by the light absorbed on the light receiving surface. The generated excitons are charge-separated by the applied electric field and move along the electric field in the transistor channel as free carriers. For this reason, at the high conductivity interface, charge transfer is performed more quickly than a layer that has not been increased in conductivity. Therefore, a high bright current value can be obtained as compared with a phototransistor that does not have a transition metal oxide layer.

Furthermore, according to the present invention, since only a part of the transistor channel has a high conductivity, the dark current value can be suppressed. As a result, a high on / off ratio (bright current / dark current) can be obtained.

According to the present invention, since free carriers are generated at the interface of the organic semiconductor layer in contact with the transition metal oxide layer, the transition metal oxide layer needs to be inserted at the interface between the electrode layer and the organic semiconductor layer. Alternatively, the film may be formed on the electrode layer.

FIG. 1 shows a side view of a phototransistor according to the present invention.
The organic thin film transistor of the present invention includes a third electrode (3), a first electrode (5) and a second electrode (6) spatially separated by an insulating layer (4) on a substrate (2). The current flowing through the organic semiconductor layer (1) can be controlled by applying a voltage to the third electrode (3).

Here, the third electrode is referred to as a gate electrode. 1A is a bottom contact bottom gate type, FIG. 1B is a bottom contact top gate type, FIG. 1C is a top contact bottom gate type, and FIG. 1D is a top contact top gate type. These are both field effect transistors (FETs).

Further, an organic semiconductor layer and a layer (7) made of a transition oxide in contact with the organic semiconductor layer are sequentially formed on the substrate. Either the organic semiconductor layer or the transition oxide layer may be formed first. Here, an example in which the organic semiconductor layer is formed first will be described.

Although it does not specifically limit as a board | substrate used for this invention, For example, a metal substrate, a glass substrate, a plastic substrate, a silicon substrate etc. are mentioned. A substrate with little dimensional change in a series of manufacturing processes can facilitate the manufacturing process.
In addition, by using a conductive substrate, the gate electrode can be used, and a structure in which the gate electrode and the conductive substrate are stacked can be used. In particular, when a plastic substrate is used, characteristics such as flexibility, weight reduction, low cost, and impact resistance can be given to a completed device.

As a plastic substrate, for example, a substrate made of polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate, cellulose triacetate, cellulose acetate propionate, etc. Is mentioned.

Various insulating film materials can be used as the material of the insulating film layer used in the present invention.
Examples thereof include inorganic insulating film materials such as silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, titanium oxide, and tantalum oxide.
In addition, as an organic insulating film, polyimide, polyamideimide, polyvinyl alcohol, polyvinylphenol, polyester, polyethylene, polyphenylene sulfide, unsubstituted or halogen atom-substituted polyparaxylylene, polyacrylonitrile, cyanoethyl pullulan, polymethyl methacrylate, silsesquioxane, Examples include polyvinyl butyral.

In order to improve insulation, an inorganic material may be added to the organic material. The method for manufacturing the insulating film can be selected as appropriate depending on the type. For example, CVD method, plasma CVD method, plasma polymerization method, vapor deposition method, spray coating method, spin coating method, dip coating method, blade coating method, bar coating method, printing method, dispenser method, ink jet method and the like can be used. . After the application, an annealing step may be included in order to obtain insulation.

The first electrode, the second electrode, and the gate electrode used in the present invention are not particularly limited as long as they are conductive materials, but Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co, Fe , Mn, Cr, Zn, Mo, W, Ru, In, Sn and the like may be used, and two or more of them may be used in combination. Of these, Au, Ag, Cu, and Ni are preferable in terms of electrical resistance, thermal conductivity, and corrosion.

The electrode materials used for the first electrode and the second electrode may be the same type or different types of materials. Further, when forming such an electrode, a conductive polymer dispersion or the like can be used.

Examples of the conductive polymer include polythiophene, polyaniline, polypyrrole, polyparaphenylene, polyacetylene, or those obtained by doping these polymers.
Among these, in terms of electrical conductivity, stability, heat resistance, and the like, a complex of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT / PSS) is preferable.

Conductive polymers are inferior in electrical properties and stability compared to metals, but can improve the electrical properties of the electrode depending on the degree of polymerization and structure, and can be formed at low temperatures because sintering is not required. Although excellent in terms, heat resistance is required for the lamination process in the subsequent step.

Moreover, it is desirable that the first electrode and the second electrode be formed of a material having a low electrical resistance at the contact surface with the organic semiconductor layer.

As a method for forming the electrode, a conductive polymer solution or dispersion, or a conductive fine particle dispersion may be directly patterned by inkjet, or may be formed from the coating film by lithography, laser ablation, or the like.
Furthermore, a method of patterning an ink containing a conductive polymer or conductive fine particles, a conductive paste, or the like by a printing method such as relief printing, intaglio printing, planographic printing, or screen printing can also be used.
In addition, a method of forming an electrode using a known photolithography method or a lift-off method using a conductive thin film formed from a material such as vapor deposition or sputtering using the above materials as a raw material, thermal transfer onto a metal foil such as aluminum or copper, You may form using the method etc. which etch using the resist by an inkjet etc. FIG.

The material used for the organic semiconductor layer is not particularly limited as long as it has p-type semiconductor characteristics and n-type organic semiconductor characteristics. However, materials having a polycyclic fused ring can be preferably used. It may contain a ring.

Examples of the material used for the organic semiconductor layer include those having the following structure as a partial structure.

Furthermore, if necessary, an alkyl group, an alkoxy group, a thioalkyl group, a trialkylsilyl group, a cycloalkyl group, a cycloalkenyl group, an allyl group, an allyl group, an allylalkyl group, an allyloxy group, a perfluoroalkyl group, a perfluoroalkenyl group, You may have soluble groups, such as an alkylcarbonyl group and an alkyl carboxyl group.

Specific examples of the soluble group include functional groups having the following structure. Here, a, b, and c are each independently an integer of 1 to 30. An integer range of 1 to 22 is more preferable from the viewpoint of solubility effect and versatility.

Furthermore, although the specific structure as an organic-semiconductor material preferably used for this invention is shown below, this invention is not limited to these.

Further, organic semiconductor materials particularly preferable for the present invention include fullerene, fullerene derivatives, fluorinated copper phthalocyanine, copper phthalocyanine, zinc phthalocyanine, tetracene, pentacene, polyalkylthiophene, and dithienobenzodithiophene represented by the following structural formula (1). Is a derivative.

The dithienobenzodithiophene derivative represented by the structural formula (1) can be formed using a precursor organic semiconductor material described in Japanese Patent Application No. 2011-029071.

Organic semiconductor layer coating methods include screen printing, offset printing, gravure printing, flexographic printing, microcontact printing, and other printing methods, conventional coating methods, spin coating methods, casting methods, spray coating methods, doctor blade methods, die printing methods. Examples of the coating method, dipping method, ink jet method, and dropping method include spin coating method, dipping method, spray coating method, and ink jet method in that the coating amount can be controlled to form a desired film thickness. preferable.

Although there is no restriction | limiting in particular as a film thickness of an organic-semiconductor layer, The thickness is selected so that a uniform thin film (namely, the gap and hole which have a bad influence on the carrier transport characteristic of an organic-semiconductor layer) may be formed. The thickness of the organic semiconductor thin film is generally 100 μm or less, particularly preferably 5 to 1000 nm.

As described above, the compound used for the organic semiconductor layer is not particularly limited as long as it is an organic compound having p-type semiconductor characteristics and / or n-type organic semiconductor characteristics.
Therefore, different types of organic semiconductor layers may be stacked or mixed, and RGB light can be detected by having the second and third organic semiconductors having absorption wavelengths different from those of the first organic semiconductor.

The transition metal oxide layer in the present invention contains a transition metal oxide.
As the transition metal, the transition metal oxide preferably has a conduction level lower than the highest occupied orbital level of the organic semiconductor material. For example, molybdenum, tungsten, vanadium, titanium, tantalum, niobium, hafnium, zirconium Transition metals such as molybdenum, tungsten, and vanadium are preferable.

As a method of forming the transition metal oxide layer, a method of forming a thin film formed by using a method such as vapor deposition or sputtering using the above-mentioned material as a raw material so as to be in contact with a part of the organic semiconductor layer through a shadow mask, Alternatively, a patterning method using the photolithography method or the lift-off method may be used.
Alternatively, a mixed film formed by co-evaporation with an organic semiconductor material may be used.

The transition metal oxide layer in the present invention is formed on a part of the light-receiving surface of the organic semiconductor layer, and a contact interface between the organic semiconductor layer and the transition metal oxide layer is between the first electrode and the second electrode. It is formed so as not to be continuous.
In addition, the transition metal thin film layer in the present invention may be formed on a part of the transistor channel portion, and as shown in FIG. 1, even if it is inserted in a part of the interface between the organic semiconductor layer and the metal electrode layer, It does not have to be inserted.

The film thickness of the transition metal oxide layer obtained by the above operation is preferably 1 nm or more and 10 μm or less, more preferably 2 nm or more and 1 μm or less.

FIG. 2 is a top view of the phototransistor according to the present invention in the case where the transition metal oxide layer is formed after the organic semiconductor layer is formed.
The transition metal oxide layer (7) may be formed only on the first electrode (5) side as shown in FIG. 2 (A), or on the second electrode (6) side as shown in FIG. 2 (B). The film may be formed only on both sides of the first electrode (5) and the second electrode (6) as shown in FIG. 2 (C). ), (E), and (F), the film may be formed only on a part of the transistor channel.

In addition, the thin film transistor of the present invention is stably driven in the atmosphere, but is protected as necessary for protection from mechanical destruction, protection from moisture and gas, or protection for the convenience of device integration. Layers can also be provided.

(Transistor array)
A plurality of the phototransistors of the present invention are arranged on a substrate as necessary, and a phototransistor array can be manufactured on the same substrate by providing a lead electrode from each electrode.

(Optical sensor / image sensor)
The phototransistor of the present invention can be used as an optical sensor for detecting light intensity by using a single element or the phototransistor array because the output photocurrent value varies depending on the intensity of incident light. . Furthermore, in the phototransistor of the present invention, since the photocurrent is shown only for light corresponding to the absorption wavelength of the organic semiconductor material to be used, the photosensor can be used as an imaging device.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example.

[Example 1]
After cleaning the silicon wafer with oxygen plasma, a polyimide film having a thickness of about 40 nm was formed by spin coating an N-methyl-2-pyrrolidone solution of polyimide resin.
Thereafter, an organic semiconductor precursor film having a thickness of about 100 nm was obtained by spin coating a chloroform solution (1 wt%) of an organic semiconductor material of the following structural formula (2). The organic semiconductor precursor film thus obtained was allowed to stand on a hot plate set at 230 ° C. for 2 hours to convert the organic semiconductor precursor film into an organic semiconductor material represented by the following structural formula (1).

After the conversion treatment, the source and drain electrodes were formed by channel-depositing silver using a shadow mask (back pressure: 10 ⁻⁴ Pa, deposition rate: 1 −2 Å / s, film thickness: 50 nm) (channel length: 150 μm) , Channel width 2 mm).
Thereafter, molybdenum trioxide is vacuum-deposited (back pressure to 10 ⁻⁴⁾ using a shadow mask so that the contact interface between the organic semiconductor layer and the transition metal oxide layer does not continue between the source electrode and the drain electrode. (Pa, deposition rate of 1-2 ２ / s, film thickness: 2 nm).

As a result of evaluating the electrical characteristics of the thus obtained device using a semiconductor parameter analyzer B1500 manufactured by Agilent, the properties as a p-type transistor device were shown. The field effect mobility was obtained from the transfer characteristics in the saturation region. The following formula was used for calculation of field effect mobility.

（ただし、Ｃｉｎはゲート絶縁膜の単位面積あたりのキャパシタンス、Ｗはチャネル幅、Ｌはチャネル長、Ｖｇはゲート電圧、Ｉｄｓはソースドレイン電流、μは移動度、Ｖｔｈはチャネルが形成し始めるゲートの閾値電圧である。）

(Where Cin is the capacitance per unit area of the gate insulating film, W is the channel width, L is the channel length, Vg is the gate voltage, Ids is the source / drain current, μ is the mobility, and Vth is the gate that the channel begins to form. (It is the threshold voltage.)

Field-effect mobility in the saturation region (μhole) is ^{_{μ hole = 0.51cm 2 / Vs,}} on / off ratio is 4.5 × 10 ⁷ of the drain current, the threshold voltage _{(V th)} is _V th = 6V met It was.

Phototransistor performance evaluation of the fabricated element was performed as follows.
The element produced in the dark room where the light source was installed was installed, and the electrical characteristics under visible light irradiation were evaluated using a semiconductor parameter analyzer B1500 manufactured by Agilent. A white LED was used as the light source.

FIG. 5 shows the emission spectrum of the white LED used in the experiment and the absorption spectrum of the organic semiconductor layer. The irradiation intensity of the used light source is 1900 lx. Under the white LED irradiation conditions, a significant increase in drain current value was observed even in a low gate voltage application state in which the dark state was turned off. The on / off ratio (bright current / dark current) before and after the white LED irradiation was 7 × 10 ⁵ .
In addition, no deterioration in properties due to atmospheric exposure was observed. Furthermore, as shown in FIG. 5, the emission spectrum of the white LED was changed using a blue cut filter, and the same measurement as described above was performed. As a result, no increase in drain current value due to light irradiation was observed. This result shows that the device fabricated according to the present invention has wavelength selectivity.
Further, the on / off ratio (bright current / dark current) = 2 × 10 ⁵ was also obtained under the condition of the source / drain voltage −10V.

[Comparative Example 1]
After cleaning the silicon wafer with oxygen plasma, a polyimide film having a thickness of about 40 nm was formed by spin coating an N-methyl-2-pyrrolidone solution of polyimide resin.
Thereafter, an organic semiconductor precursor film having a thickness of about 100 nm was obtained by spin coating a chloroform solution (1 wt%) of the organic semiconductor material of the structural formula (2). The organic semiconductor precursor film thus obtained was allowed to stand on a hot plate set at 230 ° C. for 2 hours to convert the organic semiconductor precursor film into an organic semiconductor material represented by the structural formula (1).
After the conversion treatment, the source and drain electrodes were formed by vacuum deposition of silver using a shadow mask (back pressure: 10-4 Pa, deposition rate: 1-2 Å / s, film thickness: 50 nm) (channel length: 150 μm, Channel width 2 mm).

As a result of evaluating the electrical characteristics of the thus obtained device using a semiconductor parameter analyzer B1500 manufactured by Agilent, the properties as a p-type transistor device were shown.

The field effect mobility was obtained from the transfer characteristics in the saturation region.
The field effect mobility (μ _hole ) in the saturation region is μ _hole = 0.45 cm ² / Vs, the drain current value on / off ratio is 4.5 × 10 ⁷ , and the threshold voltage (V _th ) is V _th = 6V. there were.
The on / off ratio (bright current / dark current) before and after the white LED irradiation was 1 × 10 ⁵ . FIG. 7 is a diagram comparing the photocurrents in the elements of Example 1 and Comparative Example 1 under visible light irradiation. By forming a molybdenum oxide layer, which is a transition metal oxide layer, an improvement in photocurrent value was observed as compared with an element without a molybdenum oxide layer.

[Example 2]
A transistor array in which a plurality of organic thin film transistors are arranged was manufactured in the same manner as in Example 1. When the transistor characteristics of the five elements manufactured in the same manner were evaluated, the average mobility was 0.47 cm ² / Vs, and there was little fluctuation and good transistor characteristics were obtained. In any of the transistors, a significant increase in the drain current value was observed in the low gate voltage application state in which the transistor was turned off in the dark state under the white LED irradiation condition. The on / off ratio (bright current / dark current) before and after the white LED irradiation averaged 5 × 10 ⁵ . In addition, no deterioration in properties due to atmospheric exposure was observed.

[Example 3]
A transistor array in which a plurality of organic thin film transistors are arranged was manufactured in the same manner as in Example 2. When the transistor characteristics of the five elements manufactured in the same manner were evaluated, the average mobility was 0.47 cm ² / Vs, and there was little fluctuation and good transistor characteristics were obtained.
In any of the transistors, a significant increase in the drain current value was observed in the low gate voltage application state in which the transistor was turned off in the dark state under the white LED irradiation condition. The on / off ratio (bright current / dark current) before and after the white LED irradiation averaged 5 × 10 ⁵ . In addition, no deterioration in properties due to atmospheric exposure was observed.
Next, in order to evaluate the responsiveness to the light intensity, the incident light intensity from the white light source was changed, and the phototransistor performance evaluation was performed in the same manner as in Example 1. As a result, a photocurrent value corresponding to the incident intensity was observed, and it became clear that this element functions as an incident light intensity detecting optical sensor.

[Comparative Example 2]
The same method as in Example 1 except that F4-TCNQ (Sigma Aldrich, manufactured by sublimation purification twice), which is an electron-accepting compound, was used instead of molybdenum trioxide, and a film was formed on a part of the transistor channel. Thus, a transistor was manufactured.
At this time, the field-effect mobility (μ _hole ) in the saturation region is μ _hole = 0.48 cm ² / Vs, the drain current on / off ratio is 4.1 × 10 ⁷ , and the threshold voltage (V _th ) is V _th = 8V. After that, when exposed to air (24 hours at room temperature) and measured again, the field-effect mobility (μ _hole ) in the saturation region is μ _hole = 0.1 cm ² / Vs, and the on / off ratio of the drain current value is 2. 0.0 × 10 ⁴ , the threshold voltage (V _th ) was V _th = 15 V, and a clear deterioration in characteristics was observed.

DESCRIPTION OF SYMBOLS 1 Organic-semiconductor layer 2 Board | substrate 3 3rd electrode 4 Insulating layer 5 1st electrode 6 2nd electrode 7 Transition metal oxide layer

JP 2009-176985 A JP 2007-88033 A JP 2010-80845 A JP 2005-268550 A JP 2007-19291 A

JOURNAL OF APPLIED PHYSICS 105, 024509 (2009) APPLIED PHYSICS LETTERS 87, 153506 (2005)

Claims (4)

A phototransistor having a first electrode, a second electrode, an organic semiconductor layer, an insulating film layer, and a gate electrode, wherein the insulating film layer is located between the gate electrode and the organic semiconductor layer, and the organic semiconductor layer is The first electrode and the second electrode are in contact with each other, and a transition metal oxide layer is provided on a part of a light receiving surface, and a contact interface between the organic semiconductor layer and the transition metal oxide layer is the first electrode. A phototransistor which is not continuous across an electrode and the second electrode. The phototransistor of claim 1, wherein the transition metal oxide layer includes an oxide of a metal selected from tungsten, molybdenum, and vanadium. A phototransistor array in which a plurality of the phototransistors according to claim 1 or 2 are arranged. An imaging apparatus comprising the phototransistor array according to claim 3.

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