JP2007115735A - Transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transistor in which characteristics are stabilized and mobility and ON/OFF level can be maintained at a high level by allowing a gas barrier layer to interrupt deoxidation and dehydrated vapor from a plastic base material. <P>SOLUTION: The gas barrier layer is provided between the plastic base material and an oxide semiconductor layer of the transistor provided with the oxide semiconductor layer provided on the plastic base material, a source electrode arranged in electrically contact with the oxide semiconductor layer, a drain electrode electrically contacting the oxide semiconductor layer and separately arranged on the source electrode, a gate insulation film provided on the oxide semiconductor layer positioned between the source electrode and the drain electrode when the plastic base material is viewed immediately above, and a gate electrode provided on the gate insulation film. With this configuration, the deoxidation and dehydrated vapor from the plastic base material can be prevented from influencing the oxide semiconductor film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a flexible transistor having an oxide semiconductor layer.

Generally, a transistor using an amorphous silicon semiconductor, a polycrystalline silicon semiconductor, or the like has been used as a transistor for driving an electronic device.
However, since a high-temperature amorphous silicon semiconductor or polycrystalline silicon semiconductor requires a film forming temperature of 200 ° C. or higher, it has been difficult to realize a flexible transistor using an inexpensive plastic substrate.

In order to realize a flexible transistor using an inexpensive plastic substrate, a transistor using an organic semiconductor as a semiconductor layer has been actively studied.
Since an organic semiconductor can be produced at a low temperature, it has an advantage that it can be formed on a plastic substrate.
However, the mobility of organic semiconductors is extremely low, and it is difficult to deteriorate with time.

In view of the above situation, a transistor using In—Ga—Zn—O, which is an oxide semiconductor that exhibits high mobility even when manufactured at a low temperature, has been proposed. (See Non-Patent Document 1)

According to this, by using In—Ga—Zn—O as a semiconductor layer, a transistor having an excellent semiconductor with a mobility of about 10 cm ² / Vs on a polyethylene terephthalate substrate can be manufactured at room temperature. It is said that it became.

However, in the case where In—Ga—Zn—O is formed by a sputtering method, the semiconductor characteristics are extremely sensitively influenced by the oxygen concentration on the deposition surface.

For example, when In—Ga—Zn—O is formed by sputtering using an oxygen flow rate of 1% (argon flow rate of 100%), the conductivity of the film exceeds 1 (S / cm). However, when a film is formed under a condition where the oxygen flow rate is 50%, an insulator having a film conductivity of 1 × 10 ⁻¹³ (S / cm) or less is obtained.

Since the oxygen concentration on the semiconductor film formation surface has a significant effect on the number of oxygen vacancies contained in the semiconductor film, it is extremely important to control the oxygen concentration on the semiconductor film formation surface in order to stabilize the semiconductor characteristics. It becomes.

When an inorganic material such as glass is used as the substrate, it is easy to control the oxygen concentration on the surface of the semiconductor film because deoxidation from the substrate during film formation is almost negligible. When a plastic substrate is used as the substrate, it becomes very difficult to control the oxygen concentration on the semiconductor film formation surface due to deoxygenation from the plastic substrate.

In addition, in a transistor in which an In—Ga—Zn—O semiconductor layer is formed over a plastic substrate, with the passage of time, water vapor contained in the plastic substrate diffuses into the semiconductor layer. There is a problem that the ON / OFF ratio is lowered.

K. Nomura et al. Nature, 432, 488 (2004)

An object of the present invention is to prevent deoxygenation and dewatering from a plastic substrate with a gas barrier layer so as not to go to the oxide semiconductor layer, so that the mobility and the ON / OFF ratio are stable. It provides a transistor maintained at a high level.

The invention according to claim 1 is a gas barrier material in which a gas barrier layer is provided on at least one surface of a plastic substrate, an oxide semiconductor layer provided on the gas barrier layer, A source electrode arranged in contact with each other, a drain electrode arranged in electrical contact with the oxide semiconductor layer and spaced apart from the source electrode, and when the plastic substrate is viewed from directly above A gate insulating film provided on the oxide semiconductor layer located between the source electrode and the drain electrode; and a gate electrode provided on the gate insulating film, the voltage applied to the gate electrode A transistor that turns on or off the conduction between the source electrode and the drain electrode depending on the presence or absence of the gas barrier material, wherein an oxygen permeability of the gas barrier material is 3.5 cc / m ² · day · atm. Hereinafter, the transistor has a water vapor transmission rate of 3 g / m ² / day or less.

In the present invention, deoxidation and dewatering from the plastic substrate are blocked by the gas barrier layer so as not to go to the oxide semiconductor layer, so that the characteristics and the mobility and the ON / OFF ratio are high. Thus, a flexible transistor using an oxide semiconductor, which is maintained in Step 1, can be manufactured.

An example of forming a transistor will be described with reference to FIG.

First, the gas barrier layer 2 is laminated on the plastic substrate 1. (Fig. 1 (a))

The plastic substrate materials are polymethyl methacrylate, polyarylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyethersulfene, triacetylcellulose, polyvinyl fluoride. Ride film, ethylene-tetrafluoroethylene copolymer resin, weather resistant polyethylene terephthalate, weather resistant polypropylene, glass fiber reinforced acrylic resin film, glass fiber reinforced polycarbonate, polyimide, transparent polyimide, fluorine resin, cyclic polyolefin resin, polyacryl However, it is not limited to these.

These may be used alone, but can also be used as a composite substrate in which two or more kinds are laminated.

As a material of the gas barrier layer 2, an inorganic oxide or an inorganic nitride can be used.
Specifically, any one of silicon oxide, silicon nitride, aluminum oxide, magnesium fluoride, magnesium oxide, yttrium oxide, and hafnium oxide can be used, or a mixture of two or more types can be used. Absent.
Silicon oxide, silicon nitride, and aluminum oxide are preferable from the viewpoints of good gas barrier performance, low manufacturing cost, transparency, and the like.

The gas barrier layer 2 can be laminated by vacuum deposition, ion plating, sputtering, laser ablation, plasma CVD, photo CVD, hot wire CVD, spin coating, dip coating, screen printing, A method such as a relief printing method, an intaglio printing method, a lithographic printing method, and an ink jet method can be used, but is not limited thereto.

The gas barrier layer 2 may be opaque or transparent, but a transparent transistor can be realized when the plastic substrate, the gas barrier layer, the semiconductor layer, the gate insulating film, and the electrode are all transparent.

Next, the semiconductor layer 3 is stacked on the gas barrier layer 2.

As a material of the semiconductor layer 3, zinc oxide, indium oxide, tin oxide, tungsten oxide, zinc gallium indium, which is an oxide containing one or more elements of zinc, indium, tin, tungsten, magnesium, gallium, and the like are used. Although it can be used, it is not limited to these.
The structure of these materials may be any of single crystal, polycrystal, microcrystal, crystal / amorphous mixed crystal, nanocrystal scattered amorphous, and amorphous.
The thickness of the semiconductor layer is preferably at least 20 nm.

As a method for laminating the semiconductor layer 3, sputtering, pulse laser deposition, vacuum deposition, CVD (Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), spin coating, dip coating, screen printing, letterpress A printing method, an intaglio printing method, a lithographic printing method, an ink jet method and the like can be used, but a sputtering method, a pulse laser deposition method, a vacuum evaporation method, and a CVD (Chemical Vapor Deposition) method are preferable.

Examples of the sputtering method include RF magnetron sputtering method, DC sputtering method, vacuum evaporation method includes heating evaporation, electron beam evaporation, ion plating method, and CVD methods include hot wire CVD method and plasma CVD method. It is not limited.

Next, the gate insulating film 4 is stacked on the semiconductor layer 3.

Examples of the material for the gate insulating film 4 include silicon oxide, silicon nitride, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconia oxide, titanium oxide, polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, Polyamide, polyethersulfene, polymethyl methacrylate, polycarbonate, polyallylate, polyethylene, polystyrene, Teflon (registered trademark), ebonite, epoxy, lacquer, and the like can be used.

The manufacturing method of the gate insulating film 4 includes a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD (Chemical Vapor Deposition) method, a photo CVD method, a hot wire CVD method, a spin coating method, a dip coating method. Methods such as a printing method, a screen printing method, a relief printing method, an intaglio printing method, a lithographic printing method, and an ink jet method can be used.

In order to suppress the leakage current between the metal electrodes (gate electrode 5, source electrode 6, drain electrode 7), the conductivity of the gate insulating film 4 is preferably 10 ⁻¹² S / cm or less.
The thickness of the gate insulating film 4 is desirably 50 nm to 2 mm.

In addition, if the gate insulating film 4 and the gas barrier layer 2 are made of the same material, a transistor can be manufactured at low cost.

Next, metal electrodes (gate electrode 5, source electrode 6, and drain electrode 7) were formed to obtain a transistor. (Fig. 1 (d))

As materials for the metal electrodes (gate electrode 5, source electrode 6, drain electrode 7), gold, platinum, silver, palladium, copper, aluminum, nichrome, chromium, titanium, indium, indium oxide, zinc oxide, tin oxide, oxidation Cadmium, gallium oxide, or the like can be used.

When using transparent conductive oxides such as indium oxide, zinc oxide and tin oxide, it is desirable to increase the conductivity of the metal electrode by mixing a dopant.
For example, zinc oxide is preferably mixed with gallium, aluminum, boron, etc., tin oxide with fluorine, antimony, etc., and indium oxide with tin, zinc, titanium, cerium, hafnium, zirconia, etc., and degenerated.
In addition, it is preferable to use the same base material as the oxide semiconductor as the electrode material and increase only the dopant concentration in order to increase the production efficiency.
The film thickness of the metal electrode needs to be at least 15 nm or more.
In addition, the materials of the gate electrode, the source electrode, and the drain electrode may all be the same or different.

The manufacturing method of the metal electrodes (gate electrode 5, source electrode 6, drain electrode 7) includes vacuum deposition, ion plating, sputtering, laser ablation, plasma CVD, photo CVD, hot wire CVD, Methods such as spin coating, dip coating, screen printing, letterpress printing, intaglio printing, lithographic printing, and ink jet can be used.

The gas barrier layer 2 may be formed on both surfaces of the plastic substrate 1. (Fig. 2 (d))

First, aluminum oxide was deposited to a thickness of 100 nm on a polyethylene terephthalate (hereinafter referred to as PET) having a thickness of 100 mm by using a continuous winding deposition method by an electron beam heating method.

Next, a film thickness of 40 nm is formed on the PET on which aluminum oxide is deposited by using InGaZnO ₄ as a sputtering target and by RF magnetron sputtering [sputtering gas is Ar19.4 SCCM, oxygen 0.6 SCCM (oxygen flow ratio 3%)]. A semiconductor layer containing

A gate insulating film having a thickness of 170 nm made of Y ₂ O ₃ is formed on a part of this semiconductor layer by using RF magnetron sputtering [sputtering gas is Ar1SCCM, oxygen 20SCCM] using Y ₂ O ₃ as a sputtering target. did.

Subsequently, sputtering is performed on the gate insulating film and the semiconductor layer by using In ₂ O ₃ doped with 10% of Sn as a sputtering target, using Ar20SCCM and oxygen 0.1SCCM as sputtering gases, and then performing photolithography. Using the method, the three regions of the source electrode, the drain electrode, and the gate electrode were separated to obtain a transistor.

The channel length of the transistor was 50 mm, and the channel width was 200 mm.
Table 1 summarizes the production conditions.

<Comparative Example 1>
A transistor was produced in the same manner as in Example 1 except that the gas barrier layer made of aluminum oxide was not provided on the PET substrate.

In order to confirm the effect, the characteristics of the manufactured transistor were evaluated.
The results are shown in FIGS.

When the oxygen permeability of the gas barrier material of the transistor is 3.5 cc / m ² · day · atm or less and the water vapor permeability is 3 g / m ² / day or less, the ON / OFF ratio is 10 ⁷ or more and the mobility is 4 cm ² / Vs. The above good characteristics were exhibited.
In addition, the transistor without the gas barrier layer had an ON / OFF ratio of less than 10 ⁷ and a mobility of less than 3 cm ² / Vs, which were unsuitable for transistor use.

The oxygen transmission rate of PET deposited with aluminum oxide was measured under the conditions of a temperature of 30 ° C. and a humidity of 70% RH using an oxygen transmission rate measuring device (model name: Oxytran OXTRAN) manufactured by Mocon, USA. Measured with

In addition, the water vapor transmission rate of PET deposited with aluminum oxide is a condition of a temperature of 40 ° C. and a humidity of 90% RH using a water vapor transmission rate meter (model name: Permatran PERMATRAN) manufactured by Mocon, USA. Measured below.

The transistor of the present invention includes a liquid crystal display, an organic EL display, a microcapsule type electrophoretic display, a light writing type cholesteric liquid crystal display, a twisting ball type display, a toner type display, a movable film type display, and an RFID (Radio Frequency Identification) sensor. It can be used for such devices.

FIG. 11 is an explanatory diagram showing a cross-sectional structure of an example of a transistor of the present invention. FIG. 11 is an explanatory diagram showing a cross-sectional structure of an example of a transistor of the present invention. It is explanatory drawing which shows the relationship of the oxygen permeability of a gas barrier material, mobility, and ON / OFF ratio of the transistor of this invention. It is explanatory drawing which shows the relationship of the water-vapor-permeation rate of a gas barrier material, a mobility, and ON / OFF ratio of the transistor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plastic base material 2 ... Gas barrier layer 3 ... Semiconductor layer 4 ... Gate insulating film 5 ... Gate electrode 6 ... Source electrode 7 ... Drain electrode

Claims (1)

A gas barrier material provided with a gas barrier layer on at least one surface of a plastic substrate, an oxide semiconductor layer provided on the gas barrier layer, and a source arranged in electrical contact with the oxide semiconductor layer An electrode, a drain electrode that is in electrical contact with the oxide semiconductor layer and spaced apart from the source electrode, and between the source electrode and the drain electrode when the plastic substrate is viewed from directly above. A gate insulating film provided on the oxide semiconductor layer, and a gate electrode provided on the gate insulating film, and the source electrode and the drain depending on presence or absence of a voltage applied to the gate electrode A transistor for turning on / off conduction with an electrode, wherein the gas barrier material has an oxygen permeability of 3.5 cc / m ² · day · atm or less, and a water vapor permeability of 3 g A transistor which is less than / m ² / day.