JP2004349583A - Manufacturing method of transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a bottom gate type transistor without damaging zinc oxide and without deteriorating indication quality using an ink jet method which is simple in operation and advantageous in cost when the zinc oxide is employed as a semiconductor element. <P>SOLUTION: The manufacturing method of a bottom gate type transistor is adapted such that a gate electrode 11 is formed on a glass substrate 10 into a predetermined shape, and then a gate insulating film 12 is laminated, on which film 12 a source electrode 13 and a drain electrode 14 are in turn disposed. In the manufacturing method, the source electrode 13 and the drain electrode 14 are formed into predetermined shapes, and then a channel layer 15 containing the zinc oxide is formed into a predetermined shape with an ink jet method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a bottom-gate transistor provided in a display device or the like and using zinc oxide as a semiconductor element.
[0002]
[Prior art]
In recent years, the use of a thin display device (FPD) such as a liquid crystal display device or an organic EL (electroluminescence) display device has been rapidly developing. Among these thin display devices, an amorphous silicon TFT (thin film transistor), a polysilicon TFT, and the like are particularly used for an active matrix display device capable of high-quality display. Since these materials have photosensitivity in the visible light region, when light is irradiated, carriers are generated and the resistance is reduced, thereby deteriorating the display quality. Therefore, the resistance due to light is prevented by blocking the light with a metal film or the like, but this reduces the effective display area and lowers the energy use efficiency.
[0003]
In Patent Document 1, in order to solve this problem, a transparent channel layer is formed by using zinc oxide (ZnO) or the like as a semiconductor element, and a thin film transistor which does not need to block light is formed. As a result, the effective display area of the display device increases, and the energy use efficiency increases. FIG. 4 illustrates an example of a transistor in which transparent zinc oxide is used for a channel layer.
[0004]
As shown in FIG. 4, in the transistor, a gate electrode 111, a gate insulating film 112, a source electrode (data electrode) 113, a drain electrode (connection electrode) 114, and the like are formed over an insulating substrate 110 made of, for example, a glass substrate. ing. A zinc oxide layer 115 using transparent zinc oxide is formed as a channel layer between the gate insulating film 112 and the source / drain electrodes 113 and 114.
[0005]
This transistor can be made to have no photosensitivity in the visible light region by using transparent zinc oxide as a material for the channel layer as described above. Therefore, when the transistor is used for a display device, it is not necessary to form a light-blocking layer, and the effective display area can be increased.
[0006]
[Patent Document 1]
JP 2000-150900 A (Publication date: May 30, 2000)
[0007]
[Non-patent document 1]
Apll. Phys. Lett. , Vol. 82, no. 7, pages 1171-1119 (February 17, 2003)
[0008]
[Problems to be solved by the invention]
When a bottom-gate TFT (thin film transistor) is manufactured using zinc oxide as a semiconductor element as described above, the insulating layer and the zinc oxide layer are continuously formed in order to reduce interface defects between the insulating layer and the semiconductor layer. It is desirable to film. Therefore, the source / drain electrode is usually formed in a predetermined shape after the zinc oxide layer is formed.
[0009]
However, zinc oxide has a very low resistance to chemicals, which causes a problem in the TFT manufacturing process. That is, when the source / drain electrode is formed after the formation of the zinc oxide layer, the zinc oxide layer is damaged, and the yield and the display quality are reduced. Further, in the case where a zinc oxide layer is formed by discharging a solution containing fine particles of zinc oxide by an inkjet method and then firing the solution, the channel width of the TFT portion is increased due to variations in the inkjet discharge amount and positional accuracy. The display quality may vary within a range, which causes deterioration of display quality.
[0010]
Therefore, Non-Patent Document 1 describes a method for forming a zinc oxide layer by a magnetron sputtering method. However, the formation of a zinc oxide layer by such a sputtering method has a disadvantage that the number of steps is increased and the use efficiency of the material is low as compared with the ink jet method, so that the cost is high.
[0011]
The present invention has been made in view of the above problems, and uses an inkjet method that is easy and cost-effective to damage zinc oxide or cause deterioration in display quality. And a method of manufacturing a bottom-gate transistor without using the same.
[0012]
[Means for Solving the Problems]
The method for manufacturing a transistor according to the present invention is directed to a bottom-gate transistor in which a gate electrode is formed in a predetermined shape on an insulating substrate, an insulating layer is stacked, and a source electrode and a drain electrode are arranged on the insulating layer. In the manufacturing method, after the source electrode and the drain electrode are formed in a predetermined shape, a channel layer containing zinc oxide is formed in a predetermined shape by an inkjet method.
[0013]
That is, the method for manufacturing a transistor of the present invention relates to a transistor built in a semiconductor device such as a liquid crystal display device. Among them, a gate electrode is particularly arranged on a lower side, and a source is formed on an upper layer via an insulating layer. The present invention relates to a bottom-gate transistor in which an electrode and a drain electrode are arranged. In addition, a transistor is usually provided with a channel layer which is a semiconductor element. In a transistor manufactured by this manufacturing method, the channel layer is formed including zinc oxide. Then, in this manufacturing method, after the source / drain electrodes are formed in a predetermined shape, the channel layer containing zinc oxide is formed by an inkjet method.
[0014]
As described above, by using transparent zinc oxide as a semiconductor element, a transistor that does not require a light-blocking layer can be formed, whereby an effective display area can be increased when used in a display device. Energy use efficiency can be improved. However, zinc oxide has a very low resistance to chemicals, and in the conventional manufacturing method of forming a source / drain electrode after forming a channel layer, a chemical used at the time of forming the source / drain electrode damages the channel layer containing zinc oxide. As a result, the yield and the electrical characteristics are reduced.
[0015]
Therefore, if the channel layer containing zinc oxide is formed after forming the source / drain electrode into a predetermined shape as in the manufacturing method of the present invention, the zinc oxide contained in the channel layer may be damaged by a chemical or the like. Transistors can be formed without giving a pattern. The transistor manufactured in this manner has improved electric characteristics and can prevent display quality from being deteriorated when used for a liquid crystal display device or the like. Further, the yield of zinc oxide can be improved during manufacturing.
[0016]
Further, according to the above manufacturing method, a channel layer containing zinc oxide is formed in a predetermined shape by an inkjet method; therefore, a transistor can be manufactured more easily and at lower cost than by using a sputtering method.
[0017]
Note that when an inkjet method is used in a conventional method for manufacturing a transistor, a channel width may vary on a transistor substrate due to a variation in inkjet discharge amount and positional accuracy. There is an adverse effect that the quality is deteriorated.
[0018]
However, in the method for manufacturing a transistor of the present invention, since the channel layer is formed by the ink jet method after the source electrode and the drain electrode are formed in a predetermined shape, the step of the source and the drain electrode generated on the insulating layer is formed. Can be used as a guide. That is, the solution discharged by the ink-jet method spreads preferentially over the step and becomes the channel portion (channel layer) of the transistor, so that the channel width can be easily kept constant on the substrate surface of the transistor. Therefore, according to the above manufacturing method, a transistor which does not cause deterioration in display quality even when used for a display device can be easily formed.
[0019]
In the method for manufacturing a transistor according to the present invention, a step of removing organic dirt and oxide dirt on the surface of the insulating layer is provided between the step of forming the source electrode and the drain electrode and the step of forming the channel layer. Preferably, it is included.
[0020]
According to the above manufacturing method, interface defects between the insulating layer and the channel layer can be reduced. Therefore, a transistor with improved electric characteristics can be manufactured.
[0021]
In the method of manufacturing a transistor according to the present invention, the step of removing organic dirt and oxide dirt on the surface of the insulating layer may be performed by Ar or O 2. ₂ It may be performed by a plasma treatment in an atmosphere.
[0022]
According to the above manufacturing method, the effect of reducing the interface defect between the insulating layer and the channel layer is high, so that a transistor with further improved electrical characteristics can be manufactured.
[0023]
In the method for manufacturing a transistor of the present invention, the step of removing the organic stain and the oxide stain on the surface of the insulating layer may be performed by wet etching using a mixed solution of hydrofluoric acid and ammonium fluoride.
[0024]
According to the above manufacturing method, the effect of reducing the interface defect between the insulating layer and the channel layer is high, so that a transistor with further improved electrical characteristics can be manufactured.
[0025]
In the method for manufacturing a transistor of the present invention, it is preferable that the channel layer be formed of zinc oxide and a compound or a mixture containing any of a Group IIa element, a Group IIb element, and a Group VIb element.
[0026]
According to the above manufacturing method, characteristics such as resistivity and band gap can be controlled by mixing a group IIa element, a group IIb element, and a group VIb element into zinc oxide at a predetermined concentration. The characteristics of the transistor can be further improved.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS. In addition, this invention is not limited to the following description.
[0028]
In this embodiment, a method for manufacturing a thin film transistor such as a liquid crystal display device, which is provided in an active matrix display device capable of performing high-quality display, will be described. FIG. 1 is a cross-sectional view illustrating a structure of a transistor according to the present embodiment, and FIG. 2 is a plan view schematically illustrating an arrangement state of members provided in the transistor.
[0029]
As shown in FIG. 1, the transistor has a glass substrate (insulating substrate) 10, a gate electrode 11, a gate insulating film (insulating layer) 12, a source electrode 13, a drain electrode 14, and a channel layer 15 as constituent elements. I have. Further, as shown in FIG. 2, the transistor has a gate electrode 11 and a source electrode 13 arranged in a matrix on a glass substrate 10, and a TFT portion is formed at an intersection thereof. A drain electrode 14 serving as a pixel electrode and a channel layer 15 serving as a semiconductor element are provided in the TFT portion. FIG. 1 shows a cross-sectional structure of a TFT portion of the transistor.
[0030]
A more detailed structure of the above transistor is described with reference to FIGS.
[0031]
In the above transistor, a gate electrode 11 is arranged in a predetermined shape on a glass substrate 10, and a gate insulating film 12 is laminated thereon. First, a source electrode 13 and a drain electrode 14 are provided in a predetermined shape on the gate insulating film. Further, a channel layer 15 serving as a channel portion of the semiconductor element is provided in a predetermined shape above the source electrode 13 and the drain electrode 14. More specifically, the channel layer 15 embeds a part between the source electrode 13 and the drain electrode 14 formed in a predetermined shape on the surface of the gate insulating film 12, and forms the gate insulating film 12 and the source / drain electrode 13. 14 are arranged so as to cover the step.
[0032]
As described above, in the transistor according to the present invention, the gate electrode 11 is stacked on an insulating substrate such as the glass substrate 10, and the source electrode 13 and the drain electrode 14 are arranged thereover via the gate insulating film 12. It has a structure. Such a structure of the transistor is called a bottom gate type (or an inverted staggered type).
[0033]
In the present invention, zinc oxide (ZnO), which is a transparent semiconductor, is used as the material of the channel layer 15 instead of the commonly used amorphous silicon or polysilicon. With the use of this transistor, a display device which does not require a light-blocking layer and whose effective display area is not reduced can be provided.
[0034]
Note that in a conventional bottom-gate transistor using zinc oxide as a semiconductor element, a channel layer 115 is first formed over a gate insulating layer 112, and the channel layer 115 is covered thereover, as shown in FIG. Source / drain electrodes 113 and 114 are formed as described above. In this case, the channel layer 115 made of zinc oxide is formed on the gate insulating film 112 before the source / drain electrodes 113 and 114 are formed. When the drain electrodes 113 and 114 are formed, a problem occurs that the zinc oxide included in the channel layer 115 is damaged.
[0035]
On the other hand, as described above, the transistor of the present invention has a structure obtained by forming the channel layer 15 made of zinc oxide having extremely low chemical resistance after forming the source / drain electrodes 13 and 14 in a predetermined shape. Therefore, the channel layer 15 can be formed without damaging the zinc oxide. Therefore, at the time of manufacturing the transistor, it is possible to contribute to improvement in yield and to improve electrical characteristics of the transistor.
[0036]
Next, a material of each component (member) of the transistor will be described.
[0037]
First, the channel layer 15 is formed from zinc oxide (ZnO) as described above. This channel layer 15 may have crystallinity or may be amorphous. When crystallinity is given, orientation may be given as appropriate. As a method for imparting crystallinity or orientation, a method of adjusting the film formation rate to a lower level, for example, because zinc oxide itself tends to have crystallinity or orientation, may be mentioned. In this case, the mobility of the transistor can be expected to be improved.
[0038]
The source electrode 13 and the drain electrode 14 are made of a conductive material such as a metal or a semiconductor, and are not particularly limited as long as they are formed of a material that can be ohmic-joined to the channel layer 15. Specifically, as the source electrode 13 and the drain electrode 14, for example, a transparent conductive film made of ITO or the like having a thickness of 0.1 to 1.0 μm can be used. Further, as a material of the source electrode 13 and the drain electrode 14, an Al, Ag film, an Al alloy film (for example, Al—Nd, Al—Zr alloy, or the like), or a stacked film of Al and another conductive film (for example, Al / Mo, Al / Ti, etc.) can be used. If the transistor is formed using a metal material having high reflectivity, such as Al or Ag, as a material of the source electrode 13 and the drain electrode 14, the transistor can be used for a reflective display device.
[0039]
The gate electrode 11 may be formed of a conductive material such as a metal or a semiconductor, similarly to the source / drain electrodes 13 and 14 described above. More specifically, metals such as Al, Mo, and Ta can be mentioned.
[0040]
As the gate insulating film 12, for example, SiN _X And SiO _X Or other insulating materials. In addition, Al ₂ O ₃ , MgO, CeO, ScAlMgO ₄ Or a transparent insulator such as vinyl, plastic, or the like. Note that the gate insulating film 12 is more preferably a high insulating material having good lattice matching with zinc oxide contained in the channel layer 15. ScAlMgO is a highly insulating material that has good lattice matching with zinc oxide. ₄ And the like.
[0041]
In this embodiment, the glass substrate 10 is used as an insulating substrate serving as a base of the transistor. However, the present invention is not limited to this, and various materials having an insulating property may be used as the material of the insulating substrate. Can be used. Specific examples of the insulating substrate include glass, a silicon wafer, and plastic. Note that in the case where the transistor is used for an application requiring transparency such as a liquid crystal display device, a transparent insulating substrate is preferably used.
[0042]
As described above, the channel layer of the transistor according to this embodiment is formed of zinc oxide. However, the present invention is not limited thereto. May be included.
[0043]
In addition, it is preferable that any one of a group IIa element, a group IIb element, and a group VIb element be added to the channel layer in addition to zinc oxide. According to this, characteristics such as resistivity and band gap can be controlled by mixing a group IIa element, a group IIb element, and a group VIb element into zinc oxide at a predetermined concentration. Can be further improved. The group IIa element is, for example, Be, Mg, Ca, Sr, Ba, etc., the group IIb element is, for example, Zn, Cd, Hg, etc., and the group VIb element is, for example, S , Se, Te, and the like.
[0044]
Next, an example of a method for manufacturing a transistor according to the present embodiment will be specifically described with reference to FIGS. 3A to 3E are views showing the cross-sectional structure of the transistor in the order of manufacturing steps.
[0045]
First, for example, a non-alkali glass substrate is used as the glass substrate 10. Then, as shown in FIG. 3A, a gate electrode 11 made of a metal thin film of Ta, Al, Mo or the like is formed on the glass substrate 10. These are formed by forming the metal thin film on the glass substrate 10 to a thickness of about 3000 ° by a sputtering method and then patterning the thin film into a desired shape. As a patterning method, a method including a photo-etching and a peeling step can be used. Further, as a method for forming the gate electrode 11, a vapor deposition method or an inkjet method may be used. When the ink-jet method is used, the gate electrode 11 is formed by discharging a solution containing metal fine particles having a diameter of about 5 to 100 nm made of Ta, Al, Mo, Ag, or the like by the ink-jet method and then firing.
[0046]
Next, as shown in FIG. 4B, a gate insulating film 12 made of SiNx, SiOx, or the like is formed by P-CVD on almost the entire upper surface of the glass substrate 10 so as to cover the gate electrode 11. A film is formed at 3500 °.
[0047]
Next, as shown in FIG. 3C, a source electrode 13 and a drain electrode 14 are formed in a predetermined shape above the gate electrode 11 with a gate insulating film 12 interposed therebetween. Specifically, a transparent conductive film made of ITO or the like is formed to a thickness of about 3000 ° by a sputtering method, and then the source electrode 13 and the drain electrode 14 are formed into a predetermined shape through a photo-etching and peeling process. Form. Here, by using a metal material with high reflectivity such as Al or Ag as a material of the source / drain electrodes 13 and 14, it can be applied to a reflective display device. Further, as a method for forming the source electrode 13 and the drain electrode 14, an evaporation method or an inkjet method may be used. In the case of using the ink jet method, a source electrode 13 and a drain electrode 14 are formed by discharging a solution containing metal fine particles having a diameter of about 5 to 100 nm made of ITO, Al, Ag, or the like by the ink jet method and then firing.
[0048]
Then, after forming the source / drain electrodes 13 and 14 in a predetermined shape, as shown in FIG. 3D, a channel layer 15 made of zinc oxide is formed by an inkjet method. Specifically, the channel layer 15 is formed by discharging a solution containing zinc oxide by an ink-jet method, followed by baking. The solution containing zinc oxide is a solution in which fine particles of zinc oxide having a particle size of about 30 nm are dispersed in a solvent composed of water, IPA, n-methylpyrrolidone, n-octanol, isobutanol, ethylene glycol, toluene, and the like. is there. According to this, at the time of discharging the solution containing zinc oxide, a step portion between the gate insulating film 12 and the source / drain electrodes 13 and 14 serves as a guide, and a concave portion on the gate insulating film 11 (that is, the surface of the gate insulating film 12) (The portion where the source / drain electrodes 13 and 14 are not formed), the solution spreads preferentially, so that the width (channel width) of the channel layer 15 can be easily secured. As a result, a predetermined channel length and a predetermined channel width can be secured, so that uniform electric characteristics and display quality can be secured in a plane.
[0049]
The channel layer 15 is formed in a region where a step between the gate insulating film 12 and the source / drain electrodes 13 and 14 occurs in an upper layer portion where the gate electrode 11 is arranged. That is, the channel layer 15 is formed in such a shape as to fill the step and cover a part of the source / drain electrodes 13 and 14.
[0050]
Before the channel layer 15 is formed by the inkjet method as described above, Ar or O 2 is used to remove organic stains and oxide stains. ₂ It is preferable to perform plasma treatment in an atmosphere or wet etching treatment using a solution in which hydrofluoric acid and ammonium fluoride are mixed at a ratio of 1: 100. According to this, since the channel layer 15 can be satisfactorily matched on the gate insulating layer 11 from which the contamination has been removed, interface defects between the gate insulating film 12 and the channel layer 15 can be further reduced. .
[0051]
Next, an insulating protective film 16 is formed so as to cover the channel layer 15. This protective film 16 is made of SiN by P-CVD. _X Is formed into a predetermined shape through a photo-etching and stripping process.
[0052]
Since the transistor manufactured by the above manufacturing method can be formed without damaging the channel layer 15 containing zinc oxide, the yield of zinc oxide and the electrical characteristics of the transistor can be improved. it can. Further, according to the above manufacturing method, since the channel layer is formed in a predetermined shape by the inkjet method, the transistor can be manufactured more easily and at lower cost than using the sputtering method.
[0053]
According to the above-described manufacturing method, even when the channel layer 15 is formed by using the inkjet method, the channel layer 15 is formed after the source electrode 13 and the drain electrode 14 are formed in a predetermined shape. Therefore, the step between the source and drain electrodes 13 and 14 generated on the gate insulating film 12 can be used as a guide. In other words, the solution discharged by the inkjet method preferentially spreads over the step portion and becomes the channel layer 15 of the transistor, so that the channel width can be easily kept constant on the substrate surface of the transistor. Therefore, even when the transistor is used for a display device, a transistor which does not cause deterioration in display quality can be easily formed.
[0054]
In the present embodiment, the solution discharged by the inkjet method at the time of forming the channel layer 15 contains zinc oxide. However, the present invention is not limited to this, and various solutions other than zinc oxide may be used. Compounds and elements may be added. Here, the element added to the zinc oxide is preferably any one of a group IIa element, a group IIb element, and a group VIb element. In this case, together with the zinc oxide fine particles, fine particles (particle size of about 30 nm) of the above-mentioned Group IIa element, Group IIb element and Group VIb element are mixed with water, IPA, n-methylpyrrolidone, n-octanol, iso- What is necessary is just to disperse in a solvent composed of butanol, ethylene glycol, toluene or the like to prepare a solution for ejection.
[0055]
The transistor manufactured by the manufacturing method of the present invention can be used as various semiconductor devices by stacking a semiconductor, a conductor, an insulator, or other various constituent members.
[0056]
Examples of the semiconductor device include an active matrix type liquid crystal display device and an electromagnetic wave detector, but the transistor of the present invention is not limited to this and is preferably used for various other semiconductor devices. be able to. (* If there are any possible ways to use the transistor of the present invention for the underlined parts, please give them examples.) In addition to liquid crystal displays, organic EL displays, porous silicon displays, It can be used for various displays such as an electrophoretic display, a toner display, a twist ball, and an electrochromic display.
[0057]
【The invention's effect】
As described above, the method for manufacturing a transistor of the present invention includes a method of forming a gate electrode on an insulating substrate in a predetermined shape, stacking an insulating layer, and arranging a source electrode and a drain electrode on the insulating layer. A method for manufacturing a gate transistor is characterized in that after the source electrode and the drain electrode are formed in a predetermined shape, a channel layer containing zinc oxide is formed in a predetermined shape by an inkjet method.
[0058]
According to the above manufacturing method, a transistor can be formed without damaging the channel layer with a chemical or the like. The transistor manufactured as described above has an effect that the electrical characteristics are improved and display quality can be prevented from deteriorating when used for a liquid crystal display device or the like. Further, in the manufacturing method of the present invention, a channel layer containing zinc oxide is formed in a predetermined shape by an inkjet method; therefore, a transistor can be manufactured more easily and at lower cost than using a sputtering method.
[0059]
In the method for manufacturing a transistor according to the present invention, a step of removing organic dirt and oxide dirt on the surface of the insulating layer is provided between the step of forming the source electrode and the drain electrode and the step of forming the channel layer. May be included.
[0060]
According to the above manufacturing method, interface defects between the insulating layer and the channel layer can be reduced. Therefore, there is an effect that a transistor with improved electric characteristics can be manufactured.
[0061]
In the method for manufacturing a transistor of the present invention, it is preferable that the channel layer be formed of zinc oxide and a compound or a mixture containing any of a Group IIa element, a Group IIb element, and a Group VIb element.
[0062]
According to the above manufacturing method, characteristics such as resistivity and band gap can be controlled by mixing a group IIa element, a group IIb element, and a group VIb element into zinc oxide at a predetermined concentration. There is an effect that the characteristics of the transistor can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of a transistor in one embodiment of the present invention.
FIG. 2 is a plan view schematically showing an arrangement state of each component of a transistor according to an embodiment of the present invention.
FIGS. 3A to 3E are cross-sectional views illustrating a structure in each manufacturing process of the transistor according to the embodiment in the order of the manufacturing process.
FIG. 4 is a cross-sectional view illustrating a structure of a conventional transistor.
[Explanation of symbols]
10 Glass substrate (insulating substrate)
11 Gate electrode
12 Gate insulating film (insulating layer)
13 Source electrode
14 drain electrode
15 Channel layer
16 Protective film

Claims (5)

After forming a gate electrode in a predetermined shape on an insulating substrate, a method for manufacturing a bottom-gate transistor in which an insulating layer is stacked and a source electrode and a drain electrode are provided over the insulating layer,
A method for manufacturing a transistor, comprising: forming a source electrode and a drain electrode in a predetermined shape; and then forming a channel layer containing zinc oxide in a predetermined shape by an inkjet method. The step of forming the source electrode and the drain electrode, and the step of forming the channel layer include a step of removing organic dirt and oxide dirt on the surface of the insulating layer. 2. The method for manufacturing a transistor according to 1. 3. The method according to claim ₂ , wherein the step of removing organic dirt and oxide dirt on the surface of the insulating layer is performed by plasma treatment in an Ar or O2 atmosphere. 3. The transistor according to claim 2, wherein the step of removing the organic stain and the oxide stain on the surface of the insulating layer is performed by wet etching using a mixed solution of hydrofluoric acid and ammonium fluoride. Method. 5. The device according to claim 1, wherein the channel layer is formed of zinc oxide and a compound or a mixture containing any one of a Group IIa element, a Group IIb element, and a Group VIb element. 6. A method for manufacturing the transistor described in the above.

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