Thin film transistor, display unit, and method of manufacturing thin film transistor

A thin film transistor includes: a gate electrode; a gate insulting film formed on the gate electrode; an oxide semiconductor thin film layer forming a channel region corresponding to the gate electrode on the gate insulating film; a channel protective layer that is formed at least in a region corresponding to the channel region on the gate insulating film and the oxide semiconductor thin film layer, and that includes a first channel protective layer on a lower layer side and a second channel protective layer on an upper layer side; and a source/drain electrode that is formed on the channel protective layer and is electrically connected to the oxide semiconductor thin film layer. The first channel protective layer is made of an oxide insulating material, and one or both of the first channel protective layer and the second channel protective layer is made of a low oxygen permeable material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin film transistor (TFT) including an oxide semiconductor thin film layer, a method of manufacturing the same, and a display unit including such a thin film transistor.

2. Description of the Related Art

It has been known that an oxide (oxide semiconductor) composed of zinc, indium, gallium, tin, or a mixture thereof shows superior semiconductor characteristics. Thus, in recent years, applying the oxide semiconductor to a TFT as a drive element of an active matrix display has been actively studied.

In the TFT including the oxide semiconductor, electron mobility ten times or more of that of the existing TFT including amorphous silicon is shown and favorable off-characteristics are shown. Thus, the TFT including the oxide semiconductor is largely expected to be applied to a large-screen, high-definition, and high-frame-rate liquid crystal display and an organic EL display.

Meanwhile, in the oxide semiconductor, the heat resistance is not sufficient. Thus, due to heat treatment or plasma treatment in a manufacturing process of the TFT, oxygen is detached and lattice defect is formed. The lattice defect results in forming an electrically shallow impurity level, and causes low resistance of the oxide semiconductor. Thus, in the case where the oxide semiconductor is used for an active layer of the TFT, the defect level is increased, the threshold voltage is decreased, the leakage current is increased, resulting in depression type operation in which a drain current is flown without applying a gate current. If the defect level is sufficiently increased, transistor operation is stopped to shift to semiconductor operation.

Further, in addition to the foregoing lattice defect, hydrogen has been reported as an element to form an electrically shallow impurity level. Thus, in addition to the lattice defect, an element such as hydrogen introduced in manufacturing steps of the TFT has been regarded as a substance that affects characteristics of the TFT including the oxide semiconductor.

Thus, for the purpose of resolving the foregoing disadvantages, for example, TFTs disclosed in “Improved Amorphous In—Ga—Zn-0 TFTs,” Ryo Hayashi et al., SID2008 Proceedings, 2008, pp. 621-624 and Japanese Unexamined Patent Application Publication No. 2007-115808 have been proposed.

SUMMARY OF THE INVENTION

In the foregoing “Improved Amorphous In—Ga—Zn-0 TFTs,” a channel protective layer is formed from a silicon oxide film, and a passivation film is formed from a silicon nitride film. In this technique, to prevent oxygen detachment after forming an active layer, the channel protective layer is formed by using silicon oxide immediately after forming the active layer, and then a source/drain electrode is formed and patterned. As a thin film through which oxygen hardly passes, the passivation film is formed by using the silicon nitride film.

However, in such a technique, since both protective films (the channel protective layer and the passivation film) are formed, two photolithography steps are necessitated. Further, before forming the passivation film, at least three high temperature heat steps (forming the channel protective layer, forming the source/drain electrode layer, and forming the passivation film) are performed. Thus, there has been the following disadvantage. That is, without whether or not oxygen detachment from the oxide semiconductor thin film layer is generated, after forming the passivation film, due to existence of the passivation film through which oxygen hardly passes, oxygen is hardly supplied to the oxide semiconductor thin film layer.

Meanwhile, in the foregoing Japanese Unexamined Patent Application Publication No. 2007-115808, a channel protective layer is not formed. In such a TFT structure, a first passivation film made of a silicon oxide film and a second passivation film made of a silicon nitride film are able to prevent oxygen from being detached in a step of forming passivation, and the steps are able to be simplified.

However, in such a technique, there is a disadvantage that oxygen detachment or the like is generated in a step of forming a source/drain electrode and thus favorable transistor characteristics are not able to be obtained. That is, to restore the favorable transistor characteristics, it is necessary to resupply oxygen after forming the source/drain electrode.

As described above, in the existing technologies, it has been difficult to decrease oxygen detachment in the oxide semiconductor thin film layer and to improve reliability with the use of a simple structure.

In view of the foregoing disadvantages, in the invention, it is desirable to provide a thin film transistor that includes an oxide semiconductor thin film layer and is able to improve reliability with the use of a simple structure, a method of manufacturing the same, and a display unit including such a thin film transistor.

According to an embodiment of the invention, there is provided a thin film transistor including a gate electrode; a gate insulting film formed on the gate electrode; an oxide semiconductor thin film layer forming a channel region corresponding to the gate electrode on the gate insulating film; a channel protective layer that is formed at least in a region corresponding to the channel region on the gate insulating film and the oxide semiconductor thin film layer, and that includes a first channel protective layer on a lower layer side and a second channel protective layer on an upper layer side; and a source/drain electrode that is formed on the channel protective layer and is electrically connected to the oxide semiconductor thin film layer. The first channel protective layer is made of an oxide insulating material, and one or both of the first channel protective layer and the second channel protective layer is made of a low oxygen permeable material.

According to an embodiment of the invention, there is provided a display unit including: a display device; and a thin film transistor for driving the display device.

In the thin film transistor and the display unit of the embodiments of the invention, since the first channel protective layer is made of the oxide insulating material, and one or both of the first channel protective layer and the second channel protective layer is made of the low oxygen permeable material, oxygen detachment from the oxide semiconductor thin film layer is inhibited. Further, since the source/drain electrode is formed on the upper layer of the channel protective layer, oxygen detachment from the oxide semiconductor thin film layer is inhibited at the time of forming the source/drain electrode as well. Furthermore, since the channel protective layer has a function as the existing passivation film, the structure becomes simpler than the existing structure.

According to an embodiment of the invention, there is provided a method of manufacturing a thin film transistor including the steps of forming a gate electrode and a gate insulating film in this order on a substrate; forming an oxide semiconductor thin film layer having a channel region correspondingly to the gate electrode; patterning a channel protective layer including a first channel protective layer on a lower layer side and a second channel protective layer on an upper layer side in at least a region corresponding to the channel region on the gate insulating film and the oxide semiconductor thin film layer and thereby forming a contact hole for obtaining electrical connection with the oxide semiconductor thin film layer; and forming a source/drain electrode on the channel protective layer and the contact hole. Further, an oxide insulating material is used as the first channel protective layer, and a low oxygen permeable material is used as at least one of the first channel protective layer and the second channel protective layer.

In the method of manufacturing a thin film transistor according to the embodiment of the invention, the first channel protective layer is formed by using the oxide insulating material, and at least one of the first channel protective layer and the second channel protective layer is formed by using the low oxygen permeable material. Thereby, oxygen detachment from the oxide semiconductor thin film layer is inhibited. Further, since the source/drain electrode is formed after forming the channel protective layer, oxygen detachment from the oxide semiconductor thin film layer is inhibited at the time of forming the source/drain electrode as well. Furthermore, since the channel protective layer has a function as the existing passivation film, the manufacturing steps become simpler than the existing manufacturing steps.

According to the thin film transistor, the display unit, and the method of manufacturing a thin film transistor of the embodiments of the invention, the channel protective layer that includes the first channel protective layer on the lower layer side and the second channel protective layer on the upper layer side is provided. Thus, at the time of forming the channel protective layer and the source/drain electrode, oxygen detachment from the oxide semiconductor thin film layer is able to be inhibited, and a leakage current is able to be decreased. Further, since the channel protective layer has a function as the existing passivation film, the structure and the manufacturing steps become simpler than the existing structure and the existing manufacturing steps. Thus, in the thin film transistor including the oxide semiconductor thin film layer, reliability is able to be improved with the use of a simple structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be hereinafter described in detail with reference to the drawings. The description will be given in the following order:1. First embodiment (example that a channel protective layer has a two-layer structure)2. Second embodiment (example that a hole (aperture) for supplying oxygen to an oxide semiconductor thin film layer is provided)3. Module and application examples

1. First Embodiment

(Structural Example of Display Unit)

FIG. 1illustrates a structure of a display unit according to a first embodiment of the invention. The display unit is used as an ultrathin organic light emitting color display unit or the like. In the display unit, for example, a display region110in which pixels PXLCs composed of a plurality of organic light emitting devices10R,10G, and10B described later are arranged in a matrix state as a display device is formed in a TFT substrate1. On the circumference of the display region110, a horizontal selector (HSFL)121as a signal section, and a light scanner (WSCN)131and a power source scanner (DSCN)132as a scanner section are formed.

In the display region110, signal lines DTL101to DTL10nare arranged in the column direction, and scanning lines WSL101to WSL10mand power source lines DSL101to DSL10mare arranged in the row direction. A pixel circuit140including the organic light emitting device PXLC (one of10R,10G, and10B (sub pixel)) is provided at each cross section between each signal line DTL and each scanning line WSL. Each signal line DTL is connected to the horizontal selector121. A video signal Sig is supplied from the horizontal selector121to the signal line DTL. Each scanning line WSL is connected to the light scanner131. Each power source line DSL is connected to the power source line scanner132.

FIG. 2illustrates an example of the pixel circuit140. The pixel circuit140is an active drive circuit having a sampling transistor3A, a drive transistor3B, a retentive capacity3C, and a light emitting device3D composed of the organic light emitting device PXLC. In the sampling transistor3A, its gate is connected to the corresponding scanning line WSL101, one of its source and its drain is connected to the corresponding signal line DTL101, and the other thereof is connected to a gate “g” of the drive transistor3B. In the drive transistor3B, its drain “d” is connected to the corresponding power source line DSL101, and its source s is connected to an anode of the light emitting device3D. A cathode of the light emitting device3D is connected to a ground link3H. The ground link3H is commonly wired to all pixels PXLCs. The retentive capacity3C is connected between the source s and the gate g of the drive transistor3B.

The sampling transistor3A makes conduction in accordance with a control signal supplied from the scanning line WSL101, performs sampling of a signal potential of a video signal supplied from the signal line DTL101, and retains the result into the retentive capacity3C. The drive transistor3B receives a current supply from the power source line DSL101in the first potential, and supplies a drive current to the light emitting device3D in accordance with the signal potential retained in the retentive capacity3C. The light emitting device3D emits light at luminance in accordance with the signal potential of the video signal by the supplied drive current.

(Structural Example of TFT)

FIG. 3illustrates a planar structure of part of the pixel drive circuit140of the TFT substrate1(section corresponding to the sampling transistor3A and the retentive capacity3C ofFIG. 2). In the TFT substrate1, for example, a TFT20composing the foregoing sampling transistor3A and a capacitor30composing the foregoing retentive capacity3C are formed on the substrate10made of glass or the like. Though omitted inFIG. 3, the drive transistor3B ofFIG. 2is composed similarly to the TFT20.

FIG. 4illustrates a cross sectional structure of the TFT20illustrated inFIG. 3. The TFT20is a bottom gate oxide semiconductor transistor sequentially having, for example, a gate electrode21, a gate insulating film22, an oxide semiconductor thin film layer23, a channel protective layer24, and a source/drain electrode25. The oxide semiconductor represents an oxide of zinc, indium, gallium, tin, or a mixture thereof, and is known to show superior semiconductor characteristics.

FIG. 5illustrates current voltage characteristics of an oxide semiconductor TFT composed of, for example, a mixed oxide of zinc, indium, and gallium (indium gallium zinc oxide: IGZO). The oxide semiconductor shows electron mobility from ten times to a hundred times as large as that of the amorphous silicon that has been used as a semiconductor in the past and shows favorable off-characteristics. Further, in the oxide semiconductor, the resistivity is from hundredth part to tenth part of that of the existing amorphous silicon. In addition, in the oxide semiconductor, the threshold voltage is able to be easily set low, for example, 0 V or less.

The gate electrode21controls electron density in the oxide semiconductor thin film layer23by a gate voltage applied to the TFT20. The gate electrode21has, for example, a two-layer structure composed of a molybdenum (Mo) layer having a thickness of 50 nm and an aluminum (Al) layer or an aluminum alloy layer having a thickness of 400 nm.

The gate insulating film22has, for example, a two-layer structure composed of a silicon oxide film having a thickness of 200 nm and a silicon nitride film having a thickness of 200 nm.

The oxide semiconductor thin film layer23has, for example, a thickness of 50 nm, and is composed of indium gallium zinc oxide (IGZO). In the oxide semiconductor thin film layer23, a channel region (not illustrated) is formed correspondingly to the gate electrode21. The oxide semiconductor thin film layer23is patterned in the shape of an island (not illustrated).

The channel protective layer24is formed at least in a region corresponding to the channel region in the oxide semiconductor thin film layer23. The channel protective layer24has a two-layer structure composed of a first channel protective layer24A and a second channel protective layer24B that are sequentially layered from the substrate10side.

The first channel protective layer24A is a layer that makes an oxygen amount detached from the oxide semiconductor thin film layer23small (desirably a layer that does not detach oxygen from the oxide semiconductor thin film layer23), or a layer that supplies a small amount of hydrogen to the oxide semiconductor thin film layer23(desirably a layer that does not supply hydrogen to the oxide semiconductor thin film layer23). The first channel protective layer24A has, for example, a thickness of 200 nm, and is made of an oxide insulator material (for example, silicon oxide, tantalum oxide, titanium oxide, hafnium oxide, zirconium oxide, yttrium oxide, aluminum oxide, a nitrogenous material thereof or the like). To realize the first channel protective layer24A that supplies a small amount of hydrogen as described above, the first channel protective layer24A desirably has the hydrogen concentration in the film of about 1021(cm−3) or less. As the first channel protective layer24A, a silicon nitride film may be used as long as the silicon nitride film is a film that is formed by sputtering method and has a small oxygen content.

The second channel protective layer24B is a film having oxygen passivation effect to make oxygen hardly detached in a heat step after forming the second channel protective layer24B. Further, the second channel protective layer24B has passivation effect to prevent moisture intrusion from outside. The second channel protective layer24B has, for example, a thickness of 100 nm, and is made of a material having low oxygen permeability and low water vapor permeability (for example, oxygen permeability factor of detection limit of Mocon method (0.1 (cc/m2day) or less and water vapor permeability factor of 0.1 (g/m2day) or less) (for example, silicon nitride, silicon oxynitride, aluminum oxide or the like). In the case where an aluminum oxide film is used as the first channel protective layer24A, the first channel protective layer24A has oxygen passivation effect. Thus, a silicon oxide film is able to be used as the second channel protective layer24B.

Even in the case where the first channel protective layer24A does not detach oxygen from the oxide semiconductor thin film layer23(condition A), does not supply hydrogen to the oxide semiconductor thin film layer23(condition B), does not pass oxygen (condition C), and does not pass water vapor (condition D), it is necessary to provide the second channel protective layer24B. That is, the channel protective layer24in this embodiment has a two-layer structure composed of the first channel protective layer24A and the second channel protective layer24B. The second channel protective layer24B is provided in addition to the first channel protective layer24A for the following reason. First, in the off-region in the TFT20, the capacity component of the channel protective layer24is added to a parasitic capacity formed between the source/drain electrode25and the gate electrode21. Thus, to make the parasitic capacity small, it is necessary to increase the film thickness of the channel protective layer24as much as possible to decrease the capacity component of the channel protective layer24. Therefore, in the case where the first channel protective layer24A satisfies the foregoing all conditions A to D, the material and the film thickness of the second channel protective layer24B are selected while paying attention to the foregoing parasitic capacity or the pattern shape of the channel protective layer24. Further, for the purpose of decreasing the parasitic capacity or for the purpose of keeping the pattern shape of the channel protective layer24favorable, the channel protective layer24may have a structure composed of three or more layers.

Further, the channel protective layer24also functions as a passivation layer. Thus, it is beneficial that the channel protective layer24is left on a section other than the channel formation section, for example, on a gate wiring. As illustrated inFIG. 4, it is desirable to pattern only the formation section of the source/drain electrode25.

The source/drain electrode25has a laminated structure composed of, for example, a titanium layer25A having a thickness of 50 nm, an aluminum layer25B having a thickness of 90 nm, and a titanium layer25C having a thickness of 50 nm. The source/drain electrode25is electrically connected to the oxide semiconductor thin film layer23through a contact hole.

(Example of Cross Sectional Structure of Display Region)

FIG. 6illustrates a cross sectional structure of the display region110illustrated inFIG. 1. In the display region110, the organic light emitting device10R generating red light, the organic light emitting device10G generating green light, and the organic light emitting device10B generating blue light are sequentially formed in a matrix state as a whole. The organic light emitting devices10R,10G, and10B have a reed-like planar shape, and a combination of the organic light emitting devices10R,10G, and10B adjacent to each other composes one pixel.

The organic light emitting devices10R,10G, and10B respectively have a structure in which an anode52, an interelectrode insulating film53, an organic layer54including an after-mentioned light emitting layer, and a cathode55are layered in this order over the TFT substrate1with a planarizing insulating film51in between.

The organic light emitting devices10R,10G, and10B as above are coated with a protective film56composed of silicon nitride (SiN), silicon oxide (SiO) or the like according to needs. Further, a sealing substrate71made of glass or the like is bonded to the whole area of the protective film55with an adhesive layer60made of a thermoset resin, an ultraviolet cure resin or the like in between, and thereby the organic light emitting devices10R,10G, and10B are sealed. The sealing substrate71may be provided with a color filter72and a light shielding film (not illustrated) as a black matrix according to needs.

The planarizing insulating film51is intended to planarize a front face of the TFT substrate1over which the pixel drive circuit140is formed. Since the fine connection hole51A is formed in the planarizing insulating film51, the planarizing insulating film51is preferably made of a material having favorable pattern precision. Examples of component materials of the planarizing insulating film51include an organic material such as polyimide and an inorganic material such as silicon oxide (SiO2). The drive transistor3B illustrated inFIG. 2is electrically connected to the anode52through the connection hole51A provided in the planarizing insulating film51. Further, though omitted inFIG. 6, a lower electrode31of the capacitor30composing the retentive capacity3C is also electrically connected to the anode52through a connection hole (not illustrated) provided in the planarizing insulating film51.

The anode52is formed correspondingly to the respective organic light emitting devices10R,10G, and10B. Further, the anode52has a function as a reflecting electrode to reflect light generated in the light emitting layer, and desirably has high reflectance as much as possible in order to improve light emitting efficiency. The anode52has, for example, a thickness from 100 nm to 1000 nm both inclusive. The anode52is composed of a simple substance or an alloy of a metal element such as silver (Ag), aluminum (Al), chromium (Cr), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo), copper (Cu), tantalum (Ta), tungsten (W), platinum (Pt), and gold (Au).

The interelectrode insulating film53is intended to secure insulation between the anode52and the cathode55, and to accurately obtain a desired shape of the light emitting region. For example, the interelectrode insulating film53is made of an organic material such as polyimide or an inorganic insulating material such as silicon oxide (SiO2). The interelectrode insulating film53has apertures correspondingly to the light emitting region of the anode52. The organic layer54and the cathode55may be also provided continuously on the interelectrode insulating film53in addition to on the light emitting region, but light is emitted only in the aperture of the interelectrode insulating film53.

The organic layer54has, for example, a structure in which an electron hole injection layer, an electron hole transport layer, the light emitting layer, and an electron transport layer (not illustrated) are layered in this order from the anode52side. Of the foregoing layers, the layers other than the light emitting layer may be provided according to needs. Further, the organic layer54may have a structure varying according to the light emitting color of the organic light emitting devices10R,10G,10B. The electron hole injection layer is intended to improve the electron hole injection efficiency and functions as a buffer layer to prevent leakage. The electron hole transport layer is intended to improve efficiency to transport electrons into the light emitting layer. The light emitting layer is intended to generate light due to electron-hole recombination by impressing an electric field. The electron transport layer is intended to improve efficiency to transport electrons into the light emitting layer. Component materials of the organic layer54are not particularly limited as long as the component materials are a general low molecular organic material or a general high molecular organic material.

The cathode55has, for example, a thickness from 5 nm to 50 nm both inclusive, and is composed of a simple substance or an alloy of metal elements such as aluminum (Al), magnesium (Mg), calcium (Ca), and sodium (Na). Specially, an alloy of magnesium and silver (MgAg alloy) or an alloy of aluminum (Al) and lithium (Li) (AlLi alloy) is preferable. Further, the cathode55may be composed of ITO (indium tin composite oxide) or IZO (indium zinc composite oxide).

The display unit is able to be manufactured, for example, as follows.

(Step of Forming TFT Substrate1)

FIG. 7illustrates an example of steps of forming the TFT substrate1(TFT20).

First, a two-layer structure composed of a molybdenum (Mo) layer having a thickness of 50 nm and an aluminum (Al) layer or an aluminum alloy layer having a thickness of 400 nm is formed on the substrate10made of glass by, for example, sputtering method. Next, the gate electrode21is formed by providing photolithography and etching for the two-layer structure (step S11ofFIG. 7).

Subsequently, a two-layer structure composed of a silicon oxide film having a thickness of 200 nm and a silicon nitride film having a thickness of 200 nm is formed on the whole area of the substrate10by, for example, CVD method. Thereby the gate insulating film22is formed (step S12).

After that, an indium gallium zinc oxide (IGZO) film having a thickness of 50 nm is formed by, for example, sputtering method, and the film is formed into a given shape by photolithography and etching. Thereby the oxide semiconductor thin film layer23is formed (step S13).

After the oxide semiconductor thin film layer23is formed, a silicon oxide film having a thickness of 200 nm to become the first channel protective layer24A is formed by, for example, CVD method (step S15). At this time, the composition of deposition gas preferably does not contain hydrogen. Instead of the silicon oxide film formed by CVD method, a silicon oxide film, a silicon nitride film, or an oxide aluminum film formed by sputtering method or an aluminum oxide film by atomic layer deposition (ALD) method may be formed.

Subsequently, a silicon nitride film having a thickness of 100 nm to become the second channel protective layer24B is formed by, for example, CVD method (step S17). At this time, the composition of deposition gas preferably does not contain hydrogen. Instead of the silicon nitride film formed by CVD method, a silicon nitride film or an aluminum oxide film formed by sputtering method or an aluminum oxide film formed by atomic layer deposition (ALD) method may be formed.

The first channel protective layer24A functions as a protective film at the time of forming the TFT20. Thus, the first channel protective layer24A may be formed immediately after forming the oxide semiconductor thin film layer23. In this case, the oxide semiconductor thin film layer23and the first channel protective layer24A are formed into the same shape by a photolithography step and an etching step.

Subsequently, the silicon nitride film is formed into a given shape by photolithography and etching to form a contact hole to the oxide semiconductor thin film layer23(step S19). Thereby, the channel protective layer24composed of the first channel protective layer24A and the second channel protective layer24B in the shape illustrated inFIG. 3are formed. At this time, the channel protective layer24also functions as a passivation layer. Thus, it is beneficial that the channel protective layer24is left on a section other than the channel formation section, for example, on a gate wiring. As illustrated inFIG. 4, it is desirable to pattern only the formation section of the source/drain electrode25. In this step, a contact hole to the gate electrode21may be provided in a region where the oxide semiconductor thin film layer23does not exist.

Subsequently, the titanium layer25A having a thickness of 50 nm, the aluminum layer25B having a thickness of 900 nm, and the titanium layer25C having a thickness of 50 nm are formed by, for example, sputtering method. After that, the titanium layer25A, the aluminum layer25B, and the titanium layer25C are respectively formed into a given shape by photolithography and etching. Thereby, the source/drain electrode25is formed (step S21). Accordingly, the TFT substrate1illustrated inFIG. 3andFIG. 4is formed.

(Step of Forming Organic Light Emitting Devices10R,10G, and10B)

First, the whole area of the TFT substrate1is coated with a photosensitive resin, and exposure and development are performed. Thereby, the planarizing insulating film51and the connection hole51A are formed and fired. Next, the anode52made of the foregoing material is formed by, for example, direct current sputtering. The resultant film is selectively etched and patterned into a given shape by, for example, using lithography technology. Subsequently, the interelectrode insulating film53that has the foregoing thickness and is made of the foregoing material is formed by, for example, CVD method, and an aperture is formed by using, for example, lithography technology. After that, the organic layer54and the cathode55that are made of the foregoing materials are sequentially formed by, for example, evaporation method to form the organic light emitting devices10R,10G, and10B. Subsequently, the organic light emitting devices10R,10G, and10B are covered with the protective film56made of the foregoing material.

After that, the adhesive layer60is formed on the protective film56. After that, the sealing substrate71that is provided with the color filter72and is made of the foregoing material is prepared. The TFT substrate1and the sealing substrate71are bonded with each other with the adhesive layer60in between. Accordingly, the display unit illustrated inFIG. 6is completed.

Next, a description will be given of action and effect of the display unit of this embodiment by comparison with comparative examples.FIG. 9illustrates a planar structure of part of a pixel drive circuit of a TFT substrate according to a first comparative example.FIG. 10illustrates a cross sectional structure of a TFT820illustrated inFIG. 9. Further,FIG. 11illustrates a planar structure of part of a pixel drive circuit of a TFT substrate according to a second comparative example.FIG. 12illustrates a cross sectional structure of a TFT920illustrated inFIG. 11. InFIG. 9andFIG. 10, elements corresponding to the elements ofFIG. 3andFIG. 4are affixed with a number obtained by adding800to the elements ofFIG. 3andFIG. 4. Further, inFIG. 11andFIG. 12, elements corresponding to the elements ofFIG. 3andFIG. 4are affixed with a number obtained by adding900to the elements ofFIG. 3andFIG. 4.

In this display unit, the sampling transistor3A makes conduction in accordance with a control signal supplied from the scanning line WSL, and a signal potential of a video signal supplied from the signal line DTL is sampled and retained in the retentive capacity3C. Further, a current is supplied from the power source line DSL in the first potential to the drive transistor3B, and a drive current is supplied to the light emitting device3D (organic light emitting devices10R,10G, and10B) in accordance with the signal potential retained in the retentive capacity3C. The light emitting device3D (organic light emitting devices10R,10G, and10B) emits light at luminance corresponding to the signal potential of the video signal by the supplied drive current. The light is transmitted through the cathode55, the color filter72, and the sealing substrate71and is extracted.

In the oxide semiconductor, the heat resistance is not sufficient. Thus, due to heat treatment and plasma treatment in a manufacturing process of a TFT, oxygen is detached and lattice defect is formed. The lattice defect results in forming an electrically shallow impurity level, and causes low resistance of the oxide semiconductor. Thus, in the case where the oxide semiconductor is used for an active layer of the TFT, the defect level is increased, the threshold voltage is decreased, a leakage current is increased, resulting in depression type operation in which a drain current is flown without applying a gate current. If the defect level is sufficiently increased, as illustrated inFIG. 8, transistor operation is stopped to shift to semiconductor operation.

Thus, in the first comparative example illustrated inFIG. 9andFIG. 10, a channel protective layer824is formed from a silicon oxide film, and a passivation film826is formed from a silicon nitride film. In this technique, to prevent oxygen detachment after forming an active layer, after forming the channel protective layer824by using silicon oxide immediately after forming the active layer, a source/drain electrode825(825A to825C) is formed and patterned. As a thin film through which oxygen hardly passes, the passivation film826is formed by using the silicon nitride film.

However, in the technique of the first comparative example, two photolithography steps are necessitated to form both protective films (the channel protective layer824and the passivation film826). Further, before forming the passivation film826, at least three high temperature heat steps (forming the channel protective layer824, forming the source/drain electrode layer826, and forming the passivation layer826) are performed. Thus, without whether or not oxygen detachment from the oxide semiconductor thin film layer23is generated, after forming the passivation film826, due to existence of the passivation film826through which oxygen hardly passes, oxygen is hardly supplied to the oxide semiconductor thin film layer23.

Meanwhile, in the second comparative example illustrated inFIG. 11andFIG. 12, a channel protective layer is not formed. Further, a first passivation film926A made of a silicon oxide film and a second passivation film926B made of a silicon nitride film prevent oxygen from being detached in a step of forming passivation. Further, since the channel protective layer is not formed and a source/drain electrode925(925A to925C) and the passivation films926A and926B are formed on the oxide semiconductor thin film layer23, the steps are simplified.

However, in the technique of the second comparative example, oxygen detachment or the like is generated in a step of forming the source/drain electrode925and thus favorable transistor characteristics are not able to be obtained. That is, to restore the favorable transistor characteristics, it is necessary to resupply oxygen after forming the source/drain electrode925.

Meanwhile, in this embodiment, the first channel protective layer24A made of the oxide insulating material inhibits oxygen detachment from the oxide semiconductor thin film layer23. Further, the second channel protective layer24B made of the material having low oxygen permeability on the first channel protective layer24A inhibits oxygen detachment from the oxide semiconductor thin film layer23. In addition, since the source/drain electrode25is formed on the upper layer of the channel protective layer24, oxygen detachment from the oxide semiconductor thin film layer23is inhibited at the time of forming the source/drain electrode25as well.

Further, since the channel protective layer24has a function as the existing passivation film, the structure is more simplified than the existing structure.

As described above, in this embodiment, the channel protective layer24composed of the first channel protective layer24A on the lower layer side and the second channel protective layer24B on the upper layer side is provided. Thus, at the time of forming the channel protective layer24and the source/drain electrode25, oxygen detachment from the oxide semiconductor thin film layer23is able to be inhibited, and a leakage current is able to be decreased. Further, since the channel protective layer24has a function as the existing passivation film, the structure and the manufacturing steps are more simplified than the existing structure and the existing manufacturing steps. Therefore, in a thin film transistor including the oxide semiconductor thin film layer23, reliability is able to be improved with a simple structure.

Specifically, in the existing channel protective film, under high temperature and vacuum conditions in sputtering at the time of forming the source/drain or at the time of generation of initial plasma, there is a possibility that oxygen detachment from the oxide semiconductor thin film layer around the channel protective film is generated and accordingly a weak leakage current is generated between the source electrode and the drain electrode. Meanwhile, in this embodiment, such a weak leakage current is able to be inhibited.

Further, in the display unit including such a TFT20, an inexpensive and high-quality flat panel display is able to be realized.

2. Second Embodiment

(Structural Example of TFT)

FIGS. 13A to 13Cillustrate a planar structure of part of the pixel drive circuit140of the TFT substrate1according to a second embodiment of the invention (section corresponding to the sampling transistor3A and the retentive capacity3C ofFIG. 2). This embodiment is totally the same as the foregoing first embodiment, except that a hole (aperture) described below is provided. Thus, a description will be given by affixing the same referential symbols to the corresponding elements.

First, in the foregoing first embodiment, in forming the TFT20, at the time of forming the source/drain electrode25, in some cases, there is a possibility that oxygen detachment from the oxide semiconductor thin film layer23is generated and the transistor characteristics are deteriorated.

Thus, in this embodiment, as in TFTs20A to20C illustrated inFIGS. 13A to 13C, at the time of pattering the channel protective layer24(at the time of forming the contact hole: step S19ofFIG. 7), holes (apertures) H11to H14, H21, H22, and H3penetrating to the oxide semiconductor thin film layer23are formed in the vicinity of the channel region in the channel protective layer24.

Such a hole is preferably provided in the vicinity of the channel region (from 10 μm to 20 μm both inclusive apart from the channel region). Further, it is desirable that the hole is not arranged astride the section between the source electrode25and the drain electrode25for the following reason. That is, such a hole may cause oxygen detachment in the subsequent steps. If the oxygen detachment is generated and the oxide semiconductor thin film layer23becomes an electric conductor, a region with a lower resistance than that of the channel region is prevented from being formed between the source electrode25and the drain electrode25.

Further, in the TFTs20B and20C illustrated inFIGS. 13B and 13C, to prevent influence on the section between the source electrode25and the drain electrode25even if the foregoing oxygen detachment is generated, the holes H21, H22, and H3are formed on one side of the source/drain. In this case, the holes H21, H22, and H3are preferably provided in the vicinity of the channel region (for example, from 10 μm to 20 μm both inclusive apart from the channel region).

In this case, a process for adding oxygen to the oxide semiconductor thin film layer23is performed after forming the source/drain electrode25. After that, the hole is preferably covered with the foregoing planarizing insulating film51or the like.

(Step of Forming TFT Substrate1)

The TFTs20A to20C of this embodiment is able to be formed, for example, as follows. First, in the step of forming the contact hole (step S19ofFIG. 7), a section in the vicinity of the channel region in the channel protective layer24is also patterned and thereby the foregoing holes H11to H14, H21, H22, and H3are formed (step S190ofFIG. 7). After forming the holes H11to H14, H21, H22, and H3, oxygen annealing treatment is provided and thereby oxygen is supplied to the oxide semiconductor thin film layer23through the holes (step S20or step S22ofFIG. 7).

Specifically, in the case where annealing treatment is performed after forming the source/drain electrode25(step S22), the procedure is as follows. First, after forming the source/drain electrode25, for example, in the atmosphere of oxygen:nitrogen=30:70, annealing treatment at, for example, 300 deg C. is performed for about 2 hours. Thereby, oxygen irradiated through the hole formed in the channel protective layer24is supplied into the oxide semiconductor thin film layer23, or into the channel region in the oxide semiconductor thin film layer23through the interface with an adjacent film (gate insulating film22or the first channel protective layer24A). As a result, the transistor characteristics are sufficiently restored. Subsequently, the result is coated with a photosensitive acryl resin or polyimide, baked at, for example, 130 deg C., and exposure and development are provided to perform patterning. After that, the result is fired at, for example, 220 deg C. Even after such a step, oxygen is not significantly detached through the hole, and the transistor characteristics are not deteriorated.

As described above, in this embodiment, in the step of forming the contact hole, the section in the vicinity of the channel region in the channel protective layer24is also patterned and thereby the holes H11to H14, H21, H22, and H3penetrating to the oxide semiconductor thin film layer23are formed. Thus, in addition to the effect in the foregoing first embodiment, the following effect is obtained. That is, after forming such a hole, oxygen annealing treatment is provided, and thereby oxygen is able to be supplied to the oxide semiconductor thin film layer23through the hole without adding a photolithography step.

In other words, even after forming the source/drain electrode25, oxygen is able to be supplied to the oxide semiconductor thin film layer23(oxygen is able to be supplemented), and transistor operation and reliability are able to be secured (restored).

3. Module and Application Examples

A description will be given of application examples of the display unit described in the foregoing embodiments. The display unit of the foregoing embodiments is able to be applied to electronic devices in any field such as a television device, a digital camera, a notebook personal computer, a portable terminal device such as a mobile phone, and a video camera. In other words, the display unit of the foregoing embodiments is able to be applied to a display unit of an electronic device in any field for displaying a video signal inputted from outside or a video signal generated inside as an image or a video.

Module

The display unit of the foregoing embodiments is incorporated in various electronic devices such as after-mentioned first to fifth application examples as a module as illustrated inFIG. 14, for example. In the module, for example, a region210exposed from the sealing substrate71and the adhesive layer60is provided in a side of the substrate11, and an external connection terminal (not illustrated) is formed in the exposed region210by extending wirings of a signal line drive circuit120and a scanning line drive circuit130. The external connection terminal may be provided with a Flexible Printed Circuit (FPC)220for inputting and outputting a signal.

First Application Example

FIG. 15is an appearance of a television device to which the display unit of the foregoing embodiments is applied. The television device has, for example, a video display screen section300including a front panel310and a filter glass320. The video display screen section300is composed of the display unit according to the foregoing respective embodiments.

Second Application Example

FIGS. 16A and 16Bare an appearance of a digital camera to which the display unit of the foregoing embodiments is applied. The digital camera has, for example, a light emitting section for a flash410, a display section420, a menu switch430, and a shutter button440. The display section420is composed of the display unit according to the foregoing respective embodiments.

Third Application Example

FIG. 17is an appearance of a notebook personal computer to which the display unit of the foregoing embodiments is applied. The notebook personal computer has, for example, a main body510, a keyboard520for operation of inputting characters and the like, and a display section530for displaying an image. The display section530is composed of the display unit according to the foregoing respective embodiments.

Fourth Application Example

FIG. 18is an appearance of a video camera to which the display unit of the foregoing embodiments is applied. The video camera has, for example, a main body610, a lens for capturing an object620provided on the front side face of the main body610, a start/stop switch in capturing630, and a display section640. The display section640is composed of the display unit according to the foregoing respective embodiments.

Fifth Application Example

FIGS. 19A to 19Gillustrate an appearance of a mobile phone to which the display unit of the foregoing embodiments is applied. In the mobile phone, for example, an upper package710and a lower package720are jointed by a joint section (hinge section)730. The mobile phone has a display740, a sub-display750, a picture light760, and a camera770. The display740or the sub-display750is composed of the display unit according to the foregoing respective embodiments.

While the invention has been described with reference to the first and the second embodiments and the application examples thereof, the invention is not limited to the foregoing embodiments and the like, and various modifications may be made.

For example, in view of supplying sufficient oxygen to the oxide semiconductor thin film23and decreasing oxygen detachment, oxygen annealing treatment as described below with reference toFIG. 7is preferably performed.

That is, first, ideally, the following step 1 is preferably executed.

1. At the time of forming the oxide semiconductor thin film23, the oxygen amount is optimized (refer to referential symbol P1inFIG. 7: step S130), and oxygen detachment is prevented from being generated before the channel protective layer24having sufficient oxygen barrier properties is formed.

However, in the foregoing step 1, the technique is considerably limited since the step of forming the oxide semiconductor thin film23or the first channel protective layer24A itself is a high temperature step. Thus, oxygen annealing treatment is preferably performed at the time of steps described as the following steps 2 to 5.

2. At the time after forming the oxide semiconductor thin film23and before forming the first channel protective layer24A, a process of supplying oxygen to the oxide semiconductor thin film23such as nitric oxide plasma, oxygen plasma, and ozone treatment is introduced (refer to referential symbol P2inFIG. 7: step S14).
3. At the time after forming the first channel protective layer24A and before forming the second channel protective layer24B, oxygen annealing treatment is performed (refer to referential symbol P3inFIG. 7: step S16).
4. At the time after forming the first channel protective layer24A and the second channel protective layer24B with low oxygen permeability, strong oxygen annealing treatment is performed (refer to referential symbol P4inFIG. 7: step S18).
5. At the time after forming the first channel protective layer24A and the second channel protective layer24B, a contact hole is formed (refer to referential symbol P5inFIG. 7: step S190). After that, after oxygen annealing treatment is performed, the source/drain electrode25is formed (refer to referential symbol P5inFIG. 7: step S20).

Further, in the case where oxygen detachment is generated in the step of forming the source/drain electrode25, oxygen annealing treatment is preferably performed at the time of step described as the following step 6.

6. At the time after forming the first channel protective layer24A and the second channel protective layer24B, the holes H11to H14, H21, H22, and H3described in the foregoing second embodiment are formed (refer to referential symbol P6inFIG. 7: step S190). After that, after the source/drain electrode25is formed, oxygen annealing treatment is performed (refer to referential symbol P6inFIG. 7: step S22). After that, the hole is preferably covered with the foregoing planarizing insulating film51or the like.

Further, for example, the material, the thickness, the film-forming method, the film-forming conditions and the like of each layer are not limited to those described in the foregoing embodiments and the like, but other material, other thickness, other film-forming method, and other film-forming conditions may be adopted. Specifically, in the foregoing embodiments and the like, the description has been given of the case that the second channel protective layer24B is made of the material with low oxygen permeability and low water vapor permeability, but the structure is not limited thereto. That is, for example, it is enough that one or both of the first channel protective layer24A and the second channel protective layer24B is made of the material with low oxygen permeability and low water vapor permeability.

Further, in the foregoing embodiments and the like, the description has been given of the organic light emitting devices10R,10B, and10G with the specific example. However, it is not necessary to provide all the layers, and other layer may be further included.

In addition, the invention is able to be applied to a display unit including other display device such as a liquid crystal display device, an inorganic electroluminescence device, an electrodeposition display device, and an electrochromic display device in addition to the organic light emitting device.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-308271 filed in the Japanese Patent Office on Dec. 3, 2008, the entire contents of which is hereby incorporated by reference.

It should be understood by those skilled in the art that various modifications, combinations, sub combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.