JP2017108136A - Field-effect transistor, display device, image display apparatus, and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a field-effect transistor which is large in mobility, large in ON/OFF ratio of a source-drain current, and steep in transfer property's rising edge from an OFF state to an ON state.SOLUTION: A field-effect transistor comprises: a gate electrode 26 for applying a gate voltage; a source electrode 23 and a drain electrode 24 for taking out a current; an active layer 22 including an oxide semiconductor and provided adjacently to the source and drain electrodes; and a gate insulation layer 25 provided between the gate electrode and active layer. The gate insulation layer includes a paraelectric amorphous oxide including an "A" element which is an alkali-earth metal and a "B" element which is at least any of Ga, Sc, Y and lanthanoid series. The active layer has a carrier density of 4.0×10/cmor more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a field effect transistor, a display element, an image display device, and a system.

  Liquid crystal display (LCD), organic EL (electroluminescence) display (OLED), flat and thin displays such as electronic paper (Flat Panel Display: FPD) use amorphous silicon or polycrystalline silicon as the active layer It is driven by a driving circuit including a thin film transistor (TFT). FPDs are required to have larger size, higher definition, and higher speed driving performance, and accordingly, good switching characteristics such as high carrier mobility, high on / off ratio, and steep rise from off to on. There is a need for transistors having:

  However, TFTs using amorphous silicon (a-Si) or polycrystalline silicon (especially low-temperature poly silicon: LTPS) as active layers have their merits and demerits and satisfy all requirements at the same time. It was difficult.

  For example, the a-Si TFT has a drawback that it has insufficient mobility to drive a large screen LCD (Liquid Crystal Display) at high speed, and has a large threshold voltage shift during continuous driving. The LTPS-TFT has high mobility, but there is a problem that the threshold voltage varies greatly due to the process of crystallizing the active layer by excimer laser annealing, and the mother glass size of the mass production line cannot be increased.

In view of this, InGaZnO ₄ (a-IGZO) that can form a film at room temperature and exhibits a-Si or higher mobility in an amorphous state has been proposed (see Non-Patent Document 1). Semiconductors have been actively researched.

  An object of the present invention is to provide a field effect transistor having a high mobility, a large on / off ratio of a source-drain current, and a sharp rise from the off state to the on state of the transfer characteristics.

Means for solving the problems are as follows. That is,
The field effect transistor of the present invention is
A gate electrode for applying a gate voltage;
A source electrode and a drain electrode for extracting current;
An active layer provided adjacent to the source electrode and the drain electrode and made of an oxide semiconductor;
A gate insulating layer provided between the gate electrode and the active layer;
A field effect transistor comprising:
The gate insulating layer is a paraelectric amorphous oxide containing an A element that is an alkaline earth metal and a B element that is at least one of Ga, Sc, Y, and a lanthanoid,
The carrier density of the active layer is 4.0 × 10 ¹⁷ / cm ³ or more.

  According to the present invention, it is possible to provide a field effect transistor having high mobility, a large on / off ratio of a source-drain current, and a sharp rise from the off state to the on state of the transfer characteristics.

FIG. 1 is a schematic configuration diagram showing an example of a top contact / bottom gate type field effect transistor. FIG. 2 is a schematic configuration diagram illustrating an example of a bottom contact / bottom gate type field effect transistor. FIG. 3 is a schematic configuration diagram showing an example of a top contact / top gate type field effect transistor. FIG. 4 is a schematic configuration diagram showing an example of a bottom contact / top gate field effect transistor. FIG. 5 is a schematic configuration diagram showing an example of a television device as a system of the present invention. FIG. 6 is a diagram (part 1) for explaining the image display device in FIG. FIG. 7 is a diagram (part 2) for explaining the image display device in FIG. FIG. 8 is a diagram (part 3) for explaining the image display device in FIG. FIG. 9 is a diagram for explaining an example of the display element of the present invention. FIG. 10 is a schematic configuration diagram illustrating an example of a positional relationship between an organic EL element and a field effect transistor in a display element. FIG. 11 is a schematic configuration diagram illustrating another example of the positional relationship between the organic EL element and the field effect transistor in the display element. FIG. 12 is a schematic configuration diagram illustrating an example of an organic EL element. FIG. 13 is a diagram for explaining the display control apparatus. FIG. 14 is a diagram for explaining a liquid crystal display. FIG. 15 is a diagram for explaining the display element in FIG. FIG. 16 shows the result of X-ray diffraction measurement of the gate insulating layer of Example 1. FIG. 17 is a graph showing the transfer characteristics of Example 1. FIG. 18 is a graph showing transfer characteristics of Comparative Example 1. FIG. 19 is a graph showing transfer characteristics of Comparative Example 2. FIG. 20 is a graph showing transfer characteristics of Comparative Example 3. FIG. 21 is a graph showing transfer characteristics of Comparative Example 4. FIG. 22 shows the result of X-ray diffraction measurement of the gate insulating layer of Comparative Example 5. FIG. 23 is a graph showing transfer characteristics of Comparative Example 5. FIG. 24 is a graph showing transfer characteristics of Comparative Examples 6 and 7. FIG. 25 is a graph showing transfer characteristics of Examples 2 to 5. FIG. 26 is a graph showing transfer characteristics of Examples 6 to 8. FIG. 27 is a graph showing transfer characteristics of Examples 9 to 11.

(Field effect transistor)
The field effect transistor of the present invention includes at least a gate electrode, a source electrode, a drain electrode, an active layer, and a gate insulating layer, and further includes other members as necessary.

The present inventors have intensively studied to solve the above problems. In order to achieve the above object, an oxide semiconductor having a carrier density of 4.0 × 10 ¹⁷ / cm ³ or more is used for an active layer, and an element A that is an alkaline earth metal, Ga, It has been found that it is effective to use a paraelectric amorphous oxide containing Sc, Y, and a B element which is at least one of lanthanoids for the gate insulating layer. The fact that the carrier density of the active layer is as high as 4.0 × 10 ¹⁷ / cm ³ or more is effective for increasing the current value (so-called on-current value) flowing between the source and drain when the transistor is on. is there. In addition, in order to effectively control such a large number of carriers by the gate voltage and realize a characteristic that the rise from the off state to the on state is steep, the electrical characteristics of the gate insulating layer are important, especially in alkaline earth. A paraelectric amorphous oxide containing an element A which is a similar metal and a element B which is at least one of Ga, Sc, Y, and a lanthanoid is suitable as a material for the gate insulating layer in this case. I found it. When a gate insulating layer made of this material is used, the leakage current through the gate insulating layer can be kept small, so that the off current is reduced and a high on / off ratio can be obtained. Thus, the present invention has been completed.

<Gate electrode>
The gate electrode is not particularly limited as long as it is an electrode for applying a gate voltage, and can be appropriately selected according to the purpose.
The material of the gate electrode is not particularly limited and may be appropriately selected depending on the purpose. For example, a metal or alloy such as Mo, Al, Au, Ag, or Cu, or transparent conductive oxide such as ITO or ATO. And organic conductors such as polyethylenedioxythiophene (PEDOT) and polyaniline (PANI).

  The method for forming the gate electrode is not particularly limited and may be appropriately selected depending on the intended purpose. For example, (i) a method of patterning by photolithography after film formation by sputtering, dip coating, or the like ( ii) A method of directly forming a desired shape by a printing process such as inkjet, nanoimprint, or gravure.

  There is no restriction | limiting in particular as average thickness of the said gate electrode, Although it can select suitably according to the objective, 20 nm-1 micrometer are preferable and 50 nm-300 nm are more preferable.

<Gate insulation layer>
The gate insulating layer is an insulating layer provided between the gate electrode and the active layer.

  The gate insulating layer includes an element A that is an alkaline earth metal (Be, Mg, Ca, Sr, Ba, Ra), Ga, Sc, Y, and a lanthanoid (La, Ce, Pr, Nd, Pm, Sm). , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and a B element.

  The alkaline earth metal contained in the gate insulating layer may be one type or two or more types.

  The gate insulating layer formed of an amorphous material is a preferable form in terms of improving the characteristics of the transistor. This is because when the gate insulating layer is formed using a crystalline material, leakage current due to crystal grain boundaries cannot be suppressed low, leading to deterioration of transistor characteristics.

In addition, it is necessary that the gate insulating layer is a paraelectric material in order to reduce hysteresis in the transfer characteristics of the transistor. The exception is the special case where the transistor is used for a memory or the like, but it is not preferable that hysteresis exists in a device that normally uses the switching characteristics of the transistor.
A paraelectric material is a dielectric material other than a piezoelectric material, pyroelectric material, or ferroelectric material, that is, a dielectric material that does not generate polarization due to pressure or has spontaneous polarization in the absence of an external electric field. Point to. In addition, the piezoelectric body, pyroelectric body, and ferroelectric need to be crystals in order to exhibit their characteristics. That is, when the gate insulating layer is formed of an amorphous material, the gate insulating layer necessarily becomes a paraelectric material.

  Alkaline earth metal oxides easily react with moisture and carbon dioxide in the atmosphere and easily change to hydroxides and carbonates, and are not suitable for application to electronic devices alone. In addition, simple oxides such as Ga, Sc, Y, and lanthanoids are easily crystallized, and leakage current becomes a problem. However, the inventors have found that an oxide containing an element A which is an alkaline earth metal and an element B which is at least one of Ga, Sc, Y, and a lanthanoid is stable in the atmosphere and has a wide composition range. It was found that a paraelectric amorphous film can be formed and is suitable for a gate insulating layer. Ce is specifically tetravalent among lanthanoids and forms crystals with a perovskite structure with an alkaline earth metal. Therefore, in order to obtain an amorphous phase, the element B is preferably not Ce.

  A crystal phase such as a spinel structure exists between the alkaline earth metal oxide and the Ga oxide, but these crystals do not precipitate unless the temperature is very high compared to the perovskite structure crystal (generally 1000 ° C. or more). ). In addition, the existence of a stable crystal phase has not been reported between an alkaline earth metal oxide and an oxide composed of Sc, Y, and a lanthanoid, and crystal precipitation from the amorphous phase even after a high temperature post-process. Is rare. Furthermore, when an oxide containing an alkaline earth metal and Ga, Sc, Y, and a lanthanoid is composed of three or more kinds of metal elements, the amorphous phase is further stabilized.

  From the viewpoint of producing a high dielectric constant film, it is preferable to increase the composition ratio of elements such as Ba, Sr, Lu, and La.

  The gate insulating layer preferably further includes a C element that is at least one of Al, Ti, Zr, Hf, Nb, and Ta. As a result, the amorphous phase is further stabilized, and thermal stability and denseness can be further improved.

The relative dielectric constant of the gate insulating layer is 7.0 from the viewpoint of realizing a sharp rise in transfer characteristics and high mobility when the carrier density of the active layer is as high as 4.0 × 10 ¹⁷ / cm ³ or more. It is preferably large, more preferably greater than 8.0, and even more preferably greater than 9.0. There is no restriction | limiting in particular as an upper limit of the said dielectric constant, Although it can select suitably according to the objective, The said dielectric constant is 50.0 or less, and 30.0 or less is more preferable.
The value of the relative dielectric constant can be calculated from the value of the capacitance measured by forming a capacitor with the upper and lower sides of the insulating layer sandwiched between electrode films.

  In the gate insulating layer, since the relative permittivity changes according to the ratio of the A element and the B element, it is preferable to optimize the composition of the gate insulating layer in order to achieve a preferable relative permittivity. is there.

There is no particular limitation on the atomic ratio (NA: NB) between the total number of atoms of the element A (NA) and the total number of atoms of the element B (NB) in the paraelectric amorphous oxide. Depending on the purpose, it can be appropriately selected, but the following range is preferred.
NA: NB = (3-50) at%: (50-97) at%
However, NA + NB = 100at%

The total number of atoms of the A element in the paraelectric amorphous oxide (NA), the total number of atoms of the B element (NB), and the total number of atoms of the C element (NC) There is no restriction | limiting in particular as atomic ratio (NA: NB: NC), Although it can select suitably according to the objective, It is preferable that it is the following ranges.
NA: NB: NC = (3-47) at%: (50-94) at%: (3-47) at%
However, NA + NB + NC = 100at%

  The ratio of NA, NB, and NC in the paraelectric amorphous oxide is determined by, for example, the cation of the oxide by fluorescent X-ray analysis, electron microanalysis (EPMA), dielectric coupled plasma emission spectroscopy (ICP-AES), etc. It can be calculated by analyzing the elements.

  The above materials have excellent insulating properties and a high dielectric breakdown voltage and a large relative dielectric constant. Therefore, by forming a gate insulating layer with this, an active layer is formed through the gate insulating layer when a gate voltage is applied. A transistor having good switching characteristics in which the applied electric field works efficiently and the rise from the off state to the on state is steep even when there are many carriers in the active layer can be obtained. In addition, since many carriers are effectively controlled, characteristics with a small off current and a high on current, that is, a high on / off ratio can be obtained. In the transfer curve, the difference (so-called hysteresis) between changing the gate voltage from minus to plus and changing from plus to minus is small. Further, since the gate insulating layer is amorphous, the interface between the active layer and the gate insulating layer is easily smooth and has few defects, and carrier movement is facilitated, so that transistor characteristics with high mobility can be obtained.

-Formation method of gate insulating layer-
There is no restriction | limiting in particular as a formation method of the said gate insulating layer, According to the objective, it can select suitably, For example, a sputtering method, a pulse laser deposition (PLD) method, a chemical vapor deposition (CVD) method, an atom Examples include a method of patterning by photolithography after film formation by a vacuum process such as layer deposition (ALD).
The gate insulating layer is prepared by preparing a coating liquid (a coating liquid for forming a gate insulating layer) containing the paraelectric amorphous oxide precursor, and applying or printing the coating liquid on an object to be coated. A film can also be formed by baking under appropriate conditions.

--- Coating liquid for forming gate insulation layer-
The coating liquid for forming a gate insulating layer contains at least an A-element-containing compound, a B-element-containing compound, and a solvent, preferably contains a C-element-containing compound and, if necessary, other Contains ingredients.

--- Element A-containing compound ---
Examples of the A-element-containing compound include an inorganic compound of the A element and an organic compound of the A element. Examples of the A element in the A element-containing compound include Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium).

Examples of the inorganic compound of element A include nitrate of element A, sulfate of element A, chloride of element A, fluoride of element A, bromide of element A, element A, and the like. And the like.
Examples of the nitrate of the element A include magnesium nitrate, calcium nitrate, strontium nitrate, and barium nitrate.
Examples of the element A sulfate include magnesium sulfate, calcium sulfate, strontium sulfate, and barium sulfate.
Examples of the chloride of the element A include magnesium chloride, calcium chloride, strontium chloride, and barium chloride.
Examples of the fluoride of the element A include magnesium fluoride, calcium fluoride, strontium fluoride, and barium fluoride.
Examples of the bromide of the element A include magnesium bromide, calcium bromide, strontium bromide, barium bromide and the like.
Examples of the iodide of the element A include magnesium iodide, calcium iodide, strontium iodide, barium iodide and the like.

  The organic compound of the A element is not particularly limited as long as it is a compound having the A element and an organic group, and can be appropriately selected according to the purpose. The element A and the organic group are bonded by, for example, an ionic bond, a covalent bond, or a coordinate bond.

  The organic group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include an alkyl group which may have a substituent, an alkoxy group which may have a substituent, and a substituent. An acyloxy group which may have a substituent, a phenyl group which may have a substituent, an acetylacetonate group which may have a substituent, a sulfonic acid group which may have a substituent, etc. Can be mentioned. As said alkyl group, a C1-C6 alkyl group etc. are mentioned, for example. As said alkoxy group, a C1-C6 alkoxy group etc. are mentioned, for example. Examples of the acyloxy group include an acyloxy group having 1 to 10 carbon atoms, an acyloxy group partially substituted with a benzene ring like benzoic acid, an acyloxy group partially substituted with a hydroxy group like lactic acid, Examples include oxalic acid and acyloxy groups having two or more carbonyl groups such as citric acid.

  Examples of the organic compound of the element A include, for example, magnesium methoxide, magnesium ethoxide, diethyl magnesium, magnesium acetate, magnesium formate, acetylacetone magnesium, magnesium 2-ethylhexanoate, magnesium lactate, magnesium naphthenate, magnesium citrate, Magnesium salicylate, magnesium benzoate, magnesium oxalate, magnesium trifluoromethanesulfonate, calcium methoxide, calcium ethoxide, calcium acetate, calcium formate, acetylacetone calcium, calcium dipivaloylmethanate, calcium 2-ethylhexanoate, lactic acid Calcium, calcium naphthenate, calcium citrate, calcium salicylate, calcium neodecanoate, benzoic acid Calcium, calcium oxalate, strontium isopropoxide, strontium acetate, strontium formate, acetylacetone strontium, strontium 2-ethylhexanoate, strontium lactate, strontium naphthenate, strontium salicylate, strontium oxalate, barium ethoxide, barium isopropoxide, Examples include barium acetate, barium formate, acetylacetone barium, barium 2-ethylhexanoate, barium lactate, barium naphthenate, barium neodecanoate, barium oxalate, barium benzoate, and barium trifluoromethanesulfonate.

  There is no restriction | limiting in particular as content of the said A element containing compound in the said coating liquid for gate insulating layer formation, According to the objective, it can select suitably.

--- B element-containing compound ---
Examples of the B element include Ga (gallium), Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), and Sm (samarium). ), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

  Examples of the B element-containing compound include an inorganic compound of the B element and an organic compound of the B element.

Examples of the inorganic compound of the B element include nitrate of the B element, sulfate of the B element, fluoride of the B element, chloride of the B element, bromide of the B element, iodine of the B element And the like.
Examples of the nitrate of the element B include gallium nitrate, scandium nitrate, yttrium nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, samarium nitrate, europium nitrate, gadolinium nitrate, terbium nitrate, dysprosium nitrate, holmium nitrate, Examples include erbium nitrate, thulium nitrate, ytterbium nitrate, and lutetium nitrate.
Examples of the element B sulfate include gallium sulfate, scandium sulfate, yttrium sulfate, lanthanum sulfate, cerium sulfate, praseodymium sulfate, neodymium sulfate, samarium sulfate, europium sulfate, gadolinium sulfate, terbium sulfate, dysprosium sulfate, and holmium sulfate. Erbium sulfate, thulium sulfate, ytterbium sulfate, lutetium sulfate and the like.
Examples of the fluoride of the B element include gallium fluoride, scandium fluoride, yttrium fluoride, lanthanum fluoride, cerium fluoride, praseodymium fluoride, neodymium fluoride, samarium fluoride, europium fluoride, and fluoride. Examples include gadolinium, terbium fluoride, dysprosium fluoride, holmium fluoride, erbium fluoride, thulium fluoride, ytterbium fluoride, and lutetium fluoride.
Examples of the chloride of the element B include gallium chloride, scandium chloride, yttrium chloride, lanthanum chloride, cerium chloride, praseodymium chloride, neodymium chloride, samarium chloride, europium chloride, gadolinium chloride, terbium chloride, dysprosium chloride, holmium chloride Erbium chloride, thulium chloride, ytterbium chloride, lutetium chloride and the like.
Examples of the B element bromide include gallium bromide, scandium bromide, yttrium bromide, lanthanum bromide, praseodymium bromide, neodymium bromide, samarium bromide, europium bromide, gadolinium bromide, and terbium bromide. Dysprosium bromide, holmium bromide, erbium bromide, thulium bromide, ytterbium bromide, lutetium bromide and the like.
Examples of the iodide of the B element include gallium iodide, scandium iodide, yttrium iodide, lanthanum iodide, cerium iodide, praseodymium iodide, neodymium iodide, samarium iodide, europium iodide, and iodide. Gadolinium, terbium iodide, dysprosium iodide, holmium iodide, erbium iodide, thulium iodide, ytterbium iodide, lutetium iodide, and the like.

  The organic compound of the B element is not particularly limited as long as it is a compound having the B element and an organic group, and can be appropriately selected according to the purpose. The element B and the organic group are bonded by, for example, an ionic bond, a covalent bond, or a coordinate bond.

  The organic group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include an alkyl group which may have a substituent, an alkoxy group which may have a substituent, and a substituent. And an acyloxy group which may have a substituent, an acetylacetonate group which may have a substituent, a cyclopentadienyl group which may have a substituent, and the like. As said alkyl group, a C1-C6 alkyl group etc. are mentioned, for example. As said alkoxy group, a C1-C6 alkoxy group etc. are mentioned, for example. As said acyloxy group, a C1-C10 acyloxy group etc. are mentioned, for example.

  Examples of the organic compound of the B element include gallium acetylacetonate, scandium isopropoxide, scandium acetate, tris (cyclopentadienyl) scandium, yttrium isopropoxide, yttrium 2-ethylhexanoate, and tris (acetylacetate). Nato) yttrium, tris (cyclopentadienyl) yttrium, lanthanum isopropoxide, lanthanum 2-ethylhexanoate, lanthanum tris (acetylacetonate), lanthanum tris (cyclopentadienyl) lanthanum, cerium 2-ethylhexanoate, tris (Acetylacetonato) cerium, tris (cyclopentadienyl) cerium, praseodymium isopropoxide, praseodymium oxalate, tris (acetylacetonato) praseodymium, tris ( Clopentadienyl) praseodymium, neodymium isopropoxide, neodymium 2-ethylhexanoate, trifluoroacetylacetonate neodymium, tris (isopropylcyclopentadienyl) neodymium, tris (ethylcyclopentadienyl) promethium, samarium isopropoxide Samarium 2-ethylhexanoate, tris (acetylacetonato) samarium, tris (cyclopentadienyl) samarium, europium 2-ethylhexanoate, tris (acetylacetonato) europium, tris (ethylcyclopentadienyl) europium, Gadolinium isopropoxide, gadolinium 2-ethylhexanoate, tris (acetylacetonato) gadolinium, tris (cyclopentadienyl) gadolinium, acetate Bium, tris (acetylacetonato) terbium, tris (cyclopentadienyl) terbium, dysprosium isopropoxide, dysprosium acetate, tris (acetylacetonato) dysprosium, tris (ethylcyclopentadienyl) dysprosium, holmium isopropoxide, Holmium acetate, tris (cyclopentadienyl) holmium, erbium isopropoxide, erbium acetate, tris (acetylacetonato) erbium, tris (cyclopentadienyl) erbium, thulium acetate, tris (acetylacetonato) thulium, tris ( Cyclopentadienyl) thulium, ytterbium isopropoxide, ytterbium acetate, tris (acetylacetonato) ytterbium, tris (cyclopen Tadienyl) ytterbium, lutetium oxalate, tris (ethylcyclopentadienyl) lutetium and the like.

  There is no restriction | limiting in particular as content of the said B element containing compound in the said coating liquid for gate insulating layer formation, According to the objective, it can select suitably.

--- Element C-containing compound-
Examples of the C element include Al (aluminum), Ti (titanium), Zr (zirconium), Hf (hafnium), Nb (niobium), and Ta (tantalum).

  Examples of the C element-containing compound include an inorganic compound of the C element and an organic compound of the C element.

  Examples of the inorganic compound of the C element include nitrate of the C element, sulfate of the C element, fluoride of the C element, chloride of the C element, bromide of the C element, iodine of the C element. And the like.

  The organic compound of the C element is not particularly limited as long as it is a compound having the C element and an organic group, and can be appropriately selected according to the purpose. The C element and the organic group are bonded by, for example, an ionic bond, a covalent bond, or a coordinate bond.

  The organic group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include an alkyl group which may have a substituent, an alkoxy group which may have a substituent, and a substituent. And an acyloxy group which may have a substituent, an acetylacetonate group which may have a substituent, a cyclopentadienyl group which may have a substituent, and the like. As said alkyl group, a C1-C6 alkyl group etc. are mentioned, for example. As said alkoxy group, a C1-C6 alkoxy group etc. are mentioned, for example. As said acyloxy group, a C1-C10 acyloxy group etc. are mentioned, for example.

  There is no restriction | limiting in particular as content of the said C element containing compound in the said coating liquid for gate insulating layer formation, According to the objective, it can select suitably.

--- Solvent ---
The solvent is not particularly limited as long as it is a solvent that can stably dissolve or disperse the various compounds, and can be appropriately selected according to the purpose. For example, toluene, xylene, mesitylene, cymene, pentylbenzene, dodecyl Benzene, bicyclohexyl, cyclohexylbenzene, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, tetralin, decalin, ethyl benzoate, N, N-dimethylformamide, propylene carbonate, 2-ethylhexanoic acid, mineral spirits, dimethylpropylene urea 4-butyrolactone, 2-methoxyethanol, ethylene glycol, propylene glycol, isopropyl alcohol, methanol, water and the like.

  There is no restriction | limiting in particular as content of the said solvent in the said coating liquid for gate insulating layer formation, According to the objective, it can select suitably.

The composition ratio between the A-element-containing compound and the B-element-containing compound in the gate insulating layer forming coating solution is not particularly limited and may be appropriately selected depending on the intended purpose. It is preferable that
That is, in terms of an atomic ratio (NA: NB) between the total number of atoms of the A element contained in each compound (NA) and the total number of atoms of the B element (NB), the following: A range is preferable.
NA: NB = (3-50) at%: (50-97) at%
However, NA + NB = 100at%

The composition ratio of the A-element-containing compound, the B-element-containing compound, and the C-element-containing compound in the gate insulating layer forming coating liquid is not particularly limited and is appropriately selected depending on the purpose. However, the following range is preferable.
That is, the total number of atoms of the A element contained in each compound (NA), the total number of atoms of the B element (NB), and the total number of atoms of the C element (NC) In terms of the atomic ratio (NA: NB: NC), the following range is preferable.
NA: NB: NC = (3-47) at%: (50-94) at%: (3-47) at%

--- Forming method of gate insulating layer using coating liquid for forming gate insulating layer--
An example of a method of forming the gate insulating layer using the gate insulating layer forming coating solution will be described. The method for forming the gate insulating layer includes a coating process and a heat treatment process, and further includes other processes as necessary.

  The application step is not particularly limited as long as it is a step of applying the gate insulating layer forming coating solution to an object to be coated, and can be appropriately selected according to the purpose. The application method is not particularly limited and may be appropriately selected depending on the purpose. For example, the method may be a method of patterning by photolithography after film formation by a solution process, or a printing method such as inkjet, nanoimprint, or gravure. And a method of directly forming a desired shape. Examples of the solution process include dip coating, spin coating, die coating, and nozzle printing.

  The heat treatment step is not particularly limited as long as it is a step of heat-treating the gate insulating layer forming coating solution applied to the article to be coated, and can be appropriately selected according to the purpose. When the heat treatment is performed, the gate insulating layer forming coating solution applied to the object to be coated may be dried by natural drying or the like. By the heat treatment, drying of the solvent, generation of the paraelectric amorphous oxide, and the like are performed.

  In the heat treatment step, drying of the solvent (hereinafter referred to as “drying process”) and generation of the paraelectric amorphous oxide (hereinafter referred to as “generation process”) are performed at different temperatures. preferable. That is, it is preferable that after the solvent is dried, the paraelectric amorphous oxide is generated by raising the temperature. When the paraelectric amorphous oxide is generated, for example, decomposition of the A-element-containing compound, the B-element-containing compound, and the C-element-containing compound occurs.

  There is no restriction | limiting in particular as temperature of the said drying process, According to the solvent to contain, it can select suitably, For example, 80 to 180 degreeC is mentioned. In the drying, it is effective to use a vacuum oven or the like for lowering the temperature. There is no restriction | limiting in particular as time of the said drying process, According to the objective, it can select suitably, For example, 1 minute-1 hour are mentioned.

  There is no restriction | limiting in particular as temperature of the said production | generation process, Although it can select suitably according to the objective, 100 degreeC or more and less than 550 degreeC are preferable, and 200 to 500 degreeC is more preferable. There is no restriction | limiting in particular as time of the said production | generation process, According to the objective, it can select suitably, For example, 1 hour-5 hours are mentioned.

  In the heat treatment step, the drying treatment and the generation treatment may be performed continuously, or may be divided into a plurality of steps.

  There is no restriction | limiting in particular as the method of the said heat processing, According to the objective, it can select suitably, For example, the method etc. which heat the said to-be-coated article are mentioned. There is no restriction | limiting in particular as atmosphere in the said heat processing, Although it can select suitably according to the objective, Oxygen atmosphere is preferable. By performing the heat treatment in the oxygen atmosphere, the decomposition product can be quickly discharged out of the system, and the generation of the paraelectric amorphous oxide can be promoted.

  In the heat treatment, irradiating the material after the drying treatment with ultraviolet light having a wavelength of 400 nm or less is effective in promoting the reaction of the generation treatment. By irradiating ultraviolet light with a wavelength of 400 nm or less, chemical bonds such as organic substances contained in the material after the drying treatment can be broken and the organic substances can be decomposed, so that the paraelectric amorphous oxide is efficiently formed. can do. The ultraviolet light having a wavelength of 400 nm or less is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include ultraviolet light having a wavelength of 222 nm using an excimer lamp. Moreover, it is also preferable to provide ozone instead of or in combination with the irradiation with ultraviolet light. By applying the ozone to the substance after the drying treatment, generation of oxide is promoted.

  There is no restriction | limiting in particular as average thickness of the said gate insulating layer, Although it can select suitably according to the objective, 50 nm-3 micrometers are preferable, and 100 nm-1 micrometer are more preferable.

<Active layer>
The active layer is a layer provided adjacent to the source electrode and the drain electrode.

The active layer is an oxide semiconductor having a carrier density of 4.0 × 10 ¹⁷ / cm ³ or more. The carrier density is more preferably 1.0 × 10 ¹⁸ / cm ³ or more. Moreover, although it can select suitably as an upper limit according to the objective, 1.0 * 10 < ²¹ > / cm < ³ > or less is preferable and 1.0 * 10 < ²⁰ > / cm < ³ > or less is more preferable. This is because if the number of carriers is excessive, control by the gate voltage will not be effective.

  The transistor of the present invention achieves a high on-current value by using an oxide semiconductor having a high carrier density in the active layer, and effectively controls a large number of carriers by using the above-described material for the gate insulating layer. As a result, the rising characteristic is steep and the characteristics of high mobility are obtained.

  The carrier density can be obtained by performing hole measurement on the oxide semiconductor film.

  The method for adjusting the carrier density of the active layer is not particularly limited and can be appropriately selected according to the purpose. For example, the adjustment of the oxide composition, the heating temperature in the film forming process, and the conditions of the atmosphere Adjustment etc. are mentioned.

  In a preferred embodiment, the active layer is an n-type oxide semiconductor containing at least one of In, Zn, Sn, and Ti.

  The n-type oxide semiconductor is at least one of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, a hexavalent cation, a heptavalent cation, and an octavalent cation. It is preferable that substitution doping is performed with a dopant, and the valence of the dopant is larger than the valence of a metal ion (excluding the dopant) constituting the n-type oxide semiconductor. The substitutional doping is also referred to as n-type doping.

In this substitution-doped n-type oxide semiconductor, a part of the metal ions constituting the n-type oxide semiconductor, which is the parent phase, is substituted with a dopant having a higher valence, resulting in a difference in valence. The electrons emitted in excess contribute to the carrier of n-type conduction. When carrier electrons generated by such substitutional doping have semiconductor characteristics, the characteristics are more stable. This is because the number of carrier electrons derived from oxygen vacancies is easily affected by oxidation / reduction reactions and oxygen adsorption on the film surface due to the exchange of oxygen between the semiconductor and the outside (atmosphere and adjacent layers). This is because the number of carrier electrons derived from substitutional doping is relatively unaffected by such a state change.
Another advantage is that the number of carrier electrons derived from substitutional doping is excellent in controllability and a desired carrier concentration can be easily realized. As described above, oxygen enters and exits the semiconductor relatively easily, so that it is difficult to precisely control the amount or to maintain a desired value. On the other hand, the number of carrier electrons derived from substitutional doping can be easily and precisely controlled mainly by selecting the kind of dopant element and the doping amount.

The active layer of the field effect transistor of the present invention has a carrier density of 4.0 × 10 ¹⁷ / cm ³ or more. This carrier density can be realized by appropriate selection of the type of dopant element and the doping amount. This is a preferred form. In addition, it is preferable that the oxygen vacancies in the active layer be suppressed as much as possible by adjusting the composition and film forming process conditions, so that carriers are generated mainly by substitutional doping.

In order to reduce oxygen vacancies in the active layer, it is effective to introduce more oxygen into the film in the step of forming the n-type oxide semiconductor layer (active layer). For example, when an n-type oxide semiconductor layer is formed by a sputtering method, a film with few oxygen vacancies can be formed by increasing the oxygen concentration in the sputtering atmosphere. Alternatively, in the case where the n-type oxide semiconductor layer is formed by applying and baking a coating solution, a film with less oxygen vacancies can be formed by increasing the oxygen concentration in the atmosphere during baking.
Further, the amount of oxygen vacancies can be reduced by the composition of the n-type oxide semiconductor. For example, by introducing a certain amount of metal elements having high affinity with oxygen (Si, Ge, Zr, Hf, Al, Ga, Sc, Y, Ln, alkaline earth metals, etc.), oxygen deficiency is generated. Can be suppressed.

The kind of dopant is preferably selected in consideration of the ion radius, coordination number, orbital energy, and the like. The dopant concentration can be appropriately selected according to the material of the parent phase, the kind of dopant, the site to be substituted, the film forming process, desired transistor characteristics, and the like.
Theoretically, the number of electrons generated when one atom is substituted is the value obtained by subtracting the valence of the metal atom of the parent phase constituting the n-type oxide semiconductor from the valence of the cation as the dopant. It becomes. That is, in order to generate the same number of electrons with a smaller amount of doping, it is preferable that the valence of the dopant is large. Furthermore, it is preferable that the difference between the valence of the dopant and the valence of the metal atoms constituting the n-type oxide semiconductor is large. If a large amount of dopant is present, it disturbs the crystal structure and atomic arrangement and hinders the movement of carrier electrons. Therefore, it is a preferable mode to generate necessary and sufficient carrier electrons with as little doping amount as possible.
It is also a preferred form to select a dopant whose ionic radius is close to that of the atom to be substituted. As a result, the replacement efficiency is increased, and it is possible to suppress unnecessary dopants that do not contribute to carrier generation from deteriorating transistor characteristics.
Since the carrier generation efficiency by doping depends on various process conditions at the time of manufacturing the transistor, it is also important to select a process condition that increases the generation efficiency. For example, the substrate temperature when an n-type oxide semiconductor layer is formed by sputtering, the firing temperature when an n-type oxide semiconductor layer is formed by coating and firing a coating solution, and the n-type oxide semiconductor layer are formed. By appropriately selecting the annealing temperature or the like to be applied later, a desired carrier concentration can be achieved with a smaller amount of doping.

The concentration of the dopant is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of mobility and rising characteristics, 0.01 at% to 10 at% is preferable, and 0.01 atl% to 5 at% is more preferable. 0.05 at% to 2 at% is particularly preferable. Here, “at%” means the number of atoms in the semiconductor of the metal element to be substituted (that is, the number of moles of the metal element to be substituted with the dopant contained in the n-type oxide semiconductor) and the dopant. The sum of the number of atoms and the number of atoms is 100%, and the ratio of the number of atoms of the dopant to that is expressed. By appropriately setting the process amount and the doping amount within this range, the carrier concentration of the oxide semiconductor can be 4.0 × 10 ¹⁷ cm ⁻³ or more and the carrier mobility can be 0.1 cm ² / Vs or more. These are preferable characteristics as the active layer of the field effect transistor of the present invention.

In the n-type oxide semiconductor forming the active layer, the n-type oxide semiconductor is preferably single crystal or polycrystalline in order for substitution doping to work effectively. Alternatively, even when diffraction lines are not observed by X-ray diffraction (XRD) or the like and there is no long-range order (generally called an amorphous state), the atoms are ordered with short-range order. It is preferable to have a rigid structure in which are arranged. This is because when the oxide semiconductor serving as a parent phase is a highly amorphous material, carriers are not generated because the structure is locally changed to a stable state even when substitutional doping is performed. In the case of an oxide having a rigid structure, the oxygen coordination polyhedron (for example, WO ₆ and InO ₆ octahedron) and its connection mode (for example, InO ₆ ridge shared chain) are maintained, and substitution doping works effectively. In such a structure, since the state density of the tail state specific to the amorphous state is small, subgap absorption is small, and as a result, the photodegradation property is superior to a material having high amorphous property.
Even in a single crystal / polycrystal state in which long-range order exists, doping is also effective. When the conduction band is composed of 4s, 5s, and 6s bands of heavy metal ions, the influence of grain boundaries is small, and good characteristics can be obtained even in a polycrystalline state. However, when the doping amount is excessive and the dopant segregates at the grain boundary, it is preferable to lower the dopant concentration. Also, post-annealing at 200 ° C. to 300 ° C. is preferable in order to improve the adhesion and electrical contact at the interface between the source / drain electrodes and the active layer. Further, the crystallinity may be improved by annealing at a higher temperature.

In the study by the present inventors, when an oxide containing at least one of In, Zn, Sn, and Ti is selected as a parent phase of an n-type oxide semiconductor, substitutional doping functions more effectively. Better transistor characteristics were obtained.
Further, it has been described above that it is effective to contain an element having a high oxygen affinity in the active layer in order to reduce oxygen deficiency. However, as such an element having a high oxygen affinity, Si, Ge, Zr, Hf, Al , Ga, Sc, Y, Ln, and alkaline earth metals have been found suitable.

  There is no restriction | limiting in particular as a formation method of the said active layer, According to the objective, it can select suitably.

Substitutional doping is easily achieved by adding a dopant raw material to the raw material of the mother layer when forming the active layer. For example, when the active layer is formed by sputtering, a parent phase target to which a dopant element is added at a desired concentration may be used. However, when the desired dope amount is small (for example, 0.2 at% or less), there is a problem that it is difficult to uniformly contain such a small amount of atoms in an accurate value and in the entire target.
From the viewpoint of controllability of the doping amount, it is a more preferable form that the active layer is formed by a coating process. In the coating process, a coating solution for forming an n-type oxide semiconductor film containing a semiconductor raw material compound, a compound containing an element serving as a dopant (dopant element-containing compound), and a solvent is applied onto an object to be coated. The active layer is formed by firing. In this coating solution, the desired doping is realized by making the blending ratio of the dopant element-containing compound to the semiconductor raw material compound correspond to the desired doping amount. In the coating solution, the dopant element-containing compound can be easily added and uniformly stirred in a very small proportion of the dopant amount of 0.2 at% or less, so that a method for forming a substitution-doped n-type oxide semiconductor is provided. Therefore, it can be said that the coating process is more suitable.

<Source electrode and drain electrode>
The source electrode and the drain electrode are not particularly limited as long as they are electrodes for taking out current, and can be appropriately selected according to the purpose.

  The material of the source electrode and the drain electrode is not particularly limited and may be appropriately selected according to the purpose. A metal or alloy such as Mo, Al, or Ag, or a transparent conductive oxide such as ITO or ATO. Organic conductors such as polyethylenedioxythiophene (PEDOT) and polyaniline (PANI) can be used.

  There is no restriction | limiting in particular as a formation method of the said source electrode and the said drain electrode, According to the objective, it can select suitably, For example, the same method as the formation method described in description of the said gate electrode is mentioned.

  There is no restriction | limiting in particular as average thickness of the said source electrode and the said drain electrode, Although it can select suitably according to the objective, 20 nm-1 micrometer are preferable and 50 nm-300 nm are more preferable.

<Insulating layer (protective layer)>
A structure in which an insulating layer (protective layer) is stacked over at least one of the source electrode, the drain electrode, and the active layer is also a preferable mode for the transistor. In many cases, this insulating layer serves as a so-called protective layer that prevents the source electrode, the drain electrode, and the active layer from directly contacting oxygen or moisture in the atmosphere to change their characteristics. In a display device using a field effect transistor, a display element including a light-emitting layer may be stacked on the top of the transistor. In this case, the insulating layer absorbs a step corresponding to the shape of the transistor. In some cases, it also serves as a so-called flattening film for smoothing the surface.

Examples of the material of the insulating layer is not particularly limited and may be appropriately selected depending on the purpose, for example, SiO _2, SiON, and materials being used already widely mass production of SiNx or the like, polyimide (PI) Ya Organic materials such as fluorine-based resins are exemplified.

The structure of the field effect transistor is not particularly limited and may be appropriately selected depending on the purpose. For example, the top contact / bottom gate type (FIG. 1), the bottom contact / bottom gate type (FIG. 2), Examples include a top contact / top gate type (FIG. 3) and a bottom contact / top gate type (FIG. 4).
1 to 4, reference numeral 21 denotes a base material, reference numeral 22 denotes an active layer, reference numeral 23 denotes a source electrode, reference numeral 24 denotes a drain electrode, reference numeral 25 denotes a gate insulating layer, and reference numeral 26 denotes a gate electrode. These drawings do not show the above-mentioned insulating layer (protective layer).

  The field effect transistor can be suitably used for a display element to be described later, but is not limited thereto, and can be used for an IC card, an ID tag, and the like, for example.

<Method of manufacturing field effect transistor>
An example of a method for manufacturing the field effect transistor will be described.

First, a gate electrode is formed on a base material.
There is no restriction | limiting in particular as a shape, a structure, and a magnitude | size of the said base material, According to the objective, it can select suitably.
There is no restriction | limiting in particular as a material of the said base material, According to the objective, it can select suitably, For example, a glass base material, a plastic base material, etc. are mentioned.
There is no restriction | limiting in particular as said glass base material, According to the objective, it can select suitably, For example, an alkali free glass, silica glass, etc. are mentioned.
There is no restriction | limiting in particular as said plastic base material, According to the objective, it can select suitably, For example, a polycarbonate (PC), a polyimide (PI), a polyethylene terephthalate (PET), a polyethylene naphthalate (PEN) etc. are mentioned. It is done.
The base material is preferably subjected to pretreatment such as oxygen plasma, UV ozone, and UV irradiation cleaning in terms of surface cleaning and adhesion improvement.

Subsequently, a gate insulating layer is formed on the gate electrode.
Subsequently, an active layer made of an oxide semiconductor is formed in the channel region and on the gate insulating layer.
Subsequently, a source electrode and a drain electrode are formed on the gate insulating layer so as to straddle the active layer.
Thus, a field effect transistor is manufactured. In this manufacturing method, for example, a top contact / bottom gate type field effect transistor as shown in FIG. 1 is manufactured.

(Display element)
The display element of the present invention includes at least a light control element and a drive circuit that drives the light control element, and further includes other members as necessary.

<Light control element>
The light control element is not particularly limited as long as it is an element that controls light output in accordance with a drive signal, and can be appropriately selected according to the purpose. For example, an electroluminescence (EL) element, electrochromic ( EC) element, liquid crystal element, electrophoretic element, electrowetting element and the like.

<Drive circuit>
The drive circuit is not particularly limited as long as it has the field effect transistor of the present invention, and can be appropriately selected according to the purpose.

<Other members>
There is no restriction | limiting in particular as said other member, According to the objective, it can select suitably.

  Since the display element includes the field-effect transistor of the present invention, it can be driven at high speed, and can have a long life and low power consumption.

(Image display device)
The image display device of the present invention includes at least a plurality of display elements, a plurality of wirings, and a display control device, and further includes other members as necessary.

<Multiple display elements>
The plurality of display elements are not particularly limited as long as they are a plurality of the display elements of the present invention arranged in a matrix, and can be appropriately selected according to the purpose.

<Multiple wiring>
The plurality of wirings are not particularly limited as long as the gate voltage and the signal voltage can be individually applied to each field effect transistor in the plurality of display elements, and can be appropriately selected according to the purpose.

<Display control device>
The display control device is not particularly limited as long as the gate voltage and the signal voltage of each field effect transistor can be individually controlled via the plurality of wirings according to image data. It can be selected appropriately.

<Other members>
There is no restriction | limiting in particular as said other member, According to the objective, it can select suitably.
Since the image display device includes the display element of the present invention, it is possible to reduce variation between elements, and to display a high-quality image on a large screen.

(system)
The system of the present invention includes at least the image display device of the present invention and an image data creation device.
The image data creation device creates image data based on image information to be displayed, and outputs the image data to the image display device.
Since the system includes the image display device of the present invention, it is possible to display image information with high definition.

Hereinafter, a display element, an image display device, and a system of the present invention will be described with reference to the drawings.
First, a television device as a system of the present invention will be described with reference to FIG. Note that the configuration of FIG. 5 is an example, and the television apparatus as the system of the present invention is not limited to this.

In FIG. 5, a television apparatus 100 includes a main control device 101, a tuner 103, an AD converter (ADC) 104, a demodulation circuit 105, a TS (Transport Stream) decoder 106, an audio decoder 111, a DA converter (DAC) 112, an audio output. Circuit 113, speaker 114, video decoder 121, video / OSD synthesis circuit 122, video output circuit 123, image display device 124, OSD drawing circuit 125, memory 131, operation device 132, drive interface (drive IF) 141, hard disk device 142 An optical disk device 143, an IR light receiver 151, and a communication control device 152.
The video decoder 121, the video / OSD synthesis circuit 122, the video output circuit 123, and the OSD drawing circuit 125 constitute an image data creation device.

The main control device 101 includes a CPU, a flash ROM, a RAM, and the like, and controls the entire television device 100.
The flash ROM stores a program described by codes readable by the CPU, various data used for processing by the CPU, and the like.
The RAM is a working memory.

  The tuner 103 selects a preset channel broadcast from the broadcast waves received by the antenna 210.

  The ADC 104 converts the output signal (analog information) of the tuner 103 into digital information.

  The demodulation circuit 105 demodulates the digital information from the ADC 104.

  The TS decoder 106 performs TS decoding on the output signal of the demodulation circuit 105 and separates audio information and video information.

  The audio decoder 111 decodes the audio information from the TS decoder 106.

  The DA converter (DAC) 112 converts the output signal of the audio decoder 111 into an analog signal.

  The audio output circuit 113 outputs the output signal of the DA converter (DAC) 112 to the speaker 114.

  The video decoder 121 decodes the video information from the TS decoder 106.

  The video / OSD synthesis circuit 122 synthesizes the output signal of the video decoder 121 and the output signal of the OSD drawing circuit 125.

  The video output circuit 123 outputs the output signal of the video / OSD synthesis circuit 122 to the image display device 124.

  The OSD drawing circuit 125 includes a character generator for displaying characters and figures on the screen of the image display device 124. The OSD drawing circuit 125 receives a signal including display information in response to an instruction from the operation device 132 and the IR light receiver 151. Generate.

  AV (Audio-Visual) data and the like are temporarily stored in the memory 131.

  The operation device 132 includes, for example, an input medium (not shown) such as a control panel, and notifies the main control device 101 of various information input by the user.

  The drive IF 141 is a bidirectional communication interface, and is compliant with ATAPI (AT Attachment Packet Interface) as an example.

  The hard disk device 142 includes a hard disk and a drive device for driving the hard disk. The drive device records data on the hard disk and reproduces data recorded on the hard disk.

  The optical disk device 143 records data on an optical disk (for example, a DVD) and reproduces data recorded on the optical disk.

  The IR light receiver 151 receives the optical signal from the remote control transmitter 220 and notifies the main control device 101 of it.

  The communication control device 152 controls communication with the Internet. Various information can be acquired via the Internet.

FIG. 6 is a schematic configuration diagram showing an example of the image display apparatus of the present invention.
In FIG. 6, the image display device 124 includes a display device 300 and a display control device 400.
As shown in FIG. 7, the display device 300 includes a display 310 in which a plurality of (here, n × m) display elements 302 are arranged in a matrix.
Further, as shown in FIG. 8, the display 310 has n scanning lines (X0, X1, X2, X3,..., Xn-2, Xn) arranged at equal intervals along the X-axis direction. -1) and m data lines (Y0, Y1, Y2, Y3,..., Ym-1) arranged at equal intervals along the Y-axis direction, at equal intervals along the Y-axis direction. And m current supply lines (Y0i, Y1i, Y2i, Y3i,..., Ym-1i) arranged.
Therefore, the display element can be specified by the scanning line and the data line.

Hereinafter, the display element of the present invention will be described with reference to FIG.
FIG. 9 is a schematic configuration diagram showing an example of the display element of the present invention.
As shown in FIG. 9 as an example, the display element includes an organic EL (electroluminescence) element 350 and a drive circuit 320 for causing the organic EL element 350 to emit light. The drive circuit 320 is a current-driven 2Tr-1C basic circuit, but is not limited thereto. That is, the display 310 is a so-called active matrix organic EL display.

  FIG. 10 shows an example of the positional relationship between the organic EL element 350 in the display element 302 and the field effect transistor 20 as a drive circuit. Here, the organic EL element 350 is disposed beside the field effect transistor 20. The field effect transistor 10 and the capacitor (not shown) are also formed on the same substrate.

Although not shown in FIG. 10, it is also preferable to provide a protective film on the active layer 22. As a material for the protective film, SiO ₂ , SiON, SiNx, Al ₂ O ₃ , a fluorine-based polymer, or the like can be appropriately used.

For example, as shown in FIG. 11, the organic EL element 350 may be disposed on the field effect transistor 20. In this case, since the gate electrode 26 is required to be transparent, the gate electrode 26 includes ZnO added with ITO, In ₂ O ₃ , SnO ₂ , ZnO, and Ga, ZnO added with Al, and Sb. A transparent oxide having conductivity such as SnO ₂ to which is added is used. Reference numeral 360 denotes an interlayer insulating film (flattening film). For this interlayer insulating film, polyimide, acrylic resin, or the like can be used.

FIG. 12 is a schematic configuration diagram illustrating an example of an organic EL element.
In FIG. 12, the organic EL element 350 includes a cathode 312, an anode 314, and an organic EL thin film layer 340.

  The material of the cathode 312 is not particularly limited and may be appropriately selected depending on the purpose. For example, aluminum (Al), magnesium (Mg) -silver (Ag) alloy, aluminum (Al) -lithium (Li) An alloy, ITO (Indium Tin Oxide), etc. are mentioned. A magnesium (Mg) -silver (Ag) alloy becomes a high reflectance electrode if it is sufficiently thick, and a semitransparent electrode if it is an extremely thin film (less than about 20 nm). Although light is extracted from the anode side in FIG. 12, light can be extracted from the cathode side by using a transparent or semi-transparent electrode for the cathode.

  There is no restriction | limiting in particular as a material of the anode 314, According to the objective, it can select suitably, For example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), a silver (Ag) -neodymium (Nd) alloy, etc. Is mentioned. In addition, when a silver alloy is used, it becomes a high reflectance electrode and is suitable when taking out light from the cathode side.

  The organic EL thin film layer 340 includes an electron transport layer 342, a light emitting layer 344, and a hole transport layer 346. The electron transport layer 342 is connected to the cathode 312, and the hole transport layer 346 is connected to the anode 314. When a predetermined voltage is applied between the anode 314 and the cathode 312, the light emitting layer 344 emits light.

  Here, the electron transport layer 342 and the light emitting layer 344 may form one layer, an electron injection layer may be provided between the electron transport layer 342 and the cathode 312, and hole transport is further performed. A hole injection layer may be provided between the layer 346 and the anode 314.

  Further, the case of so-called “bottom emission” in which light is extracted from the substrate side has been described, but “top emission” in which light is extracted from the side opposite to the substrate may be used.

The drive circuit 320 in FIG. 9 will be described.
The drive circuit 320 includes two field effect transistors 10 and 20 and a capacitor 30.

  The field effect transistor 10 operates as a switch element. The gate electrode G of the field effect transistor 10 is connected to a predetermined scanning line, and the source electrode S of the field effect transistor 10 is connected to a predetermined data line. The drain electrode D of the field effect transistor 10 is connected to one terminal of the capacitor 30.

  The field effect transistor 20 supplies current to the organic EL element 350. The gate electrode G of the field effect transistor 20 is connected to the drain electrode D of the field effect transistor 10. The drain electrode D of the field effect transistor 20 is connected to the anode 314 of the organic EL element 350, and the source electrode S of the field effect transistor 20 is connected to a predetermined current supply line.

  The capacitor 30 stores the state of the field effect transistor 10, that is, data. The other terminal of the capacitor 30 is connected to a predetermined current supply line.

  Therefore, when the field effect transistor 10 is turned on, image data is stored in the capacitor 30 via the signal line Y2, and even after the field effect transistor 10 is turned off, the field effect transistor 10 is turned on. The organic EL element 350 is driven by holding 20 in the “on” state corresponding to the image data.

FIG. 13 is a schematic configuration diagram showing another example of the image display device of the present invention.
In FIG. 13, the image display device includes a display element 302, wiring (scanning line, data line, current supply line), and a display control device 400.
The display control device 400 includes an image data processing circuit 402, a scanning line driving circuit 404, and a data line driving circuit 406.
The image data processing circuit 402 determines the luminance of the plurality of display elements 302 in the display based on the output signal of the video output circuit 123.
The scanning line driving circuit 404 individually applies voltages to the n scanning lines in accordance with an instruction from the image data processing circuit 402.
The data line driving circuit 406 individually applies voltages to the m data lines in accordance with an instruction from the image data processing circuit 402.

  Moreover, although the said embodiment demonstrated the case where a light control element was an organic EL element, it is not limited to this, For example, a light control element may be an electrochromic element. In this case, the display is an electrochromic display.

  The light control element may be a liquid crystal element. In this case, the display is a liquid crystal display, and a current supply line to the display element 302 ′ is not required as shown in FIG. 14. Further, as shown in FIG. 15, the drive circuit 320 ′ can be configured by one field effect transistor 40 similar to the field effect transistors 10 and 20. In the field effect transistor 40, the gate electrode G is connected to a predetermined scanning line, and the source electrode S is connected to a predetermined data line. Further, the drain electrode D is connected to the capacitor 361 and the pixel electrode of the liquid crystal element 370.

  The light control element may be an electrophoretic element, an inorganic EL element, or an electrowetting element.

  As described above, the case where the system of the present invention is a television device has been described. However, the present invention is not limited to this, and the image display device 124 may be provided as a device for displaying images and information. For example, a computer system in which a computer (including a personal computer) and an image display device 124 are connected may be used.

  In addition, the image display device 124 is used as a display unit in portable information devices such as mobile phones, portable music playback devices, portable video playback devices, electronic BOOKs and PDAs (Personal Digital Assistants), and imaging devices such as still cameras and video cameras. Can be used. In addition, the image display device 124 can be used as a display unit for various information in a mobile system such as a car, an aircraft, a train, and a ship. Furthermore, the image display device 124 can be used as a display unit for various information in a measurement device, an analysis device, a medical device, and an advertising medium.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
<Fabrication of field effect transistor>
-Formation of gate electrode-
On the glass substrate, Al was vapor-deposited so as to have a thickness of 100 nm, and a gate electrode was formed by performing photolithography and patterning in a line shape.

-Formation of gate insulation layer-
La (thd) ₃ and Ba (thd) ₂ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) dissolved in tetraethylene glycol dimethyl ether (tetraglyme) and tetrahydrofuran (THF), respectively. A LaBa oxide insulating film having a thickness of about 100 nm was formed on a glass substrate including a gate electrode by a CVD method as a liquid raw material, and this was used as a gate insulating layer. The ratio of the number of La and Ba atoms in the oxide insulating film is La: Ba = 9: 1.

-Formation of active layer-
An argon (Ar) and oxygen (O ₂ ) gas is introduced into the chamber, and a MgIn ₂ O ₄ film serving as an active layer is formed by performing a DC sputtering method at room temperature using a MgIn ₂ O ₄ sintered body target. A film was formed. The oxygen ratio in the flow rate of the gas introduced into the chamber during film formation was 1.0% of oxygen with respect to the total flow rate (sum of the flow rates of argon gas and oxygen gas). Patterning was performed by forming a film through a metal mask. Subsequently, heat treatment was performed in the atmosphere at 300 ° C. for 1 hour using an oven. Such annealing treatment is generally performed for the purpose of improving transistor characteristics by reducing the interface defect level density between the active layer and the gate insulating layer film.

-Formation of source and drain electrodes-
A source electrode and a drain electrode having a thickness of 100 nm were formed on the gate insulating layer and the active layer by vacuum deposition. Al was used as a deposition source. The patterning was performed by forming a film through a metal mask, and the channel width was 200 μm and the channel length was 50 μm. Subsequently, in order to improve the electrical contact between the active layer and the source / drain electrodes, a heat treatment was performed in an atmosphere at 200 ° C. for 1 hour using an oven.

  Through the above process, a top contact / bottom gate type field effect transistor similar to FIG. 1 was obtained.

<Measurement of carrier density of active layer>
In order to produce an element for measuring holes, an MgIn ₂ O ₄ film was formed on another glass substrate under the same conditions as the active layer. When sputtering, a shadow mask was used to form an 8 mm square pattern. Subsequently, a contact electrode for hole measurement was formed using a shadow mask at four corners on the MgIn ₂ O ₄ film using a vacuum deposition method. Al was used as a deposition source.
With respect to this Hall measuring element, specific resistance measurement and Hall effect measurement were performed using a Hall effect measuring system (ResiTest 8300, manufactured by Toyo Technica Co., Ltd.), and the electron carrier density (/ cm ³ ) of the MgIn ₂ O ₄ film was obtained. The result was 5.7 × 10 ¹⁷ / cm ³ .

<Measurement of relative dielectric constant of gate insulating layer>
In order to produce an element for measuring the relative dielectric constant, Al was evaporated on another glass substrate to form a lower electrode, and then a LaBa oxide insulating film was formed under the same conditions as the gate insulating layer. Subsequently, Al was deposited to form an upper electrode. In all the film formations, a desired pattern was formed using a shadow mask, and a capacitor having an area of 0.5 mm ² was obtained. On the other hand, capacitance measurement was performed to calculate a relative dielectric constant. The relative dielectric constant at a frequency of 1 kHz was 11.8.

<Measurement of crystallinity of gate insulating layer>
In order to perform an X-ray diffraction experiment, a LaBa oxide insulating film was formed on another glass substrate under the same conditions as the gate insulating layer. Subsequently, in order to make the thermal history the same as that of the gate insulating layer of the transistor, heat treatment at 300 ° C. for 1 hour and heat treatment at 200 ° C. for 1 hour were performed. FIG. 16 shows the result of X-ray diffraction measurement performed on this film using X'PertPro manufactured by Philips. The X-ray used was a Cu Kα ray (wavelength 1.5405 mm). A diffraction peak was not observed, and it was found that the gate insulating layer was an amorphous oxide film.

<Measurement of transistor characteristics>
About the obtained field effect transistor, transistor performance evaluation was implemented using the semiconductor parameter analyzer apparatus (Agilent Technology company make, semiconductor parameter analyzer 4156C). The source-drain voltage Vds was set to 10 V, the gate voltage Vg was changed from -15 V to +15 V, the source-drain current Ids was measured, and the transfer characteristics (Vg-Ids characteristics) were evaluated. The obtained results are shown in FIG. Further, Ids was continuously measured while changing Vg from +15 V to −15 V, but the obtained transfer characteristics overlapped with FIG. 17, and no hysteresis was observed. FIG. 17 also shows the absolute value of the gate current Ig. It was confirmed that the leakage current was sufficiently small as 0.1 pA or less.
Based on the transfer characteristics shown in FIG. 17, the field effect mobility μ in the saturation region was calculated. Also, the Ids on / off ratio was calculated. Here, the Ids in the on state was calculated as a value at Vg = 15V, and the Ids in the off state was calculated as an average value of values in Vg = −15V to −10V. Further, an s value (a gate voltage difference required to increase Ids by one digit) indicating the steepness of the rise from the off state to the on state was calculated. The results are shown in Table 1.
In the figures and tables, “e” and “E” represent powers of 10. That is, “1e-3” and “1E-3” represent “1 × 10 ⁻³ ”, and “1e-10” and “1E-10” represent “1 × 10 ⁻¹⁰ ”.

(Comparative Example 1)
A field effect transistor was produced in the same manner as in Example 1 except that the method for forming the gate insulating layer was as follows.

-Formation of gate insulation layer-
An SiO ₂ film having a thickness of 200 nm was formed on a glass substrate including a gate electrode by an RF sputtering method, and this was used as a gate insulating layer. A SiO ₂ glass target was used as the sputtering target. During film formation, argon gas and oxygen gas were flowed into the chamber, and the flow rate ratio of oxygen gas was 25.0%. Further, when the relative dielectric constant of the SiO ₂ film was measured in the same manner as in Example 1, it was 3.9.

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. 18, and the calculated field effect mobility and on / off ratio values are shown in Table 1. However, here, the value of the off-current is calculated as Ids when Vg is −15V. Also, the s value was unknown because there was no clear off state in the current measurement range (Vg = -15V to 15V) and the rising could not be defined.

(Comparative Example 2)
A field effect transistor was produced in the same manner as in Example 1 except that the method for forming the gate insulating layer was as follows.

-Formation of gate insulation layer-
On a glass substrate including a gate electrode, a SiON film having a thickness of 200 nm was formed at a temperature of 200 ° C. using SiH ₄ gas and N ₂ O gas as a raw material by plasma CVD, and this was used as a gate insulating layer. Further, when the relative dielectric constant of the SiON film was measured in the same manner as in Example 1, it was 7.0.

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. 19, and the calculated field effect mobility, on / off ratio, and s value are shown in Table 1. However, here, the value of the off-current is calculated as Ids when Vg is −15V.

(Comparative Example 3 and Comparative Example 4)
A field effect transistor was fabricated in the same manner as in Comparative Example 1 except that the method for forming the active layer was changed as follows. (Comparative Example 3)
A field effect transistor was produced in the same manner as in Comparative Example 2 except that the method for forming the active layer was changed as follows. (Comparative Example 4)

-Formation of active layer-
An argon (Ar) and oxygen (O ₂ ) gas is introduced into the chamber, and a MgIn ₂ O ₄ film serving as an active layer is formed by performing a DC sputtering method at room temperature using a MgIn ₂ O ₄ sintered body target. A film was formed. The oxygen ratio in the flow rate of the gas introduced into the chamber during film formation was 40.0% of oxygen with respect to the total flow rate. Patterning was performed by forming a film through a metal mask. Subsequently, heat treatment was performed in the atmosphere at 300 ° C. for 1 hour using an oven. Further, the carrier density of this MgIn ₂ O ₄ film was determined in the same manner as in Example 1, and it was 7.51 × 10 ¹⁶ / cm ³ .

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. 20 (Comparative Example 3) and FIG. 21 (Comparative Example 4). The calculated field effect mobility, on / off ratio, and s value are shown in Table 1.

(Comparative Example 5)
A field effect transistor was fabricated in the same manner as in Example 1 except that the method for forming the gate insulating layer was changed as follows.

-Formation of gate insulation layer-
12 mL of toluene is mixed with 11 mL of 2-ethylhexanoate yttrium toluene solution (Y content 8 wt%) and 0.4 mL of 2-ethylhexanoate calcium mineral spirit solution (Ca content 5 wt%), and an yttrium calcium oxide insulating film A forming coating solution was obtained. The ratio of the number of atoms in the coating solution is Y: Ca = 10: 0.5.
The coating solution is spin-coated on a glass substrate including a gate electrode, dried in an atmosphere at 120 ° C. for 1 hour using an oven, and then fired at 400 ° C. for 3 hours in an oxygen atmosphere to form a gate insulating layer. did. The average thickness of the gate insulating layer was 105 nm. When the relative dielectric constant of this film was measured in the same manner as in Example 1, it was 11.4. Moreover, the result of having measured X-ray diffraction like Example 1 was shown in FIG. Peaks are observed at 2θ of about 29 degrees, about 34 degrees, about 48.5 degrees, and about 58 degrees, which are ( _{2, 2, 2} ), yttria (Y ₂ O ₃ ) of fluorite structure. It corresponds to the (4,0,0), (4,4,0), (6,2,2) diffraction peaks. That is, it was found that polycrystalline yttria was present in this film.

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. The value of the gate leakage current is also shown in the figure. The calculated field effect mobility, on / off ratio, and s value are shown in Table 1.

In Table 1, “E” represents “power of 10”. For example, “1E + 5” represents “100000”.

In Example 1, a LaBa oxide insulating film (LaBa film) is used as a gate insulating layer for an active layer having a carrier density of 5.73 × 10 ¹⁷ / cm ³ . The relative dielectric constant of the LaBa film is as high as 11.8. In this case, the obtained transistor showed good switching characteristics and realized a high mobility of 5.33 cm ² / Vs. The off-state current and gate leakage current were extremely low at 0.1 pA or less, and no hysteresis was observed in the transfer characteristics. Therefore, it can be said that this amorphous LaBa film formed a paraelectric gate insulating layer having excellent insulating properties. . On / off ratio exceeding 10 ^9, is sufficient good characteristics in view of the practical aspect. The s value indicating the steepness of the rise was a sufficiently small value of 0.39 V / decade.

In Comparative Example 1, SiO ₂ is used for the gate insulating layer for the active layer having the same carrier density as in Example 1. In the transfer characteristic, although Ids modulation corresponding to Vg is seen, there is no clear off state in the range of Vg = −15V to 15V. On / a ratio of the maximum value of Ids as a corresponding value in the off ratio and minimum take 10 only ^five rather, s value for the rise is unclear could not be calculated.

In Comparative Example 2, SiON is used for the gate insulating layer for the active layer having the same carrier density as in Example 1. The transfer characteristic has a strong tendency of so-called depression with a negative rise. Although the off state exists, the off current value is slightly higher than the pA level. On / off ratio 10 ⁷ units of Example 1 from 2-digit decrease, s value as high as 1.54V / decade.

In Comparative Example 3 and Comparative Example 4, a SiO ₂ film and a SiON film are used for the gate insulating layer, respectively. The difference from Comparative Examples 1 and 2 is the carrier density of the active layer, and the carrier density is reduced by increasing the oxygen flow rate ratio when forming the active layer. The rising voltage moves in the positive direction due to the decrease in carriers, and the off state can be confirmed in Comparative Example 3 even when the gate insulating layer is made of SiO ₂ (FIG. 20). However, compared with Example 1 (FIG. 17), there is clearly a difference in the steepness of the rise, and when the s value is seen, Comparative Example 3 and Comparative Example 4 exceed 1 V / decade and have practically sufficient characteristics. I can't say that.

In Comparative Example 5, an oxide film containing Ca and Y is used for the gate insulating layer. This insulating layer has a high content of Y oxide, and as can be seen from the result of X-ray diffraction shown in FIG. 22, polycrystals of Y ₂ O ₃ are present in the film. The active layer of Comparative Example 5 is formed under the same conditions as in Example 1 and has the same carrier density. A transfer characteristic shown in FIG. 23, Example 1 (FIG. 17) high OFF current value as compared with the on / off ratio 10 ^five and small. The off-current value matches the value of the gate leakage current shown in the figure, and it can be seen that the off-current increases due to the influence of leakage through the gate insulating layer. That is, since the CaY oxide film of the gate insulating layer is not amorphous but polycrystalline, gate leakage occurs due to the crystal grain boundary and deteriorates the transistor characteristics.

Although the characteristics required for a transistor in consideration of practical use are different depending on the application, in general, the mobility is 1 cm ² / Vs or more, more preferably 5 cm ² / Vs or more, and the on / off ratio is Is 10 ⁶ or more, more preferably 10 ⁷ or more, still more preferably 10 ⁸ or more, and the s value is 1 V / decade or less, more preferably 0.5 V / decade or less. Example 1 satisfies this condition, but the characteristics of the comparative example are insufficient.

(Comparative Examples 6 and 7 and Examples 2 to 5)
A field effect transistor was fabricated in the same manner as in Example 1 except that the method for forming the gate insulating layer and the active layer was changed as follows.

-Formation of gate insulation layer-
La (thd) ₃ , Mg (thd) ₂ (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) dissolved in tetraethylene glycol dimethyl ether (tetraglyme) and tetrahydrofuran (THF), respectively A LaMg oxide insulating film having a thickness of about 100 nm was formed by a CVD method using a liquid material, and this was used as a gate insulating film. The ratio of the number of La and Mg atoms in the oxide insulating film is La: Mg = 8: 2. When the relative dielectric constant of this film was measured in the same manner as in Example 1, it was 8.1. Further, when X-ray diffraction was measured in the same manner as in Example 1, no peak was observed and it was found to be amorphous.

-Formation of active layer-
35.488 g of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) was weighed and dissolved in 100 mL of ethylene glycol monomethyl ether to obtain Liquid A.
2.330 g of zirconium chloride (ZrCl ₄ ) was weighed and dissolved in 100 mL of ethylene glycol monomethyl ether to obtain a solution B.
3.965 g of tungsten chloride (WCl ₆ ) was weighed and dissolved in 100 mL of ethylene glycol monomethyl ether to obtain solution C.
Liquid A, liquid B, liquid C, and ethylene glycol monomethyl ether and 1,2-propanediol were mixed in the amounts shown in Table 2 with respect to each of Comparative Examples 6 and 7, and Examples 2 to 5, and room temperature. To prepare a coating solution for forming an oxide semiconductor film.

Next, the oxide semiconductor film-forming coating solution was applied to a desired place on the gate insulating layer by an inkjet method, and baked in the atmosphere at 400 ° C. for 1 hour to form an active layer.
Under the conditions of Comparative Example 6, an InZrO film is formed by applying a coating solution on a substrate and baking it. The ratio of the number of In and Zr atoms is 100: 5, and Zr is added for the purpose of suppressing the occurrence of oxygen vacancies. In Comparative Example 7 and Examples 2 to 5, a portion of In (+3 valence) in the InZrO film that is the parent phase is substituted and doped with W (+6 valence), thereby generating carriers. The percentage of the total number of In sites that W is replacing is defined as the W concentration, and the value is shown in Table 2. Further, the carrier density of these films was determined by hole measurement in the same manner as in Example 1, and the results are shown in Table 2. It has been found that the carrier density increases as the W concentration increases, and that carriers are effectively generated by the substitutional doping of W.

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. 24 (Comparative Examples 6 and 7) and FIG. 25 (Examples 2 to 5), and the calculated field effect mobility, on / off ratio, and s value are shown in Table 3. In any of Comparative Examples 6 and 7 and Examples 2 to 5, no hysteresis was observed in the transfer characteristics.

In Comparative Examples 6 and 7 and Examples 2 to 5, films having the same composition are used for the gate insulating layer, but the carrier density of the active layer is different. In the carrier density of 4.0 × ¹⁰ 17 / cm ³ or less in Comparative Examples 6 and 7, the mobility is ^{1 cm} 2 / Vs or less, the on / off ratio of 10 ⁷ or less, s value 0.5V / decade or more As is apparent from the transfer characteristics of FIG. 24, the switching behavior is not sufficiently good. On the other hand, in Examples 2 to 5 in which the carrier density is 4.0 × 10 ¹⁷ / cm ³ or more, the mobility is 1 cm ² / Vs or more, the on / off ratio is 10 ⁷ or more, and the s value is 0.5 V / decade or less. Good switching characteristics in which Ids rises sharply from the off state to the on state are obtained (FIG. 25). From the viewpoint of increasing mobility, it can be seen that the carrier density is particularly preferably 1.0 × 10 ¹⁸ / cm ³ or more.

(Examples 6 to 11)
A field effect transistor was fabricated in the same manner as in Example 4 except that the method for forming the gate insulating layer was changed as follows.

-Formation of gate insulation layer-
Toluene, lanthanum 2-ethylhexanoate toluene solution (La content 7% by weight) and 2-ethylhexanoate magnesium toluene solution (Mg content 3% by weight) are mixed in the amounts shown in Table 4 to form a gate insulating layer. A coating solution was obtained.
The coating solution is spin-coated on a glass substrate including a gate electrode, dried in an atmosphere at 120 ° C. for 1 hour using an oven, and then fired in an oxygen atmosphere at 400 ° C. for 3 hours to form a LaMg oxide insulating film. A gate insulating layer was formed. Table 4 shows the ratio of the number of La and Mg atoms in the oxide film. The average thickness of the gate insulating layer was 120 nm. The relative permittivity of these films was measured in the same manner as in Example 1. The results are shown in Table 4. Further, when X-ray diffraction was measured in the same manner as in Example 1, no peak was observed and it was found to be amorphous.

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The transfer characteristics are shown in FIG. 26 (Examples 6 to 8) and FIG. 27 (Examples 9 to 11), and the calculated field effect mobility, on / off ratio, and s value are shown in Table 5. In any of the examples, no hysteresis was observed in the transfer characteristics.

In any of Examples 6 to 11, sufficiently good characteristics are obtained in view of practical use. Looking at the tendency of transistor characteristics when the dielectric constant is lowered by changing the composition of the gate insulating layer, the s-value tends to increase as the relative dielectric constant decreases. In particular, the relative dielectric constant is 7.0 or less. Then, the slope of the rising of the transfer curve becomes prominent (FIG. 27). For the oxide active layer having a carrier density of 4.0 × 10 ¹⁷ / cm ³ or more, the gate insulating layer It can be seen that the relative dielectric constant is more preferably larger than 7.0.

(Examples 12 to 20)
A field effect transistor was fabricated in the same manner as in Example 1 except that the method for forming the gate insulating layer and the method for forming the active layer were changed as follows.

−Preparation of coating liquid for gate insulating layer formation−
-Example 12-
After dissolving 0.37 mg of gallium acetylacetonate in 10 mL of toluene, 1.7 mL of 2-ethylhexanoic acid barium toluene solution (Ba content 8 wt%) was added and mixed to obtain a coating solution for forming a barium gallium oxide insulating film. The ratio of the number of atoms in the coating solution is Ga: Ba = 1: 1.

-Example 13-
2 mL of 2-ethylhexanoic acid magnesium toluene solution (Mg content 3 wt%), 11 mL of 2-ethylhexanoic acid yttrium toluene solution (Y content 8 wt%), and titanium n-butoxide 0.35 mL were mixed, and 15 mL of toluene was further added. In addition, dilution was performed to obtain a coating liquid for forming a magnesium titanium yttrium oxide insulating film. The ratio of the number of atoms in the coating solution is Mg: Y: Ti = 2.5: 10: 1.

-Example 14-
20 mL of toluene, 0.94 mL of aluminum di (s-butoxide) acetoacetate chelate (Al content 8.4 wt%), 5 mL of magnesium 2-ethylhexanoate toluene solution (Mg content 3 wt%), and yttrium 2-ethylhexanoate 11 mL of a toluene solution (Y content 8 wt%) was mixed to obtain a coating solution for forming a magnesium aluminum yttrium oxide insulating film. The ratio of the number of atoms in the coating solution is Al: Mg: Y = 3: 6.25: 10.

-Example 15-
Dissolve 0.48 g of barium neodecanoate (Ba content 29 wt%) in 10 mL of toluene, 4 mL of 2-ethylhexanoic acid lanthanum toluene solution (La content 7 wt%), and bis (2-ethylhexanoic acid) zirconium oxide mineral spirit The solution (Zr content 12 wt%) 0.76 mL was mixed to obtain a coating solution for forming a barium zirconium lanthanum oxide insulating film. The ratio of the number of atoms in the coating solution is Ba: La: Zr = 1: 2: 1.

-Example 16-
0.43 g of strontium neodecanoate (Sr content 20 wt%) was dissolved in 10 mL of toluene, and 4 mL of 2-ethylhexanoic acid lanthanum toluene solution (La content 7 wt%) and 2-ethyl hexanoic acid niobium (IV) 2-ethyl were dissolved therein. Hexanoic acid solution (Nb content 11 wt%) 0.83 mL was mixed to obtain a coating solution for forming a strontium niobium lanthanum oxide insulating film. The ratio of the number of atoms in the coating solution is Sr: La: Nb = 1: 2: 1.

-Example 17-
2 mL of 2-ethylhexanoic acid magnesium toluene solution (Mg content 3 wt%), 20 mL of 2-ethylhexanoic acid lanthanum toluene solution (La content 7 wt%), and 1 mL of tantalum ethoxide (purity 99.98%) were mixed. Further, 25 mL of toluene was further diluted to obtain a coating solution for forming a magnesium tantalum lanthanum oxide insulating film. The ratio of the number of atoms in the coating solution is Mg: La: Ta = 2.5: 10: 4.

-Example 18-
In 15 mL of 1,2-ethanediol, 0.77 g of magnesium nitrate hexahydrate, 4.3 g of lanthanum nitrate hexahydrate, and 0.82 g of hafnium (IV) dichloride oxide octahydrate are dissolved. A coating solution for forming a hafnium lanthanum oxide insulating film was obtained. The ratio of the number of atoms in the coating solution is Mg: La: Hf = 3: 10: 2.

-Example 19-
In 10 mL of propylene glycol, 0.32 g of scandium nitrate pentahydrate and 0.27 g of strontium chloride hexahydrate were dissolved to obtain a coating solution for forming a scandium strontium oxide insulating film. The ratio of the number of atoms in the coating solution is Sc: Sr = 1: 1.

-Example 20-
20 mL of 2-ethylhexanoic acid lanthanum toluene solution (La content 7 wt%) and 0.8 mL of 2-ethyl hexanoic acid calcium mineral spirit solution (Ca content 5 wt%) are mixed, and further diluted with 12 mL of toluene, and lanthanum calcium A coating solution for forming an oxide insulating film was obtained. The ratio of the number of atoms in the coating solution is La: Ca = 10: 1.

-Formation of gate insulation layer-
The coating solution is spin-coated on a glass substrate including a gate electrode, dried in an atmosphere at 120 ° C. for 1 hour using an oven, and then fired at 400 ° C. for 3 hours in an oxygen atmosphere to form a gate insulating layer. did. The average thickness of the gate insulating layer was 120 nm. The relative permittivity of these films was measured in the same manner as in Example 1. The results are shown in Table 6. Further, when X-ray diffraction was measured in the same manner as in Example 1, no peak was observed, and it was found that this insulating layer was amorphous.

-Formation of active layer-
35.488 g of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) was weighed and dissolved in 100 mL of ethylene glycol monomethyl ether to obtain Liquid A.
29.749 g of zinc nitrate (Zn (NO ₃ ) ₂ .6H ₂ O) was weighed and dissolved in 100 mL of ethylene glycol monomethyl ether to prepare a B solution.
1.631 g of molybdenum dioxide (VI) bis (acetylacetonate) was weighed and dissolved in 500 mL of ethylene glycol monomethyl ether to obtain solution C.
A solution 99.8 mL, B solution 100 mL, and C solution 20 mL, ethylene glycol monomethyl ether 180.2 mL, and 1,2-propanediol 400 mL were mixed and stirred at room temperature to prepare a coating solution for forming an oxide semiconductor film. did.

Next, the oxide semiconductor film-forming coating solution was applied to a desired region on the gate insulating layer by an inkjet method, and baked in the air at 400 ° C. for 1 hour to form an active layer. The ratio of elements other than oxygen in the active layer thus obtained is In: Zn: Mo = 99.8: 100: 0.2. Mo (+6 valence) is substituted and doped at a concentration of 0.2 at% with respect to In (+3 valence) in In ₂ Zn ₂ O ₅ which is a parent phase, thereby generating carriers.

When the carrier density of this oxide semiconductor film was measured by hole measurement in the same manner as in Example 1, it was 1.21 × 10 ¹⁸ / cm ³ .

<Measurement of transistor characteristics>
Similar to Example 1, transistor characteristics were evaluated. The calculated field effect mobility, on / off ratio, and s value are shown in Table 6. In any of the examples, no hysteresis was observed in the transfer characteristics.
In any of Examples 12 to 20, a high mobility, a high on / off ratio, and a small s value were obtained, and sufficiently good characteristics were obtained in view of practical use.

Aspects of the present invention are as follows, for example.
<1> a gate electrode for applying a gate voltage;
A source electrode and a drain electrode for extracting current;
An active layer provided adjacent to the source electrode and the drain electrode and made of an oxide semiconductor;
A gate insulating layer provided between the gate electrode and the active layer;
A field effect transistor comprising:
The gate insulating layer is a paraelectric amorphous oxide containing an A element that is an alkaline earth metal and a B element that is at least one of Ga, Sc, Y, and a lanthanoid,
The field effect transistor is characterized in that the carrier density of the active layer is 4.0 × 10 ¹⁷ / cm ³ or more.
<2> The field effect transistor according to <1>, wherein the gate insulating layer further includes a C element that is at least one of Al, Ti, Zr, Hf, Nb, and Ta. <3> The field effect transistor according to any one of <1> to <2>, wherein a relative dielectric constant of the gate insulating layer is greater than 7.0.
<4> The field effect transistor according to any one of <1> to <3>, wherein the active layer is an n-type oxide semiconductor containing at least one of In, Zn, Sn, and Ti. .
<5> The n-type oxide semiconductor is at least one of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, a hexavalent cation, a hexavalent cation, and an octavalent cation. Substitutional doping with
The field effect transistor according to <4>, wherein a valence of the dopant is larger than a valence of a metal ion (excluding the dopant) constituting the n-type oxide semiconductor.
<6> The field effect transistor according to any one of <1> to <5>, wherein the active layer has a carrier density of 1.0 × 10 ¹⁸ / cm ³ or more.
<7> a light control element whose light output is controlled according to a drive signal;
A drive circuit including the field effect transistor according to any one of <1> to <6>, and driving the light control element;
It is a display element characterized by comprising.
<8> An image display device that displays an image according to image data,
A plurality of display elements according to <7>, arranged in a matrix;
A plurality of wirings for individually applying a gate voltage and a signal voltage to each field effect transistor in the plurality of display elements;
A display control device that individually controls the gate voltage and the signal voltage of each field-effect transistor through the plurality of wirings according to the image data;
An image display apparatus comprising:
<9> The image display device according to <8>,
Creating image data based on image information to be displayed, and outputting the image data to the image display device;
It is a system characterized by comprising.

DESCRIPTION OF SYMBOLS 10 Field effect transistor 20 Field effect transistor 22 Active layer 23 Source electrode 24 Drain electrode 25 Gate insulating layer 26 Gate electrode 40 Field effect transistor 302, 302 'Display element 310 Display 320, 320' Drive circuit 370 Liquid crystal element 400 Display Control device

K. Nomura, et al., “Room-temperament fabrication of transparent flexible thin-film transformers using amorphous semiconductors”, NATURE, VOL4. 25, NOVEMBER, 2004, p. 488-492

Claims (9)

A gate electrode for applying a gate voltage;
A source electrode and a drain electrode for extracting current;
An active layer provided adjacent to the source electrode and the drain electrode and made of an oxide semiconductor;
A gate insulating layer provided between the gate electrode and the active layer;
A field effect transistor comprising:
The gate insulating layer is a paraelectric amorphous oxide containing an A element that is an alkaline earth metal and a B element that is at least one of Ga, Sc, Y, and a lanthanoid,
A field effect transistor having a carrier density of the active layer of 4.0 × 10 ¹⁷ / cm ³ or more.   2. The field effect transistor according to claim 1, wherein the gate insulating layer further includes a C element that is at least one of Al, Ti, Zr, Hf, Nb, and Ta.   The field effect transistor according to claim 1, wherein a relative dielectric constant of the gate insulating layer is larger than 7.0.   The field effect transistor according to any one of claims 1 to 3, wherein the active layer is an n-type oxide semiconductor containing at least one of In, Zn, Sn, and Ti. The n-type oxide semiconductor is a dopant of at least one of a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, a hexavalent cation, a hexavalent cation, and an octavalent cation. Substitution doping,
The field effect transistor according to claim 4, wherein the valence of the dopant is larger than the valence of a metal ion (excluding the dopant) constituting the n-type oxide semiconductor. The carrier density in the active layer, the field-effect transistor according to any one of claims 1 to 5 is 1.0 × ¹⁰ 18 / cm ³ or more. A light control element whose light output is controlled according to a drive signal;
A drive circuit including the field effect transistor according to claim 1 and driving the light control element;
A display element comprising: An image display device that displays an image according to image data,
A plurality of display elements according to claim 7 arranged in a matrix;
A plurality of wirings for individually applying a gate voltage and a signal voltage to each field effect transistor in the plurality of display elements;
A display control device that individually controls the gate voltage and the signal voltage of each field-effect transistor through the plurality of wirings according to the image data;
An image display device comprising: An image display device according to claim 8,
Creating image data based on image information to be displayed, and outputting the image data to the image display device;
A system comprising: