JP2011228679A - Semiconductor device and method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film transistor using an oxide semiconductor film, the transistor which has stable electrical characteristics and excellent reliability.SOLUTION: A semiconductor device having stable electrical characteristics can be manufactured by adjusting an off-current value per 1 μm of a channel width to 1×10A or less within the temperature limits of -25°C and 150°C for a channel length, which is within the limits of 1.5 μm and 100 μm, or preferably within the limits of 3 μm and 10 μm, of a thin-film transistor using an oxide semiconductor film. Power consumption due to variation of an off-current can be reduced particularly in a display device as one embodiment of a semiconductor device.

Description

The present invention relates to a semiconductor device using an oxide semiconductor and a manufacturing method thereof.

Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

In recent years, a technique for forming a thin film transistor (TFT) using a semiconductor thin film (having a thickness of about several to several hundred nm) formed on a substrate having an insulating surface has attracted attention. Thin film transistors are widely applied to electronic devices such as ICs and electro-optical devices, and development of switching devices for image display devices is urgently required. Further, metal oxides have attracted attention as semiconductor thin films, and there are various metal oxides that are used in various applications. In particular, indium oxide is a well-known material as a metal oxide, and is used as a transparent electrode material required for liquid crystal displays and the like.

Some metal oxides exhibit semiconductor properties. Examples of metal oxides that exhibit semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, and zinc oxide. Thin film transistors that use such metal oxides that exhibit semiconductor characteristics as a channel formation region are already known. (Patent Document 1 and Patent Document 2).

JP 2007-123861 A JP 2007-96055 A

In an active matrix display device, the electrical characteristics of the thin film transistors constituting the circuit are important, and the electrical characteristics affect the performance of the display device. In particular, power consumption during non-operation (power consumption during standby) due to an increase in off-state current (also referred to as leakage current or Ioff) is important among the electrical characteristics of thin film transistors.

In the case of an n-channel thin film transistor, a thin film transistor in which a channel is formed and drain current flows only after a positive voltage is applied to the gate voltage. A thin film transistor in which an off-current flows in a state where a voltage applied to a gate is negative is not suitable as a thin film transistor used for a circuit.

For example, when a thin film transistor included in a circuit in a semiconductor device has a large off current, current leakage due to the increase in the off current may occur. An object of one embodiment of the present invention is to provide a thin film transistor that operates stably in a wide temperature range and a semiconductor device using the thin film transistor. Note that in this specification and the like, the off-state current of a thin film transistor refers to a current value when a voltage applied to a gate is a negative voltage.

One embodiment of the present invention disclosed in this specification includes a gate electrode layer over a substrate having an insulating surface, a gate insulating layer over the gate electrode layer, and an oxide semiconductor layer over the gate insulating layer. An insulating layer in contact with a part of the oxide semiconductor layer over the gate insulating layer, the oxide semiconductor layer, the source electrode layer, and the drain electrode layer; In a temperature range of −25 ° C. to 150 ° C., the semiconductor device is characterized in that the off-state current value per channel width is 1 × 10 ⁻¹² A or less.

In the above structure, the channel length of the oxide semiconductor layer may be not less than 1.5 μm and not more than 100 μm. The channel length of the oxide semiconductor layer may be 3 μm or more and 10 μm or less.

In one embodiment of the present invention disclosed in this specification, a gate electrode layer is formed over a substrate having an insulating surface, the gate insulating layer is formed over the gate electrode layer, and the oxide semiconductor is formed over the gate insulating layer. After forming an oxide semiconductor layer, a first heat treatment and a second heat treatment are performed to form a source electrode layer and a drain electrode layer over the oxide semiconductor layer, a gate insulating layer, an oxide layer An insulating layer in contact with part of the oxide semiconductor layer is formed over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer, and after the insulating layer is formed, a third heat treatment is performed. Is the method.

In the above structure, the first heat treatment is preferably performed in a nitrogen atmosphere or a rare gas atmosphere. Further, the first heat treatment is preferably performed at a temperature of 350 ° C to 750 ° C.

In the above structure, the second heat treatment is preferably performed in an air atmosphere or an oxygen atmosphere. The second heat treatment is preferably performed at 100 ° C. or higher and lower than the first heat treatment temperature.

The above configuration solves at least one of the above problems.

A thin film represented by InMO ₃ (ZnO) _m (m> 0) is formed using the oxide semiconductor used in this specification, and a thin film transistor using the thin film as an oxide semiconductor layer is manufactured. However, m is not necessarily an integer. Note that M represents one metal element or a plurality of metal elements selected from Ga, Fe, Ni, Mn, and Co. For example, M may be Ga, and may contain the above metal elements other than Ga, such as Ga and Ni or Ga and Fe. In addition to the metal element contained as M, the oxide semiconductor may contain Fe, Ni, other transition metal elements, or oxides of the transition metal in addition to the metal element contained as M. In this specification, among oxide semiconductor layers having a structure represented by InMO ₃ (ZnO) _m (m> 0), an oxide semiconductor having a structure containing Ga as M is represented by In—Ga—Zn—O-based oxidation. It is called a physical semiconductor and its thin film is also called an In—Ga—Zn—O-based non-single-crystal film.

In addition to the above oxide semiconductors applied to the oxide semiconductor layer, In—Sn—Zn—O-based, In—Al—Zn—O-based, Sn—Ga—Zn—O-based, Al—Ga— Zn-O, Sn-Al-Zn-O, In-Zn-O, In-Ga-O, Sn-Zn-O, Al-Zn-O, In-O, Sn-O And Zn—O-based oxide semiconductors can be used. Further, silicon oxide may be included in the oxide semiconductor layer. By including silicon oxide (SiOx (X> 0)) that inhibits crystallization in the oxide semiconductor layer, crystallization is suppressed when heat treatment is performed after the formation of the oxide semiconductor layer during the manufacturing process. can do. Note that the oxide semiconductor layer is preferably in an amorphous state and may be partially crystallized.

Further, depending on the heat treatment conditions or the material of the oxide semiconductor layer, the oxide semiconductor layer may be changed from an amorphous state to a microcrystalline film or a polycrystalline film. Even in the case of a microcrystalline film or a polycrystalline film, switching characteristics can be obtained as a TFT.

A thin film transistor having a small electric current fluctuation range and stable electric characteristics can be manufactured and provided. Thus, a semiconductor device including a thin film transistor with favorable electric characteristics and high reliability can be provided.

8A and 8B illustrate a manufacturing process of a semiconductor device. 6A and 6B illustrate a semiconductor device. FIG. 9 shows an analysis method and a hydrogen concentration in an oxide semiconductor layer. 3 is a graph showing off-current characteristics of the thin film transistor of Example 1. The figure which shows the cross-sectional structure used for the calculation of a semiconductor device. FIG. 6 illustrates a structure assumed in calculation of a semiconductor device. FIG. 10 illustrates a block diagram of a semiconductor device. 8A and 8B illustrate a structure and operation of a signal line driver circuit. FIG. 3 is a circuit diagram illustrating a configuration of a shift register. 6 is a configuration and timing chart illustrating the operation of a shift register. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a pixel equivalent circuit of a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. FIG. 6 is a circuit diagram illustrating a configuration of a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. 6A and 6B illustrate a semiconductor device. FIG. 6 is a circuit diagram illustrating a configuration of a semiconductor device. FIG. 9 illustrates an example of an electronic book. FIG. 11 illustrates an example of a television device and a digital photo frame. The figure which shows the example of a game machine. The figure which shows the example of a portable computer and a mobile telephone. 4A and 4B illustrate calculation results of a semiconductor device. 4A and 4B illustrate calculation results of a semiconductor device. 4A and 4B illustrate calculation results of a semiconductor device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

(Embodiment 1)
In this embodiment, one embodiment of a method for manufacturing the thin film transistor 150 illustrated in FIG. 1E is described with reference to FIGS. 1A to 1E which are cross-sectional views of a thin film transistor manufacturing process. Note that FIG. 1F is a top view of the thin film transistor 150 illustrated in FIG. The thin film transistor 150 has one of bottom gate structures called a channel etch type.

First, in order to form a metal conductive film over a substrate 100 which is a substrate having an insulating surface and process it into a desired shape, the gate electrode layer 101 is provided by performing a photolithography process and an etching process using a photomask. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

As the substrate 100, a glass substrate is preferably used. As the glass substrate used as the substrate 100, a glass substrate having a strain point of 730 ° C. or higher is preferably used when the temperature of the subsequent heat treatment is high. The substrate 100 is made of a glass material such as aluminosilicate glass, aluminoborosilicate glass, or barium borosilicate glass. A more practical heat-resistant glass can be obtained by containing more barium oxide (BaO) than boric acid. For this reason, it is preferable to use a glass substrate containing more BaO than B ₂ O ₃ .

Note that a substrate formed of an insulator such as a ceramic substrate, a quartz glass substrate, a quartz substrate, or a sapphire substrate may be used instead of the substrate 100 described above. In addition, crystallized glass or the like can be used.

An insulating film serving as a base film may be provided between the substrate 100 and the gate electrode layer 101. The base film has a function of preventing diffusion of an impurity element from the substrate 100 and has a stacked structure including one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. Can be formed.

By including a halogen element such as chlorine or fluorine in the base film, the function of preventing diffusion of impurity elements from the substrate 100 can be further enhanced. The concentration of the halogen element contained in the base film is such that the concentration peak obtained by analysis using SIMS (secondary ion mass spectrometer) is 1 × 10 ¹⁵ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. do it.

As the gate electrode layer 101, a metal conductive film can be used. As a material for the metal conductive film, an element selected from Al, Cr, Cu, Ta, Ti, Mo, W, an alloy containing the above-described elements as a component, or an alloy combining the above-described elements may be used. preferable. For example, an aluminum layer on a titanium layer and a three-layer structure in which a titanium layer is laminated on the aluminum layer, or a three-layer structure in which an aluminum layer is laminated on a molybdenum layer and a molybdenum layer is laminated on the aluminum layer. A structure is preferable. Of course, the metal conductive film may have a single layer, a two-layer structure, or a stacked structure of four or more layers.

Next, the gate insulating layer 102 is formed over the gate electrode layer 101.

The gate insulating layer 102 can be formed as a single layer or a stack of silicon oxide layers, silicon nitride layers, silicon oxynitride layers, or silicon nitride oxide layers by a plasma CVD method, a sputtering method, or the like. For example, a silicon oxynitride layer may be formed by a plasma CVD method using SiH ₄ , oxygen, and nitrogen as a deposition gas. The thickness of the gate insulating layer 102 is 100 nm to 500 nm. In the case of stacking, for example, the first gate insulating layer having a thickness of 50 nm to 200 nm and the thickness of 5 nm to 300 nm on the first gate insulating layer are used. The following second gate insulating layer is stacked.

Further, before the oxide semiconductor film is formed, heat treatment (400 ° C. or higher and lower than the strain point of the substrate) is performed in an inert gas atmosphere (nitrogen, helium, neon, argon, or the like), and hydrogen contained in the layer Alternatively, the gate insulating layer 102 from which impurities such as water are removed may be used.

Next, an oxide semiconductor film with a thickness of 5 nm to 200 nm, preferably 10 nm to 50 nm, is formed over the gate insulating layer 102. In order to make the oxide semiconductor film amorphous even when heat treatment for dehydration or dehydrogenation is performed after the oxide semiconductor film is formed, the film thickness is preferably as thin as 50 nm or less. By reducing the thickness of the oxide semiconductor film, crystallization can be suppressed when heat treatment is performed after the oxide semiconductor layer is formed.

Note that before the oxide semiconductor film is formed by a sputtering method, argon gas is introduced to generate plasma, and reverse sputtering is performed to remove dust attached to the surface of the gate insulating layer 102. . Reverse sputtering is a method in which a voltage is applied to the substrate side using an RF power source in an argon atmosphere without applying a voltage to the target side, so that the substrate surface is exposed to plasma and the surface is modified. Note that nitrogen, helium, or the like may be used instead of the argon atmosphere.

An oxide semiconductor film includes an In—Ga—Zn—O-based non-single-crystal film, an In—Sn—Zn—O-based film, an In—Al—Zn—O-based film, a Sn—Ga—Zn—O-based film, and an Al—Ga— film. Zn-O, Sn-Al-Zn-O, In-Ga-O, In-Zn-O, Sn-Zn-O, Al-Zn-O, In-O, Sn-O And Zn—O-based oxide semiconductor films are used. In this embodiment, for example, the film is formed by a sputtering method using an In—Ga—Zn—O-based metal oxide target. The oxide semiconductor film is formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a rare gas (typically argon) and oxygen atmosphere. Can do. Further, in the case of using a sputtering method, film formation is performed using a target containing 2 wt% or more and 10 wt% or less of SiO _2, and SiOx (X> 0) that inhibits crystallization is included in the oxide semiconductor film. It is preferable to suppress crystallization during the heat treatment for dehydration or dehydrogenation performed in this step. Note that a pulse direct current (DC) power supply is preferably used as the power supply because dust can be reduced and the film thickness can be uniform.

The relative density of the metal oxide in the metal oxide target is preferably 95% or more, more preferably 99% or more. Thus, the impurity concentration in the formed oxide semiconductor film can be reduced, and a thin film transistor with high electrical characteristics or high reliability can be obtained. In this embodiment, a metal oxide target with a relative density of metal oxide of 97% is used.

Sputtering methods include an RF sputtering method using a high frequency power source as a sputtering power source and a DC sputtering method using a direct current power source, and also a pulse DC sputtering method that applies a bias in a pulsed manner. The RF sputtering method is mainly used when an insulating film is formed, and the DC sputtering method is mainly used when a metal film is formed.

There is also a multi-source sputtering apparatus in which a plurality of targets of different materials can be installed. In the multi-source sputtering apparatus, different material films can be stacked in the same chamber, or a plurality of types of materials can be discharged simultaneously in the same chamber.

Further, there are a sputtering apparatus using a magnetron sputtering method having a magnet mechanism inside a chamber, and a sputtering apparatus using an ECR sputtering method using plasma generated using microwaves without using glow discharge.

In addition, as a film forming method using a sputtering method, a reactive sputtering method in which a target material and a sputtering gas component are chemically reacted during film formation to form a compound thin film thereof, or a voltage is applied to the substrate during film formation. There is also a bias sputtering method.

Alternatively, the gate insulating layer 102 and the oxide semiconductor film may be formed successively without exposure to the air. By depositing the film without exposing it to the atmosphere, each stacked interface can be formed without being contaminated by atmospheric components such as water and hydrocarbons and impurity elements floating in the atmosphere. Can be reduced.

Next, the oxide semiconductor film is processed into an island-shaped oxide semiconductor layer 103 by a photolithography process (see FIG. 1A). Further, a resist mask for forming the island-shaped oxide semiconductor layer 103 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Next, first heat treatment is performed so that the oxide semiconductor layer 103 is dehydrated or dehydrogenated. The temperature of the first heat treatment for dehydration or dehydrogenation is 350 ° C to 750 ° C, preferably 425 ° C. Note that when the temperature is 425 ° C. or higher, the heat treatment time may be one hour or shorter, but when the temperature is lower than 425 ° C., the heat treatment time is longer than one hour. For example, after a substrate is introduced into an electric furnace that is one of heat treatment apparatuses and the oxide semiconductor layer 103 is subjected to heat treatment in a nitrogen atmosphere, the oxide semiconductor layer 103 is not exposed to the air. The oxide semiconductor layer 103 can be obtained by preventing re-mixing of water and hydrogen. In this embodiment, the same furnace is used from the heating temperature T at which dehydration or dehydrogenation of the oxide semiconductor layer 103 is performed to a sufficient temperature at which water does not enter again. Slowly cool in a nitrogen atmosphere until the temperature drops to 100 ° C. or higher. Further, the present invention is not limited to a nitrogen atmosphere, and dehydration or dehydrogenation is performed in an inert gas atmosphere (helium, neon, argon, or the like).

Through the first heat treatment, atomic level rearrangement of the oxide semiconductor included in the oxide semiconductor layer 103 is performed. The first heat treatment is important in that it can release strain that hinders carrier movement in the oxide semiconductor layer 103.

Note that in the first heat treatment, it is preferable that water, hydrogen, or the like be not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm). Or less, preferably 0.1 ppm or less).

The heat treatment apparatus for the first heat treatment is not limited to an electric furnace, and may include a device for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

Further, depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, the oxide semiconductor layer may be crystallized to be a microcrystalline film or a polycrystalline film. Here, the oxide semiconductor layer may be a microcrystalline film with a crystallization rate of 80% or more. Further, depending on the material of the oxide semiconductor layer, the oxide semiconductor layer may have no crystal.

The first heat treatment of the oxide semiconductor layer can be performed on the oxide semiconductor layer before being processed into the island-shaped oxide semiconductor layer 103. In that case, after the first heat treatment, the substrate is taken out of the heating apparatus and a photolithography process is performed.

Here, the results of hydrogen concentration analysis when dehydrogenation is performed in the oxide semiconductor layer and when it is not performed will be described. FIG. 3A is a schematic cross-sectional view of a sample used in this analysis. An oxide oxynitride insulating layer 401 was formed over a glass substrate 400 by a plasma CVD method, and an In—Ga—Zn—O-based oxide semiconductor layer 402 was formed on the oxynitride insulating layer 401 to have a thickness of about 40 nm. The prepared sample was divided, one was not dehydrogenated, and the other was dehydrogenated at 650 ° C. for 6 minutes in a nitrogen atmosphere by the GRTA method. For each sample, the hydrogen concentration in the oxide semiconductor layer was measured to investigate the effect of dehydrogenation by heat treatment.

The hydrogen concentration in the oxide semiconductor layer was analyzed by secondary ion mass spectrometry (SIMS). FIG. 3B illustrates SIMS analysis results indicating the hydrogen concentration distribution in the film thickness direction of the oxide semiconductor layer. The horizontal axis indicates the depth from the sample surface, and the position at the depth of 0 nm at the left end corresponds to the sample outermost surface (the outermost surface of the oxide semiconductor layer). An analysis direction 403 illustrated in FIG. 3A indicates an analysis direction of SIMS analysis. The analysis was performed in a direction from the outermost surface of the oxide semiconductor layer toward the glass substrate 400. That is, the measurement was performed from the left end toward the right end on the horizontal axis in FIG. The vertical axis in FIG. 3B shows the hydrogen concentration in the sample at a specific depth and the oxygen ion intensity on a logarithmic axis.

In FIG. 3B, a hydrogen concentration profile 412 indicates a hydrogen concentration profile in the oxide semiconductor layer that is not dehydrogenated, and the hydrogen concentration profile 413 is obtained after dehydrogenation by heat treatment. 2 shows a hydrogen concentration profile in an oxide semiconductor layer. The oxygen ion intensity profile 411 indicates the oxygen ion intensity acquired at the same time when the hydrogen concentration profile 412 is measured. Since the oxygen ion intensity profile 411 does not have an extreme fluctuation and an almost constant ion intensity is obtained, it is understood that SIMS analysis is performed accurately. It should be noted that the oxygen ion intensity was measured in the same manner during the measurement of the hydrogen concentration profile 413, and an almost constant ion intensity was also obtained here. The hydrogen concentration profile 412 and the hydrogen concentration profile 413 are quantified using a standard sample manufactured using the same In—Ga—Zn—O-based oxide semiconductor layer as the sample.

In addition, it is known that SIMS analysis has difficulty in accurately obtaining data in the vicinity of the sample surface and in the vicinity of the laminated film interface of different materials. In this analysis, it is considered that accurate data has not been obtained from the outermost surface of the sample to a depth of about 15 nm, and therefore, evaluation was performed using a profile after a depth of 15 nm.

From the hydrogen concentration profile 412, hydrogen is about 3 × 10 ²⁰ atoms / cm ³ or more, about 5 × 10 ²⁰ atoms / cm ³ or less, and an average hydrogen concentration is about 4 in an oxide semiconductor layer that has not been dehydrogenated. It can be seen that × 10 ²⁰ atoms / cm ^{3 is} contained. In addition, the hydrogen concentration profile 413 indicates that the average hydrogen concentration in the oxide semiconductor layer can be reduced to about 2 × 10 ¹⁹ atoms / cm ³ by dehydrogenation.

In this analysis, the hydrogen concentration was reduced by SIMS analysis of a sample that had been heat-treated at 650 ° C. for 6 minutes in a nitrogen atmosphere by the GRTA method, so that dehydrogenation from the oxide semiconductor layer was confirmed in this heat-treatment step. did it.

Next, a second heat treatment is performed. The temperature of the second heat treatment is 100 ° C. or higher and lower than the temperature of the first heat treatment. For example, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and heat treatment is performed in an air atmosphere or an oxygen atmosphere.

Next, a conductive film for forming a source electrode layer and a drain electrode layer is formed over the gate insulating layer 102 and the oxide semiconductor layer 103.

As the conductive film for forming the source electrode layer and the drain electrode layer, a metal conductive film can be used like the gate electrode layer 101. As a material for the metal conductive film, an element selected from Al, Cr, Cu, Ta, Ti, Mo, W, an alloy containing the above-described elements as a component, or an alloy combining the above-described elements may be used. preferable. For example, an aluminum layer on a titanium layer and a three-layer structure in which a titanium layer is laminated on the aluminum layer, or a three-layer structure in which an aluminum layer is laminated on a molybdenum layer and a molybdenum layer is laminated on the aluminum layer. A structure is preferable. Of course, the metal conductive film may have a single layer, a two-layer structure, or a stacked structure of four or more layers.

A source electrode layer 105a and a drain electrode layer 105b are formed from a conductive film for forming a source electrode layer and a drain electrode layer by a photolithography process using a photomask (see FIG. 1B). At this time, part of the oxide semiconductor layer 103 is also etched, whereby the oxide semiconductor layer 103 having a groove (a depressed portion) is formed.

Note that a resist mask for forming the source electrode layer 105a and the drain electrode layer 105b may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Further, an oxide conductive layer whose resistance is lower than that of the oxide semiconductor layer 103 may be formed between the oxide semiconductor layer 103 and the source electrode layer 105a and the drain electrode layer 105b. With such a stacked structure, the breakdown voltage of the thin film transistor can be improved. Specifically, the carrier concentration of the oxide conductive layer with low resistance is preferably in the range of, for example, 1 × 10 ²⁰ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less.

Next, the insulating layer 107 which covers the gate insulating layer 102, the oxide semiconductor layer 103, the source electrode layer 105a, and the drain electrode layer 105b and is in contact with part of the oxide semiconductor layer 103 is formed (see FIG. 1C). . The insulating layer 107 has a thickness of at least 1 nm and can be formed as appropriate by a method such as CVD or sputtering that does not mix impurities such as water and hydrogen into the insulating layer 107. Here, the insulating layer 107 is formed by a sputtering method. The insulating layer 107 formed in contact with part of the oxide semiconductor layer 103 does not contain impurities such as moisture, hydrogen ions, oxygen ions, and OH ⁻ , and blocks the entry of these from the outside. As the insulating film, a silicon oxide film, a silicon nitride oxide film, a silicon nitride film, a gallium oxide film, an aluminum oxide film, an aluminum oxynitride film, or an aluminum nitride film can be typically used.

The insulating layer 107 may have a structure in which a silicon nitride film or an aluminum nitride film is stacked over a silicon oxide film, a silicon nitride oxide film, an aluminum oxide film, or an aluminum oxynitride film. In particular, a silicon nitride film is preferable because it does not contain moisture, hydrogen ions, oxygen ions, OH ^−, or the like and easily blocks entry of these from the outside.

The substrate temperature at the time of forming the insulating layer 107 may be room temperature or higher and 300 ° C. or lower, and the silicon oxide film is formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or It can be performed in a rare gas (typically argon) and oxygen atmosphere. Further, a silicon oxide target or a silicon target can be used as the target. For example, silicon oxide can be formed by a sputtering method in an oxygen atmosphere using a silicon target.

Next, a third heat treatment is performed. The third heat treatment is performed at a temperature of 100 ° C. or higher and lower than the temperature of the first heat treatment. For example, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and heat treatment is performed in a nitrogen atmosphere. The third heat treatment may be performed at any time as long as it is a step after the formation of the insulating layer 107.

Through the above steps, the gate electrode layer 101 is provided over the substrate 100 which is a substrate having an insulating surface, the gate insulating layer 102 is provided over the gate electrode layer 101, and the oxide semiconductor layer is provided over the gate insulating layer 102. 103, the source electrode layer 105a and the drain electrode layer 105b are provided over the oxide semiconductor layer 103, and cover the gate insulating layer 102, the oxide semiconductor layer 103, the source electrode layer 105a, and the drain electrode layer 105b. A channel-etched thin film transistor 150 provided with the insulating layer 107 in contact with part of the physical semiconductor layer 103 can be formed (see FIG. 1E).

FIG. 1F is a top view of the thin film transistor 150 described in this embodiment. FIG. 1E illustrates a cross-sectional structure of the portion X1-X2 in FIG. In FIG. 1 (F), L indicates the channel length, and W indicates the channel width. A indicates the length of a region where the oxide semiconductor layer 103 does not overlap with the source electrode layer 105a and the drain electrode layer 105b in a direction parallel to the channel width direction. Ls indicates a length in which the source electrode layer 105a and the gate electrode layer 101 overlap, and Ld indicates a length in which the drain electrode layer 105b and the gate electrode layer 101 overlap.

In this embodiment, the thin film transistor 150 is described using a single-gate thin film transistor; however, a multi-gate thin film transistor including a plurality of channel formation regions and a second gate electrode layer over the insulating layer 107 as needed. A thin film transistor having a structure can be provided.

In this embodiment, the method for manufacturing the channel-etched thin film transistor 150 is described; however, the structure of this embodiment is not limited to this. A bottom contact type (also called reverse coplanar type) thin film transistor 160 having a bottom gate structure as shown in FIG. 2A and a channel protection type (channel having a channel protection layer 110 as shown in FIG. 2B). The thin film transistor 170 or the like (also referred to as a stop type) can be formed using a similar material and method. FIG. 2C illustrates another example of a channel-etched thin film transistor. The width of the gate electrode layer 101 of the thin film transistor 180 illustrated in FIG. 2C is larger than the width of the oxide semiconductor layer 103.

Note that the channel length of the thin film transistor (L in FIG. 1F) is defined by the distance between the source electrode layer 105a and the drain electrode layer 105b, but the channel length of the channel protective thin film transistor is the direction in which carriers flow. Is defined by the width of the channel protective layer in the direction parallel to.

According to this embodiment, the off-state current per channel width of a thin film transistor including an oxide semiconductor layer can be 1 × 10 ⁻¹² A or less.

In addition, when the channel length of the thin film transistor is in the range of 3 μm to 10 μm or in the range of 1.5 μm to 100 μm, the channel width of the thin film transistor in the operating temperature range from −25 ° C. to 150 ° C. It can be 1 × 10 ⁻¹² A or less. It is preferable to set the channel length of the thin film transistor to 1.5 μm or more, or 3 μm or more because the short channel effect can be suppressed.

Here, evaluation results of thin film transistor characteristics in an environment from −25 ° C. to 150 ° C. using the thin film transistor having the cross-sectional structure shown in FIG.

First, a tungsten layer is formed as a gate electrode layer 802 with a thickness of 100 nm over a glass substrate 801, and an oxynitride layer is formed as a gate insulating layer 803 with a thickness of 100 nm over the gate electrode layer 802. An In—Ga—Zn—O-based oxide semiconductor layer 804 is formed to a thickness of 30 nm over the insulating layer 803, and a titanium layer is formed as the source electrode layer 805 and the drain electrode layer 806 over the oxide semiconductor layer 804. The thin film transistor was formed. The channel length L of the thin film transistor was 3 μm, and the channel width W was 20 μm.

Next, for the thin film transistor, the substrate temperature at the time of measurement is changed to −25 ° C., 0 ° C., 25 ° C., 50 ° C., 100 ° C., and 150 ° C., and the off current of the thin film transistor at each substrate temperature (operating temperature). Was measured. The off-current characteristics were measured by setting the voltage between the source and the drain (hereinafter referred to as the drain voltage or Vd) to 10V, and the voltage between the source and the gate (hereinafter referred to as the gate voltage or Vg) at -10V. .

FIG. 4B shows the off-current measurement result obtained in this measurement. The measurement temperature on the horizontal axis indicates the substrate temperature (operating temperature) when measuring the off-current of the thin film transistor on a linear scale, and the vertical axis indicates the off-current (Ioff) at each substrate temperature on the log scale.

In FIG. 4B, “□” in the figure indicates the off-state current when the amorphous silicon film is used as the semiconductor layer, and “●” in the figure indicates the case where the oxide semiconductor film is used as the semiconductor layer. Off current is shown.

FIG. 4B shows that the off-current when the amorphous silicon film is used as the semiconductor layer increases as the substrate temperature at the time of measurement increases. When the oxide semiconductor film is used as the semiconductor layer, the off-state current is 1 pA, that is, 1 × 10 ⁻¹² A or less even when the substrate temperature at the time of measurement is increased.

Here, the temperature dependence of the off-state current (Ioff) will be considered below.

It is generally known that the off-state current of a thin film transistor flows due to the generation of electrons and holes (hereinafter referred to as carrier generation) and the recombination of electrons and holes (hereinafter referred to as carrier recombination). . In addition, as carrier recombination, electrons are excited through a direct recombination in which electrons are excited from a valence band (Ev) to a conduction band (Ec) and a localized level (Et) in a band gap (Eg). There is an indirect recombination.

In the case of a semiconductor with a narrow band gap, the heat energy for exciting electrons is small, so that direct recombination and indirect recombination are likely to occur. However, in the case of a semiconductor with a wide band gap (Eg) such as an oxide semiconductor. It is assumed that direct recombination and indirect recombination are unlikely to occur because excitation of electrons requires large thermal energy.

In addition, when the band gap is wide, the intrinsic carrier concentration of the semiconductor is extremely reduced, and the total number of carriers is extremely reduced. As a result of the small total number of carriers, the probability of carrier generation and carrier recombination is also reduced, so that the off-current is assumed to be small.

An attempt was made to calculate the temperature dependence of the off-state current of a thin film transistor in semiconductors having different band gaps (Eg).

The structure assumed in the calculation is shown in FIG. A tungsten layer is formed to a thickness of 100 nm as the gate electrode layer 701, an oxynitride layer is formed to a thickness of 100 nm as the gate insulating layer 702, and a semiconductor layer is formed over the gate insulating layer 702. A thin film transistor in which 703 is formed with a thickness of 30 nm and a source electrode layer 704 and a drain electrode layer 705 are formed over the semiconductor layer 703 is assumed.

The size of the TFT was L / W = 10/1 μm. It is assumed that the semiconductor band gap Eg = 1.1 eV, 1.8 eV, 3.15 eV, and the oxide semiconductor has a band gap Eg = 3.15 eV. Further, the electron affinity χ was assumed to be 4.3 eV, and the work function of the metal used for the source electrode layer 704 and the drain electrode layer 705 was assumed to be 4.3 eV, which is the same as the electron affinity of the oxide semiconductor. The calculation was performed at three conditions of temperature T = 25 ° C., 100 ° C., and 150 ° C. For the calculation, device simulation software Atlas manufactured by Silvaco was used.

In amorphous semiconductors, it is considered that the defect level has a strong influence on the temperature characteristics, and the calculation was performed on the assumption of only direct recombination and on the assumption of both direct recombination and indirect recombination. The level of indirect recombination was assumed at the center of the band gap. The structure assumed in the calculation is shown in FIGS. 6 (A) and 6 (B). Calculation was performed in two types, FIG. 6A assuming only direct recombination and FIG. 6B assuming both direct recombination and indirect recombination.

In FIGS. 6A and 6B, “Ev” indicates a valence band, “Ec” indicates a conductor, and “Et” indicates a localized level. The solid line assumes carrier generation, and the broken line assumes carrier recombination.

The calculation results are shown in FIG. FIG. 29 shows a calculation result when it is assumed that the band gap (Eg) = 1.1 eV, FIG. 29A shows a calculation result when only direct recombination is assumed, and FIG. 29B shows direct recombination. It is a calculation result when both indirect recombination is assumed.

29A shows a calculation result assuming that spectrum 201 is 25 ° C., spectrum 202 is 100 ° C., spectrum 203 is 150 ° C., and spectrum 301 shown in FIG. 25 ° C, spectrum 302 is 100 ° C, and spectrum 303 is a calculation result assuming 150 ° C.

The calculation results are shown in FIG. FIG. 30 shows a calculation result when it is assumed that the band gap (Eg) = 1.8 eV, FIG. 30A shows a calculation result when only direct recombination is assumed, and FIG. 30B shows direct recombination. It is a calculation result when both indirect recombination is assumed.

Note that the spectrum 311 shown in FIG. 30A is a calculation result assuming that 25 ° C., the spectrum 312 is 100 ° C., and the spectrum 313 is 150 ° C. The spectrum 321 shown in FIG. 25 ° C., spectrum 322 is calculated at 100 ° C., and spectrum 323 is calculated at 150 ° C.

The calculation results are shown in FIG. FIG. 31 shows the calculation results when it is assumed that the band gap (Eg) = 3.15 eV, FIG. 31A shows the calculation results when only direct recombination is assumed, and FIG. 31B shows direct recombination. It is a calculation result when both indirect recombination is assumed.

Note that the spectrum 451 shown in FIG. 31A is a calculation result assuming 25 ° C., the spectrum 452 is 100 ° C., and the spectrum 453 is 150 ° C. The spectrum 461 shown in FIG. 25 ° C., spectrum 462 is calculated at 100 ° C., and spectrum 463 is calculated at 150 ° C.

From FIG. 29B, when it is assumed that the band gap (Eg) = 1.1 eV, an off-current of 1 × 10 ⁻¹³ A or more is confirmed at 25 ° C., and 1 × 10 ⁻¹⁰ at 150 ° C. An off current greater than or equal to A has been confirmed, indicating that there is temperature dependence.

From FIG. 30B, when it is assumed that the band gap (Eg) = 1.8 eV, the off-current at 25 ° C. is 1 × 10 6 compared to the band gap (Eg) = 1.1 eV in FIG. ^{At -16} A or less and 150 ° C., an off-current of 1 × 10 ⁻¹³ A or less is confirmed, indicating that there is temperature dependence.

From FIG. 31B, assuming that the band gap (Eg) = 3.15 eV, the band gap (Eg) = 1.1 eV in FIG. 29B and the band gap (Eg) in FIG. 30B. = 1.8 eV, and the calculated off-state current is 25 ° C, 100 ° C, and 150 ° C under the three conditions, the off-state current is 1 × 10 ^-16 A or less, and there is no temperature dependence. .

As described above, in the case of a semiconductor with a narrow band gap, the thermal energy for exciting electrons is small, so that direct recombination and indirect recombination are likely to occur. However, the band gap (Eg) as in an oxide semiconductor is likely to occur. In the case of a wide semiconductor, since large heat energy is required for excitation of electrons, a calculation result in which direct recombination and indirect recombination hardly occur is obtained.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 2)
In this embodiment, an example in which at least part of a driver circuit and a thin film transistor placed in a pixel portion are formed over the same substrate will be described below.

The thin film transistor provided in the pixel portion is formed according to Embodiment Mode 1. In addition, since the thin film transistor described in Embodiment 1 is an n-channel TFT, a part of the driver circuit that can be formed using the n-channel TFT is formed over the same substrate as the thin film transistor in the pixel portion. .

An example of a block diagram of an active matrix display device is illustrated in FIG. A pixel portion 5301, a first scan line driver circuit 5302, a second scan line driver circuit 5303, and a signal line driver circuit 5304 are provided over a substrate 5300 of the display device. In the pixel portion 5301, a plurality of signal lines are extended from the signal line driver circuit 5304, and a plurality of scan lines are extended from the first scan line driver circuit 5302 and the scan line driver circuit 5303. Yes. Note that pixels each having a display element are arranged in a matrix in the intersection region between the scanning line and the signal line. Further, the substrate 5300 of the display device is connected to a timing control circuit 5305 (also referred to as a controller or a control IC) through a connection portion such as an FPC (Flexible Printed Circuit).

In FIG. 7A, the first scan line driver circuit 5302, the second scan line driver circuit 5303, and the signal line driver circuit 5304 are formed over the same substrate 5300 as the pixel portion 5301. For this reason, the number of components such as a drive circuit provided outside is reduced, so that cost can be reduced. In addition, when the driver circuit is provided outside the substrate 5300, the number of connections in the connection portion by extending the wiring can be reduced, so that the reliability or the yield can be improved.

Note that the timing control circuit 5305 is, for example, a first scan line driver circuit start signal (GSP1) (start pulse) and a scan line driver circuit clock signal (GCK1) with respect to the first scan line driver circuit 5302. Supply. In addition, for example, the timing control circuit 5305 outputs, to the second scan line driver circuit 5303, a second scan line driver circuit start signal (GSP2) (also referred to as a start pulse), a scan line driver circuit clock signal ( GCK2) is supplied. For the signal line driver circuit 5304, as an example, a signal line driver circuit start signal (SSP), a signal line driver circuit clock signal (SCK), video signal data (DATA) (also simply referred to as a video signal), a latch signal (LAT) shall be supplied. Note that each clock signal (GCK1, GCK2, SCK) may be a plurality of clock signals with shifted periods, or may be supplied together with a signal (CKB) obtained by inverting the clock signal. Note that one of the first scan line driver circuit 5302 and the second scan line driver circuit 5303 can be omitted.

In FIG. 7B, circuits with low driving frequencies (eg, the first scan line driver circuit 5302 and the second scan line driver circuit 5303) are formed over the same substrate 5300 as the pixel portion 5301, and the signal line driver circuit 5304 is formed. Is formed on a different substrate from the pixel portion 5301. With this structure, a driver circuit formed over the substrate 5300 can be formed using a thin film transistor whose field-effect mobility is lower than that of a transistor including a single crystal semiconductor. Therefore, an increase in the size of the display device, a reduction in the number of steps, a reduction in cost, an improvement in yield, or the like can be achieved.

The thin film transistor described in Embodiment 1 is an n-channel TFT. 8A and 8B illustrate an example of a structure and operation of a signal line driver circuit including n-channel TFTs.

The signal line driver circuit includes a shift register 5601 and a switching circuit portion 5602. The switching circuit portion 5602 includes a plurality of circuits called switching circuits 5602_1 to 5602_N (N is a natural number). The switching circuits 5602_1 to 5602_N each include a plurality of transistors called thin film transistors 5603_1 to 5603_k (k is a natural number). An example in which the thin film transistors 5603_1 to 5603_k are n-channel TFTs will be described.

A connection relation of the signal line driver circuit is described by using the switching circuit 5602 1 as an example. First terminals of the thin film transistors 5603_1 to 5603_k are connected to wirings 5604_1 to 5604_k, respectively. Second terminals of the thin film transistors 5603_1 to 5603_k are connected to signal lines S1 to Sk, respectively. The gates of the thin film transistors 5603_1 to 5603_k are connected to the wiring 5605_1.

The shift register 5601 has a function of sequentially outputting H-level signals (also referred to as an H signal and a high power supply potential level) to the wirings 5605_1 to 5605_N and sequentially selecting the switching circuits 5602_1 to 5602_N.

The switching circuit 5602_1 has a function of controlling conduction between the wirings 5604_1 to 5604_k and the signal lines S1 to Sk (conduction between the first terminal and the second terminal), that is, the potential of the wirings 5604_1 to 5604_k is changed to the signal lines S1 to S604. It has a function of controlling whether or not to supply to Sk. As described above, the switching circuit 5602 1 has a function as a selector. The thin film transistors 5603_1 to 5603_N each have a function of controlling electrical continuity between the wirings 5604_1 to 5604_k and the signal lines S1 to Sk, that is, a function of supplying the potentials of the wirings 5604_1 to 5604_k to the signal lines S1 to Sk. As described above, the thin film transistors 5603_1 to 5603_N each have a function as a switch.

Note that video signal data (DATA) is input to each of the wirings 5604_1 to 5604_k. The video signal data (DATA) is often an image signal or an analog signal corresponding to the image signal.

Next, operation of the signal line driver circuit in FIG. 8A is described with reference to a timing chart in FIG. FIG. 8B illustrates an example of the signals Sout_1 to Sout_N and the signals Vdata_1 to Vdata_k. The signals Sout_1 to Sout_N are examples of output signals of the shift register 5601, and the signals Vdata_1 to Vdata_k are examples of signals input to the wirings 5604_1 to 5604_k, respectively. Note that one operation period of the signal line driver circuit corresponds to one gate selection period in the display device. As an example, one gate selection period is divided into a period T1 to a period TN. The periods T1 to TN are periods for writing video signal data (DATA) to the pixels belonging to the selected row.

Note that signal waveform rounding and the like in each structure illustrated in the drawings and the like in this embodiment are exaggerated for simplicity in some cases. Therefore, it is added that it is not necessarily limited to the scale.

In the periods T1 to TN, the shift register 5601 sequentially outputs H-level signals to the wirings 5605_1 to 5605_N. For example, in the period T1, the shift register 5601 outputs a high-level signal to the wiring 5605_1. Then, the thin film transistors 5603_1 to 5603_k are turned on, so that the wirings 5604_1 to 5604_k and the signal lines S1 to Sk are brought into conduction. At this time, Data (S1) to Data (Sk) are input to the wirings 5604_1 to 5604_k. Data (S1) to Data (Sk) are written to the pixels in the first to kth columns among the pixels belonging to the selected row through the thin film transistors 5603_1 to 5603_k, respectively. Thus, in the periods T1 to TN, video signal data (DATA) is sequentially written to the pixels belonging to the selected row by k columns.

As described above, the number of video signal data (DATA) or the number of wirings can be reduced by writing video signal data (DATA) to pixels by a plurality of columns. Therefore, the number of connections with external circuits can be reduced. In addition, since the video signal is written to the pixels in a plurality of columns, the writing time can be extended and insufficient writing of the video signal can be prevented.

Note that as the shift register 5601 and the switching circuit portion 5602, a circuit including the thin film transistor described in Embodiment 1 can be used. In this case, the polarity of all the transistors included in the shift register 5601 can be an n-channel type.

Next, the configuration of the scanning line driving circuit will be described. The scan line driver circuit includes a shift register and a buffer. In some cases, a level shifter may be provided. In the scan line driver circuit, when a clock signal (CK) and a start pulse signal (SP) are input to the shift register, a selection signal is generated. The generated selection signal is buffered and amplified in the buffer and supplied to the corresponding scanning line. A gate electrode of a transistor of a pixel for one line is connected to the scanning line. Since the transistors of pixels for one line must be turned on all at once, a buffer that can flow a large current is used.

One mode of a shift register used for part of the scan line driver circuit and / or the signal line driver circuit is described with reference to FIGS.

A shift register of the scan line driver circuit and the signal line driver circuit is described with reference to FIGS. The shift register includes the first pulse output circuit 10_1 to the Nth pulse output circuit 10_N (N is a natural number of 3 or more) (see FIG. 9A). In the first pulse output circuit 10_1 to the Nth pulse output circuit 10_N of the shift register illustrated in FIG. 9A, the first clock signal CK1 from the first wiring 11 and the second pulse output circuit 10_N from the second wiring 12 are second. The third clock signal CK3 is supplied from the clock signal CK2, the third wiring 13, and the fourth clock signal CK4 is supplied from the fourth wiring 14. In the first pulse output circuit 10_1, the start pulse SP1 (first start pulse) from the fifth wiring 15 is input. In the second and subsequent nth pulse output circuits 10_n (n is a natural number of 2 or more and N or less), a signal (referred to as the previous stage signal OUT (n-1)) from the previous stage pulse output circuit (n is 2). The above natural number) is input. In the first pulse output circuit 10_1, the signal from the third pulse output circuit 10_3 in the second stage, or in the second and subsequent nth pulse output circuits 10_n, the (n + 2) th pulse in the second stage. A signal from the output circuit 10_n + 2 (referred to as a post-stage signal OUT (n + 2)) is input. Further, the pulse output circuit at each stage has a first output signal OUT (1) (SR) for input to the preceding and / or subsequent pulse output circuit, and a second output signal OUT (1) to another wiring or the like. ) Is output. Note that as shown in FIG. 9A, since the latter stage signal OUT (n + 2) is not input to the last two stages of the shift register, as an example, the second start pulse SP2 and the third stage are separately provided. The start pulse SP3 may be input.

Note that the clock signal (CK) is a signal that repeats an H level and an L level (also referred to as an L signal or a low power supply potential level) at regular intervals. Here, the first clock signal (CK1) to the fourth clock signal (CK4) are sequentially delayed by ¼ period. In this embodiment, driving of the pulse output circuit is controlled by using the first clock signal (CK1) to the fourth clock signal (CK4). Note that although the clock signal is sometimes referred to as GCK or SCK depending on the input driving circuit, it is described here as CK.

  The first input terminal 21, the second input terminal 22, and the third input terminal 23 are electrically connected to any one of the first wiring 11 to the fourth wiring 14. For example, in FIG. 9B, in the first pulse output circuit 10_1, the first input terminal 21 is electrically connected to the first wiring 11, and the second input terminal 22 is connected to the second wiring 12. The third input terminal 23 is electrically connected to the third wiring 13. In the second pulse output circuit 10_2, the first input terminal 21 is electrically connected to the second wiring 12, the second input terminal 22 is electrically connected to the third wiring 13, and the second pulse output circuit 10_2 is electrically connected to the third wiring 13. 3 input terminals 23 are electrically connected to the fourth wiring 14.

Each of the first pulse output circuit 10_1 to the Nth pulse output circuit 10_N includes a first input terminal 21, a second input terminal 22, a third input terminal 23, a fourth input terminal 24, and a fifth input terminal. It is assumed that an input terminal 25, a first output terminal 26, and a second output terminal 27 are included (see FIG. 9B). In the first pulse output circuit 10_1, the first clock signal CK1 is input to the first input terminal 21, the second clock signal CK2 is input to the second input terminal 22, and the third input terminal 23 is input. The third clock signal CK3 is input, the start pulse SP1 is input to the fourth input terminal 24, the post-stage signal OUT (3) is input to the fifth input terminal 25, and the first output terminal 26 receives the first signal. Output signal OUT (1) (SR) is output, and the second output signal OUT (1) is output from the second output terminal 27.

Note that each of the first pulse output circuit 10_1 to the Nth pulse output circuit 10_N can use a four-terminal thin film transistor in addition to the three-terminal thin film transistor. A transistor 28 illustrated in FIG. 9C means the four-terminal thin film transistor described in Embodiment 1 and is used in the drawings and the like below. The transistor 28 performs electrical control between the In terminal and the Out terminal by the first control signal G1 input to the first gate electrode and the second control signal G2 input to the second gate electrode. It is an element that can.

The threshold voltage of the transistor 28 illustrated in FIG. 9C is that a gate electrode is provided above and below a channel formation region of the transistor 28 with a gate insulating film interposed therebetween, and the potential of the upper and / or lower gate electrode is controlled. Thus, the desired value can be controlled.

Next, an example of a specific circuit configuration of the pulse output circuit will be described with reference to FIG.

  The first pulse output circuit 10_1 includes a first transistor 31 to a thirteenth transistor 43 (see FIG. 9D). In addition to the first input terminal 21 to the fifth input terminal 25, the first output terminal 26, and the second output terminal 27 described above, the power supply line 51 to which the first high power supply potential VDD is supplied, A signal or power supply potential is supplied to the first transistor 31 to the thirteenth transistor 43 from the power supply line 52 to which the second high power supply potential VCC is supplied and the power supply line 53 to which the low power supply potential VSS is supplied. Here, the power supply potential of each power supply line in FIG. 9D is set such that the first power supply potential VDD> the second power supply potential VCC> the third power supply potential VSS. Note that the first clock signal (CK1) to the fourth clock signal (CK4) are signals that repeat the H level and the L level at regular intervals, and are VDD when the level is H and VSS when the level is the L level. And Note that by making the potential VCC of the power supply line 52 lower than the potential VDD of the power supply line 51, the potential applied to the gate electrode of the transistor can be kept low without affecting the operation. Shift can be reduced and deterioration can be suppressed. Note that, as illustrated in FIG. 9D, among the first transistor 31 to the thirteenth transistor 43, the first transistor 31, the sixth transistor 36 to the ninth transistor 39 are illustrated in FIG. It is preferable to use the four-terminal transistor 28 shown in FIG. The operation of the first transistor 31 and the sixth transistor 36 to the ninth transistor 39 is a transistor in which the potential of a node to which one of the source and drain electrodes is connected is switched by a control signal of the gate electrode. In this transistor, the response to the control signal input to the gate electrode is fast (the on-state current rises sharply), so that the malfunction of the pulse output circuit can be reduced. Therefore, the threshold voltage can be controlled by using the four-terminal transistor 28 shown in FIG. 9C, and a pulse output circuit in which malfunctions can be further reduced can be obtained. Note that in FIG. 9C, the first control signal G1 and the second control signal G2 are the same control signal, but different control signals may be input.

  9D, the first transistor 31 has a first terminal electrically connected to the power supply line 51, a second terminal electrically connected to the first terminal of the ninth transistor 39, and a gate electrode ( A first gate electrode and a second gate electrode) are electrically connected to the fourth input terminal 24. The second transistor 32 has a first terminal electrically connected to the power supply line 53, a second terminal electrically connected to the first terminal of the ninth transistor 39, and a gate electrode connected to the fourth transistor 34. It is electrically connected to the gate electrode. The third transistor 33 has a first terminal electrically connected to the first input terminal 21 and a second terminal electrically connected to the first output terminal 26. The fourth transistor 34 has a first terminal electrically connected to the power supply line 53 and a second terminal electrically connected to the first output terminal 26. The fifth transistor 35 has a first terminal electrically connected to the power supply line 53, a second terminal electrically connected to the gate electrode of the second transistor 32 and the gate electrode of the fourth transistor 34, and a gate The electrode is electrically connected to the fourth input terminal 24. The sixth transistor 36 has a first terminal electrically connected to the power supply line 52, a second terminal electrically connected to the gate electrode of the second transistor 32 and the gate electrode of the fourth transistor 34, and a gate The electrodes (first gate electrode and second gate electrode) are electrically connected to the fifth input terminal 25. The seventh transistor 37 has a first terminal electrically connected to the power supply line 52, a second terminal electrically connected to the second terminal of the eighth transistor 38, and a gate electrode (first gate electrode and The second gate electrode) is electrically connected to the third input terminal 23. The eighth transistor 38 has a first terminal electrically connected to the gate electrode of the second transistor 32 and the gate electrode of the fourth transistor 34, and a gate electrode (first gate electrode and second gate electrode). Are electrically connected to the second input terminal 22. The ninth transistor 39 has a first terminal electrically connected to the second terminal of the first transistor 31 and the second terminal of the second transistor 32, and a second terminal connected to the gate electrode of the third transistor 33 and The gate electrode (first gate electrode and second gate electrode) of the tenth transistor 40 is electrically connected to the power supply line 52. The tenth transistor 40 has a first terminal electrically connected to the first input terminal 21, a second terminal electrically connected to the second output terminal 27, and a gate electrode connected to the ninth transistor 39. It is electrically connected to the second terminal. The eleventh transistor 41 has a first terminal electrically connected to the power supply line 53, a second terminal electrically connected to the second output terminal 27, and a gate electrode connected to the gate electrode of the second transistor 32 and The fourth transistor 34 is electrically connected to the gate electrode. The twelfth transistor 42 has a first terminal electrically connected to the power supply line 53, a second terminal electrically connected to the second output terminal 27, and a gate electrode of the seventh transistor 37 ( The first gate electrode and the second gate electrode). The thirteenth transistor 43 has a first terminal electrically connected to the power supply line 53, a second terminal electrically connected to the first output terminal 26, and a gate electrode of the seventh transistor 37 ( The first gate electrode and the second gate electrode).

  In FIG. 9D, a connection point between the gate electrode of the third transistor 33, the gate electrode of the tenth transistor 40, and the second terminal of the ninth transistor 39 is a node A. In addition, the gate electrode of the second transistor 32, the gate electrode of the fourth transistor 34, the second terminal of the fifth transistor 35, the second terminal of the sixth transistor 36, the first terminal of the eighth transistor 38, A node B is connected to the gate electrode of the eleventh transistor 41 (see FIG. 10A).

Note that a thin film transistor is an element having at least three terminals including a gate, a drain, and a source, has a channel region between the drain region and the source region, and the drain region, the channel region, and the source region. A current can be passed through. Here, since the source and the drain vary depending on the structure and operating conditions of the thin film transistor, it is difficult to limit which is the source or the drain. Thus, a region functioning as a source and a drain may not be referred to as a source or a drain. In that case, as an example, there are cases where they are referred to as a first terminal and a second terminal, respectively.

9D and 10A, a capacitor for performing a bootstrap operation by bringing the node A into a floating state may be additionally provided. Further, in order to hold the potential of the node B, a capacitor in which one electrode is electrically connected to the node B may be separately provided.

Here, FIG. 10B illustrates a timing chart of a shift register including a plurality of pulse output circuits illustrated in FIG. Note that in the case where the shift register is a scan line driver circuit, a period 61 in FIG. 10B corresponds to a vertical blanking period, and a period 62 corresponds to a gate selection period.

As shown in FIG. 10A, the provision of the ninth transistor 39 to which the second power supply potential VCC is applied at the gate has the following advantages before and after the bootstrap operation. .

When there is no ninth transistor 39 to which the second potential VCC is applied to the gate electrode, when the potential of the node A is increased by the bootstrap operation, the potential of the source that is the second terminal of the first transistor 31 is increased. As a result, the potential becomes higher than the first power supply potential VDD. Then, the source of the first transistor 31 is switched to the first terminal side, that is, the power supply line 51 side. Therefore, in the first transistor 31, a large bias voltage is applied between the gate and the source and between the gate and the drain, so that a large stress is applied, which can cause deterioration of the transistor. Therefore, by providing the ninth transistor 39 to which the second power supply potential VCC is applied to the gate electrode, the potential of the node A rises by the bootstrap operation, but the second terminal of the first transistor 31 It is possible to prevent the potential from increasing. That is, by providing the ninth transistor 39, the value of the negative bias voltage applied between the gate and the source of the first transistor 31 can be reduced. Therefore, with the circuit configuration of this embodiment, the negative bias voltage applied between the gate and the source of the first transistor 31 can be reduced, so that deterioration of the first transistor 31 due to stress is suppressed. be able to.

Note that the ninth transistor 39 is provided so as to be connected between the second terminal of the first transistor 31 and the gate of the third transistor 33 via the first terminal and the second terminal. Any configuration may be used. Note that in the case of a shift register including a plurality of pulse output circuits in this embodiment, the ninth transistor 39 may be omitted in a signal line driver circuit having more stages than a scanning line driver circuit, and the number of transistors is reduced. It is an advantage.

Note that by using an oxide semiconductor as the semiconductor layers of the first transistor 31 to the thirteenth transistor 43, off-state current of the thin film transistor can be reduced, on-state current and field-effect mobility can be increased, and the degree of deterioration Therefore, malfunctions in the circuit can be reduced. In addition, a transistor using an oxide semiconductor is less deteriorated when a high potential is applied to a gate electrode than a transistor using amorphous silicon. Therefore, even if the first power supply potential VDD is supplied to the power supply line that supplies the second power supply potential VCC, the same operation can be obtained, and the number of power supply lines routed between the circuits can be reduced. The circuit can be reduced in size.

Note that the clock signal supplied from the third input terminal 23 to the gate electrode (first gate electrode and second gate electrode) of the seventh transistor 37, and the gate electrode (first gate) of the eighth transistor 38. The clock signal supplied to the second input terminal 22 by the second input terminal 22 is connected to the second input terminal to the gate electrode (first gate electrode and second gate electrode) of the seventh transistor 37. 22 and the gate signal (first gate electrode and second gate electrode) of the eighth transistor 38 are connected to each other so that the clock signal is supplied from the third input terminal 23. Even if it is replaced, the same effect is obtained. Note that in the shift register illustrated in FIG. 10A, when the seventh transistor 37 and the eighth transistor 38 are both on, the seventh transistor 37 is off and the eighth transistor 38 is on. When the seventh transistor 37 is turned off and the eighth transistor 38 is turned off, the potential of the node B is lowered by the potential of the second input terminal 22 and the third input terminal 23 being lowered. Occurs twice due to a decrease in the potential of the gate electrode of the seventh transistor 37 and a decrease in the potential of the gate electrode of the eighth transistor 38. On the other hand, in the shift register shown in FIG. 10A, the seventh transistor 37 is turned on, the seventh transistor 37 is turned on, and the seventh transistor 37 and the eighth transistor 38 are turned on, as in the period of FIG. 8 transistor 38 is turned off, then the seventh transistor 37 is turned off and the eighth transistor 38 is turned off, so that the potentials of the second input terminal 22 and the third input terminal 23 are lowered. Thus, the decrease in the potential of the node B can be reduced at a time due to the decrease in the potential of the gate electrode of the eighth transistor 38. Therefore, the clock signal supplied from the third input terminal to the gate electrodes (first gate electrode and second gate electrode) of the seventh transistor 37, and the gate electrode (first gate electrode) of the eighth transistor 38. And the second gate electrode) are preferably used as the clock signal supplied from the second input terminal because the fluctuation in the potential of the node B can be reduced to reduce noise.

  As described above, by setting the signal to be periodically supplied to the node B during the period in which the potentials of the first output terminal 26 and the second output terminal 27 are held at the L level, the pulse output is performed. A malfunction of the circuit can be suppressed.

By manufacturing the thin film transistor of the driver circuit using the method for manufacturing the thin film transistor described in Embodiment 1, high-speed operation of the thin film transistor in the driver circuit portion can be realized, and power saving can be achieved.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 3)
In this embodiment, the case where a thin film transistor is manufactured and a semiconductor device having a display function (also referred to as a display device) is manufactured using the thin film transistor in a pixel portion and further in a driver circuit will be described. In addition, by using a thin film transistor, part or the whole of a driver circuit can be formed over the same substrate as the pixel portion to form a system-on-panel.

The display device includes a display element. As the display element, a liquid crystal element (also referred to as a liquid crystal display element) or a light-emitting element (also referred to as a light-emitting display element) can be used. The light-emitting element includes, in its category, an element whose luminance is controlled by current or voltage, and specifically includes inorganic EL (Electro Luminescence), organic EL, and the like. In addition, a display medium whose contrast is changed by an electric effect, such as electronic ink, can be used.

The display device includes a panel in which the display element is sealed, and a module in which an IC including a controller is mounted on the panel. Further, in the display device, an element substrate corresponding to one embodiment before the display element is completed in the process of manufacturing the display device includes a unit for supplying current to the display element in each of the plurality of pixels. Specifically, the element substrate may be in a state where only the pixel electrode of the display element is formed, or after the conductive film to be the pixel electrode is formed, the pixel electrode is formed by etching. The previous state may be used, and all forms are applicable.

Note that a display device in this specification refers to an image display device or a light source (including a lighting device). Also, a connector, for example, a module with a FPC (Flexible printed circuit) or TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package), a module with a printed wiring board at the end of a TAB tape or TCP, or a display It is assumed that the display device includes all modules in which an IC (integrated circuit) is directly mounted on the element by a COG (Chip On Glass) method.

In this embodiment, an example of a liquid crystal display device is described as a semiconductor device which is one embodiment of the present invention. First, the appearance and cross section of a liquid crystal display panel, which is one embodiment of a semiconductor device, will be described with reference to FIGS. 11 illustrates a highly reliable thin film transistor 4010, 4011 and a liquid crystal element 4013 each including an In—Ga—Zn—O-based non-single-crystal film formed over a first substrate 4001 as a semiconductor layer. FIG. 11B is a top view of a panel sealed with a sealant 4005 between 4006 and 4006, and FIG. 11B corresponds to a cross-sectional view taken along line MN in FIGS. 11A1 and 11A2.

A sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and the scan line driver circuit 4004. A second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Therefore, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with the liquid crystal layer 4008 by the first substrate 4001, the sealant 4005, and the second substrate 4006. A signal line driver circuit 4003 formed of a single crystal semiconductor film or a polycrystalline semiconductor film is mounted over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. Has been.

Note that a connection method of a driver circuit which is separately formed is not particularly limited, and a COG method, a wire bonding method, a TAB method, or the like can be used. FIG. 11A1 illustrates an example in which the signal line driver circuit 4003 is mounted by a COG method, and FIG. 11A2 illustrates an example in which the signal line driver circuit 4003 is mounted by a TAB method.

In addition, the pixel portion 4002 and the scan line driver circuit 4004 provided over the first substrate 4001 include a plurality of thin film transistors. In FIG. 11B, a thin film transistor 4010 included in the pixel portion 4002 and a scan are scanned. A thin film transistor 4011 included in the line driver circuit 4004 is illustrated. Insulating layers 4020 and 4021 are provided over the thin film transistors 4010 and 4011.

As the thin film transistors 4010 and 4011, the highly reliable thin film transistor including the oxide semiconductor layer described in Embodiment 1 can be used. In this embodiment mode, the thin film transistors 4010 and 4011 are n-channel thin film transistors.

A conductive layer 4040 is provided over the insulating layer 4021 so as to overlap with a channel formation region of the oxide semiconductor layer of the thin film transistor 4011 for the driver circuit. By providing the conductive layer 4040 so as to overlap with the channel formation region of the oxide semiconductor layer, the amount of change in the threshold voltage of the thin film transistor 4011 before and after the BT test can be reduced. The conductive layer 4040 may have the same potential as the gate electrode layer of the thin film transistor 4011 or a different potential, and can function as a second gate electrode layer. Further, the potential of the conductive layer 4040 may be GND, 0 V, or a floating state.

In addition, the pixel electrode layer 4030 included in the liquid crystal element 4013 is electrically connected to the thin film transistor 4010. A counter electrode layer 4031 of the liquid crystal element 4013 is formed over the second substrate 4006. A portion where the pixel electrode layer 4030, the counter electrode layer 4031, and the liquid crystal layer 4008 overlap corresponds to the liquid crystal element 4013. Note that the pixel electrode layer 4030 and the counter electrode layer 4031 are each provided with an insulating layer 4032 and an insulating layer 4033 that function as alignment films, and the liquid crystal layer 4008 is interposed between the insulating layer 4032 and the insulating layer 4033.

Note that as the first substrate 4001 and the second substrate 4006, glass, metal (typically stainless steel), ceramics, or plastic can be used. As the plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a polyester film, or an acrylic resin film can be used. A sheet having a structure in which an aluminum foil is sandwiched between PVF films or polyester films can also be used.

The spacer 4035 is a columnar spacer obtained by selectively etching the insulating film, and is provided to control the distance (cell gap) between the pixel electrode layer 4030 and the counter electrode layer 4031. . A spherical spacer may be used. The counter electrode layer 4031 is electrically connected to a common potential line provided over the same substrate as the thin film transistor 4010. Using the common connection portion, the counter electrode layer 4031 and the common potential line can be electrically connected to each other through conductive particles disposed between the pair of substrates. Note that the conductive particles are included in the sealant 4005.

Alternatively, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. The blue phase is one of the liquid crystal phases. When the temperature of the cholesteric liquid crystal is increased, the blue phase appears immediately before the transition from the cholesteric phase to the isotropic phase. Since the blue phase appears only in a narrow temperature range, a liquid crystal composition in which 5% by weight or more of a chiral agent is mixed is used for the liquid crystal layer 4008 in order to improve the temperature range. A liquid crystal composition containing a liquid crystal exhibiting a blue phase and a chiral agent has a response speed as short as 1 msec or less and is optically isotropic, so alignment treatment is unnecessary and viewing angle dependence is small.

Note that although the liquid crystal display device described in this embodiment is an example of a transmissive liquid crystal display device, the liquid crystal display device can be applied to a reflective liquid crystal display device or a transflective liquid crystal display device.

In the liquid crystal display device described in this embodiment, a polarizing plate is provided on the outer side (viewing side) of the substrate, a colored layer is provided on the inner side, and an electrode layer used for the display element is provided in this order. It may be provided inside. Further, the stacked structure of the polarizing plate and the colored layer is not limited to this embodiment mode, and may be set as appropriate depending on the material and manufacturing process conditions of the polarizing plate and the colored layer. Further, a light shielding film functioning as a black matrix may be provided as necessary.

In this embodiment, in order to reduce the surface unevenness of the thin film transistor and improve the reliability of the thin film transistor, the insulating layer functions as a protective film or a planarization insulating film (the insulating layer 4020 and the insulating layer 4021). It is configured to cover with. Note that the protective film is for preventing entry of contaminant impurities such as organic substances, metal substances, and water vapor floating in the atmosphere, and a dense film is preferable. The protective film is formed by a sputtering method using a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, or an aluminum nitride oxide film, Alternatively, a stacked layer may be formed. Although an example in which the protective film is formed by a sputtering method is described in this embodiment mode, it is not particularly limited and may be formed by various methods.

Here, an insulating layer 4020 having a stacked structure is formed as the protective film. Here, as the first layer of the insulating layer 4020, a silicon oxide film is formed by a sputtering method. The use of a silicon oxide film as the protective film is effective in preventing hillocks of the aluminum film used as the source electrode layer and the drain electrode layer.

In addition, an insulating layer is formed as a second layer of the protective film. Here, as the second layer of the insulating layer 4020, a silicon nitride film is formed by a sputtering method. When a silicon nitride film is used as the protective film, ions such as sodium can be prevented from entering the semiconductor region and changing the electrical characteristics of the TFT.

Further, after forming the protective film, the semiconductor layer may be annealed (300 ° C. to 400 ° C.).

In addition, the insulating layer 4021 is formed as the planarization insulating film. As the insulating layer 4021, an organic material having heat resistance such as polyimide, acrylic, benzocyclobutene, polyamide, or epoxy can be used. In addition to the organic material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus boron glass), or the like can be used. Note that the insulating layer 4021 may be formed by stacking a plurality of insulating films formed using these materials.

Note that the siloxane-based resin corresponds to a resin including a Si—O—Si bond formed using a siloxane-based material as a starting material. Siloxane resins may use organic groups (for example, alkyl groups and aryl groups) and fluoro groups as substituents. The organic group may have a fluoro group.

The formation method of the insulating layer 4021 is not particularly limited, and depending on the material, a sputtering method, an SOG method, spin coating, dipping, spray coating, a droplet discharge method (ink jet method, screen printing, offset printing, etc.), doctor A knife, roll coater, curtain coater, knife coater or the like can be used. In the case where the insulating layer 4021 is formed using a material solution, the semiconductor layer may be annealed (300 ° C. to 400 ° C.) at the same time as the baking step. By combining the baking process of the insulating layer 4021 and annealing of the semiconductor layer, a semiconductor device can be efficiently manufactured.

The pixel electrode layer 4030 and the counter electrode layer 4031 include indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, and indium tin oxide ( Hereinafter, it is referred to as ITO), and a light-transmitting conductive material such as indium zinc oxide or indium tin oxide to which silicon oxide is added can be used.

The pixel electrode layer 4030 and the counter electrode layer 4031 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). The pixel electrode formed using the conductive composition preferably has a sheet resistance of 10,000 Ω / □ or less and a light transmittance of 70% or more at a wavelength of 550 nm. Moreover, it is preferable that the resistivity of the conductive polymer contained in the conductive composition is 0.1 Ω · cm or less.

As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer of two or more kinds thereof can be given.

In addition, a variety of signals and potentials are supplied to the signal line driver circuit 4003 which is formed separately, the scan line driver circuit 4004, or the pixel portion 4002 from an FPC 4018.

In this embodiment, the connection terminal electrode 4015 is formed using the same conductive film as the pixel electrode layer 4030 included in the liquid crystal element 4013, and the terminal electrode 4016 is the same conductive film as the source and drain electrode layers of the thin film transistors 4010 and 4011. It is formed with.

The connection terminal electrode 4015 is electrically connected to a terminal included in the FPC 4018 through an anisotropic conductive film 4019.

FIG. 11 illustrates an example in which the signal line driver circuit 4003 is separately formed and mounted on the first substrate 4001; however, this embodiment is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.

FIG. 12 illustrates an example in which a TFT substrate 2600 is used for a liquid crystal display module corresponding to one embodiment of a semiconductor device.

FIG. 12 illustrates an example of a liquid crystal display module, in which a TFT substrate 2600 and a counter substrate 2601 are fixed by a sealant 2602, a pixel portion 2603 including a TFT or the like therebetween, a display element 2604 including a liquid crystal layer, a colored layer 2605, a polarizing plate 2606 is provided to form a display area. The colored layer 2605 is necessary for color display. In the case of the RGB method, a colored layer corresponding to each color of red, green, and blue is provided corresponding to each pixel. A polarizing plate 2606, a polarizing plate 2607, and a diffusion plate 2613 are provided outside the TFT substrate 2600 and the counter substrate 2601. The light source is composed of a cold cathode tube 2610 and a reflector 2611. The circuit board 2612 is connected to the wiring circuit portion 2608 of the TFT substrate 2600 by a flexible wiring board 2609, and an external circuit such as a control circuit or a power circuit is incorporated. Yes. Moreover, you may laminate | stack in the state which had the phase difference plate between the polarizing plate and the liquid-crystal layer.

The liquid crystal display module includes TN (Twisted Nematic) mode, IPS (In-Plane-Switching) mode, FFS (Fringe Field Switching) mode, MVA (Multi-domain Vertical Alignment) mode, PVA (SMB) Axial Symmetrical Aligned Micro-cell (OCB) mode, OCB (Optical Compensated Birefringence) mode, FLC (Ferroelectric Liquid Crystal) mode, AFLC (Anti-Ferroelectric Crypto Liquid) mode, etc. Door can be.

Through the above process, a highly reliable liquid crystal display device as a semiconductor device can be manufactured.

When a thin film transistor in a pixel portion of a liquid crystal display device is manufactured using the thin film transistor described in Embodiment 1, an increase in power consumption due to variation in off-state current of the thin film transistor in each pixel can be suppressed.

In addition, by manufacturing the thin film transistor of the driver circuit of the liquid crystal display device using the method for manufacturing the thin film transistor described in Embodiment 1, high-speed operation of the thin film transistor of the driver circuit portion can be realized, and power saving can be achieved.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 4)
An example of electronic paper will be described as an embodiment of a semiconductor device.

The thin film transistor of Embodiment 1 may be used for electronic paper in which electronic ink is driven using an element electrically connected to a switching element. Electronic paper is also called an electrophoretic display device (electrophoretic display), and has the same readability as paper, low power consumption compared to other display devices, and the advantage that it can be made thin and light. ing.

The electrophoretic display can be considered in various forms, and a plurality of microcapsules including first particles having a positive charge and second particles having a negative charge are dispersed in a solvent or a solute. In other words, by applying an electric field to the microcapsules, the particles in the microcapsules are moved in opposite directions to display only the color of the particles assembled on one side. Note that the first particle or the second particle contains a dye and does not move in the absence of an electric field. In addition, the color of the first particles and the color of the second particles are different (including colorless).

As described above, the electrophoretic display is a display using a so-called dielectrophoretic effect in which a substance having a high dielectric constant moves to a high electric field region.

A solution in which the above microcapsules are dispersed in a solvent is referred to as electronic ink. This electronic ink can be printed on a surface of glass, plastic, cloth, paper, or the like. Color display is also possible by using particles having color filters or pigments.

In addition, an active matrix display device can be completed by arranging a plurality of the above microcapsules so as to be appropriately sandwiched between two electrodes on an active matrix substrate, and display can be performed by applying an electric field to the microcapsules. it can. For example, an active matrix substrate obtained by the thin film transistor of Embodiment 1 can be used.

Note that the first particle and the second particle in the microcapsule are a conductor material, an insulator material, a semiconductor material, a magnetic material, a liquid crystal material, a ferroelectric material, an electroluminescent material, an electrochromic material, or a magnetophoresis. A kind of material selected from the materials or a composite material thereof may be used.

FIG. 13 illustrates active matrix electronic paper as an example of a semiconductor device. A thin film transistor 581 used for the semiconductor device can be manufactured similarly to the thin film transistor described in Embodiment 1, and is a highly reliable thin film transistor including an oxide semiconductor layer.

The electronic paper in FIG. 13 is an example of a display device using a twisting ball display system. The twist ball display method is a method in which spherical particles separately painted in white and black are arranged between a first electrode layer and a second electrode layer which are electrode layers used for a display element, and the first electrode layer and the second electrode layer are arranged. In this method, a potential difference is generated in the two electrode layers to control the orientation of the spherical particles.

The thin film transistor 581 is a bottom-gate thin film transistor and is covered with an insulating film 583 which is in contact with the semiconductor layer. A source electrode layer or a drain electrode layer of the thin film transistor 581 is in contact with and electrically connected to the first electrode layer 587 through an opening formed in the insulating layer 585. Between the first electrode layer 587 and the second electrode layer 588, spherical particles 589 including a cavity 594 having a black region 590a and a white region 590b and being filled with a liquid are provided. The periphery of the spherical particles 589 is filled with a filler 595 such as a resin (see FIG. 13). The first electrode layer 587 corresponds to a pixel electrode, and the second electrode layer 588 corresponds to a common electrode. The second electrode layer 588 is electrically connected to a common potential line provided over the same substrate as the thin film transistor 581. With the use of the common connection portion, the second electrode layer 588 and the common potential line can be electrically connected to each other through conductive particles arranged between the pair of substrates.

Further, instead of the twisting ball, an electrophoretic element can be used. A microcapsule having a diameter of about 10 μm to 200 μm in which transparent liquid, positively charged white microparticles, and negatively charged black microparticles are enclosed is used. In the microcapsule provided between the first electrode layer and the second electrode layer, when an electric field is applied by the first electrode layer and the second electrode layer, the white particles and the black particles are in opposite directions. And can display white or black. A display element using this principle is an electrophoretic display element, and is generally called electronic paper. Since the electrophoretic display element has higher reflectance than the liquid crystal display element, an auxiliary light is unnecessary, power consumption is small, and the display portion can be recognized even in a dim place. Further, even when power is not supplied to the display portion, an image once displayed can be held; therefore, a semiconductor device with a display function from a radio wave source (simply a display device or a semiconductor having a display device) Even when the device is also moved away, the displayed image can be stored.

Through the above steps, highly reliable electronic paper as a semiconductor device can be manufactured.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 5)
An example of a light-emitting display device will be described as a semiconductor device. As a display element included in the display device, a light-emitting element utilizing electroluminescence is used here. A light-emitting element using electroluminescence is distinguished depending on whether the light-emitting material is an organic compound or an inorganic compound. Generally, the former is called an organic EL element and the latter is called an inorganic EL element.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are respectively injected from the pair of electrodes into the layer containing the light emitting organic compound, and a current flows. Then, these carriers (electrons and holes) recombine, whereby the light-emitting organic compound forms an excited state, and emits light when the excited state returns to the ground state. Due to such a mechanism, such a light-emitting element is referred to as a current-excitation light-emitting element.

Inorganic EL elements are classified into a dispersion-type inorganic EL element and a thin-film inorganic EL element depending on the element structure. The dispersion-type inorganic EL element has a light-emitting layer in which particles of a light-emitting material are dispersed in a binder, and the light emission mechanism is donor-acceptor recombination light emission using a donor level and an acceptor level. The thin-film inorganic EL element has a structure in which a light emitting layer is sandwiched between dielectric layers and further sandwiched between electrodes, and the light emission mechanism is localized light emission utilizing inner-shell electron transition of metal ions. Note that description is made here using an organic EL element as a light-emitting element.

FIG. 14 is a diagram illustrating an example of a pixel configuration to which digital time grayscale driving can be applied as an example of a semiconductor device.

A structure and operation of a pixel to which digital time gray scale driving can be applied will be described. Here, an example is shown in which two n-channel transistors each using an oxide semiconductor layer for a channel formation region are used for one pixel.

The pixel 6400 includes a switching transistor 6401, a driving transistor 6402, a light-emitting element 6404, and a capacitor 6403. The switching transistor 6401 has a gate connected to the scanning line 6406, a first electrode (one of the source electrode and the drain electrode) connected to the signal line 6405, and a second electrode (the other of the source electrode and the drain electrode) connected to the driving transistor. 6402 is connected to the gate. The driving transistor 6402 has a gate connected to the power supply line 6407 through the capacitor 6403, a first electrode connected to the power supply line 6407, and a second electrode connected to the first electrode (pixel electrode) of the light emitting element 6404. ing. The second electrode of the light emitting element 6404 corresponds to the common electrode 6408. The common electrode 6408 is electrically connected to a common potential line formed over the same substrate.

Note that a low power supply potential is set for the second electrode (the common electrode 6408) of the light-emitting element 6404. Note that the low power supply potential is a potential that satisfies the low power supply potential <the high power supply potential with reference to the high power supply potential set in the power supply line 6407. For example, GND, 0V, or the like is set as the low power supply potential. Also good. The potential difference between the high power supply potential and the low power supply potential is applied to the light emitting element 6404 and a current is caused to flow through the light emitting element 6404 so that the light emitting element 6404 emits light. Each potential is set to be equal to or higher than the forward threshold voltage.

Note that the capacitor 6403 can be omitted by using the gate capacitance of the driving transistor 6402 instead. As for the gate capacitance of the driving transistor 6402, a capacitance may be formed between the channel region and the gate electrode.

Here, in the case of the voltage input voltage driving method, a video signal is input to the gate of the driving transistor 6402 so that the driving transistor 6402 is sufficiently turned on or off. That is, the driving transistor 6402 is operated in a linear region. Since the driving transistor 6402 operates in a linear region, a voltage higher than the voltage of the power supply line 6407 is applied to the gate of the driving transistor 6402. Note that a voltage equal to or higher than (power supply line voltage + Vth of the driving transistor 6402) is applied to the signal line 6405.

In addition, when analog grayscale driving is performed instead of digital time grayscale driving, the same pixel configuration as that in FIG. 14 can be used by changing a signal input method.

In the case of performing analog gradation driving, a voltage equal to or higher than the forward voltage of the light emitting element 6404 + Vth of the driving transistor 6402 is applied to the gate of the driving transistor 6402. The forward voltage of the light-emitting element 6404 refers to a voltage for obtaining desired luminance, and includes at least a forward threshold voltage. Note that when a video signal that causes the driving transistor 6402 to operate in a saturation region is input, a current can flow through the light-emitting element 6404. In order to operate the driving transistor 6402 in the saturation region, the potential of the power supply line 6407 is set higher than the gate potential of the driving transistor 6402. By making the video signal analog, current corresponding to the video signal can be supplied to the light-emitting element 6404 to perform analog gradation driving.

Note that the pixel structure illustrated in FIG. 14 is not limited thereto. For example, a switch, a resistor, a capacitor, a transistor, a logic circuit, or the like may be newly added to the pixel illustrated in FIG.

Next, the structure of the light-emitting element will be described with reference to FIG. Here, the cross-sectional structure of the pixel will be described with an example in which the driving TFT is an n-type. TFTs 7001, 7011, and 7021 which are driving TFTs used for the light-emitting elements in FIGS. 15A, 15B, and 15C can be manufactured in a manner similar to the thin film transistor described in Embodiment 1 and include an oxide semiconductor layer. Thin film transistor.

In order to extract light emitted from the light-emitting element, at least one of the anode and the cathode may be transparent. Then, a thin film transistor and a light emitting element are formed on the substrate, and a top emission that extracts light from a surface opposite to the substrate, a bottom emission that extracts light from a surface on the substrate, and a surface opposite to the substrate and the substrate are provided. There is a light-emitting element having a dual emission structure in which light emission is extracted from the pixel, and the pixel structure can be applied to a light-emitting element having any emission structure.

A light-emitting element having a bottom emission structure will be described with reference to FIG.

A cross-sectional view of a pixel in the case where the driving TFT 7011 is n-type and light emitted from the EL layer 7014 is emitted to the cathode 7013 side is shown. In FIG. 15A, a cathode 7013 of a light-emitting element 7012 is formed over a light-transmitting conductive film 7017 electrically connected to the driving TFT 7011. An EL layer 7014 and an anode 7015 are formed over the cathode 7013. Are sequentially stacked. Note that the light-transmitting conductive film 7017 is electrically connected to the drain electrode layer of the driving TFT 7011 through a contact hole formed in the oxide insulating layer 7031.

As the light-transmitting conductive film 7017, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide ( Hereinafter, a light-transmitting conductive film such as indium zinc oxide or indium tin oxide to which silicon oxide is added can be used.

Although various materials can be used for the cathode 7013, a material having a low work function, for example, an alkali metal such as Li or Cs, and an alkaline earth metal such as Mg, Ca, or Sr, and In addition to alloys containing these (Mg: Ag, Al: Li, etc.), rare earth metals such as Yb and Er are preferred. In FIG. 15A, the thickness of the cathode 7013 is set to transmit light (preferably, approximately 5 nm to 30 nm). For example, an aluminum film having a thickness of 20 nm is used as the cathode 7013.

Note that after the light-transmitting conductive film and the aluminum film are stacked, the light-transmitting conductive film 7017 and the cathode 7013 may be selectively etched to form the same mask. Can be etched.

Further, the peripheral edge portion of the cathode 7013 is covered with a partition wall 7019. A partition 7019 is formed using an organic resin film such as polyimide, acrylic, polyamide, or epoxy, an inorganic insulating film, or organic polysiloxane. The partition wall 7019 is preferably formed using a photosensitive resin material so that an opening is formed on the cathode 7013 and the side wall of the opening has an inclined surface formed with a continuous curvature. In the case where a photosensitive resin material is used for the partition 7019, a step of forming a resist mask can be omitted.

Further, the EL layer 7014 formed over the cathode 7013 and the partition wall 7019 may be formed using either a single layer or a stack of a plurality of layers. In the case where the EL layer 7014 includes a plurality of layers, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, and a hole injection layer are stacked in this order over the cathode 7013. Note that it is not necessary to provide all of these layers.

Further, the order of stacking is not limited, and a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer may be stacked on the cathode 7013 in this order. However, when power consumption is compared, it is preferable to stack the electron injection layer, the electron transport layer, the light emitting layer, the hole transport layer, and the hole injection layer in this order on the cathode 7013 because power consumption is small.

For the anode 7015 formed over the EL layer 7014, various materials can be used; however, a material having a high work function such as titanium nitride, ZrN, Ti, W, Ni, Pt, Cr, or the like Transparent conductive materials such as IZO (indium zinc oxide) and ZnO are preferable. Further, a shielding film 7016, for example, a metal that blocks light, a metal that reflects light, or the like is formed over the anode 7015. In this embodiment, an ITO film is used as the anode 7015 and a Ti film is used as the shielding film 7016.

A region where at least the EL layer 7014 is sandwiched between the cathode 7013 and the anode 7015 corresponds to the light-emitting element 7012. In the case of the element structure illustrated in FIG. 15A, light emitted from the light-emitting element 7012 is emitted to the cathode 7013 side as indicated by an arrow.

Note that FIG. 15A illustrates an example in which a light-transmitting conductive film is used as a gate electrode layer, and light emitted from the light-emitting element 7012 passes through the color filter layer 7033 and is a TFT 7011 which is a driving TFT. The light is emitted through the gate electrode layer and the source electrode layer. An aperture ratio can be improved by using a light-transmitting conductive film as a gate electrode layer or a source electrode layer of the TFT 7011.

The color filter layer 7033 is formed by a droplet discharge method such as an inkjet method, a printing method, an etching method using a photolithography technique, or the like.

The color filter layer 7033 is covered with an overcoat layer 7034 and further covered with an insulating layer 7035. Note that although the overcoat layer 7034 is illustrated as being thin in FIG. 15A, the overcoat layer 7034 has a function of planarizing unevenness caused by the color filter layer 7033.

In addition, the contact hole formed in the insulating layer 7035 and reaching the drain electrode layer is provided so as to overlap with the partition wall 7019. In FIG. 15A, the aperture ratio can be improved by a layout in which the contact hole reaching the drain electrode layer and the partition wall 7019 are stacked.

Next, a light-emitting element having a dual emission structure will be described with reference to FIG.

In FIG. 15B, a cathode 7023 of a light-emitting element 7022 is formed over a light-transmitting conductive film 7027 which is electrically connected to a TFT 7021 which is a driving TFT, and an EL layer 7024 is formed over the cathode 7023. The anode 7025 is sequentially stacked. Note that the light-transmitting conductive film 7027 is electrically connected to the drain electrode layer of the TFT 7021 through a contact hole formed in the oxide insulating layer 7041.

As the light-transmitting conductive film 7027, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide ( Hereinafter, a light-transmitting conductive film such as indium zinc oxide or indium tin oxide to which silicon oxide is added can be used.

Although various materials can be used for the cathode 7023, materials having a low work function, such as, specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, and In addition to alloys containing these (Mg: Ag, Al: Li, etc.), rare earth metals such as Yb and Er are preferred. In this embodiment, the thickness of the cathode 7023 is set so as to transmit light (preferably, about 5 nm to 30 nm). For example, an aluminum film having a thickness of 20 nm is used as the cathode 7023.

Note that after the light-transmitting conductive film and the aluminum film are stacked, the light-transmitting conductive film 7027 and the cathode 7023 may be selectively etched to form the same mask. Can be etched.

Further, the periphery of the cathode 7023 is covered with a partition wall 7029. A partition 7029 is formed using an organic resin film such as polyimide, acrylic, polyamide, or epoxy, an inorganic insulating film, or organic polysiloxane. The partition wall 7029 is preferably formed using a photosensitive resin material so that an opening is formed on the cathode 7023 and the side wall of the opening has an inclined surface formed with a continuous curvature. In the case where a photosensitive resin material is used for the partition wall 7029, a step of forming a resist mask can be omitted.

Further, the EL layer 7024 formed over the cathode 7023 and the partition wall 7029 may be formed using either a single layer or a stack of a plurality of layers. In the case where the EL layer 7024 includes a plurality of layers, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, and a hole injection layer are stacked over the cathode 7023 in this order. Note that it is not necessary to provide all of these layers.

Further, the order of stacking is not limited, and a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer may be stacked in this order on the cathode 7023. However, when power consumption is compared, it is preferable to stack the electron injection layer, the electron transport layer, the light emitting layer, the hole transport layer, and the hole injection layer in this order on the cathode 7023 because power consumption is small.

Various materials can be used for the anode 7025 formed over the EL layer 7024, but a material having a high work function, for example, a transparent conductive material such as ITO, IZO, or ZnO is preferable. In this embodiment, an ITO film containing silicon oxide is used as the anode 7026.

A region where the EL layer 7024 is sandwiched between the cathode 7023 and the anode 7025 corresponds to the light-emitting element 7022. In the case of the element structure illustrated in FIG. 15B, light emitted from the light-emitting element 7022 is emitted to both the anode 7025 side and the cathode 7023 side as indicated by arrows.

Note that FIG. 15B illustrates an example in which a light-transmitting conductive film is used for the gate electrode layer. Light emitted from the light-emitting element 7022 to the cathode 7023 side passes through the color filter layer 7043, and the TFT 7021 The light is emitted through the gate electrode layer and the source electrode layer. By using a light-transmitting conductive film as the gate electrode layer or the source electrode layer of the TFT 7021, the aperture ratio on the anode 7025 side and the aperture ratio on the cathode 7023 side can be made substantially the same.

The color filter layer 7043 is formed by a droplet discharge method such as an inkjet method, a printing method, an etching method using a photolithography technique, or the like.

The color filter layer 7043 is covered with an overcoat layer 7044 and further covered with an insulating layer 7045.

Further, the contact hole formed in the insulating layer 7045 and reaching the drain electrode layer is provided at a position overlapping with the partition wall 7029. By arranging the contact hole reaching the drain electrode layer and the partition wall 7029 to overlap each other, the aperture ratio on the anode 7025 side and the aperture ratio on the cathode 7023 side can be made substantially the same.

A contact hole which is formed in the insulating layer 7045 and reaches the light-transmitting conductive film 7027 is provided so as to overlap with the partition wall 7029.

However, when a light emitting element having a dual emission structure is used and both display surfaces are full color display, light from the anode 7025 side does not pass through the color filter layer 7043. Therefore, a sealing substrate having a separate color filter layer is used as the anode. 7025 is preferably provided above.

Next, a light-emitting element having a top emission structure will be described with reference to FIG.

FIG. 15C is a cross-sectional view of the pixel in the case where the TFT 7001 which is a driving TFT is n-type and light emitted from the light-emitting element 7002 passes to the anode 7005 side. In FIG. 15C, a cathode 7003 of a light-emitting element 7002 electrically connected to the TFT 7001 through a connection electrode layer is formed, and an EL layer 7004 and an anode 7005 are sequentially stacked over the cathode 7003.

Although various materials can be used for the cathode 7003, a material having a low work function, for example, an alkali metal such as Li or Cs, and an alkaline earth metal such as Mg, Ca, or Sr, and In addition to alloys containing these (Mg: Ag, Al: Li, etc.), rare earth metals such as Yb and Er are preferred.

Further, the peripheral edge portion of the cathode 7003 is covered with a partition wall 7009. A partition 7009 is formed using an organic resin film such as polyimide, acrylic, polyamide, or epoxy, an inorganic insulating film, or organic polysiloxane. The partition 7009 is preferably formed using a photosensitive resin material so that an opening is formed on the cathode 7003 and the side wall of the opening has an inclined surface formed with a continuous curvature. In the case where a photosensitive resin material is used for the partition 7009, a step of forming a resist mask can be omitted.

Further, the EL layer 7004 formed over the cathode 7003 and the partition 7009 may be a single layer or a stack of a plurality of layers. In the case where the EL layer 7004 includes a plurality of layers, an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer, and a hole injection layer are stacked in this order over the cathode 7003. Note that it is not necessary to provide all of these layers.

Further, the order of stacking is not limited, and a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer may be stacked on the cathode 7003 in this order. In the case of stacking in this order, the cathode 7003 functions as an anode.

In FIG. 15C, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are stacked in this order on a stacked film in which a Ti film, an aluminum film, and a Ti film are stacked in this order, and Mg is formed thereon. : A laminate of an Ag alloy thin film and ITO is formed.

However, when the power consumption is compared, it is preferable to stack the electron injection layer, the electron transport layer, the light emitting layer, the hole transport layer, and the hole injection layer in this order on the cathode 7003 because the power consumption is small.

The anode 7005 is formed using a light-transmitting conductive material such as indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, or titanium oxide. A light-transmitting conductive film such as indium tin oxide, indium tin oxide, indium zinc oxide, or indium tin oxide to which silicon oxide is added may be used.

A region where the EL layer 7004 is sandwiched between the cathode 7003 and the anode 7005 corresponds to the light-emitting element 7002. In the case of the pixel shown in FIG. 15C, light emitted from the light-emitting element 7002 is emitted to the anode 7005 side as indicated by an arrow.

In FIG. 15C, an example in which the thin film transistor 150 is used as the TFT 7001 is shown; however, there is no particular limitation, and thin film transistors 160, 170, and 180 can be used.

In FIG. 15C, the drain electrode layer of the TFT 7001 is electrically connected to the connection electrode layer through the oxide insulating layer 7051, and the connection electrode layer is connected to the cathode through the insulating layer 7052 and the insulating layer 7055. 7003 is electrically connected. The planarization insulating layer 7053 can be formed using a resin material such as polyimide, acrylic, benzocyclobutene, polyamide, or epoxy. In addition to the resin material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus boron glass), or the like can be used. Note that the planarization insulating layer 7053 may be formed by stacking a plurality of insulating films formed using these materials. There is no particular limitation on the formation method of the planarization insulating layer 7053, and a sputtering method, an SOG method, spin coating, dip coating, spray coating, a droplet discharge method (an inkjet method, screen printing, offset printing, or the like) is used depending on the material. A doctor knife, a roll coater, a curtain coater, a knife coater, or the like can be used.

In addition, a partition 7009 is provided to insulate the cathode 7003 from the cathodes of adjacent pixels. A partition 7009 is formed using an organic resin film such as polyimide, acrylic, polyamide, or epoxy, an inorganic insulating film, or organic polysiloxane. The partition 7009 is preferably formed using a photosensitive resin material so that an opening is formed on the cathode 7003 and the side wall of the opening has an inclined surface formed with a continuous curvature.

In the structure of FIG. 15C, when full color display is performed, for example, the light emitting element 7002 is a green light emitting element, one adjacent light emitting element is a red light emitting element, and the other light emitting element is a blue light emitting element. To do. Alternatively, a light-emitting display device capable of full color display may be manufactured using not only three types of light-emitting elements but also four types of light-emitting elements including white elements.

In the structure of FIG. 15C, a light-emitting display capable of full-color display has a structure in which a plurality of light-emitting elements to be arranged are all white light-emitting elements and a sealing substrate having a color filter or the like is disposed above the light-emitting elements 7002. A device may be made. A full-color display can be performed by forming a material that emits monochromatic light such as white and combining a color filter and a color conversion layer.

Of course, monochromatic light emission may be displayed. For example, a lighting device may be formed using white light emission, or an area color type light emitting device may be formed using monochromatic light emission.

If necessary, an optical film such as a polarizing film such as a circularly polarizing plate may be provided.

Note that although an organic EL element is described here as a light-emitting element, an inorganic EL element can also be provided as a light-emitting element.

Although an example in which a thin film transistor (driving TFT) for controlling driving of a light emitting element and the light emitting element are electrically connected is shown, a current control TFT is connected between the driving TFT and the light emitting element. It may be a configuration.

Next, the appearance and cross section of a light-emitting display panel (also referred to as a light-emitting panel), which is one embodiment of a semiconductor device, will be described with reference to FIGS. FIG. 16A is a plan view of a panel in which a thin film transistor and a light-emitting element formed over a first substrate are sealed with a sealant between the second substrate and FIG. 16B. 16 corresponds to a cross-sectional view taken along line HI in FIG.

A sealant 4505 is provided so as to surround the pixel portion 4502, the signal line driver circuits 4503a and 4503b, and the scan line driver circuits 4504a and 4504b which are provided over the first substrate 4501. A second substrate 4506 is provided over the pixel portion 4502, the signal line driver circuits 4503a and 4503b, and the scan line driver circuits 4504a and 4504b. Therefore, the pixel portion 4502, the signal line driver circuits 4503a and 4503b, and the scan line driver circuits 4504a and 4504b are sealed together with the filler 4507 by the first substrate 4501, the sealant 4505, and the second substrate 4506. Thus, it is preferable to package (enclose) with a protective film (bonded film, ultraviolet curable resin film, etc.) or a cover material that has high air tightness and little degassing so as not to be exposed to the outside air.

Further, the pixel portion 4502, the signal line driver circuits 4503a and 4503b, and the scan line driver circuits 4504a and 4504b provided over the first substrate 4501 include a plurality of thin film transistors. In FIG. A thin film transistor 4510 included in 4502 and a thin film transistor 4509 included in the signal line driver circuit 4503a are illustrated.

As the thin film transistors 4509 and 4510, the highly reliable thin film transistor including the oxide semiconductor layer described in Embodiment 1 can be used. In this embodiment mode, the thin film transistors 4509 and 4510 are n-channel thin film transistors.

A conductive layer 4540 is provided over the insulating layer 4544 so as to overlap with a channel formation region of the oxide semiconductor layer of the thin film transistor 4509 for the driver circuit. By providing the conductive layer 4540 so as to overlap with the channel formation region of the oxide semiconductor layer, the amount of change in the threshold voltage of the thin film transistor 4509 before and after the BT test can be reduced. The conductive layer 4540 may have the same potential as the gate electrode layer of the thin film transistor 4509 or a different potential, and can function as a second gate electrode layer. Further, the potential of the conductive layer 4540 may be GND, 0 V, or a floating state.

In the thin film transistor 4509, an insulating layer 4541 is formed in contact with a semiconductor layer including a channel formation region as an insulating film. The insulating layer 4541 may be formed using a material and a method similar to those of the insulating layer 107 described in Embodiment 1. In addition, in order to reduce surface unevenness of the thin film transistor, the structure is covered with an insulating layer 4544 functioning as a planarization insulating film. Here, as the insulating layer 4541, a silicon oxide film is formed by a sputtering method as in the insulating layer 107 described in Embodiment 1.

In addition, an insulating layer 4544 is formed as the planarization insulating film. The insulating layer 4544 may be formed using a material and a method similar to those of the insulating layer 4021 described in Embodiment 2. Here, acrylic is used for the insulating layer 4544.

4511 corresponds to a light-emitting element, and a first electrode layer 4517 which is a pixel electrode included in the light-emitting element 4511 is electrically connected to a source electrode layer or a drain electrode layer of the thin film transistor 4510. Note that the structure of the light-emitting element 4511 is a stacked structure of the first electrode layer 4517, the electroluminescent layer 4512, and the second electrode layer 4513; however, the structure is not limited to the structure shown. The structure of the light-emitting element 4511 can be changed as appropriate depending on the direction of light extracted from the light-emitting element 4511 or the like.

A partition 4520 is formed using an organic resin film, an inorganic insulating film, or organic polysiloxane. In particular, a photosensitive material is preferably used so that an opening is formed over the first electrode layer 4517 and the side wall of the opening has an inclined surface formed with a continuous curvature.

The electroluminescent layer 4512 may be composed of a single layer or a plurality of layers stacked.

A protective film may be formed over the second electrode layer 4513 and the partition 4520 so that oxygen, hydrogen, moisture, carbon dioxide, or the like does not enter the light-emitting element 4511. As the protective film, a silicon nitride film, a silicon nitride oxide film, a DLC film, or the like can be formed.

In addition, a variety of signals and potentials are supplied to the signal line driver circuits 4503a and 4503b, the scan line driver circuits 4504a and 4504b, or the pixel portion 4502 from FPCs 4518a and 4518b.

The connection terminal electrode 4515 is formed from the same conductive film as the first electrode layer 4517 included in the light-emitting element 4511, and the terminal electrode 4516 is formed from the same conductive film as the source and drain electrode layers included in the thin film transistors 4509 and 4510. ing.

The connection terminal electrode 4515 is electrically connected to a terminal included in the FPC 4518a through an anisotropic conductive film 4519.

The substrate located in the direction in which light is extracted from the light-emitting element 4511 must be light-transmitting. In that case, a light-transmitting material such as a glass plate, a plastic plate, a polyester film, or an acrylic film is used.

In addition to inert gas such as nitrogen and argon, an ultraviolet curable resin or a thermosetting resin can be used as the filler 4507. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicone resin, PVB (Polyvinyl butyral) or EVA (ethylene vinyl acetate) can be used. For example, nitrogen may be used as the filler.

If necessary, an optical film such as a polarizing plate, a circular polarizing plate (including an elliptical polarizing plate), a retardation plate (λ / 4 plate, λ / 2 plate), a color filter, or the like is provided on the light emitting element exit surface. You may provide suitably. Further, an antireflection film may be provided on the polarizing plate or the circularly polarizing plate. For example, anti-glare treatment can be performed that diffuses reflected light due to surface irregularities and reduces reflection.

The signal line driver circuits 4503a and 4503b and the scan line driver circuits 4504a and 4504b may be mounted with a driver circuit formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a separately prepared substrate. Further, only the signal line driver circuit, or a part thereof, or only the scanning line driver circuit, or only a part thereof may be separately formed and mounted, and is not limited to the structure of FIG.

Through the above process, a highly reliable light-emitting display device (display panel) as a semiconductor device can be manufactured.

By manufacturing the thin film transistor in the pixel portion of the light-emitting display device using the method for manufacturing the thin film transistor described in Embodiment 1, power consumption due to variation in off-state current of the thin film transistor in each pixel can be reduced.

In addition, by manufacturing the thin film transistor of the driver circuit of the light-emitting display device using the method for manufacturing the thin film transistor described in Embodiment 1, high-speed operation of the thin film transistor of the driver circuit portion can be realized, and power saving can be achieved.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 6)
In this embodiment, an example of a liquid crystal display device using the liquid crystal element including the thin film transistor described in Embodiment 1 as one embodiment of a semiconductor device will be described with reference to FIGS. The TFT 628 and the TFT 629 used in the liquid crystal display device in FIGS. 17 to 20 can employ the thin film transistor described in Embodiment 1, and can be manufactured in the same manner as in the process described in Embodiment 1. The electrical characteristics and reliability are high. It is a thin film transistor. The TFTs 628 and 629 are thin film transistors having an oxide semiconductor layer as a channel formation region. Although FIGS. 17 to 20 illustrate the case where the thin film transistor illustrated in FIG. 2C is used as an example of a thin film transistor, the present invention is not limited to this.

Hereinafter, a VA (Vertical Alignment) type liquid crystal display device will be described. A VA liquid crystal display device is a type of a method for controlling the alignment of liquid crystal molecules of a liquid crystal display panel. The VA liquid crystal display device is a method in which liquid crystal molecules face a vertical direction with respect to a panel surface when no voltage is applied. In the present embodiment, the pixel (pixel) is divided into several regions (sub-pixels), and each molecule is devised to tilt the molecules in different directions. This is called multi-domain or multi-domain design. In the following description, a liquid crystal display device considering multi-domain design will be described.

18 and 19 show a pixel electrode and a counter electrode, respectively. FIG. 18 is a plan view of the substrate side on which the pixel electrode is formed, and FIG. 17 shows a cross-sectional structure corresponding to the cutting line EF shown in the drawing. FIG. 19 is a plan view of the substrate side on which the counter electrode is formed. The following description will be given with reference to these drawings.

FIG. 17 illustrates a state in which a liquid crystal is injected by superimposing a substrate 600 on which a TFT 628, a pixel electrode 624 connected thereto, and a storage capacitor portion 630 are formed, and a counter substrate 601 on which a counter electrode 640 and the like are formed. Show.

A first colored film 636, a second colored film (not shown), a third colored film (not shown), and a counter electrode 640 are formed at positions where columnar spacers are formed on the counter substrate 601. . With this structure, the height of the protrusion 644 and the spacer for controlling the alignment of the liquid crystal is made different. An alignment film 648 is formed over the pixel electrode 624, and similarly, an alignment film 646 is formed over the counter electrode 640. In the meantime, a liquid crystal layer 650 is formed.

Although the spacer is shown here using a columnar spacer, a bead spacer may be dispersed. Here, the columnar spacer is an organic film or an inorganic film formed on one substrate patterned and etched to a predetermined size by a photolithography process, or a positive or negative patternable organic film. The columnar spacer can control the thickness of the liquid crystal layer. Further, a spacer may be formed over the pixel electrode 624 formed over the substrate 600.

A TFT 628, a pixel electrode 624 connected to the TFT 628, and a storage capacitor portion 630 are formed over the substrate 600. The pixel electrode 624 is connected to the wiring 618 through a contact hole 623 that passes through the insulating film 620 that covers the TFT 628, the wiring 616, and the storage capacitor portion 630 and the third insulating film 622 that covers the insulating film 620. As the TFT 628, the thin film transistor described in Embodiment 1 can be used as appropriate. The storage capacitor portion 630 is a capacitor wiring 604 that is a first capacitor wiring formed at the same time as the gate wiring 602 of the TFT 628, a second capacitor wiring that is formed at the same time as the gate insulating film 606, and the wirings 616 and 618. The capacitor wiring 617 is used.

The pixel electrode 624, the liquid crystal layer 650, and the counter electrode 640 overlap with each other to form a liquid crystal element.

FIG. 18 shows a structure on the substrate 600. The pixel electrode 624 is represented by indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, or indium tin oxide (hereinafter referred to as ITO). ), A light-transmitting conductive material such as indium zinc oxide or indium tin oxide to which silicon oxide is added can be used.

The pixel electrode 624 can be formed using a conductive composition containing a conductive high molecule (also referred to as a conductive polymer). The pixel electrode formed using the conductive composition preferably has a sheet resistance of 10,000 Ω / □ or less and a light transmittance of 70% or more at a wavelength of 550 nm. Moreover, it is preferable that the resistivity of the conductive polymer contained in the conductive composition is 0.1 Ω · cm or less.

As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer of two or more kinds thereof can be given.

The pixel electrode 624 is provided with a slit 625. The slit 625 is for controlling the alignment of the liquid crystal.

The TFT 628 and the pixel electrode 626 and the storage capacitor portion 631 connected to the TFT 628 shown in FIG. 18 can be formed in the same manner as the TFT 628, the pixel electrode 624, and the storage capacitor portion 630, respectively. Both the TFT 628 and the TFT 629 are connected to the wiring 616. A pixel (pixel) of this liquid crystal display panel includes a pixel electrode 624 and a pixel electrode 626. The pixel electrode 624 and the pixel electrode 626 constitute a subpixel.

FIG. 19 shows a structure on the counter substrate side. The counter electrode 640 is preferably formed using a material similar to that of the pixel electrode 624. On the counter electrode 640, a protrusion 644 for controlling the alignment of the liquid crystal is formed.

An equivalent circuit of this pixel structure is shown in FIG. The TFTs 628 and 629 are both connected to the gate wiring 602 and the wiring 616. In this case, the liquid crystal element 651 and the liquid crystal element 652 can be operated differently by changing the potentials of the capacitor wiring 604 and the capacitor wiring 605. That is, by controlling the potentials of the capacitor wiring 604 and the capacitor wiring 605 individually, the orientation of the liquid crystal is precisely controlled to widen the viewing angle.

When a voltage is applied to the pixel electrode 624 provided with the slit 625, an electric field distortion (an oblique electric field) is generated in the vicinity of the slit 625. By arranging the slits 625 and the protrusions 644 on the counter substrate 601 to alternately engage with each other, an oblique electric field is effectively generated to control the alignment of the liquid crystal, so that the direction in which the liquid crystal is aligned is determined. It is different depending on. That is, the viewing angle of the liquid crystal display panel is widened by multi-domain.

Next, a VA liquid crystal display device different from the above is described with reference to FIGS.

21 and 22 show a pixel structure of a VA liquid crystal display panel. FIG. 22 is a plan view of the substrate 600, and FIG. 21 shows a cross-sectional structure corresponding to the cutting line YZ shown in the drawing. The following description will be given with reference to both the drawings.

In this pixel structure, a single pixel has a plurality of pixel electrodes, and a TFT is connected to each pixel electrode. Each TFT is configured to be driven by a different gate signal. In other words, a multi-domain designed pixel has a configuration in which signals applied to individual pixel electrodes are controlled independently.

The pixel electrode 624 is connected to the TFT 628 through a wiring 618 in the contact hole 623. The pixel electrode 626 is connected to the TFT 629 through a wiring 619 in the contact hole 627. The gate wiring 602 of the TFT 628 and the gate wiring 603 of the TFT 629 are separated so that different gate signals can be given. On the other hand, the wiring 616 functioning as a data line is used in common by the TFT 628 and the TFT 629. As the TFT 628 and the TFT 629, the thin film transistor described in Embodiment 1 can be used as appropriate. In addition, a capacitor wiring 690 is provided.

The pixel electrode 624 and the pixel electrode 626 have different shapes and are separated by a slit 625. A pixel electrode 626 is formed so as to surround the outside of the V-shaped pixel electrode 624. The timing of the voltage applied to the pixel electrode 624 and the pixel electrode 626 is made different by the TFT 628 and the TFT 629, thereby controlling the alignment of the liquid crystal. An equivalent circuit of this pixel structure is shown in FIG. The TFT 628 is connected to the gate wiring 602, and the TFT 629 is connected to the gate wiring 603. By giving different gate signals to the gate wiring 602 and the gate wiring 603, the operation timing of the TFT 628 and the TFT 629 can be made different.

A colored film 636 and a counter electrode 640 are formed on the counter substrate 601. In addition, a planarization film 637 is formed between the coloring film 636 and the counter electrode 640 to prevent alignment disorder of the liquid crystal. FIG. 23 shows a structure on the counter substrate side. The counter electrode 640 is a common electrode between different pixels, but a slit 641 is formed. By disposing the slits 641 and the slits 625 on the pixel electrode 624 and pixel electrode 626 sides alternately, an oblique electric field can be effectively generated to control the alignment of the liquid crystal. Thereby, the direction in which the liquid crystal is aligned can be varied depending on the location, and the viewing angle is widened.

The pixel electrode 624, the liquid crystal layer 650, and the counter electrode 640 overlap with each other, so that a first liquid crystal element is formed. In addition, the pixel electrode 626, the liquid crystal layer 650, and the counter electrode 640 overlap with each other, so that a second liquid crystal element is formed. In addition, the multi-domain structure in which the first liquid crystal element and the second liquid crystal element are provided in one pixel.

In this embodiment, the VA liquid crystal display device is described as the liquid crystal display device including the thin film transistor described in Embodiment 1. However, the present invention can also be applied to an IPS liquid crystal display device, a TN liquid crystal display device, and the like. is there.

By manufacturing the thin film transistor in the pixel portion of the light-emitting display device using the method for manufacturing the thin film transistor described in Embodiment 1, power consumption due to variation in off-state current of the thin film transistor in each pixel can be reduced.

(Embodiment 7)
The semiconductor device disclosed in this specification can be applied as electronic paper. Electronic paper can be used for electronic devices in various fields as long as they display information. For example, the electronic paper can be applied to an electronic book (electronic book), a poster, an advertisement in a vehicle such as a train, and a display on various cards such as a credit card. An example of the electronic device is illustrated in FIG.

FIG. 25 illustrates an example of an electronic book 2700. For example, the electronic book 2700 includes two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are integrated with a shaft portion 2711 and can be opened / closed using the shaft portion 2711 as an axis. With such a configuration, an operation like a paper book can be performed.

A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. By adopting a configuration in which different screens are displayed, for example, a sentence can be displayed on the right display unit (display unit 2705 in FIG. 25) and an image can be displayed on the left display unit (display unit 2707 in FIG. 25). .

FIG. 25 illustrates an example in which the housing 2701 is provided with an operation unit and the like. For example, the housing 2701 is provided with a power supply 2721, operation keys 2723, a speaker 2725, and the like. Pages can be turned with the operation keys 2723. Note that a keyboard, a pointing device, or the like may be provided on the same surface as the display portion of the housing. In addition, an external connection terminal (such as an earphone terminal, a USB terminal, or a terminal that can be connected to various cables such as an AC adapter and a USB cable), a recording medium insertion unit, and the like may be provided on the back and side surfaces of the housing. . Further, the e-book reader 2700 may have a structure having a function as an electronic dictionary.

Further, the e-book reader 2700 may have a configuration capable of transmitting and receiving information wirelessly. It is also possible to adopt a configuration in which desired book data or the like is purchased and downloaded from an electronic book server wirelessly.

(Embodiment 8)
The semiconductor device disclosed in this specification can be applied to a variety of electronic devices (including game machines). Examples of the electronic device include a television device (also referred to as a television or a television receiver), a monitor for a computer, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (a mobile phone or a mobile phone). Large-sized game machines such as portable game machines, portable information terminals, sound reproduction apparatuses, and pachinko machines.

FIG. 26A illustrates an example of a television device 9600. In the television device 9600, a display portion 9603 is incorporated in a housing 9601. Images can be displayed on the display portion 9603. Here, a structure in which the housing 9601 is supported by a stand 9605 is illustrated.

The television device 9600 can be operated with an operation switch provided in the housing 9601 or a separate remote controller 9610. Channels and volume can be operated with operation keys 9609 provided in the remote controller 9610, and an image displayed on the display portion 9603 can be operated. The remote controller 9610 may be provided with a display portion 9607 for displaying information output from the remote controller 9610.

Note that the television set 9600 is provided with a receiver, a modem, and the like. General TV broadcasts can be received by a receiver, and connected to a wired or wireless communication network via a modem, so that it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between each other or between recipients).

FIG. 26B illustrates an example of a digital photo frame 9700. For example, a digital photo frame 9700 has a display portion 9703 incorporated in a housing 9701. The display portion 9703 can display various images. For example, by displaying image data captured by a digital camera or the like, the display portion 9703 can function in the same manner as a normal photo frame.

Note that the digital photo frame 9700 includes an operation portion, an external connection terminal (a terminal that can be connected to various types of cables such as a USB terminal and a USB cable), a recording medium insertion portion, and the like. These configurations may be incorporated on the same surface as the display portion, but it is preferable to provide them on the side surface or the back surface because the design is improved. For example, a memory that stores image data captured by a digital camera can be inserted into the recording medium insertion unit of the digital photo frame to capture the image data, and the captured image data can be displayed on the display unit 9703.

Further, the digital photo frame 9700 may be configured to transmit and receive information wirelessly. A configuration may be employed in which desired image data is captured and displayed wirelessly.

FIG. 27A illustrates a portable game machine including two housings, a housing 9881 and a housing 9891, which are connected with a joint portion 9893 so that the portable game machine can be opened or folded. A display portion 9882 is incorporated in the housing 9881, and a display portion 9883 is incorporated in the housing 9891. In addition, the portable game machine shown in FIG. 27A includes a speaker portion 9884, a recording medium insertion portion 9886, an LED lamp 9890, input means (operation keys 9885, a connection terminal 9887, a sensor 9888 (force, displacement, position). , Speed, acceleration, angular velocity, number of revolutions, distance, light, liquid, magnetism, temperature, chemical, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, smell or infrared A microphone 9889) and the like. Needless to say, the structure of the portable game machine is not limited to that described above, and may be any structure as long as it includes at least a semiconductor device disclosed in this specification, and can have a structure in which other accessory facilities are provided as appropriate. The portable game machine shown in FIG. 27A reads out a program or data recorded in a recording medium and displays the program or data on a display unit, or performs wireless communication with another portable game machine to share information. It has a function. Note that the function of the portable game machine illustrated in FIG. 27A is not limited to this, and the portable game machine can have a variety of functions.

FIG. 27B illustrates an example of a slot machine 9900 which is a large-sized game machine. In the slot machine 9900, a display portion 9903 is incorporated in a housing 9901. In addition, the slot machine 9900 includes operation means such as a start lever and a stop switch, a coin slot, a speaker, and the like. Needless to say, the structure of the slot machine 9900 is not limited to that described above, and may be any structure as long as it includes at least a semiconductor device disclosed in this specification.

FIG. 28A is a perspective view illustrating an example of a portable computer.

A portable computer in FIG. 28A has an upper housing 9301 having a display portion 9303 with a hinge unit connecting the upper housing 9301 and the lower housing 9302 closed, and a lower housing 9302 having a keyboard 9304. Are convenient to carry, and when the user performs keyboard input, the hinge unit is opened and an input operation can be performed while viewing the display portion 9303.

In addition to the keyboard 9304, the lower housing 9302 includes a pointing device 9306 that performs an input operation. When the display portion 9303 is a touch input panel, an input operation can be performed by touching part of the display portion. The lower housing 9302 has arithmetic function units such as a CPU and a hard disk. The lower housing 9302 has an external connection port 9305 into which another device, for example, a communication cable compliant with the USB communication standard is inserted.

The upper housing 9301 further includes a display portion 9307 that can be stored inside the upper housing 9301 by being slid therein, so that a wide display screen can be realized. Further, the user can adjust the orientation of the screen of the display portion 9307 that can be stored. Further, when the storable display portion 9307 is a touch input panel, an input operation can be performed by touching a part of the storable display portion.

The display portion 9303 or the retractable display portion 9307 uses a video display device such as a liquid crystal display panel, a light-emitting display panel such as an organic light-emitting element or an inorganic light-emitting element.

In addition, the portable computer in FIG. 28A can be provided with a receiver and the like and can receive a television broadcast to display an image on the display portion or the display portion. In addition, with the hinge unit connecting the upper housing 9301 and the lower housing 9302 closed, the display unit 9307 is slid to expose the entire screen, and the screen angle is adjusted to allow the user to watch TV broadcasting. You can also. In this case, since the hinge unit is opened and the display portion 9303 is not displayed and only the circuit for displaying the television broadcast is activated, the power consumption can be minimized, and the battery capacity can be limited. It is useful in portable computers that are used.

FIG. 28B is a perspective view showing an example of a mobile phone having a form that can be worn on a user's arm like a wristwatch.

This cellular phone includes a communication device having a telephone function and a battery, a main body having a battery, a band portion for attaching the main body to an arm, an adjustment portion 9205 for adjusting a fixing state of the band portion with respect to the arm, a display portion 9201, a speaker 9207, And a microphone 9208.

Further, the main body has an operation switch 9203, and in addition to a power input switch, a display changeover switch, an imaging start instruction switch, for example, when a button is pressed, an Internet program is started.

This input operation of the cellular phone is performed by touching the display portion 9201 with a finger, an input pen, or the like, by operating the operation switch 9203, or by inputting voice to the microphone 9208. Note that FIG. 28B illustrates a display button 9202 displayed on the display portion 9201, and input can be performed by touching with a finger or the like.

In addition, the main body includes a camera unit 9206 having an imaging unit that converts a subject image formed through the photographing lens into an electronic image signal. Note that the camera unit is not necessarily provided.

In addition, the cellular phone illustrated in FIG. 28B includes a television broadcast receiver and the like, can receive television broadcast and display video on the display portion 9201, and can be a storage device such as a memory. The TV broadcast can be recorded in the memory. The mobile phone illustrated in FIG. 28B may have a function of collecting position information such as GPS.

The display portion 9201 uses a video display device such as a liquid crystal display panel, a light-emitting display panel such as an organic light-emitting element or an inorganic light-emitting element. Since the cellular phone shown in FIG. 28B is small and lightweight, its battery capacity is limited, and a display device used for the display portion 9201 is preferably a panel that can be driven with low power consumption.

Note that FIG. 28B illustrates an electronic device of a type attached to an “arm”; however, there is no particular limitation, and any electronic device that has a shape that can be carried may be used.

In this example, a thin film transistor is manufactured using the manufacturing method described in Embodiment Mode 1, and off-state current of a thin film transistor characteristic in an environment of −25 ° C. to 150 ° C. is evaluated.

In this example, a plurality of thin film transistors with a channel length L of 3 μm were formed over a glass substrate, and the off-state current of the thin film transistor characteristics in an environment of −25 ° C. to 150 ° C. was evaluated. The channel width W was 20 μm. First, a method for manufacturing a thin film transistor is described.

First, a 100-nm-thick silicon oxynitride film was formed as a base film over a glass substrate by a CVD method, and a 100-nm-thick tungsten film was formed as a gate electrode layer over the silicon oxynitride film by a sputtering method. Here, the tungsten film was selectively etched to form a gate electrode layer.

Next, a 100-nm-thick silicon oxynitride film was formed as a gate insulating layer over the gate electrode layer by a CVD method.

Next, an In—Ga—Zn—O-based oxide semiconductor target (In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1) is used between the substrate and the target over the gate insulating layer. Is formed at 200 ° C. under an atmosphere of 80 mm, pressure 0.4 Pa, direct current (DC) power supply 5 kW, argon and oxygen (argon: oxygen = 50 sccm: 50 sccm) to form an oxide semiconductor layer having a thickness of 30 nm. did. Here, the oxide semiconductor layer was selectively etched to form an island-shaped oxide semiconductor layer.

Next, the oxide semiconductor layer was subjected to a first heat treatment at 650 ° C. for 6 minutes in a nitrogen atmosphere, and then, a second heat treatment was performed at 450 ° C. for 1 hour in an air atmosphere.

Next, a stack of a titanium film (film thickness: 100 nm), an aluminum film (film thickness: 300 nm), and a titanium film (film thickness: 100 nm) as a source electrode layer and a drain electrode layer over the oxide semiconductor layer is formed at 100 ° C. by a sputtering method. Formed with. Here, the source electrode layer and the drain electrode layer were selectively etched so that the channel length L of the thin film transistor was 3 μm and the channel width W was 20 μm.

Next, a silicon oxide film having a thickness of 300 nm was formed as an insulating layer at 200 ° C. so as to be in contact with the oxide semiconductor layer by a sputtering method. Here, the silicon oxide film, which is a protective layer, was selectively etched to form openings on the gate electrode layer, the source electrode layer, and the drain electrode layer. Thereafter, a third heat treatment was performed at 250 ° C. for 1 hour in a nitrogen atmosphere.

Through the above steps, a plurality of thin film transistors having a channel length L of 3 μm and a channel width W of 20 μm were formed over a glass substrate.

Subsequently, the off current of the thin film transistor was measured. The off-current characteristics were measured by setting the voltage between the source and the drain (hereinafter referred to as the drain voltage or Vd) to 10V, and the voltage between the source and the gate (hereinafter referred to as the gate voltage or Vg) at -10V. . FIG. 4B shows the off-state current of the thin film transistor at each substrate temperature (operating temperature) by changing the substrate temperature during measurement to −25 ° C., 0 ° C., 25 ° C., 50 ° C., 100 ° C., and 150 ° C. . The measurement temperature on the horizontal axis indicates the substrate temperature (operating temperature) when measuring the off-current of the thin film transistor on a linear scale, and the vertical axis indicates the off-current (Ioff) at each substrate temperature on the log scale.

It was confirmed that the thin film transistor manufactured in this example had an off-current value of 1 × 10 ⁻¹² A or less in an environment of −25 ° C. to 150 ° C.

10 pulse output circuit 11 wiring 12 wiring 13 wiring 14 wiring 15 wiring 21 input terminal 22 input terminal 23 input terminal 24 input terminal 25 input terminal 26 output terminal 27 output terminal 28 transistor 31 transistor 32 transistor 33 transistor 34 transistor 35 transistor 36 transistor 37 Transistor 38 Transistor 39 Transistor 40 Transistor 41 Transistor 42 Transistor 43 Transistor 51 Power supply line 52 Power supply line 53 Power supply line 61 Period 62 Period 100 Substrate 101 Gate electrode layer 102 Gate insulating layer 103 Oxide semiconductor layer 107 Insulating layer 110 Channel protective layer 150 Thin film transistor 160 thin film transistor 170 thin film transistor 180 thin film transistor 201 spectrum 202 spectrum 203 Spectrum 301 Spectrum 302 Spectrum 303 Spectrum 311 Spectrum 311 Spectrum 313 Spectrum 321 Spectrum 322 Spectrum 323 Spectrum 400 Glass substrate 401 Oxynitride insulating layer 402 In—Ga—Zn—O-based oxide semiconductor layer 403 Analysis direction 411 Oxygen ion intensity profile 412 Hydrogen Concentration profile 413 Hydrogen concentration profile 451 Spectrum 452 Spectrum 453 Spectrum 461 Spectrum 462 Spectrum 463 Spectrum 581 Thin film transistor 583 Insulating film 585 Insulating layer 587 Electrode layer 588 Electrode layer 589 Spherical particle 594 Cavity 595 Filler 600 Substrate 601 Counter substrate 602 Gate wiring 603 Gate Wiring 604 Capacitance wiring 605 Capacitance wiring 606 Gate insulating film 6 6 wires 617 capacity wire 618 wire 619 wire 620 insulating film 622 insulating film 623 a contact hole 624 pixel electrode 625 slit 626 pixel electrode 627 contact hole 628 TFT
629 TFT
630 Holding capacitor portion 631 Holding capacitor portion 636 Colored film 637 Flattening film 640 Counter electrode 641 Slit 644 Protrusion 646 Alignment film 648 Alignment film 650 In nitrogen atmosphere 650 Liquid crystal layer 651 Liquid crystal element 652 Liquid crystal element 690 Capacitance wiring 701 Gate electrode layer 702 Gate Insulating layer 703 Semiconductor layer 704 Source electrode layer 705 Drain electrode layer 801 Glass substrate 802 Gate electrode layer 803 Gate insulating layer 804 Oxide semiconductor layer 805 Source electrode layer 806 Drain electrode layer 105a Source electrode layer 105b Drain electrode layer 2600 TFT substrate 2601 Opposite Substrate 2602 Sealing material 2603 Pixel portion 2604 Display element 2605 Colored layer 2606 Polarizing plate 2607 Polarizing plate 2608 Wiring circuit portion 2609 Flexible wiring substrate 2610 Cold cathode tube 2611 Reflecting plate 2612 times Road substrate 2613 Diffusion plate 2700 Electronic book 2701 Case 2703 Case 2705 Display portion 2707 Display portion 2711 Shaft portion 2721 Power supply 2723 Operation key 2725 Speaker 4001 Substrate 4002 Pixel portion 4003 Signal line driver circuit 4004 Scan line driver circuit 4005 Sealant 4006 Substrate 4008 Liquid crystal layer 4010 Thin film transistor 4011 Thin film transistor 4013 Liquid crystal element 4015 Connection terminal electrode 4016 Terminal electrode 4018 FPC
4019 Anisotropic conductive film 4020 Insulating layer 4020 Insulating layer (insulating layer 4021 Insulating layer 4030 Pixel electrode layer 4031 Counter electrode layer 4032 Insulating layer 4040 Conductive layer 4501 Substrate 4502 Pixel portion 4505 Sealing material 4506 Substrate 4507 Filler 4509 Thin film transistor 4510 Thin film transistor 4511 Light emitting element 4512 Electroluminescent layer 4513 Electrode layer 4515 Connection terminal electrode 4516 Terminal electrode 4517 Electrode layer 4519 Anisotropic conductive film 4520 Partition wall 4540 Conductive layer 4541 Insulating layer 4544 Insulating layer 5300 Substrate 5300 Substrate 5301 Pixel portion 5302 Scanning line driver circuit 5303 Scan line driver circuit 5304 Signal line driver circuit 5305 Timing control circuit 5601 Shift register 5602 Switching circuit portion 5602 Switching circuit 5603 Thin film transistor Transistor 5604 wiring 5605 wiring 590a black region 590b white region 6400 pixel 6401 switching transistor 6402 driving transistor 6403 capacitor element 6404 light emitting element 6405 signal line 6406 scanning line 6407 power supply line 6408 common electrode 7001 TFT
7002 Light emitting element 7003 Cathode 7004 EL layer 7005 Anode 7009 Partition 7011 TFT
7012 Light emitting element 7013 Cathode 7014 EL layer 7015 Anode 7016 Shielding film 7017 Conductive film 7019 Partition 7021 TFT
7022 Light emitting element 7023 Cathode 7024 EL layer 7025 Anode 7026 Anode 7027 Conductive film 7029 Partition 7031 Oxide insulating layer 7033 Color filter layer 7034 Overcoat layer 7035 Insulating layer 7041 Oxide insulating layer 7043 Color filter layer 7044 Overcoat layer 7045 Insulating layer 704a Drain electrode layer 704b Source electrode layer 7051 Oxide insulating layer 7052 Insulating layer 7053 Flattening insulating layer 7055 Insulating layer 9201 Display portion 9202 Display button 9203 Operation switch 9205 Adjusting portion 9206 Camera portion 9207 Speaker 9208 Microphone 9301 Upper housing 9302 Lower housing 9303 Display unit 9304 Keyboard 9305 External connection port 9306 Pointing device 9307 Display unit 9600 Television apparatus 9601 Body 9603 Display unit 9605 Stand 9607 Display unit 9609 Operation key 9610 Remote control unit 9700 Digital photo frame 9701 Case 9703 Display unit 9881 Case 9882 Display unit 9883 Display unit 9984 Speaker unit 9985 Input unit (operation key 9886 Recording medium insertion unit 9877 Connection terminal 9888 Sensor 9889 Microphone 9890 LED lamp 9891 Housing 9893 Connection unit 9900 Slot machine 9901 Housing 9903 Display unit 4503a Signal line driver circuit 4504a Scan line driver circuit 4518a FPC

Claims (8)

A gate electrode layer on a substrate having an insulating surface;
A gate insulating layer on the gate electrode layer;
An oxide semiconductor layer on the gate insulating layer;
A source electrode layer and a drain electrode layer on the oxide semiconductor layer;
An insulating layer in contact with a part of the oxide semiconductor layer on the gate insulating layer, the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
A semiconductor device, wherein a channel width is 1 × 10 ⁻¹² A or less in a temperature range of −25 ° C. to 150 ° C. In claim 1,
The semiconductor device is characterized in that a channel length of the oxide semiconductor layer is 1.5 μm or more and 100 μm or less. In claim 1,
A channel length of the oxide semiconductor layer is 3 μm to 10 μm. Forming a gate electrode layer over a substrate having an insulating surface;
Forming a gate insulating layer on the gate electrode layer;
Forming an oxide semiconductor layer on the gate insulating layer;
After forming the oxide semiconductor layer, a first heat treatment and a second heat treatment are performed,
Forming a source electrode layer and a drain electrode layer on the oxide semiconductor layer;
Forming an insulating layer in contact with part of the oxide semiconductor layer over the gate insulating layer, the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
A method for manufacturing a semiconductor device is characterized in that after the insulating layer is formed, third heat treatment is performed. In claim 4,
The method for manufacturing a semiconductor device, wherein the first heat treatment is performed at a temperature of 350 ° C to 750 ° C. In claim 4 or claim 5,
The method for manufacturing a semiconductor device, wherein the first heat treatment is performed in a nitrogen atmosphere or a rare gas atmosphere. In claim 4 or claim 6,
The method for manufacturing a semiconductor device, wherein the second heat treatment is performed at a temperature of 100 ° C. to a temperature of the first heat treatment. In any one of Claims 4 thru | or 7,
The method for manufacturing a semiconductor device, wherein the second heat treatment is performed in an air atmosphere or an oxygen atmosphere.

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