Patent ID: 12191312

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the present invention can be carried out in many different modes. As is easily known to a person skilled in the art, the mode and the detail of the invention can be variously changed without departing from the spirit and the scope of the invention. Therefore, the present invention is not to be construed with limitation to what is described in the embodiment modes.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

A light-emitting device of an embodiment of the invention is characterized in that an element formation layer comprising a TFT, an electrode of a light-emitting element, and the like is supported by a plastic substrate through an adhesive and that a color filter is provided between the plastic substrate and the light-emitting element.

The light-emitting device having such a structure can be manufactured by the following method and the like. First, the element formation layer including the TFT, the color filter, and a first pixel electrode of the light-emitting element is formed over a substrate with low flexibility, such as a substrate formed of glass, ceramics, and the like, with a separation layer sandwiched between the element formation layer and the substrate. Next, the substrate and the element formation layer are separated from each other at the separation layer, and the separated element formation layer is bonded to the plastic substrate using the adhesive.

As to the light-emitting device manufactured in this way, the color filter is formed using the substrate having low flexibility. Therefore, even in the case of a pixel arrangement directed to a full color display in high resolution, misalignment of the color filter is negligible, which allows the formation of a flexible display capable of displaying a full color image with high resolution.

Note that a protective insulating film may be provided over the color filter in order to reduce adverse influence of degasification from the color filter upon the light-emitting element.

FIGS.1A to1Ceach illustrate a view showing the light-emitting device of the present embodiment.

In the light-emitting device shown inFIG.1A, an adhesive111is provided over a plastic substrate110. The adhesive111is provided so as to be in contact with an insulating layer112, allowing an element formation layer113and the plastic substrate110to be bonded to each other. In the element formation layer113, a pixel TFT114, a TFT115in a driving circuit portion, a color filter116, a first pixel electrode117of a light-emitting element121electrically connected to the pixel TFT114, and a partition layer118are provided.FIG.1Aillustrates a part of these members. The light-emitting element121is formed of the first pixel electrode117exposed from the partition layer118, an EL layer119which overlaps at least the first pixel electrode117and contains a light-emitting substance, and a second pixel electrode120which overlaps the EL layer119.

Light emitted from the light-emitting element121is preferably red, green, blue, or white. The EL layer119and the second pixel electrode120of the light-emitting element121are formed after the element formation layer113is bonded to the plastic substrate110. Note that since the EL layer119and the second pixel electrode120of the light-emitting element121are formed over all pixels in common, misalignment in the formation thereof does not provide a serious problem although they are formed using the plastic substrate110.

In the light-emitting devices shown inFIGS.1A to1C, the color filter116is formed after the TFTs are formed. Note that it is preferred that the color filter116is formed over a first protective insulating film122which is provided over the TFTs since the first protective insulating film122is able to protect the TFTs from a contaminant released from the color filter116.

FIG.1Bshows a structure in which a second protective insulating film123is provided over the color filter116. This structure enables the production of a light-emitting device with higher reliability because adverse influence of degasification from the color filter116upon the light-emitting element121can be reduced.

FIG.1Cillustrates a structure in which the color filter124is patterned to be located on a position corresponding to the first pixel electrode117of the light-emitting element. In this structure, at least in a vicinity of the color filter124, the first protective insulating film122and the second protective insulating film123which covers the color filter124are in contact with each other, which allows the color filter124to be completely surrounded by the protective insulating films. Therefore, diffusion of the contaminant from the color filter124, such as a gas, can be more effectively prevented. Note that it is preferred that the first protective insulating film122and the second protective insulating film123are formed by using the same material. Moreover, these protective insulating films are preferably formed by using silicon nitride or silicon oxynitride which has a composition of nitrogen higher than that of oxygen.

Next, a manufacturing process of the light-emitting device of this embodiment is explained with reference toFIGS.3A to3DandFIGS.1A to1C.

First, the element formation layer113comprising the TFT, the color filter, the first pixel electrode, and the like is formed over the substrate200having an insulating surface with a separation layer201interposed between the element formation layer113and the substrate200(see,FIG.3A).

As the substrate200, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate over which an insulating layer is formed, and the like can be used. In the manufacturing process of the light-emitting device, the substrate200can be selected as appropriate in accordance with the conditions of the process.

Since a substrate with low flexibility, which is frequently used in the manufacture of usual displays, is used as the substrate200, the pixel TFT and the color filter can be placed in an arrangement suitable for a high-resolution display.

The separation layer201is formed by a sputtering method, a plasma CVD method, a coating method, a printing method, or the like, so as to have either a single-layer structure or a stacked structure by using an element selected from tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and silicon (Si); an alloy containing these elements as a main component; or a compound containing these elements as a main component. A crystal structure of a layer containing silicon may be amorphous, microcrystal, or polycrystal. Note that the coating method includes a spin-coating method, a droplet discharge method, a dispensing method, a nozzle printing method, and a slot die coating method in its category here.

In the case that the separation layer201has a single-layer structure, it is preferred to form a tungsten layer, a molybdenum layer, a layer containing a mixture of tungsten and molybdenum, a layer containing an oxide or an oxynitride of tungsten, a layer containing an oxide or an oxynitride of molybdenum, or a layer containing an oxide or an oxynitride of a mixture of tungsten and molybdenum as the separation layer201. Note that the mixture of tungsten and molybdenum corresponds to an alloy of tungsten and molybdenum, for example.

In the case where the separation layer201has a stacked structure, a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum is formed as a first layer, and a layer containing: an oxide, a nitride, an oxynitride, or a nitride oxide of tungsten; an oxide, a nitride, an oxynitride, or a nitride oxide of molybdenum; or an oxide, a nitride, an oxynitride, or a nitride oxide of a mixture of tungsten and molybdenum is formed as a second layer.

In the case where the stacked layer of a layer containing tungsten and a layer containing an oxide of tungsten is formed as the separation layer201, the layer containing tungsten may be formed first, which is followed by the formation of an insulating layer formed of an oxide (for example, a silicon oxide layer) over the layer containing tungsten so that a layer containing an oxide of tungsten is formed at the interface between the tungsten layer and the insulating layer. Further, a surface of the tungsten layer may be subjected to thermal oxidation treatment, oxygen plasma treatment, or treatment with a strong oxidizing solution such as water containing ozone to form the layer containing the oxide of tungsten. Further, plasma treatment or heat treatment may be performed in an atmosphere of oxygen, nitrogen, dinitrogen monoxide, or a mixed gas of these gases and another gas. The formation of a layer containing a nitride, an oxynitride, and a nitride oxide of tungsten can be similarly performed. Specifically, after forming the layer including tungsten, an insulating layer formed of a nitride, an oxynitride, or a nitride oxide (for example, a silicon nitride layer, a silicon oxynitride layer, or a silicon nitride oxide layer) is preferably formed over the layer including tungsten.

The insulating layer to be a base can be formed as a single layer or a stacked layer by using an inorganic insulating film such as silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, or the like.

As a material of the semiconductor layer included in the TFT, an amorphous semiconductor (hereinafter referred to as “AS”), a polycrystalline semiconductor, a microcrystalline semiconductor (semiamorphous or microcrystal, hereinafter referred to as “SAS”), a semiconductor which has an organic material as a main component, or the like can be used. The semiconductor layer can be formed by a sputtering method, an LPCVD method, a plasma CVD method, or the like.

Note that the microcrystalline semiconductor belongs to a metastable state which is an intermediate between an amorphous state and a single crystal state according to Gibbs free energy. That is, the microcrystalline semiconductor is a semiconductor having a third state which is stable in terms of free energy and has a short range order and lattice distortion. In the microcrystalline semiconductor, columnar-like or needle-like crystals grow in a normal direction with respect to a surface of a substrate. The Raman spectrum of microcrystalline silicon, which is a typical example of a microcrystalline semiconductor, is shifted to a small wavenumber region below 520 cm−1which corresponds to the wavenumber of the Raman spectrum peak of single-crystalline silicon. That is, the peak of the Raman spectrum of the microcrystalline silicon exists between 520 cm−1which represents single-crystalline silicon and 480 cm−1which represents amorphous silicon. The microcrystalline semiconductor includes at least 1 at. % of hydrogen or halogen to terminate a dangling bond. Moreover, a rare gas element such as helium, argon, krypton, or neon may be included to further promote lattice distortion, so that stability is enhanced and a favorable microcrystalline semiconductor film can be obtained.

The microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method with a frequency of several tens to several hundreds of megahertz or a microwave plasma CVD method with a frequency of 1 GHz or more. Typically, the microcrystalline semiconductor film can be formed by using a gas obtained by diluting a silicon hydride or a silicon halide, such as SiH4, Si2H6, SiH2Cl2, SiHCl3, SiCl4, SiF4, or the like, with hydrogen. Additionally, the microcrystalline semiconductor film can be formed by using a gas containing a silicon hydride and hydrogen which is diluted by rare gas elements selected from helium, argon, krypton, and neon. In this case, the flow rate of hydrogen is set to be greater than or equal to 5 times and less than or equal to 200 times, preferably greater than or equal to 50 time and less than or equal to 150 times, much more preferably 100 times as much as that of silicon hydride.

A hydrogenated amorphous silicon can be typically exemplified as the amorphous semiconductor, while a polysilicon or the like can be typically exemplified as a crystalline semiconductor layer. Examples of polysilicon (polycrystalline silicon) include so-called high-temperature polysilicon that contains polysilicon as a main component and is formed at a process temperature greater than or equal to 800° C., so-called low-temperature polysilicon that contains polysilicon as a main component and is formed at a process temperature less than or equal to 600° C., polysilicon obtained by crystallizing amorphous silicon by using an element that promotes crystallization or the like, and the like. Note that as mentioned above, a microcrystalline semiconductor or a semiconductor containing a crystal phase in part of a semiconductor layer may be used.

As a material of the semiconductor, as well as an element of silicon (Si), germanium (Ge), or the like, a compound semiconductor such as GaAs, InP, SiC, ZnSe, GaN, SiGe, or the like can be used. Alternatively, an oxide semiconductor such as zinc oxide, tin oxide, magnesium zinc oxide, gallium oxide, indium oxide, an oxide semiconductor formed of a plurality of the above oxide semiconductors, and the like may be used. For example, an oxide semiconductor formed of zinc oxide, indium oxide, and gallium oxide may be used. In the case of using zinc oxide for the semiconductor layer, a gate insulating film is preferably formed using yttrium oxide, aluminum oxide, titanium oxide, a stack of any of the above substances, or the like. For a gate electrode layer, a source electrode layer, and a drain electrode layer, ITO, Au, Ti, or the like is preferably used. In addition, In, Ga, or the like can be added into zinc oxide.

In the case of using a crystalline semiconductor layer for the semiconductor layer, the crystalline semiconductor layer may be formed by any of various methods (such as a laser crystallization method, a thermal crystallization method, a thermal crystallization method using an element promoting crystallization such as nickel), and the like. Also, a microcrystalline semiconductor, which is an SAS, can be crystallized by irradiating laser light to increase its crystallinity. In a case where an element which promotes crystallization is not used, before the amorphous silicon film is irradiated with a laser beam, the amorphous silicon film is heated at 500° C. for one hour in a nitrogen atmosphere to reduce a hydrogen concentration in the amorphous silicon film to less than or equal to 1×1020atoms/cm3. This is because, if the amorphous silicon layer contains much hydrogen, the amorphous silicon layer may be destroyed by laser beam irradiation.

Any method can be used for introducing a metal element into the amorphous semiconductor layer as long as the method allows the metal element to exist on the surface of or inside the amorphous semiconductor layer. For example, a sputtering method, a CVD method, a plasma process method (including a plasma CVD method), an adsorption method, a method of applying a solution of a metal salt, or the like can be used. Among the above-mentioned processes, the method using a solution is convenient and has an advantage of easily adjusting the concentration of a metal element. It is preferable to form an oxide film on the amorphous semiconductor layer by UV light irradiation in an oxygen atmosphere, a thermal oxidation treatment, treatment with ozone water or hydrogen peroxide including a hydroxyl radical, or the like in order to improve wettability of the surface of the amorphous semiconductor layer and to spread the aqueous solution over the entire surface of the amorphous semiconductor layer.

The crystallization may be performed by adding an element which promotes crystallization (also referred to as a catalyst element or a metal element) to an amorphous semiconductor layer and performing a heat treatment (at 550° C. to 750° C. for 3 minutes to 24 hours) in a crystallization step in which the amorphous semiconductor layer is crystallized to form a crystalline semiconductor layer. As the element which promotes (accelerates) the crystallization, one or more of iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au) can be used.

In order to remove or reduce the element promoting crystallization from the crystalline semiconductor layer, a semiconductor layer containing an impurity element is formed in contact with the crystalline semiconductor layer and is made to function as a gettering sink. The impurity element may be an impurity element imparting n-type conductivity, an impurity element imparting p-type conductivity, a rare gas element, or the like. For example, one or a plurality of elements selected from phosphorus (P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used. Specifically, the above-mentioned semiconductor layer containing the impurity element is formed in contact with the crystalline semiconductor layer containing the element which promotes crystallization, and heat treatment (at temperature ranging from 550 to 750° C. for 3 minutes to 24 hours) is performed. The element that promotes crystallization in the crystalline semiconductor layer is transported to the semiconductor layer containing the impurity element; thus, the element that promotes crystallization in the crystalline semiconductor layer is removed or reduced. After that, the semiconductor layer containing the impurity element functioning as the gettering sink is removed.

In addition, thermal treatment and laser light irradiation may be combined to crystallize the amorphous semiconductor layer. The thermal treatment and/or the laser light irradiation may be independently performed a plurality of times.

In addition, a crystalline semiconductor layer may be directly formed over the substrate by a plasma treatment method. Alternatively, the crystalline semiconductor layer may be selectively formed over a substrate by using a plasma treatment method.

As a semiconductor film mainly containing an organic material, a semiconductor film mainly containing carbon can be used. Specifically, pentacene, tetracene, thiophene oligomers, polyphenylenes, phthalocyanine compounds, polyacetylenes, polythiophenes, a cyanine dye, and the like are given as examples.

As to the gate insulating film and the gate electrode, a known structure may be applied, and a known method may be used for the formation thereof. For instance, the gate insulating film may be formed according to a known structure such as a single layer of silicon oxide, a stacked structure of silicon oxide and silicon nitride, and the like. The gate electrode may be formed of an element selected from Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Si, Ge, Zr, and Ba; or an alloy or a compound containing any of these elements as its main component by using the CVD method, the sputtering method, the droplet discharging method, or the like. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus, or AgPdCu alloy may be used. Either a single layer structure or a layered structure may be applied.

Note that although an example is shown inFIGS.1A to1Cin which transistors with a top-gate structure are used, a transistor with a known structure such as a bottom-gate structure and the like may be used.

The first protective insulating film122is formed over the gate insulating film and the gate electrode. The first protective insulating film122may be formed of a silicon oxide layer, a silicon oxynitride film, a silicon nitride oxide film, or a silicon nitride film, or may be formed as a stacked film in which any of these films are combined. In any case, the first protective insulating film122is formed of an inorganic insulating material. The formation of the first protective insulating film122allows the reduction of pollution of the TFT caused by the color filter116formed later. The use of a silicon nitride film or a silicon nitride oxide film which has a composition of nitrogen higher than that of oxygen is preferred because the contaminant from the color filter116can be effectively blocked.

The color filter116is formed over the first protective insulating film122. Although a color filter with a single color is shown inFIGS.1A to1C, a color filter which transmits red light, a color filter which transmits blue light, and a color filter which transmits green light are formed in an appropriate arrangement and shape. Any arrangement can be adopted for the arrangement of the color filter116, including a stripe pattern, a diagonal mosaic arrangement, a triangle mosaic arrangement, an RGBW four pixel arrangement, and the like. The RGBW four pixel arrangement is a pixel arrangement having: a pixel mounted with a color filter transmitting red light; a pixel mounted with a color filter transmitting blue light; a pixel mounted with a color filter transmitting green light; and a pixel without color filter, and is effective in reducing power consumption and so on.

The color filter116can be formed by using a known material. In the case of using a photosensitive resin as the color filter116, patterning of the color filter116may be performed by exposing the color filter116itself to light and then developed. It is preferred to perform patterning by dry etching when a minute pattern is formed.

After the formation of the color filter116, an interlayer insulating film formed using an organic insulating material is formed over the color filter116. As the organic insulating material, an acrylic, a polyimide, a polyamide, a polyimideamide, a benzocyclobutene-based resin, and the like can be used.

The second protective insulating film123may be provided between the color filter116and the interlayer insulating film in order to suppress the influence of degasification from the color filter116(seeFIG.1B). The second protective insulating film123can be formed with a similar material to that of the first protective insulating film122. It is a preferred structure in which the second protective insulating film123is formed using a silicon nitride film or a silicon nitride oxide film having a composition of nitrogen higher than oxygen since degasification from the color filter116can be effectively suppressed. Note that a structure is preferred in which the first protective insulating film122and the second protective insulating film123are in contact with each other in a vicinity of the color filter124because influence of a contaminant and degasification can be more effectively suppressed (see,FIG.1C). In this case, the use of the same material for the first protective insulating film122and the second protective insulating film123allows the improvement of adhesion therebetween, which contributes to further reduction of influence of the contaminant and degasification. The reduction of influence of the contaminant and degasification improves reliability of the light-emitting device.

After the formation of the interlayer insulating film, the first pixel electrode117is formed using a transparent conductive film. When the first pixel electrode117is an anode, indium oxide, an alloy of indium oxide and tin oxide (ITO), and the like can be used as a material of the transparent conductive film. Alternatively, an alloy of indium oxide and zinc oxide (IZO) may be used. In a similar manner, zinc oxide is also an appropriate material, and moreover, zinc oxide (GZO) to which gallium (Ga) is added to increase conductivity and transmissivity with respect to visible light may be used. When the first pixel electrode117is used as a cathode, an extremely thin film of a material with a low work function such as aluminum can be used. Alternatively, a stacked structure which has a thin layer of such a material and the above-mentioned transparent conductive film can be employed. Note that the first pixel electrode117can be formed by a sputtering method, a vacuum evaporation method, or the like.

Next, etching is performed on the interlayer insulating film, (the second protective insulating film123), (the color filter116), the first protective insulating film122, and the gate insulating film to result in formation of a contact hole which reaches the semiconductor layer of the TFT. Then a conductive metal film is formed by a sputtering method or a vacuum evaporation method, which is followed by etching to result in an electrode of the TFT and a wiring. One of a source electrode and a drain electrode of the pixel TFT114is formed so as to overlap with the first pixel electrode117in order to achieve electrical connection therebetween.

After that, an insulating film is formed using an organic insulating material or an inorganic insulating material so that the insulating film covers the interlayer insulating film and the first pixel electrode117. The insulating film is then processed to allow a surface of the first pixel electrode117to be exposed and an end portion of the first pixel electrode117to be covered by the insulating film, leading to the formation of the partition layer118.

Through the above-mentioned process, the element formation layer113can be formed.

Next, the element formation layer113and a provisional supporting substrate202are bonded to each other using a first adhesive203, which is followed by separation of the element formation layer113from the substrate200at the separation layer201. By this process, the element formation layer113is placed over the provisional supporting substrate202(see,FIG.3B).

As the provisional supporting substrate202, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate on which an insulating surface is formed, and the like can be used. Further, a plastic substrate which can resist a temperature of the manufacturing process of this embodiment or a flexible substrate such as a film may be used.

As the first adhesive203used here, an adhesive, which is soluble in a solvent such as water or is capable of plasticizing upon irradiation of UV light, and the like, is used so that the provisional supporting substrate202can be chemically or physically separated from the element formation layer113when necessary.

Any of following methods can be applied in the transferring process from the substrate200to the provisional supporting substrate202: forming the separation layer201between the substrate200and the element formation layer113, forming a metal oxide film between the separation layer201and the element formation layer113, embrittling the metal oxide film by crystallizing thereof, and separating the element formation layer113; forming an amorphous silicon film containing hydrogen between the substrate200having high thermal resistivity and the element formation layer113, removing the amorphous silicon film by irradiation with laser light or etching, and separating the element formation layer113; forming the separation layer201between the substrate200and the element formation layer113, forming a metal oxide film between the separation layer201and the element formation layer113, embrittling the metal oxide film by crystallizing thereof, removing a part of the separation layer201by etching using a solution or a halogen fluoride gas such as NF3, BrF3, ClF3, and the like, and performing the separation at the embrittled metal oxide film; and removing the substrate200over which the element formation layer113is formed mechanically or by etching using a solution or a halogen fluoride gas such as NF3, BrF3, ClF3, and the like. Alternatively, a method may be used in which a film containing nitrogen, oxygen, or hydrogen (for example, an amorphous silicon film containing hydrogen, an alloy film containing hydrogen, or an alloy film containing oxygen) is used as the separation layer201, and the separation layer201is irradiated with laser light to release the nitrogen, oxygen, or hydrogen contained in the separation layer201, thereby promoting separation between the element formation layer113and the substrate200.

When the above-described separation methods are combined, the transfer step can be conducted easily. For example, separation can be performed with physical force (by a machine and the like) after performing: laser light irradiation; etching to the separation layer201with a gas, a solution, or the like; and mechanical removal with a sharp knife, scalpel, or the like, so that the separation layer201and the element formation layer113can be easily peeled off from each other.

Alternatively, separation of the element formation layer113from the substrate200may be carried out after penetrating a liquid into an interface between the separation layer201and the element formation layer113.

Next, the element formation layer113which is separated from the substrate200to expose the separation layer201or the insulating layer112is bonded to the plastic substrate110using a second adhesive204which is different from the first adhesive203(see,FIG.3C).

As the second adhesive204, various curable adhesives such as a reactive curable adhesive, a thermal curable adhesive, a photo curable adhesive such as an ultraviolet curable adhesive, an anaerobic adhesive, and the like can be used.

As the plastic substrate110, a variety of substrates having flexibility and light-transmitting ability, a film of an organic resin, and the like can be used. The plastic substrate110may be a structure body comprising a fibrous body and an organic resin. It is preferred to use the structure body comprising the fibrous body and the organic resin as the plastic substrate110since resistivity to the breaking caused by bending is improved, and thus, reliability is increased.

The structure body comprising the fibrous body and the organic resin can be used as a film which can simultaneously function as the second adhesive204and the plastic substrate110. In this case, as the organic resin of the structure body, a resin such as a reactive curable resin, a thermosetting resin, and a photo curable resin, and the like whose curing is promoted by an additional treatment are preferably used.

After the bonding of the plastic substrate110to the element formation layer113, the provisional supporting substrate202is removed by dissolving or plasticizing the first adhesive203. After the provisional supporting substrate202is removed, the first adhesive203is removed using a solvent such as water to allow a surface of the first pixel electrode117of the light-emitting element to be exposed (see,FIG.3D).

Through the above-mentioned process, the element formation layer113, which comprises the color filter116, the TFTs114and115, the first pixel electrode117of the light-emitting element, and the like, can be manufactured over the plastic substrate110.

After the surface of the first pixel electrode117is exposed, the EL layer119is formed. A stacked structure of the EL layer119is not particularly limited. A layer containing a substance having high electron-transporting ability, a layer containing a substance having high hole-transporting ability, a layer containing a substance having high electron injection ability, a layer containing a substance having high hole injection ability, a layer containing a bipolar substance (a substance having high electron-transporting ability and high hole transporting ability), and the like are appropriately combined. For example, an appropriate combination of a hole injecting layer, a hole-transporting layer, a light-emitting layer, an electron-transporting layer, an electron injection layer, and the like can be performed. In this embodiment, a structure is explained in which the EL layer119comprises a hole injection layer, a hole-transporting layer, a light-emitting layer, and an electron-transporting layer. Specific materials to form each of the layers are given below.

The hole injection layer is a layer that is provided in contact with an anode and contains a material with high hole injection ability. Specifically, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used. Alternatively, the hole injection layer can be formed using any one of the following materials: phthalocyanine compounds such as phthalocyanine (H2PC) and copper phthalocyanine (CuPc); aromatic amine compounds such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB) and 4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl (DNTPD); polymer compounds such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS); and the like.

Alternatively, as the hole injection layer, a composite material comprising a substance with high hole-transporting ability and an acceptor substance may be used. It is to be noted that, by using the composite material comprising the substance with high hole-transporting ability and the acceptor substance, a material used to form an electrode may be selected regardless of its work function. In other words, besides a material with a high work function, a material with a low work function may also be used as the anode. As the acceptor substance, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, and the like can be given. In addition, a transition metal oxide is given. In addition, oxides of metals that belong to Group 4 to Group 8 of the periodic table can be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because of a high electron accepting property. Among these metal oxides, molybdenum oxide is especially preferable since it can be easily treated due to its stability in the air and low hygroscopic property.

As the substance having high hole-transporting ability used for the composite material, any of various organic compounds such as an aromatic amine compound, a carbazole derivative, an aromatic hydrocarbon, and a high-molecular compound (such as an oligomer, a dendrimer, or a polymer) can be used. The organic compound used for the composite material preferably has a hole mobility of 10−6cm2/Vs or higher is preferably used. However, other materials than these materials may also be used as long as hole-transporting ability is higher than electron-transporting ability. The organic compound that can be used for the composite material is specifically shown below.

Examples of the aromatic amine compounds include N,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviated to DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviated to DPAB), 4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated to DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviated to DPA3B), and the like.

Examples of a carbazole derivative include 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2), 3-[N-(1-naphtyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA), 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and the like.

Examples of the aromatic hydrocarbons include 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA), 9,10-di(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth), 2-tert-butylanthracene (t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl, 10,10′-diphenyl-9,9′-bianthryl, 10,10′-bis(2-phenylphenyl)-9,9′-bianthryl, 10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene, tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, and the like. As well as these compounds, pentacene, coronene, or the like can be used. Note that when a film of the above-mentioned aromatic hydrocarbons is formed by an evaporation method, the number of the carbon atoms participating in their condensed ring preferably ranges from 14 to 42 from the viewpoint of the evaporation behavior of the aromatic hydrocarbons and the quality of the formed film.

The aromatic hydrocarbon that can be used for the composite material may have a vinyl skeleton. As an aromatic hydrocarbon having a vinyl group, for example, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), and the like are given.

The polymeric compounds are exemplified by poly(N-vinylcarbazole) (abbreviated to PVK), poly(4-vinyltriphenylamine) (abbreviated to PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviated to PTPDMA), poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviated to Poly-TPD), and the like.

The hole-transporting layer is a layer that contains a substance with high hole-transporting ability. Examples of the substance having high hole-transporting ability include aromatic amine compounds such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbr.: NPB), N,N-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbr.: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbr.: TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbr.: MTDATA), 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbr.: BSPB), and the like. The materials described here are mainly substances having hole mobility of 10−6cm2/Vs or more. However, a material other than the above-described substances may be used as long as it has higher hole-transporting ability than electron-transporting ability. Note that the layer containing the substance with high hole-transporting ability is not limited to a single layer, and two or more layers containing the aforementioned substances may be stacked.

Further, a high molecular compound such as poly(N-vinylcarbazole) (abbr.: PVK) or poly(4-vinyltriphenylamine) (abbr.: PVTPA) can also be used for the hole-transporting layer.

The light-emitting layer is a layer containing a light-emitting substance. The light-emitting layer may be a so-called single layer light-emitting layer and a so-called host-guest type light-emitting layer in which a light-emitting substance is dispersed in a host material, as long as the emission from the light-emitting layer is located in the visible region. For example, followings are provided as the light-emitting layer: a light-emitting layer containing a light-emitting substance having a broad emission spectrum (see,FIG.6A); a light-emitting layer containing a plurality of light-emitting substances having a different emission wavelength region (see,FIG.6B); a light-emitting layer containing a plurality of layers which each include a light-emitting substance with a different emission wavelength region (see,FIG.6C); and the like. These structures may be combined to each other. Note that inFIGS.6A to6C, a reference numeral600represents the first pixel electrode of the light-emitting element; a reference numeral601represents a second pixel electrode of the light-emitting element; a reference numeral602represents the EL layer; reference numerals603,603-1, and603-2each represent the light-emitting layer; and reference numerals604,604-1, and604-2each represent the light-emitting substance.

In the case of the structures shown inFIGS.6B and6C, a combination of the light-emitting substances (corresponding to the light-emitting substances604-1and604-2, but being not limited to two kinds of substances) with different wavelength regions is generally exemplified by a combination of two kinds of light-emitting substances which emit light of complementary colors to each other (for example, blue light and yellow light) or by a combination of three kinds of substances with red, blue and green emission colors.

In the case of the combination of two kinds of light-emitting substances with complementary emission colors in the structure shown inFIG.6C, it is preferred to employ a structure in which, as shown inFIG.7A, a three-layer structure containing a first light-emitting layer603-1, a second light-emitting layer603-2, and a third light-emitting layer603-3in that order from a side of the first pixel electrode600is provided as the light-emitting layer603; and a layer (the second light-emitting layer603-2) containing a light-emitting substance604-2capable of emitting light with a long wavelength is interposed between layers (the first light-emitting layer603-1and the third light-emitting layer603-3) each containing a light-emitting substance604-1capable of emitting light with a short wavelength. Note that, in the structure ofFIG.7A, carrier-transporting ability of each of the light-emitting layers is tuned by appropriately selecting host materials to allow recombination of electrons and holes to occur in the vicinity of an interface of the layer (the second light-emitting layer603-2) containing the light-emitting substance604-2which is located on the side of the second pixel electrode601(i.e., an interface between the second light-emitting layer603-2and the third light-emitting layer603-3). By using such structure, the lifetime of the light-emitting element can be improved, and the emission from the light-emitting substance capable of emitting light with the long wavelength and that from the light-emitting substance capable of emitting light with the short wavelength can be readily balanced.

Here, in the case where the first pixel electrode600and the second pixel electrode601are used as the anode and the cathode, respectively, “recombination of holes and electrons in the vicinity of an interface of the layer, containing the light-emitting substance capable of emitting light with the long wavelength, the interface of which is located on the side of the second pixel electrode, by tuning carrier transporting ability of each of the light-emitting layers through the appropriate selection of the host materials” can be achieved by designing the light-emitting element so that the layer (the third light-emitting layer603-3), which is located on the side of second pixel electrode601and contains the light-emitting substance604-1capable of emitting light with short wavelength, has electron-transporting ability and the layer (the first light-emitting layer603-1), which is located on the anode side and contains the light-emitting substance604-1capable of emitting light with the short wavelength, and the layer (the second light-emitting layer603-2), which contains the light-emitting substance604-2capable of emitting light with the long wavelength, have hole-transporting ability. When the first pixel electrode600and the second pixel electrode601are used as the cathode and the anode, respectively, the combination concerning the carrier-transporting ability is reversed.

As a result, electrons, which cannot participate to recombination in the vicinity of the cathode side interface (the interface between the second light-emitting layer603-2and the third light-emitting layer603-3) of the layer (the second light-emitting layer603-2) containing the light-emitting substance capable of emitting light with the long wavelength, are provided with an opportunity to undergo recombination in the layer (the first light-emitting layer603-1) which is located on the anode side and contains the light-emitting substance capable of emitting light with the short wavelength. Thus, deterioration resulting from a phenomenon that a carrier (electron or hole) reaches to a carrier-transporting layer which has carrier-transporting ability opposite to the respective carrier can be retarded, which contributes to improvement in lifetime of the light-emitting element.

Energy obtained by recombination of holes and electrons is readily transferred from a substance which emits light with a short wavelength to a substance which emits light with a long wavelength. In such a case, light emitted from the substance which emits light with the long wavelength is enhanced, which makes it difficult to balance the intensities of emissions from the substance which emits light with the short wavelength and from the substance which emits light with the long wavelength. However, by using the above-mentioned structure, the electron which fails to participate to recombination in the vicinity of the interface between the second light-emitting layer603-2and the third light-emitting layer603-3can be subjected to recombination in the layer (the first light-emitting layer603-1) which is located on the anode side and contains the light-emitting substance capable of emitting light with the short wavelength. Thus, a well balanced emission is attainable, and an emission with desired color can be obtained.

In such a structure, when an anthracene derivative, which has electron-transporting ability as well as hole-transporting ability, is used as a host material of the first light-emitting layer603-1and the second light-emitting layer603-2in which a light-emitting substance is dispersed, the effect of improving the lifetime is more effectively obtained.

When three kinds of light-emitting substances, i.e., red, blue, and green-emissive light-emitting substances, are combined in the structure shown inFIG.6C, it is preferred, as shown inFIG.7B, to employ a structure in which a light-emitting layer603is formed as a four-layer structure containing, from the side of the first pixel electrode600, a first light-emitting layer603-1, a second light-emitting layer603-2, a third light-emitting layer603-3, and a fourth light-emitting layer603-4and in which the layer (the third light-emitting layer603-3) containing a green-emissive light-emitting substance604-7and the layer (the second light-emitting layer603-2) containing a red-emissive light-emitting substance604-6are sandwiched between the layers (the first light-emitting layer603-1and the fourth light-emitting layer603-4) containing a blue-emissive light-emitting substance604-5. Note that, in the structure shown inFIG.7B, carrier-transporting ability of each of the light-emitting layers is tuned to allow the region for recombination of holes and electrons to be located in the vicinity of the interface between the cathode-side layer (the fourth light-emitting layer603-4) containing the blue-emissive light-emitting substance604-5and the layer (the third light-emitting layer603-3) containing the green-emissive light-emitting substance604-7. By using such structure, the lifetime of the light-emitting element can be improved, and the emission from the light-emitting substance capable of emitting light with the long wavelength and that from the light-emitting substance capable of emitting light with the short wavelength can be readily balanced.

Note that, when the first pixel electrode600and the second pixel electrode601are respectively the anode and cathode, recombination in the vicinity of the interface between the fourth light-emitting layer603-4and the third light-emitting layer603-3can be achieved by designing the light-emitting element so that: the cathode-side layer (the fourth light-emitting layer603-4) containing the blue-emissive light-emitting substance604-5has electron-transporting ability; and the layer (the third light-emitting layer603-3) containing the green-emissive light-emitting substance604-7, the layer (the second light-emitting layer603-2) containing the red-emissive light-emitting substance604-6, and the anode-side layer (the first light-emitting layer603-1) containing the blue-emissive light-emitting substance604-5have hole-transporting ability. When the first pixel electrode600and the second pixel electrode601are the cathode and the anode, respectively, the carrier-transporting ability of each layer is reversed. Note that carrier-transporting ability of each of the light-emitting layers can be determined by carrier-transporting ability of the substance which is contained at the highest composition in the corresponding light-emitting layers.

As a result, electrons, which cannot participate to recombination in the vicinity of the interface between the cathode-side layer (the fourth light-emitting layer603-4) containing the blue-emissive light-emitting substance604-5and the layer (the third light-emitting layer603-3) containing the green-emissive light-emitting substance604-7, are provided with an opportunity to undergo recombination in the anode-side layer (the first light-emitting layer603-1) containing the blue-emissive light-emitting substance604-5. Thus, deterioration resulting from a phenomenon that a carrier (electron or hole) reaches to a carrier-transporting layer which has carrier-transporting ability opposite to the respective carrier can be retarded, which contributes to improvement in lifetime of the light-emitting element.

Energy obtained by recombination of holes and electrons is readily transferred from a substance which emits light with a short wavelength to a substance which emits light with a long wavelength. In such a case, light emitted from the substance which emits light with the long wavelength is enhanced, which makes it difficult to balance the intensities of emissions from the substance which emits light with the short wavelength and from the substance which emits light with the long wavelength. However, by using the above-mentioned structure, the electron which once fails to participate to recombination is subjected to recombination in the anode-side layer (the first light-emitting layer603-1) containing the blue-emissive light-emitting substance604-5, giving an emission of light with the short wavelength. Thus, a well-balanced emission is attainable, and an emission with desired color can be obtained.

The light-emitting substance used is not particularly limited, and known fluorescent substances or phosphorescent substances can be used. As fluorescent substances, for example, in addition to N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine (abbreviation: YGA2S) and 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), and the like, there are fluorescent substances with an emission peak equal to or greater than 450 nm, such as 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N,N-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N′,N-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,13-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), and 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM). As phosphorescent substances, for example, in addition to bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), there are phosphorescent substances with an emission wavelength in the range of 470 nm to 500 nm, such as bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III)picolinate (abbreviation: FIrpic), bis[2-(3′,5′bistrifluoromethylphenyl)pyridinato-N,C2′]iridium(III)picolinate (abbreviation: Ir(CF3ppy)2(pic)), and bis[2-(4′,6′-difluorophenyl)pyridinato-N, C2′]iridium(III)acetylacetonate (abbreviation: FIracac); phosphorescent materials with an emission wavelength equal to or greater than 500 nm (materials which emit green light), such as tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)3), bis(2-phenylpyridinato)iridium(III)acetylacetonate (abbreviation: Ir(ppy)2(acac)), bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate (abbreviation: Ir(pbi)2(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(acac)3(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)2(acac)), bis(2,4-diphenyl-1,3-oxazolato-N,C2′)iridium(III)acetylacetonate (abbreviation: Ir(dpo)2(acac)), bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)2(acac)), bis(2-phenylbenzothiazolato-N,C2′)iridium(III)acetylacetonate (abbreviation: Ir(bt)2(acac)), bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C3′]iridium(III)acetylacetonate (abbreviation: Ir(btp)2(acac)), bis(1-phenylisoquinolinato-N,C2′)iridium(III)acetylacetonate (abbreviation: Ir(piq)2(acac)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)2(acac)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinatoplatinum(II) (abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)3(Phen)), and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)). The light-emitting substances can be selected from the above-mentioned materials or other known materials in consideration of emission colors (or peak wavelengths of an emission) of each of the light-emitting layers.

When the host material is used, the following can be given: metal complexes such as tris(8-quinolinolato)aluminum(III) (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq3), bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); heterocyclic compounds such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11); and aromatic amine compounds such as NPB (or α-NPD), TPD, and BSPB. In addition, condensed polycyclic aromatic compounds such as anthracene derivatives, phenanthrene derivatives, pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chrysene derivatives are given. The following is specifically given as the condensed polycyclic aromatic compound: 9,10-diphenylanthracene (DPAnth); N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (CzA1PA); 4-(10-phenyl-9-anthryl)triphenylamine (DPhPA); 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (YGAPA); N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (PCAPA); N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine (PCAPBA); N-9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine (2PCAPA); 6,12-dimethoxy-5,11-diphenylchrysene, N,N,N′,N′,N″,N″,N′″, N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine (DBC1); 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA); 3,6-diphenyl-9-[4-(10-phenyl-9-antryl)phenyl]-9H-carbazole (DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 9,10-di(2-naphthyl)anthracene (DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 9,9′-bianthryl (BANT), 9,9′-(stilbene-3,3′-diyl)diphenanthrene (DPNS), 9,9′-(stilbene-4,4′-diyl)diphenanthrene (DPNS2), 3,3′,3″-(benzene-1,3,5-triyl)tripyrene (TPB3) and the like. From these substances or other known substances, the host material may be selected so that the host material has a larger energy gap (or a triplet energy if the light-emitting substance emits phosphorescence) than the light-emitting substance dispersed in the light-emitting layer and has carrier-transporting ability required for each of the light-emitting layers.

The electron-transporting layer is a layer that contains a substance with high electron-transporting ability. For example, a layer containing a metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq2), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq) can be used. Alternatively, a metal complex having an oxazole-based or thiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)2) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ)2) can be used. Besides the metal complexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or the like can also be used. The substances described here are mainly those having electron mobility of 10−6cm2/Vs or more. It is to be noted that a substance other than the above substances may be used as long as it has higher electron-transporting ability than hole transporting ability.

Further, the electron-transporting layer may be formed as not only a single layer but also as a stacked layer in which two or more layers formed using the above mentioned substances are stacked.

Further, a layer for controlling transport of electron may be provided between the electron-transporting layer and the light-emitting layer. Note that the layer for controlling transport of electron is a layer in which a small amount of a substance having high electron-trapping ability is added to a layer containing the above-mentioned substances having high electron-transporting ability. The layer for controlling transport of electron controls transport of electron, which enables adjustment of carrier balance. Such a structure is very effective in suppressing a problem (such as shortening of element lifetime) caused by a phenomenon that electron passes through the light-emitting layer.

Further, an electron injection layer may be provided so as to be in contact with an electrode functioning as a cathode. As the electron injection layer, alkali metal, alkaline earth metal, or a compound of thereof such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), and the like can be employed. For example, a layer which contains both a substance having electron-transporting ability and an alkali metal, an alkaline earth metal, or a compound thereof (a layer of Alq including magnesium (Mg) for example) can be used. Note that electron can be efficiently injected from the cathode by using, as the electron injection layer, a substance having electron-transporting ability to which an alkali metal or an alkaline earth metal is mixed.

When the second pixel electrode601is used as the cathode, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (specifically, work function of smaller than or equal to 3.8 eV), can be used as a substance for the second pixel electrode601. As a specific example of such a cathode material, an element belonging to Group 1 or Group 2 in the periodic table, i.e., an alkali metal such as lithium (Li) or cesium (Cs), or an alkaline earth metal such as magnesium (Mg), calcium (Ca), or strontium (Sr); an alloy containing any of these metals (such as MgAg or AlLi); a rare earth metal such as europium (Eu) or ytterbium (Yb); an alloy containing such a rare earth metal; or the like can be used. However, when the electron injection layer is provided between the cathode and the electron-transporting layer, any of a variety of conductive materials such as Al, Ag, ITO, and indium oxide-tin oxide containing silicon or silicon oxide, and the like can be used regardless of its work function as the cathode. Films of these electrically conductive materials can be formed by a sputtering method, an ink-jet method, a spin coating method, or the like.

It is preferable that, when the second pixel electrode601is used as the anode, the second pixel electrode601is formed using a metal, an alloy, or a conductive compound, a mixture thereof, or the like having a high work function (specifically greater than or equal to 4.0 eV). Specifically, an example thereof is indium oxide-tin oxide (ITO: indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (IZO: indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide (IWZO), or the like. Such conductive metal oxide films are usually formed by a sputtering method, but may also be formed by using a sol-gel method or the like. For example, indium zinc oxide (IZO) can be formed by a sputtering method using a target in which 1 to 20 wt % of zinc oxide is added to indium oxide. Indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which 0.5 wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1 wt % of zinc oxide are contained in indium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), a nitride of a metal (such as titanium nitride), or the like can be given. By forming the above-mentioned composite material so as to be in contact with the anode, a material for the anode can be selected regardless the magnitude of its work function.

Note that, as to the above-mentioned EL layer, a plurality of EL layer may be formed between the first pixel electrode600and the second pixel electrode601as shown inFIG.8. In this case, a charge generation layer803is preferably provided between the stacked EL layers800and801. The charge generation layer803can be formed by using the above-mentioned composite material. Further, the charge generation layer803may have a stacked structure comprising a layer containing the composite material and a layer containing another material. In this case, as the layer containing another material, a layer containing an electron donating substance and a substance with high electron-transporting ability, a layer comprising a transparent conductive material, and the like can be used. Such a structure allows the formation of a light-emitting element with high emission efficiency and a long lifetime. Moreover, a light-emitting element which provides a phosphorescent emission from one of the EL layers and a fluorescent emission from the other of the EL layers can be readily obtained. Note that this structure can be combined with the above-mentioned structures of the EL layer. For instance, the EL layer having the structure ofFIG.6Cand the EL layer having the structure ofFIG.6Acan be stacked. Specifically, it is readily achieved to obtain blue and green fluorescent emissions from the EL layer800having the structure ofFIG.6Cand simultaneously obtain a red phosphorescent emission from the EL layer801having the structure ofFIG.6A, where the charge generation layer803is sandwiched therebetween. In a similar way, green and red phosphorescent emissions are obtained from the EL layer800having the structure ofFIG.6C, and a blue fluorescent emission is simultaneously obtained from the EL layer801having the structure ofFIG.6A, where the charge generation layer803is sandwiched therebetween. In particular, the structure which provides the green and red phosphorescent emissions and the blue fluorescent emission is preferred since a white emission with well-balanced emission efficiencies of the EL layers is attainable.

Through the above-mentioned process, the light-emitting devices shown inFIGS.1A to1Ccan be obtained.

After the formation of the element formation layer and the light-emitting layer, it is preferred to seal the light-emitting element with an organic resin400, a protective film401, and the like as shown inFIGS.4A and4Bin order to prevent a substance which promotes deterioration of the EL layer from entering from the outside. A sealing substrate may be used instead of the organic resin400and the protective film401. However, the protective film401is not necessarily formed over input and output terminals which are connected to an FPC and the like later.

Since the light-emitting device of the present embodiment displays an image toward the plastic substrate110side through the color filter, it is possible to use the above-mentioned organic resin400, the protective film401, and the sealing substrate even if they are colored or have low transmissivity with respect to visible light. In the case where the organic resin400, the protective film401, and the sealing substrate each are formed using light-transmitting materials, a monochromic image can be also supplied from the sealing substrate side if the second pixel electrode is formed by a light-transmitting material or in a shape which allows visible light to be transmitted therethrough. A material similar to that for the plastic substrate110can be used for the sealing substrate.

Next, the FPC402is bonded to each of electrodes of the input and output terminals with an anisotropic conductive material. An IC chip may be mounted thereover if necessary.

By the above-mentioned process, manufacture of a module of the light-emitting device to which the FPC402is connected is completed.

Note that, in the case where the semiconductor layer of the TFT included in the light-emitting device of the present embodiment is not subjected to treatment performed at a high-temperature or a laser irradiation, a structure shown inFIG.2can be employed.

In the structure shown inFIG.2, an adhesive111is provided over a plastic substrate110and bonds an element formation layer formed over a first insulating layer112to the plastic substrate110. A color filter300is provided over the first insulating layer112, and a TFT302is provided while a second insulating layer301formed over the color filter300is sandwiched between the color filter300and the TFT302. The second insulating layer301can be formed by using an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, silicon nitride oxide, and the like or an organic insulating material such as an acrylic, a polyimide, and the like. The use of the organic insulating material is preferred since the organic insulating material can reduce a step caused by formation of the color filter300. Furthermore, it is preferred to provide a protective insulating film over the second insulating layer301in order to suppress an adverse influence of contaminant, such as a gas released from the color filter300, upon the TFT302. The protective insulating film is preferably formed using an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, silicon nitride oxide, and the like. In particular, it is preferred to use silicon nitride or silicon nitride oxide which has a composition of nitrogen higher than that of oxygen. Note that the protective insulating film is not necessarily provided in the case where the second insulating layer301is formed by an inorganic insulating film.

As shown inFIGS.1A to1C, after a separation layer and the first insulating layer112are formed, the color filter300and the second insulating layer301are formed over a substrate with low flexibility, which is followed by the formation of the TFT302. The TFT302may have a known structure and be formed by a known method which does not require high temperature treatment. For instance, a TFT having a semiconductor such as the above-mentioned microcrystalline semiconductor, the amorphous semiconductor, the oxide semiconductor, the semiconductor containing an organic material as a main component, and the like is exemplified. After forming the TFT302, a first pixel electrode303of a light-emitting element and a partition layer304are formed. Then, the separation is carried out in a similar manner to that mentioned above to achieve the transfer to a plastic substrate110, leading to the formation of a light-emitting device similarly to that shown inFIGS.1A to1C.

In the light-emitting device with such a structure, the second insulating layer301is singly able to suppress adverse influence of a contaminant from the color filter300upon the TFT302and the light-emitting element, which contributes to reduction of manufacturing process.

It should be noted that even in the structure shown inFIG.2, the color filter is formed using the substrate with low flexibility. Therefore, similarly to the structure shown inFIGS.1A to1C, the light-emitting device with the structure ofFIG.2can display a full color image with high resolution in spite of its flexibility.

Embodiment 2

A top view and a sectional view of a module of a light-emitting device (also referred to as an EL module) are illustrated inFIGS.4A and4B, respectively.

FIG.4Ais a top view showing the EL module, andFIG.4Bis a view showing a part of a cross section taken along line A-A′ ofFIG.4A. InFIG.4A, an insulating layer501is formed over a plastic substrate110with an adhesive500(for example, the second adhesive and the like) sandwiched therebetween, over which a pixel portion502, a source side driving circuit504, and a gate side driving circuit503are formed. These elements can be obtained by the manufacturing method demonstrated in embodiment 1.

Reference numerals400and401denote an organic resin and a protective film, respectively, and the pixel portion502, the source side driving circuit504, and the gate side driving circuit503are covered by the organic resin400which is further covered by the protective film401. Sealing by a cover material can be further conducted by using an adhesive. The cover material can be bonded as a supporting base before the separation process.

A reference numeral508denotes a wiring for transmitting signals inputted to the source side driver circuit504and the gate side driver circuit503and receives video signals, clock signals, and the like from an FPC (Flexible Printed Circuit)402which functions as an external input terminal. Although only the FPC402is depicted inFIGS.4A and4B, a printed wiring board (PWB) may be provided to the FPC402. The light-emitting device according to the embodiments of the invention includes not only a light-emitting device itself but also a state in which an FPC or a PWB is attached thereto.

Next, a sectional structure is described with reference toFIG.4B. The insulating layer501is provided over and in contact with the adhesive500, and the pixel portion502and the gate side driving circuit503are formed over the insulating layer501. The pixel portion502comprises a plurality of pixels515, and the plurality of pixels515include a current control TFT511and a first pixel electrode512which is electrically connected to one of source and drain electrodes of the current control TFT511. AlthoughFIG.4Bshows only one of the plurality of pixels515, they are arranged in a matrix form in the pixel portion502. The gate side driver circuit503is formed using a CMOS circuit in which a plurality of n-channel TFTs513and a plurality of p-channel TFTs514are combined.

Embodiment 3

In this embodiment, electronic devices which include the light-emitting devices described in embodiments 1 and 2 are described.

Examples of the electronic devices which include the light-emitting devices described in embodiments 1 or 2 include cameras such as video cameras and digital cameras, goggle type displays, navigation systems, audio playback devices (e.g., car audio systems and audio systems), computers, game machines, portable information terminals (e.g., mobile computers, mobile phones, portable game machines, and electronic books), image playback devices in which a recording medium is provided (specifically, devices that are capable of playing back recording media such as digital versatile discs (DVDs) and equipped with a display unit that can display images), and the like. Specific examples of such electronic devices are shown inFIGS.5A to5D.

FIG.5Aillustrates a television device which includes a housing9101, a supporting base9102, a display portion9103, speaker portions9104, video input terminals9105, and the like. The television device is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion9103. The television device, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion9103to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG.5Billustrates a computer which includes a main body9201, a housing9202, a display portion9203, a keyboard9204, an external connection port9205, a pointing device9206, and the like. The computer is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion9203. The computer, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion9203to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG.5Cillustrates a mobile phone, which includes a main body9401, a housing9402, a display portion9403, an audio input portion9404, an audio output portion9405, operation keys9406, an external connection port9407, an antenna9408, and the like. The mobile phone is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion9403. The mobile phone, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion9403to possess a curved shape, is lightweight, and supplies an image with high quality. In addition, the lightweight mobile phone can have appropriate weight even if a variety of additional values are added thereto, and thus the mobile phone is suitable as a highly functional mobile phone.

FIG.5Dillustrates a camera which includes a main body9501, a display portion9502, a housing9503, an external connecting port9504, a remote control receiving portion9505, an image receiving portion9506, a battery9507, an audio input portion9508, operation keys9509, an eyepiece portion9510, and the like. The camera is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion9502. The camera, in which the flexible light-emitting device capable of displaying a full color image with high resolution is mounted, allows the display portion9502to possess a curved shape, is lightweight, and supplies an image with high quality.

FIG.5Eillustrates a flexible display which includes a main body9601, a display portion9602, an insert portion of an external memory9603, a speaker portion9604, operation keys9605, and the like. A television receiving antenna, an external input, an external output terminal, a battery, and the like may be mounted on the main body9601. The flexible display is manufactured by using the light-emitting device shown in embodiment 1 or 2 in the display portion9602. The display portion9602can possess a curved shape, is lightweight, and supplies an image with high quality. When the display portions of the electronic devices shown inFIGS.5A to5Dare manufactured so as to have a curved shape and the flexible display shown inFIG.5Eis mounted on the display portions, a electronic device having a display portion with a curved shape can be supplied.

As described above, the range of application of the light-emitting device manufactured by using the light-emitting element shown in embodiment 1 or 2 is extremely wide, and the light-emitting device can be applied to electronic devices in a wide variety of fields.

This application is based on Japanese Patent Application serial no. 2008-180229 filed with Japan Patent Office on Jul. 10, 2008, the entire contents of which are hereby incorporated by reference.