KR101048676B1 - Photosensitive Organic Thin Film Transistors - Google Patents

Abstract

The present invention is an organic thin film transistor including a substrate, a gate electrode, an insulating layer, a source and a drain electrode, and an organic active layer, and includes a portion where the gate electrode overlaps the source electrode or the drain electrode based on a direction in which external light is incident. An organic thin film transistor having a first region and a second region including a portion where the gate electrode does not overlap with the organic active layer, amplify an on-state current by external light. do.

Description

Photosensitive Organic Thin Film Transistors {Photo-Sensitive Organic Thin-Film Transistors}

The present invention relates to a photosensitive organic thin film transistor, and more particularly, to an organic thin film transistor including a substrate, a gate electrode, an insulating layer, a source and a drain electrode, and an organic active layer, based on a direction in which external light is incident. A first region including a region where the gate electrode overlaps with the source electrode or the drain electrode, and a second region including a region where the gate electrode does not overlap with the organic active layer, thereby being turned on by external light (On-State The present invention relates to an organic thin film transistor which amplifies a current.

Recently, there is an increasing need for materials capable of excellent image quality and a large screen, low power consumption, light weight, and small size as information display materials in various fields such as TVs, monitors, mobile phones, and video mobile communications. However, conventional inorganic thin film transistors such as TFTs (thin-film transistors) mostly use silicon (silicon), an inorganic semiconductor as an active layer, silicon is not bent due to its characteristics, it is fragile and expensive to manufacture, there is a limit in the application.

As one of the next generation materials to solve this problem, an organic thin film transistor (OTFT) is emerging. OTFT uses an organic film instead of a silicon film as an active layer, and according to the material of the organic film, a low molecular weight organic thin film transistor such as oligothiophene, pentacene, etc., and a polymer organic thin film such as polythiophene series It is divided into transistors.

OTFT has 10 to ³ times lower charge mobility than conventional single crystal silicon semiconductors, which limits the application of high-speed switching devices, but it is easy to make large area, transparent and flexible, and manufactured at low temperature and low cost. It has many advantages, such as being possible.

Therefore, research for using OTFT as a drive circuit of a liquid crystal display device, an organic electroluminescent display using a plastic substrate, etc. is actively progressing. In addition, the application of organic thin film transistors to integrated circuits extends the range of applications to display devices such as electronic price tags, stamps, radio frequency identification tags, smart cards, and electronic paper. have.

The organic thin film transistor forms a gate electrode by vacuum deposition or sputtering a metal such as gold or aluminum on a glass or plastic substrate, or by patterning indium tin oxide (ITO) using photolithography. The gate insulating film is formed thereon by vacuum deposition or spin coating, and then vacuum deposition of the source electrode and the drain electrode using a shadow mask is carried out on the channel formed between the source electrode and the drain electrode. An organic semiconductor is manufactured by forming into a film by vacuum vapor deposition or spin coating.

The organic thin film transistor using the organic semiconductor or the polymer semiconductor as the active layer changes in the transistor output current in response to external light due to an energy bandgap characteristic of about 1 to 2 eV of the organic semiconductor. By using such characteristics, various optical sensitive electronic devices such as an optical sensor and an optical scanner can be implemented.

In the conventional organic thin film transistor, the off-state current is changed by light irradiation, and its size is several hundred pico amps (pA) or less. This is significantly lower than the field effect current formed in the conductive channel in the device by applying an external voltage to the source, drain, and gate electrodes of the transistor, and an additional amplifier or circuit is additionally required for optical signal detection. In addition, when overlapping with an external electrical noise signal (noise signal) may be impossible to distinguish.

However, at present, a technique for amplifying the off-state current of the organic thin film transistor by external light irradiation has not been developed, and if the off-state current is significantly increased, the transistor characteristics may be lost.

In addition, when the optical signal is applied from the top of the device as shown in Figure 1a and 1b, the optical loss may occur by the device protection layer, and the optical signal is applied through the bottom of the substrate as shown in Figure 2a and 2b In this case, there is a restriction to use a transparent gate electrode such as ITO.

There has not been reported a technique that can solve the above problems of the conventional techniques to date.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application efficiently control the on-state current by external light when controlling the overlapping region between the gate electrode and the source electrode or the gate electrode and the drain electrode of the organic thin film transistor. It was found that it can be amplified, and came to complete the present invention.

Therefore, the organic thin film transistor (OTFT) according to the present invention is an organic thin film transistor (OTFT) composed of a substrate, a gate electrode, a source and a drain electrode, an insulating layer, and an organic active layer, and based on a direction in which external light is incident, A first region including a region where the electrode overlaps with the source electrode or a drain electrode, and a second region including a region where the gate electrode does not overlap with the organic active layer, and is on-state by external light An organic thin film transistor is provided, which amplifies a current.

The organic thin film transistor (OTFT) may include a source electrode and a drain electrode separated from each other; An organic active layer contacting the source electrode and the drain electrode, respectively, and forming a channel between the source electrode and the drain electrode; A gate electrode insulated from the source electrode, the drain electrode, and the organic active layer; And a gate insulating film that insulates the gate electrode from the source electrode, the drain electrode, and the organic active layer.

The material of the electrode (gate, source, drain) is not particularly limited, and a known electrode material may be used, for example, indium-tin oxide (ITO), chromium (Cr), Consisting of copper (Cu), molybdenum (Mo), aluminum (Al), aluminum alloy (Al alloy), tungsten (W), doped silicon, gold, silver, nickel, palladium, platinum, tantalum, barium, calcium and titanium It may be one or two or more selected from the group, it is not limited to these. It can be used in various forms such as alloys, combinations, multilayers thereof. In addition, conductive polymers such as polyaniline, poly (3,4-ethylenedioxythiophene) / poly (styrene sulfonate) (PEDOT: PSS), and the like can also be used.

The substrate is not particularly limited, and a glass substrate, a plastic substrate, a metal substrate, and the like may all be used. The metal substrate may be, for example, steel usestainless (SUS), or the like, and the plastic substrate may be, for example, polyethersulphone (PES), polyacrylate, polyether imide (PEI, polyetherimide, polyethylene naphthalate (PEN, polyethyelenennapthalate), polyethylene terephthalate (PET, polyethyeleneterepthalate), polyphenylene sulfide (PPS), polyimide, polycarbonate (PC), cellulose triacetate (TAC) And, and cellulose acetate propionate (cellulose acetate propinonate: CAP) may be one or two or more selected from the group consisting of, but not limited to these.

The organic active layer is, for example, pentacene (tetracene), tetracene (tetracene), anthracene (anthracene), naphthalene (naphthalene), alpha-6- thiophene, perylene (rubylene), rubrene, Coronene, perylene tetracarboxylic diimide, perylene tetracarboxylic dianhydride, polythiophene, polyparaperylenevinylene, polyfluorene, Polythiophenevinylene, polyparaphenylene, polythiophene-heterocyclic aromatic copolymer, oligoacene of naphthalene, oligothiophene of alpha-5-thiophene, phthalocyanine with or without metal, pyromellitic Dianhydrides, pyromellitic diimides, perylenetetracarboxylic acid dianhydrides, naphthalene tetracarboxylic acid diimides, naphthalene tetracarboxylic acid dianhydrides, and derivatives thereof It may be one or two or more selected from the group consisting of, but is not limited to these.

The insulating layer is not particularly limited and may be an inorganic insulating layer, an organic insulating layer, or an organic-inorganic hybrid film.

The inorganic insulating layer may include, for example, a nitride film such as silicon nitride (SiN _x ), an oxide film such as silicon oxide (SiO _x ), strontate, tantalate, titanate, zirconate, aluminum oxide, or tantalum oxide. , Titanium oxide, barium titanate, barium strontium titanate, barium zirconate titanate, zinc selenide, zinc sulfide and the like.

The organic insulating layer is selected from, for example, polyvinylidene fluoride (PVDF), cyanocellulose, epoxy, benzocyclobutene (BCB, benzocyclobutene), polyimide, parylene and polyvinylphenol (PVP, polyvinylphenol) It may be one or two or more. In addition, an organic layer having a high dielectric constant may also be used, for example, Ba _x Sr _1-x TiO ₃ (Barium Strontium Titanate, BST), Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , PbZr _x Ti _{1 -x} O ₃ (PZT), Bi ₄ Ti ₃ O ₁₂ , BaMgF ₄ , SrBi ₂ (Ta _1-x Nb _x ) ₂ O ₉ , Ba (Zr _1-x Ti _x ) O ₃ (BZT), BaTiO ₃ , SrTiO ₃ , Bi ₄ Ti ₃ O ₁₂ , and the like.

In one preferred embodiment, the insulating layer is an organic-inorganic mixed insulator of a polymer and inorganic particles, the organic-inorganic mixed insulator is a structure in which inorganic particles of high dielectric constant is evenly dispersed in the insulating polymer, or on the polymer layer It is composed of a structure in which a high dielectric constant inorganic film is formed, and may be electrically stable and compensate for low dielectric properties of the polymer. An insulating layer of such a structure is disclosed in Korean Patent Application No. 2006-0056692 to the applicant, which is incorporated by reference in the context of the present invention.

In the organic thin film transistor according to the present invention, the first region may be a portion where the gate electrode overlaps the source electrode, or a portion where the gate electrode overlaps the drain electrode.

External light may be incident on the top and bottom of the device, but as described above, when the optical signal is applied from the top of the device, light loss is caused by the device passivation layer. It is preferred to be incident through the bottom layer.

However, when external light is incident through the lower layer of the substrate, as described above, the conventional organic thin film transistor is a transparent material such as ITO because the external light must pass through the gate electrode when applying the light signal from the bottom There is a restriction to make a low gate electrode, a transparent electrode such as ITO has a problem that the efficiency as an electrode is inferior and expensive compared to the general opaque metal electrode.

In the case of the organic thin film transistor according to the present invention, since an optical signal may be applied to the organic active layer through the second region, an opaque metal as well as a transparent gate electrode such as ITO may be used to solve this problem. In this case, it is preferable to use an opaque metal for the gate electrode as described above.

In one preferred example, when external light is incident on the lower layer of the substrate as described above, the structure may be a black matrix formed so that at least part of the organic active layer is exposed to the incident external light. have.

More preferably, the black matrix may have a structure in which the first region is shielded against incident external light and at least a portion of the second region is shielded.

In this structure, it is more preferable that the organic active layer in the second region is formed so as to shield a portion overlapping with the source electrode and the drain electrode.

The organic thin film transistor of the present invention can be manufactured using a vacuum deposition method such as thermal deposition or sputtering or a printing technique such as screen printing or inkjet printing.

The change of the overlapping region of the gate electrode and the source electrode or the gate electrode and the drain electrode in the device may use a shadow mask and a photo-lithography process in the vacuum deposition manufacturing process, and a mesh and layout design in the printing manufacturing process. Can be.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

3A and 3B schematically show organic thin film transistors 102 and 102a having a lower gate structure according to an exemplary embodiment of the present invention.

3A and 3B, a black matrix 180 is formed below the substrate 110, a gate electrode 120 is formed on the substrate 110, and a substrate on which the gate electrode 120 is formed. An insulating film 130 is formed thereon, an organic active layer 140 is formed on the insulating film 130, and a source (or drain) electrode 151 and a drain (or source) electrode 161 are formed thereon. Passivation 170 is formed on the organic active layer 140, the source (or drain) electrode 151, and the drain (or source) electrode 161.

When the external optical signal 200 is applied through the lower part of the substrate, the optical signal may reach the organic active layer 140 through the second region 400 without passing through the gate electrode 120.

In contrast, in the case of the conventional organic thin film transistors 101 and 101a of FIGS. 2A and 2B, since the external optical signal 200 reaches the organic active layer 140 through the gate electrode 120, the gate electrode 120 is moved to the organic electrode layer 140. Although the transparent metal electrode should be used, the organic thin film transistor of the present invention can solve the problem of using the transparent metal electrode as the gate electrode 120 by configuring the second region 400.

4A and 4B are graphs showing conversion characteristics and output amplification characteristics of the organic thin film transistors due to light irradiation when the second region 400 is formed between the source and the gate electrodes.

4A and 4B, ID, IG, VD, and VG represent an output drain current, a gate leakage current, a drain-source voltage, and a gate-source voltage, respectively, and the device proposed in the present invention is Off- Unlike the amplification of the state current, it shows the amplification characteristic of the on-state output current.

5A and 5B are graphs illustrating conversion characteristics and output amplification characteristics of the organic thin film transistor by light irradiation when the second region 400 is formed between the drain and the gate electrode.

5A and 5B, similarly to the results of FIGS. 4A and 4B, on-state output current amplification characteristics may be confirmed by light irradiation.

In the photosensitive On-State current amplification implemented through the present invention, the space charge formed in the second region 400 between the gate electrode and the source electrode or the gate electrode and the drain electrode is activated by external light to contribute to the output current conduction. It appears to have appeared.

Through the above results, it can be confirmed that the technique proposed in the present invention is effective for amplifying the on-state current by photosensitive organic thin film transistor. In addition, the magnitude of the amplified current by light irradiation may be effectively controlled according to the area control of the second region 400 and the type of the irradiation light source.

Although described above with reference to the drawings according to an embodiment of the present invention, those of ordinary skill in the art will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the organic thin film transistor according to the present invention adjusts an overlap region of the gate electrode and the source electrode or the drain electrode and the drain electrode to conduct a space charge formed therein to be conducted by external light. There is an advantage that can significantly improve the light response characteristics by using the increment.

1A and 1B are cross-sectional views of an organic thin film transistor in which an external optical signal is applied through an upper portion of an organic thin film transistor according to the prior art;

2A and 2B are cross-sectional views of an organic thin film transistor according to the prior art, to which an external optical signal is applied through a substrate bottom of the device;

3A and 3B are cross-sectional views of organic thin film transistors according to an embodiment of the present invention;

4A and 4B are graphs showing On-State output current amplification characteristics by light irradiation of a device in which a second region is formed between a source and a gate electrode;

5A and 5B are graphs showing On-State output current amplification characteristics by light irradiation of a device in which a second region is formed between a drain and a gate electrode;

<Description of Major Symbols in Drawing>

110: substrate 120: gate electrode

130: gate insulating film 140: organic active layer

150: source electrode 160: drain electrode

170: Passivation 180: Black Matrix

200: external light 300: first region

400: second area

Claims (8)

An organic thin film transistor comprising a substrate, a gate electrode, an insulating layer, a source and a drain electrode, and an organic active layer, A source electrode and a drain electrode separated from each other; An organic active layer in contact with the source electrode and the drain electrode, respectively, and forming a channel between the source electrode and the drain electrode; A gate electrode insulated from the source electrode, the drain electrode, and the organic active layer; And a gate insulating film insulating the gate electrode from the source electrode, the drain electrode, and the organic active layer. A first region including a region where the gate electrode overlaps the source electrode or the drain electrode, and a second region including a region where the gate electrode does not overlap the organic active layer, based on a direction in which external light is incident, An organic thin film transistor which amplifies an on-state current by external light. delete The organic thin film transistor of claim 1, wherein the first region is a portion where the gate electrode overlaps the source electrode. The organic thin film transistor of claim 1, wherein the first region is a portion where the gate electrode overlaps the drain electrode. The organic thin film transistor of claim 1, wherein the external light is incident through the lower layer of the substrate. The organic thin film transistor of claim 5, wherein a black matrix is formed in a lower layer of the substrate to expose at least a portion of the organic active layer to incident external light. The organic thin film transistor of claim 6, wherein the black matrix is formed such that the first region is shielded against incident external light and at least a portion of the second region is shielded. The organic thin film transistor according to claim 7, wherein the black matrix is formed so as to shield a portion where the organic active layer overlaps the source electrode and the drain electrode in the second region.

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