JP7143601B2 - FIELD EFFECT TRANSISTOR, DISPLAY DEVICE, IMAGE DISPLAY DEVICE, AND SYSTEM - Google Patents

Description

The present invention relates to field effect transistors, display elements, image display devices, and systems.

A liquid crystal display (LCD), an organic EL (electroluminescence) display (OLED), and a flat panel display (FPD) such as electronic paper use amorphous silicon or polycrystalline silicon as an active layer. It is driven by a driving circuit including a thin film transistor (TFT). In the development of FPDs, there is a technique of fabricating TFTs using an oxide semiconductor film with high carrier mobility and small variation between elements in the channel forming region of the TFTs, and applying the TFTs to electronic devices, optical devices, and the like. Attention has been paid. For example, the FET using zinc oxide (ZnO), In ₂ O ₃ , In--Ga--Zn--O, or the like as an oxide semiconductor film has been proposed.

As a field effect transistor using an oxide semiconductor, specifically, a field effect transistor using a crystalline oxide semiconductor containing zinc oxide, indium oxide, and gallium oxide has been proposed (for example, patent Reference 1). Also, the group consisting of aluminum (Al), boron (B), gallium (Ga), indium (In), titanium (Ti), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb). A field-effect transistor using an oxide semiconductor film having a low-resistance region containing at least one of them as a dopant has been proposed (see, for example, Patent Document 2).

An object of the present invention is to provide a field effect transistor that can be easily manufactured, has good contact between the source electrode and the drain electrode and the oxide semiconductor, and has little variation in characteristics.

Means for solving the above problems are as follows. Namely
The field effect transistor of the present invention is
a source electrode and a drain electrode;
an active layer made of an oxide semiconductor;
A field effect transistor comprising
the source electrode and the drain electrode contain a gold alloy in contact with the oxide semiconductor;
The gold alloy is characterized by containing a first element of gold and a second element of at least one of germanium, tin, zinc and indium.

According to the present invention, it is possible to provide a field effect transistor that can be easily manufactured, has good contact between the source electrode and the drain electrode and the oxide semiconductor, and has little variation in characteristics.

FIG. 1 is a schematic cross-sectional view showing an example of a bottom-gate/bottom-contact field effect transistor. FIG. 2 is a schematic cross-sectional view showing an example of a bottom-gate/top-contact field effect transistor. FIG. 3 is a schematic cross-sectional view showing an example of a top-gate/bottom-contact field effect transistor. FIG. 4 is a schematic cross-sectional view showing an example of a top-gate/top-contact field effect transistor. FIG. 5 is a schematic configuration diagram showing an example of a television apparatus 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 showing an example of the positional relationship between an organic EL element and a field effect transistor in a display element. FIG. 11 is a schematic configuration diagram showing 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 showing an example of an organic EL element. FIG. 13 is a diagram for explaining a display control device. FIG. 14 is a diagram for explaining a liquid crystal display. 15 is a diagram for explaining the display element in FIG. 14. FIG. 16 is a current-voltage characteristic curve of the field effect transistor of Example 1. FIG. 17 is a current-voltage characteristic curve of the field effect transistor of Comparative Example 1. FIG.

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

The present inventors have found that, in a field-effect transistor using an oxide semiconductor for the active layer, a transistor having high field-effect mobility can be realized when gold is used for the source electrode and the drain electrode, but switching failure found that it may occur.
Therefore, as a result of intensive studies, the contact between the source electrode and the drain electrode and the oxide semiconductor is improved by containing a specific gold alloy at least in the portion where the source electrode and the drain electrode are in contact with the oxide semiconductor. I found out. Here, the specific gold alloy contains a first element of gold and a second element of at least one of germanium, tin, zinc, and indium.
In addition, in the case of the specific gold alloy, the contact resistance with the oxide semiconductor is considered to be lower than in the case of gold, resulting in poor contact resistance between the source and drain electrodes and the oxide semiconductor. Variation in characteristics can be suppressed.
Furthermore, by using the specific gold alloy, it is necessary to provide a low-resistance layer between the source and drain electrodes and the active layer in order to improve the contact resistance between the source and drain electrodes and the active layer. There is no In this respect, the field effect transistor of the present invention can be manufactured by a simple manufacturing process without the need for a low-resistance layer.
As described above, the present invention has been completed.

<Source electrode and drain electrode>
The source electrode and the drain electrode contain a gold alloy in contact with the oxide semiconductor.
The source and drain electrodes may be the gold alloy itself, or may be a composite of the gold alloy and another composition (for example, gold).
Examples of the composite include a laminate structure of the gold alloy layer and the gold layer.

The gold alloy contains at least a first element and a second element.

The first element is gold. Gold is thermally stable, resistant to oxidation, and has low electrical resistivity. By using gold as the main component of the gold alloy, the source electrode and the drain electrode are stable in the manufacturing process, contributing to stabilization of device characteristics. In addition, by using gold, which has a low electrical resistivity, it is possible to reduce the influence of wiring delay.
The gold alloy contains gold as a main component. Therefore, the gold content in the gold alloy is, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more. The upper limit of the content of gold in the gold alloy is not particularly limited and can be appropriately selected according to the purpose. The content of gold in the gold alloy is, for example, less than 100% by weight. . However, the sum of the content of gold and the content of the second element naturally does not exceed 100% by weight.

The second element is at least one of germanium, tin, zinc, and indium. Since the gold alloy contains the second element, the adhesion between the source electrode and the drain electrode and the layer in contact with the gold alloy is improved, which contributes to the prevention of film peeling of the electrodes. In addition, the inclusion of the second element improves electrical contact with an oxide semiconductor, which will be described later, and contributes to higher performance and uniformity of device characteristics.
The content of the second element in the gold alloy is not particularly limited, and can be appropriately selected according to the purpose. The following are more preferred. If the content is within the preferable range, the contact between the source electrode and the drain electrode and the oxide semiconductor will be better.
When the second element is germanium, the content of the second element in the gold alloy is preferably 3% by weight or more and 15% by weight or less.
When the second element is tin, the content of the second element in the gold alloy is preferably 15% by weight or more and 30% by weight or less.

Also, the contents of gold and the second element in the gold alloy may be appropriately selected based on the melting temperature of the gold alloy. In this case, the melting temperature of the gold alloy is preferably higher than the heating temperature applied to the source electrode and the drain electrode when manufacturing the field effect transistor. In a field effect transistor using an oxide semiconductor as an active layer, the device characteristics may be stabilized by performing an annealing treatment at a temperature of about 250° C. to 300° C. after manufacturing the transistor. In this regard, the melting temperature of the gold alloy is preferably 250° C. or higher, more preferably 300° C. or higher, and particularly preferably 350° C. or higher.
The melting temperature can be measured, for example, by DSC (differential scanning calorimetry) measurement, structural observation by a microscope using a DSC hot stage for microscopes, or the like.

The average thickness of the source electrode and the drain electrode is not particularly limited and can be appropriately selected depending on the purpose.

The method for forming the source electrode and the drain electrode is not particularly limited and can be appropriately selected according to the purpose. (ii) a step of directly forming a film in a desired shape by a printing process such as inkjet, nanoimprint, gravure, and the like.

<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 can be appropriately selected depending on the intended purpose. metals, alloys thereof, mixtures of these metals, and the like. In addition, indium oxide, zinc oxide, tin oxide, gallium oxide, niobium oxide, In ₂ O ₃ (ITO) to which tin (Sn) is added, ZnO to which gallium (Ga) is added, and aluminum (Al) is added. conductive oxides such as ZnO, antimony ₍ Sb)-added SnO2, composite compounds thereof, mixtures thereof, and the like.

The average thickness of the gate electrode is not particularly limited and can be appropriately selected depending on the purpose.

The method for forming the gate electrode is not particularly limited and can be appropriately selected according to the purpose. , a step of patterning by photolithography, and (ii) a step of directly forming a film in a desired shape by a printing process such as inkjet, nanoimprint, or gravure.

<Gate insulating layer>
The gate insulating layer is not particularly limited as long as it is an insulating layer formed between the gate electrode and the active layer, for example, and can be appropriately selected according to the purpose.
The material of the gate insulating layer is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include inorganic insulating materials and organic insulating materials.
Examples of the inorganic insulating material include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, zirconium oxide, silicon nitride, aluminum nitride, and mixtures thereof.
Examples of the organic insulating material include polyimide, polyamide, polyacrylate, polyvinyl alcohol, and novolac resin.

The average thickness of the gate insulating layer is not particularly limited and can be appropriately selected depending on the intended purpose.

The method for forming the gate insulating layer is not particularly limited and can be appropriately selected depending on the intended purpose. After that, a step of patterning by photolithography, (ii) a step of directly forming a film in a desired shape by a printing process such as inkjet, nanoimprint, gravure, and the like are included.

<Active layer>
The active layer is made of an oxide semiconductor.
The active layer is provided, for example, adjacent to the source and drain electrodes.
The oxide semiconductor is not particularly limited and can be appropriately selected depending on the purpose, but an n-type oxide semiconductor is preferable.

The oxide semiconductor preferably contains at least one of indium, zinc, tin, gallium, and titanium.
The oxide semiconductor preferably contains an alkaline earth element.
The oxide semiconductor preferably contains a rare earth element.

The n-type oxide semiconductor can be appropriately selected depending on the purpose, but preferably contains at least one of indium, zinc, tin, gallium, and titanium. Examples of the n-type oxide semiconductor include ZnO, SnO ₂ , In ₂ O ₃ , TiO ₂ and Ga ₂ O ₃ . In--Zn-based oxides, In--Sn-based oxides, In--Ga-based oxides, Sn--Zn-based oxides, Sn--Ga-based oxides, Zn--Ga-based oxides, In--Zn--Sn-based oxides Oxide, In--Ga--Zn-based oxide, In--Sn--Ga-based oxide, Sn--Ga--Zn-based oxide, In--Al--Zn-based oxide, Al--Ga--Zn-based oxide, Sn- An oxide containing a plurality of metals, such as an Al--Zn-based oxide, an In--Hf--Zn-based oxide, or an In--Al--Ga--Zn-based oxide, can also be used.
The n-type oxide semiconductor has at least one of indium, zinc, tin, gallium, and titanium, and an alkaline earth element, because high field-effect mobility can be obtained and electron carrier concentration can be appropriately controlled. and more preferably indium and an alkaline earth metal.
Examples of the alkaline earth elements include beryllium, magnesium, calcium, strontium, barium, and radium.
The electron carrier concentration of indium oxide varies from about 10 ¹⁸ cm ⁻³ to 10 ²⁰ cm ⁻³ depending on the amount of oxygen deficiency. However, indium oxide tends to cause oxygen vacancies, and unintentional oxygen vacancies may occur in a post-process after formation of the oxide semiconductor film. Forming an oxide mainly from two metals, indium and an alkaline earth element that bonds more easily with oxygen than indium, prevents unintended oxygen vacancies, facilitates composition control, and appropriately adjusts the electron carrier concentration. It is particularly preferable in terms of easy control.

The electron carrier concentration of the active layer can be controlled within an appropriate range by the elements constituting the active layer, manufacturing process conditions, post-treatment after film formation, and the like.
The average thickness of the active layer is not particularly limited and can be appropriately selected depending on the intended purpose.

The method for forming the active layer is not particularly limited and can be appropriately selected according to the purpose. , a step of patterning by photolithography, and (ii) a step of directly forming a film in a desired shape by a printing process such as inkjet, nanoimprint, or gravure.

<Base material>
The shape, structure, and size of the substrate are not particularly limited and can be appropriately selected according to the purpose.
The material of the base material is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include a glass base material.
The glass substrate is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include alkali-free glass and silica glass.
From the viewpoint of cleaning the surface and improving adhesion, the substrate is preferably subjected to pretreatment such as oxygen plasma, UV ozone, and UV irradiation cleaning.

The structure of the field effect transistor is not particularly limited and can be appropriately selected depending on the purpose. Top gate/bottom contact type (FIG. 3), top gate/top contact type (FIG. 4), and the like. 1 to 4, 1 represents a substrate, 2 a gate electrode, 3 a gate insulating layer, 4 a source electrode, 5 a drain electrode, and 6 an active layer.

(Display element)
The display element of the present invention has at least a light control element and a drive circuit for driving the light control element, and further has 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. EC) elements, liquid crystal elements, electrophoresis elements, electrowetting elements, 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 parts>
The other members are not particularly limited and can be appropriately selected according to the purpose.

Since the display element has the field effect transistor of the present invention, it can be driven at high speed, has a long life, and can reduce variations between elements. Further, even if the display element changes with time, the driving transistor can be operated with a constant gate voltage.

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

<Plural display elements>
The plurality of display elements are not particularly limited as long as they are the plurality of 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 image data signal can be applied individually 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 signal voltage of each field effect transistor can be individually controlled via the plurality of wirings according to image data. It can be selected as appropriate.

<Other parts>
The other members are not particularly limited and can be appropriately selected according to the purpose.

Since the image display device has the display element of the present invention, it is possible to reduce variations between the elements and display high-quality images on a large screen.

(system)
A 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, the display device, image display device, and system of the present invention will be described with reference to the drawings.
First, a television apparatus as a system of the present invention will be described with reference to FIG.

5, television apparatus 100 includes main controller 101, tuner 103, AD converter (ADC) 104, demodulation circuit 105, TS (Transport Stream) decoder 106, audio decoder 111, DA converter (DAC) 112, 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 receiver 151 and a communication control device 152 .
A video decoder 121, a video/OSD synthesizing circuit 122, a video output circuit 123, and an OSD rendering circuit 125 constitute an image data generating device.

The main controller 101 is composed of a CPU, a flash ROM, a RAM, and the like, and controls the television apparatus 100 as a whole.
The flash ROM stores a program written in code that can be read by the CPU, various data used for processing by the CPU, and the like.
Also, the RAM is a working memory.

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

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

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

The TS decoder 106 TS-decodes the output signal of the demodulation circuit 105 and separates audio information and video information.

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

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

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

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

The video/OSD synthesizing 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 synthesizing circuit 122 to the image display device 124 .

The OSD drawing circuit 125 has a character generator for displaying characters and graphics on the screen of the image display device 124, and generates signals containing display information according to instructions from the operation device 132 and the IR receiver 151. Generate.

The memory 131 temporarily stores AV (Audio-Visual) data and the like.

The operation device 132 includes 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 two-way communication interface, and conforms to ATAPI (AT Attachment Packet Interface) as an example.

The hard disk device 142 is composed of a hard disk, a drive device for driving the hard disk, and the like. The drive device records data on the hard disk and reproduces the data recorded on the hard disk.

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

IR receiver 151 receives an optical signal from remote control transmitter 220 and notifies main controller 101 of it.

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

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

The display element of the present invention will be described below with reference to FIG.
FIG. 9 is a schematic configuration diagram showing an example of the display element of the present invention.
The display element, as shown in FIG. 9 as an example, has an organic EL (electroluminescence) element 350 and a drive circuit 320 for causing the organic EL element 350 to emit light. That is, the display 310 is a so-called active matrix organic EL display. The display 310 is a 32-inch color display. Note that the size is not limited to this.

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 the drive circuit. Here, an organic EL element 350 is arranged beside the field effect transistor 20 . A field effect transistor 10 and a 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 top of the active layer 22 . As a material for the protective film, SiO ₂ , SiN _x , Al ₂ O ₃ , fluorine-based polymer, or the like can be appropriately used.

Also, for example, as shown in FIG. 11, an organic EL element 350 may be arranged on the field effect transistor 20 . _In this case _, the gate _electrode 26 is required to be transparent. Conductive transparent oxides such as SnO ₂ doped with are used. Reference numeral 360 denotes an interlayer insulating film (flattening film). Polyimide, acrylic resin, or the like can be used for this interlayer insulating film.

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

The material of the cathode 312 is not particularly limited and can be appropriately selected depending on the purpose. Examples include aluminum (Al), magnesium (Mg)-silver (Ag) alloy, aluminum (Al)-lithium (Li). alloys, ITO (Indium Tin Oxide), and the like. The magnesium (Mg)-silver (Ag) alloy becomes a highly reflective electrode if it is sufficiently thick, and becomes a translucent electrode if it is extremely thin (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 making the cathode a transparent or translucent electrode.

The material of the anode 314 is not particularly limited and can be appropriately selected according to the purpose. is mentioned. In addition, when a silver alloy is used, it becomes a highly reflective electrode, and is suitable for extracting light from the cathode side.

The organic EL thin film layer 340 has an electron transport layer 342 , a light emitting layer 344 and a hole transport layer 346 . Electron transport layer 342 is connected to cathode 312 and hole transport layer 346 is connected to 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-transporting layer 342 and the light-emitting layer 344 may form one layer, an electron-injecting layer may be provided between the electron-transporting layer 342 and the cathode 312, and a hole-transporting layer may be provided. A hole injection layer may be provided between layer 346 and anode 314 .

Also, although the case of so-called "bottom emission" in which light is extracted from the substrate side has been described, "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.
Drive circuit 320 has two field effect transistors 10 and 20 and capacitor 30 .

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

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

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

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 has display elements 302 , wiring (scanning lines, data lines, current supply lines), and a display control device 400 .
The display control device 400 has 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 brightness 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 according to instructions from the image data processing circuit 402 .
The data line driving circuit 406 individually applies voltages to the m data lines according to instructions from the image data processing circuit 402 .

Further, in the above embodiments, the case where the light control element is an organic EL element has been described, but the light control element is not limited to this, and for example, the light control element may be an electrochromic element. In this case, the display becomes an electrochromic display.

Also, the light control element may be a liquid crystal element, in which case the display will be a liquid crystal display, and as shown in FIG. Also, as shown in FIG. 15, the drive circuit 320' can be composed of one field effect transistor 40 similar to the field effect transistors 10 and 20. FIG. 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. Also, the drain electrode D is connected to the capacitor 361 and the pixel electrode of the liquid crystal element 370 .

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

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

In addition, the image display device 124 is used as a display means in portable information devices such as a mobile phone, a portable music player, a portable video player, an electronic book, a PDA (Personal Digital Assistant), and an imaging device such as a still camera or a video camera. can be used. In addition, the image display device 124 can be used as means for displaying various types of information in mobile systems such as cars, airplanes, trains, and ships. Furthermore, the image display device 124 can be used as means for displaying various types of information in measurement devices, analysis devices, medical devices, and advertising media.

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

(Example 1)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
-Formation of gate electrode-
An Al alloy film was formed on a glass substrate using a sputtering method. A gate electrode was patterned into a desired shape by photolithography and etching.

-Formation of gate insulating layer-
Next, a gate insulating layer was formed by depositing SiO ₂ to a thickness of 200 nm by plasma CVD.

-Formation of active layer-
A Mg—In based oxide semiconductor film (active layer) was formed by sputtering on the formed gate insulating layer by the method described in the example of JP-A-2010-74148. A polycrystalline sintered body having a composition of In ₂ MgO ₄ was used as the target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. The total pressure was set to 0.3 Pa by adjusting the flow rates of the argon gas and the oxygen gas during sputtering. The thickness of the obtained oxide semiconductor film (active layer) was 50 nm.

-Formation of source and drain electrodes-
On the formed active layer, using a vacuum deposition method and a shadow mask, Au—Ge 7.4 (manufactured by Tanaka Kikinzoku Co., Ltd., Au 92.6% by weight, Ge 7.4% by weight) was vapor-deposited to form a source electrode and a drain electrode. formed.

As described above, a bottom-gate/top-contact field effect transistor was manufactured.

<Transistor performance evaluation>
Regarding the obtained field effect transistor, it was confirmed whether or not the source/drain electrodes were peeled off. The case where there was no peeling was evaluated as ◯, the case where there was partial peeling was evaluated as Δ, and the case where there were many peeled portions was evaluated as ×. Also, the transistor performance was evaluated using a semiconductor parameter analyzer (Semiconductor parameter analyzer B1500A manufactured by Agilent Technologies). The source/drain voltage Vds was set to 10 V, and the gate voltage was changed from Vg=-15 V to +15 V to evaluate current-voltage characteristics (transfer characteristics). Measurement elements were set at 18 locations within the substrate surface. The case where the value changed by one digit or more between the element with the maximum on-current and the element with the minimum on-current was evaluated as x, and the others were evaluated as ◯. In addition, current-voltage characteristics were evaluated between the source electrode, the oxide semiconductor, and the drain electrode in a state in which no gate voltage was applied. When the current-voltage characteristic curve was linear, it was evaluated as ◯, and when it was non-linear, it was evaluated as ×. The resulting current-voltage characteristic curve is shown in FIG. In addition, in FIG. 16, "E" means "power of 10". That is, "10E-6" means "10 ^-6 ". The same applies to FIG. 17 as well.

(Comparative example 1)
A field effect transistor was fabricated in the same manner as in Example 1, except that Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). In addition, the transistor performance was evaluated in the same manner as in Example 1. The resulting current-voltage characteristic curve is shown in FIG.

(Example 2)
<Fabrication of Bottom Gate/Bottom Contact Type Field Effect Transistor>
-Formation of gate electrode-
An Al alloy film was formed on a glass substrate using a sputtering method. A gate electrode was patterned into a desired shape by photolithography and etching.

-Formation of gate insulating layer-
Next, a gate insulating layer was formed by depositing SiO ₂ to a thickness of 200 nm by plasma CVD.

-Formation of source and drain electrodes (SD electrodes)-
Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was vapor-deposited on the formed active layer by a vacuum vapor deposition method. Then, by photolithography and etching, a source electrode and a drain electrode with desired shapes were formed.

-Formation of active layer-
An Mg—In based oxide semiconductor film (active layer) was formed by sputtering on the formed gate insulating layer and source/drain electrodes by the method described in the example of Japanese Patent Application Laid-Open No. 2010-74148. A polycrystalline sintered body having a composition of In ₂ MgO ₄ was used as the target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. The total pressure was set to 0.3 Pa by adjusting the flow rates of the argon gas and the oxygen gas during sputtering. The thickness of the obtained oxide semiconductor film (active layer) was 50 nm.

As described above, a bottom-gate/bottom-contact field effect transistor was manufactured.

<Transistor performance evaluation>
Regarding the obtained field effect transistor, it was confirmed whether or not the source/drain electrodes were peeled off. The case where there was no peeling was evaluated as ◯, the case where there was partial peeling was evaluated as Δ, and the case where there were many peeled portions was evaluated as ×. Also, the transistor performance was evaluated using a semiconductor parameter analyzer (Semiconductor parameter analyzer B1500A manufactured by Agilent Technologies). The source/drain voltage Vds was set to 10 V, and the gate voltage was changed from Vg=-15 V to +15 V to evaluate current-voltage characteristics (transfer characteristics). Measurement elements were set at 18 locations within the substrate surface. The case where the value changed by one digit or more between the element with the maximum on-current and the element with the minimum on-current was evaluated as x, and the others were evaluated as ◯. In addition, current-voltage characteristics were evaluated between the source electrode, the oxide semiconductor, and the drain electrode in a state in which no gate voltage was applied. When the current-voltage characteristic curve was linear, it was evaluated as ◯, and when it was non-linear, it was evaluated as ×.

(Comparative example 2)
In Example 2, in the same manner as in Example 2, except that Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd., Au92.6 wt%, Ge7.4 wt%) was changed to Au (manufactured by Tanaka Kikinzoku Co., Ltd.) A field effect transistor was fabricated. Also, the transistor performance was evaluated in the same manner as in Example 2.

(Example 3)
<Fabrication of Top Gate/Top Contact Type Field Effect Transistor>
-Formation of active layer-
A Mg—In-based oxide semiconductor film (active layer) was formed on a glass substrate by a method described in an example of Japanese Patent Application Laid-Open No. 2010-74148 by sputtering. A polycrystalline sintered body having a composition of In ₂ MgO ₄ was used as the target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. The total pressure was set to 0.3 Pa by adjusting the flow rates of the argon gas and the oxygen gas during sputtering. The thickness of the obtained oxide semiconductor film (active layer) was 50 nm.

-Formation of source and drain electrodes-
On the formed active layer, using a vacuum deposition method and a shadow mask, Au—Ge 7.4 (manufactured by Tanaka Kikinzoku Co., Ltd., Au 92.6% by weight, Ge 7.4% by weight) was vapor-deposited to form a source electrode and a drain electrode. formed.

-Formation of gate insulating layer-
Next, a gate insulating layer was formed by depositing SiO ₂ to a thickness of 200 nm by plasma CVD.

-Formation of gate electrode-
An Al alloy film was formed on the gate insulating layer using a sputtering method. A gate electrode was patterned into a desired shape by photolithography and etching.

As described above, a top-gate/top-contact field effect transistor was fabricated.

<Transistor performance evaluation>
Regarding the obtained field effect transistor, it was confirmed whether or not the source/drain electrodes were peeled off. The case where there was no peeling was evaluated as ◯, the case where there was partial peeling was evaluated as Δ, and the case where there were many peeled portions was evaluated as ×. Also, the transistor performance was evaluated using a semiconductor parameter analyzer (Semiconductor parameter analyzer B1500A manufactured by Agilent Technologies). The source/drain voltage Vds was set to 10 V, and the gate voltage was changed from Vg=-15 V to +15 V to evaluate current-voltage characteristics (transfer characteristics). Measurement elements were set at 18 locations within the substrate surface. The case where the value changed by one digit or more between the element with the maximum on-current and the element with the minimum on-current was evaluated as x, and the others were evaluated as ◯. In addition, current-voltage characteristics were evaluated between the source electrode, the oxide semiconductor, and the drain electrode in a state in which no gate voltage was applied. When the current-voltage characteristic curve was linear, it was evaluated as ◯, and when it was non-linear, it was evaluated as ×.

(Comparative Example 3)
A field effect transistor was fabricated in the same manner as in Example 1, except that in Example 3, Au—Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). Also, the transistor performance was evaluated in the same manner as in Example 3.

(Example 4)
<Fabrication of top gate/bottom contact type field effect transistor>
-Formation of source and drain electrodes-
Au--Ge 7.4 (manufactured by Tanaka Kikinzoku Co., Ltd., Au 92.6% by weight, Ge 7.4% by weight) was vapor-deposited on the glass substrate by a vacuum vapor deposition method. Then, by photolithography and etching, a source electrode and a drain electrode with desired shapes were formed.

-Formation of active layer-
A Mg—In-based oxide semiconductor film (active layer) was formed on the formed source/drain electrodes and glass substrate by a method described in an example of Japanese Patent Application Laid-Open No. 2010-74148 by sputtering. A polycrystalline sintered body having a composition of In ₂ MgO ₄ was used as the target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. The total pressure was set to 0.3 Pa by adjusting the flow rates of the argon gas and the oxygen gas during sputtering. The thickness of the obtained oxide semiconductor film (active layer) was 50 nm.

-Formation of gate insulating layer-
Next, a gate insulating layer was formed by depositing SiO ₂ to a thickness of 200 nm by plasma CVD.

-Formation of gate electrode-
An Al alloy film was formed on the gate insulating layer using a sputtering method. A gate electrode was patterned into a desired shape by photolithography and etching.

As described above, a top-gate/bottom-contact field effect transistor was fabricated.

<Transistor performance evaluation>
Regarding the obtained field effect transistor, it was confirmed whether or not the source/drain electrodes were peeled off. The case where there was no peeling was evaluated as ◯, the case where there was partial peeling was evaluated as Δ, and the case where there were many peeled portions was evaluated as ×. Also, the transistor performance was evaluated using a semiconductor parameter analyzer (Semiconductor parameter analyzer B1500A manufactured by Agilent Technologies). The source/drain voltage Vds was set to 10 V, and the gate voltage was changed from Vg=-15 V to +15 V to evaluate current-voltage characteristics (transfer characteristics). Measurement elements were set at 18 locations within the substrate surface. The case where the value changed by one digit or more between the element with the maximum on-current and the element with the minimum on-current was evaluated as x, and the others were evaluated as ◯. In addition, current-voltage characteristics were evaluated between the source electrode, the oxide semiconductor, and the drain electrode in a state in which no gate voltage was applied. When the current-voltage characteristic curve was linear, it was evaluated as ◯, and when it was non-linear, it was evaluated as ×.

(Comparative Example 4)
A field effect transistor was fabricated in the same manner as in Example 1, except that in Example 4, Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). Also, the transistor performance was evaluated in the same manner as in Example 4.

(Example 5)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
In Example 1, except that Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was changed to Au-Ge12.5 (manufactured by Tanaka Kikinzoku Co., Ltd., Au87.5% by weight, Ge12.5% by weight). A field effect transistor was fabricated in the same manner as in the above. In addition, the transistor performance was evaluated in the same manner as in Example 1.

(Examples 6-8)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
A bottom-gate/top-contact field-effect transistor was fabricated in the same manner as in Example 1, except that "formation of active layer" was changed to the following method. Moreover, the same evaluation as in Example 1 was performed.

<Example 6>
-Formation of active layer-
--Preparation of coating solution 1 for forming n-type oxide semiconductor film--
In a beaker, weigh 3.55 g of indium nitrate (In(NO ₃ ) _{3.3H 2} O) and 0.139 g of strontium chloride (SrCl 2.6H ₂ O), add ₂₀ mL of 1,2-propanediol and ethylene glycol. 20 mL of monomethyl ether was added and mixed and dissolved at room temperature to prepare a coating liquid 1 for forming an n-type oxide semiconductor film used in Example 6.

The coating liquid 1 for forming an n-type oxide semiconductor film was applied onto the formed gate insulating layer in a predetermined pattern using an inkjet device. After the substrate was dried on a hot plate heated to 120° C. for 10 minutes, it was baked at 400° C. for 1 hour in an air atmosphere to form an In—Sr oxide film as an active layer.

<Example 7>
-Formation of active layer-
--Preparation of coating liquid 2 for forming n-type oxide semiconductor film)--
Similarly, 3.55 g of indium nitrate (In(NO ₃ ) _{3.3H 2} O) and 0.125 g of calcium nitrate (Ca(NO ₃ ) _{2.4H 2 O} ) were weighed into a beaker. - 20 mL of propanediol and 20 mL of ethylene glycol monomethyl ether were added and mixed and dissolved at room temperature to prepare coating liquid 2 for forming an n-type oxide semiconductor film used in Example 7.

The coating liquid 2 for forming an n-type oxide semiconductor film was applied onto the formed gate insulating layer in a predetermined pattern using an inkjet device. The substrate was dried on a hot plate heated to 120° C. for 10 minutes and then baked at 400° C. for 1 hour in an air atmosphere to form an In—Ca oxide film as an active layer.

<Example 8>
-Formation of active layer-
--Preparation of coating solution 3 for forming n-type oxide semiconductor film--
Similarly, 3.55 g of indium nitrate (In(NO ₃ ) _{3.3H 2} O) and 0.125 g of barium chloride (BaCl 2.2H ₂ O) were weighed into a beaker, and ₂₀ mL of 1,2-ethanediol was added. and 20 mL of ethylene glycol monomethyl ether were added and mixed and dissolved at room temperature to prepare a coating liquid 3 for forming an n-type oxide semiconductor film used in Example 8.

The coating liquid 3 for forming the n-type oxide semiconductor film was applied on the formed gate insulating layer in a predetermined pattern using an inkjet device. After the substrate was dried on a hot plate heated to 120° C. for 10 minutes, it was baked at 400° C. for 1 hour in an air atmosphere to form an In—Ba oxide film as an active layer.

The table shows the composition of the coating solution for forming the n-type oxide semiconductor film.

(Comparative Examples 5-7)
Field effect transistors were fabricated in the same manner as in Examples 6 to 8, except that in Examples 6 to 8, Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). In addition, transistor performance was evaluated in the same manner as in Examples 6-8.

(Example 9)
A bottom-gate/top-contact field-effect transistor was fabricated in the same manner as in Example 1, except that "formation of active layer" was changed to the following method. Moreover, the same evaluation as in Example 1 was performed.

-Formation of active layer-
A Zn—Sn-based oxide thin film was formed on the formed gate insulating layer using high-frequency sputtering. Here, a polycrystalline sintered body (size: 4 inches in diameter) having a composition of Zn ₂ SnO ₄ was used as a target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. By adjusting the flow rates of argon gas and oxygen gas that flow during sputtering, the amount of oxygen in the oxide semiconductor film can be controlled, and the electron carrier concentration can be controlled. The total pressure was 0.3 Pa. During sputtering, the temperature of the substrate was controlled within the range of 15° C. to 35° C. by cooling the holder holding the substrate with water. A Zn—Sn oxide film having a thickness of 50 nm was formed with a sputtering power of 150 W and a sputtering time of 20 minutes.

(Comparative Example 8)
A field effect transistor was fabricated in the same manner as in Example 9, except that Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). Also, the transistor performance was evaluated in the same manner as in Example 9.

(Example 10)
A bottom-gate/top-contact field-effect transistor was fabricated in the same manner as in Example 1, except that "formation of active layer" was changed to the following method. Moreover, the same evaluation as in Example 1 was performed.

-Formation of active layer-
A Zn--Ti oxide thin film was formed on the formed insulating layer by using high-frequency sputtering. Here, a polycrystalline sintered body (size: 4 inches in diameter) having a composition of Zn ₂ TiO ₄ was used as a target. The ultimate vacuum in the sputtering chamber was set to 2×10 ⁻⁵ Pa. By adjusting the flow rates of argon gas and oxygen gas that flow during sputtering, the amount of oxygen in the oxide semiconductor film can be controlled, and the electron carrier concentration can be controlled. The total pressure was 0.3 Pa. During sputtering, the temperature of the substrate was controlled within the range of 15° C. to 35° C. by cooling the holder holding the substrate with water. A Zn—Ti oxide film having a thickness of 50 nm was formed with a sputtering power of 140 W and a sputtering time of 25 minutes.

(Comparative Example 9)
A field effect transistor was fabricated in the same manner as in Example 10, except that Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). Further, the transistor performance was evaluated in the same manner as in Example 10.

(Example 11)
A bottom-gate/top-contact field-effect transistor was fabricated in the same manner as in Example 1, except that "formation of active layer" was changed to the following method. Moreover, the same evaluation as in Example 1 was performed.

-Formation of active layer-
An InLaWO film was formed on the formed insulating layer using an RF magnetron sputtering method. Here, an oxide sintered body having a composition ratio of In:La:W=99.5:5:0.5 was used as the target. Argon gas and oxygen gas were introduced as sputtering gases. The total pressure was fixed at 1.1 Pa and the oxygen concentration was 20% by volume. The resulting InLaWO film had a thickness of 50 nm.

(Comparative Example 10)
A field effect transistor was fabricated in the same manner as in Example 11, except that Au--Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was replaced with Au (manufactured by Tanaka Kikinzoku Co., Ltd.). Also, the transistor performance was evaluated in the same manner as in Example 11.

(Example 12)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
In Example 1, except that Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was changed to Au-Ge3.0 (manufactured by Tanaka Kikinzoku Co., Ltd., Au97.0 wt%, Ge3.0 wt%) A field effect transistor was fabricated in the same manner as in the above. In addition, the transistor performance was evaluated in the same manner as in Example 1.

(Example 13)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
In Example 1, except that Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was changed to Au-Zn5.0 (manufactured by Yamamoto Kikinzoku Co., Ltd., Au95.0 wt%, Zn5.0 wt%) A field effect transistor was fabricated in the same manner as in Example 1. In addition, the transistor performance was evaluated in the same manner as in Example 1.

(Example 14)
<Fabrication of Bottom Gate/Top Contact Type Field Effect Transistor>
Field effect was measured in the same manner as in Example 1 except that Au-Ge7.4 (manufactured by Tanaka Kikinzoku Co., Ltd.) was changed to Au-Sn (manufactured by Furuuchi Chemical Co., Ltd., Au80% by weight, Sn20% by weight). type transistor was fabricated. In addition, the transistor performance was evaluated in the same manner as in Example 1.

The evaluation results of Examples 1 to 14 are shown in Table 2-1.
Evaluation results of Comparative Examples 1 to 10 are shown in Table 2-2.

<Effect of invention>
For Examples 1 to 14, it was confirmed that there was no film peeling on the source/drain electrodes.
On the other hand, in Comparative Examples 1 to 10, film peeling of the source/drain electrodes occurred in some of the transistors during the manufacturing process. In Examples 1 to 14, the inclusion of Ge, Zn, or Sn in the source/drain electrodes is thought to improve the adhesion to the underlying film and prevent film peeling.

As a result of evaluating the transistor operating characteristics of Examples 1 to 14, it was confirmed that variations in on-current were small. Also, it was confirmed that the shape of the current-voltage characteristic curve between the source electrode/oxide semiconductor/drain electrode is linear.
On the other hand, in Comparative Examples 1 to 10, it was found that there were elements that operated as transistors and obtained a high on-current, but that variations were large. It was also found that the shape of the current-voltage characteristic curve between the source electrode/oxide semiconductor/drain electrode is nonlinear.
In Examples 1 to 14, since the source/drain electrodes contain Ge, Zn, or Sn, the work function of the electrodes is shallow, the electrical connection with the oxide semiconductor is good, and the on-current variation is small. This is thought to contribute to the reduction of

That is, according to the present invention, it is possible to provide a field effect transistor that can be easily manufactured, has good contact between the source electrode and the drain electrode and the oxide semiconductor, and has little variation in characteristics.

Aspects of the present invention are, for example, as follows.
<1> a source electrode and a drain electrode;
an active layer made of an oxide semiconductor;
A field effect transistor comprising
the source electrode and the drain electrode contain a gold alloy in contact with the oxide semiconductor;
The field effect transistor is characterized in that the gold alloy contains gold as a first element and a second element as at least one of germanium, tin, zinc and indium.
<2> The field effect transistor according to <1>, wherein the content of the second element in the gold alloy is 3% by weight or more and 30% by weight or less.
<3> The field effect transistor according to any one of <1> to <2>, wherein the oxide semiconductor contains at least one of indium, zinc, tin, gallium, and titanium.
<4> The field effect transistor according to any one of <1> to <3>, wherein the oxide semiconductor contains an alkaline earth element.
<5> The field effect transistor according to any one of <1> to <4>, wherein the oxide semiconductor contains a rare earth element.
<6> a light control element whose light output is controlled according to a drive signal;
a drive circuit that includes the field effect transistor according to any one of <1> to <5> and drives the light control element;
A display element comprising:
<7> The display element according to <6>, wherein the light control element includes either an electroluminescence element or an electrochromic element.
<8> The display element according to <6>, wherein the light control element includes either a liquid crystal element or an electrophoretic element.
<9> An image display device for displaying an image corresponding to image data,
a plurality of display elements according to any one of <6> to <8> arranged in a matrix;
a plurality of wirings for individually applying a gate voltage to each field effect transistor in the plurality of display elements;
a display control device that individually controls gate voltages of the field effect transistors through the plurality of wirings according to the image data;
An image display device comprising:
<10> The image display device according to <9>;
an image data creation device that creates image data based on image information to be displayed and outputs the image data to the image display device;
A system characterized by comprising

The field effect transistor according to <1> to <5>, the display device according to <6> to <8>, the image display device according to <9>, and the system according to <10> can achieve the object of the present invention.

Reference Signs List 1 base material 2 gate electrode 3 gate insulating layer 4 source electrode 5 drain electrode 6 active layer 10 field effect transistor 20 field effect transistor 21 base material 22 active layer 23 source electrode 24 drain electrode 25 gate insulating layer 26 gate electrode 30 capacitor 40 field effect transistor 100 television device 101 main controller 103 tuner 104 AD converter (ADC)
105 demodulation circuit 106 TS (Transport Stream) decoder 111 audio decoder 112 DA converter (DAC)
113 audio output circuit 114 speaker 121 video decoder 122 video/OSD synthesizing circuit 123 video output circuit 124 image display device 125 OSD drawing circuit 131 memory 132 operating device 141 drive interface (drive IF)
142 hard disk device 143 optical disk device 151 IR receiver 152 communication control device 210 antenna 220 remote control transmitter 300 display device 302, 302' display element 310 display 312 cathode 314 anode 320, 320' drive circuit (driving circuit)
340 organic EL thin film layer 342 electron transport layer 344 light emitting layer 346 hole transport layer 350 organic EL element 360 interlayer insulating film 361 capacitor 370 liquid crystal element 400 display control device 402 image data processing circuit 404 scanning line driving circuit 406 data line driving circuit

JP 2011-129938 A JP 2011-228622 A

Claims (10)

a source electrode and a drain electrode;
an active layer made of an oxide semiconductor;
A field effect transistor comprising
the source electrode and the drain electrode contain a gold alloy in contact with the oxide semiconductor;
The gold alloy contains a first element of gold and a second element of at least one of germanium, tin, zinc, and indium,
A field effect transistor , wherein the content of the second element in the gold alloy is 3% by weight or more and 20% by weight or less . a source electrode and a drain electrode;
an active layer made of an oxide semiconductor;
A field effect transistor comprising
the source electrode and the drain electrode contain a gold alloy in contact with the oxide semiconductor;
A field effect transistor, wherein the gold alloy contains gold and germanium. 3. The field effect transistor according to claim 1, wherein said oxide semiconductor contains at least one of indium, zinc, tin, gallium, and titanium. 4. The field effect transistor according to claim 1, wherein said oxide semiconductor contains an alkaline earth element. 5. The field effect transistor according to claim 1, wherein said oxide semiconductor contains a rare earth element. a light control element whose light output is controlled according to a drive signal;
a drive circuit that includes the field effect transistor according to any one of claims 1 to 5 and drives the light control element;
A display element comprising: 7. The display device according to claim 6, wherein said light control device includes either an electroluminescence device or an electrochromic device. 7. The display element according to claim 6, wherein the light control element includes either a liquid crystal element or an electrophoretic element. An image display device for displaying an image according to image data,
a plurality of display elements according to any one of claims 6 to 8 arranged in a matrix;
a plurality of wirings for individually applying a gate voltage to each field effect transistor in the plurality of display elements;
a display control device that individually controls gate voltages of the field effect transistors through the plurality of wirings according to the image data;
An image display device comprising: an image display device according to claim 9;
an image data creation device that creates image data based on image information to be displayed and outputs the image data to the image display device;
A system characterized by comprising:

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