JP2013128127A - Display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a hysteresis by devising an oxide material used for a channel of a transistor.SOLUTION: A display unit comprises, as a switching element, a thin film transistor including a channel layer which is an oxide semiconductor film containing any one combination of Ga, In and Zn, Sn, In and Zn, In, Zn, Ga and Mg, In and Sn, In and Ga, and In and Zn, has an electron carrier concentration of not less than 10/cmand not more than 10/cm, and which contains hydrogen atoms of not less than 10/cmand not more than 10/cm.

Description

  The present invention relates to a field effect transistor having transistor characteristics that can be applied to a display device or the like using a film made of an amorphous oxide as a channel layer.

  A field effect transistor (FET) includes a gate electrode, a source electrode, and a drain electrode.

  The electronic active element controls the current flowing through the channel layer by applying a voltage to the gate electrode and controlling the current between the source electrode and the drain electrode.

  In particular, an FET using a thin film formed on an insulating substrate such as ceramics, glass, or plastic as a channel layer is called a thin film transistor (TFT).

  Since the above TFT uses thin film technology, it has an advantage that it can be easily formed on a substrate having a relatively large area, and is widely used as a driving element for flat panel display elements such as liquid crystal display elements. ing.

  That is, in an active liquid crystal display element (ALCD), individual image pixels are turned on / off using TFTs formed on a glass substrate.

  Also, in future high performance organic LED displays (OLED), it is considered that pixel current driving by TFT is effective.

  Furthermore, a higher-performance liquid crystal display device has been realized in which TFT circuits for driving and controlling the entire image are formed on a substrate around the image display area.

  Currently, the most widely used TFT is a polycrystalline silicon film or an amorphous silicon film as a channel layer material.

  These are called Metal-Insulator-Semiconductor Field Effect Transistor (MIS-FET) elements.

  Amorphous silicon TFTs are put into practical use for pixel driving, and high-performance polycrystalline silicon TFTs are put into practical use for driving and controlling the entire image.

  However, TFTs that have been developed so far, including amorphous silicon and polysilicon TFTs, require a high-temperature process for device fabrication, and are difficult to fabricate on a substrate such as a plastic plate or film.

  On the other hand, in recent years, development has been actively conducted to realize a flexible display by forming a TFT on a substrate such as a polymer plate or a film and using it as a drive circuit for an LCD or OLED.

  As a material that can be formed on a plastic film or the like, an organic semiconductor film that can be formed at a low temperature and exhibits electrical conductivity has attracted attention.

  For example, as an organic semiconductor film, research and development of pentacene or the like is underway.

  These organic semiconductors all have an aromatic ring, and a large carrier mobility can be obtained in the lamination direction of the aromatic ring when crystallized.

For example, when pentacene is used as the active layer, the carrier mobility is about 0.5 cm ² (Vs) ⁻¹ , which is reported to be equivalent to an amorphous Si-MOSFET.

  However, organic semiconductors such as pentacene have the disadvantages of low thermal stability (<150 ° C.) and toxicity (carcinogenicity), and practical devices have not been realized.

  Recently, an oxide material has attracted attention as a material applicable to a channel layer of a TFT.

  For example, TFTs using a transparent conductive oxide polycrystalline thin film containing ZnO as a main component for a channel layer are being actively developed.

  The thin film can be formed at a relatively low temperature, and can be formed on a substrate such as a plastic plate or a film.

  However, a compound containing ZnO as a main component cannot form a stable amorphous phase at room temperature, and becomes a polycrystalline phase. Therefore, electron mobility cannot be increased due to scattering at the interface of the polycrystalline particles.

  In addition, since the shape and interconnection of the polycrystalline particles vary greatly depending on the film forming method, the characteristics of the TFT element vary.

  Recently, a thin film transistor using an In—Ga—Zn—O-based amorphous oxide has been reported (Non-Patent Document 1).

  This transistor can be formed on a plastic or glass substrate at room temperature. Furthermore, normally-off transistor characteristics with a field effect mobility of about 6-9 are obtained.

  Moreover, it has the characteristic that it is transparent with respect to visible light.

K. Nomura et.al, Nature VOL. 432, P. 488-492 (2004-11)

  When a thin film transistor using an amorphous In—Ga—Zn—O-based oxide was examined, there was a hysteresis in the transistor characteristics (Id-Vg characteristics) of the TFT, depending on the composition and manufacturing conditions. There was a case.

  The occurrence of hysteresis, for example, when used in a pixel circuit of a display, causes variations in the operation of an organic LED or a liquid crystal to be driven, and ultimately leads to a reduction in image quality on the display.

  Accordingly, an object of the present invention is to devise the oxide material used for the channel of the transistor to reduce the hysteresis.

Further, when an amorphous oxide material is used for the channel layer of the TFT, it is preferable that the electron carrier concentration is in a desired range (for example, about 10 ¹⁴ to 10 ¹⁸ / cm ³ ).

  Further, in order to ensure the reproducibility and uniformity of transistor characteristics, a means for precisely controlling the electron carrier concentration is desired.

  In view of the above, an object of the present invention is to provide a method for producing a thin film having a desired electron carrier concentration with good control by devising a method for producing an oxide material used for a channel of a transistor.

In order to solve the above problems, the present invention provides an oxide containing any one of Ga and In and Zn, Sn and In and Zn, In and Zn and Ga and Mg, In and Sn, In and Ga, and In and Zn. Switching a thin film transistor having a channel layer which is a semiconductor film and has an electron carrier concentration of 10 ¹⁴ / cm ³ or more and 10 ¹⁸ / cm ³ or less and containing hydrogen atoms of 10 ¹⁶ / cm ³ or more and 10 ²⁰ / cm ³ or less It is a display which has as an element.

  Furthermore, according to the present invention, the field effect transistor can be formed on a substrate such as a plastic plate or a film because it can be implemented in a low temperature process.

  Further, according to the present invention, a field effect transistor can be formed with good reproducibility. In particular, an amorphous oxide having a low electron carrier concentration can be formed with good control.

2A and 2B are cross-sectional views illustrating a configuration example of a thin film transistor according to the present invention, where FIG. 1A shows a top gate structure and FIG. 1B shows a bottom gate structure. It is a graph which shows the TFT characteristic of the thin-film transistor concerning this invention, (a) shows a transistor characteristic, (b) shows a transfer characteristic. It is a graph which shows the hysteresis characteristic of the thin-film transistor concerning this invention. It is a graph which shows the relationship between the electron carrier density | concentration of an In-Ga-Zn-O type amorphous oxide film, and the oxygen partial pressure during film-forming. It is a figure which shows the manufacturing apparatus of an amorphous oxide film. It is a figure which shows the relationship between the addition amount of hydrogen, and a resistivity of an In-Ga-Zn-O type amorphous oxide film. It is the depth direction profile of the hydrogen concentration evaluated by SIMS.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  1A and 1B are cross-sectional views showing an embodiment of a thin film transistor which is a field effect transistor as one embodiment of the present invention.

  FIG. 1A is a cross-sectional view showing an example of a top gate structure in which a gate insulating film 12 and a gate electrode 15 are sequentially formed on a semiconductor channel layer 11.

  FIG. 1B is a cross-sectional view showing an example of a bottom gate structure in which the gate insulating film 12 and the semiconductor channel layer 11 are formed in this order on the gate electrode 15.

  Due to the arrangement relationship between the electrode and the channel layer-insulating layer interface, the structure in FIG. 1A is called a staggered structure, and the structure in FIG. 1B is called an inverted staggered structure.

  As shown in FIG. 1A, a source electrode 13, a drain electrode 14, a gate insulating film 12, and a gate electrode 15 are sequentially formed on a semiconductor channel layer 11 formed on a substrate 10. Thus, a field effect transistor having a top gate structure (staggered structure) is formed.

  As shown in FIG. 1B, a gate insulating film 12, a semiconductor channel layer 11, a source electrode 13, and a drain electrode 14 are sequentially formed on a gate electrode 15 formed on the substrate 10. In this way, a field effect transistor having a bottom gate structure (inverse stagger structure) is formed.

  The field effect transistor shown in FIGS. 1A and 1B is a three-terminal element including a gate electrode 15, a source electrode 13, and a drain electrode 14.

  This is an electronic active element that applies a voltage Vg to the gate electrode to control the current Id flowing through the channel layer and to control the current Id between the source electrode and the drain electrode.

  The configuration of the TFT is not limited to the above configuration, and any top / bottom gate structure or stagger / inverse stagger structure can be used.

  FIG. 2 is a graph showing typical characteristics of a field effect transistor (TFT) as an embodiment of the present invention.

  The characteristics of the TFT relate to a field-effect transistor created under the configuration and manufacturing conditions of Example 1 described later.

  When a voltage Vd of about 5 to 20 V is applied between the source and drain electrodes, the gate voltage Vg is turned on / off between 0 V and about 5 to 20 V, thereby controlling the current Id between the source and drain electrodes ( On / off).

  2A is an example of Id-Vd characteristics at various Vg, and FIG. 2B is an example of Id-Vg characteristics (transfer characteristics) at Vd = 6V.

  The channel layer of the TFT of the above embodiment is made of an amorphous oxide film containing hydrogen atoms or deuterium atoms.

  The effect of adding hydrogen to the channel layer, that is, the reduction of hysteresis will be described with reference to FIGS.

  FIGS. 3A and 3B show an example of TFT transfer characteristics when hydrogen is not added to the channel layer of Comparative Example 1 and Example 1, which will be described later, and when it is added.

  Hysteresis is a value in which Id is different between when the voltage rises and when it falls when Vd is fixed and Vg is swept (up and down) as shown in FIG. Say to show.

  If the hysteresis is large, the value of Id obtained with respect to the set Vg varies. Therefore, an element having a small hysteresis is preferable.

  When no hydrogen atom is contained, the hysteresis characteristic as shown in FIG. 3A is shown. However, by applying a channel layer containing a hydrogen atom, the hysteresis is reduced as shown in FIG. A small element can be obtained.

  The physical reason why hysteresis is reduced by applying an oxide containing hydrogen atoms to the channel layer is not clear.

  One possible reason is that by adding hydrogen, the disorder of the local structure in the amorphous thin film is alleviated, and an amorphous structure in which carriers are not easily trapped (the trap level becomes shallow) is realized. That is.

  In addition, it is considered that by adding hydrogen to the channel layer, the disorder of the structure at the interface between the channel layer and the insulating layer is alleviated and a channel layer / insulating layer interface in which carriers are not easily trapped is realized.

  Hysteresis is evaluated by fixing the source / drain voltage Vd to an appropriate value between 5 and 30 V, and sweeping (up and down) the gate voltage Vg in the range of −10 to 30 V to obtain Id (source-drain current). This is done by measuring.

  Here, Vd uses a voltage whose transistor characteristics indicate a saturation region, and Vg sweeps between an off state and an on state.

  However, the values of Vg and Vd can be set depending on the characteristics and configuration of the transistor, and are not necessarily limited to the above ranges.

  The magnitude of the hysteresis can be evaluated by comparing the Id-Vg curve when the gate voltage is increased with the Id-Vg curve when the voltage is decreased.

  For example, the area of the loop drawn by the Id-Vg curve when the voltage rises and the Id-Vg curve when the voltage falls can be used as the evaluation criterion.

  When this area is small, it can be said that the hysteresis is small.

  In addition, the evaluation can be performed by using the difference ΔVt = | Vtu−Vtd | between the threshold voltage Vtu estimated from the Id−Vg curve at the time of voltage increase and the threshold voltage Vtd estimated from the Id−Vg curve at the time of voltage decrease. it can.

  Hereinafter, this ΔVt is referred to as a threshold shift amount. A small value ΔVt means that the hysteresis is small.

  In a thin film transistor in which an oxide containing a hydrogen atom is applied to a channel layer, a thin film and a transistor having a small ΔVt can be realized.

  Since the threshold shift amount of the thin film transistor depends on the element configuration, channel material, evaluation conditions, and the like, it is preferable to fix the voltage applied to the element under the same conditions when performing the evaluation.

  As an example of evaluation of a thin film transistor, the threshold shift amount when Vd = 10 V is fixed and Vg is swept (up and down) at a sweep speed of 100 mV / sec over a range of −5 V to 15 V can be evaluated.

  Specifically, under the above evaluation conditions, the threshold shift amount can be 2 V or less, more preferably 1 V or less, and even more preferably 0.5 V or less.

  The required degree of hysteresis depends on the application of the thin film transistor and the circuit configuration used.

  For example, when it is used for a liquid crystal display device, an electrophoretic display device, etc., the requirements are relatively low, but higher characteristics (small hysteresis) are required when applied to an organic EL display device or an arithmetic circuit. It becomes.

  For example, considering application to an organic EL display device, the threshold shift amount is preferably 2 V or less, more preferably 1 V or less. Further, in a high-performance organic EL display device, the voltage is preferably 0.5 V or less.

(Hydrogen concentration and electron carrier concentration)
In addition, a thin film transistor in which an amorphous oxide is applied to the channel layer was examined.

  In order to obtain good TFT characteristics, a semi-insulating amorphous oxide film having an electric conductivity of 0.1 S / cm or less and 0.0001 S / cm or more in the channel layer was suitable.

In order to obtain such electric conductivity, it is preferable to form an amorphous oxide film having an electron carrier concentration of about 10 ¹⁴ to 10 ¹⁸ / cm ³ depending on the material composition of the channel layer.

  When the electrical conductivity exceeds 0.1 S / cm, it is difficult to form a normally-off transistor, and the on / off ratio cannot be increased.

  In an extreme case, even when a gate voltage is applied, the current between the source and drain electrodes is not turned on / off, and transistor operation is not exhibited.

  On the other hand, when the insulator, that is, the electric conductivity is less than 0.0001 S / cm, it is difficult to increase the on-current.

  In an extreme case, even when a gate voltage is applied, the current between the source and drain electrodes is not turned on / off, and transistor operation is not exhibited.

  Usually, in order to control the electric conductivity electron and carrier concentration of an oxide, it is carried out by controlling the oxygen partial pressure during film formation.

  That is, by controlling the oxygen partial pressure, mainly the amount of oxygen vacancies in the thin film is controlled, thereby controlling the electron carrier concentration.

  FIG. 4 is a diagram illustrating an example of the oxygen partial pressure dependence of the carrier concentration when an In—Ga—Zn—O-based oxide thin film is formed by a sputtering method.

Actually, by controlling the oxygen partial pressure to a high degree, an amorphous oxide semi-insulating film having an electron carrier concentration of 10 ¹⁴ to 10 ¹⁸ / cm ³ and having semi-insulating properties can be obtained. A good TFT can be produced by applying such a thin film to the channel layer.

  As shown in FIG. 4, typically, a semi-insulating thin film can be obtained by forming a film at an oxygen partial pressure of about 0.005 Pa.

  If it exceeds 0.01 Pa, insulation is obtained. On the other hand, if it is less than 0.001 Pa, the electric conductivity is too high, which is not preferable as a channel layer of a transistor.

  However, as shown in FIG. 4, since the carrier concentration changes sensitively with respect to the oxygen partial pressure, a slight change in film forming conditions greatly affects the characteristics, and it tends to be difficult to obtain TFT characteristics with good reproduction. .

  The electron carrier concentration is controlled by adding hydrogen (or deuterium).

  As a result of intensive studies, it was found that the amount of electron carriers can be controlled by adding hydrogen to the amorphous oxide film.

For ^example, in order to realize an electronic carrier concentration of approximately ¹⁰ 18 / cm ³ varies depending on the oxygen partial pressure and the material composition during the deposition, the 10 ¹⁸ / cm ³ or more ¹⁰ 20 / cm ³ or less hydrogen It can be realized by adding.

  At this time, the electron carrier concentration can be controlled by the amount of hydrogen dopant. Further, the electron carrier concentration may be controlled using both the hydrogen doping amount and the oxygen deficiency amount.

Based on the above, in order to create a TFT having good characteristics, the hydrogen concentration range is preferably in the range of 10 ¹⁶ / cm ^{3 to} 10 ²⁰ / cm ³ .

Although depending on the oxygen partial pressure and the material composition, an oxide thin film having an electron carrier concentration of 10 ¹⁴ / cm ³ or more and 10 ¹⁸ / cm ³ or less within this range and suitable as a channel layer of a TFT can be realized. it can.

In particular, the hydrogen concentration is preferably 10 ¹⁹ / cm ³ or less because a normally-off operation and a large ON / OFF ratio of the transistor can be realized.

Furthermore, it is preferable to set the hydrogen concentration to 10 ¹⁷ / cm ³ or more because the hysteresis of the transistor can be more effectively reduced.

  The measurement of the hydrogen concentration can be evaluated by SIMS (secondary ion mass spectrometry).

Although it depends on the evaluation device, the detection limit is about 10 ¹⁷ / cm ³ . Below the detection limit, it may be indirectly calculated by extrapolation assuming linearity in the relationship between the hydrogen content in the thin film and the hydrogen addition process parameters (deposition hydrogen partial pressure and ion implantation amount described later). it can.

Constituent components of channel layer made of amorphous oxide containing hydrogen atoms (excluding hydrogen)
[(Sn _1−x M4 _x ) O ₂ ] a · [(In _1−y M3 _y ) ₂ O ₃ ] b · [(Zn _1−z M2 _z O)] c
Here, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a <1, 0 ≦ b <1, 0 ≦ c <1,
And a + b + c = 1,
M4 is a group 4 element (Si, Ge, Zr) having an atomic number smaller than Sn,
M3 is a group 3 element (B, Al, Ga, Y) having a smaller atomic number than In or Lu,
M2 is a group 2 element (Mg, Ca)] having an atomic number smaller than that of Zn.
Among these, in particular, [(In _1-y Ga _y ) ₂ O ₃ ] b · [(ZnO)] c 0 ≦ y ≦ 1, 0 <b <1, 0 <c <1, and [SnO ₂ ] a [[In ₂ O ₃ ) b · [(ZnO)] c where 0 ≦ a ≦ 1, 0 <b <1, and 0 <c <1 are preferable.

  For example, an amorphous oxide film containing hydrogen atoms can be realized by the following composition.

That is, a binary or ternary composition located inside a triangle having vertices of Ga ₂ O ₃ , In ₂ O ₃ and ZnO, or a triangle having vertices of SnO ₂ , In ₂ O ₃ and ZnO It is a binary system or a ternary system composition located inside.

  Depending on the composition ratio of the ternary composition, crystallization may occur in a certain composition ratio range. In particular, a one-component composition is not preferable because it crystallizes.

  For example, among the binary composition (composition located on the side of the triangle) including two of the above three kinds of compounds, In is in the In—Zn—O system, In is 20 atomic% or more and 70 atomic% or less. An amorphous film can be formed with the included composition.

  In the case of the Sn—In—O system, an amorphous film can be formed with a composition containing In of 20 atomic% or more and 80 atomic% or less.

  By adding hydrogen to the amorphous oxide film, the amorphous film at room temperature can be further stabilized.

  Thereby, an amorphous oxide can be formed in a wide ternary composition range.

(Production method)
As a method for producing an amorphous oxide containing hydrogen atoms, the following methods can be mentioned.
1) Method of forming a film while introducing a gas containing hydrogen (except for water vapor) at a predetermined partial pressure into the film forming apparatus at the time of film formation 2) Method of forming a film using a material source containing hydrogen 3) Method of adding hydrogen into the film by a method such as ion implantation or hydrogen plasma treatment after film formation Among these, the method of ion implantation of 3) is preferable from the viewpoint of controllability of hydrogen content. However, there is a concern that the number of steps increases because it is a subsequent step, and that a hydrogen concentration distribution is generated in the depth direction of the thin film.

  On the other hand, 2) is simple in the film formation process, but it is difficult to prepare a material source made of a hydrogen compound and it is difficult to control the hydrogen content in the film.

  The method of controlling the hydrogen content in the thin film by the hydrogen partial pressure in the atmosphere of 1) has good controllability and is relatively easy in the manufacturing process.

  Therefore, the method 1) for forming a film in a gas containing hydrogen at the time of film formation is most preferable.

  Examples of the gas containing hydrogen in the method 1) include hydrogen gas, deuterium gas, and hydrocarbon gas. In view of controllability of gas partial pressure and gas safety, hydrogen gas diluted with argon or the like is particularly preferable.

As ion species used in the ion implantation method of 3), H ⁺ ions, H ⁻ ions, D ⁺ ions (deuterium ions), H ₂ ⁺ ions (hydrogen molecular ions), and the like can be used.

  As a film formation method of the amorphous oxide, a vapor phase method such as a sputtering method (SP method), a pulse laser vapor deposition method (PLD method), or an electron beam vapor deposition method is preferably used.

  Among the gas phase methods, the SP method is suitable from the viewpoint of mass productivity.

  However, the film forming method is not limited to these methods. The temperature of the substrate during film formation can be maintained at substantially room temperature without intentional heating.

  In general, it is known that an amorphous oxide film having a low electron carrier concentration can be heat-treated in a hydrogen atmosphere to increase oxygen deficiency and increase the electron carrier concentration. However, a high-temperature heat treatment is required. There is a problem. Also, precise carrier concentration control is difficult.

As described above, the electron carrier concentration is controlled by the hydrogen-containing concentration in the amorphous oxide film by a method of film formation in a gas containing hydrogen at the time of film formation, ion implantation after the film formation, or the like. An amorphous oxide film having a semi-insulating property can be obtained with good reproducibility when the electron carrier concentration is in the range of 10 ¹⁴ / cm ³ or more and 10 ¹⁸ / cm ³ or less.

  By applying such an amorphous oxide containing a hydrogen atom to the channel layer of a thin film transistor, a transistor with small hysteresis can be formed with good reproducibility.

  In the transistor of this embodiment, the material of the gate insulating layer 12 is not particularly limited as long as it has a good insulating property.

For example, as the gate insulating layer 12, a mixture containing at least one of Al ₂ O ₃ , Y ₂ O ₃ , SiO ₂ or HfO ₂ or a compound thereof can be used.

As a result, the leakage current between the source and gate electrodes and between the drain and gate electrodes can be reduced to about 10 ⁻⁷ amperes.

  Further, the material of the source electrode 13, the drain electrode 14, and the gate electrode 15 is not particularly limited as long as it can provide good electrical conductivity and electrical connection to the channel layer.

For example, a transparent conductive film such as In ₂ O ₃ : Sn or ZnO or a metal film such as Au, Pt, Al, or Ni can be used.

  As the substrate 10, a glass substrate, a plastic substrate, a plastic film, or the like can be used.

  Since the channel layer and the gate insulating layer are transparent to visible light, a transparent thin film transistor can be obtained by using a transparent material for the electrode and the substrate.

  For the channel layer of this embodiment, an amorphous oxide including at least one element of Sn, In, and Zn can be applied.

Furthermore, when Sn is selected as at least a part of the constituent elements of the amorphous oxide, Sn is Sn _1-x M4 _x (0 <x <1, M4 is a group 4 element having an atomic number smaller than Sn, Ge, Ge Or selected from Zr).

In addition, when In is selected as at least a part of the constituent elements of the amorphous oxide, In is converted to In _1-y M3 _y (0 <y <1, M3 is a group III element having a smaller atomic number than Lu or In. , Al, Ga, or Y).

In addition, when Zn is selected as at least a part of the constituent elements of the amorphous oxide, Zn is replaced by Zn _1-Z M2 _Z (0 <z <1, M2 is a group 2 element Mg having an atomic number smaller than Zn or It is also possible to substitute it with Ca.

  Specifically, the amorphous materials applicable to this embodiment are the following oxides. In-Ga-Zn oxide, In-Sn-Zn oxide, In-Zn-Ga-Mg oxide, In oxide, In-Sn oxide, In-Ga oxide, In-Zn oxide, Zn- Ga oxide, In—Sn—Zn oxide, and the like.

  Of course, the composition ratio of the constituent materials is not necessarily 1: 1.

  In addition, Zn or Sn alone may be difficult to form an amorphous state, but an amorphous layer is easily formed by including In.

  For example, in the case of an In—Zn-based material, a composition in which the ratio of the number of atoms excluding oxygen is 20 atomic% or more and 70 atomic% or less is included.

  In the case of the Sn—In system, it is preferable that the ratio of the number of atoms excluding oxygen is such that In is included in an amount of 20 atomic% to 80 atomic%.

  In the case of an In—Sn—Zn-based composition, a composition in which an atomic ratio excluding oxygen is 15 atomic% or more is preferably included.

  Amorphous is confirmed by the fact that a clear diffraction peak is not detected (ie, a halo pattern is observed) when X-ray diffraction is performed on a thin film to be measured at a low incident angle of about 0.5 degrees. it can.

  Note that in the case where the above material is used for a channel layer of a field effect transistor, it does not exclude that the channel layer includes a constituent material in a microcrystalline state.

  Another embodiment is a method for producing an amorphous oxide film used for a channel layer of a field effect transistor having the following first and second steps.

  The first step is a step of placing the substrate in the film forming apparatus.

  The second step is a step of forming an amorphous oxide film on the substrate while introducing a gas containing hydrogen (excluding water vapor) and oxygen gas into the film forming apparatus at a predetermined partial pressure. .

  As already shown in FIG. 4, when the electric conductivity and the carrier concentration are to be controlled only by the oxygen partial pressure, it is necessary to set the region where the change due to the oxygen partial pressure is severe.

  As in this method, by using a gas containing hydrogen atoms such as hydrogen, for example, the oxygen partial pressure is set to a region of 0.008 Pa or more, and the partial pressure of the gas containing hydrogen atoms is changed to change the atmosphere. Can be adjusted. The oxygen partial pressure is preferably 0.01 Pa or more.

  In the above-exemplified range, the oxygen concentration pressure dependency of the carrier concentration is not high compared with, for example, the vicinity of the oxygen partial pressure of 0.005 Pa.

  The carrier concentration can also be changed by hydrogen, and the dependency of the carrier concentration on hydrogen is lower than that on oxygen. As a result, the controllability of the atmosphere during film formation is enhanced.

  In addition, as an upper limit of oxygen partial pressure, it is 0.1 Pa, for example. The upper limit value can be appropriately set in the range of 0.05 Pa to 0.5 Pa.

  The hydrogen partial pressure depends on the oxygen partial pressure, but is in the range of, for example, 0.001 Pa to 0.01 Pa.

  Use of water vapor is not preferable because it may make it difficult to control the partial pressure of oxygen and hydrogen.

  Note that the oxide film is not necessarily required to contain hydrogen in the oxide film in the deposition step. By adding in the step after forming the oxide film, hydrogen can be contained in the oxide film.

  Specific methods for adding hydrogen include ion implantation and plasma treatment in an atmosphere containing hydrogen.

[Example 1]
In this example, the top gate TFT element shown in FIG. 1A is manufactured. In this embodiment, a channel layer made of an In—Ga—Zn—O-based amorphous oxide is formed by sputtering in an atmosphere containing H ₂ .

  First, an amorphous oxide film containing hydrogen is formed as a channel layer on a glass substrate (Corning 1737).

  In this embodiment, an In—Zn—Ga—O amorphous oxide film containing hydrogen is formed by high-frequency sputtering in a mixed atmosphere of argon gas, oxygen gas, and hydrogen gas.

  A sputter deposition apparatus as shown in FIG. 5 is used.

  In FIG. 5, 51 is a sample, 52 is a target, 53 is a vacuum pump, 54 is a vacuum gauge, 55 is a substrate holding means, 56 is a gas flow rate control means provided for each gas introduction system, and 57 is a pressure control. Means 58 is a film forming chamber.

  A vacuum pump 53 serves as an exhaust unit for exhausting the inside of the film forming chamber 58. 55 is a substrate holding means for holding the substrate on which the oxide film is formed in the film forming chamber.

  Reference numeral 52 denotes a solid material source (target) 52 disposed to face the substrate holding means.

  Furthermore, an energy source (high-frequency power source not shown) for evaporating material from the solid material source, means for supplying hydrogen gas into the film formation chamber, and means for supplying oxygen gas into the film formation are provided.

As the gas introduction system, there are three systems: argon, a mixed gas of argon and oxygen (Ar: O ₂ = 80: 20), and a mixed gas of argon and hydrogen (Ar: H ₂ = 98: 2).

  A predetermined gas atmosphere can be obtained in the film forming chamber by the gas flow rate control means 56 that can control each gas flow rate independently and the pressure control means 57 for controlling the exhaust speed.

  Although a mixed gas of argon and oxygen or a mixed gas of argon and hydrogen is used here, pure hydrogen or pure oxygen may be used.

  Here, gas introduction is performed by three systems of argon, a mixed gas of argon and oxygen, and a mixed gas of argon and hydrogen. However, the gas may be introduced by one or two systems as described below. There are one system consisting of a mixed gas of argon, oxygen and hydrogen, and two systems of a mixed gas of argon and oxygen and a mixed gas of argon and hydrogen.

In this embodiment, a polycrystalline sintered body having a 2-inch size InGaO ₃ (ZnO) composition is used as a target (material source), and the input RF power is 100 W.

The atmosphere during film formation is a total pressure of 0.4 Pa. At that time, the gas flow rate ratio is Ar: O ₂ : H ₂ = 100: 4: 1. The film formation rate is 12 nm / min. The substrate temperature is 25 ° C.

  When the obtained film was subjected to grazing incidence X-ray diffraction (thin film method incident angle 0.5 degree) on the film surface, a clear diffraction peak was not detected, and the produced In—Zn—Ga—O-based film was amorphous. It turns out that it is a film | membrane.

  Furthermore, as a result of spectroscopic ellipsometry measurement and pattern analysis, it was found that the mean square roughness (Rrms) of the thin film was about 0.5 nm and the film thickness was about 60 nm.

  As a result of X-ray fluorescence (XRF) analysis, the metal composition ratio of the thin film was In: Ga: Zn = 39: 37: 24.

Further, by performing composition analysis by SIMS, the hydrogen concentration in the thin film is estimated to be about 4 × 10 ¹⁸ (1 / cm ³ ).

In addition, it is estimated that the electric conductivity is about 10 ⁻¹ s / cm, the electron carrier concentration is 4 × 10 ¹⁶ / cm ³ , and the electron mobility is about 2 cm ² / V · second.

  From the analysis of the light absorption spectrum, the forbidden band energy width of the produced amorphous oxide film is about 3 eV.

  Next, the drain electrode 14 and the source electrode 13 were formed by patterning using a photolithography method and a lift-off method. The electrode material is Au, and the thickness is 30 nm.

  Next, the gate insulating layer 12 was patterned by photolithography and lift-off.

The gate insulating film is a Y ₂ O ₃ film formed by electron beam evaporation and has a thickness of 150 nm. The relative dielectric constant of the Y ₂ O ₃ film is about 15.

  Further, the gate electrode 15 was formed by a photolithography method and a lift-off method. The channel length is 50 μm and the channel width is 200 μm. The electrode material is Au and the thickness is 30 nm.

(Comparative Example 1)
At the time of forming the channel layer, a TFT was produced by supplying only argon and oxygen without introducing hydrogen.

At the time of film formation, the atmosphere is a total pressure of 0.4 Pa. At that time, the gas flow rate ratio is Ar: O ₂ = 100: 1. The oxygen partial pressure corresponds to 0.004 Pa.

  The film formation rate is 14 nm / min. The substrate temperature is 25 ° C.

  FIG. 4 shows the change in the electrical conductivity of the amorphous oxide thin film when the oxygen partial pressure is changed as in the comparative example.

  As shown in FIG. 4, in the oxygen partial pressure used for TFT fabrication, the electrical conductivity changes greatly with a minute change in oxygen partial pressure, so it is necessary to control the oxygen partial pressure with high accuracy.

(Characteristic evaluation of TFT elements)
FIG. 2 shows an example of current-voltage characteristics of the TFT element measured at room temperature. 2A shows the Id-Vd characteristic, and FIG. 2B shows the Id-Vg characteristic.

  As shown in FIG. 2A, a constant gate voltage Vg was applied, and the dependency of Id on the drain voltage Vd of the source-drain current accompanying the change in Vd was measured. The behavior of a typical semiconductor transistor saturated (pinch off) at about Vd = 6V is shown.

Examination of the gain characteristics, the threshold of the gate voltage _{V G} at Vd = 4V was applied was about -0.5 V. When Vg = 10 V, a current of about Id = 1.0 × 10 ⁻⁵ A flowed.

The on / off ratio of the transistor was more than 10 ⁶ .

Further, when the field effect mobility was calculated from the output characteristics, a field effect mobility of about 8 cm ² (Vs) ⁻¹ was obtained in the saturation region. A similar measurement was performed by irradiating the fabricated device with visible light, but no change in transistor characteristics was observed.

  In addition, the TFT of this example has less hysteresis when compared with the TFT of the comparative example. FIG. 3 compares Id-Vg of the present example and the comparative example.

  FIG. 3A shows an example of a comparative example, and FIG. 3B shows an example of TFT characteristics of this example.

  Thus, by adding hydrogen atoms to the channel layer, the hysteresis of the TFT can be reduced.

  Further, in this embodiment, TFTs can be produced with better reproducibility than in the comparative example, and there is a tendency that variation in characteristics when a plurality of elements are produced is small.

  In this example, it is considered that TFTs can be formed with good reproducibility by performing film formation at a higher oxygen partial pressure than in the comparative example.

  In addition, it is considered that by forming a film in an atmosphere to which hydrogen is added at the time of forming the channel layer, fluctuations in TFT characteristics are reduced with respect to minute fluctuations in oxygen partial pressure, thereby reducing characteristic variations.

  Actually, in the comparative example, the oxygen partial pressure is around 5 mPa, but in this example, it is about 0.015 Pa.

  In the comparative example, the oxygen partial pressure is controlled without adding hydrogen in the sputtering method. Then, a thin film having an electron carrier concentration suitable for the TFT channel layer is produced.

  For that purpose, it is necessary to set the oxygen partial pressure to a value in the vicinity of 5 mPa.

  As described above (see FIG. 4), since the carrier concentration changes sensitively to the oxygen partial pressure under this condition, a slight change in the film forming conditions greatly affects the characteristics, and TFT characteristics that are reproducible can be obtained. It tends to be difficult to obtain.

  On the other hand, in this embodiment, the electron carrier concentration is controlled by adding hydrogen. Under the conditions of this embodiment, hydrogen is added and the partial pressure of oxygen is 0.01 Pa or higher.

  As shown in FIG. 4, a film formed without adding hydrogen at this oxygen partial pressure (> 0.01 Pa) is an insulator, and oxygen vacancies and electron carrier concentrations are sufficiently small.

  In this embodiment, the film is formed in an atmosphere in which hydrogen is added to this relatively high oxygen partial pressure. In this method, a desired electron carrier concentration can be obtained without being greatly influenced by minute fluctuations in oxygen partial pressure. Accordingly, a transistor with small characteristic variation can be manufactured with good reproducibility.

  In addition, when the hydrogen partial pressure of the atmosphere during film formation was changed and the electron carrier concentration and the carrier concentration of the amorphous oxide film containing hydrogen were evaluated, the carrier concentration and the electron mobility were increased by increasing the hydrogen partial pressure. Both tend to increase. Hall mobility measurement is used for evaluation.

  In a normal compound, as the carrier concentration increases, the electron mobility decreases due to scattering between carriers, but in an amorphous oxide containing a hydrogen atom, the electron mobility increases as the electron carrier concentration increases. Its physical mechanism is not clear.

  When a voltage is applied to the gate electrode, electrons can be injected into the amorphous oxide channel layer, so that a current flows between the source and drain electrodes and the two electrodes are turned on.

  In the amorphous oxide film, as the electron carrier concentration increases, the electron mobility increases, so that the current when the transistor is on can be further increased. That is, the saturation current and the on / off ratio can be further increased.

  The field effect transistor having the relatively large field effect mobility can be expected to use an organic light emitting diode for an operation circuit.

[Example 2]
In this embodiment, an amorphous oxide film to which hydrogen is used for a channel layer of a field effect transistor will be described. First, an insulating thin film made of an amorphous oxide was formed on a quartz substrate.

  The method for forming the amorphous oxide is in accordance with the method of the first embodiment.

The target (material source) is InGaO ₃ (ZnO), and the atmosphere during film formation is a total pressure of 0.3 Pa. At that time, the gas flow ratio is Ar: O ₂ = 95: 5, and the oxygen partial pressure corresponds to 0.015 Pa.

  Hydrogen gas is not introduced. The film thickness was about 400 nm. When the resistance of the formed thin film was measured by the four-terminal method, the conductivity was not more than the measurement limit (0.0001 S / cm or less) and was an insulator.

  Next, hydrogen ion implantation treatment was performed on the amorphous oxide thin film.

Here, at the time of ion implantation, H + (proton) is used as the ion species, and the acceleration voltage is 20 kV. As ion irradiation amount per area, samples having various irradiation amounts were prepared in the range of 1 × 10 ¹² to 1 × 10 ¹⁶ (1 / cm ² ).

FIG. 7 shows the result of performing a composition analysis in the depth direction by SIMS on a sample that has been subjected to treatment with a hydrogen ion irradiation amount per area of 1 × 10 ¹⁶ (1 / cm ² ).

  The vertical axis is the hydrogen concentration (arbitrary axis), and the horizontal axis is the depth.

A depth profile having a peak around 200 nm deep from the surface was obtained. Further, the hydrogen concentration in the thin film is about 2 × 10 ²⁰ (1 / cm ³ ).

For example, a sample having an ion irradiation amount per area of 1 × 10 ¹³ (1 / cm ² ) cannot be quantitatively measured because the hydrogen concentration is below the detection limit of SIMS. However, using the above results, the hydrogen concentration can be estimated to be about 2 × 10 ¹⁷ (1 / cm ³ ).

  FIG. 6 shows the electric conductivity of the amorphous InGaZnO thin film with respect to the hydrogen ion implantation amount.

  Here, the horizontal axis represents the hydrogen injection amount estimated by the above method, and the vertical axis represents the logarithm of resistivity.

  Thus, it was found that the electrical conductivity can be controlled by adding hydrogen to the amorphous oxide film.

In particular, it can be seen that the electrical conductivity changes greatly when the hydrogen concentration is around 10 ¹⁸ (1 / cm ³ ). That is, a semiconductor can be formed by ion-implanting hydrogen of about 10 ¹⁸ (1 / cm ³ ) into an insulating In—Ga—Zn oxide.

When the hole mobility of the sample subjected to 1 × 10 ¹⁵ (1 / cm ² ) hydrogen ion implantation per area was evaluated, the polarity of the carrier was negative, the hole mobility was 9 cm ² / Vsec, and the carrier concentration was 6 × 10 ¹⁸ (1 / cm ³ ).

  When an amorphous oxide semiconductor is applied to an active layer of a thin film transistor, a semi-insulating oxide having an electrical conductivity of 0.1 S / cm or less and 0.0001 S / cm or more is empirically determined. A film is preferred.

From this, it can be seen that in the manufacturing method of this example, the hydrogen injection amount is preferably about 10 ¹⁸ (1 / cm ³ ).

  The method using ion implantation of this embodiment can accurately control the hydrogen content and the carrier concentration by the ion irradiation amount (irradiation time).

  Therefore, when applied to the manufacture of a thin film transistor, the resistivity and carrier concentration of the channel layer can be controlled with high accuracy, so that there is an advantage that the device can be manufactured with good reproducibility.

[Example 3]
In this example, the top gate TFT element shown in FIG. 1A is manufactured.

  In addition, a channel layer formed of an amorphous oxide containing hydrogen atoms (or deuterium atoms) by ion implantation of hydrogen or deuterium into an In—Ga—Zn—O-based amorphous oxide formed by a PLD method. Is forming.

  First, an In—Zn—Ga—O-based amorphous oxide film was deposited over a glass substrate (Corning Corporation 1737) by a pulsed laser deposition method (PLD method) using a KrF excimer laser.

An In—Zn—Ga—O based amorphous oxide film was deposited using a polycrystalline sintered body having an InGaO ₃ (ZnO) ₄ composition as a target. The oxygen partial pressure during film formation is 7 Pa.

The power of the KrF excimer laser is 1.5 × 10 ⁻³ mJ / cm ² / pulse, the pulse width is 20 nsec, and the repetition frequency is 10 Hz. The substrate temperature is 25 ° C.

  As a result of X-ray fluorescence (XRF) analysis, the metal composition ratio of the thin film was In: Ga: Zn = 0.97: 1.01: 4.

Furthermore, as a result of performing spectroscopic ellipsometry and analyzing the pattern, the mean square roughness (Rrms) of the thin film is about 0.6 nm and the film thickness is about 100 nm. The electrical conductivity is an insulator having 10 ⁻³ S / cm or less (measurement limit or less).

  Next, hydrogen (or deuterium) ion implantation was performed on the amorphous oxide thin film.

H ⁺ (proton) is used as the ion species, and the acceleration voltage is 10 kV.

Various ion doses ranging from 1 × 10 ¹¹ to 1 × 10 ¹⁵ (1 / cm ² ) are prepared as ion doses per area. Separately, a sample into which deuterium D ⁺ ions are implanted is also prepared.

When composition analysis is performed by SIMS to evaluate the hydrogen content, a sample subjected to ion irradiation of 2 × 10 ¹⁴ (1 / cm ² ) has a hydrogen concentration of 1 × 10 ¹⁹ (1 / cm ³ ) in the thin film. Degree.

Thereby, for example, a sample having an ion irradiation amount of 2 × 10 ¹² (1 / cm ² ) cannot be measured at a hydrogen concentration below the detection limit, but can be estimated to be about 1 × 10 ¹⁷ (1 / cm ³ ).

  With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, but no clear diffraction peak was detected, and the produced In—Zn—Ga—O-based film Is an amorphous film.

For the thin film transistor of this example to be described later, an amorphous oxide having an ion irradiation amount of 2 × 10 ¹³ (1 / cm ² ) is used.

The hydrogen concentration is estimated to be about 1 × 10 ¹⁸ (1 / cm ³ ). Moreover, electrical conductivity shows a semi-insulating property of about 10 ⁻² S / cm.

  The drain electrode 14 and the source electrode 13 were formed by patterning using a photolithography method and a lift-off method. Each electrode material is gold and the thickness is 30 nm.

Next, the gate insulating layer 12 was patterned by photolithography and lift-off. As the gate insulating film, an HfO ₂ film having a thickness of 150 nm was formed by a laser deposition method.

  Further, the gate electrode 15 was formed by a photolithography method and a lift-off method. The electrode material was Au, and the thickness was 50 nm. The channel length was 50 μm and the channel width was 200 μm.

(Comparative Example 2)
Except for the creation of the channel layer, the second embodiment is followed. The channel layer is formed with the oxygen partial pressure during film formation of 6 Pa by the PLD method. Further, ion implantation of hydrogen and deuterium is not performed. Since the oxygen partial pressure is lower than that of the example, a semi-insulating amorphous oxide film can be formed by oxygen deficiency.

(Characteristic evaluation of TFT elements)
The thin film transistor of this example showed the behavior of a typical semiconductor transistor that saturates (pinch off) at about Vd = 6V. The on / off ratio of the transistor is more than 10 ⁶ and the field effect mobility is about 7 cm ² (Vs) ⁻¹ . There is no significant difference in characteristics between hydrogen ion implantation and deuterium ion implantation.

  Further, the TFT of Example 2 has a smaller hysteresis than the TFT of Comparative Example 2. There is a tendency for characteristic variation to be small when a plurality of elements are produced.

  In this example, it is considered that TFTs can be formed with good reproducibility by performing film formation at a higher oxygen partial pressure than in the comparative example.

  Further, since there is almost no variation in TFT characteristics with respect to a minute variation in oxygen partial pressure during the formation of the channel layer, it is considered that this reduces the characteristic variation.

  Further, when the hydrogen content of the channel layer is small, the effect of reducing the hysteresis is small, and when the hydrogen content is large, the on / off ratio tends to be small.

Accordingly, the hydrogen content is preferably 10 ¹⁷ (1 / cm ³ ) or more and 10 ¹⁹ (1 / cm ³ ) or less.

  When the electron carrier concentration and the electron mobility of the amorphous oxide film containing hydrogen were evaluated by changing the hydrogen ion implantation amount, both the carrier concentration and the electron mobility tend to increase by increasing the hydrogen implantation amount.

  In an ordinary compound, as the carrier concentration increases, the electron mobility decreases due to scattering between carriers, etc., but in an amorphous oxide containing hydrogen, the electron mobility increases as the electron carrier concentration increases. Its physical mechanism is not clear.

  When a voltage is applied to the gate electrode, electrons can be injected into the amorphous oxide channel layer, so that a current flows between the source and drain electrodes and the two electrodes are turned on.

  In the amorphous oxide film, as the electron carrier concentration increases, the electron mobility increases, so that the current when the transistor is on can be increased. That is, the saturation current and the on / off ratio can be further increased.

  The field effect transistor having the relatively large field effect mobility can be expected to use an organic light emitting diode for an operation circuit.

[Example 4]
This example is an example in which the bottom gate TFT element shown in FIG.

  First, a gate electrode made of Ta having a thickness of 200 nm is formed on a glass substrate by sputtering. For the patterning, a photolithography method and a dry etching method are used.

  Next, an insulating layer made of a-SiN having a thickness of 250 nm is formed by plasma CVD.

  Next, a channel layer made of an amorphous oxide containing hydrogen is formed.

  In this embodiment, the channel layer forming method is the same as that of the first embodiment.

However, a polycrystalline sintered body having a 2 inch size In ₂ O ₃ (SnO ₂ ) composition is used as the target, and the input RF power is 100 W.

The atmosphere during film formation is a total pressure of 0.4 Pa. At that time, the gas flow rate ratio is Ar: O ₂ : H ₂ = 100: 10: 1. The film formation rate is 11 nm / min. The substrate temperature is 25 ° C.

  With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, and a clear diffraction peak was not detected, and the produced In—Sn—O-based film was It is an amorphous film.

  As a result of fluorescent X-ray (XRF) analysis, the metal composition ratio is In: Sn = 0.95: 1.

(Characteristic evaluation of TFT elements)
The TFT of this embodiment has a small hysteresis and tends to have a small variation in characteristics when a plurality of elements are formed. The on / off ratio of the transistor is more than 10 ⁶ and the field-effect mobility is about 9 cm ² (Vs) ⁻¹ .

[Example 5]
In this example, the top gate type TFT element shown in FIG. 1A is formed on a plastic substrate. The production method and configuration are the same as in Example 1.

  However, a polyethylene terephthalate (PET) film is used as the substrate.

In this example, in channel layer deposition, a polycrystalline sintered body having a 2 inch size In ₂ O ₃ .ZnO composition is used as the target, and the input RF power is 100 W.

The atmosphere during film formation is a total pressure of 0.4 Pa. At that time, the gas flow rate ratio is Ar: O ₂ : H ₂ = 100: 6: 1. The film formation rate is 12 nm / min. The substrate temperature is 25 ° C.

  With respect to the obtained film, grazing incidence X-ray diffraction (thin film method, incident angle 0.5 degree) was performed on the film surface, and a clear diffraction peak was not detected, and the produced In—Zn—O-based film was It is an amorphous film.

  As a result of the X-ray fluorescence (XRF) analysis, the metal composition ratio is In: Zn = 1.1: 0.9.

The source electrode, the drain electrode, and the gate electrode were transparent conductive films made of In ₂ O ₃ : Sn. The thickness is 100 nm.

(Characteristic evaluation of TFT elements)
The measurement was performed at room temperature of the TFT formed on the PET film. The on / off ratio of the transistor is more than 10 ³ . Moreover, when the field effect mobility was calculated, it was a field effect mobility of about 3 cm ² (Vs) ⁻¹ .

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

  The thin film transistor created in this example is transparent to visible light and is formed on a flexible substrate.

  The present invention can be used for switching elements of LCDs and organic EL displays. In addition, it can be widely applied to flexible displays, see-through displays, IC cards and ID tags.

10 substrate 11 channel layer 12 insulating layer 13 source electrode 14 drain electrode 15 gate electrode 51 sample 52 target (material source)
53 Vacuum pump 54 Vacuum gauge 55 Substrate holding means 56 Gas flow control means 57 Pressure control means 58 Deposition chamber

Claims (5)

An oxide semiconductor film containing any one of Ga and In and Zn, Sn and In and Zn, In and Zn and Ga and Mg, In and Sn, In and Ga, or In and Zn, and having an electron carrier concentration of 10 A display including a thin film transistor having a channel layer containing hydrogen atoms of ^{14 16} / cm ³ or more and 10 ¹⁸ / cm ³ or less and 10 ¹⁶ / cm ³ or more and 10 ²⁰ / cm ³ or less as a switching element. The display according to claim 1, wherein the channel layer contains 10 ¹⁷ / cm ³ or more and 10 ¹⁹ / cm ³ or less hydrogen atoms.   The display according to claim 1, wherein the channel layer contains at least In and Zn, and a ratio of the number of In atoms excluding oxygen in the oxide film is 20 atomic% or more and 70 atomic% or less. .   2. The display according to claim 1, wherein the channel layer contains at least In and Sn, and a ratio of the number of In atoms excluding oxygen in the oxide film is 20 atomic% or more and 80 atomic% or less. .   The display according to claim 1, wherein the channel layer is an In—Ga—Zn oxide film.

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