JP2006165530A - Sensor and non-planar imager - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor and a non-planar X-ray imager using an amorphous oxide. <P>SOLUTION: A sensor comprises a lower electrode, an amorphous oxide semiconductor layer, and an upper electrode which are formed on a transparent substrate. An imager comprises the sensor and a TFT. For X-ray detection, combination with a scintillator may be used. A TFT can be manufactured by using the film. The amorphous oxide layer is formed by means of a pulse laser deposition method. The film has an electron carrier concentration of less than 10<SP>18</SP>/cm<SP>3</SP>. The electron mobility of the film increases with increasing number of conduction electrons. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sensor that detects received electromagnetic waves, such as an optical sensor, a solar cell, and an X-ray sensor. The present invention also relates to a non-planar imaging apparatus.

  A thin film transistor (TFT) using an oxide semiconductor thin film containing ZnO has been actively developed (Patent Document 1).

  Since the thin film can be formed at a low temperature and is transparent to visible light, it is said that a flexible transparent TFT can be formed on a substrate such as a plastic plate or a film.

  Attempts have also been made to use ZnO for optical sensors and solar cells.

  On the other hand, in nuclear power plants and the like, complicated piping is laid.

  A great amount of cost and time are spent in inspecting the corrosion state of the pipe, and a non-planar X-ray imager (imaging device) that can be inserted between complicated pipes is desired.

  In the medical field, the current situation is that a great burden is placed on the patient in the X-ray diagnosis by mammography or the like. A non-planar X-ray imager is desired as an X-ray diagnostic method with less burden on the patient.

  A non-planar imager is generally composed of a thin film transistor and an X-ray sensor.

  A thin film transistor (Thin Film Transistor, TFT) is a three-terminal element including a gate terminal, a source terminal, and a drain terminal. The TFT is combined with the sensor and used as a switch or an amplifier for selecting the sensor.

As a sensor for detecting electromagnetic waves and a non-planar X-ray imaging device, a flexible device with better performance has been demanded.
Japanese Patent Laid-Open No. 2003-298062

  An object of the present invention is to provide a novel sensor or imaging device using an amorphous oxide.

Another object of the present invention is to provide an amorphous oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ or an amorphous oxide having a tendency to increase electron mobility as the electron carrier concentration increases. It is to provide a sensor and a non-planar imaging apparatus using the sensor.

  Still another object of the present invention is to provide an imaging apparatus including an X-ray sensor and a normally-off field effect transistor.

  Sensors for detecting received electromagnetic waves in the present invention include optical sensors as well as sensors for detecting invisible light such as ultraviolet sensors and sensors for detecting radiation such as X-ray sensors.

  The present invention will be specifically described below.

The sensor for detecting the received electromagnetic wave according to the present invention,
It is characterized by comprising a first electrode, a second electrode, and an amorphous oxide layer provided between the first and second electrodes.

Here, the electron carrier concentration of the amorphous oxide layer is preferably less than 10 ¹⁸ / cm ³ .

  The first electrode is preferably transmissive to light in a wavelength region where the amorphous oxide layer is sensitive.

  The present invention also includes a sensor in which an organic dye is provided in the amorphous oxide layer.

The sensor according to the present invention is
An amorphous oxide layer provided between the first electrode and the second electrode,
The amorphous oxide layer is an amorphous oxide that tends to increase the electron mobility as the electron carrier concentration increases.

In addition, an imaging apparatus according to the present invention includes:
A flexible substrate;
An X-ray sensor provided on the flexible substrate;
A field effect transistor electrically connected to the X-ray sensor;
The field effect transistor has an amorphous oxide as an active layer, and the amorphous oxide has an electron carrier concentration of less than 10 ¹⁸ / cm ³ , or the amorphous oxide The oxide is characterized in that the electron carrier concentration increases and the electron mobility tends to increase.

  In particular, it is more preferable that the imaging device has a non-planar imaging region.

  The present invention also includes a non-planar imager in which the X-ray sensor includes a scintillator that converts X-rays into light and a photoelectric conversion element.

  In the present invention, the X-ray sensor includes a semiconductor layer, and the semiconductor layer includes an amorphous oxide.

In addition, an imaging apparatus according to the present invention includes:
A substrate having a non-planar region;
An X-ray sensor provided on the substrate;
A field effect transistor for reading a signal from the X-ray sensor,
The field effect transistor is a normally-off transistor having an active layer made of an amorphous oxide.

  By the way, an inorganic thin film transistor is generally formed on a plane and used in a planar shape. A conventional inorganic thin film transistor typified by amorphous silicon requires a high-temperature process for film formation, and it is difficult to form it on a flexible substrate such as a plastic resin.

  As a thin film transistor that can be formed over a flexible substrate, a thin film transistor using an organic semiconductor such as pentacene has been studied, but its transistor characteristics are not yet sufficient.

  Recently, as described above, TFTs using ZnO polycrystalline oxide as a channel layer have been actively developed.

  When the present inventor examined an oxide semiconductor, it was found that ZnO generally cannot form a stable amorphous phase. Since most ZnO exhibits a polycrystalline phase, carriers are scattered at the interface between the polycrystalline particles, and as a result, it seems that the electron mobility cannot be increased.

  In addition, oxygen defects are easily introduced into ZnO, and a large number of carrier electrons are generated. Therefore, it is difficult to reduce the electrical conductivity. For this reason, it was found that even when the gate voltage of the transistor is not applied, a large current flows between the source terminal and the drain terminal, and the normally-off operation of the TFT cannot be realized. It also seems difficult to increase the on / off ratio of the transistor.

Further, the present inventor has amorphous oxide film _{Zn x M y In z O (} x + 3y / 2 + 3z / 2) ( in the formula as described in JP 2000-044236, M is Al And at least one element of Ga). This material has an electron carrier concentration of 10 ¹⁸ / cm ³ or more, and is a suitable material as a simple transparent electrode.

However, it has been found that when an oxide having an electron carrier concentration of 10 ¹⁸ / cm ³ or more is used for the TFT channel layer, the on / off ratio is not sufficient, which is not suitable for a normally-off type TFT.

That is, in the conventional amorphous oxide film, a film having an electron carrier concentration of less than 10 ¹⁸ / cm ³ could not be obtained.

Therefore, the present inventor fabricated a TFT using an amorphous oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ as an active layer of a field effect transistor, and a TFT having desired characteristics was obtained. They have found that it can be applied to image display devices such as light-emitting devices.

As a result of intensive research and development on InGaO ₃ (ZnO) _m and film formation conditions of this material, the present inventors have controlled the oxygen atmosphere conditions during film formation to reduce the electron carrier concentration to 10 It has been found that it can be less than ¹⁸ / cm ³ .

  The present invention relates to a sensor or an imaging apparatus using a film that achieves a desired electron carrier concentration.

The present invention provides a novel sensor and imaging device.
In particular, when X-ray transmission measurement is performed on an object to be measured using a non-planar imager, an image with less distortion can be obtained compared to a planar imager.

  Further, when performing X-ray measurement of the human body, the physical burden on the measurement subject is reduced.

  The present invention relates to a sensor and a non-planar imager using an amorphous oxide.

  In the following, in the first embodiment, the optical sensor will be described in detail, and then the non-planar imager will be described in the second embodiment.

  After that, the amorphous oxide common to both embodiments will be described in detail together with its characteristics.

(First embodiment)
FIG. 8 shows a schematic structural diagram of a sensor for detecting received electromagnetic waves according to the present invention.

  The sensor according to the present invention includes a lower electrode (702), an amorphous oxide semiconductor layer (703), and an upper electrode (704) on a substrate (701).

  The upper electrode may be referred to as a first electrode and the lower electrode may be referred to as a second electrode.

In the present embodiment, for example, an oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ is used as the amorphous oxide layer.

  The layer thickness of the amorphous oxide layer is appropriately optimized depending on the wavelength of light to be irradiated and the dye-sensitized dye, but is preferably 10 nm to 1 μm. More preferably, it is 10 nm to 500 nm.

  In the case where the amorphous oxide is a semiconductor containing In—Ga—Zn—O, n-type conduction is exhibited.

It is also preferable to form a photodiode by forming a junction between the oxide semiconductor and a metal having a high work function such as Pt. Alternatively, the n-type oxide semiconductor and the p-type oxide semiconductor SrCu ₂ O ₂ may be stacked to form a semiconductor junction to form a photodiode.

The sensor according to the present invention can be used not only as an optical sensor for ultraviolet rays or X-rays but also as a sensor for visible light by using an organic dye described later.
FIG. 9 shows a second schematic structural diagram of the sensor according to the present invention.

  The sensor of the second aspect of the present invention includes a lower electrode (802) on a substrate (801) field, a multilayer structure semiconductor layer (803) formed by laminating a plurality of amorphous oxide semiconductors, and an upper electrode (804). It is configured.

  It is also a preferred embodiment that the semiconductor layer having a multilayer structure is formed by appropriately optimizing the thickness of each semiconductor layer depending on the wavelength of light to be irradiated. The layer thickness of the constituent semiconductor layer of the multilayer structure semiconductor layer is preferably 1 nm to 100 nm, more preferably 5 nm to 50 nm. The total thickness of the multilayer structure semiconductor layer is preferably 10 nm to 1 μm. More preferably, it is 10 nm to 500 nm.

  Such a multi-layered semiconductor layer is composed of, for example, amorphous oxide layers having different constituent materials or amorphous oxide layers having different thicknesses.

  In the case of irradiating light from the upper electrode, it is necessary to select a material / film thickness that transmits the irradiated light for the upper electrode. For example, an oxide transparent conductive film is preferable. In the case of irradiating light from the substrate side, a quartz material or acrylic resin having excellent translucency is preferable as the substrate material. In that case, an oxide transparent conductive film having a wide band gap is also preferable as the lower electrode.

  A case where the amorphous oxide semiconductor of the present invention is sensitized with an organic dye will be described.

  As shown in FIG. 8, when light is incident from above the photosensor element, after depositing an amorphous oxide semiconductor film, it is immersed in an organic solvent in which the organic dye is dissolved to adsorb the organic dye to the semiconductor. . Alternatively, an organic dye is deposited on the semiconductor by a vacuum deposition method. Thereafter, the upper electrode is formed by vacuum deposition or sputtering.

  When light is incident from the substrate side, an organic dye is adsorbed on the lower electrode, and then an amorphous oxide semiconductor is formed by a laser ablation method or a sputtering method.

  Further, as shown in FIG. 9, when organic dye sensitization is performed on a semiconductor layer having a multilayer structure, it is possible to form the organic dye by repeatedly laminating it by a dipping method, a vapor deposition method or the like every time the semiconductor layer is laminated. it can.

  In this case, it is preferable to distribute a dye that absorbs light of a long wavelength from a dye that absorbs light of a short wavelength as the light enters the semiconductor layer from the light incident side.

  The substrate used in the present invention may be conductive or electrically insulating. Examples of the conductive support include metals such as NiCr, stainless steel, Al, Cr, Mo, Au, Nb, Ta, V, Ti, Pt, and Pb, or alloys thereof. Examples of the electrically insulating support include acrylic resin, polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide and other synthetic resin films or sheets, glass, ceramic, paper, and the like. It is done. These electrically insulating substrates are preferably subjected to conductive treatment on at least one surface thereof, and a light receiving layer is provided on the surface subjected to the conductive treatment.

For example, in the case of glass, a thin film made of NiCr, Al, Cr, Mo, Au, Ir, Nb, Ta, V, Ti, Pt, Pd, InO ₃ , ITO (In ₂ O ₃ + Sn) or the like is formed on the surface. By providing, conductivity is imparted. Alternatively, if it is a synthetic resin film such as a polyester film, a thin film of metal such as NiCr, Al, Ag, Pb, Zn, Ni, Au, Cr, Mo, Ir, Nb, Ta, V, Tl, or Pt is vacuum-deposited. It is provided on the surface by electron beam evaporation, sputtering or the like to impart conductivity. Moreover, in the case of synthetic resin films, such as a polyester film, the surface can be laminated with the said metal and electroconductivity can also be provided to the surface. The substrate is preferably a flexible substrate, that is, it can be deformed (particularly bent).

  The oxide transparent conductive film used in the present invention desirably has a light transmittance of 60% or more, more preferably 85% or more. Furthermore, it is desirable that the sheet resistance value is 100Ω or less so that it does not become a resistance component with respect to the output of the photovoltaic element. The light transmittance means the light transmittance in the wavelength range to be detected by the optical sensor.

Metal oxides such as SnO ₂ , In ₂ O ₃ , ITO (SnO ₂ + In ₂ O ₃ ), ZnO, CdO, Cd ₂ SnO ₄ , TiO ₂ , and Ti ₃ N ₄ as materials having such characteristics, Examples thereof include a metal thin film in which a metal such as Au, Al, Cu or the like is extremely thin and semi-transparent.

  Of these, indium oxide and indium-tin oxide transparent electrodes are particularly suitable. As these manufacturing methods, a resistance heating vapor deposition method, an electron beam heating vapor deposition method, a sputtering method, a spray method, and the like can be used and are appropriately selected as desired. However, a sputtering method and a vacuum vapor deposition method are optimum. It is.

  Examples of the organic dye include a cyanine dye, a merocyanine dye, a phthalocyanine dye, a naphthalocyanine dye, a phthalo / naphthalene mixed phthalocyanine dye, a dipyridyl Ru complex dye, a terpyridyl Ru complex dye, and a phenanthroline Ru complex that can be chemically bonded to the semiconductor. It is selected from among dyes, phenylxanthene dyes, triphenylmethane dyes, coumarin dyes, acridine dyes, and azo metal complex dyes. Of course, you may combine with several pigment | dye.

  As the organic dye sensitizer suitable for the present invention, an organic oxide sensitizer having the In-Ga-Zn-O of the present invention as a main component and a compound that forms a bond in which photoexcited charges easily move is preferable. is there.

  The dye that adsorbs to the semiconductor layer and functions as a photosensitizer has absorption in various visible light regions and / or infrared light regions.

  In order to firmly adsorb the dye to the semiconductor layer, the dye molecule has a carboxylic acid group, carboxylic anhydride group, alkoxy group, hydroxyalkyl group, sulfonic acid group, hydroxyl group, ester group, mercapto group, phosphonyl group, etc. Those are preferred.

  Among these, a carboxylic acid group and a carboxylic anhydride group are particularly preferable. The groups provide an electrical bond that facilitates electron transfer between the excited state dye and the conductive band of the amorphous oxide semiconductor.

  Examples of the dye having the group include a ruthenium bipyridine dye, an azo dye, a quinone dye, a quinoneimine dye, a quinacridone dye, a triphenylmethane dye, and a xanthene dye. In addition, squarylium dyes, cyanine dyes, merocyanine dyes, porphyrin dyes, phthalocyanine dyes, berylene dyes, indigo dyes, naphthalocyanine dyes, and the like can be given.

  Examples of the method for adsorbing the dye to the semiconductor layer include a method in which a semiconductor layer formed on a conductive support is immersed in a solution in which the dye is dissolved (dye adsorption solution), and a method in which an organic dye is deposited. Other methods include heating the organic dye, transporting the organic dye with an inert gas such as helium and nitrogen, and adsorbing the organic dye onto the semiconductor. The organic dye is preferably formed in a monomolecular layer on the amorphous oxide semiconductor.

  The solvent for dissolving the dye may be any solvent that dissolves the dye. Specifically, alcohols such as ethanol, ketones such as acetone, ethers such as diethyl ether and tetrahydrofuran, and nitrogen compounds such as acetonitrile. There is. Other examples include halogenated aliphatic hydrocarbons such as chloroform, aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, esters such as ethyl acetate, and water. Two or more of these solvents can be used in combination.

The concentration of the dye in the solution can be appropriately adjusted depending on the kind of the dye and the solvent to be used, but it is preferably as high as possible in order to improve the adsorption function. The dye concentration may be, for example, 1 × 10 ⁻⁵ mol / l or more, more preferably 1 × 10 ⁻⁴ mol / l or more.

  In the present invention, it is preferable to appropriately select and use an organic dye corresponding to a target wavelength range as an optical sensor element. As the dye for that purpose, a single dye may be used, or a plurality of dyes may be used in combination.

(Second Embodiment)
A schematic diagram of an imaging apparatus according to the present invention is shown in FIG. The invention according to this embodiment is, for example, an X-ray image sensor. The present invention includes a lower electrode 902, a semiconductor layer 903 serving as a photoelectric conversion element, an upper electrode 904, and a scintillator 905 on a substrate 901 having a variable shape. As the configuration from the substrate 901 to the upper electrode 904, the configurations shown in FIGS. 8 and 9 can be used. For example, the semiconductor layer is formed using an amorphous oxide containing at least In—Ga—Zn—O.

  Note that the imaging apparatus according to the present invention preferably has a non-planar portion at least in part. Of course, it is also preferable that the imaging apparatus can be deformed into a non-planar shape even at a certain moment.

As the semiconductor layer 903, an amorphous oxide (details are described later) can be used, or amorphous silicon or the like can be used. As described later, the amorphous oxide has an electron carrier concentration of less than 10 ¹⁸ / cm ³ , or the amorphous oxide increases the electron mobility as the electron carrier concentration increases. An oxide exhibiting a tendency can be used.

  As the substrate, in addition to a glass substrate or the like, resin, plastic, or PET (polyethylene terephthalate) can be applied. A flexible substrate is preferable.

  Note that the scintillator 905 in which a phosphor is mainly used as an X-ray sensor may be used as necessary, and may be omitted if the above-described semiconductor layer has sensitivity to X-rays.

As scintillators, NaI (Tl) (deliquescent), CsI (Tl) (deliquescent), Cs (Na) (deliquescent), CsI (pure), CaF ₂ (Eu), BaF ₂ and CdWO ₄ are used. Is done. The thickness of the scintillator layer is preferably 100 μm to 500 μm as a thickness that can absorb sufficient X-rays. For the scintillator layer, a sputtering method is preferable. When using a deliquescent scintillator, it is necessary to perform a moisture-proof treatment. As the moisture-proof treatment, it is preferable that a moisture-proof layer such as a silicon nitride layer or a silicon oxide layer is laminated on the back surface of the substrate 901 and the scintillator surface to a thickness of 100 nm or more.

  The present invention comprises a TFT using an amorphous oxide such as In-Ga-Zn-O as an active layer and a photoelectric conversion element using a scintillator and an oxide semiconductor containing In-Ga-Zn-O according to the present invention. A circuit per pixel using an X-ray sensor is shown in FIG.

  Note that, here, a normally-off TFT is preferably used for the active layer of the TFT by using an amorphous oxide described later.

  The sensing operation of such a three-transistor pixel structure imaging sensor is as follows.

  In the X-ray sensor 1006, X-rays are incident on the scintillation and converted into visible light, and the light is converted into electricity by the dye-sensitized In-Ga-Zn-O-containing oxide semiconductor. The converted signal charge changes the potential of the floating node 1005 that is the source end of the reset TFT 1001. As a result, the gate potential of the select TFT 1004 that is a driver of the pixel level source follower is changed. The bias of the source end of the select TFT 1004 or the drain node of the access TFT 1007 is changed.

  In this way, while the signal charge is accumulated, the potential at the source end of the reset TFT 1001 and the source end of the select TFT 1004 changes. At this time, when a row selection signal is input to the gate of the access TFT 1007 via the row selection signal input terminal 1008, a potential difference due to the signal charge generated by the X-ray sensor 1006 is output to the column selection line 1009.

  Thus, after detecting the signal level due to the charge generation of the X-ray sensor 1006, the reset transistor 1 is turned on by the reset signal via the reset signal input terminal 1002, and the signal charge accumulated in the X-ray sensor 1006 is Everything is reset.

In the case of using a semiconductor layer having sensitivity to X-rays, the organic dye can be omitted as well as the scintillator. The active layer of the TFT can be formed of, for example, an amorphous oxide described later. An amorphous oxide, for example, has an electron carrier concentration of less than 10 ¹⁸ / cm ³ , or the amorphous oxide is an oxide that tends to increase electron mobility as the electron carrier concentration increases. Can be used. The TFT can be provided beside the photoelectric conversion portion by using the upper electrode 904, the semiconductor layer 903, and the lower electrode 902 shown in FIG. In addition, a separate layer for the TFT may be provided between the substrate 901 and the lower electrode 902.

  For X-ray absorption, the thickness of the oxide semiconductor layer is 50 μm or more, preferably 100 μm or more, and more preferably 300 μm or more.

  Further, both the semiconductor of the X-ray sensor and the active layer of the TFT for receiving (or reading) a signal from the sensor can be made of an amorphous oxide. This is a preferred configuration when high flatness is required.

  A non-planar imager was configured by arranging a plurality of imaging sensor units shown in FIG. 11 formed on a substrate having a variable shape. The imager resolution was set to XGA (1024 x 768), SXGA (1280 x 1024) or higher. An example of a method for creating a non-planar imager is shown in FIG. The sensor unit created on the plane is cut by a broken line as shown in the left figure of FIG. 12, and is formed into a spherical shape as shown in the right figure. By doing so, a hemispherical non-planar imager is constructed. Reference numeral 1101 denotes a TFT and a sensor formed on a plane. Reference numeral 1102 denotes a TFT and a sensor unit. Reference numeral 1103 denotes a hemispherical non-planar imager provided with the TFT and the sensor.

  The arrangement of the TFT and the sensor unit on the non-planar imager can also be realized as follows. For example, first, a TFT or the like is provided on a flexible substrate such as plastic or PET, that is, on a flat surface. Then, in a state where the flexible substrate is heated, the substrate is pressed against a non-planar mold to deform the planar substrate into a non-planar shape. Of course, the non-planar imager referred to in the present invention encompasses both an imager having a non-planar region as well as an imager that can be transformed from a planar state to a non-planar state.

An example of a measurement method using the non-planar imager of the present invention is shown in FIG. The object 1203 to be measured is placed in the non-planar imager 1201 formed in FIG. 12, and the object 1203 is measured by irradiating an X-ray 1204 from the outside. In order to prevent the sensor unit from entering between the X-ray light source and the object to be measured, it is also a preferred embodiment that the sensor unit is formed in half of the hemispherical planar imager.
(Amorphous oxide)
As described above, in the present invention, an amorphous oxide having a predetermined electron carrier concentration is used as the photosensor part itself or as an active layer of a field effect transistor used in the photosensor. Of course, you may use for both.

The electron carrier concentration of the amorphous oxide according to the present invention is a value when measured at room temperature. The room temperature is, for example, 25 ° C., specifically, a certain temperature appropriately selected from the range of about 0 ° C. to 40 ° C. Note that the electron carrier concentration of the amorphous oxide according to the present invention does not need to satisfy less than 10 ¹⁸ / cm ³ in the entire range of 0 ° C. to 40 ° C. For example, a carrier electron density of less than 10 ¹⁸ / cm ³ may be realized at 25 ° C. Further, when the electron carrier concentration is further reduced to 10 ¹⁷ / cm ³ or less, more preferably 10 ¹⁶ / cm ³ or less, a normally-off TFT can be obtained with a high yield.
The electron carrier concentration can be measured by Hall effect measurement.

  In the present invention, an amorphous oxide refers to an oxide that exhibits a halo pattern in an X-ray diffraction spectrum and does not exhibit a specific diffraction line.

The lower limit of the electron carrier concentration in the amorphous oxide of the present invention is not particularly limited as long as it can be applied as a TFT channel layer. The lower limit is, for example, 10 ¹² / cm ³ .
Therefore, in the present invention, the material, composition ratio, production conditions, etc. of the amorphous oxide are controlled as in the examples described later, for example, the electron carrier concentration is 10 ¹² / cm ³ or more and 10 ¹⁸ / cm ^3. Less than. More preferably, it is in the range of 10 ¹³ / cm ³ or more and 10 ¹⁷ / cm ³ or less, and more preferably 10 ¹⁵ / cm ³ or more and 10 ¹⁶ / cm ³ or less.
As the amorphous oxide, in addition to InZnGa oxide, In oxide, In _x Zn _1-x oxide (0.2 ≦ x ≦ 1), In _x Sn _1-x oxide (0.8 ≦ x ≦ 1) or In _x (Zn, Sn) _1-x oxide (0.15 ≦ x ≦ 1).
Note that an In _x (Zn, Sn) _1-x oxide can be described as an In _x (Zn _y Sn _1-y ) _1-x oxide, and the range of y is 1 to 0.

Note that in the case of an In oxide containing no Zn and Sn, part of In can be substituted with Ga. That is, it is the case of In _x Ga _1-x oxide (0 ≦ x ≦ 1). Hereinafter, an amorphous oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ successfully produced by the present inventors will be described in detail.

The oxide includes In—Ga—Zn—O, the composition in the crystalline state is represented by InGaO ₃ (ZnO) _m (m is a natural number less than 6), and the electron carrier concentration is 10 ¹⁸ / cm ^3. It is characterized by being less than.

The oxide includes In—Ga—Zn—Mg—O, and the composition of the crystalline state is InGaO ₃ (Zn _1−x Mg _× O) _m (m is a natural number less than 6, 0 <x ≦ 1 The electron carrier concentration is less than 10 ¹⁸ / cm ³ .

Note that it is also preferable to design a film formed using these oxides so that the electron mobility exceeds 1 cm ² / (V · sec).

When the above film is used for a channel layer, transistor characteristics with a normally-off gate current of less than 0.1 microampere and an on / off ratio of more than 10 ³ can be realized. In addition, a flexible TFT having transparency or translucency with respect to visible light is realized.

  The film is characterized in that the electron mobility increases as the number of conduction electrons increases. As the substrate on which the transparent film is formed, a glass substrate, a resin plastic substrate, a plastic film, or the like can be used.

When the amorphous oxide film is used as a channel layer, a gate insulating layer of a mixed crystal compound containing at least one of Al ₂ O ₃ , Y ₂ O ₃ , or HfO ₂ or a compound thereof is used. Available for membranes.

  In addition, it is also preferable to form a film in an atmosphere containing oxygen gas without intentionally adding impurity ions for increasing electric resistance to the amorphous oxide.

  The present inventors have found that the semi-insulating oxide amorphous thin film has a unique characteristic that the electron mobility increases as the number of conduction electrons increases. Then, a TFT was formed using the film, and it was found that transistor characteristics such as an on / off ratio, a saturation current in a pinch-off state, and a switch speed were further improved. That is, it has been found that a normally-off type TFT can be realized by using an amorphous oxide.

When an amorphous oxide thin film is used as the channel layer of the film transistor, the electron mobility can exceed 1 cm ² / (V · sec), preferably 5 cm ² / (V · sec).

When the electron carrier concentration is less than 10 ¹⁸ / cm ³ , preferably less than 10 ¹⁶ / cm ³ , the current between the drain and source terminals when off (when no gate voltage is applied) is less than 10 microamperes, Preferably it can be less than 0.1 microamperes.

When the film is used, when the electron mobility is more than 1 cm ² / (V · sec), preferably more than 5 cm ² / (V · sec), the saturation current after pinch-off can be more than 10 microamperes, The on / off ratio can be greater than 10 ³ .

In the TFT, in a pinch-off state, a high voltage is applied to the gate terminal, and high-density electrons exist in the channel.
Therefore, according to the present invention, the saturation current value can be further increased by the amount of increase in electron mobility. As a result, improvements in transistor characteristics such as an increase in on / off ratio, an increase in saturation current, and an increase in switching speed can be expected.

  In a normal compound, when the number of electrons increases, electron mobility decreases due to collisions between electrons.

The TFT structure includes a stagger (top gate) structure in which a gate insulating film and a gate terminal are sequentially formed on a semiconductor channel layer, or a reverse structure in which a gate insulating film and a semiconductor channel layer are sequentially formed on a gate terminal. A staggered (bottom gate) structure can be used.
(First film formation method: PLD method)
An amorphous oxide thin film whose composition in the crystalline state is represented by InGaO ₃ (ZnO) _m (m is a natural number less than 6) is amorphous up to a high temperature of 800 ° C. or higher when the value of m is less than 6. Quality condition is kept stable. However, as the value of m increases, that is, the ratio of ZnO to InGaO ₃ increases, and as it approaches the ZnO composition, it becomes easier to crystallize.

  Therefore, the value of m is preferably less than 6 for the channel layer of the amorphous TFT.

As a film forming method, a vapor phase film forming method is preferably used with a polycrystalline sintered body having an InGaO ₃ (ZnO) _m composition as a target. Of the vapor deposition methods, sputtering and pulsed laser deposition are suitable. Furthermore, the sputtering method is most suitable from the viewpoint of mass productivity.

However, when the amorphous film is formed under normal conditions, oxygen vacancies mainly occur, and until now, the electron carrier concentration has been less than 10 ¹⁸ / cm ³ and the electric conductivity has not been reduced to 10 S / cm or less. It was. When such a film is used, a normally-off transistor cannot be formed.

The present inventors produced In—Ga—Zn—O produced by a pulse laser deposition method using the apparatus shown in FIG. Film formation was performed using a PLD film formation apparatus as shown in FIG.
In the figure, 701 is an RP (rotary pump), 702 is a TMP (turbo molecular pump), 703 is a preparation chamber, 704 is an RHEED electron gun, and 705 is a substrate holding means for rotating and moving the substrate up and down. 706 is a laser incident window, 707 is a substrate, 708 is a target, 709 is a radical source, 710 is a gas inlet, 711 is a target holding means for rotating and moving the target up and down, and 712 is a bypass line. Reference numeral 713 denotes a main line, 714 denotes a TMP (turbo molecular pump), 715 denotes an RP (rotary pump), 716 denotes a titanium getter pump, and 717 denotes a shutter. In the figure, 718 is an IG (ion vacuum gauge), 719 is a PG (Pirani vacuum gauge), 720 is a BG (Baratron vacuum gauge), and 721 is a growth chamber (chamber).

An In-Ga-Zn-O amorphous oxide semiconductor thin film was deposited on a SiO ₂ glass substrate (Corning 1737) by pulsed laser deposition using a KrF excimer laser. As a pre-deposition treatment, the substrate was degreased and cleaned with ultrasonic waves for 5 minutes each using acetone, ethanol, and ultrapure water, and then dried at 100 ° C. in air. As the polycrystalline target, an InGaO ₃ (ZnO) ₄ sintered body target (size 20 mmΦ5 mmt) was used. This is because, as a starting material, In ₂ O ₃ : Ga ₂ O ₃ : ZnO (each 4N reagent) is wet-mixed (solvent: ethanol), calcined (1000 ° C .: 2 h), dry pulverized, main sintered ( 1550 ° C: 2 hours). The electric conductivity of the target thus prepared was 90 (S / cm).

The film was formed while the ultimate vacuum in the growth chamber was 2 × 10 ⁻⁶ (Pa) and the oxygen partial pressure during growth was controlled to 6.5 (Pa). The partial pressure of oxygen in the chamber 721 is 6.5 Pa, and the substrate temperature is 25 ° C. The distance between the target 708 and the film formation substrate 707 is 30 (mm), and the power of the KrF excimer laser incident from the incident window 716 is 1.5-3 (mJ / cm ² / pulse). It is a range. The pulse width was 20 (nsec), the repetition frequency was 10 (Hz), and the irradiation spot diameter was 1 × 1 (mm square). Thus, film formation was performed at a film formation rate of 7 (nm / min).
The thin film obtained was subjected to grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) of the thin film, and no clear diffraction peak was observed. Thus, the produced In-Ga-Zn-O thin film Can be said to be amorphous.

Furthermore, as a result of measuring the X-ray reflectivity and analyzing the pattern, it was found that the mean square roughness (Rrms) of the thin film was about 0.5 nm and the film thickness was about 120 nm. As a result of X-ray fluorescence (XRF) analysis, the metal composition ratio of the thin film was In: Ga: Zn = 0.98: 1.02: 4.
The electrical conductivity was less than about ^10-2 S / cm. The electron carrier concentration is estimated to be about 10 ¹⁶ / cm ³ or less, and the electron mobility is estimated to be about 5 cm ² / (V · sec).
From the analysis of the light absorption spectrum, the energy band gap of the fabricated amorphous thin film was found to be about 3 eV. From the above, the fabricated In-Ga-Zn-O-based thin film exhibits an amorphous phase close to the composition of crystalline InGaO ₃ (ZnO) ₄ , has a small oxygen deficiency, and has a low electrical conductivity and is a transparent flat surface. It turned out to be a thin film.
This will be specifically described with reference to FIG. This figure shows a transparent amorphous oxide thin film composed of In-Ga-Zn-O and having a composition expressed by InGaO ₃ (ZnO) _m (m is a number less than 6) assuming a crystalline state. It shows the characteristics when created under the same conditions as the example. The characteristic diagram of FIG. 1 shows the change in the electron carrier concentration of the deposited oxide when the oxygen partial pressure is changed.
By forming a film in an atmosphere where the oxygen partial pressure is higher than 4.5 Pa under the same conditions as in this example, the electron carrier concentration can be reduced to less than 10 ¹⁸ / cm ³ as shown in FIG. did it. In this case, the temperature of the substrate is maintained at substantially room temperature without intentionally heating. In order to use a flexible plastic film as a substrate, the substrate temperature is preferably kept below 100 ° C.

If the oxygen partial pressure is further increased, the electron carrier concentration can be further reduced. For example, as shown in FIG. 1, in the InGaO ₃ (ZnO) ₄ thin film formed at a substrate temperature of 25 ° C. and an oxygen partial pressure of 5 Pa, the number of electron carriers could be further reduced to 10 ¹⁶ / cm ³ .
The obtained thin film had an electron mobility of more than 1 cm ² / (V · sec) as shown in FIG. However, in the pulse laser vapor deposition method of the present embodiment, when the oxygen partial pressure is set to 6.5 Pa or more, the surface of the deposited film becomes uneven, making it difficult to use it as a TFT channel layer.

Therefore, it is expressed by the composition InGaO ₃ (ZnO) _m (m is a number of less than 6) in a crystalline state by pulse laser deposition in an atmosphere having an oxygen partial pressure of more than 4.5 Pa, desirably more than 5 Pa and less than 6.5 Pa. If a transparent amorphous oxide thin film is used, a normally-off transistor can be formed.
Further, the electron mobility of the thin film was obtained to exceed 1 cm ² / V · second, and the on / off ratio could be increased to more than 10 ³ .
As described above, when an InGaZn oxide film is formed by the PLD method under the conditions shown in this embodiment, the oxygen partial pressure can be controlled to be 4.5 Pa or more and less than 6.5 Pa. desirable.
Note that, in order to realize the electron carrier concentration of less than 10 ¹⁸ / cm ³ , the electron carrier concentration depends on the oxygen partial pressure conditions, the configuration of the film formation apparatus, the material and composition of the film formation, and the like.

Next, an amorphous oxide was produced under the condition of an oxygen partial pressure of 6.5 Pa in the above apparatus, and a top gate type MISFET element shown in FIG. 5 was produced. Specifically, first, a semi-insulating amorphous InGaO ₃ (ZnO) having a thickness of 120 nm used as a channel layer (2) is formed on the glass substrate (1) by the above-described method for producing an amorphous In—Ga—Zn—O thin film. _Four films were formed.
Further, an InGaO ₃ (ZnO) ₄ film and a gold film having a large electric conductivity were stacked in a thickness of 30 nm by a pulse laser deposition method with an oxygen partial pressure in the chamber of less than 1 Pa. Then, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method. Finally, a Y ₂ O ₃ film used as the gate insulating film (3) is formed by electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 10 ^-3 A when 0.5 MV / cm is applied) / cm ² ), and a gold film was formed thereon. And the gate terminal (4) was formed by the photolithographic method and the lift-off method.
FIG. 6 shows the current-voltage characteristics of the MISFET element measured at room temperature. As the drain voltage V _DS increases, the drain current I _DS increases, which indicates that the channel is an n-type semiconductor. This is consistent with the fact that amorphous In-Ga-Zn-O based semiconductors are n-type. I _DS shows the behavior of a typical semiconductor transistor that saturates (pinch off) at about V _DS = 6 V. When the gain characteristic was examined, the threshold value of the gate voltage V _GS when V _DS = 4 V was applied was about −0.5 V. When V _G = 10 V, a current of I _DS = 1.0 × 10 ⁻⁵ A flowed. This corresponds to the fact that carriers can be induced in the In-Ga-Zn-O amorphous semiconductor thin film of the insulator by the gate bias.

The on / off ratio of the transistor was more than 10 ³ . When the field effect mobility was calculated from the output characteristics, a field effect mobility of about 7 cm ² (Vs) ⁻¹ was obtained in the saturation region. A similar measurement was performed by irradiating the fabricated device with visible light, but no change in transistor characteristics was observed.
According to this embodiment, it is possible to realize a thin film transistor having a channel layer having a low electron carrier concentration, a high electrical resistance, and a high electron mobility.
The above-described amorphous oxide had excellent characteristics that the electron mobility increased with an increase in the electron carrier concentration and further exhibited degenerate conduction.
In this embodiment, a thin film transistor is formed on a glass substrate. However, since the film formation itself can be performed at room temperature, a substrate such as a plastic plate or a film can be used. Further, the amorphous oxide obtained in this example hardly absorbs visible light and can realize a transparent flexible TFT.

(Second film formation method: sputtering method (SP method))
A case where a film is formed by a high-frequency SP method using argon gas as an atmosphere gas will be described.
The SP method was performed using the apparatus shown in FIG. In the figure, reference numeral 807 denotes a film formation substrate, 808 denotes a target, 805 denotes a substrate holding means with a cooling mechanism, 814 denotes a turbo molecular pump, 815 denotes a rotary pump, and 817 denotes a shutter. Reference numeral 818 denotes an ion vacuum gauge, 819 denotes a Pirani vacuum gauge, 821 denotes a growth chamber (chamber), and 830 denotes a gate valve. As the film formation substrate 807, a SiO ₂ glass substrate (1737 manufactured by Corning) was prepared. As pre-deposition treatment, the substrate was subjected to ultrasonic degreasing and cleaning with acetone, ethanol, and ultrapure water for 5 minutes each and then dried at 100 ° C. in air.
As a target material, a polycrystalline sintered body (size 20 mmΦ5 mmt) having an InGaO ₃ (ZnO) ₄ composition was used.

In this sintered body, as a starting material, In ₂ O ₃ : Ga ₂ O ₃ : ZnO (each 4N reagent) is wet-mixed (solvent: ethanol), calcined (1000 ° C .: 2 h), dry pulverized, main-fired It was produced after crystallization (1550 ° C: 2h). The electric conductivity of the target 808 was 90 (S / cm) and was in a semi-insulating state.

The ultimate vacuum in the growth chamber 821 is 1 × 10 ⁻⁴ (Pa), and the total pressure of oxygen gas and argon gas during growth is constant in the range of 4 to 0.1 × 10 ⁻¹ (Pa). The value of And the partial pressure ratio of argon gas and oxygen was changed, and the oxygen partial pressure was changed in the range of 10 < ^-3 > -2 * 10 <^-1> (Pa).

  The substrate temperature was room temperature, and the distance between the target 808 and the deposition target substrate 807 was 30 (mm).

The input power was RF 180 W, and the film formation rate was 10 (nm / min).
With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, but no clear diffraction peak was detected, and the produced In—Zn—Ga—O-based film was amorphous. It was shown to be a membrane.

  Furthermore, as a result of measuring the X-ray reflectivity and analyzing the pattern, it was found that the mean square roughness (Rrms) of the thin film was about 0.5 nm and the film thickness was about 120 nm. As a result of X-ray fluorescence (XRF) analysis, the metal composition ratio of the thin film was In: Ga: Zn = 0.98: 1.02: 4.

The oxygen partial pressure of the atmosphere during film formation was changed, and the electrical conductivity of the obtained amorphous oxide film was measured. The result is shown in FIG.
As shown in FIG. 3, the electrical conductivity could be reduced to less than 10 S / cm by forming a film in an atmosphere having a high oxygen partial pressure exceeding 3 × 10 ⁻² Pa.
By further increasing the oxygen partial pressure, the number of electron carriers could be reduced.
For example, as shown in FIG. 3, in an InGaO ₃ (ZnO) ₄ thin film formed at a substrate temperature of 25 ° C. and an oxygen partial pressure of 10 ⁻¹ Pa, the electrical conductivity is further reduced to about 10 ⁻¹⁰ S / cm. I was able to. In addition, the InGaO ₃ (ZnO) ₄ thin film formed at an oxygen partial pressure exceeding 10 ⁻¹ Pa had an electrical resistance that was too high to measure the electrical conductivity. In this case, although the electron mobility could not be measured, the electron mobility was estimated to be about 1 cm ² / V · second by extrapolating from the value in the film having a high electron carrier concentration.

The transistor is composed of In-Ga-Zn-O produced by sputter deposition in an argon gas atmosphere with an oxygen partial pressure of more than 3 × 10 ^-2 Pa, preferably more than 5 × 10 ^-1 Pa. A transparent amorphous oxide thin film represented by ₃ (ZnO) _m (m is a natural number of less than 6) was used. As a result, a transistor having a normally-off and an on / off ratio exceeding 10 ³ could be formed.
In the case of using the apparatus and materials shown in this embodiment, the oxygen partial pressure during film formation by sputtering is, for example, in the range of 3 × 10 ⁻² Pa to 5 × 10 ⁻¹ Pa. In the thin film formed by the pulse laser deposition method and the sputtering method, as shown in FIG. 2, the electron mobility increases as the number of conduction electrons increases.

  As described above, by controlling the oxygen partial pressure, oxygen defects can be reduced, and as a result, the electron carrier concentration can be reduced. In the amorphous state, unlike the polycrystalline state, there is essentially no particle interface, so that an amorphous thin film with high electron mobility can be obtained.

Even when a polyethylene terephthalate (PET) film having a thickness of 200 μm was used instead of the glass substrate, the obtained InGaO ₃ (ZnO) ₄ amorphous oxide film showed similar characteristics. If polycrystalline InGaO ₃ (Zn _1-x Mg _x O) _m (m is a natural number less than 6 and 0 <x ≦ 1) is used as a target, a high-resistance amorphous material even under an oxygen partial pressure of less than 1 Pa. An InGaO ₃ (Zn _1-x Mg _x O) _m film can be obtained.

For example, when a target in which Zn is replaced with 80 at% Mg is used, the electron carrier concentration of the film obtained by the pulse laser deposition method is less than 10 ¹⁶ / cm ^{3 in} an atmosphere with an oxygen partial pressure of 0.8 Pa. (The electric resistance value is about 10 ⁻² S / cm).

The electron mobility of such a film is lower than that of the Mg-free film, but the degree is small, and the electron mobility at room temperature is about 5 cm ² / (V · sec), which is one digit that of amorphous silicon. A large value is shown. When the film is formed under the same conditions, both the electrical conductivity and the electron mobility decrease as the Mg content increases, so the Mg content is preferably more than 20% and less than 85% (x). 0.2 <x <0.85).

In the thin film transistor using the above-described amorphous oxide film, a gate insulating film is preferably formed using a mixed crystal compound including at least two of Al ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , or a compound thereof.

If there is a defect at the interface between the gate insulating thin film and the channel layer thin film, the electron mobility is lowered and the transistor characteristics are hysteresis. Further, the leakage current varies greatly depending on the type of the gate insulating film. For this purpose, it is necessary to select a gate insulating film suitable for the channel layer. If an Al ₂ O ₃ film is used, leakage current can be reduced. Further, the hysteresis can be reduced by using a Y ₂ O ₃ film. Further, if a high dielectric constant HfO ₂ film is used, the electron mobility can be increased. Further, by using mixed crystals of these films, a TFT with small leakage current and hysteresis and high electron mobility can be formed. In addition, since the gate insulating film formation process and the channel layer formation process can be performed at room temperature, both a staggered structure and an inverted staggered structure can be formed as the TFT structure.

  The TFT thus formed is a three-terminal element having a gate terminal, a source terminal, and a drain terminal. In this TFT, a semiconductor thin film formed on an insulating substrate such as ceramic, glass, or plastic is used as a channel layer through which electrons or holes move. Further, the TFT is an active element having a function of switching a current between the source terminal and the drain terminal by applying a voltage to the gate terminal to control a current flowing in the channel layer.

  It is important in the present invention that the desired electron carrier concentration can be achieved by controlling the oxygen deficiency.

  In the above description, the amount of oxygen (oxygen deficiency) in the amorphous oxide film is controlled by performing it in an atmosphere containing oxygen at a predetermined concentration during film formation. However, it is also preferable to control (reduce or increase) the amount of oxygen vacancies after film formation by post-processing the oxide film in an atmosphere containing oxygen.

  In order to effectively control the oxygen deficiency, the temperature in the atmosphere containing oxygen is 0 ° C. or higher and 300 ° C. or lower, preferably 25 ° C. or higher and 250 ° C. or lower, more preferably 100 ° C. or higher and 200 ° C. or lower. Is good.

Needless to say, the film formation may be performed in an atmosphere containing oxygen, and the post-treatment after the film formation may be performed in the atmosphere containing oxygen. If a predetermined electron carrier concentration (less than 10 ¹⁸ / cm ³ ) can be obtained, oxygen partial pressure control is not performed during film formation, and post-treatment after film formation is performed in an atmosphere containing oxygen. Also good.

Note that the lower limit of the electron carrier concentration in the present invention is, for example, 10 ¹⁴ / cm ³ or more, although it depends on what kind of element, circuit or device the oxide film obtained is used for.
(Expansion of materials)
Furthermore, as a result of expanding the composition system and researching it, an amorphous oxide composed of an oxide of at least one of Zn, In and Sn, an amorphous material with a low electron carrier concentration and a high electron mobility. It has been found that an oxide film can be produced.

  Further, the present inventors have found that this amorphous oxide film has a unique characteristic that the electron mobility increases as the number of conduction electrons increases.

  A TFT is formed using the film, and a normally-off type TFT excellent in transistor characteristics such as an on / off ratio, a saturation current in a pinch-off state, and a switch speed can be formed.

  Of the above Zn, In, and Sn, a composite oxide containing the following elements can be formed on an amorphous oxide containing at least one element.

  Group 2 element M2 having an atomic number smaller than Zn (M2 is Mg, Ca), Group 3 element M3 having an atomic number smaller than In (M3 is B, Al, Ga, Y), and an atomic number smaller than Sn 4 The genus element M4 (M4 is Si, Ge, Zr), the genus element M5 (M5 is V, Nb, Ta) and at least one element of Lu and W.

In the present invention, an oxide having the following characteristics (a) to (h) can be used.
(A) An amorphous oxide having an electron carrier concentration at room temperature of less than 10 ¹⁸ / cm ³ .
(B) An amorphous oxide characterized by an increase in electron carrier concentration and an increase in electron mobility.

Here, room temperature refers to a temperature of about 0 ° C. to 40 ° C. Amorphous refers to a compound in which only a halo pattern is observed in an X-ray diffraction spectrum and does not show a specific diffraction line. Moreover, the electron mobility here means the electron mobility obtained by Hall effect measurement.
(C) The amorphous oxide described in the above (a) or (b), wherein the electron mobility at room temperature is more than 0.1 cm ² / V · sec.
(D) The amorphous oxide described in any one of (b) to (c) above showing degenerate conduction. Here, degenerate conduction refers to a state in which the thermal activation energy in the temperature dependence of electrical resistance is 30 meV or less.
(E) The amorphous oxide described in any one of (a) to (d) above, which contains at least one element of Zn, In, and Sn as a constituent component.
(F) To the amorphous oxide described in (e) above, the Group 2 element M2 having an atomic number smaller than Zn (M2 is Mg, Ca), the Group 3 element M3 having an atomic number smaller than In (M3 is B, Among Al, Ga, Y), Sn group 4 element M4 (M4 is Si, Ge, Zr), group 5 element M5 (M5 is V, Nb, Ta) and Lu, W An amorphous oxide film containing at least one element.
(G) the crystal composition in a state that _{In 1-x M3 x O 3} (Zn 1-y M2 y O) m (0 ≦ x, y ≦ 1, m is 0 or less than 6 natural number) is a compound alone or m The amorphous oxide film according to any one of (a) to (f), which is a mixture of different compounds. M3 is, for example, Ga, and M2 is, for example, Mg.
(h) The amorphous oxide film according to the above (a) to (g) provided on a glass substrate, metal substrate, plastic substrate or plastic film.

  The present invention is (10) a field effect transistor using the amorphous oxide or the amorphous oxide film described above as a channel layer.

Note that a field effect type in which an amorphous oxide film having an electron carrier concentration of less than 10 ¹⁸ / cm ^{3 and more} than 10 ¹⁵ / cm ³ is used for a channel layer, and a gate terminal is arranged via a source terminal, a drain terminal, and a gate insulating film. A transistor is formed. When a voltage of about 5 V is applied between the source and drain terminals, the current between the source and drain terminals when no gate voltage is applied can be about 10 ⁻⁷ ampere.

The electron mobility of the oxide crystal increases as the s orbital overlap of the metal ions increases, and the oxide crystal of Zn, In, Sn having a large atomic number has a value of 0.1 to 200 cm ² / (V · sec). It has a large electron mobility.

  Further, in the oxide, oxygen and metal ions are ionically bonded.

  Therefore, even in the amorphous state where there is no chemical bond directionality, the structure is random, and the bond direction is non-uniform, the electron mobility should be comparable to the electron mobility in the crystalline state. Is possible.

On the other hand, by substituting Zn, In, and Sn with an element having a small atomic number, the electron mobility is reduced. As a result, the electron mobility of the amorphous oxide according to the present invention is about 0.01 cm ² / (V · second) to 20 cm ² / (V · second).

In the case where a channel layer of a transistor is formed using the above oxide, in the transistor, a mixed crystal compound containing at least two of Al ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , or a compound thereof is used as a gate insulating film. It is preferable.

If there is a defect at the interface between the gate insulating thin film and the channel layer thin film, the electron mobility is lowered and the transistor characteristics are hysteresis. Further, the leakage current varies greatly depending on the type of the gate insulating film. For this purpose, it is necessary to select a gate insulating film suitable for the channel layer. If an Al ₂ O ₃ film is used, leakage current can be reduced. Further, the hysteresis can be reduced by using a Y ₂ O ₃ film. Furthermore, if a high dielectric constant HfO ₂ film is used, the field effect mobility can be increased. In addition, by using a film made of a mixed crystal of these compounds, a TFT with small leakage current and hysteresis and high field effect mobility can be formed. In addition, since the gate insulating film formation process and the channel layer formation process can be performed at room temperature, both a staggered structure and an inverted staggered structure can be formed as the TFT structure.

The In ₂ O ₃ oxide film can be formed by a vapor phase method, and an amorphous film can be obtained by adding about 0.1 Pa of moisture to the atmosphere during film formation.

In addition, although it is difficult to obtain an amorphous film of ZnO and SnO ₂ , an amorphous film can be obtained by adding In ₂ O ₃ to about 20 atomic% in the case of ZnO and about 90 atomic% in the case of SnO _2. Can be obtained. In particular, in order to obtain a Sn—In—O-based amorphous film, nitrogen gas may be introduced into the atmosphere at about 0.1 Pa.

  From the group II element M2 (M2 is Mg, Ca) having an atomic number smaller than Zn, and the group 3 element M3 (M3 is B, Al, Ga, Y), Sn having an atomic number smaller than In Consists of at least one complex oxide of group 4 element M4 having a small atomic number (M4 is Si, Ge, Zr), group 5 element M5 (M5 is V, Nb, Ta) and Lu, W Can be added.

  Thereby, the amorphous film at room temperature can be further stabilized. Moreover, the composition range in which an amorphous film is obtained can be expanded.

  In particular, the addition of B, Si, and Ge, which has strong covalent bonding, is effective for stabilizing the amorphous phase, and the complex phase composed of ions having a large difference in ionic radius stabilizes the amorphous phase.

  For example, in the case of the In—Zn—O system, it is difficult to obtain an amorphous film that is stable at room temperature unless In is in a composition range of more than about 20 atomic%. With this composition range, a stable amorphous film can be obtained.

In film formation by a vapor phase method, an amorphous oxide film having an electron carrier concentration of less than 10 ¹⁸ / cm ^{3 and more} than 10 ¹⁵ / cm ³ can be obtained by controlling the atmosphere.

As a film formation method of the amorphous oxide, it is preferable to use a vapor phase method such as a pulse laser deposition method (PLD method), a sputtering method (SP method), or an electron beam evaporation method. Among the gas phase methods, the PLD method is suitable from the viewpoint of easily controlling the composition of the material system, and the SP method is suitable from the viewpoint of mass productivity. However, the film forming method is not limited to these methods.
(Formation of In-Zn-Ga-O-based amorphous oxide film by PLD method)
An In—Zn—Ga—O amorphous oxide film was deposited on a glass substrate (1737 manufactured by Corning) by a PLD method using a KrF excimer laser. At this time, polycrystalline sintered bodies having InGaO ₃ (ZnO) and InGaO ₃ (ZnO) ₄ compositions were used as targets, respectively.

  As the film forming apparatus, the apparatus described in FIG. 14 described above was used, and the film forming conditions were the same as in the case of using the apparatus.

  The substrate temperature is 25 ° C. The obtained film was subjected to grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree, SAXS; small angle X-ray scattering method) on the film surface. Then, no clear diffraction peak was detected, indicating that both In—Zn—Ga—O-based films prepared from two types of targets were amorphous films.

  Furthermore, the X-ray reflectivity measurement of the In—Zn—Ga—O-based amorphous oxide film on the glass substrate was performed and the pattern was analyzed. As a result, the mean square roughness (Rrms) of the thin film was about 0.5 nm. The film thickness was found to be about 120 nm.

As a result of X-ray fluorescence (XRF) analysis, the metal composition ratio of a film obtained using a polycrystalline sintered body having an InGaO ₃ (ZnO) composition as a target was In: Ga: Zn = 1.1: 1.1: 0. .9. The metal composition ratio of the film obtained using the polycrystalline sintered body having the InGaO (ZnO) ₄ composition as a target was In: Ga: Zn = 0.98: 1.02: 4.

The oxygen partial pressure of the atmosphere during film formation was changed, and the electron carrier concentration of the amorphous oxide film obtained using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target was measured. The result is shown in FIG. By forming a film in an atmosphere having an oxygen partial pressure of over 4.2 Pa, the electron carrier concentration could be lowered to less than 10 ¹⁸ / cm ³ . In this case, the temperature of the substrate is maintained at substantially room temperature without intentionally heating. When the oxygen partial pressure was less than 6.5 Pa, the surface of the obtained amorphous oxide film was flat.

When the oxygen partial pressure is 5 Pa, the electron carrier concentration of an amorphous oxide film obtained using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target is 10 ¹⁶ / cm ³ , and the electric conductivity is 10 ^−2. S / cm. The electron mobility was estimated to be about 5 cm ² / V · sec. From the analysis of the light absorption spectrum, the band gap energy width of the fabricated amorphous oxide film was found to be about 3 eV.

Increasing the oxygen partial pressure further reduced the electron carrier concentration. As shown in FIG. 1, an In—Zn—Ga—O-based amorphous oxide film formed at a substrate temperature of 25 ° C. and an oxygen partial pressure of 6 Pa has an electron carrier concentration of 8 × 10 ¹⁵ / cm ³ (electric conduction: about 8 × 10 ⁻³ S / cm). The obtained film was estimated to have an electron mobility exceeding 1 cm ² / (V · sec). However, in the PLD method, when the oxygen partial pressure is set to 6.5 Pa or more, the surface of the deposited film becomes uneven, making it difficult to use as a TFT channel layer.

Regarding the In—Zn—Ga—O amorphous oxide film formed with different oxygen partial pressures, targeting a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition, the relationship between the electron carrier concentration and the electron mobility is as follows. Examined. The result is shown in FIG. It is shown that as the electron carrier concentration increases from 10 ¹⁶ / cm ³ to 10 ²⁰ / cm ³ , the electron mobility increases from about 3 cm ² / (V · sec) to about 11 cm ² / (V · sec). It was done. Further, with regard InGaO 3 _(ZnO) amorphous oxide film obtained as a target, a polycrystalline sintered body having a composition, similar trend was observed.

Even when a polyethylene terephthalate (PET) film having a thickness of 200 μm was used instead of the glass substrate, the obtained In—Zn—Ga—O-based amorphous oxide film exhibited similar characteristics.
(Formation of In-Zn-Ga-Mg-O-based amorphous oxide film by PLD method)
Polycrystalline InGaO ₃ (Zn _1-x Mg _x O) ₄ (0 <x ≦ 1) was used as a target, and InGaO ₃ (Zn _1-x Mg _x O) ₄ (0 <x ≦ 1) A film was formed.

  As the film forming apparatus, the apparatus shown in FIG. 14 was used.

As a film formation substrate, a SiO ₂ glass substrate (1737 manufactured by Corning) was prepared. As a pretreatment, the substrate was subjected to ultrasonic degreasing cleaning with acetone, ethanol, and ultrapure water for 5 minutes each, and then dried at 100 ° C. in air. As a target, an InGa (Zn _1-x Mg _x O) ₄ (x = 1-0) sintered body (size 20 mmΦ5 mmt) was used.

The target is starting material In ₂ O ₃ : Ga ₂ O ₃ : ZnO: MgO (each 4N reagent), wet mixing (solvent: ethanol), calcining (1000 ° C: 2h), dry grinding, main sintering (1550 (C: 2h).

The growth chamber reaching vacuum was 2 × 10 ⁻⁶ (Pa), and the oxygen partial pressure during growth was 0.8 (Pa). The substrate temperature was room temperature (25 ° C.), and the distance between the target and the deposition target substrate was 30 (mm).

The power of the KrF excimer laser is 1.5 (mJ / cm ² / pulse), the pulse width is 20 (nsec), the repetition frequency is 10 (Hz), and the irradiation spot diameter is 1 × 1 (mm square) ).

  The film formation rate was 7 (nm / min).

  The atmosphere is an oxygen partial pressure of 0.8 Pa, and the substrate temperature is 25 ° C. With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, but no clear diffraction peak was detected, and the produced In—Zn—Ga—Mg—O-based film Was shown to be an amorphous film. The surface of the obtained film was flat.

  The electric conductivity, electron carrier concentration, and electron mobility x of an In—Zn—Ga—Mg—O-based amorphous oxide film formed in an atmosphere having an oxygen partial pressure of 0.8 Pa using targets with different x values. The value dependency was examined.

The result is shown in FIG. It was shown that when the x value exceeds 0.4, the electron carrier concentration can be made less than 10 ¹⁸ / cm ³ in the amorphous oxide film formed by the PLD method in an atmosphere having an oxygen partial pressure of 0.8 Pa. Further, in the amorphous oxide film having an x value exceeding 0.4, the electron mobility was more than 1 cm ² / V · second.

As shown in FIG. 4, when a target in which Zn is replaced with 80 atomic% Mg is used, the electron carrier concentration of the film obtained by the pulse laser deposition method is 10 ¹⁶ / in an atmosphere with an oxygen partial pressure of 0.8 Pa. It can be less than cm ³ (the electrical resistance is about 10 ⁻² S / cm). The electron mobility of such a film is lower than that of the Mg-free film, but the degree is small, and the electron mobility at room temperature is about 5 cm ² / (V · sec), which is one digit that of amorphous silicon. A large value is shown. When the film is formed under the same conditions, both the electrical conductivity and the electron mobility decrease with an increase in the Mg content. Therefore, the Mg content is preferably more than 20 atomic% and less than 85 atomic% ( x is 0.2 <x <0.85), and more preferably 0.5 <x <0.85. Even when a polyethylene terephthalate (PET) film having a thickness of 200 μm is used instead of the glass substrate, the obtained InGaO ₃ (Zn _1-x Mg _x O) ₄ (0 <x ≦ 1) amorphous oxide film is Showed similar characteristics.
(In ₂ O ₃ amorphous oxide film deposition by PLD method)
An In ₂ O ₃ film was formed on a 200 μm thick PET film by using a PLD method using a KrF excimer laser and targeting an In ₂ O ₃ polycrystalline sintered body.

As the apparatus, the apparatus shown in FIG. 14 was used. A SiO ₂ glass substrate (1737 manufactured by Corning) was prepared as a film formation substrate.

  As a pretreatment of this substrate, ultrasonic degreasing was performed for 5 minutes each with acetone, ethanol, and ultrapure water, and then dried at 100 ° C. in air.

As a target, an In ₂ O ₃ sintered body (size 20 mmΦ5 mmt) was used. This was prepared by calcining the starting material In ₂ O ₃ (4N reagent) through calcining (1000 ° C .: 2 h), dry grinding and main sintering (1550 ° C .: 2 h).

The growth chamber reaching vacuum was 2 × 10 ⁻⁶ (Pa), the oxygen partial pressure during growth was 5 (Pa), and the substrate temperature was room temperature.

  The oxygen partial pressure was 5 Pa, the water vapor partial pressure was 0.1 Pa, and 200 W was applied to the oxygen radical generator to generate oxygen radicals.

The distance between the target and the deposition substrate is 40 (mm), the power of the KrF excimer laser is 0.5 (mJ / cm ² / pulse), the pulse width is 20 (nsec), the repetition frequency is 10 (Hz), The irradiation spot diameter was 1 × 1 (mm square). The film formation rate was 3 (nm / min).

  Regarding the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, and no clear diffraction peak was detected, and the produced In-O film was an amorphous film. It has been shown. The film thickness was 80 nm.

The obtained In—O amorphous oxide film had an electron carrier concentration of 5 × 10 ¹⁷ / cm ³ and an electron mobility of about 7 cm ² / V · sec.
(Formation of In-Sn-O amorphous oxide film by PLD method)
By using a PLD method using a KrF excimer laser, an In-Sn-O-based oxide film is formed on a PET film having a thickness of 200 [mu] m with a (In _{< 0.9} > _Sn0.1 ) _O3.1 polycrystalline sintered body as a target. Was deposited.

Specifically, a SiO ₂ glass substrate (Corning 1737) was prepared as a film formation substrate. As the substrate pretreatment, ultrasonic degreasing was performed for 5 minutes each using acetone, ethanol, and ultrapure water. Then, it was dried in air at 100 ° C. As a target, an In ₂ O ₃ —SnO ₂ sintered body (size 20 mmΦ5 mmt) was prepared. As a starting material, In ₂ O ₃ -SnO ₂ (4N reagent) is wet mixed (solvent: ethanol), calcined (1000 ° C: 2h), dry pulverized, and finally sintered (1550 ° C: 2h). can get.

  The substrate temperature is room temperature. The oxygen partial pressure was 5 (Pa), the nitrogen partial pressure was 0.1 (Pa), and 200 W was applied to the oxygen radical generator to generate oxygen radicals.

The distance between the target and the deposition substrate was 30 (mm), the power of the KrF excimer laser was 1.5 (mJ / cm ² / pulse), the pulse width was 20 (nsec), and the repetition frequency Was 10 (Hz), and the irradiation spot diameter was 1 × 1 (mm square). The film formation rate was 6 (nm / min).

  With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, but no clear diffraction peak was detected, and the produced In—Sn—O film was an amorphous film. It was shown that there is.

The obtained In—Sn—O amorphous oxide film had an electron carrier concentration of 8 × 10 ¹⁷ / cm ³ and an electron mobility of about 5 cm 2 / V · sec. The film thickness was 100 nm.
(Formation of In-Ga-O amorphous oxide film by PLD method)
A SiO ₂ glass substrate (1737 manufactured by Corning) was prepared as a film formation substrate. As a pretreatment of the substrate, ultrasonic degreasing cleaning was performed for 5 minutes each using acetone, ethanol, and ultrapure water, and then dried at 100 ° C. in air.

As a target, an (In ₂ O ₃ ) _1-x- (Ga ₂ O ₃ ) _x (X = 0-1) sintered body (size 20 mmΦ5 mmt) was prepared. For example, when x = 0.1, the target is an (In _0.9 Ga _0.1 ) ₂ O ₃ polycrystalline sintered body.

This consists of starting material: In ₂ O ₃ -Ga ₂ O ₂ (4N reagent), wet mixing (solvent: ethanol), calcining (1000 ° C: 2h), dry grinding, main sintering (1550 ° C: 2h) It is obtained through

The growth chamber reaching vacuum was 2 × 10 ⁻⁶ (Pa), and the oxygen partial pressure during growth was 1 (Pa).

The substrate temperature is room temperature, the distance between the target and the deposition substrate is 30 (mm), the power of the KrF excimer laser is 1.5 (mJ / cm ² / pulse), the pulse width is 20 (nsec), The repetition frequency was 10 (Hz), and the irradiation spot diameter was 1 × 1 (mm square). The film formation rate was 6 (nm / min).

  The substrate temperature is 25 ° C. The oxygen partial pressure was 1 Pa. The resulting film was subjected to grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) on the film surface. Then, a clear diffraction peak was not detected, indicating that the manufactured In—Ga—O-based film was an amorphous film. The film thickness was 120 nm.

The obtained In—Ga—O amorphous oxide film had an electron carrier concentration of 8 × 10 ¹⁶ / cm ³ and an electron mobility of about 1 cm 2 / V · sec.
(Production of TFT element using In—Zn—Ga—O amorphous oxide film (glass substrate))
Fabrication of TFT Element A top gate TFT element shown in FIG. 5 was fabricated.

First, on a glass substrate (1), a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition is used as a target, and the above-described PLD apparatus is used under the condition of an oxygen partial pressure of 5 Pa. An O-based amorphous oxide film was prepared. An In-Ga-Zn-O-based amorphous film having a thickness of 120 nm used as the channel layer (2) was formed.

  Further, an In—Ga—Zn—O-based amorphous film and a gold film having a high electric conductivity were stacked by 30 nm by the PLD method with an oxygen partial pressure in the chamber of less than 1 Pa. Further, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method.

Finally, a Y ₂ O ₃ film used as the gate insulating film (3) was formed by electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 10 ^-3 A when 0.5 MV / cm applied) / cm ² ). A gold film was formed thereon, and a gate terminal (4) was formed by a photolithography method and a lift-off method. The channel length was 50 μm and the channel width was 200 μm.

FIG. 6 shows the current-voltage characteristics of the TFT element measured at room temperature. As the drain voltage V _DS increases, the drain current I _DS increases, indicating that the channel is n-type conductive.

This is consistent with the fact that the amorphous In—Ga—Zn—O amorphous oxide film is an n-type conductor. I _DS shows the behavior of a typical semiconductor transistor that saturates (pinch off) at about V _DS = 6 V. When the gain characteristic was examined, the threshold value of the gate voltage V _GS when V _DS = 4 V was applied was about −0.5 V.

When V _G = 10 V, a current of I _DS = 1.0 × 10 ⁻⁵ A flowed. This corresponds to the fact that carriers can be induced in the insulator In-Ga-Zn-O amorphous oxide film by the gate bias.

The on / off ratio of the transistor was more than 10 ³ . When the field effect mobility was calculated from the output characteristics, a field effect mobility of about 7 cm ² (Vs) ⁻¹ was obtained in the saturation region. A similar measurement was performed by irradiating the fabricated device with visible light, but no change in transistor characteristics was observed.

In addition, it can apply as a channel layer of TFT by making the electron carrier density | concentration of an amorphous oxide less than 10 < ¹⁸ > / cm < ³ >. The electron carrier concentration is more preferably 10 ¹⁷ / cm ³ or less, and even more preferably 10 ¹⁶ / cm ³ or less.
(Production of TFT element using In-Zn-Ga-O-based amorphous oxide film (amorphous substrate))
The top gate type TFT element shown in FIG. 5 was produced. First, an In—Zn—Ga—O-based amorphous oxide film having a thickness of 120 nm used as a channel layer (2) on an polyethylene terephthalate (PET) film (1) by an PLD method in an atmosphere having an oxygen partial pressure of 5 Pa. Formed. The target was a polycrystalline sintered body having an InGaO ₃ (ZnO) composition.

Further, an In—Zn—Ga—O-based amorphous oxide film and a gold film having a high electric conductivity were stacked by 30 nm by a PLD method with an oxygen partial pressure in the chamber of less than 1 Pa. Further, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method. Finally, a gate insulating film (3) was formed by an electron beam evaporation method, gold was formed thereon, and a gate terminal (4) was formed by a photolithography method and a lift-off method. The channel length was 50 μm and the channel width was 200 μm. Three types of TFTs having the above-described structures using Y ₂ O ₃ (thickness: 140 nm), Al ₂ O ₃ (thickness: 130 μm) and HfO ₂ (thickness: 140 μm) as gate insulating films were prepared. .

Characteristic Evaluation of TFT Element The current-voltage characteristic measured at room temperature of the TFT formed on the PET film was the same as that shown in FIG. That is, as the drain voltage V _DS increases, the drain current I _DS increases, indicating that the channel has n-type conduction. This is consistent with the fact that the amorphous In—Ga—Zn—O-based amorphous oxide film is an n-type conductor. I _DS shows the behavior of a typical transistor that saturates (pinch off) at around V _DS = 6 V. Further, when V _g = 0, a current of I _DS = 2.0 × 10 ⁻⁵ A flowed when I _ds = 10 ⁻⁸ A and Vg = 10 V. This corresponds to the fact that electron carriers can be induced in the In-Ga-Zn-O amorphous oxide film of the insulator by the gate bias.

The on / off ratio of the transistor was more than 10 ³ . When the field effect mobility was calculated from the output characteristics, a field effect mobility of about 7 cm ² (Vs) ⁻¹ was obtained in the saturation region.

  The device prepared on the PET film was bent with a curvature radius of 30 mm, and the same transistor characteristics were measured, but no change was observed in the transistor characteristics. Further, the same measurement was performed by irradiating visible light, but no change in transistor characteristics was observed.

The TFT using the Al ₂ O ₃ film as the gate insulating film also showed transistor characteristics similar to those shown in FIG. 6, but when V _g = 0, I _ds = 10 ⁻⁸ A, Vg = 10 V Occasionally, a current of I _DS = 5.0 × 10 ⁻⁶ A flowed. On-off ratio of the transistor was 10 greater than ^2. When the field effect mobility was calculated from the output characteristics, a field effect mobility of about 2 cm ² (Vs) ⁻¹ was obtained in the saturation region.

The TFT using the HfO ₂ film as the gate insulating film also showed similar transistor characteristics to those shown in FIG. 6, but when V _g = 0, I _ds = 10 ⁻⁸ A, and Vg = 10 V, A current of I _DS = 1.0 × 10 ⁻⁶ A flowed. On-off ratio of the transistor was 10 greater than ^2. Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 10 cm ² (Vs) ⁻¹ was obtained in the saturation region.
(Creation of TFT element using In ₂ O ₃ amorphous oxide film by PLD method)
The top gate type TFT element shown in FIG. 5 was produced. First, an 80 nm thick In ₂ O ₃ amorphous oxide film used as a channel layer (2) was formed on a polyethylene terephthalate (PET) film (1) by a PLD method.

Further, an In ₂ O ₃ amorphous oxide film and a gold film having a high electric conductivity are formed by PLD method by setting the oxygen partial pressure in the chamber to less than 1 Pa and further applying zero voltage to the oxygen radical generator. Each was laminated with 30 nm. Then, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method. Finally, a Y ₂ O ₃ film used as a gate insulating film (3) is formed by an electron beam evaporation method, gold is formed thereon, and a gate terminal (4) is formed by a photolithography method and a lift-off method. Formed.

Characteristic Evaluation of TFT Element A current-voltage characteristic measured at room temperature of a TFT formed on a PET film was measured. As the drain voltage V _DS increases, the drain current I _DS increases, which indicates that the channel is an n-type semiconductor. This is consistent with the fact that the In—O amorphous oxide film is an n-type conductor. I _DS shows the behavior of a typical transistor that saturates (pinch off) at about V _DS = 5 V. In addition, when V _g = 0V, a current of 2 × 10 ⁻⁸ A flows, and when V _G = 10 V, a current of I _DS = 2.0 × 10 ⁻⁶ A flows. This corresponds to the fact that electron carriers can be induced in the In-O amorphous oxide film of the insulator by the gate bias.

On-off ratio of the transistor was about 10 ^2. Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 10 cm ² (Vs) ⁻¹ was obtained in the saturation region. The TFT element formed on the glass substrate also showed similar characteristics.

The device prepared on the PET film was bent with a radius of curvature of 30 mm and the same transistor characteristics were measured, but no change was observed in the transistor characteristics.
(Preparation of TFT element using In-Sn-O amorphous oxide film by PLD method)
The top gate type TFT element shown in FIG. 5 was produced. First, an In—Sn—O-based amorphous oxide film having a thickness of 100 nm used as a channel layer (2) was formed on a polyethylene terephthalate (PET) film (1) by a PLD method. Further, an In-Sn-O amorphous oxide film having a high electrical conductivity and a PLD method are used by setting the partial pressure of oxygen in the chamber to less than 1 Pa, further reducing the voltage applied to the oxygen radical generator to zero. Each gold film was laminated to 30 nm. Then, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method. Finally, a Y ₂ O ₃ film used as a gate insulating film (3) is formed by an electron beam evaporation method, gold is formed thereon, and a gate terminal (4) is formed by a photolithography method and a lift-off method. did.

Characteristic Evaluation of TFT Element A current-voltage characteristic measured at room temperature of a TFT formed on a PET film was measured. As the drain voltage V _DS increases, the drain current I _DS increases, which indicates that the channel is an n-type semiconductor. This is consistent with the fact that the In—Sn—O-based amorphous oxide film is an n-type conductor. I _DS shows the behavior of a typical transistor that saturates (pinch off) at about V _DS = 6 V. Further, when V _g = 0V, a current of 5 × 10 ⁻⁸ A flows, and when V _G = 10 V, a current of I _DS = 5.0 × 10 ⁻⁵ A flows. This corresponds to the fact that electron carriers could be induced in the insulator In—Sn—O amorphous oxide film by the gate bias.

The on / off ratio of the transistor was about 10 ³ . Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 5 cm ² (Vs) ⁻¹ was obtained in the saturation region. The TFT element formed on the glass substrate also showed similar characteristics.

The device prepared on the PET film was bent with a radius of curvature of 30 mm and the same transistor characteristics were measured, but no change was observed in the transistor characteristics.
(Preparation of TFT element using In-Ga-O amorphous oxide film by PLD method)
The top gate type TFT element shown in FIG. 5 was produced. First, an In—Ga—O-based amorphous oxide film having a thickness of 120 nm used as the channel layer (2) was formed on the polyethylene terephthalate (PET) film (1) by the film forming method shown in Example 6. . Further, an In—Ga—O amorphous oxide film having a high electrical conductivity is formed by the PLD method by setting the oxygen partial pressure in the chamber to less than 1 Pa and further applying zero voltage to the oxygen radical generator. And 30 nm thick gold films. Then, the drain terminal (5) and the source terminal (6) were formed by the photolithography method and the lift-off method. Finally, a Y ₂ O ₃ film used as a gate insulating film (3) is formed by an electron beam evaporation method, gold is formed thereon, and a gate terminal (4) is formed by a photolithography method and a lift-off method. did.

Characteristic Evaluation of TFT Element A current-voltage characteristic measured at room temperature of a TFT formed on a PET film was measured. As the drain voltage V _DS increases, the drain current I _DS increases, which indicates that the channel is an n-type semiconductor. This is consistent with the fact that the In—Ga—O amorphous oxide film is an n-type conductor. I _DS shows the behavior of a typical transistor that saturates (pinch off) at about V _DS = 6 V. Further, when V _g = 0V, a current of 1 × 10 ⁻⁸ A flows, and when V _G = 10 V, a current of I _DS = 1.0 × 10 ⁻⁶ A flows. This corresponds to the fact that electron carriers could be induced in the insulator In-Ga-O amorphous oxide film by the gate bias.

On-off ratio of the transistor was about 10 ^2. Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 0.8 cm ² (Vs) ⁻¹ was obtained in the saturation region. The TFT element formed on the glass substrate also showed similar characteristics.

  The device prepared on the PET film was bent with a radius of curvature of 30 mm and the same transistor characteristics were measured, but no change was observed in the transistor characteristics.

In addition, it can apply as a channel layer of TFT by making the electron carrier density | concentration of an amorphous oxide less than 10 < ¹⁸ > / cm < ³ >. The electron carrier concentration is more preferably 10 ¹⁷ / cm ³ or less, and even more preferably 10 ¹⁶ / cm ³ or less.

The transmittance of an amorphous oxide semiconductor layer composed of In-Ga-Zn-O, whose composition in the crystalline state is represented by InGa ₃ (Zn) _m (m is a natural number less than 6) at a thickness of 200 nm 7 shows. The band gap is about 3 eV. In particular, it has a strong sensitivity to ultraviolet light whose transmittance on the shorter wavelength side than 400 nm is 60% or less. In addition, it is composed of In-Ga-Zn-Mg-O, and the composition of the crystalline state is represented by InGaO ₃ (Zn _1-x Mg _x O) _m (m is a natural number less than 6, 0 <x ≦ 1) Amorphous oxide semiconductor layers also show similar transmittance and are sensitive to ultraviolet light.

  In addition, if organic dyes are used, amorphous oxide semiconductors mainly composed of In-Ga-Zn-O, which has a high electron mobility, will expand the sensitivity wavelength range of light from the ultraviolet wavelength range to the visible wavelength range. And high photoelectric conversion efficiency.

Examples are shown below.
Example 1
The optical sensor element shown in FIG. 8 is formed. A 100 nm Al electrode is formed on a glass substrate (Corning 1737) by vacuum deposition to form a lower electrode. Subsequently, an In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited by using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target by a pulse laser deposition method using a Kr excimer laser. On top of that, In ₂ O ₃ (SnO ₂ ) is stacked by about 20 nm at a substrate temperature of room temperature to form an upper electrode by vacuum deposition. In this way, an optical sensor is formed. In use, a negative bias is applied to the upper electrode on the light incident side, and a positive bias is applied to the lower electrode. And it can confirm that it functions as an ultraviolet sensor by irradiating an optical sensor element with the ultraviolet light of wavelength 365nm from a mercury lamp.
(Example 2)
The optical sensor element shown in FIG. 8 is formed. A 100 nm Al electrode is formed on a glass substrate (Corning 1737) by vacuum deposition to form a lower electrode. Subsequently, an In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited by using a polycrystalline sintered body having a composition of InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ by a pulse laser deposition method using a Kr excimer laser. Let The amorphous oxide semiconductor film is formed to a thickness of 100 nm. On top of that, In ₂ O ₃ (SnO ₂ ) is stacked by about 20 nm at a substrate temperature of room temperature to form an upper electrode by vacuum deposition. A voltage of 1 V is applied to the photosensor element thus formed. In use, a negative bias is applied to the upper electrode on the light incident side, and a positive bias is applied to the lower electrode. And it can confirm that it functions as an ultraviolet sensor by irradiating an optical sensor element with the ultraviolet light of wavelength 365nm from a mercury lamp.
(Example 3)
The optical sensor element shown in FIG. 9 is formed. A 100 nm Al electrode is formed on a glass substrate (Corning 1737) by vacuum deposition to form a lower electrode. Deposit 5 nm of In-Ga-Zn-O amorphous oxide semiconductor thin film using polycrystalline sintered compact with InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ composition as a target by pulsed laser deposition using Kr excimer laser . Subsequently, an In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited to a thickness of 5 nm using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target. This operation is repeated 20 times to laminate a 200 nm multilayer semiconductor layer. The amorphous oxide semiconductor film is formed to a thickness of 100 nm. On top of that, In ₂ O ₃ (SnO ₂ ) is deposited by vacuum deposition at a substrate temperature of room temperature to a thickness of about 20 nm to form the upper electrode.
Example 4
In the optical sensor element shown in Example 1, after depositing 100 nm of amorphous oxide semiconductor, 0.01% of cyanine dye was dissolved in a mixed solution of methanol and chloroform, and the amorphous oxide semiconductor was immersed in the dye solution. An organic dye is adsorbed onto the semiconductor. After volatilizing the organic solvent, about 20 nm of In ₂ O ₃ (SnO ₂ ) is laminated on the substrate at a room temperature of room temperature by vacuum deposition to form the upper electrode. A voltage of 1 V is applied to the photosensor element thus formed. A negative bias is applied to the upper electrode on the light incident side, and a positive bias is applied to the lower electrode. And it can confirm that it functions as an ultraviolet sensor by irradiating an optical sensor element with the ultraviolet light of wavelength 365nm from a mercury lamp.
(Example 5)
The optical sensor element shown in FIG. 9 is formed. A 100 nm Al electrode is formed on a glass substrate (Corning 1737) by vacuum deposition to form a lower electrode. Deposit 5 nm of In-Ga-Zn-O amorphous oxide semiconductor thin film using polycrystalline sintered compact with InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ composition as a target by pulsed laser deposition using Kr excimer laser . Subsequently, an In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited to a thickness of 5 nm using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target. This operation is repeated 20 times to laminate a 200 nm multilayer semiconductor layer. A voltage of 1 V is applied to the photosensor element thus formed. A negative bias is applied to the upper electrode on the light incident side, and a positive bias is applied to the lower electrode. And it can confirm that it functions as an ultraviolet sensor by irradiating an optical sensor element with the ultraviolet light of wavelength 365nm from a mercury lamp.
(Example 6)
A top gate type MISFET shown in FIG. 5 is formed as a TFT of a non-planar imager. As the substrate, a polyimide sheet having a thickness of 0.3 mm is used.

In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited on a polyimide sheet using a polycrystalline sintered body with InGaO ₃ (ZnO) ₄ composition as a target by pulsed laser deposition using KrF excimer laser . An amorphous oxide semiconductor layer InGaO ₃ (ZnO) ₄ film having a thickness of 120 nm used as a channel layer is formed. Further, an InGaO ₃ (ZnO) ₄ and a gold film having a large electric conductivity were laminated to 30 nm by a pulse laser deposition method with an oxygen partial pressure in the chamber of less than 1 Pa. Then, a drain terminal and a source terminal are formed by a photolithography method and a lift-off method. Finally, a Y ₂ O ₃ film used as a gate insulating film was formed by electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 10 ⁻³ A / cm ² when 0.5 MV / cm applied) ), And a gold film was formed thereon. Then, a gate terminal is formed by a photolithography method and a lift-off method.

The optical sensor element shown in FIG. 8 is formed as a sensor of a non-planar imager. An Al electrode having a thickness of 100 nm is formed on the polyimide substrate by vacuum deposition to form a lower electrode. Subsequently, an In-Ga-Zn-O-based amorphous oxide semiconductor thin film is deposited by using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target by a pulse laser deposition method using a Kr excimer laser. The amorphous oxide semiconductor film is formed to a thickness of 100 nm. The cyanine dye is dissolved in a mixed solution of methanol and chloroform by 0.01%, and the amorphous oxide semiconductor is immersed in the dye solution to adsorb and bond the organic dye onto the semiconductor.

On top of that, In ₂ O ₃ (SnO ₂ ) is deposited by vacuum deposition at a substrate temperature of room temperature to a thickness of about 20 nm to form the upper electrode. A 400 μm thick CdWO ₄ layer is deposited on the upper electrode as a scintillator by sputtering. Then, the X-ray sensor shown in FIG. 10 is formed. A circuit shown in FIG. 11 is formed by combining such a TFT and an X-ray sensor to constitute a non-planar imager shown in FIG. In such a non-planar imager, a small digital camera is installed as a non-measurement object to perform x-ray measurement. An image with less distortion can be obtained than an image using a conventional planar x-ray imager.
(Example 7)
A top gate type MISFET shown in FIG. 5 is created as a TFT of a non-planar imager. As the substrate, a plastic sheet having a thickness of 0.3 mm is used. An In-Ga-Zn-O-based amorphous oxide semiconductor thin film is deposited on a polyimide sheet by pulsed laser deposition using a KrF excimer laser. At this time, a polycrystalline sintered body having an InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ composition is used as a target. An amorphous oxide semiconductor layer InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ film having a thickness of 120 nm used as a channel layer is formed. Further, an InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ and a gold film having a _high electric conductivity are laminated to 30 nm by a pulse laser deposition method with an oxygen partial pressure in the chamber of less than 1 Pa. Then, a drain terminal and a source terminal are formed by a photolithography method and a lift-off method. Finally, a Y ₂ O ₃ film used as a gate insulating film was formed by electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 10 ⁻³ A / cm ² when 0.5 MV / cm applied) ), And a gold film was formed thereon. Then, a gate terminal is formed by a photolithography method and a lift-off method.

The optical sensor element shown in FIG. 9 is formed as a sensor of a non-planar imager. An Al electrode having a thickness of 100 nm is formed on the plastic substrate by vacuum deposition to form a lower electrode. 5 nm of In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited using a polycrystalline sintered body with InGaO ₃ (Zn _0.9 Mg _0.1 O) ₄ composition as a target by pulsed laser deposition using Kr excimer laser . Subsequently, an In-Ga-Zn-O amorphous oxide semiconductor thin film is deposited to a thickness of 5 nm using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target. This operation is repeated 20 times to laminate a 200 nm multilayer semiconductor layer. The amorphous oxide semiconductor film is formed to a thickness of 100 nm. Each time the oxide semiconductor layers are stacked, a phthalocyanine dye is vacuum-deposited, and a monomolecular film is stacked on the oxide semiconductor layer. On top of that, In ₂ O ₃ (SnO ₂ ) is deposited by vacuum deposition at a substrate temperature of room temperature to a thickness of about 20 nm to form the upper electrode.

  A circuit shown in FIG. 11 is formed by combining such a TFT and an X-ray sensor to constitute a non-planar imager shown in FIG. In such a non-planar imager, a small digital camera is installed as a non-measurement object and X-ray measurement is performed. An image with less distortion than that obtained using a conventional planar X-ray imager can be obtained.

  The present invention can be applied to sensors and non-planar imagers having high sensitivity to ultraviolet light, visible light, and X-rays.

4 is a graph showing the relationship between the electron carrier concentration of an In—Ga—Zn—O amorphous oxide semiconductor film formed by pulsed laser deposition and the oxygen partial pressure during film formation. 4 is a graph showing the relationship between the electron carrier concentration and the electron mobility of an In—Ga—Zn—O amorphous oxide semiconductor film formed by pulsed laser deposition. 4 is a graph showing the relationship between the electric conductivity of an In—Ga—Zn—O-based amorphous oxide semiconductor film formed by sputtering using argon gas and the oxygen partial pressure during film formation. ₃ is a graph showing changes in electrical conductivity, carrier concentration, and electron mobility with respect to the value of x of InGaO ₃ (Zn _1-x Mg _x O) formed by pulse laser deposition in an atmosphere with an oxygen partial pressure of 0.8 Pa. FIG. 3 is a schematic structural diagram of a TFT created for evaluating an amorphous oxide semiconductor used in the optical sensor of the present invention. It is a graph which shows the current-voltage characteristic of a top gate type MISFET element. It is a graph of the transmittance | permeability of the amorphous semiconductor layer (200 nm) comprised from In-Ga-Zn-O. It is typical explanatory drawing of the optical sensor of this invention. It is typical explanatory drawing of the 2nd example of the optical sensor of this invention. It is a typical structure figure of the X-ray sensor of the present invention. It is a pixel circuit diagram of the non-planar imager of the present invention. It is typical explanatory drawing of the creation method of the non-planar imager of the present invention. It is typical explanatory drawing of a X-ray measurement using the non-planar imager of this invention. It is a schematic diagram which shows a pulse laser vapor deposition apparatus. It is a schematic diagram which shows a sputtering film-forming apparatus.

Explanation of symbols

701, 801, 901 Substrate 702, 802, 902 Lower electrode 703, 903 Semiconductor layer 704, 804, 904 Upper electrode 803 Multilayer semiconductor layer 905 Scintillator

Claims (15)

A sensor for detecting received electromagnetic waves,
A sensor comprising: a first electrode; a second electrode; and an amorphous oxide layer provided between the first and second electrodes. The sensor according to claim 1, wherein the amorphous oxide layer has an electron carrier concentration of less than 10 ¹⁸ / cm ³ .   The sensor according to claim 1, wherein the amorphous oxide layer includes at least one of In, Zn, and Sn. The amorphous oxide layer is any one of an oxide containing In, Zn and Sn, an oxide containing In and Zn, an oxide containing In and Sn, or an oxide containing In. The sensor according to claim 1 or 2.   The sensor according to claim 1, wherein the amorphous oxide layer contains In, Ga, and Zn.   The sensor according to any one of claims 1 to 5, wherein the first electrode is transmissive to light in a wavelength region in which the amorphous oxide layer is sensitive.   6. The sensor according to claim 1, wherein an organic dye is provided on the amorphous oxide layer.   The sensor according to any one of claims 1 to 7, wherein the first and second electrodes and the amorphous oxide layer are provided on a flexible substrate.   The sensor according to any one of claims 1 to 8, wherein a plurality of amorphous oxide layers are provided between the first electrode and the second electrode. A sensor for detecting received electromagnetic waves,
An amorphous oxide layer provided between the first electrode and the second electrode,
The sensor, wherein the amorphous oxide layer is an amorphous oxide having a tendency to increase electron mobility as electron carrier concentration increases. An imaging device comprising:
A flexible substrate;
An X-ray sensor provided on the flexible substrate;
A field effect transistor for reading a signal from the X-ray sensor,
The field effect transistor has an amorphous oxide as an active layer, and the amorphous oxide has an electron carrier concentration of less than 10 ¹⁸ / cm ³ , or the amorphous oxide An imaging device, characterized in that the imaging device is an oxide that has a tendency to increase electron mobility as electron carrier concentration increases.   The imaging device according to claim 11, wherein the imaging device has a non-planar imaging region.   The imaging apparatus according to claim 11 or 12, wherein the X-ray sensor includes a scintillator that converts X-rays into light and a photoelectric conversion element.   The imaging apparatus according to claim 11, wherein the X-ray sensor includes a semiconductor layer, and the semiconductor layer is made of an amorphous oxide. An imaging device comprising:
A substrate having a non-planar region;
An X-ray sensor provided on the substrate;
A field effect transistor for reading a signal from the X-ray sensor,
The field effect transistor is a normally-off transistor having an active layer made of an amorphous oxide.