JP5126729B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device using an amorphous oxide for an active layer of a transistor.

  2. Description of the Related Art In recent years, flat and thin image display devices (Flat Panel Displays: FPD) have been put into practical use due to advances in liquid crystal and electroluminescence (EL) technologies.

  These FPDs are driven by an active matrix circuit of a field effect thin film transistor (TFT) using an amorphous silicon thin film or a polycrystalline silicon thin film provided on a glass substrate as an active layer.

  On the other hand, in order to further reduce the thickness, weight, and breakage resistance of these FPDs, an attempt has been made to use a lightweight and flexible resin substrate instead of a glass substrate.

  However, the manufacture of the transistor using the above-described silicon thin film requires a relatively high temperature thermal process and is generally difficult to form directly on a resin substrate having low heat resistance.

  In view of this, TFTs that can be formed at a low temperature and that use an oxide semiconductor thin film made of, for example, ZnO have been actively developed (Patent Document 1).

On the other hand, a TFT using a conventional oxide semiconductor thin film has not yet reached the technical level for developing its application technology because the characteristics sufficient to match those of a TFT using silicon have not been obtained.
Japanese Patent Laid-Open No. 2003-298062

  An object of the present invention is to provide a novel image display device using a transistor using an oxide as an active layer.

The first aspect of the present invention is an image display device,
A light control element including a liquid crystal and a field effect transistor for driving the light control element, and the active layer of the field effect transistor includes an In—Zn—Ga—O-based oxide. In-Zn-Ga-Mg-O-based oxide, In-Zn-O-based oxide, In-Sn-O-based oxide, In-O-based oxide, In-Ga-O-based oxide, and Sn An amorphous oxide which is any one of —In—Zn—O-based oxides, and the amorphous oxide has an electron carrier concentration of 10 ¹⁵ / cm ³ or more and less than 10 ¹⁸ / cm ³ . ,
The field effect transistor has a current between source and drain terminals of less than 10 microamperes when no gate voltage is applied, a field effect mobility of more than 2 cm ² / (V · sec), and the field effect transistor An alignment film and an insulating film are provided in this order from the liquid crystal side between the gate electrode of the transistor and the liquid crystal.

  Further, an alignment film and an insulating film are preferably provided in this order from the liquid crystal side between the gate electrode of the field effect transistor and the liquid crystal.

  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 discovered that it can be applied to image display 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 an image display device using a film realizing a desired electron carrier concentration.

  The present invention will be specifically described below.

  The light control element used in the present invention is a non-self-luminous electro-optical element such as a liquid crystal element or an element including electrophoretic particles.

The light control element may be configured using liquid crystal, and an alignment film and an insulating film may be provided in this order from the liquid crystal side between the active layer and the liquid crystal.

The light control element may be configured using liquid crystal, and an alignment film and an insulating film may be provided in this order from the liquid crystal side between the gate electrode of the field effect transistor and the liquid crystal.

  The insulating film is, for example, a silicon oxide film or a silicon nitride film.

  The present invention relates to a light control element in which light transmittance or light reflectance is controlled by an output of a field effect transistor.

The electrode of the light transmittance control element or the light reflectance control element is provided with an amorphous semiconductor having an electron carrier concentration containing In, Ga, Zn, and O of less than 10 ¹⁸ / cm ³ as an active layer. The output terminal of the field effect transistor is connected.

  One embodiment of the present invention is characterized in that the light-emitting element is an electroluminescence element.

  Alternatively, an embodiment of the present invention is characterized in that the light transmittance control element or the light reflectance control element is a liquid crystal cell.

  Alternatively, an embodiment of the present invention is characterized in that the light transmittance control element or the light reflectance control element is an electrophoretic particle cell.

  Furthermore, an embodiment of the present invention is characterized in that the electrophoretic particle cell is a cell in which a capsule in which a fluid and particles are sealed is sandwiched between counter electrodes.

  In one embodiment of the present invention, the light control element is provided on a flexible resin substrate.

  Alternatively, an embodiment of the present invention is characterized in that the light control element is provided on a light-transmitting substrate.

  One embodiment of the present invention is also characterized in that a plurality of the light control elements are two-dimensionally arranged together with the plurality of field effect transistors wired in an active matrix type.

  One embodiment of the present invention also relates to a broadcast moving image display device such as a television receiver, and is characterized by comprising the above image display device.

  An embodiment of the present invention also relates to a digital information processing device such as a computer, and is characterized by including the above-described image display device.

  One embodiment of the present invention also relates to a portable information device such as a mobile phone, a portable music player, and a portable video player, and is characterized by comprising the above image display device.

  An embodiment of the present invention also relates to an imaging device such as a still camera or a movie camera. The image display device is provided for a viewfinder of the imaging device, for confirming a captured image, or for displaying photographing information. It is characterized by.

  One embodiment of the present invention also relates to a building structure such as a window, a door, a ceiling, a floor, an inner wall, an outer wall, and a partition, and includes the above-described image display device for displaying an image on the surface. To do.

  One embodiment of the present invention also relates to a component such as a window, a door, a ceiling, a floor, an inner wall, an outer wall, and a partition of a moving body such as a vehicle, an aircraft, and a ship, and displays the image on the surface. An image display device is provided.

  An embodiment of the present invention also relates to an advertising device in a public transportation vehicle, an advertising device such as an advertising board in a city, an advertising tower, and the like, and includes the above image display device for displaying an image thereon. And

In one embodiment of the present invention, an amorphous oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ at room temperature is used as an active layer for an electrode of a light transmittance control element or a light reflectance control element. The output terminal of the field effect transistor is the light control element connected.

  In one embodiment of the present invention, an active layer is an amorphous oxide that increases the electron carrier concentration and the electron mobility at the electrode of the light transmittance control element or the light reflectance control element. It is a light control element to which the output terminal of a field effect transistor is connected.

  According to the present invention, it is possible to provide a novel image display device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
The active matrix type image display apparatus according to the present invention will be described with reference to FIG.

In the figure, 11 is a substrate or substrate, 12 is an amorphous oxide, 13 is a source electrode, 14 is a drain electrode, 18 is an electrode (pixel electrode), 15 is a gate insulating film, 16 is a gate electrode, 21 and 22 Is a high resistance film, and 23 is a portion containing liquid crystal or electrophoretic particles. This 23 constitutes a part of the light control element in the present invention. Reference numeral 20 denotes an electrode (or a substrate provided with an electrode). For the electrode, for example, a transparent electrode such as ITO is preferably used.
In the present invention, an output terminal (corresponding to the drain electrode 14) of a field effect transistor for driving a light control element composed of liquid crystal or the like is connected to an electrode 18 constituting the light control element.

  The light control element in the present invention can also be called a light modulation element.

As the active layer 12 of the field effect transistor, an amorphous oxide having an electron carrier concentration of less than 10 ¹⁸ / cm ³ is used.

  In addition, as the amorphous oxide used in the present invention, an amorphous oxide that tends to increase the electron mobility as well as the electron mobility can be used.

  When liquid crystal is used as the light control element, the high resistance film 21 or 22 is an alignment film (for example, polyimide) for aligning the liquid crystal.

  In FIG. 8, reference numeral 17 denotes an interlayer insulating film. However, the insulating film 17 and the high resistance film 21 may be made of the same material.

  However, from the viewpoint of enhancing the insulating properties, the high resistance film (alignment film) 21 and the insulating film 17 are preferably formed of different materials. For example, silicon oxide or silicon nitride is used as the insulating film 17.

  In particular, it is preferable to separate the liquid crystal from the amorphous oxide or gate insulating film 15 using the insulating film 17 made of silicon nitride or the like. This is to suppress unexpected entry of atoms, ion species, and the like from the liquid crystal into the gate insulating film and the amorphous oxide constituting the field effect transistor. The materials of the gate insulating film 15 and the insulating film 17 can be different.

In addition to the alignment film, another layer may be interposed between the liquid crystal and the insulating film 17.
(Amorphous oxide)
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 term “less than 10 ¹⁸ / cm ^3” is preferably less than 1 × 10 ¹⁸ / cm ³ , and more preferably less than 1.0 × 10 ¹⁸ / cm ³ .

  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 is formed of Al ₂ O ₃ , Y ₂ O ₃ , HfO ₂ , or a mixed crystal compound containing at least two of these compounds. 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 RP (rotary pump), 702 is TMP (turbo molecular pump), 703 is a preparation chamber, 704 is an electron gun for RHEED, 705 is a substrate holding means for rotating and moving the substrate up and down, and 706 is This 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, 712 is a bypass line, 713 is a main line, 714 is TMP ( Turbo molecular pump). Reference numeral 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 is a characteristic view in the case of creating under the same conditions as the example. This characteristic diagram 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, the pulse laser deposition method is used 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. When a transparent amorphous oxide thin film represented by the composition InGaO ₃ (ZnO) _m (m is a number less than 6) in a crystalline state is produced by this method, 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 _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, 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.

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: 2h), 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.

That is, it is composed of In—Ga—Zn—O produced by sputter deposition in an argon gas atmosphere with an oxygen partial pressure of over 3 × 10 ⁻² Pa, preferably over 5 × 10 ⁻¹ Pa, and the composition InGaO in the crystalline state. A transparent amorphous oxide thin film represented by ₃ (ZnO) _m (m is a natural number of less than 6) was prepared. Using this transparent amorphous oxide thin film, a normally-off transistor with an on / off ratio exceeding 10 ³ could be constructed.

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 containing 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. Electrons or holes move through a semiconductor thin film formed on an insulating substrate such as ceramics, glass, or plastic. This is used as a channel layer. The TFT is an active element having a function of switching a current between a source terminal and a drain terminal by applying a voltage to a gate terminal to control a current flowing in a 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.

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. 9 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. 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, and no clear diffraction peak was detected. In—Zn—Ga— produced from two types of targets All of the O-based films were shown to be 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. 9 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 and washing 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. 9 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 _0.9 Sn _0.1 ) O _3.1 polycrystalline sintered body is used as a target and an In—Sn—O-based oxide film is formed on a 200 μm-thick PET film. 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 at 100 ° C. in the air.

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), and the pulse width was 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).

  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), and the pulse width is 20 (nsec) there were. 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. Regarding 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—Ga—O film was an amorphous film. It was shown that there is. 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. And the drain terminal (5) and the source terminal (6) were formed by the photolithographic method and the lift-off method.

Finally, a Y ₂ O ₃ film used as a 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 ). And gold | metal | money was formed on it and the gate terminal (4) was formed with the photolithographic method and the 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. At this time, a polycrystalline sintered body having an InGaO ₃ (ZnO) composition was used as a target.

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. And the drain terminal (5) and the source terminal (6) were formed by the photolithographic 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 the gate insulating film (3) was formed by electron beam evaporation. And gold | metal | money was formed into a film on it and the gate terminal (4) was formed with the photolithographic method and the lift-off method.

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 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.
(Second Embodiment)
In the present invention, a light emitting element such as an electroluminescence element, a light transmittance control element of a liquid crystal cell or an electrophoretic particle cell, or an input electrode of a light reflectance control element is connected to a drain which is an output terminal of a field effect TFT. The present invention relates to a connected light control element.

  This will be described with reference to FIG.

A TFT is constituted by the amorphous oxide semiconductor film 12 deposited and patterned on the substrate 11, the source electrode 13, the drain electrode 14, the gate insulating film 15, and the gate electrode 16.
An electrode 18 is connected to the drain electrode 14 via an interlayer insulating film 17. The electrode 18 is in contact with the light emitting layer 19, and the light emitting layer 19 is in contact with the electrode 20.

  The current injected into the light emitting layer 19 is controlled by the value of current flowing from the source electrode 13 to the drain electrode 14 through the channel formed in the amorphous oxide semiconductor film 12. That is, it can be controlled by the voltage applied by the gate electrode 16.

  Here, the light emitting layer 19 is preferably an inorganic or organic electroluminescence element.

  Further, as shown in FIG. 8, the drain electrode 14 is extended to serve also as the electrode 18, and the light transmittance control comprising the liquid crystal cell and the electrophoretic particle cell 23 sandwiched between the high resistance films 21 and 22. An electrode 18 that applies a voltage to the element or the light reflectance control element may be used.

  With this configuration, the voltage applied to these light transmittance control elements or light reflectance control elements is determined by the value of current flowing from the source electrode 13 to the drain electrode 14 through the channel formed in the amorphous oxide semiconductor film 12. It becomes possible to control.

  That is, it can be controlled by the voltage of the gate 6 of the TFT. Here, when the light transmittance control element or the light reflectance control element is a capsule in which a fluid and particles are sealed in an insulating film, the high resistance films 21 and 22 are unnecessary.

  In the above-described two examples, the TFT is represented by a top gate coplanar configuration, but the present invention is not necessarily limited to this configuration. Other configurations such as a stagger type are possible as long as the connection between the drain electrode, which is the output terminal of the TFT, and the light emitting element are topologically identical.

  Further, in the above two examples, an example in which a pair of electrodes for driving the light emitting element, the light transmittance control element or the light reflectance control element is provided in parallel with the base body is illustrated. It is not limited to.

  If the connection between the drain electrode, which is the output terminal of the TFT, and the light emitting element is topologically the same, either or both electrodes may be provided perpendicular to the substrate.

  Furthermore, in the above two examples, only one TFT connected to the light emitting element, the light transmittance control element, or the light reflectance control element is shown, but the present invention is not necessarily limited to this configuration.

  The TFT shown in the figure may be further connected to another TFT according to the present invention, and the TFT in the figure may be the final stage of the circuit using these TFTs.

  Here, when a pair of electrodes for driving the light emitting element, the light transmittance control element, or the light reflectance control element is provided in parallel with the base, if any of the electrodes is a light emitting element or a light reflectance control element, It must be transparent to the emission wavelength or the wavelength of the reflected light. Or if it is a light transmittance control element, both electrodes need to be transparent with respect to transmitted light. In the present invention, the term “transparent” is a concept that includes light-transmitting substances as well as being substantially transparent.

  Furthermore, in the TFT of the present invention, it is possible to make all the constituents transparent, whereby a transparent light control element can be formed. Further, such a light control element can be provided on a low heat-resistant substrate such as a lightweight, flexible and transparent resin plastic substrate.

  A plurality of the light control elements described in the first or second embodiment may be two-dimensionally arranged together with the plurality of TFTs wired in an active matrix type.

  For example, the gate electrode 5 of one TFT that drives the light control element is connected to the gate line of the active matrix, and the active matrix circuit is configured in which the source electrode of the TFT is wired to the signal destination. By doing so, it is possible to provide an image display device in which each light control element is a pixel.

Furthermore, a color image display device can be provided if one pixel is constituted by a plurality of adjacent light control elements having different emission wavelengths, transmitted light wavelengths, or reflected light wavelengths. Of course, a color filter can also be used in this case.
(Other embodiments)
Further, the present invention is a broadcast moving image display device such as a television receiver including the image display device. The image display device of the present invention has an effect of providing light weight, flexibility, and safety at the time of breakage, particularly to a portable broadcast moving image display device.

  The present invention also relates to a digital information processing device such as a computer provided with the image display device.

  Since the image display apparatus of the present invention is lightweight and flexible, it provides a degree of freedom and portability for installing a stationary computer display. In addition, for example, portable digital information processing devices such as notebook computers and personal digital support devices have the effect of reducing weight, flexibility, and safety when damaged.

  The present invention also relates to a portable information device such as a mobile phone, a portable music player, a portable video player, a head mounted display, etc. provided with the image display device. The image display device of the present invention has an effect of giving these portable information devices light weight, flexibility, and safety at breakage. In particular, when a transparent image display device of the present invention is used for a head-mounted display, a see-through device can be provided.

  Further, the present invention is an imaging device such as a still camera or a movie camera provided with the image display device. The image display device of the present invention has an effect of giving these imaging devices light weight, flexibility, and safety when damaged.

  Moreover, this invention is building structures, such as a window, a door, a ceiling, a floor | bed, an inner wall, an outer wall, a partition, provided with the said image display apparatus. Since the image display device of the present invention is lightweight and flexible and can be made transparent, it can be easily added to those building structures, and when the image is not displayed, the appearance as a building structure is impaired. Has no effect.

  Moreover, this invention is structures, such as a window, a door, a ceiling, a floor | bed, an inner wall, an outer wall, and a partition of moving bodies, such as a vehicle, an aircraft, and a ship, which were provided with the said image display apparatus.

  Since the image display device of the present invention is lightweight and flexible and can be made transparent, it can be easily added to these building structures. Furthermore, when the image is not displayed, the appearance as a building structure is not impaired. When the transparent image display device of the present invention is used for a transparent window for monitoring and observing the outside of a moving body, an information image is displayed only when necessary, and monitoring and observation of the outside world are not impaired when unnecessary. Has an effect.

The present invention is also an advertising device such as an advertising means in a public transportation vehicle, an advertising board in a city, an advertising tower, etc., provided with the image display device. The image display device of the present invention can be changed to an advertising device as needed, and can also be expressed as a moving image, as previously supported mainly by non-variable media such as printed matter.
(Example)
Examples of the present invention will be described below.

  First, a method for forming a TFT using an amorphous oxide applicable to the present invention will be described.

(Formation of amorphous In-Ga-Zn-OTFT)
Using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target by sputtering, a surface-treated polyethersulfine-based transparent plastic substrate with a thickness of 50 nm In-Ga-Zn- An O-based amorphous oxide semiconductor film is deposited.

The oxygen partial pressure in the chamber is 5 × 10 ⁻² Pa, and the substrate temperature is 25 ° C. This amorphous oxide semiconductor film is patterned into 30 μm × 15 μm islands by photolithography.

  Next, using the same film formation method and patterning method, two types of islands of 35 μm × 10 μm and 30 μm × 10 μm made of 50 nm thick ITO film are formed in parallel with the long side direction of this island. Formed at 5 μm intervals in the center of the membrane island.

  However, the islands of the ITO film are aligned with the islands of the amorphous oxide semiconductor film of 30 μm × 10 μm in the long side direction.

  That is, the island of the 30 μm × 10 μm amorphous oxide semiconductor film is in contact with the ITO film in the region of 30 μm × 5 μm at both ends in the short side direction.

  The island of 35 μm × 10 μm ITO film protrudes from the island of amorphous oxide semiconductor film by 5 μm in the short side direction and 5 μm on one side of the long side, and the island of ITO film of 30 μm × 10 μm is 5 μm only in the short side direction. It protrudes from the island of the amorphous oxide semiconductor film.

Next, in the same manner, a 100 nm thick Y ₂ O ₃ film is formed as an island of 40 μm × 15 μm, an island of an amorphous oxide semiconductor film of 30 μm × 15 μm, and the center of gravity and the long side are provided.

  Finally, an ITO film having a thickness of 50 nm is formed as an island of 30 μm × 5 μm, and a long side is formed in parallel at the center of the island of an amorphous oxide semiconductor film of 30 μm × 15 μm.

Through the above steps, the ITO film islands of 35 μm × 10 μm and 30 μm × 10 μm become the source electrode and the drain electrode, respectively. The amorphous oxide semiconductor film located in the gap between these two islands becomes a channel region, and the Y ₂ O ₃ film becomes a gate insulating layer. The island of the ITO film of 30 μm × 5 μm at the top is the gate electrode. Thus, a field effect type n-channel TFT is configured.

Such a TFT exhibits characteristics such as a field effect mobility of 5 cm ² V ⁻¹ s ⁻¹ , a threshold voltage of 1 V, and an on / off ratio of about 3 digits or more.

  In addition, when used for a light-transmitting substrate as in an embodiment of the present invention, for example, when used as a light-transmitting member such as a spectacle-type information device, a building structure, or a moving object window Thus, a so-called see-through image display device can be provided.

Since the field effect transistor according to the present invention is transparent or transparent to visible light including the active layer, the external light transmitted through the window and the display image of the device and apparatus of the present invention are displayed. This is because they can be seen on the same optical axis.
(Example 1: Production of light control element using TFT)
In the above TFT, extend the short side of the ITO film island forming the drain electrode to 100 μm, leave the extended 90 μm portion, and secure the wiring to the source and gate electrodes, and then cover the TFT with an insulating layer To do.

  A polyimide film (alignment film) is applied thereon and a rubbing process is performed.

  On the other hand, an ITO film and a polyimide film are similarly formed on a plastic substrate and a rubbing process is performed. A substrate on which the TFT is formed and a separately prepared substrate are arranged facing each other with a 5 μm gap, and a nematic liquid crystal is injected therein.

  Further, a pair of polarizing plates is provided on both sides of the structure.

  Here, when a voltage is applied to the source electrode of the TFT and the applied voltage of the gate electrode is changed, the light transmittance changes only in the 30 μm × 90 μm region that is a part of the island of the ITO film extended from the drain electrode. To do.

  The transmittance can be continuously changed by the source-drain voltage under the gate voltage at which the TFT is turned on.

  In this embodiment, a white plastic substrate is used as a substrate for forming a TFT, and each electrode of the TFT is replaced with gold. And the capsule which coat | covered the particle | grains and the fluid with the insulating film is filled into the space | gap of a white and transparent plastic substrate, without using a polyimide film and a polarizing plate. Electrophoretic particles are used as the particles.

  The above-described TFT controls the voltage between the extended drain electrode and the upper ITO film. When the particles in the capsule move up and down, the reflectance of the extended drain electrode region viewed from the transparent substrate side can be controlled.

  Further, in this embodiment, a plurality of TFTs are formed adjacent to each other to form a current control circuit having a normal 4-transistor 1-capacitor configuration, for example. The light emitting element can also be driven using the TFT shown in FIG. 7 as one of the final stage transistors.

For example, using the above-mentioned TFT with the ITO film as the drain electrode, an organic electroluminescence element consisting of a charge injection layer and a light-emitting layer is formed in a 30 μm x 90 μm region that is part of the island of the ITO film extended from the drain electrode To do.
(Example 2: Image display device using the light control element)
The above-described light control elements are arranged two-dimensionally. For example, the light transmittance control element or light reflectance control element of Example 1 is used.

  7425 × 1790 light control elements occupying an area of about 30 μm × 115 μm, including TFTs, are arranged in a 40 μm pitch in the short side direction and 120 μm pitch in the long side direction. 1790 gate wirings are provided through the gate electrodes of 7425 TFTs in the long side direction. Then, 7425 signal wirings are provided in which the source electrode of 1790 TFTs penetrates the portion protruding from the island of the amorphous oxide semiconductor film by 5 μm in the short side direction.

  Each is connected to a gate driver circuit and a source driver circuit. Further, a color filter having the same size as each light control element and having a position where RGB repeats in the long side direction is provided on the surface. In this way, an A4 size active matrix type color image display device can be configured at about 211 ppi.

  Also in the light control element using the light emitting element of Example 1, among the four TFTs included in one light control element, the gate electrode of the first TFT is wired to the gate line, and the source electrode of the second TFT is used. Connect to the signal line. Furthermore, if the light emission wavelength of the light emitting element is repeated in RGB in the long side direction, a light emitting color image display device with the same resolution can be configured.

Here, the driver circuit for driving the active matrix may be configured using the same TFT of the present invention as the pixel TFT, or an existing IC chip may be used.
(Example 3: Apparatus provided with the image display device)
A device essential to a broadcast moving image display device such as a broadcast receiving device or an audio image processing device is added to the above-described image display device, and the device is housed in a thin casing together with a power source and an interface. This provides a broadcast video display device that is lightweight and thin and highly safe against dropping or impact.

  In addition, a device essential to digital information processing equipment such as a central processor, a storage device, and a network device is connected to the above-described image display device, and is housed in a thin casing together with a power source and an interface. As a result, an integrated digital information processing apparatus that is lightweight, thin, and highly portable is provided.

  In addition, the area of the image display device and the number of light control elements are reduced to limit the diagonal to about 2-5 inches, and devices essential to portable information devices such as processors, storage devices, and network devices are connected thereto. It is housed in a small and thin casing along with the power supply and interface. This provides a portable information device that is lightweight, thin and highly safe against dropping and impact.

  In addition, an essential device for an imaging device such as an imaging device, a storage device, and a signal processing device is connected to the same small image display device, and the device is housed in a small and lightweight casing together with a power source and an interface. This provides an imaging device that is lightweight and compact and highly safe against dropping and impact.

  On the contrary, any image can be displayed by enlarging the size of one light control element and attaching or incorporating an image display device with an enlarged display area to the above-described building structure. Providing those building structures.

  In addition, by incorporating the above-described image display device as a moving object component, a moving object component capable of displaying an arbitrary image is provided.

  Moreover, by incorporating the above-described image display device as a part of the advertising device, the advertising device capable of displaying an arbitrary image is provided.

  The light control element and the image display device according to the present invention are a light and thin broadcast video display device, a digital information processing device, a portable information device, an imaging device, a building structure, a moving object, and an advertisement that are highly safe against damage. It can be widely used for equipment.

It is a graph which shows the relationship between the electron carrier density | concentration of the In-Ga-Zn-O type amorphous oxide formed into a film by the pulse laser vapor deposition method, and the oxygen partial pressure during film-forming. It is a graph which shows the relationship between the electron carrier density | concentration of the In-Ga-Zn-O type | system | group amorphous oxide film | membrane formed into a film by the pulse laser vapor deposition method, and an electron mobility. It is a graph which shows the relationship between the electrical conductivity of the In-Ga-Zn-O type | system | group amorphous oxide film | membrane formed into a film by the high frequency sputtering method using argon gas, and the oxygen partial pressure during film-forming. Changes in electrical conductivity, electron carrier concentration, and electron mobility with respect to the x value of InGaO ₃ (Zn _1-x Mg _x O) _{4 formed} by pulsed laser deposition in an atmosphere with an oxygen partial pressure of 0.8 Pa. It is a graph to show. It is a schematic diagram which shows a top gate type TFT element structure. Y ₂ O ₃ the current of the top gate type TFT element using as a gate insulating film - is a graph showing the voltage characteristic. It is a typical sectional view of a light control element. It is a typical sectional view of a light control element. 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

DESCRIPTION OF SYMBOLS 11 Base body 12 Amorphous oxide semiconductor film 13 Source electrode 14 Drain electrode 15 Gate insulating film 16 Gate electrode 17 Interlayer insulating film 18 Electrode 19 Light emitting layer 20 Electrode 21 and 22 High resistance film 23 Liquid crystal cell or electrophoretic particle cell

Claims (7)

A light control element including a liquid crystal and a field effect transistor for driving the light control element, and the active layer of the field effect transistor includes an In—Zn—Ga—O-based oxide. In-Zn-Ga-Mg-O-based oxide, In-Zn-O-based oxide, In-Sn-O-based oxide, In-O-based oxide, In-Ga-O-based oxide, and Sn An amorphous oxide which is any one of —In—Zn—O-based oxides, and the amorphous oxide has an electron carrier concentration of 10 ¹⁵ / cm ³ or more and less than 10 ¹⁸ / cm ³ . ,
The field effect transistor has a current between source and drain terminals of less than 10 microamperes when no gate voltage is applied, a field effect mobility of more than 2 cm ² / (V · sec), and the field effect transistor An image display device having an alignment film and an insulating film in this order from a liquid crystal side between a gate electrode of a transistor and the liquid crystal.   The image display device according to claim 1, wherein the insulating film is a silicon oxide film or a silicon nitride film.   The image display device according to claim 1, wherein the light control element is provided on a flexible resin substrate.   The image display device according to claim 1, wherein the light control element is provided on a light-transmitting substrate.   The broadcast moving image display apparatus which has an image display apparatus of any one of the said Claims 1-4, a broadcast receiving apparatus, and an audio processing apparatus.   An integrated digital information processing apparatus comprising the image display device according to any one of claims 1 to 4, a central processor, and a storage device.   The portable information processing apparatus which has an image display apparatus of any one of the said Claims 1-4, a processor, and a memory | storage device.