BRPI0517562B1 - LIGHT-EMITTING DEVICE, ELECTROPHOTOGRAPHIC DEVICE, ACTIVE MATRIX DISPLAY DEVICE, AND, DISPLAY ARTICLE - Google Patents

Abstract

LIGHT-EMITTING DEVICE, ELECTROPHOTOGRAPHIC DEVICE, ACTIVE MATRIX DISPLAY DEVICE, AND, DISPLAY ARTICLE. An object of the present invention is to provide a novel light-emitting device using an amorphous oxide. The light-emitting device has a light-emitting layer (78) that exists between the first and second electrodes (77, 79) and a field-effect transistor, of which the active layer (72) is an amorphous oxide.

Description

TECHNICAL FIELD

[0001] The present invention relates to a light-emitting device that uses an oxide and, particularly, that uses an organic EL element and an inorganic EL element. The light-emitting device according to the present invention also concerns a top-emitting type or a bottom-emitting type.

BASICS OF THE INVENTION

[0002] In recent years, flat panel monitor (MTP) has been in practical use as a result of the progress of technologies related to liquid crystal, electroluminescence (EL). The MTP is driven by an active matrix circuit comprising a field-effect thin-film transistor (TFT) that uses an amorphous silicon thin film or polycrystalline silicon thin film provided on a glass substrate as the active layer.

[0003] On the other hand, an attempt was made to use a light and flexible resin substrate in place of the glass substrate, in search of further improvement in reducing thickness, decreasing weight and increasing the rupture resistance of an MTP. However, because a thermal process at a relatively high temperature is required to manufacture the transistor using the above-described silicon thin film, it is difficult to form the silicon thin film on a resin substrate with a low thermal resistance.

[0004] For this reason, a TFT using an oxide semiconductor thin film basically containing ZnO, for example, which can be formed into a film at a low temperature, has been actively developed (open Japanese patent application 2003-298062 ).

[0005] However, the TFT using a conventional oxide semiconductor thin film does not reach a technical level of development of the applied technology, probably due to not having reached sufficient characteristics, such as in a TFT using silicon.

DISCLOSURE OF THE INVENTION

[0006] An object of the present invention is to provide a novel light-emitting device, an electronography apparatus and a display unit that employ a transistor that uses an oxide as an active layer.

[0007] According to one aspect of the present invention, there is provided a light-emitting device having a light-emitting element comprising first and second electrodes and a light-emitting layer existing between the first and second electrodes, and a transistor field-effect transistor to activate the light-emitting element, wherein the active layer of the field-effect transistor is formed from an amorphous oxide that has an electron carrier concentration of less than 1018/cm3.

[0008] The amorphous oxide preferably includes at least one of In, Zn and Sn.

[0009] Alternatively, the amorphous oxide is preferably any one selected from the group consisting of an oxide containing In, Zn and Sn; an oxide that contains In and Zn; an oxide that contains In and Sn; and an oxide that contains In.

[00010] Alternatively, the amorphous oxide preferably includes In, Zn and Ga.

[00011] The light-emitting element and the field-effect transistor are preferably arranged on an optically transparent substrate, and the light emitted by the light-emitting layer passes through the substrate. The field effect transistor is preferably arranged between the substrate and the light-emitting layer.

[00012] Alternatively, the light-emitting element and the field-effect transistor are preferably arranged on an optically transparent substrate, and the light emitted by the light-emitting layer passes through the substrate and the amorphous oxide. The field effect transistor is preferably arranged between the substrate and the light-emitting layer.

[00013] In the light-emitting device, at least one of the drain electrode of the field effect transistor and the second electrode is preferably formed from an optically transparent electroconductive oxide.

[00014] The light-emitting element is preferably an electroluminescent element.

[00015] In the light-emitting device, preferably a plurality of light-emitting elements arranged at least in a single row. The light-emitting element is preferably arranged to be adjacent to the field effect transistor.

[00016] According to another aspect of the present invention, an electrophotographic device is provided that has:

[00017] a photoreceptor,

[00018] an electrifier for electrifying the photoreceptor,

[00019] an exposure light source to expose the photoreceptor to form a latent image on the photoreceptor, and

[00020] a developing unit for developing the latent image, wherein the exposure light source has the light-emitting device.

[00021] According to yet another aspect of the present invention, there is provided a light-emitting device that has a light-emitting element comprising first and second electrodes and a light-emitting layer that exists between the first and second electrodes, and a field-effect transistor to activate the light-emitting element, wherein the electron mobility of an active layer of the field-effect transistor tends to increase with increasing electron carrier concentration.

[00022] According to a further aspect of the present invention, a light-emitting device having a light-emitting element comprising first and second electrodes and a light-emitting layer existing between the first and second electrodes, and a transistor field effect to activate the light-emitting element, wherein the active layer of the field effect transistor includes a transparent amorphous oxide semiconductor capable of realizing a normally off state. The transparent amorphous oxide semiconductor preferably has an electron carrier concentration of less than 1018/cm3, which is low enough to realize the normally off state.

[00023] According to a further aspect of the present invention, an active matrix display device comprising a light-emitting element comprising first and second electrodes and a light-emitting layer existing between the first and second electrodes and a transistor field-effect transistor to activate the light-emitting element, and an imaging element circuit arranged in the form of a two-dimensional array, wherein the active layer of the field-effect transistor includes such a transparent amorphous oxide semiconductor capable of performing a normally off state. The transparent amorphous oxide semiconductor has an electron carrier concentration of less than 1018/cm3, which is low enough to realize the normally off state.

[00024] According to a further aspect of the present invention, a display article is provided comprising:

[00025] a light-emitting element comprising first and second electrodes and a light-emitting layer existing between the first and second electrodes and a field-effect transistor for activating the light-emitting element, wherein

[00026] an active layer of the field effect transistor includes an amorphous oxide semiconductor.

[00027] The amorphous oxide is preferably any selected from the group consisting of oxides containing In, Zn and Sn; an oxide that contains In and Zn; an oxide that contains In and Sn; and an oxide that contains In.

[00028] Alternatively, the transistor is preferably a normally-off type transistor.

[00029] The present invention can provide a novel light-emitting device, electronography apparatus and active matrix display unit.

[00030] As a result of having studied a ZnO semiconductor oxide, the present inventors observed that a general process cannot form a stable amorphous phase. Furthermore, it appeared that most of the generally produced ZnO presents a polycrystalline phase, scatters the carriers at the interfaces of the polycrystalline grains and consequently cannot increase electron mobility. Furthermore, ZnO tends to form oxygen defects and, consequently, produces many carrier electrons, and has difficulty decreasing electrical conductivity. For this reason, it was observed that a TFT using a ZnO semiconductor allows a lot of current to pass between a source terminal and a drain terminal, even when a transistor gate voltage is not applied, and cannot perform an operation. normally turned off. It also appears that the TFT using the ZnO semiconductor presents difficulties in increasing the on/off ratio.

[00031] Furthermore, an amorphous oxide film ZnxMyInzO(x+3y/2+3z/2) (where M is at least one element of Al and Ga) was studied, described in the open Japanese patent application 2000- 044236. The material has an electron carrier concentration of 1x1018/cm3 or more and is therefore suitable for use simply as a transparent electrode. However, it has been noted that the material is not suitable for a normally disconnected type of a TFT, because when the TFT employs an oxide with an electron carrier concentration of 1x1018/cm3 or more for its channel layer, the TFT cannot provide a sufficient on/off ratio.

[00032] In other words, a conventional amorphous oxide film cannot obtain an electron carrier concentration lower than 1x1018/cm3.

[00033] The properties of InGaO3(ZnO)m and the film formation condition for the material were intensively researched and, as a result of this, it was observed that the electron carrier concentration can be reduced to less than 1x1018/cm3 by controlling the condition oxygen atmosphere during film formation.

[00034] Consequently, it was observed that a TFT prepared using an amorphous oxide containing electron carriers with a concentration less than 1x1018/cm3 as an active layer of a field effect transistor can exhibit desired characteristics, and can be applied to a monitor flat panel, such as a light-emitting device.

[00035] As for an electronography apparatus provided with a linear array light source and a photoreceptor using a light-emitting device in accordance with the present invention, there are a copying machine, a page printer and an integral drum cartridge .

BRIEF DESCRIPTION OF THE DRAWINGS

[00036] Figure 1 is a diagrammatic drawing that shows a relationship between the electron carrier concentration in an In-Ga-Zn-O based power supply formed with a pulsed laser vapor deposition method and a pressure partial oxygen while the film is being formed;

[00037] Figure 2 is a diagrammatic drawing that shows a relationship between the number of electron carriers and electron mobility in an amorphous film based on In-Ga-Zn-O formed with a laser vapor deposition method. pulsed;

[00038] Figure 3 is a diagrammatic drawing that shows a relationship between the electrical conductivity in an amorphous film based on In-Ga-Zn-O formed with a sputtering method using an argon gas and a partial pressure of oxygen while the film is being formed;

[00039] Figures 4A, 4B and 4C are diagrammatic drawings showing changes in electrical conductivity, carrier concentration and electron mobility with respect to a value of x of the InGaZn1-xMgxO4 film formed with a vapor deposition method with pulsed laser in an atmosphere with an oxygen partial pressure of 0.8 Pa;

[00040] Figure 5 is a schematic block diagram showing the structure of a top gate MISFET element prepared in embodiment 1;

[00041] Figure 6 is a diagrammatic drawing showing current-voltage characteristics of a top gate type MISFET element prepared in embodiment 1;

[00042] Figure 7 is a schematic block diagram showing a cross section of a light-emitting device in accordance with the present invention;

[00043] Figure 8 is a circuit diagram when a light-emitting device in accordance with the present invention is used for a monitor;

[00044] Figure 9 is a diagrammatic drawing showing a cross section of a light-emitting device according to the present invention;

[00045] Figure 10 is a diagrammatic drawing that describes the electrical connection of a light source with a linear arrangement according to the present invention;

[00046] Figure 11 is a sectional view depicting an example configuration of a linear array light source in accordance with the present invention;

[00047] Figure 12 is a sectional view (arrangement just above) that describes an example configuration of a linear array light source in accordance with the present invention;

[00048] Figure 13 is a diagrammatic drawing showing an exemplary arrangement of a copying machine, a page printer, a photoconductive drum in an integral drum cartridge and a linear array light source;

[00049] Figure 14 is a schematic block diagram showing a pulsed laser vapor deposition apparatus; It is

[00050] Figure 15 is a schematic block diagram showing a sputtering film forming apparatus.

BEST WAY TO CARRY OUT THE INVENTION

[00051] A basic configuration according to the present invention will now be described with reference to figure 7, which shows the first embodiment.

[00052] In the drawing, the numeric character 70 denotes a drain electrode, the numeric character 71 a substrate, the numeric character 72 active layer, the numeric character 73 a gate insulating film, numeric character 74 a gate electrode, numeric character 75 a source electrode, numeric character 77 a second electrode, numeric character 78 a light-emitting layer, and numeric character 79 a first electrode. In the first embodiment, the second electrode (hereinafter referred to as "bottom electrode") is arranged closer to a substrate than a light-emitting layer, the light-emitting layer is an organic EL layer, and the first electrode (hereinafter referred to as "counter electrode") is arranged further from the substrate than the light-emitting layer. Gaps between the above-described components are filled with an interlayer insulating layer 76.

[00053] First, each component will be described in detail.

(1. Substrate)

[00054] Glass is generally used for a substrate material in a light-emitting device. However, because the TFT used in the present invention can be formed at a low temperature, a plastic substrate that was difficult to use in an active matrix can be used in the present invention. Thus, a light-emitting device can be provided that is light, difficult to damage and bendable to a certain extent. In fact, a semiconductor substrate such as Si and a ceramic substrate can be used. A substrate that has an insulating layer provided on a metal base sheet can also be used, provided that the substrate is flat.

(2. Transistor)

[00055] An active layer of a transistor can be of any material, as long as it has the desired characteristics, specifically an electron carrier concentration less than 1x1018/cm3 and an electron mobility greater than 1 cm2/v.s. The material includes, for example, an amorphous oxide semiconductor based on In-Ga-Zn-O. Amorphous oxide is a transparent film. Here, the word transparency means not only the case of being substantially transparent at least in a part of the visible light range, but also includes the case of being optically transparent at least in a part of the visible light range. As for optical transparency, the In-Ga-Zn-O based amorphous oxide semiconductor preferably has a transmittance of 50% or more, and more preferably 80% or more. The aforementioned composition may contain substituted or added Mg. When a light-emitting device employs a TFT that uses the In-Ga-Zn-O-based active layer, it presents a functional performance, due to the TFT providing a sufficient activation force of both voltage and current at a organic EL element.

[00056] The amorphous oxide will be described separately in detail.

[00057] A sputtering technique and a pulsed laser vapor deposition method are suitable for forming an active layer, as described previously, but such various sputtering techniques are preferable because they have an advantage in productivity. It is also effective in properly arranging a damping layer between the active layer and the substrate.

[00058] As a door insulating film, any one of Al2O3, Y2O3 and HfO2, or a mixed crystalline component containing at least two or more of their compounds is preferable, but it may be another compound.

[00059] A source electrode and drain electrode used include an electroconductive oxide represented by ITO and a metal such as Au. However, the electrode may preferably be connected ohmically, or nearly ohmically, to an active layer. The drain electrode can also be connected directly to a light-emitting layer without bypassing a second electrode.

(3. Light-emitting layer)

[00060] The light-emitting layer is not limited as long as it can be activated by a TFT, but an organic EL is particularly advantageous. The organic EL layer 78 used in the present invention is rarely used as a single layer, but is generally used in a configuration consisting of a plurality of layers, as shown below. In the following, an "electron transport layer" means a light-emitting layer that has a function of transporting electrons.

[00061] Hole transport layer/light-emitting layer + electron transport layer

[00062] Hole transport layer/light-emitting layer/electron transport layer

[00063] Hole injection layer/hole transport layer/light emitting layer/electron transport layer

[00064] Hole injection layer/hole transport layer/light emitting layer/electron transport layer/electron injection layer

[00065] An electron barrier layer and an adhesion improvement layer are occasionally disposed between a plurality of layers.

[00066] In general, there are two principles, fluorescence and phosphorescence, in a light emission principle from a light-emitting layer, but phosphorescence is effective from the point of view of luminous efficiency. An iridium complex is used as a phosphorescent material. Either a low molecular weight polymer or a high molecular weight polymer can be used as a polymer used in a base metal for the light-emitting layer. When the low molecular weight polymer is employed, the light-emitting layer can generally be formed with a vapor deposition technique and, when the high molecular weight polymer is employed, the light-emitting layer with an inkjet method or a printing process can be formed. For example, low MW (molecular weight) materials include an amine complex, anthracene, a rare earth complex, and a noble metal complex; and high MW materials include a conjugated polymer and a pigmented polymer.

[00067] An electron injection layer includes an alkali metal, an alkaline earth metal and a compound thereof, and an organic layer doped with an alkali metal. Furthermore, an electron transport layer includes a complex of aluminum, oxadiazole, triazole, and fenatroline.

[00068] A hole injection layer includes arylamines, phthalocyanines and an organic layer doped with a Lewis acid; and a hole transport layer includes arylamine.

[00069] By the way, figure 7 shows an example configuration of an organic EL element, but the same configuration can be used for an inorganic EL element.

(4. First electrode)

[00070] A first electrode will be described in case it is a counter electrode. The preferred material for counter electrode varies depending on whether or not it is used in a top emission type or a base emission type, and whether it is used as a cathode or an anode.

[00071] When a counter electrode is used in a top emission type, transparency is required; and, when it is used as an anode, a usable material includes ITO, electroconductive titanium oxide, ZnO and In-Zn-O based oxide and electroconductive In-Ga-Zn-O with an electron carrier concentration of 1x1018 /cm3 or more, which are all transparent electroconductive oxides. When it is used as a cathode, the counter electrode can be made by forming an alloy doped with an alkali metal or an alkaline earth metal into a film several tens of nanometers or less and forming the transparent electroconductive oxide on top. .

[00072] When a bottom emission type is used, transparency is not necessary, and thus, when it is used as an anode, an Au alloy and a Pt alloy are usable for it, and when it is used as an anode cathode, Mg with added Ag, Al with added Li, a silicide, a boride and a nitride can be used.

(5. Second electrode)

[00073] A second electrode is connected to a drain electrode. The second electrode may have the same or different composition as the drain electrode.

[00074] The second electrode may be a lower electrode. The bottom electrode can be made in the form of a layer over a substrate or a light-emitting layer.

[00075] When the light-emitting layer is of the current injection type, represented by an organic EL element, there is a preferred lower electrode according to the configuration.

[00076] When the light-emitting layer connected to a lower electrode is a cathode, the lower electrode preferably is a metal with a small functional role. The bottom electrode includes, for example, Mg with added Ag, Al with added Li, a silicide, a boride and a nitride. In this case, it is more advantageous to be connected to a drain part of a TFT via wiring rather than directly connected to it.

[00077] When a light-emitting layer connected to a lower electrode is the anode, the lower electrode is preferably a metal with a large functional role. The bottom electrode includes, for example, ITO, electroconductive tin oxide, electroconductive ZnO, In-Zn-O, a Pt alloy and an Au alloy. Furthermore, In-Ga-Zn-O based oxide with an electron carrier concentration of 1x1018/cm3 or more can be used. In this case, the higher the carrier concentration, the more preferable as the bottom electrode is the oxide, which is different from the case used for a TFT. For example, carrier concentration of 1x1019/cm3 or more is preferable. When the bottom electrode is made of ITO or In-Ga-Zn-O based oxide (with high carrier concentration), it can provide a high open area ratio, even if it is being employed in a bottom emission type. , by virtue of being transparent. When the bottom electrode is directly connected to a drain electrode, particularly ITO, the above-described In-Ga-Zn-O based oxide (with high carrier concentration) and an Au alloy are particularly preferred for it.

[00078] When the bottom electrode is directly connected to a drain electrode, the bottom electrode is preferably a hole injection type. Particularly preferred materials for the bottom electrode are ITO, ZnO doped with Al or Ga, and In-Ga-Zn-O based oxide with the carrier concentration of 1x1018/cm3 or more. Particularly, when an In-Ga-Zn-O based oxide is employed as an electrode and an active layer, the carrier concentration of a part of an In-Ga-Zn-O active layer can be increased by a technique of introducing an oxygen defect into it, or similar, and the light-emitting device is configured in a simple and effective way. In this case, at a glance, a hole transport layer and a hole injection layer are formed in the active layer. This configuration should be within the scope of the present invention. Specifically, it means the configuration in which the bottom electrode and the drain electrode are integrated with a part of the active layer.

(6. Interlayer insulation layer)

[00079] Particularly, when a second electrode is a bottom electrode, an interlayer insulating layer 76 considered as an underlying layer of the bottom electrode 77 can employ exactly the same material as in a gate insulating film. In fact, the insulating layer with the use of the other material can be formed to obtain a flat layer. For example, a polyimide film can be spin coated, and silicon oxide can be formed with a plasma CVD method, a PECVD method and an LPCVD method, or by coating and lining with silicon alkoxide. The interlayer insulating layer must properly have a contact hole for connection to a source electrode or a drain electrode formed therein.

(7. Electrode wire and others)

[00080] An electrode wire such as a scanning electrode wire and a signal electrode wire which are a gate electrode wire may employ a metal such as Al, Cr and W and silicide such as WSi as the material.

[00081] Next, the relationship between each of the components will be described in detail.

[00082] Firstly, a first embodiment will be described with reference to figure 7, in which a lower electrode is particularly connected to a drain electrode by wiring.

(First modality)

[00083] A source electrode 75 and a drain electrode 70 are directly connected to an active layer 72, and the current passing through the active layer 72 is controlled by a gate electrode 74 through a gate insulating film 73.

[00084] An organic EL layer 78 of a light-emitting layer is connected to a drain electrode 70, through a lower electrode 77 and a wire in a contact hole. An interlayer insulating layer 76 exists between the bottom electrode 77 and a section of the TFT to electrically isolate them. The interlayer insulating layer 76 need not necessarily be a single layer, but generally consists of insulating layers arranged on the gate insulating film and the top of the gate electrode, and the overall interlayer insulating layer for leveling purposes.

[00085] A counter electrode 79 exists on top of the organic EL layer 78, and applies voltage to the organic EL layer 78 to make it emit light when a TFT is turned on.

[00086] Here, a drain electrode 70 is electrically connected to a second electrode, or is the second electrode itself.

[00087] Figure 7 shows an example of a high open area ratio in which there is an organic EL layer 78 even on top of a TFT, but the organic EL layer 78 can be formed elsewhere without being a part of the TFT. , as long as it does not cause problems in the application. However, when the organic EL layer 78 is used in a configuration shown in Figure 7, the bottom of the organic EL layer 78 is preferably as flat as possible.

[00088] Although the drain electrode 70 is connected to the bottom electrode 77 in figure 7, the source electrode 75 is connected to the bottom electrode 77, depending on the manner of use. That is, the present invention is characterized by connecting any of the source electrode and the drain electrode of a transistor containing an amorphous oxide to an electrode, pressing a light-emitting layer. In the case where the lower electrode 77 under the light-emitting layer 78 is an anode, a constitution in which a source electrode of the TFT is connected to the anode is also preferable.

(Regarding the preparation of the light-emitting device)

[00089] Here, a process for manufacturing a light-emitting device in accordance with the present invention will be described, with reference to an example of the configuration in which the drain electrode is connected to a lower electrode by means of wiring, and an EL organic is employed as a light-emitting element.

(Transistor preparation)

[00090] A transistor is prepared by the steps of:

[00091] deposit a thin film of an In-Ga-Zn-O-based amorphous oxide semiconductor on a glass substrate at a thickness of 120 nm with a pulsed laser vapor deposition method, in a condition such as make the electron carrier concentration 1x1018/cm3, which will be described in detail below, while using a polycrystalline sintered compact with the composition of InGaO3(ZnO)4 as a target;

[00092] additionally, layer the InGaO3(ZnO)4 film with high electroconductivity on it at a thickness of 30 nm with the pulsed laser deposition method in a chamber that has an oxygen partial pressure controlled at less than 1 Pa, and forming the Au film thereon in the thickness of 50 nm as a source electrode and a drain electrode with an electron beam vapor deposition method; It is

[00093] additionally form each Y2O3 film as a gate insulating film and Au as a gate electrode in thicknesses of 90 nm and 50 nm, respectively, with the electron beam vapor deposition method. In a series of the above-described processes, each layer is formed to a desired size with a photolithographic method and peeling technology. Furthermore, an insulating layer is formed on them with a similar method. Then, a contact hole for a drain electrode is also formed in it.

(Preparation of the lower electrode layer)

[00094] After that, the bottom electrode is made by forming the ITO film in the thickness of 300 nm with a sputtering technique, and then it is connected to a drain electrode and the bottom electrode through the wiring formed in a contact hole.

(Preparation of organic EL light-emitting layer)

[00095] In the next step, the organic EL light-emitting layer is prepared by forming the following films with a thermal resistance vapor deposition method: the 4,4'-bis{N,N-diamino] film -4"phenyl-triphenyl amine with the thickness of 60 nm with a hole injection layer; 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl film with the thickness of 20 nm as a hole transport layer therein; the 40 nm thick 4,4'-bis(2,2-diphenyl)vinyl film as a light-emitting layer; and the tris(8-quinolinol)aluminum film with a thickness of 20 nm as an electron transport layer.

(Counter electrode preparation)

[00096] Finally, a counter electrode is prepared by forming the Al and Ag alloy film at a thickness of 50 nm with a double vapor deposition method, and the Al film at a thickness of 50 nm.

[00097] When the above-described element is activated by placing a probe in contact with it, blue light is emitted from behind a substrate, in other words, a type of emission beneath the element is obtained.

[00098] In the present embodiment, it is important that the amorphous oxide semiconductor based on In-Ga-Zn-O acquires the desired electron carrier concentration by controlling the amount of oxygen defect.

[00099] In the description presented, the amount of oxygen (amount of oxygen defect) in a transparent oxide film is controlled by forming a film in an atmosphere with a predetermined concentration of oxygen, but it is also preferable to control (reduce or increase) the amount of oxygen defect by post-treatment of the oxide film formed in the previous step in the oxygen atmosphere.

[000100] In order to effectively control the amount of oxygen defect, the temperature in the oxygen atmosphere is controlled at 0°C or more and 300°C or less, preferably at 25°C or more and 250°C or less, and even more preferably at 100°C or more and 200°C or less.

[000101] In fact, the film can be formed in an oxygen atmosphere and then post-treated in the oxygen atmosphere. Furthermore, the film can be formed in an atmosphere of which the partial pressure of oxygen is not controlled, and be post-treated in the oxygen atmosphere, if the method provides the predetermined electron carrier concentration (less than 1x1018/cm3 ).

[000102] Here, the lower limit of the electron carrier concentration in the present invention depends on what type of element, circuit and device the obtained oxide film is used in, but, for example, it is 1x1014/cm3 or more.

[000103] Next, with reference to figure 9, a second embodiment will be described in which the lower electrode is connected directly to a drain electrode without wiring between them.

(Second modality)

[000104] In figure 9, reference number 91 denotes a substrate, reference number 92 an active layer made of a semiconductor material peculiar to the present invention, reference number 93 a gate insulating film, reference number 94 a gate electrode, reference number 95 a source electrode, reference number 96 an insulating layer, and reference number 97 a bottom electrode. The lower electrode 97 is layered on a drain electrode or is identical to the drain electrode, in other words, it is the drain electrode itself. Reference number 98 denotes an organic EL layer, and reference number 99 a counter electrode.

[000105] The present embodiment has basically the same type of configuration as the first embodiment in which a portion of a lower electrode makes contact with a drain electrode through wiring, but has a different configuration in which the drain electrode and the layer emitting light are arranged in layers in the same overlapping area, viewed from the position above the substrate 91, and the lower electrode exists between them.

[000106] The drain electrode can be the same element as the bottom electrode. In this case, the drain electrode needs to have a capability to effectively inject an electron or a hole into an organic EL layer.

[000107] It is preferable to control the electron carrier density in a part of an active layer corresponding to a lower part of a drain electrode at 1x1018/cm3 or more by increasing oxygen defects. So, it can function as the drain electrode and a bottom electrode at the same time. In this case, it is preferable that the active layer is made of an In-Ga-Zn-O film, which functions as a hole injection layer and is connected to an anode part of a light-emitting layer.

[000108] Figure 9 shows an example of a light-emitting layer arranged on the top of a TFT layer, but a configuration is acceptable in which a counter electrode of a first electrode and a bottom electrode of a second electrode are turned towards each other. low, and the first electrode is directly layered on a drain electrode, if it does not cause a functional problem. In this case, the second electrode which was the bottom electrode exists similarly on the top, but is functionally the same as long as it is connected to the drain electrode. Particularly, when an inorganic EL layer is used, the opposite case can be adopted, due to it having greater resistance to processing than an organic EL layer.

[000109] In a preferred configuration of a light-emitting device according to the present invention, first and second electrodes are a counter electrode and a bottom electrode, a field effect transistor is a TFT, an active layer of the TFT includes In , Ga and Zn, at least a part of the active layer is an amorphous oxide, and a part of a light-emitting layer is electrically connected to a drain electrode of the TFT.

[000110] In a light-emitting device according to the present invention, a part of the light-emitting layer is directly connected to a drain electrode, or a part of the light-emitting layer can be connected to the drain electrode by wiring. It is preferred that a part of the light-emitting layer so connected is an anode side or a cathode side of the light-emitting layer.

[000111] It is preferable that at least one of the drain electrode and the bottom electrode described above is a transparent electroconductive oxide.

[000112] Next, a third modality will be described which is an example of configuring the application to a monitor with reference to figure 8.

[000113] Although the drain electrode 97 is used as the bottom electrode in figure 9, the source electrode 95 can be used as the bottom electrode, depending on the constitution of the layer structure of the light-emitting layer. That is, the present invention is characterized by connecting any of the source electrode and the drain electrode of a transistor containing an amorphous oxide to an electrode pressing a light-emitting layer.

(Third modality)

[000114] In figure 8, reference number 81 denotes a transistor for activating an organic EL layer 84, which passes a current to a light-emitting element having the organic EL layer 84 and a pair of electrodes that press the EL layer organic 84. Reference number 82 is a transistor 2 for selecting an imaging element, which supplies an imaging signal for determining a current to pass to the light-emitting element, at a gate of the transistor 81.

[000115] Furthermore, a capacitor 83 is placed in order to maintain a selected condition, store electrical charges between a common electrode wire 87 and a source electrode part of the transistor 2, and retain the gate signal of the transistor 1 The imaging element is selected and determined by a scanning electrode wire 85 and a signal electrode wire 86.

[000116] The configuration will now be described more specifically.

[000117] At the same time as a row selection signal is applied to a gate electrode by a driven circuit (not shown) through a scanning electrode 85 in the form of a pulse signal, the image signal is applied to a transistor 82 by another circuit driven (not shown) through a signal electrode 86 to select an image element.

[000118] At this time, the transistor 82 is turned on and the electrical charge is stored in a capacitor 83 placed between the signal electrode wire 86 and the source electrode of the transistor 82. Thus, a gate voltage of the transistor 81 is maintained at a desired voltage corresponding to the image signal, and the transistor 81 passes a current corresponding to the image signal between the source electrode and a drain electrode. The state is retained until the transistors receive the next signal. Although transistor 81 passes current, current is also continuously supplied to an organic EL layer 84 and light emission is maintained.

[000119] The example in figure 8 shows a configuration using two transistors and a capacitor for an image element, but the configuration can include more transistors in order to improve performance.

[000120] It is essential that a light-emitting device can realize a normally off type of a TFT using a TFT that has an active layer of an amorphous oxide illustrated by the In-Ga-Zn-O based oxide that is transparent and that can be formed at a low temperature in accordance with the present invention, in a part of the transistor, and consequently inhibits unnecessary light emission. Said TFT can also provide an electronography apparatus and a high contrast display unit.

(Fourth modality)

[000121] A fourth embodiment according to the present invention is a type of emission from below a light-emitting device shown in figures 11 and 12.

[000122] Specifically, the light-emitting device has the above-described light-emitting layer and the above-described field-effect transistor arranged on an optically transparent substrate, and emits light by the above-described light-emitting layer through the above-described substrate. In Figure 11, an active layer (channel layer 2101) formed from an amorphous oxide is also arranged just below a light-emitting element 2160, but does not need to be arranged just below it. In fact, in a configuration of Figure 11, light emitted by the light-emitting layer 2108 passes through the active layer formed from the amorphous oxide described above and the substrate 2100.

[000123] By the way, a light source can be produced by arranging a light-emitting device according to the present invention in one dimension, and can make an apparatus by combining it with a photoconductive drum 2350 of a photoreceptor shown in the figure 13. Specifically, an electronography apparatus may be comprised of photoreceptor 2350, an electrifier (not shown) for electrifying the photoreceptor, an exposure light source 2300 for illuminating the photoreceptor with light 2101 to form a latent image on the photoreceptor, and a developing unit (not shown) for developing the above-described latent image.

[000124] An amorphous oxide described in the first and second embodiments described above will be explained below.

(Amorphous oxide)

[000125] The active layer used in the aforementioned embodiments 1 to 3 of the invention is explained below.

[000126] The concentration of electron carriers in the amorphous oxide in the present invention is a value measured at room temperature. Ambient temperature is a temperature in the range of 0°C to about 40°C, for example 25°C. The concentration of electron carriers in the amorphous oxide in the present invention need not be less than 1x1018/cm3 throughout the range from 0 to 40°C. For example, electron carrier concentration less than 1018/cm3 at a temperature of 25°C is acceptable. At a lower electron carrier concentration, no more than 1x1017/cm3, or no more than 1x1016/cm3 of a normally off TFT can be produced in high yield.

[000127] In the present specification, the description "less than 1018/cm3" means "preferably less than 1x1018/cm3 and more preferably less than 1.0x1018/cm3".

[000128] The concentration of electron carriers can be measured by measuring the Hall effect.

[000129] The amorphous oxide in the present invention is an oxide that presents a halo pattern and no characteristic diffraction line in an X-ray diffraction spectrometry.

[000130] In the amorphous oxide of the present invention, the lower limit of the electron carrier concentration is, for example, 1x1012/cm3, but is not so limited, as long as it is applicable as a channel layer of a TFT.

[000131] In this way, in the present invention, the concentration of electron carriers is adjusted by controlling the material, composition ratio, production conditions and so on of the amorphous oxide, as in the examples described later, in a range, for example, from 1x1012/cm3 to 1x1018/cm3, preferably from 1x1013/cm3 to 1x1017/cm3, more preferably from 1x1015/cm3 to 1x1016/cm3.

[000132] The amorphous oxide, in addition to InZnGa oxides, can be appropriately selected from In oxides, InxZni-x oxides (0.2 < x < 1), InxSn1-x oxides (0.8 < x < 1 ) and Inx(Zn, Sn)1-x oxides (0.15 < x < 1). The Inx(Zn, Sn)1-x oxide can also be represented by Inx(ZnySn1-y)1-x (0 < y <1).

[000133] When In oxide contains neither Zn nor Sn, In can be partially replaced by Ga: InxGa1-x oxide (0 < x < 1).

[000134] An amorphous oxide of an electron carrier concentration of 1x1018/cm3 that is prepared of the present invention is described below in detail.

[000135] A group of the aforementioned oxides is characteristically constituted by In-Ga-Zn-O represented by InGaO3(ZnO)m (m: a natural number less than 6) in a crystalline state, and containing electron carriers at a lower concentration than 1x1018/cm3.

[000136] The other group of the aforementioned oxides is characteristically made up of In-Ga-Zn-Mg-O, represented by InGaO3(Zn1-xMgxO)m (m: a natural number less than 6, and 0 < x < 1) in a crystalline state, and containing electron carriers at a concentration less than 1x1018/cm3.

[000137] The film made up of such an oxide is preferably designed to preferably have an electron mobility greater than 1 cm2/V.s.

[000138] By using this film as the channel layer, one can prepare a TFT that is normally turned off with a gate current of less than 0.1 microamps in an off state of the transistor that has an on-off ratio greater than 1x103 which is transparent to visible light and is flexible.

[000139] In the aforementioned film, electron mobility increases with the increase in conduction electrons. The substrate for forming the transparent film includes glass sheets, plastic sheets and plastic films.

[000140] Using the aforementioned amorphous oxide film as the channel layer, at least one of the layers consisting of Al2O3, Y2O3 or HfO2 or a mixed crystalline compound thereof is used as the door insulating film.

[000141] In a preferred embodiment, the film is formed in an oxygen gas atmosphere without intentional addition of an impurity to increase electrical resistance to the amorphous oxide.

[000142] In the present invention it was observed that amorphous thin films of semi-insulating oxides have characteristics in which the electron mobility increases with the increase in the number of conduction electrons, and they additionally observed that a TFT prepared by using the film has better characteristics of the transistor, such as the on-off ratio, the saturation current in a throttled state, and the switching rate. Thus, a normally off type TFT can be produced using the amorphous oxide.

[000143] Using the amorphous oxide thin film as the channel layer of a film transistor, the electron mobility can be made greater than 1 cm2/V.s, preferably greater than 5 cm2/V.s. The current between the drain terminal and the source terminal in an off state (no gate voltage applied) can be controlled to less than 10 microamps, preferably less than 0.1 microamps at carrier concentration less than 1x1018/cm3, preferably less than 1x1016/cm3. Additionally by use of this thin film, the saturation current after throttling can be increased to 10 microamperes or more, and the on-off ratio can be increased above 1x103 for an electron mobility greater than 1 cm2/V.s, preferably greater than 5 cm2/V.s.

[000144] In a throttled state of the TFT, a high voltage is applied to the gate terminal, and electrons exit at a high density into the channel. Therefore according to the present invention, the saturation current can be increased in correspondence with the increase in electron mobility. Thus, the characteristics of the transistor can be improved, such as increasing the on-off ratio, increasing the saturation current and increasing the switching rate. On the contrary, in a usual compound, the increase in electrons decreases the electron mobility because of the collision of electrons.

[000145] The above-mentioned TFT structure may be an offset structure (upper gate) in which a gate insulating film and a gate terminal are successively formed on a semiconductor channel layer, or an inverted offset structure (lower gate) in which a gate insulating film and a semiconductor channel layer are successively formed on a gate terminal.

(First Process for Film Formation: PLD Process)

[000146] The amorphous oxide thin film with the composition InGaO3(ZnO)m (m: a natural number less than 6) in a crystalline state is stable up to a high temperature of 800°C or more, when m is less than 6 , whereas, with an increase in m, namely, with an increase in the ratio of ZnO to InGaO3 close to the composition of ZnO, the oxide tends to crystallize. Therefore, the m value of the oxide is preferably less than 6 for use as the channel layer of the amorphous TFT.

[000147] Film formation is preferably conducted by a gas phase film formation process using a target of a sintered polycrystalline compact with an InGaO3(ZnO)m composition. Of the gas phase film forming processes, sputtering and pulsed laser vapor deposition are suitable. Sputtering is particularly suitable for large-scale production.

[000148] However, in the formation of the amorphous film under usual conditions, oxygen defect may occur, and thus the electron carrier concentration less than 1x1018/cm3 and electrical conductivity less than 10 X/cm cannot be achieved. With a film like this, a normally off transistor cannot be formed.

[000149] In the present invention, an In-Ga-Zn-O film was produced by pulsed laser vapor deposition using the apparatus shown in figure 14.

[000150] Film formation was carried out using a PLD film forming apparatus like the one shown in figure 14.

[000151] In figure 14, the numbers indicate the following: 701, an RP (rotary pump), 702, a TMP (turbomolecular pump); 703, a preliminary chamber, 704, an electron gun for RHEED, 705, a substrate holding mechanism for rotating and vertically moving the substrate, 706, a laser introduction window, 707, a substrate, 708, a target, 709, a radical source, 710, a gas inlet, 711, a target holding mechanism for rotating and vertically moving the target, 712, a bypass line, 713, a main line, 714, a TMP (turbo pump molecular), 715, a RP (rotary pump); 716, a titanium sump pump; 717, an obturator, 718, an IG (ionic pressure gauge), 719, a PG (Pirani pressure gauge); 720, a BG (barometric pressure gauge) and 721, a growth chamber.

[000152] An In-Ga-Zn-O type amorphous oxide semiconductor thin film was deposited on a SiO2 glass substrate (Corning Co.: 1737) through pulsed laser vapor deposition employing a KrF excimer laser. As pre-treatment before deposition, the substrate was ultrasonically washed for degreasing with acetone, ethanol and ultra-pure water, each for five minutes, and air-dried at 100°C.

[000153] The polycrystalline target was a sintered compact of InGaO3 (ZnO)4 (size: 20 mm in diameter, 5 mm in thickness), which was prepared by wet mixing In2O3, GaxO3 and ZnO (each 4N reagent) as the source material (solvent: ethanol), calcination of the mixture (1,000°C, 2 hours), dry grinding and sintering (1,550°C, 2 hours). The target had an electroconductivity of 90 S/cm.

[000154] Film formation was conducted by controlling the final vacuum of the growth chamber at 2x10-6 Pa and the partial pressure of oxygen during growth at 6.5 Pa. The partial pressure of oxygen in the growth chamber 721 was 6.5 Pa, and the substrate temperature was 25°C. The distance between the target 708 and the film holding substrate 707 was 30 mm, the power introduced through the introduction window 716 was in the range of 1.5 - 3 mJ/cm2/pulse. The pulse width was 20 ns, the repetition frequency was 10 Hz, and the irradiation spot size was 1x1 square millimeter. Under the aforementioned conditions, the film was formed at a speed of 7 nm/minute.

[000155] The resulting thin film was examined by the small angle X-ray scattering (SAXS) method (thin film method, incidence angle 0.5 o): no defined diffraction peak was observed. Thus, the In-Ga-Zn-O thin film obtained was considered amorphous. From the X-ray reflectivity and its pattern analysis, the root mean square roughness (Rrms) was found to be about 0.5 nm, and the film thickness was about 120 nm. By fluorescence X-ray spectrometric analysis (XRF), the metal composition of the film was found to be In:Ga:Zn = 0.98:1.02:4. The electrical conductivity was less than about 1x10-2 S/cm. The electron carrier concentration was estimated to be no more than 1x10-16/cm3. The electron mobility was estimated to be about 5 cm2/V.s. From analysis of the absorption spectrum, the optical band gap energy range of the resulting amorphous thin film was estimated to be about 3 eV.

[000156] The results presented show that the In-Ga-Zn-O type thin film obtained is a transparent flat thin film that has an amorphous phase of a composition close to that of a crystalline InGaO3(ZnO)4 that has fewer oxygen defects and which has lower electrical conductivity.

[000157] The formation of the aforementioned film is explained specifically by reference to figure 1. Figure 1 shows the dependence of the concentration of electron carriers in the transparent amorphous oxide thin film formed on the partial pressure of oxygen for the film of an InGaO3 composition (ZnO)m (m: an integer less than 6) in a crystalline state considered under the same film formation conditions as in the previous example.

[000158] By forming the film in an atmosphere with oxygen partial pressure greater than 4.5 Pa under the same conditions as in the previous example, the concentration of electron carriers can be reduced below 1x1018/cm3, as shown in figure 1. In this film formation, the substrate was maintained at approximately room temperature without intentional heating. For using a flexible plastic film as the substrate, the temperature of the substrate is preferably maintained at a temperature lower than 100°C.

[000159] The greater partial pressure of oxygen allows the concentration of electron carriers to be reduced. For example, as shown in figure 1, the InGaO3(ZnO)4 thin film formed at substrate temperature of 25°C and oxygen partial pressure of 5 Pa had a lower electron carrier concentration of 1x1016/cm3.

[000160] In the thin film obtained, the electron mobility was greater than 1 cm2/V.s, as shown in figure 2. However, the film deposited by pulsed laser vapor deposition at an oxygen partial pressure greater than 6.5 Pa as in this example it has a rough surface, not suitable for a TFT channel layer.

[000161] In this way, a normally-off type transistor can be constructed using a transparent thin amorphous oxide represented by InGaO3(ZnO)m (m: a number less than 6) in a crystalline state formed at an oxygen partial pressure greater than 4.5 Pa, preferably greater than 5 Pa, but less than 6.5 Pa by a pulsed laser vapor deposition method in the previous example.

[000162] The thin film obtained previously showed an electron mobility greater than 1 cm2/V, and the on-off ratio can be increased above 1x103.

[000163] As previously described, in the formation of an InGaZn oxide film by a PLD method under the conditions shown in this example, the partial pressure of oxygen is preferably controlled in the range of 4.5 Pa to 6.5 Pa.

[000164] To achieve an electron carrier concentration of 1x1018/cm3, the oxygen partial pressure conditions, the constitution of the film-forming apparatus and the type and composition of the film-forming material must be controlled.

[000165] Next, an upper gate type MISFET element shown in figure 5 was produced by forming an amorphous oxide with the aforementioned apparatus at an oxygen partial pressure of 6.5 Pa. Specifically, on the glass substrate 1, a 120 nm thick semi-insulating amorphous InGaO3(ZnO)4 film was formed for use for channel layer 2 by the aforementioned Ga-Ga-Zn-O amorphous thin film forming method. Additionally, an InGaO3(ZnO)4 film with a higher electroconductivity and a gold film were respectively laminated to a thickness of 30 nm by pulsed laser deposition at an oxygen partial pressure of less than 1 Pa in the chamber. Then, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peel-off method. Finally, a Y2O3 film for gate insulator 3 was formed by an electron beam vapor deposition method (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 1x10-3 A/ cm3 with application of 0.5 MC/cm). On it, a gold layer was formed, and the gate terminal 4 was formed by photolithography and detachment.

Assessment of MISFET Element Characteristics

[000166] Figure 6 shows the current-voltage characteristics of the MISFET element measured at room temperature. It is understood that the channel is an n-type semiconductor of the IDS drain current increasing with the VDS drain voltage increasing. This is consistent with the fact that an amorphous semiconductor of an In-Ga-Zn-O type is of an n-type. The IDS becomes saturated (throttled) at VDS = 6V, which is typical behavior of a semiconductor transistor. By examining the gain characteristics, the threshold value of the gate voltage VGS under application of VDS = 4V was found to be about -0.5 V. A passing current IDS = 1.0x10-5 A was caused at VG = 10 V. This corresponds to carrier induction by gate polarization in the In-Ga-Zn-O type amorphous semiconductor thin film.

[000167] The on-off ratio of the transistor was greater than 1x103. From the output characteristics, the field effect mobility was calculated to be about 7 cm2 (Vs)-1. Visible light irradiation did not change the transistor characteristics of the element produced according to the same measurement.

[000168] According to the present invention, a thin film transistor can be produced that has a channel layer that contains electron carriers at a lower concentration to achieve greater electrical resistance and that presents greater electron mobility.

[000169] The aforementioned amorphous oxide has excellent characteristics in that electron mobility increases with increasing concentration of electron carriers, and presents degenerate conduction. In this example, the thin film was formed on a glass substrate. However, a plastic sheet or film is used as the substrate since film formation can be conducted at room temperature. Additionally, the amorphous oxide obtained in this example absorbs only little visible light to give a transparent flexible TFT.

(Second Process for Film Formation: Sputtering Process (SP Process))

[000170] Film formation by the high-frequency SP process using argon gas as the atmosphere gas is explained below.

[000171] The SP process was conducted using the apparatus shown in figure 15. In figure 15, the numbers indicate the following: 807, a substrate for film formation; 808, a target; 805, a substrate holding device equipped with a cooling mechanism; 814, a turbomolecular bomb; 815, a rotary pump; 817, a shutter; 818, an ionic manometer; 819, a Pirani manometer; 821, a growth chamber and 830, a gate valve.

[000172] Substrate 807 for film formation was a SiO2 glass substrate (Corning Co. 1737) that was ultrasonically washed for degreasing with acetone, ethanol and ultra-pure water, respectively, for 5 minutes, and dried at 100 °C in air.

[000173] The target was a polycrystalline sintered compact with a composition of InGaO3(ZnO)4 (size: 20 mm in diameter, 5 mm in thickness) that was prepared by wet mixing In2O3, Ga2O3 and ZnO (each 4N reagent) as the source material (solvent: ethanol), calcination of the mixture (1,000°C, 2 hours), dry grinding and sintering (1,550°C, 2 hours). Target 808 had an electroconductivity of 90 S/cm, making it semi-insulating.

[000174] The final vacuum degree of growth chamber 821 was 1x10-4 Torr. During growth, the total pressure of oxygen and argon gas was kept constant in the range of 4 to 0.1x10-1 Pa. The partial pressure ratio of argon to oxygen changed in the oxygen partial pressure range of 1x10-3 to 2x10 -1 Pa.

[000175] The substrate temperature was room temperature. The distance between the target 808 and the substrate 807 for film formation was 30 mm.

[000176] The electrical power fed was RF 180 W and the film formation rate was 10 nm/minute.

[000177] The resulting thin film was examined by the small angle X-ray scattering (SAXS) method (thin film method, incidence angle 0.5 o): no distinct diffraction peak was observed. Thus, the In-Ga-Zn-O thin film obtained was considered amorphous. Using the X-ray reflectivity and analysis of its pattern, the average surface roughness (Rrms) was found to be about 0.5 nm, and the film thickness was about 120 nm. By fluorescence X-ray spectrometric analysis (XRF), the metal composition of the film was found to be In:Ga:Zn = 0.98:1.02:4.

[000178] The films were formed at various atmospheric oxygen partial pressures, and the resulting amorphous oxide films were measured for electrical conductivity. Figure 3 shows the result.

[000179] As shown in figure 3, electrical conductivity can be reduced to less than 10 S/cm leading to film formation in an atmosphere that has an oxygen partial pressure greater than 3x10-2 Pa. The number of electron carriers can be reduced by increasing the partial pressure of oxygen.

[000180] As shown in figure 3, for example, the InGaO3(ZnO)4 thin film formed at a substrate temperature of 25°C and oxygen partial pressure of 1x10-1 P1 had a lower electrical conductivity of about 1x10- 10 S/cm. Additionally, the InGaO3(ZnO)4 thin film formed at oxygen partial pressure of 1x10-1 Pa had excessively high electrical resistance, and unmeasurable electrical conductivity. With this film, although the electron mobility was not measurable, the electron mobility was estimated to be about 1 cm2/V.s by extrapolating the values from films with a high concentration of electron carriers.

[000181] Thus, the normally off transistor with the on-off ratio greater than 1x103 can be obtained by using a transparent thin amorphous oxide film consisting of In-Ga-Zn-O represented in a crystalline state by InGaO3(ZnO) m (m: a natural number less than 6) produced by sputtering vapor deposition in an argon atmosphere containing oxygen at a partial pressure greater than 3x10-2 Pa, preferably greater than 5x10-1 Pa.

[000182] In the use of the apparatus and material employed in this example, the formation of the film by sputtering is conducted at the partial pressure of oxygen varying from 3x10-2 Pa to 5x10-1 Pa. Incidentally, in the thin film produced by vapor deposition by pulsed laser or sputtering, electron mobility increases with the increase in the number of conducting electrons, shown in figure 2.

[000183] As described previously, by controlling the partial pressure of oxygen, the oxygen defect can be reduced, and thus the concentration of electron carriers can be reduced. In the amorphous thin film, electron mobility can be high, since there is essentially no grain interface in the amorphous state, unlike the polycrystalline state.

[000184] Incidentally, replacing the glass substrate with a 200 μm thick poly(ethylene terephthalate) (PET) does not change the properties of the amorphous InGaO3(ZnO)4 oxide film formed on it.

[000185] A high-strength amorphous film of InGaO3(Zn1-xMgxO)m (m: a natural number less than 6; 0 < x < 1) can be obtained using polycrystalline InGaO3(Zn1-xMgxO)m as the target, even at a partial pressure of oxygen less than 1 Pa. For example, with a target in which 80 atomic% of Zn is replaced by Mg, the electron carrier concentration less than 1x1016 /cm (resistance: about 1x10-2 S/ cm) can be achieved by the use of pulsed laser deposition in an oxygen atmosphere at a partial pressure of 0.8 Pa. In a film like this, the electron mobility is lower than that of the film without Mg, but the decrease is modest: electron mobility is about 5 cm2/V.s at room temperature, about one digit higher than that of amorphous silicon. When films are formed under the same conditions, increasing Mg content decreases both electrical conductivity and electron mobility. Therefore, the Mg content preferably varies from 20% to 85% (0.2 < x < 0.85).

[000186] In the thin film transistor employing said amorphous oxide film, the gate insulating film preferably contains a mixed crystalline compound containing two or more of Al2O3, Y2O3, HfO2 and their compounds.

[000187] The presence of a defect at the interface of the gate insulating thin film and the channel layer thin film decreases electron mobility and causes hysteresis of the transistor characteristics. Furthermore, current leakage depends greatly on the type of door insulator. Therefore, the port insulator must be selected to be suitable for the channel layer. Leakage current can be decreased by using an Al2O3 film, hysteresis can be reduced by using a Y2O3 film, and electron mobility can be increased by using an HfO2 film with a high dielectric constant. By using the mixed crystal of the aforementioned compounds, TFT can be formed, which causes less current leakage, less hysteresis and has greater electron mobility. Since the gate insulator formation process and the channel layer formation process can be conducted at room temperature, the TFT can be formed in a mismatched constitution or in an inverted mismatched constitution.

[000188] The TFT thus formed is a three-terminal element that has a gate terminal, a source terminal and a drain terminal. This TFT is formed by the formation of a thin semiconductor film on an insulating substrate of a ceramic, glass or plastic as the channel layer for transporting electrons or holes, and serves as an active element that has the function of controlling the passage of current. through the channel layer by applying a voltage to the gate terminal, and switching the current between the source terminal and the drain terminal.

[000189] In the present invention, it is important that the targeted electron carrier concentration is achieved by controlling the amount of oxygen defect.

[000190] In the description presented, the amount of oxygen in the amorphous oxide film is controlled by controlling the concentration of oxygen in the film-forming atmosphere. Otherwise, the amount of oxygen defect can be controlled (reduced or increased) by post-treating the oxide film in an oxygen atmosphere as a preferred embodiment.

[000191] For effective control of the amount of oxygen defect, the temperature of the oxygen atmosphere is controlled in the range of 0°C to 300°C, preferably from 25°C to 250°C, more preferably from 100°C to 200°C.

[000192] Naturally, a film can be formed in an oxygen atmosphere and additionally post-treated in an oxygen atmosphere. Otherwise, the film is formed without controlling the oxygen partial pressure and the post-treatment is conducted in an oxygen atmosphere as long as the targeted electron carrier concentration (less than 1x1018/cm3) can be obtained.

[000193] The lower limit of the concentration of electron carriers in the present invention is, for example, 1x1014/cm3, depending on the type of element, circuit or device that employs the oxide film produced.

(Wider Range of Materials)

[000194] After investigation of other materials for the system, it was observed that the amorphous oxide composed of at least one oxide of the elements Zn, In and Sn is used for an amorphous oxide film of a low carrier concentration and high mobility of electrons. It was observed that this amorphous oxide film has a specific property that increase in the number of conducting electrons in it increases the electron mobility. With the use of this film, one can produce a normally off type TFT which is excellent in transistor properties such as on-off ratio, saturation current in throttled state and switching rate.

[000195] In the present invention, an oxide with any of the characteristics from (a) to (h) below is used:

[000196] (a) An amorphous oxide that has an electron carrier concentration less than 1x1018/cm3;

[000197] (b) An amorphous oxide in which electron mobility increases with increasing electron carrier concentration.

[000198] (Room temperature means a temperature in the range of about 0°C to about 40°C. The term "amorphous compound" means a compound that presents a halo pattern only, without presenting a characteristic diffraction pattern in the spectrum X-ray diffraction. Electron mobility means mobility measured by the Hall effect).

[000199] (c) An amorphous oxide mentioned in previous items (a) or (b), in which the electron mobility at room temperature is greater than 0.1 cm2/V.s;

[000200] (d) An amorphous oxide mentioned in any of items (b) to (c) that presents degenerate conduction;

[000201] (The term "degenerate conduction" means the state in which the thermal activation energy as a function of the temperature of the electrical resistance is not greater than 30 meV).

[000202] (e) An amorphous oxide mentioned in any of the previous items (a) to (d) that contains at least one of the elements Zn, In and Sn as the constituent element;

[000203] (f) An amorphous oxide film composed of the amorphous oxide mentioned in item (e) above and additionally at least one of:

[000204] Group 2 M2 elements with an atomic number lower than that of Zn (Mg and Ca),

[000205] Group 3 M3 elements with an atomic number lower than that of In (B, Al, Ga and Y);

[000206] Group 4 M4 elements with an atomic number lower than that of Sn (Si, Ge and Zr);

[000207] Group 5 elements M5 (V, Nv and Ta) and Lu and W to reduce the concentration of electron carriers;

[000208] (g) An amorphous oxide film, mentioned in any of the previous items (a) to (f), consisting of a single compound with a composition of Ini-xM3xθ3(Zni-yM2yO)m (0 < x < 1 : 0 < y < 1; m: 0 or a natural number less than 6) in a crystalline state, or a mixture of compounds with a number other than m, an example of M3 being Ga, and an example of M2 being Mg; It is

[000209] (h) An amorphous oxide film, mentioned in any of the previous items (a) to (g), formed on a plastic substrate or a plastic film.

[000210] The present invention also provides a field effect transistor that employs the aforementioned amorphous oxide or amorphous oxide film as the channel layer.

[000211] A field effect transistor is prepared in which an amorphous oxide film with an electron carrier concentration less than 1x1018/cm3 but greater than 1x1015/cm3 is employed as the channel layer, and with a terminal of source and a drain terminal, and a gate terminal with interposition of a gate insulator. When a voltage of about 5 V is applied between the source and drain terminals without applying gate voltage, the electrical current between the drain and source terminals is about 1x10-7 amps.

[000212] The mobility of electrons in the oxide crystal increases with increasing overlap of the metal ions' orbits. In a crystal of Zn, In or Sn oxide with a higher atomic number, the electron mobility is in the range of 0.1 to 200 cm2/V.s.

[000213] In an oxide, oxygen and metal ions are linked by ionic bonds without orientation of chemical bonds, with a random structure. Therefore, in the oxide in an amorphous state, the electron mobility can be compared with that in a crystalline state.

[000214] On the other hand, replacing Zn, In or Sn with an element of a lower atomic number decreases electron mobility. Thus, the electron mobility in the amorphous oxide of the present invention ranges from about 0.01 to 20 cm2/V.s.

[000215] In the transistor with a channel layer consisting of said oxide, the gate insulator is preferably formed from Al2O3, Y2O3, HfO2 or a mixed crystalline compound containing two or more of these.

[000216] The presence of a defect at the interface of the gate insulating thin film and the channel layer thin film reduces electron mobility and causes hysteresis of the transistor characteristics. Furthermore, current leakage largely depends on the type of door insulation film. Therefore, the gate insulator must be selected to be suitable for the channel layer. Leakage current can be decreased by using an Al2O3 film, hysteresis can be reduced by using a Y2O3 film, and electron mobility can be increased by using an HfO2 film with a high dielectric constant. By using the mixed crystal of the aforementioned compounds, TFT can be formed, which causes less current leakage, less hysteresis and presents greater electron mobility. Since the gate insulator formation process and the channel layer formation process can be conducted at room temperature, the TFT can be formed in a mismatched constitution or in an inverted mismatched constitution.

[000217] The In2O3 oxide film can be formed through a gas phase process, and adding moisture at a partial pressure of about 0.1 Pa to the film-forming atmosphere makes the film formed amorphous.

[000218] ZnO and SnO2, respectively, cannot be easily formed in an amorphous film state. For the formation of the ZnO film in an amorphous state, In2O3 is added in an amount of 20 atomic%. For the formation of the SnO2 film in an amorphous state, In2O3 is added in an amount of 90 atomic%. In the formation of the Sn-In-O type amorphous film, nitrogen gas is introduced at a partial pressure of about 0.1 Pa into the film-forming atmosphere.

[000219] To the previous amorphous film, an element capable of forming a complex oxide can be added, selected from the elements of Group 2 M2 with an atomic number lower than that of Zn (Mg and Ca), elements of Group 3 M3 with an atomic number lower than that of In (B, Al, Ga and Y), elements of Group 4 M4 with an atomic number lower than that of Sn (Si, Ge and Zr), elements of Group 5 M5 (V, Nv and Ta ) and Lu and W. The addition of said element stabilizes the amorphous film at room temperature and expands the composition range for the formation of amorphous film.

[000220] In particular, the addition of B, Si or Ge that tends to form a covalent bond is effective for stabilizing the amorphous phase. The addition of a complex oxide made up of ions with very different ionic radii is effective for stabilizing the amorphous phase. For example, in an In-Zn-O system, for the formation of a stable film at room temperature, In must be limited to more than about 20 atomic %. However, the addition of Mg in an amount equivalent to In allows the formation of a stable amorphous film in the In composition range of no less than about 15 atomic %.

[000221] In gas-phase film formation, an amorphous oxide film of electron carrier concentration ranging from 1x1015/cm3 to 1x1018/cm3 can be obtained by controlling the film-forming atmosphere.

[000222] An amorphous oxide film can be suitably formed by a vapor phase process such as a pulsed laser vapor deposition process (PLD process), a sputtering process (SP process) and a vapor deposition process is an electron beam. Of the vapor phase processes, the PLD process is suitable in view of the ease of controlling the material composition, while the SP process is suitable in view of large-scale production. However, the film formation process is not limited to this.

(Formation of In-Zn-Ga-O Type Amorphous Oxide Film by PLD Process)

[000223] An amorphous oxide type In-Zn-Ga-O was deposited on a glass substrate (Corning Co.: 1737) by a PLD process employing a KrF excimer laser with a polycrystalline sintered compact as the target with a composition of InGaO3(ZnO) or InGaO3(ZnO)4.

[000224] The apparatus shown in figure 11 was employed, which was mentioned previously, and the film formation conditions were the same as those mentioned previously for the apparatus.

[000225] The substrate temperature was 25°C.

[000226] The two resulting thin films were examined by the small-angle X-ray scattering (SAXS) method (thin film method, angle of incidence: 0.5 o): no distinct diffraction peak was observed, which shows that the obtained In-Ga-Zn-O thin films produced with two different targets were both amorphous.

[000227] From the X-ray reflectivity of the In-Zn-Ga-O type amorphous oxide film on the glass substrate and its pattern analysis, the root mean square roughness (Rrms) of the thin films was determined to be about 0.5 nm, and the film thickness at about 120 nm. By fluorescence X-ray spectrometry (XRF) analysis, it was determined that the film obtained with the InGaO3(ZnO) polycrystalline sintered compact target contained the metals at a composition ratio In:Ga:Zn = 1.1 :1.1:0.9, while it was determined that the film obtained with the target of the InGaO3(ZnO)4 polycrystalline sintered compact contains the metals at a composition ratio In:Ga:Zn = 0.92: 1.02:4.

[000228] Amorphous oxide films were formed at various oxygen partial pressures of the film-forming atmosphere, the target having the composition of InGaO3(ZnO)4. The formed amorphous oxide films were measured with respect to electron carrier concentration. Figure 1 shows the results. By film formation in an atmosphere with an oxygen partial pressure greater than 4.2 Pa, the electron carrier concentration can be reduced to less than 1x1018/cm3, as shown in figure 1. In this film formation, the substrate was maintained at approximately room temperature without intentional heating. At oxygen partial pressure lower than 6.5 Pa, the surfaces of the obtained amorphous oxide films were flat.

[000229] At the oxygen partial pressure of 5 Pa, the amorphous film formed with the InGaO3(ZnO)4 target, the electron carrier concentration was 1x1016/cm3, the electroconductivity was 1x10-2 S/cm and the electron mobility electrons in it was estimated to be about 5 cm2/V.s. By analyzing the light absorption spectrum, the energy span of the optical band gap of the formed amorphous oxide film was estimated to be about 3 eV.

[000230] The greater partial pressure of oxygen further reduced the concentration of electron carriers. As shown in figure 1, in the In-Zn-Ga-O type amorphous oxide film formed at a substrate temperature of 25°C at an oxygen partial pressure of 6 Pa, the electron carrier concentration dropped to 8x1015/cm3 (electroconductivity: about 8x10-3 S/cm). The electron mobility in the film was estimated to be 1 cm2/V.s or more. However, by the PLD process, at oxygen partial pressure of 6.5 Pa or more, the deposited film has a rough surface and is not suitable for use as the channel layer of TFT.

[000231] In-Zn-Ga-O type amorphous oxide films were formed at various oxygen partial pressures in the film-forming atmosphere with the target consisting of a polycrystalline sintered compact with the composition of InGaO3(ZnO)4. The resulting films were examined with respect to the relationship between electron carrier concentration and electron mobility. Figure 2 shows the results. Corresponding to the increase in electron carrier concentration from 1x1016/cm3 to 1x1020/cm3, the electron mobility increased from about 3 cm2/V.s to about 11 cm2/V.s. The same trend was observed with amorphous oxide films obtained with sintered polycrystalline InGaO3(ZnO) target.

[000232] The In-Zn-Ga-O type amorphous oxide film that formed on a 200 μm thick poly(ethylene terephthalate) (PET) film in place of the glass substrate had similar characteristics.

(Formation of Amorphous Oxide Film Type In-Zn-Ga-Mg-O by PDL Process)

[000233] An InGaO3(Zni-xMgxO)4 (0 < x < 1) film was formed on a glass substrate by a PLD process with an InGaO3(Zn1-xMgxO)4 (0 < x < 1) target. The device used was shown in figure 11.

[000234] A SiO2 glass substrate (Corning Co.: 1737) was used as the substrate. As pre-treatment, the substrate was ultrasonically washed for degreasing with acetone, ethanol and ultra-pure water, each for five minutes, and air-dried at 100°C. The target was a compact sintered InGaO3(Zni-xMgxO)4 (x = 1 - 0) (size: 20 mm diameter, 5 mm thickness).

[000235] The target was prepared by wet mixing source materials In2O3, Ga2O3 and ZnO (each 4N reagent) (solvent: ethanol), calcining the mixture (1,000°C, 2 hours), dry grinding and sintering (1,550° C, 2 hours). The final pressure in the growth chamber was 2x10-6 Pa. The partial pressure of oxygen during growth was controlled at 0.8 Pa. The substrate temperature was room temperature (25°C). The distance between the target and the substrate for film formation was 30 mm. The KrF excimer laser was irradiated at a power of 1.5 mJ/cm2/pulse with the pulse width of 20 ns, the repetition frequency of 10 Hz and the irradiation spot size of 1x1 square mm. The film formation rate was 7 nm/min. The partial pressure of oxygen in the film-forming atmosphere was 0.8 Pa. The substrate temperature was 25°C.

[000236] The resulting thin film was examined by the small angle X-ray scattering (SAXS) method (thin film method, angle of incidence: 0.5°): no distinct diffraction peak was observed. Therefore, the In-Ga-Zn-Mg-O thin film was amorphous. The resulting film had a flat surface.

[000237] Using targets of different x values (different Mg contents), In-Zn-Ga-Mg-O type amorphous oxide films were formed at oxygen partial pressure of 0.8 Pa in a film-forming atmosphere to investigate the dependence of conductivity, electron carrier concentration and electron mobility on the value of x.

[000238] Figures 4A, 4B and 4C show the results. At values of x greater than 0.4, in the amorphous oxide films formed by the PLD process at an oxygen partial pressure of 0.8 Pa in the atmosphere, the concentration of electron carriers decreased to less than 1x1018/cm3. In the amorphous film with x value greater than 0.4, the electron mobility was greater than 1 cm2/V.

[000239] As shown in figures 4A, 4B and 4C, an electron carrier concentration of less than 1x1016/cm3 can be obtained in the film prepared by a pulsed laser deposition process with the target in which 80 atomic% of Zn is replaced by Mg and at oxygen partial pressure of 0.8 Pa (electrical resistance: about 1x10-2 S.cm). In a film like this, electron mobility decreases compared to the Mg-free film, but the decrease is modest. The electron mobility in the films is about 5 cm2/V.s, which is about single digits higher than that of amorphous silicon. Under the same film formation conditions, both the electrical conductivity and electron mobility in the film decreased with increasing Mg content. Therefore, the Mg content in the film is preferably greater than 20 atomic% and less than 85 atomic% (0.2 < x < 0.85), more preferably 0.5 < x < 0.85.

[000240] The amorphous InGaO3(Zni-xMgxO)4 (0 < x < 1) film formed on a 200 μm thick poly(ethylene terephthalate) (PET) film in place of the glass substrate had similar characteristics.

(Formation of Amorphous In2O3 Oxide Film by PLD Process)

[000241] An In2O3 film was formed on a 200 μm thick PET film by using a target consisting of compact sintered polycrystalline In2O3 by a PLD process employing a KrF excimer laser.

[000242] The apparatus used is shown in figure 11. The substrate for film formation was a SiO2 glass substrate (Corning Co.: 1737).

[000243] As pre-treatment before deposition, the substrate was ultrasonically washed for degreasing with acetone, ethanol and ultrapure water, each for five minutes, and air-dried at 100°C.

[000244] The target was a sintered In2O3 compact (size: 20 mm diameter, 5 mm thick), which was prepared by calcining the In2O3 source material (4N reagent) (1,000°C, 2 hours), dry spraying and sintering (1,550°C, 2 hours).

[000245] The final vacuum of the growth chamber was 2x10-6 Pa, the partial pressure of oxygen during growth was 5 Pa and the substrate temperature was 25°C.

[000246] The partial pressure of water vapor was 0.1 Pa, and oxygen radicals were generated by the oxygen radical generation set by applying 200 W.

[000247] The distance between the target and the film holding substrate was 40 mm, the Krf excimer laser power was 0.5 mJ/cm2/pulse, the pulse width was 20 ns, the repetition frequency was 10 Hz and the irradiation spot size was 1x1 mm square.

[000248] The film formation rate was 3 nm/minute.

[000249] The resulting thin film was examined by the small angle X-ray scattering (SAXS) method (thin film method, angle of incidence: 0.5 o); no distinct diffraction peak was observed, which shows that the In-O type oxide film obtained was amorphous. The film thickness was 80 nm.

[000250] In the In-O type amorphous oxide film obtained, the concentration of electron carriers was 5x1017/cm3, and the electron mobility was about 7 cm2/V.s.

(Formation of In-Sn-O Type Amorphous Oxide Film by PLD Process)

[000251] An In-Sn-O type oxide film was formed on a 200 μm thick PET film by using a target consisting of sintered polycrystalline compact of (In0.9Sn0.1)O3.1 by a process that employs KrF excimer laser. The device used is shown in figure 14.

[000252] The substrate for film formation was a SiO2 glass substrate (Corning Co.: 1737).

[000253] As the pre-treatment before deposition, the substrate was ultrasonically washed for degreasing with acetone, ethanol and ultrapure water, each for five minutes, and air-dried at 100°C.

[000254] The target was a sintered In2O3-SnO2 compact (size: 20 mm diameter, 5 mm thick), which was prepared by wet mixing In2O3-SnO2 source materials (4N reagents) (solvent: ethanol), calcination mixing (1,000°C, 2 hours), dry grinding and sintering (1,550°C, 2 hours).

[000255] The substrate was kept at room temperature. The partial pressure of oxygen was 5 Pa. The partial pressure of nitrogen was 0.1 Pa. Oxygen radicals were generated by the oxygen radical generation set by applying 200 W.

[000256] The distance between the target and the film holding substrate was 30 mm, the Krf excimer laser power was 1.5 mJ/cm2/pulse, the pulse width was 20 ns, the repetition frequency was 10 Hz and the irradiation spot size was 1x1 mm square.

[000257] The film formation rate was 6 nm/minute.

[000258] The resulting thin film was examined by the small-angle X-ray scattering (SAXS) method (thin film method, angle of incidence; 0.5 o): no distinct diffraction peak was detected, which shows that the In-Sn-O type oxide film obtained is amorphous.

[000259] In the In-Sn-O type amorphous oxide film obtained, the concentration of electron carriers was 8x1017/cm3, and the electron mobility was about 5 cm2/V.s. The film thickness was 100 nm.

(Formation of In-Ga-O Type Amorphous Oxide Film by PLD Process)

[000260] The substrate for the film was a SiO2 glass substrate (Corning Co.: 1737).

[000261] As pre-treatment before deposition, the substrate was ultrasonically washed for degreasing with acetone, ethanol and ultrapure water, each for five minutes, and air-dried at 100°C.

[000262] The target was a sintered compact of (In2θ3)i-x-(Ga2θ3)x (x = 0 - 1) (size: 20 mm diameter, 5 mm thick). For example, at x - 0.1, the target is a polycrystalline sintered compact of (In0.9Ga0.1)xO3.

[000263] This target was prepared by wet mixing the source materials In2O3-Ga2O2 (4N reagents) (solvent: ethanol), calcining the mixture (1,000°C, 2 hours), dry grinding and sintering (1,550°C, 2 hours ).

[000264] The final pressure of the growth chamber was 2x10-6 Pa. The partial pressure of oxygen during growth was 1 Pa.

[000265] The substrate was brought to room temperature. The distance between the target and the film holding substrate was 30 mm. The Krf excimer laser power was 1.5 mJ/cm2/pulse. The pulse width was 20 ns. The repetition frequency was 10 Hz. The irradiation spot size was 1x1 square mm. The film formation rate was 6 nm/minute.

[000266] The substrate temperature was 25°C. The oxygen pressure was 1 Pa. The resulting film was examined by the small-angle X-ray scattering (SAXS) method (thin film method, angle of incidence: 0.5 o): no distinct diffraction peak was detected , which shows that the In-Ga-O type oxide film obtained is amorphous. The film thickness was 120 nm.

[000267] In the In-Ga-O type amorphous oxide film obtained, the concentration of electron carriers was 8x1016/cm3, and the electron mobility was about 1 cm2/V.s.

(Preparation of TFT Element with Amorphous Type Oxide Film (Glass Substrate))

[000268] A top door type TFT element shown in figure 5 was prepared.

[000269] Firstly, an amorphous oxide film type In-Ga-Zn-O was prepared on glass substrate 1 by the aforementioned PLS apparatus with a target consisting of a polycrystalline sintered compact with a composition of InGaO3(ZnO)4 at a pressure partial oxygen concentration of 5 Pa. The formed In-Ga-Zn-O film had a thickness of 120 nm, and was used as channel 2 layer.

[000270] Additionally, another amorphous film type In-Ga-Zn-O with greater electroconductivity and a layer of gold were laminated, each 30 nm thick, by the PLD method at oxygen partial pressure less than 1 Pa in the camera. Hence, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peeling method.

[000271] Finally, a Y2O3 film as the gate 3 insulating film was formed by electron beam vapor deposition (thickness: 90 nm, relative dielectric constant: about 15, leakage current density: 1x10-3 A /cm2 by applying 0.5 MV/cm). In addition to this, a gold film was formed and from it the gate terminal 4 was formed by photolithography and a peel-off method. The channel length was 50 μm and the channel width was 200 μm.

Evaluation of TFT Element Characteristics

[000272] Figure 6 shows current-voltage characteristics of the TFT element at room temperature. The drain current IDS increased with increasing drain voltage VDS, which shows that the channel is n-type conduction.

[000273] This is consistent with the fact that an amorphous In-Ga-Zn-O semiconductor is of an n-type. The IDS became saturated (throttled) at VDS = 6 V, which is typical behavior of a semiconductor transistor. For examination of the gain characteristics, the threshold value of the gate voltage VGS by applying VDS - 4 V observed was about -0.5 V. A current flow of IDS = 1.0x10-5 A was caused to VG = 10 V. This corresponds to carrier induction by a gate polarization in the In-Ga-Zn-O type amorphous semiconductor thin film as the insulator.

[000274] The on-off ratio of the transistor was greater than 1x103. From the output characteristics, the field effect mobility was calculated to be about 7 cm2(Vs)-1 in the saturation region. Visible light irradiation does not change the transistor characteristics of the element produced according to the same measurement.

[000275] The amorphous oxide of electron carrier concentration less than 1x1018/cm3 is used as a channel layer of a TFT. The electron carrier concentration is more preferably less than 1x1017/cm3, even more preferably less than 1x1016/cm3.

(Preparation of TFT Element with Amorphous oxide Film type In-Zn-Ga-O (Amorphous Substrate))

[000276] A top door type TFT element shown in figure 5 was prepared.

[000277] Firstly, an amorphous oxide film type In-Ga-Zn-O was prepared on poly(ethylene terephthalate) (PET) film 1 by the aforementioned PLS apparatus with a target consisting of a polycrystalline sintered compact with a composition of InGaO3(ZnO) at an oxygen partial pressure of 5 Pa in the atmosphere. The film formed had a thickness of 120 nm, and was used as channel 2 layer.

[000278] Additionally, another amorphous film type In-Ga-Zn-O with greater electroconductivity and a gold layer were laminated, each 30 nm thick, by the PLD method at oxygen partial pressure less than 1 Pa in the camera. Hence, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peeling method.

[000279] Finally, an insulating film of port 3 was formed by electron beam vapor deposition. In addition to this, a gold film was formed and from it the gate terminal 4 was formed by photolithography and a peel-off method. The channel length was 50 μm and the channel width was 200 μm. Three TFTs from the above structure were prepared respectively using one of three types of gate insulators: Y2O3 (140 nm thick), Al2O3 (130 μm thick), and HfO2 (140 μm thick).

Evaluation of TFT Element Characteristics

[000280] The TFT elements formed in a PET film had current voltage characteristics similar to those shown in figure 6 at room temperature. The drain current IDS increased with increasing drain voltage VDS, which shows that the channel is n-type conduction. This is consistent with the fact that an amorphous In-Ga-Zn-O type semiconductor is of an n-type. The IDS became saturated (throttled) at VDS = 6 V, which is typical behavior of a semiconductor transistor. A current flow of IDS = 1.0x10- 8 A was caused at VG = 0 V, and a current flow of IDS = 2.0x10-5 A was caused at VG = 10 V. This corresponds to carrier induction. electrons by gate polarization in the insulator, the amorphous semiconductor oxide film type In-Ga-Zn-O.

[000281] The on-off ratio of the transistor was greater than 1x103. From the output characteristics, the field effect mobility was calculated to be about 7 cm2(Vs)-1 in the saturation region.

[000282] The elements formed in the PET film were curved to a curvature radius of 30 mm and, in this state, the characteristics of the transistor were measured. However, no change in the characteristics of the transistor was observed. Visible light irradiation does not change the characteristics of the transistor.

[000283] The TFT that employs the Al2O3 film as the gate insulating film also has transistor characteristics similar to those shown in figure 6. A current flow of IDS = 1.0x10-8 A was caused at VG = 0 V, and a current flow of IDS = 5.0x10-6 was caused at VG = 10 V. The on-slip ratio of the transistor was greater than 1x102. From the output characteristics, the field effect mobility was calculated to be about 2 cm2(Vs)-1 in the saturation region.

[000284] The TFT employing the HfO2 film as the gate insulating film also has transistor characteristics similar to those shown in figure 6. A current flow of IDS 1x10-8 was caused at VG = 0 V, and a flow of current of IDS = 1.0x10-6 was caused at VG = 10 V. The on-off ratio of the transistor was greater than 1x102. From the output characteristics, the mobility of the field effect was calculated to be about 10 cm2(Vs)-1 in the saturation region.

(Preparation of TFT Element Employing In2O3 Amorphous Oxide Film by PLD Process)

[000285] An upper door type TFT element shown in figure 5 was prepared.

[000286] Firstly, an amorphous oxide film type In2O3 was formed on poly(ethylene terephthalate) (PET) film 1 by the PLD method as channel layer 2 at a thickness of 80 nm.

[000287] Additionally, another amorphous film type In2O3 with greater electroconductivity and a gold layer were laminated, each 30 nm thick, by the PLD method at oxygen partial pressure less than 1 Pa in the chamber, and in the application of zero volt voltage to the oxygen radical generation assembly. Hence, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peeling method.

[000288] Finally, a Y2O3 gate insulator was formed by electron beam vapor deposition. In addition to this, a gold film was formed and from it the gate terminal 4 was formed by photolithography and a peel-off method.

Evaluation of TFT Element Characteristics

[000289] TFT elements formed on a PET film were examined with regard to current-voltage characteristics at room temperature. The drain current IDS increased with increasing drain voltage VDS, which shows that the channel is an n-type conductor. This is consistent with the fact that an amorphous In-O amorphous oxide film is an n-type conductor. The IDS became saturated (throttled) at about VDS = 6 V, which is typical behavior for a transistor. A current flow of IDS = 2.0x10-8 A was caused at VG = 0 V, and a current flow of IDS = 2.0x1-6 A was caused at VG = 10 V. This corresponds to carrier induction. electrons by gate polarization in the insulator, the In-O type amorphous oxide film.

[000290] The on-off ratio of the transistor was about 1x102. From the output characteristics, the mobility of the field effect was calculated to be about 1x102 cm2(Vs)-1 in the saturation region. The TFT element formed on a glass substrate had similar characteristics.

[000291] The elements formed in the PET film were curved to a curvature radius of 30 mm and, in this state, the characteristics of the transistor were measured. No change in transistor characteristics was observed.

(Preparation of TFT Element Using In-Sn-O Amorphous Oxide Film by PLD Process)

[000292] A top door type TFT element shown in figure 5 was prepared.

[000293] Firstly, an In-Sn-O type amorphous oxide film was formed at a thickness of 100 nm as channel layer 2 on a poly(ethylene terephthalate) (PET) film 1 by the PDL method.

[000294] Additionally, another In-Sn-O type amorphous film with greater electroconductivity and a gold layer were laminated, each 30 nm thick, by the PLD method at oxygen partial pressure less than 1 Pa in the chamber and applying a voltage of zero volts to the oxygen radical generation assembly. Hence, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peeling method.

[000295] Finally, a film of Y2O3 as the gate insulator 3 was formed by electron beam vapor deposition. In addition to this, a gold film was formed and from it the gate terminal 4 was formed by photolithography and a peel-off method.

Evaluation of TFT Element Characteristics

[000296] TFT elements formed in a PET film were examined with regard to current-voltage characteristics at room temperature. The drain current IDS increased with increasing drain voltage VDS, which shows that the channel is an n-type conductor. This is consistent with the fact that an amorphous In-Sn-O type amorphous oxide film is an n-type conductor. The IDS became saturated (throttled) at about VDS = 6 V, which is typical behavior for a transistor. A current flow of IDS = 5x10-8 A was caused at VG = 0 V, and a current flow of IDS = 5x10-5 A was caused at VG = 10 V. This corresponds to electron carrier induction by polarization of door on the insulator, the amorphous oxide film type In-Sn-O.

[000297] The on-off ratio of the transistor was about 1x103. From the output characteristics, the field effect mobility was calculated to be about 5 cm2(Vs)-1 in the saturation region. The TFT element formed on a glass substrate had similar characteristics.

[000298] The elements formed in the PET film were curved to a curvature radius of 30 mm and, in this state, the characteristics of the transistor were measured. No changes were caused to the characteristics of the transistor.

(Preparation of the TFT Electrode Using Amorphous Oxide Film type In-Ga-O by PLD Process)

[000299] A top door type TFT element shown in figure 5 was prepared.

[000300] Firstly, an In-Ga-O type amorphous oxide film was formed at a thickness of 120 nm as channel layer 2 on a poly(ethylene terephthalate) (PET) film 1 by the PDL method shown in example 6 .

[000301] Additionally, another In-Ga-O type amorphous film with greater electroconductivity and a gold layer were laminated, each 30 nm thick, by the PLD method at oxygen partial pressure less than 1 Pa in the chamber and applying a voltage of zero volts to the oxygen radical generation assembly. Hence, the drain terminal 5 and the source terminal 6 were formed by photolithography and a peeling method.

[000302] Finally, a Y2O3 film as gate insulator 3 was formed by an electron beam vapor deposition method. In addition to this, a gold film was formed and from it the gate terminal 4 was formed by photolithography and a peel-off method.

Evaluation of TFT Element Characteristics

[000303] TFT elements formed in a PET film were examined with regard to current-voltage characteristics at room temperature. The drain current IDS increased with increasing drain voltage VDS, which shows that the channel is an n-type conductor. This is consistent with the fact that an amorphous In-Ga-O type amorphous oxide film is an n-type conductor. The IDS became saturated (throttled) at about VDS = 6 V, which is typical behavior for a transistor. A current flow of IDS = 1x10-8 A was caused at VG = 0 V, and a current flow of IDS = 1x10-5 A was caused at VG = 10 V. This corresponds to electron carrier induction by the polarization of door on the insulator, the amorphous oxide film type In-Ga-O.

[000304] The on-off ratio of the transistor was about 1x102. From the output characteristics, the mobility of the field effect was calculated to be about 0.8 cm2(Vs)-1 in the saturation range. The TFT element formed on a glass substrate had similar characteristics.

[000305] The elements formed in the PET film were curved to a curvature radius of 30 mm and, in this state, the characteristics of the transistor were measured. This does not cause a change in the characteristics of the transistor.

[000306] The amorphous oxide of electron carrier concentration less than 1x1018/cm2 is used as the channel layer of the TFT. The electron carrier concentration is preferably not greater than 1x1017/cm3, even more preferably not greater than 1x1016/cm3.

[000307] An embodiment of a light-emitting device according to the present invention will now be shown below.

(Example 1)

[000308] An example of a light-emitting device will be described in detail with reference to an embodiment.

[000309] An amorphous thin film of In-Ga-Zn-O was formed on a substrate in order to acquire a composition of In:Ga:Zn = 0.98:1.02:4 using the PLD method already described.

[000310] An upper gate type MISFET element shown in figure 5 was prepared by the steps of:

[000311] firstly, form a semi-insulating amorphous InGaO3(ZnO)4 film in a thickness of 120 nm on the glass substrate (1), which is used as a channel layer (2), with the method of preparing the amorphous In-Ga-Zn-O thin film described above; layer an InGaO3(ZnO)4 film with high electroconductivity and a gold film, respectively, in a thickness of 30 nm and additionally on it with a pulsed laser deposition method in a chamber with an oxygen partial pressure less than 1 Pa, and form a drain terminal (5) and a source terminal (6) with a photolithographic method and a detachment technology; and finally forming a Y2O3 film that is used as a gate insulating film (3) with an electron beam vacuum deposition method (thickness: 90 nm, relative permittivity: about 15, and current density of leakage: 1x10-3A/cm2 when 0.5 MV/cm is applied), form a gold film on it and form a gate terminal (4) with the photolitrographic method and detachment technology.

(Evaluation of MISFET element characteristics)

[000312] Figure 6 shows current/voltage characteristics of a MISFET element measured at room temperature. When the drain voltage VDS increases, the drain current IDS also increases, which shows that a channel is an n-type semiconductor. The result is not contradictory to the fact that an amorphous semiconductor based on In-Ga-Zn-O is an n-type. The MISFET element showed the typical behavior of a semiconductor transistor in which an IDS saturates (throttles) at a VDS of about 6 V. As a result of having examined a gain characteristic, the threshold value of the gate voltage VGS showed about -0.5 V when a 4 V VDS was applied. Furthermore, an IDS current showed 1.0 x 10-5 amps when a FG of 10 V was applied. The result means that an amorphous semiconductor film based on In-Ga-Zn-O of an insulating material induced a carrier in it by a gate bias.

[000313] The on/off ratio of a transistor exceeded 1x103. Furthermore, as a result of calculating the electron field effect mobility from the output characteristics, the electron field effect mobility was about 7 cm2 (Vs)-1 in a saturation range. Similar measurement was made on the prepared element during irradiation of it with visible light, the element did not show any change in transistor characteristics. From this, it is understood that the prepared element can be used with an opening also in a type of emission from below, without needing to interrupt the light transistor region.

[000314] A MISFET element was formed with approximately the same method described above. But, after the MISFET element was prepared, an insulating film in the thickness of 300 nm was formed from it with a pulsed laser deposition method. At the same time, a contact hole for connecting a drain or source terminal with the bottom electrode was formed.

[000315] Subsequently, the Al film was formed in the thickness of 300 nm with a vacuum deposition method with resistance heating, and the film of an alloy of Al and Ag was formed in the thickness of 50 nm on it to a lower electrode . The bottom electrode was connected to a drain or source electrode through a contact hole.

[000316] Subsequently, a light-emitting layer of organic EL was prepared by forming the following films with a resist vapor deposition method: the tris(8-quinolinol)aluminum film with a thickness of 20 nm as a layer electron transport: 4,41-bis(2,2-diphenyl)vinyl film with the thickness of 40 nm as the light-emitting layer therein; the 4,4'-bis[1-naphthyl)-N-phenylamino]biphenyl film with the thickness of 20 nm as a hole transport layer; and the 4,4'-bis[N,N-diamino]-4'-phenyl-triphenylamine] film with the thickness of 60 nm as a hole injection layer.

[000317] Finally, the ITO film was formed at a thickness of 200 nm for a counter electrode with a target sputtering technique.

[000318] When the above-described element was activated by placing a source on it, blue light was emitted from the upper surface of the substrate, in other words, a type of emission from above the element.

(Example 2: type of emission from below)

[000319] Subsequently, an example of a preparation process for a light-emitting device of a bottom emission type, in which a drain electrode and a bottom electrode are directly connected will be described with reference to figure 9.

[000320] A MISFET element was formed with approximately the same method as modality 1 described above. But the drain electrode was not formed, and an active layer 92 was left with the same area as the light-emitting layer. Subsequently, the InGaO3(ZnO)4 film with high electroconductivity was formed in the thickness of 200 nm on it, with an electrode 97 serving as the drain (or source) electrode and a bottom electrode, with a pulsed laser deposition method. in a chamber with an oxygen partial pressure of less than 1 Pa.

[000321] Next, a light-emitting layer of organic EL was made, forming an organic layer in a reverse order of modality 1 with a resistance evaporation method, and all integrated layers were referred to as the light-emitting layer. organic EL light.

[000322] Finally, the Li-doped Al film was formed at a thickness of 50 nm, and the Al film at a thickness of 200 nm as a counter electrode 99, with a resistance heating method.

[000323] When the above-described element is activated by placing a probe in contact with it, blue light was emitted from the back side of the substrate, in other words, a type of emission from below was obtained.

(Example 3: linear array light source)

[000324] A linear array light source according to the present invention will be described with reference to figure 10.

[000325] A plurality of light-emitting elements 101 and thin film transistors (TFT) 102 were arranged on a substrate in linear form, and they were electrically connected, as shown in figure 10. A linear array light source was prepared connecting a control circuit 103 to control light emission with the light-emitting elements and the TFTs. One output of the TFT (a source electrode or a drain electrode) was connected to a power source Vd through the light-emitting element, and the other was connected to a common electrical potential COM. Furthermore, the control circuit was connected to the gate electrode of the TFT.

[000326] When a TFT was turned on by a signal output of a control circuit, a light-emitting element emitted light. Specifically, the linear array light source could emit a desired linear light emission pattern when a signal from the control circuit was properly controlled.

[000327] Here, the light-emitting element may employ an arbitrary light-emitting element such as an organic electroluminescent element (an organic EL), an inorganic electroluminescent element (an inorganic EL), and an LED. Furthermore, the circuit configuration is not limited to this, but a plurality of TFTs can be arranged relative to a light-emitting element.

[000328] Thus, a configuration for activating a light-emitting element by an amorphous oxide TFT can be manufactured extremely easily, and inexpensively provide a linear array light source.

[000329] Figure 11 shows a sectional view of an example that has a configuration of a linear array light source in accordance with the present invention.

[000330] As shown in Figure 11, a linear array light source is prepared by arranging a TFT part and a section of the light-emitting element on a substrate, and each element on each portion. Figure 11 shows a case of using an organic EL element as a light-emitting element, and the above-described amorphous oxide TFT in a portion of the TFT.

[000331] In the figure, reference number 2100 denotes a substrate, reference number 2101 a channel layer, reference number 2102 a source electrode, reference number 2103 a gate insulating film, reference number 2104 a gate electrode, reference number 2105 a drain electrode, reference number 2106 a top electrode (first electrode), reference number 2107 an electron transport layer, reference number 2108 an emitting layer reference number 2109 a hole transport layer, reference number 2110 a transparent electrode layer, reference number 2111 an insulating layer, reference number 2150 a TFT section and reference number 2160 a section of the light-emitting element.

[000332] Figure 11 shows an example of connecting the drain electrode 2105 to the transparent electrode layer 2110 of the light-emitting element section. However, there is also a case of connecting the source electrode 2102 to the transparent electrode layer 2110, depending on the layer constitution of the light-emitting layer.

[000333] As for a preparation method, the linear array light source was prepared by the steps of forming an amorphous oxide TFT at a predetermined position on a substrate with the above-described technique, then an organic EL element, and additionally the electrical connection to each other.

[000334] At this time, when a gate oxide film was formed from an amorphous oxide TFT, the same insulating layer was formed on a portion in which an organic EL element was arranged. The organic EL element was prepared by placing a mask on a substrate, and sequentially forming a transparent electrode layer, subsequently a hole transport layer, a light emitting layer, an electron transport layer and a top electrode layer. During the aforementioned steps, the transparent electrode layer was connected to a drain electrode layer. Finally, several wirings were formed by an aluminum film or similar.

[000335] Here, an arbitrary transparent electroconductive film such as In2O3:Sn can be used as a transparent electrode layer. A material that is used in a general organic EL element can be applied to a hole transport layer, a light-emitting layer, an electron transport layer and an upper electrode layer. For example, α-NPD can be used as the hole transport layer, CBP doped with 6% IR(ppy)3 as the light-emitting layer, Alq3 as the electron transport layer, and AgMg as the top electrode layer .

[000336] In the description presented,

[000337] Alq3 means an aluminum-quinolinol complex;

[000338] α-NPD; It is

[000339] Ir(ppy)3 means an iridium-phenyl pyridine complex.

[000340] In the presented configuration, light emitted by a light-emitting element passed through a transparent electrode and was emitted from one side of the substrate, as shown by arrow 2170 in the figure.

[000341] Thus, the linear array light source was small, light and cheap.

[000342] As another configuration of a linear array light source, there may be the array configuration of an organic EL element on a top of a TFT placed on a substrate, as shown in figure 12. The linear array light source The aforementioned linear arrangement can make the light emitted by a light-emitting element pass through a section of the TFT and emanate from the substrate side, making an amorphous oxide TFT a transparent device by preparing an electrode with a transparent electrode, such as In2O3:Sn .

[000343] In Figure 12, reference number 2200 denotes a substrate, reference number 2201 a channel layer, reference number 2202 a source electrode, reference number 2203 a gate insulating film, number number reference number 2204 a gate electrode, reference number 2205 a drain electrode, reference number 2206 a top electrode (a first electrode), reference number 2207 an electron transport layer, reference number 2208 a layer reference number 2209 a hole transport layer, reference number 2210 a transparent electrode layer, reference number 2211 an insulating layer, reference number 2250 a TFT section and reference number 2260 a section of the light-emitting element.

[000344] Figure 12 shows an example of connecting the drain electrode 2205 to the transparent electrode layer 2210 of the light-emitting element section. However, there is also a case of connecting the source electrode 2202 to the transparent electrode layer 2210, depending on the layer constitution of the light-emitting layer.

[000345] The configuration thus formed causes light to emanate in the manner indicated by arrow 2270, allows the substrate surface to be effectively used, and can make the organic EL elements of the linear array light source arrangement therein at a high density, and /or acquire a large light-emitting area (an open area ratio). The linear array light source thus obtained is small, light and inexpensive.

(Example 4: application to a copy machine and page printer)

[000346] Next, a linear array light source applied to a copying machine or a page printer will be described.

[000347] Most copy machines or page printers generally have a system for printing data on a traction medium, scanning a laser beam onto a photoconductive drum using a lens and a polygonal mirror to print data onto it, and recording the data on the photoconductor drum.

[000348] On the other hand, the aforementioned devices can be small and cheap, if a linear array light source is used in accordance with the present invention, by virtue of directly irradiating a photoconductive drum with light emitted from a light-emitting element without passing light through a lens system, as shown in figure 13. As a result, the aforementioned devices do not require a large optical system and, correspondingly, can be miniaturized and reduce manufacturing costs. If necessary, the aforementioned devices can be arranged in a single optical system such as a SELFOC lens between the light-emitting element and the drum.

[000349] In figure 13, reference number 2300 denotes a linear array light source, and reference number 2350 a photoconductive drum.

[000350] During the preparation of the cited page copying machine or printer, it is preferable to unify the cited linear array light source with the photoconductive drum cartridge.

[000351] The linear array light source is cheap and therefore disposable, and as a result, it can make the copy machine or page printer maintenance-free by preparing a single-piece structure combined with the photoconductive drum, while at the same time making use of the aforementioned characteristics. The above-described light source may be arranged outside the photoconductor (a photoconductor drum) shown in the present embodiment, or may also be arranged on the inside.

[000352] When an electronography apparatus employs the linear array light source in accordance with the present embodiment, the electronography apparatus forms an image by using an electrifier to electrify the photoreceptor (a photoconductive drum), and exposing the light source to illuminating the photoreceptor to form a latent image in the photoreceptor and a developing device for revealing the aforementioned latent image; and employs the linear array light source according to the present invention for exposure light source. (Industrial Applicability)

[000353] The light-emitting device according to the present invention forms a thin film of a semiconductor on a flexible material including a plastic film, and can be applied to a wide area of uses, including a flexible display unit, a IC board and an ID tag.

[000354] The light-emitting device can also be applied to a linear array light source, a copying machine, a page printer and an integrated drum cartridge.

[000355] This application claims priority to Japanese patent application 2004-326687 filed on November 10, 2004, which is hereby incorporated herein by reference.

Claims (16)

1. Light-emitting device having a light-emitting element (77-79; 97-99; 2106-2110; 2206-2210) comprising first and second electrodes (77; 79; 97, 99; 2106, 2110; 2206 , 2210) and a light-emitting layer (78; 98; 2108; 2208) that exists between the first and second electrodes, and a field effect transistor (70; 72-75; 92-95; 2101-2105; 2201 -2205) is to activate the light-emitting element, characterized by the fact that the active layer of the field effect transistor is formed from an amorphous oxide that has an electron carrier concentration of less than 1018/cm3 at a temperature of 25 °C; wherein the amorphous oxide is any one selected from the group consisting of an oxide containing In, Zn and Sn and an oxide containing In, Zn and Ga; wherein the active layer presents a halo pattern and no characteristic diffraction lines in X-ray diffraction spectrometry; and the active layer has an electron mobility greater than 1 cm2/V.s. 2. Light-emitting device according to claim 1, characterized by the fact that the light-emitting element and the field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) are arranged on an optically transparent substrate, and the light emitted by the light-emitting layer (78; 98; 2108; 2208) passes through the substrate. 3. Light-emitting device according to claim 2, characterized by the fact that the field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) is arranged between the substrate and the light-emitting layer (78; 98; 2108; 2208). 4. Light-emitting device according to claim 1, characterized by the fact that the light-emitting element and the field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) are arranged on an optically transparent substrate, and the light emitted by the light-emitting layer (78; 98; 2108; 2208) passes through the substrate and the amorphous oxide. 5. Light-emitting device according to claim 4, characterized by the fact that the field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) is arranged between the substrate and the light-emitting layer (78; 98; 2108; 2208). 6. Light-emitting device according to claim 1, characterized by the fact that at least one of the drain electrode of the field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) and the second electrode is formed from an optically transparent electroconductive oxide. 7. Light-emitting device according to claim 1, characterized in that the light-emitting element is an electroluminescent element. 8. The light-emitting device of claim 1, wherein a plurality of light-emitting elements are arranged in at least a single row. 9. The light-emitting device of claim 8, wherein the light-emitting element is arranged to be adjacent to the field-effect transistor. 10. An electrophotographic device comprising: a photoreceptor, an electrifier for electrifying the photoreceptor, an exposure light source for exposing the photoreceptor to form a latent image on the photoreceptor, and a developing unit for revealing the latent image, the electrophotographic device being characterized by the fact that the exposure light source has the light emitting device as defined in claim 8. 11. Light-emitting device having a light-emitting element comprising first and second electrodes (77; 79; 97, 99; 2106, 2110; 2206, 2210) and a light-emitting layer (78; 98; 2108; 2208 ) that exists between the first and second electrodes, and a field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) to activate the light-emitting element, characterized by the fact that the active layer of the field effect transistor includes such a transparent amorphous oxide semiconductor capable of realizing a normally off state; and the transparent amorphous oxide semiconductor is any one selected from the group consisting of an oxide containing In, Zn and Sn and an oxide containing In, Zn and Ga; the active layer presents a halo pattern and no characteristic diffraction lines in an X-ray diffraction spectrometry; and the active layer has an electron mobility greater than 1 cm2/V.s. 12. The light-emitting device of claim 11, wherein the transparent amorphous oxide semiconductor has an electron carrier concentration of less than 1018/cm3 at a temperature of 25°C that is sufficiently low to perform the normally off state. 13. An active matrix display device comprising a light-emitting element comprising first and second electrodes (77; 79; 97, 99; 2106, 2110; 2206, 2210) and a light-emitting layer (78; 98; 2108; 2208) that exists between the first and second electrodes and a field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) for activating the light-emitting element, and a light-emitting element circuit image arranged in the form of a two-dimensional matrix, characterized by the fact that the active layer of the field effect transistor includes a transparent amorphous oxide semiconductor capable of realizing a normally off state; and the transparent amorphous oxide semiconductor is any one selected from the group consisting of an oxide containing In, Zn and Sn and an oxide containing In, Zn and Ga; the active layer presents a halo pattern and no characteristic diffraction lines in an X-ray diffraction spectrometry; and the active layer has an electron mobility greater than 1 cm2/V.s. 14. The active matrix display device of claim 13, wherein the transparent amorphous oxide semiconductor has an electron carrier concentration of less than 1x1018/cm3, which is sufficiently low to realize the normally off state. 15. Display article comprising: a light-emitting element comprising first and second electrodes (77; 79; 97, 99; 2106, 2110; 2206, 2210) and a light-emitting layer (78; 98; 2108; 2208) that exists between the first and second electrodes and a field effect transistor (70; 72-75; 92-95; 2101-2105; 2201-2205) to activate the light-emitting element, characterized by the fact that an active layer of the field effect transistor includes an amorphous oxide semiconductor; and the amorphous oxide semiconductor is any one selected from the group consisting of an oxide containing In, Zn and Sn and an oxide containing In, Zn and Ga; the active layer presents a halo pattern and no characteristic diffraction lines in an X-ray diffraction spectrometry; and the active layer has an electron mobility greater than 1 cm2/V.s. 16. The display article of claim 15, wherein the transistor is a normally-off type transistor.