JP2006303463A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device and its method for manufacturing, in which a layer having oxygen can be formed on an electrode without increasing a contact resistance even when a highly reflective material such as aluminum is used for the electrode. <P>SOLUTION: The light emitting device is a light emitting device having light emitting elements or a light emitting element having an electrode cosisting of a laminated structure provided with conducting films composed of high melting point metal prepared on the conducting films, wherein the conducting films of high reflectivity such as aluminum, silver, alloy containing aluminum, or alloy containing silver are used for the electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a light emitting device including a light emitting element including a mixed layer having a metal oxide.

A display device having a light-emitting element (hereinafter referred to as a light-emitting device) has advantages of a wide viewing angle, low power consumption, and high response speed as compared with a liquid crystal display device, and its research and development is actively performed. It has been broken.

The light-emitting element has a structure in which a light-emitting substance is provided between a pair of electrodes, and light from the light-emitting substance appears according to the light-transmitting property of the electrode.

For example, when light is desired to appear in one direction, one electrode provided on the one direction side is formed using a light-transmitting material and the other electrode is formed using a reflective material. The light extraction efficiency can be increased by effectively using the reflection by the other electrode.

In addition, a display device has been proposed in which a resonator structure in which an optical distance between a pair of electrodes satisfies a certain mathematical formula is introduced, and the resonance wavelength is matched with the peak wavelength of the spectrum of light to be extracted (patent) Reference 1).
JP 2004-178930 A

By the way, since the anode is used as a reflective electrode in a panel emitting upward as in Patent Document 1, a material having a high visible light reflectance such as aluminum or silver is desirable. Since silver is difficult to process, aluminum is often used for the anode.

However, a material having high reflectivity such as aluminum or silver is easily oxidized. For example, when a layer containing oxygen is formed on a conductive film such as aluminum or silver, the conductive film is oxidized. After oxidation, the contact resistance increases because it approaches the insulating characteristics. As a result, a sufficient current cannot be supplied, the driving voltage becomes high, and it is difficult to use as an electrode.

Therefore, the present invention provides a light emitting device capable of forming a layer containing oxygen on an electrode without increasing contact resistance even when a material having a high visible light reflectance such as aluminum is used for the electrode. It is an object to provide a manufacturing method thereof.

In view of the above problems, the present invention provides an electrode (referred to as a reflective electrode) that is required to have high reflectance, aluminum (Al), silver (Ag), an alloy containing aluminum (Al alloy), or an alloy containing silver (Ag alloy). ) And the like, and an electrode having a laminated structure of a conductive film made of a refractory metal material provided in an upper layer of the conductive film. The light-emitting device of the present invention includes a light-emitting element in which a mixed layer including a metal oxide that is a layer containing oxygen is provided over a conductive film made of a refractory metal material. That is, the present invention is characterized in that a mixed layer having a metal oxide is formed in contact with a conductive film made of a refractory metal material which is one of electrodes having a laminated structure.
A highly reflective conductive film such as aluminum (Al), silver (Ag), an alloy containing aluminum (Al alloy), or an alloy containing silver (Ag alloy) may be oxidized by a mixed layer containing a metal oxide. Although concerned, oxidation can be prevented by providing a conductive film made of a refractory metal material.

Note that the conductive film made of a refractory metal material may be a material that is not oxidized by the mixed layer containing the metal oxide or a material that exhibits conductivity even when oxidized. A conductive film made of a refractory metal material can be expressed as a material having low contact resistance with a metal oxide. As a material for the conductive film made of such a refractory metal material, titanium (Ti), tungsten (W), molybdenum (Mo), or a compound having these, for example, titanium nitride (TiN) which is a titanium compound is used. Can do.

In such a light emitting device of the present invention, a transparent electrode material such as indium oxide tin oxide alloy (ITO) is used for the transparent electrode on the side where light from the light emitting device is emitted. In addition to ITO, a reflective material having a high reflectivity, in other words, a non-light-transmitting material, and a material whose thickness is reduced to such an extent that light can be transmitted may be used. In this way, when a thin material having reflectivity is used for the electrode on the light emission side, the light from the light emitting element can be interfered with the reflective electrode, and the light extraction efficiency is increased. be able to.

In the light-emitting element of the present invention, the light from the light-emitting layer reflected by the reflective electrode and the light directly emitted from the light-emitting layer can be interfered with each other, so that the light extraction efficiency of the light-emitting element can be increased. In order to increase the extraction efficiency in this way, the film thickness of any one of the electroluminescent layers, specifically, the layer between the reflective electrode and the light emitting layer is controlled. Further, the film thickness may be controlled so as to be different for each emission color so that the extraction efficiency is increased.

Below, the concrete form of this invention is shown.

The present invention includes a stacked first electrode, an electroluminescent layer provided on the first electrode, and a second electrode provided on the electroluminescent layer, and the electroluminescent layer includes: The light-emitting device includes a mixed layer including a metal oxide on a side in contact with the first electrode, and the first electrode includes a conductive film made of a material having low contact resistance with the mixed layer including the metal oxide. The material having a low contact resistance with the mixed layer containing a metal oxide is a refractory metal material.

In another embodiment of the present invention, the first conductive layer and the second conductive layer of the first electrode, the electroluminescent layer provided in contact with the second conductive layer, and the electroluminescent layer are provided. A mixed layer including a metal oxide in a region in contact with the second conductive layer in the electroluminescent layer, and the second conductive layer includes a metal oxide. It is a light emitting device made of a conductive film made of a material having low contact resistance with a layer. The material having a low contact resistance with the mixed layer containing a metal oxide is a refractory metal material.

Another embodiment of the present invention is a reflective first electrode having a reflectivity, an electroluminescent layer provided on the first electrode, and a translucent first electrode provided on the electroluminescent layer. The first electrode includes a conductive film made of a refractory metal material on a side in contact with the electroluminescent layer, and the electroluminescent layer has a metal oxide on the side in contact with the first electrode. A light emitting device including a mixed layer. An example of the refractory metal material is titanium nitride.

Another embodiment of the present invention includes a first conductive layer and a second conductive layer included in a reflective first electrode, an electroluminescent layer provided in contact with the second conductive layer, and an electroluminescent layer And the second conductive layer is made of a refractory metal material. In the electroluminescent layer, the region in contact with the second conductive layer is oxidized with metal. The light-emitting device is provided with a mixed layer including an object. An example of the refractory metal material is titanium nitride.

Another embodiment of the present invention provides a red, green, and first electrode having a stacked first electrode, an electroluminescent layer provided on the first electrode, and a second electrode provided on the electroluminescent layer, and The first electrode has a conductive film made of titanium nitride on a side in contact with the electroluminescent layer, and the electroluminescent layer has a metal oxide on the side in contact with the first electrode. In the light-emitting element exhibiting red, green, and blue including the mixed layer, the thickness of the first electrode is the same, and the thickness of the electroluminescent layer, specifically, the mixed layer including the metal oxide is different. It is a light emitting device.

In another embodiment of the present invention, the first conductive layer and the second conductive layer of the first electrode, the electroluminescent layer provided in contact with the second conductive layer, and the electroluminescent layer are provided. A plurality of light emitting elements of red, green, and blue having a second electrode, the second conductive layer is made of titanium nitride, and a region in contact with the second conductive layer in the electroluminescent layer is made of metal In a light-emitting element having a mixed layer having an oxide and exhibiting red, green, and blue colors, the thickness of the first electrode is the same, and the thickness of the electroluminescent layer, specifically a metal oxide It is a light emitting device in which the film thickness of the mixed layer having different is different.

In the present invention, a thin film transistor is connected to the first electrode as a switching element. The thin film transistor has an n-channel type or a p-channel type.

Note that in the electroluminescent layer, a layer that is in contact with the first electrode may be a transparent conductive layer such as indium tin oxide alloy (ITO) instead of a mixed layer of metal oxide. When the transparent conductive layer is used, a refractory metal material having low contact resistance with the transparent conductive layer may be used as the upper layer of the first electrode.

Moreover, you may use an aluminum alloy, silver, or a silver alloy for a reflective electrode instead of aluminum. This is because aluminum alloy, silver, and silver alloy are also reflective metal materials. Further, instead of titanium nitride, titanium (Ti), tungsten (W), or molybdenum (Mo) may be used. When these materials are substituted, a refractory metal material having a low contact resistance with the layer is used as an upper layer of the first electrode on the lower layer of the electroluminescent layer and in contact with the mixed layer having a metal oxide. .

By using a laminated structure composed of a highly reflective electrode material such as aluminum and a refractory metal material such as titanium nitride for the reflective electrode of the light emitting element, a mixed layer having a metal oxide and a contact resistance of the reflective electrode And at the same time high light extraction efficiency can be obtained. As a result, it is possible to provide a light-emitting element and a light-emitting device having high luminance as compared with the case of using an aluminum single layer or a titanium nitride single layer as a conventional reflective electrode.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of this embodiment mode. Note that in all the drawings for describing the embodiments, the same portions or portions having similar functions are denoted by the same reference numerals, and repetitive description thereof is omitted.

(Embodiment 1)
In this embodiment mode, a structure of a light-emitting element will be described.

As illustrated in FIG. 1, the light-emitting element of the present invention includes a first electrode 101 and a second electrode 102 that face each other, and a first layer 111 and a second layer 112 are sequentially formed from the first electrode 101. The third layer 113 is laminated. Such a light-emitting element can emit light when a potential difference is applied between the first electrode 101 and the second electrode 102. For example, when the potential of the first electrode is made higher than the potential of the second electrode, holes are injected from the first layer 111 to the second layer 112 and electrons are transferred from the third layer 113 to the second layer 112. Is injected. Holes and electrons recombine in the second layer 112, bringing the light-emitting substance into an excited state. The excited light-emitting substance emits light when returning to the ground state and can emit light from the second electrode 102. Such light emission can be obtained from the light-transmitting second electrode 102. In other words, a light-transmitting material is used for the electrode on the side from which light emission is to be extracted.

The first electrode 101 has reflectivity, and the second electrode 102 has translucency. An electrode having reflectivity can be referred to as a reflective electrode, and an electrode having translucency can be referred to as a transparent electrode.

In such a light-emitting element, the first electrode 101 includes at least two conductive layers 101a and 101b. That is, the first electrode 101 is formed by a stacked structure. As a result, the reflectance of the light with respect to the first electrode 101 is increased, and at the same time, even when a layer containing oxygen such as a mixed layer containing a metal oxide is used for the first layer 111, the first layer The contact resistance with 111 can be made favorable.

For the first conductive layer 101a, highly reflective aluminum, silver, an aluminum alloy, a silver alloy, or an alloy including any of these can be used. Since such a highly reflective material is easily oxidized, it has been found that when the first layer 111 is formed later, an oxide may be formed on the surface. When the oxide is formed, the insulating properties are exhibited, and the contact resistance increases. In addition, a light-emitting element having a mixed layer containing a metal oxide was preferable because of its high characteristics. Therefore, a refractory metal material such as titanium nitride, titanium, tungsten, or molybdenum is used for the second conductive layer 101b. That is, the conductive layer made of a refractory metal material used as the second conductive layer 101b is a material that does not oxidize due to the formation of a mixed layer having a metal oxide, or a material that exhibits conductivity even when oxidized. is there.

Note that the mixed layer having a metal oxide is a layer in which the metal oxide and an organic compound are mixed. The mixed layer does not have to be a mixture of the metal oxide and the organic compound strictly, and includes a state where the mixture is mixed to the extent produced by the co-evaporation method. For example, as a result of being manufactured by a co-evaporation method, a state where each layer is stacked very thin is also included.

With this configuration, the reflectivity of the first electrode 101 can be improved, and at the same time, the contact resistance with the first layer 111 can be improved.

For the transparent electrode that is the second electrode 102, ITO, ITSO in which silicon is mixed in ITO, indium oxide containing 2 to 20% zinc oxide, or the like can be used. Alternatively, the reflective material may be thinned and formed into a thin film so as to have translucency. By using such a thin reflective material, light emission can be interfered between the first electrode 101 and the second electrode 102, and extraction efficiency can be increased.

These reflective electrodes and transparent electrodes can be formed using a sputtering method, a vapor deposition method, or the like. In the reflective electrode, the first conductive layer 101a and the second conductive layer 101b can be formed continuously without being exposed to the atmosphere. Furthermore, the first electrode 101 to the second electrode 102 can be continuously formed without being exposed to the atmosphere. This is advantageous in that impurity contamination of the light emitting element is prevented.

Next, the structure of the first layer 111 to the third layer 113 will be described.

The first layer 111 is a layer that generates holes. As such a layer, for example, a layer containing a hole transporting substance and a substance showing an electron accepting property for the substance can be given. In addition, a substance having an electron accepting property with respect to a hole transporting substance has a molar ratio of 0.5 to 2 (= a substance having an electron accepting property with respect to a hole transporting substance / hole transporting substance). Thus, the first layer 111 is preferably included.

The hole-transporting substance is a substance that has a higher hole-transporting property than electrons. For example, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: α- NPD), 4,4′-bis [N- (3-methylphenyl) -N-phenylamino] biphenyl (abbreviation: TPD), 4,4 ′, 4 ″ -tris (N, N-diphenylamino) tri Phenylamine (abbreviation: TDATA), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA), 4,4′-bis [N Aromatic amine compounds such as-{4- (N, N-di-m-tolylamino) phenyl} -N-phenylamino] biphenyl (abbreviation: DNTPD), phthalocyanine (abbreviation: H ₂ Pc), copper phthalocyanine (abbreviation) : CuPc), Bana An organic compound such as a phthalocyanine compound such as zirphthalocyanine (abbreviation: VOPc) can be used. Note that the hole transporting substance is not limited to these.

In addition, substances that have electron acceptability with respect to hole transporting substances include, for example, vanadium oxide, molybdenum oxide, niobium oxide, rhenium oxide, tungsten oxide, ruthenium oxide, titanium oxide, and chromium oxide. Any metal oxide such as an oxide, zirconium oxide, hafnium oxide, and tantalum oxide can be used. Note that a substance that exhibits an electron accepting property with respect to a hole transporting substance is not limited thereto.

A mixed layer in which an organic compound serving as a hole-transporting substance and a metal oxide that exhibits an electron accepting property are mixed can be manufactured by a co-evaporation method. Specifically, the first layer 111 is a co-evaporation method by resistance heating deposition, a co-evaporation method by electron beam deposition, a co-evaporation method by resistance heating deposition and electron beam deposition, a film formation by resistance heating deposition and sputtering method, It can be formed by combining the same or different methods such as electron beam evaporation and film formation by sputtering. Moreover, although the said example assumes the layer containing 2 types of materials, when it contains 3 or more types of materials, it can form similarly, combining the same kind and different types of methods.

Note that the first layer 111 may contain another organic compound. Other organic compounds include rubrene and the like. Reliability can be improved by adding rubrene.

In addition, the first layer 111 may be a layer made of a metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, cobalt oxide, or copper oxide.

However, it is preferable that the first layer 111 be formed from a mixed layer including an organic compound and a metal oxide as described above because of high conductivity. When the conductivity is high, the first layer 111 can be thickened and a short circuit between the first electrode 101 and the second electrode 102 can be prevented.

Further, in the light-emitting element, interference from light from the light-emitting layer reflected by the first electrode 101 and light directly emitted from the light-emitting layer can be generated, so that light extraction efficiency of the light-emitting element can be increased. In order to increase the extraction efficiency in this way, the film thickness of the first layer 111 may be controlled. In addition, the thickness of the first layer 111 is preferably different for each emission color depending on light from the light-emitting element.

A material having favorable contact resistance with the first layer 111 is used for the second conductive layer 101 b which is the upper layer of the first electrode 101. In this embodiment, a mixed layer containing molybdenum oxide is used for the first layer 111, titanium nitride is used for the second conductive layer 101 b, and the first conductive layer 101 a that is the lower layer of the first electrode 101 is used. Uses aluminum. As a result, the contact resistance between the first electrode 101 and the first layer 111 can be improved, and at the same time, high light extraction efficiency can be obtained.

The second layer 112 is a layer including a light emitting layer. The structure of the second layer 112 may be a single layer or a multilayer. For example, as shown in FIG. 1, the second layer 112 can include functionally different layers such as a hole transport layer 121, an electron transport layer 123, and an electron injection layer 124 in addition to the light emitting layer 122. Needless to say, the second layer 112 may be a single layer including only the light emitting layer 122.

The second layer 112 may include a layer in which a light-emitting substance is dispersed and included in a layer formed using a substance having an energy gap larger than that of the light-emitting substance. Note that the light-emitting substance is a substance that has favorable emission efficiency and can emit light with a desired emission wavelength. Note that the energy gap is an energy gap between the LUMO level and the HOMO level.

Examples of the substance used for dispersing the luminescent substance include an anthracene derivative such as 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-BuDNA), or 4,4′-di In addition to carbazole derivatives such as (N-carbazolyl) biphenyl (abbreviation: CBP), bis [2- (2′-hydroxyphenyl) pyridinato] zinc (abbreviation: Znpp ₂ ), bis [2- (2′-hydroxyphenyl) Metal complexes such as benzoxazolate] zinc (abbreviation: ZnBOX) can be used. However, substances used for dispersing the light-emitting substance are not limited to these materials. With the above structure, light emission from the light-emitting substance can be prevented from being quenched due to concentration.

When red light emission is desired, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] is added to the second layer 112. -4H-pyran (abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation) : DCJT), 4-dicyanomethylene-2-tert-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTB) and Periflanthene, 2,5-dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] benzene, bis [2,3-bis ( 4-Fluo Phenyl) Kinokisarinaito] iridium (acetylacetonate) (abbreviation: Ir _[Fdpq] 2 acac), or the like can be used. However, the present invention is not limited to these materials, and a substance exhibiting light emission having a peak of an emission spectrum at 600 nm to 680 nm can be used.

When green light emission is desired, the second layer 112 is formed with N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6 or coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), or the like. Can be used. However, the present invention is not limited to these materials, and a substance exhibiting light emission having an emission spectrum peak at 500 nm or more and 550 nm or less can be used.

In order to obtain blue light emission, the second layer 112 is provided with 9,10-di (2-naphthyl) -tert-butylanthracene (abbreviation: t-BuDNA), 9,9′-bianthryl, 9,10. -Diphenylanthracene (abbreviation: DPA), 9,10-di (2-naphthyl) anthracene (abbreviation: DNA), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-gallium (abbreviation: BGaq), Bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq) or the like can be used. However, the present invention is not limited to these materials, and a substance exhibiting light emission having a peak of an emission spectrum at 420 nm to 500 nm can be used.

Note that by providing the hole transport layer 121 as shown in FIG. 1, the distance between the first electrode 101 and the light-emitting layer 122 can be increased, and light emission is quenched due to metal. Can be prevented. Note that the hole-transport layer 121 is a layer having a function of transporting holes injected from the first electrode 101 to the light-emitting layer 122. As specific materials, α-NPD, TPD, TDATA, MTDATA, DNTPD and the like described above can be used. However, the hole transport layer 121 is not limited thereto, and can be formed using a hole transport material having a higher hole mobility than the above-described electron mobility. Specifically, the hole transport layer 121 is preferably formed using a substance having a hole mobility of 10 ⁻⁶ cm ² / Vs or higher. The hole transport layer 121 may be a layer having a multilayer structure formed by combining two or more layers made of the substances described above.

In addition, as illustrated in FIG. 1, an electron transport layer 123 can be provided between the second electrode 102 and the light emitting layer 122. Thus, by providing the electron transport layer 123, the distance between the second electrode 102 and the light-emitting layer 122 can be increased, and the light emission can be prevented from being quenched due to the metal. The electron transport layer 123 is a layer having a function of transporting injected electrons to the light emitting layer 122. Specific materials are formed using Alq ₃ , Almq ₃ , BeBq ₂ , BAlq, Zn (BOX) ₂ , Zn (BTZ) ₂ , PBD, OXD-7, TAZ, p-EtTAZ, BPhen, BCP, and the like. be able to. However, the electron transporting layer 123 is not limited thereto, and may be formed using an electron transporting substance having a higher electron mobility than a hole mobility. Specifically, the electron transport layer 123 is preferably formed using a substance having an electron mobility of 10 ⁻⁶ cm ² / Vs or higher. Further, the electron transport layer 123 may be a layer having a multilayer structure formed by combining two or more layers made of the substances described above.

Further, as shown in FIG. 1, an electron injection layer 124 may be provided between the second electrode 102 and the electron transport layer 123. Note that the electron injection layer 124 is a layer having a function of assisting injection of electrons from the second electrode 102 or the like into the electron transport layer 123. Specific examples of the material include calcium fluoride, lithium fluoride, alkali metal salts such as lithium oxide and lithium chloride, alkaline earth metal salts, and the like. In addition, a layer in which a donor compound such as lithium is added to a so-called electron transporting material such as tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ) or bathocuproine (abbreviation: BCP) can also be used. Alternatively, the electron-injecting layer 124 may be formed using a layer containing the above-described electron-transporting substance and a substance that exhibits an electron-donating property with respect to the substance. However, the electron injection layer 124 is not limited to these.

Note that a layer in contact with the first layer 111 among the layers included in the second layer 112 corresponds to the hole-transport layer 121 when the second layer 112 has a stacked structure.

The third layer 113 is a layer that generates electrons. As such a layer, for example, a layer containing an electron transporting substance and a substance showing an electron donating property to the substance can be given. Note that an electron-transporting substance is a substance having a higher electron-transporting property than holes. For example, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum ( Abbreviations: Almq ₃ ), bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), Bis [2- (2′-hydroxyphenyl) benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2′-hydroxyphenyl) benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ) In addition to metal complexes such as 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole Abbreviation: PBD), 1,3-bis [5- (4-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), 3- (4-biphenylyl) -4- (4-ethylphenyl) -5 (4-tert-butylphenyl) -1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), 4,4′-bis (5-methyl- Benzoxazol-2-yl) stilbene (abbreviation: BzOs) or the like can be used. However, the electron transporting substance is not limited to these.

Examples of the substance that exhibits an electron donating property with respect to the electron transporting substance include alkali metals such as lithium and cesium, alkaline earth metals such as magnesium and calcium, and rare earth metals such as erbium and ytterbium. . However, the substance that exhibits an electron donating property with respect to the electron transporting substance is not limited thereto. It should be noted that the substance exhibiting electron donating property with respect to the electron transporting substance has a molar ratio of 0.5 to 2 (= the substance exhibiting electron donating property with respect to the electron transporting substance / electron transporting substance). It is preferably included in the third layer 113.

The third layer 113 may be a layer made of a substance such as zinc oxide, zinc sulfide, zinc selenide, tin oxide, or titanium oxide.

In addition, the second layer 112 may have a single-layer structure including only a light-emitting layer, or may not include the hole transport layer 121 or the like. In such a case, when the light-emitting layer is in contact with the third layer 113, the substance included in the layer in contact with the third layer 113 among the layers included in the second layer 112 is in a dispersed state. It corresponds to the substance to do. Moreover, it may correspond to the luminescent substance itself. The light-emitting substance itself is a layer made of only Alq ₃ without being dispersed in the case of a light-emitting substance that can emit light without being particularly dispersed, such as Alq ₃ , and has good carrier transportability. This is because can function as a light emitting layer.

In this manner, by bonding the second layer 112 and the third layer 113, injection of electrons from the second layer 112 to the third layer 113 is facilitated.

In the light-emitting element as described above, a conductive layer made of a refractory metal material in contact with the mixed layer containing a metal oxide is formed as the first electrode. Note that the conductive layer provided in contact with the mixed layer having a metal oxide may be a material that does not oxidize or a material that exhibits conductivity even when oxidized by forming the mixed layer having the metal oxide. . According to the present invention, the reflectivity of the first electrode 101 can be improved, and at the same time, the contact resistance between the first electrode 101 and the first layer 111 can be improved. Note that the present invention is not limited to the structure of the light emitting element shown in FIG. 1 as long as the above effects can be obtained. For example, in the case where the second electrode 102 is a reflective electrode and a mixed layer including a metal oxide is used for the third layer 113, the second electrode 102 having a stacked structure is in contact with the mixed layer including a metal oxide. Then, a conductive layer made of a refractory metal material is formed. As a result, the reflectivity of the second electrode 102 can be improved, and at the same time, the contact resistance with the third layer 113 can be improved.

(Embodiment 2)
Furthermore, in the present invention, the thickness of any one of the electroluminescent layers may be made different for each light emitting element exhibiting each emission color (red, green, blue). As a result, light extraction efficiency can be increased for light-emitting elements having different emission wavelengths. In this embodiment, in addition to the electrode structure described in Embodiment 1, an electroluminescent layer, that is, a light-emitting element in which any one of the layers excluding the first electrode and the second electrode has a different thickness is used. explain.

As shown in FIG. 2, the light-emitting element that emits red (R), green (G), and blue (B) light has a reflective first electrode 101 and a light-transmitting property. The thickness of the second electrode 102 is the same, and the thickness of any one of the first layers 111R, 111G, and 111B, the second layers 112R, 112G, and 112B, and the third layers 113R, 113G, and 113B is set. Make it different. For example, the first layers 111R, 111G, and 111B are made different for each emission color. As a result, light extraction efficiency can be increased for light-emitting elements having different emission wavelengths.

  In this case, when light from the light emitting region is incident, phase inversion occurs in the reflected light from the first electrode 101 serving as a reflective electrode, and an optical interference effect is generated by the direct light and the inverted light. As a result, the optical distance (equivalent to refractive index × distance) between the light emitting region and the reflective electrode is [(2m−1) / 4] times the emission wavelength (m is an arbitrary positive integer), specifically When the optical distance is 1/4, 3/4, 5/4, or the like, the light extraction efficiency is increased. This is a condition for strengthening the interference of light. Since there are a number of optical distances that satisfy the strengthening conditions, the optical distance itself may be different for each emission color. For example, the blue color whose film thickness is reduced due to the wavelength satisfies the optical distance = 3/4, and the other red and green colors satisfy the optical distance = 1/4. As a result, in the blue color, the film thickness can be increased when the optical distance = 3/4 is satisfied, and the short circuit between the electrodes can be prevented, compared with the case where the optical distance = ¼. Of course, the numerical value of the optical distance is an example. On the other hand, m / 2 times (m is an arbitrary positive integer) Specifically, when m = 1/2, 1, 3/2. This is a condition in which light interference weakens.

  Therefore, in the light-emitting element of the present invention, the first layer is formed such that the optical distance between the light-emitting region and the reflective electrode is (2m−1) / 4 times the emission wavelength (m is an arbitrary positive integer). The thickness of any of the layers 111 to 113 is preferably different for each light-emitting element.

In particular, in the first layer 111 to the third layer 113, it is preferable that the film thickness of the layer between the light emitting region where electrons and holes are recombined and the reflective electrode be different. Further, the thickness of the layer between the light emitting region and the second electrode 102 which is a transparent electrode may be varied. Furthermore, the thicknesses of both layers may be different. Thus, the film thickness of each layer is determined so that emitted light can be efficiently extracted outside.

In order to change the film thickness of any of the first layer 111 to the third layer 113, the layer needs to be thickened. Therefore, the present invention is characterized in that a mixed layer in which an organic compound and a metal oxide that is an inorganic compound are mixed is used for the layer to be thickened.

In general, increasing the thickness of the light emitting element layer is not preferable because the driving voltage increases. However, even when the mixed layer including the organic compound and the metal oxide that is an inorganic compound is thickened, the driving voltage is not increased. Furthermore, the drive voltage itself can be lowered.

Further, by increasing the thickness of any of the first layer 111 to the third layer 113, the first electrode 101 and the second electrode 102 can be prevented from being short-circuited, and mass productivity can be increased. Very preferred.

In the case where the first layer 111 to the third layer 113 are formed by an evaporation method, an evaporation mask can be used as it is. On the other hand, when the film thicknesses of the reflective electrode and the transparent electrode are made different, it is considered that the photolithography method process and the etching process are required, and the number of processes increases. It is preferable to change the thickness of any of the layers 113.

By combining structures having different film thicknesses in this way, light extraction efficiency can be further increased.

(Embodiment 3)
In this embodiment mode, a cross-sectional structure of a pixel including the light-emitting element of the present invention is described. Further, a transistor that controls supply of current to the light emitting element (hereinafter referred to as a driving transistor) is a p-type thin film transistor (TFT).

The pixel cross-sectional view of FIG. 3 shows a so-called upward emission type in which light emitted from each of the light emitting elements 603R, 603G, and 603B is extracted from the second electrode 102 side. Each of the light emitting elements 603R, 603G, and 603B can exhibit each light emission color (RGB) (hereinafter, also referred to as a light emitting element 603). The light-emitting element 603 includes a stacked first electrode 101 (consisting of a first conductive layer 101a and a second conductive layer 101b) and a second electrode 102, and an electroluminescent layer 605R, 605G and 605B are provided. The electroluminescent layers 605R, 605G, and 605B correspond to the first layer 111 to the third layer 113. The first electrode 101 and the TFTs 601R, 601G, and 601B are electrically connected to each other.

The TFTs 601R, 601G, and 601B each have a thickness of 10 to 200 nm and have a channel formation region using a semiconductor film separated into island shapes. As the semiconductor film, any of an amorphous semiconductor film, a crystalline semiconductor film, and a microcrystalline semiconductor film may be used. For example, in the case of forming a crystalline semiconductor film, an amorphous semiconductor film can be formed first, and a crystalline semiconductor film crystallized by heat treatment can be formed. The heat treatment can be a heating furnace, laser irradiation, irradiation of light emitted from a lamp instead of laser light (hereinafter referred to as lamp annealing), or a combination thereof.

When laser irradiation is used, a continuous wave laser (CW laser) or a pulsed laser (pulse laser) can be used.

In addition, it is a pulse oscillation type laser that oscillates laser light at a repetition frequency that can irradiate laser light of the next pulse from the time when the semiconductor film is melted by the laser light and solidifies in the scanning direction. Crystal grains grown continuously can be obtained. That is, it is possible to use a pulse beam in which the lower limit of the repetition frequency is set so that the period of pulse oscillation is shorter than the time until the semiconductor film is completely solidified after being melted. The oscillation frequency of the pulse beam that can be actually used is 10 MHz or more, and a frequency band that is significantly higher than the frequency band of several tens to several hundreds Hz that is normally used is used.

As another heat treatment, when a heating furnace is used, the amorphous semiconductor film is heated at 500 to 550 ° C. for 2 to 20 hours. At this time, the temperature may be set in multiple stages in the range of 500 to 550 ° C. so that the temperature gradually increases. In the first low-temperature heating step, hydrogen or the like of the amorphous semiconductor film comes out, so that so-called hydrogen dipping that reduces film roughness during crystallization can be performed. Furthermore, it is preferable to form a metal element that promotes crystallization, such as Ni, on the amorphous semiconductor film because the heating temperature can be reduced. Even crystallization using such a metal element may be heated to 600 to 950 ° C.

However, when a metal element is formed, there is a concern that the electrical characteristics of the semiconductor element may be adversely affected. Therefore, it is necessary to perform a gettering step for reducing or removing the metal element. For example, a step of capturing a metal element using an amorphous semiconductor film as a gettering sink may be performed.

Further, the TFTs 601R, 601G, and 601B each include a gate insulating film that covers the semiconductor film, a gate electrode in which a first conductive layer and a second conductive layer are stacked, and an insulating film on the gate electrode.

The TFTs 601R, 601G, and 601B each include a semiconductor film having a p-type impurity region. In this embodiment mode, a so-called single drain structure having only a high concentration impurity region as an impurity region is employed. Of course, the TFTs 601R, 601G, and 601B may have an LDD (low concentration drain) structure having a low concentration impurity region and a high concentration impurity region in a semiconductor film, or a GOLD (Gate Overlapped Drain) structure in which the impurity region overlaps with a gate electrode.

The TFTs 601R, 601G, and 601B are covered with an interlayer insulating film 607, and a partition wall 608 having an opening is formed over the interlayer insulating film 607. In the opening, the stacked first electrode 101 is exposed, and the electroluminescent layers 605R, 605G, and 605B, and the second electrode 102 are sequentially stacked on the first electrode 101.

The electroluminescent layers 605R, 605G, and 605B correspond to the first layer 111, the second layer 112, and the third layer 113. Therefore, in the electroluminescent layer, the light extraction efficiency can be increased by changing the film thickness of any of the first to third layers for each emission color. Since this embodiment mode is a top emission type, the thickness of the first layer 111 close to the stacked first electrode 101 is preferably different for each emission color.

More preferably, when a mixed layer in which an organic compound and a metal oxide are mixed is used for the first layer 111, an increase in driving voltage due to an increase in thickness can be prevented. When using a mixed layer in which an organic compound and a metal oxide are mixed in this way, the second conductive layer 101b, which is the upper layer of the stacked first electrode 101, is a refractory metal material such as titanium nitride, A material having low contact resistance with the mixed layer is used. The first conductive layer 101a is made of a highly reflective material such as aluminum. Note that the above embodiment mode can be referred to for details of the first conductive layer 101a and the second conductive layer 101b.

As a result, the contact resistance between the mixed layer and the first electrode 101 can be improved, and at the same time, high light extraction efficiency can be obtained. In addition, the light extraction efficiency can be further increased by making the film thickness of the first layer 111 different for each emission color.

Since this embodiment mode is a top emission type, the stacked first electrode 101 includes a first conductive layer 101a made of a highly reflective material, a refractory metal material, and a first layer. The second conductive layer 101b is made of a material having a good contact resistance with respect to 111. Embodiment 1 can be referred to for materials of the first conductive layer 101a and the second conductive layer 101b.

The material of the second electrode 102 is formed from a light-transmitting material. Embodiment 1 can be referred to for specific materials.

Note that in this embodiment, the first electrode 101 functions as an anode, and the second electrode 102 functions as a cathode. Therefore, the first electrode 101 is preferably made of a material having a low work function, and the second electrode 102 is preferably made of a material having a high work function.

Since the TFTs 601R, 601G, and 601B are p-type, the wiring connected to the TFT can function as the first electrode 101 as an anode as it is. Thus, the number of processes can be reduced by sharing the wiring.

The first electrode 101 or the second electrode 102 can be formed by a sputtering method, an evaporation method, or the like.

The interlayer insulating film 607 can be formed using an insulator including an Si—O—Si bond formed of an organic resin material, an inorganic insulating material, or a siloxane-based resin (hereinafter referred to as a siloxane insulator). A siloxane-based resin corresponds to a resin including a Si—O—Si bond. Siloxane has a skeleton structure formed of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (for example, an alkyl group or an aromatic hydrocarbon) is used. A fluoro group may be used as a substituent. Alternatively, an organic group containing at least hydrogen and a fluoro group may be used as a substituent. For the interlayer insulating film 607, a material called a low dielectric constant material (low-k material) may be used.

The partition wall 608 can be formed using an organic resin material, an inorganic insulating material, or a siloxane insulator. For example, acrylic resin, polyimide, and polyamide can be used as the organic resin material, and silicon oxide, silicon nitride oxide, and the like can be used as the inorganic insulating material. In particular, a photosensitive organic resin material is used for the partition wall 608 so that an opening is formed on the first electrode 101 so that the side wall of the opening has an inclined surface formed with a continuous curvature. Thus, film formation failure of the electroluminescent layer, so-called disconnection, can be prevented, and a short circuit between the first electrode 101 and the second electrode 102 can be prevented.

As described above, it is possible to provide a top emission type light emitting device that can extract light emitted from the light emitting element 603 from the second electrode 102 side as indicated by an arrow.

The present invention is characterized in that the first electrode 101 has a stacked structure, and a conductive layer made of a refractory metal material is formed on the side in contact with the mixed layer containing a metal oxide. Note that the conductive layer provided in contact with the mixed layer having a metal oxide may be a material that does not oxidize or a material that exhibits conductivity even when oxidized by forming the mixed layer having the metal oxide. . According to the present invention, the reflectivity of the first electrode 101 can be improved, and at the same time, the contact resistance with the first layer 111 which is an electroluminescent layer can be improved.

The present invention is not limited to the pixel structure shown in FIG. 3 as long as the above effects can be obtained. For example, in the case where the second electrode 102 is a reflective electrode and a mixed layer including a metal oxide is used for the third layer 113 which is an electroluminescent layer, the second electrode 102 having a stacked structure includes a metal oxide. A conductive layer made of a refractory metal material may be formed in contact with the mixed layer, and light may be extracted from below. Even in such a configuration, the reflectivity of the second electrode 102 can be improved, and at the same time, the contact resistance with the third layer 113 which is an electroluminescent layer can be improved.

(Embodiment 4)
In this embodiment mode, a cross-sectional structure of a pixel in the case where the driving transistor is an n-type TFT will be described. Note that in this embodiment mode, the first electrode functions as a cathode and the second electrode functions as an anode. Therefore, the light-emitting element is reverse to the stacked structure of the light-emitting element in FIG.

In such a stacked structure of light-emitting elements, a mixed layer containing a metal oxide can be used as a layer in contact with the reflective electrode in the electroluminescent layer. When a highly reflective material, aluminum, silver, an aluminum alloy, or a silver alloy is used for the reflective electrode, the surface is oxidized and the contact resistance with the mixed layer is increased. Thus, even in the light-emitting element in this embodiment, titanium nitride, titanium, tungsten, molybdenum, or the like, which is a refractory metal material, can be used for the upper layer of the reflective electrode in consideration of contact resistance.

The pixel cross-sectional view of FIG. 4 shows a top emission type in which light emitted from each of the light emitting elements 613R, 613G, and 613B is extracted from the second electrode 102 side. Similarly to FIG. 3, the light emitting elements 613R, 613G, and 613B can each emit light colors (RGB) (hereinafter, collectively referred to as the light emitting element 613). The light-emitting element 613 includes a stacked first electrode 101 (consisting of a first conductive layer 101a and a second conductive layer 101b) and a second electrode 102, and an electroluminescent layer 615R, 615G and 615B are provided. The electroluminescent layers 615R, 615G, and 615B correspond to the first layer 111 to the third layer 113, respectively. The electroluminescent layers 615R, 615G, and 615B have different thicknesses for each emission color. The first electrode 101 and the TFTs 611R, 611G, and 611B are electrically connected to each other.

The TFTs 611R, 611G, and 611B can be formed in the same manner as the TFTs 601R, 601G, and 601B in the above embodiment.

Since this embodiment mode is a case of a top emission type, the stacked first electrode 101 has good contact resistance between the first conductive layer 101a made of a highly reflective material and the first layer 111. And a second conductive layer 101b made of any material. Embodiment 1 can be referred to for materials of the first conductive layer 101a and the second conductive layer 101b.

The material of the second electrode 102 is formed from a light-transmitting material. Embodiment 1 can be referred to for specific materials.

Note that the first electrode 101 functions as a cathode, and the second electrode 102 functions as an anode. Therefore, the first electrode 101 is preferably made of a material having a high work function, and the second electrode 102 is preferably made of a material having a low work function.

Note that since the driving transistor is n-type, the wiring connected to the TFTs 611R, 611G, and 611B can be used as it is as the first electrode 101 functioning as a cathode. Thus, the number of processes can be reduced by sharing the wiring.

The electroluminescent layers 615R, 615G, and 615B correspond to the first layer 111, the second layer 112, and the third layer 113, respectively. Therefore, in the electroluminescent layer, the light extraction efficiency can be increased by changing the film thickness of any of the first to third layers for each emission color. Since this embodiment mode is a top emission type, the thickness of the first layer 111 close to the stacked first electrode 101 is preferably different for each emission color.

Further, a mixed layer in which an organic compound and a metal oxide are mixed can be used for the first layer 111, and an increase in driving voltage due to an increase in thickness can be prevented. Such metal oxides include lithium oxide (Li ₂ O), calcium oxide (CaO), sodium oxide (Na ₂ O), potassium oxide (K ₂ O), magnesium oxide (MgO), Examples thereof include lithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF ₂ ). The second conductive layer 101b, which is an upper layer of the stacked first electrode 101, is a refractory metal material such as titanium nitride, titanium, tungsten, or molybdenum, and has a low contact resistance. The first conductive layer 101a is a highly reflective material such as aluminum, silver, an aluminum alloy, or a silver alloy.

As a result, the contact resistance between the mixed layer and the first electrode 101 can be improved, and at the same time, high light extraction efficiency can be obtained. In addition, the light extraction efficiency can be further increased by making the film thickness of the first layer 111 different for each emission color.

In this manner, a top emission type light emitting device in which light emitted from the light emitting element 613 is extracted from the second electrode 102 side as shown by an arrow can be provided.

The present invention is characterized in that a conductive layer made of a refractory metal material is formed as the first electrode 101 in contact with a mixed layer containing a metal oxide. Note that the conductive layer provided in contact with the mixed layer having a metal oxide may be a material that does not oxidize or a material that exhibits conductivity even when oxidized by forming the mixed layer having the metal oxide. . According to the present invention, the reflectivity of the first electrode 101 can be improved, and at the same time, the contact resistance with the first layer 111 which is an electroluminescent layer can be improved. The present invention is not limited to the pixel structure shown in FIG. 4 as long as the above effects can be obtained. For example, in the case where the second electrode 102 is a reflective electrode and a mixed layer including a metal oxide is used for the third layer 113 which is an electroluminescent layer, the second electrode 102 having a stacked structure includes a metal oxide. A conductive layer made of a refractory metal material may be formed in contact with the mixed layer, and light may be extracted from below. Even in such a configuration, the reflectivity of the second electrode 102 can be improved, and at the same time, the contact resistance with the third layer 113 which is an electroluminescent layer can be improved.

(Embodiment 5)
In this embodiment, a cross-sectional structure of a pixel in the case where a transistor having an amorphous semiconductor film (amorphous transistor) is used for each transistor will be described.

In the pixel structure described in this embodiment mode, a layer in contact with the reflective electrode in the electroluminescent layer or a mixed layer including a metal oxide can be used. If aluminum, silver, an aluminum alloy, or a silver alloy, which is a highly reflective material, is used for the reflective electrode, the surface thereof is oxidized, and the contact resistance with the mixed layer increases. Thus, even in the light-emitting element in this embodiment, titanium nitride, titanium, tungsten, molybdenum, or the like, which is a refractory metal material, can be used for the upper layer of the reflective electrode in consideration of contact resistance.

Note that in this embodiment, the amorphous transistor includes an n-type semiconductor film. Such an n-type semiconductor film can improve the contact resistance between the source electrode and the drain electrode. Since the transistors 621R, 621G, and 621B having n-type are used, the structure in which the first electrode functions as a cathode and the second electrode functions as an anode is similar to that in Embodiment 4. Other configurations are the same as those of the third and fourth embodiments, and thus description thereof is omitted.

The pixel cross-sectional view in FIG. 13 illustrates a top emission type in which light emitted from each of the light emitting elements 623R, 623G, and 623B (hereinafter also collectively referred to as the light emitting element 623) is extracted from the second electrode 102 side. Similarly to FIG. 3, the light-emitting element 623 includes a stacked first electrode 101 (consisting of a first conductive layer 101 a and a second conductive layer 101 b) and a second electrode 102. Are provided with electroluminescent layers 625R, 625G, and 625B. The electroluminescent layers 625R, 625G, and 625B correspond to the first layer 111 to the third layer 113. The electroluminescent layers 625R, 625G, and 625B have different film thicknesses for each emission color. The first electrode 101 and the TFTs 621R, 621G, and 621B are electrically connected to each other.

Since this embodiment mode is a case of a top emission type, the stacked first electrode 101 has good contact resistance between the first conductive layer 101a made of a highly reflective material and the first layer 111. The second conductive layer 101b is made of any material. Embodiment 1 can be referred to for materials of the first conductive layer 101a and the second conductive layer 101b.

The material of the second electrode 102 is formed from a light-transmitting material. Embodiment 1 can be referred to for specific materials.

Note that the first electrode 101 functions as a cathode, and the second electrode 102 functions as an anode. Therefore, the first electrode 101 is preferably made of a material having a high work function, and the second electrode 102 is preferably made of a material having a low work function.

Thus, a top emission type light-emitting device that can extract light emitted from the light-emitting element 623 from the second electrode 102 side as shown by an arrow can be provided.

When such an amorphous transistor is used, the driver circuit is formed by the chip 630. Then, the chip 630 is electrically connected to the amorphous transistor using the connection wiring. Further, the chip 630 is electrically connected to an external circuit through another connection wiring 631.

When such an amorphous transistor is provided in the pixel portion, flatness is high and the number of stacked layers is smaller than that of a top-gate transistor, so that the display device can be thinned.

The present invention is characterized in that a conductive layer made of a refractory metal material is formed as the first electrode 101 in contact with a mixed layer containing a metal oxide. Note that the conductive layer provided in contact with the mixed layer having a metal oxide may be a material that does not oxidize or a material that exhibits conductivity even when oxidized by forming the mixed layer having the metal oxide. . According to the present invention, the reflectivity of the first electrode 101 can be improved, and at the same time, the contact resistance with the first layer 111 which is an electroluminescent layer can be improved. Note that the present invention is not limited to the pixel structure shown in FIG. 13 as long as the above effects can be obtained. For example, in the case where the second electrode 102 is a reflective electrode and a mixed layer including a metal oxide is used for the third layer 113 which is an electroluminescent layer, the second electrode 102 having a stacked structure includes a metal oxide. A conductive layer made of a refractory metal material may be formed in contact with the mixed layer, and light may be extracted from below. Even in such a configuration, the reflectivity of the second electrode 102 can be improved, and at the same time, the contact resistance with the third layer 113 which is an electroluminescent layer can be improved.

(Embodiment 6)
In this embodiment, a passive pixel structure is described with reference to FIGS.

FIG. 14 illustrates a pixel structure in which a light-emitting element 633 is provided over a substrate having an insulating surface (insulating substrate). Note that an insulating film functioning as a base film may be provided over the substrate. The light-emitting element 633 includes a stacked first electrode 101 (consisting of a first conductive layer 101 a and a second conductive layer 101 b) and a second electrode 102. The first electrode 101 and the second electrode 102 are provided so as to cross each other.

An electroluminescent layer 625 is provided between the first electrode 101 and the second electrode 102, that is, at the intersection between the first electrode 101 and the second electrode 102. The electroluminescent layer 625 corresponds to the first layer 111 to the third layer 113. For example, a mixed layer containing a metal oxide is used for the first layer 111.

Note that in the passive pixel, an adjacent electroluminescent layer is separated by an insulating film 628 functioning as a partition or a bank (in this embodiment, the first insulating film 628a and the second insulating film 628b). Can do. A first insulating film 628 a and a second insulating film 628 b are formed over the first electrode 101. After processing into a predetermined shape, that is, after patterning, the second insulating film 628b has a shape that becomes thinner downward. That is, the side surface of the second insulating film 628b has a so-called reverse taper shape that is inclined at a certain angle. As a result, even when the electroluminescent layer 625 is formed over the entire surface, the electroluminescent layer 625 can be divided by the insulating film 628, and adjacent electroluminescent layers can be separated.

In addition, a transistor 635 functioning as a switching element is connected to the first electrode 101. In this embodiment, a thin film transistor having an amorphous semiconductor film formed over the same substrate is used as the transistor, but the present invention is not limited to this, and the thin film transistor having a crystalline semiconductor film or single crystal silicon is used. An IC chip may be used.

In such a passive pixel structure, the present invention in which a conductive layer made of a refractory metal material is formed on the first electrode 101 in contact with the mixed layer containing a metal oxide is also applied to the passive pixel structure. Can be applied. Note that the present invention is not limited to the pixel structure shown in FIG. 14 as long as the above effects can be obtained. For example, in the case where the second electrode 102 is a reflective electrode and a mixed layer including a metal oxide is used for the third layer 113, the second electrode 102 having a stacked structure is in contact with the mixed layer including a metal oxide. Then, a conductive layer made of a refractory metal material is formed. As a result, the reflectivity of the second electrode 102 can be improved, and at the same time, the contact resistance with the third layer 113 can be improved.

(Embodiment 7)
In this embodiment, an equivalent circuit diagram of a pixel including a light-emitting element will be described with reference to FIGS.

FIG. 5A illustrates an example of an equivalent circuit diagram of a pixel. A signal line 6114, a power supply line 6115, a scanning line 6116, and a light-emitting element 6113, transistors 6110 and 6111, and a capacitor element at an intersection thereof. 6112. A video signal is input to the signal line 6114 from the signal line driver circuit. The transistor 6110 is controlled to be turned on / off in accordance with a selection signal input to the scan line 6116 from the scan line driver circuit, and can control supply of current input to the transistor 6111. Such a transistor 6110 can be referred to as a switching transistor. When the transistor 6110 is turned on, charge is accumulated in the capacitor 6112. When the charge exceeds the gate-source potential of the transistor 6111, the transistor 6111 is turned on and current is supplied from the power supply line 6115. Then, current is supplied to the light emitting element 6113. In this manner, light emission of the light emitting element 6113 can be controlled. Such a transistor 6111 can be referred to as a driving transistor. Note that although the capacitor 6112 is illustrated in FIG. 5A, the capacitor 6112 is not necessarily provided when it can be covered by the gate capacitance of the transistor 6111 or another parasitic capacitance.

FIG. 5B is an equivalent circuit diagram of a pixel in which a transistor 6118 and a scan line 6119 are newly provided in the pixel shown in FIG. With the transistor 6118, the gate and the source of the transistor 6111 can be set to the same potential, so that a state where no current flows through the light-emitting element 6113 can be forcibly created. Specifically, the source electrode and the drain electrode of the transistor 6118 are connected to both ends of the capacitor element 6112 in order to discharge the charge accumulated in the capacitor element 6112. The scan line 6119 controls on / off of the transistor 6118. Such a transistor 6118 can be referred to as an erasing transistor.

With the transistor 6118, the length of the subframe period can be shorter than the period in which the video signal is input to all the pixels. Further, depending on the driving method, even in the pixel illustrated in FIG. 5A, a state in which no current flows forcibly through the light-emitting element 6113 can be created.

FIG. 5C is an equivalent circuit diagram of a pixel in which a transistor 6125 and a wiring 6126 are newly provided in the pixel illustrated in FIG. The potential of the gate of the transistor 6125 is fixed by the wiring 6126. The transistor 6111 and the transistor 6125 are connected in series between the power supply line 6115 and the light-emitting element 6113. Thus, in FIG. 5C, the value of the current supplied to the light-emitting element 6113 is controlled by the transistor 6125, and the presence or absence of current supply to the light-emitting element 6113 can be controlled by the transistor 6111.

FIG. 12 shows a pixel circuit provided with a diode 6128 in order to make the gate and source of the transistor 6111 have the same potential and forcibly prevent current from flowing through the light-emitting element 6113. The diode 6128 is connected to the gate electrode of the transistor 6111 and the scan line 6119. When the scan line 6119 is selected, the diode 6128 is turned on, the potential of the scan line 6119 and the gate potential of the transistor 6111 are the same, and the transistor 6111 is turned off. As a result, current from the power supply line 6115 is not supplied to the light emitting element 6113. In this embodiment, an n-type diode and a p-type transistor are used so that the transistor 6111 is turned off when the diode 6128 is turned on, and a high signal is input to the scan line 6119.

In the pixel structure of this embodiment mode, when the light-emitting element 6113 is kept in a light-emitting state, a Low signal is input to the scan line 6119. Then, the diode 6128 is turned off, so that the gate potential of the transistor 6111 can be maintained.

Note that although the diode 6128 uses a diode-connected transistor (a form in which a gate and a drain are connected because it is an n-type transistor), any element having a rectifying property may be used. For example, a PN diode, a PIN diode, a Schottky diode, or a Zener diode may be used.

Note that the pixel circuit of the present invention is not limited to the structure shown in this embodiment mode. This embodiment can be freely combined with the above embodiment.

(Embodiment 8)
As an electronic device including the light-emitting device of the present invention, a television device (also simply referred to as a television or a television receiver), a camera such as a digital camera or a digital video camera, or a mobile phone device (also simply referred to as a mobile phone or a mobile phone). ), Portable information terminals such as PDAs, portable game machines, computer monitors, computers, sound reproduction apparatuses such as car audio, and image reproduction apparatuses equipped with recording media such as home game machines. A specific example will be described with reference to FIG.

A portable information terminal device illustrated in FIG. 6A includes a main body 9201, a display portion 9202, and the like. The light emitting device of the present invention can be applied to the display portion 9202. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Accordingly, it is possible to provide a portable information terminal device in which the drive voltage is suppressed.

A digital video camera shown in FIG. 6B includes a display portion 9701, a display portion 9702, and the like. The light emitting device of the present invention can be applied to the display portion 9701. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Thus, a digital video camera with a reduced driving voltage can be provided.

A cellular phone shown in FIG. 6C includes a main body 9101, a display portion 9102, and the like. The light emitting device of the present invention can be applied to the display portion 9102. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Accordingly, it is possible to provide a mobile phone with a reduced driving voltage.

A portable television device illustrated in FIG. 6D includes a main body 9301, a display portion 9302, and the like. The light emitting device of the present invention can be applied to the display portion 9302. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Thus, a portable television device with a reduced driving voltage can be provided. In addition, the present invention can be applied to a wide variety of television devices, from a small one mounted on a portable terminal such as a cellular phone to a medium-sized one that can be carried and a large one (for example, 40 inches or more). The light emitting device can be applied.

A portable computer illustrated in FIG. 6E includes a main body 9401, a display portion 9402, and the like. The light emitting device of the present invention can be applied to the display portion 9402. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Accordingly, a portable computer with a reduced driving voltage can be provided.

A television set shown in FIG. 6F includes a main body 9501, a display portion 9502, and the like. The light emitting device of the present invention can be applied to the display portion 9502. As a result, the contact resistance becomes good and a sufficient current can flow. Further, the light extraction efficiency can be improved by controlling the film thickness. Accordingly, it is possible to provide a television device in which the driving voltage is suppressed.

In this way, an electronic device in which the driving voltage is suppressed by the light emitting device of the present invention in which the contact resistance is good and a sufficient current can flow and the light extraction efficiency is improved by controlling the film thickness. Can be provided.

In this embodiment, a simulation for confirming that the use of a reflective electrode in which aluminum and titanium nitride are laminated in a light-emitting element improves contact resistance with a mixed layer containing a metal oxide and can increase light emission luminance. Results are shown. In this simulation, molybdenum oxide was used as the metal oxide.

FIG. 7 shows the structure of the light emitting element used in the simulation. The light-emitting element includes a reflective electrode (50 nm) as the first electrode 101, a mixed layer having molybdenum oxide as the first layer 111 (arbitrary film thickness different for each emission color), and each emission color as the second layer 112. The third layer 113 has a stack of Alq ₃ (20 nm), and the second electrode 102 has a stack of BzOs: Li (20 nm) and silver (15 nm). The light emitting layer contains tBuDNA and Alq _3. Further, since the silver film used for the second electrode 102 is very thin, it has a light-transmitting property and becomes a top emission type light-emitting element.

When a voltage of 6 V is applied to such a light emitting element (element region 2 × 2 mm), the current value is 0.375 (mA / cm ² ) when aluminum is used for the reflective electrode, and a refractory metal material In the case of using titanium nitride which is, it was 7.825 (mA / cm ² ). This shows that aluminum has a high contact resistance with the mixed layer containing molybdenum oxide, and a sufficient current cannot flow. On the other hand, titanium nitride has a low contact resistance with the mixed layer containing molybdenum oxide, indicating that a sufficient current can flow. Therefore, it can be seen that it is preferable to use titanium nitride, which is a refractory metal material, for the reflective electrode of the layer in contact with the mixed layer containing molybdenum oxide.

In addition, since the light-emitting element has a structure in which a light source is provided, if a translucent film such as aluminum, silver, an aluminum alloy, or a silver alloy that is formed thin enough to have translucency is used as a transparent electrode, strong interference is caused. As a result, the light extraction efficiency can be improved.
In this way, in order to increase the light extraction efficiency by applying light interference by silver or the like, the distance between the light emitting region and the reflective electrode may be varied depending on each light emitting color.

FIG. 8A shows the light extraction efficiency η _opt when aluminum is used as the reflective electrode with respect to the viewing angle. The light extraction efficiency is a value standardized with light from a light source having no interference as 1.
In FIG. 8A, a red light emitting element is shown as its emission wavelength of 630 nm, a green light emitting element is shown as its emission wavelength of 530 nm, and a blue light emitting element is shown as its emission wavelength of 450 nm. The film thickness of the mixed layer containing molybdenum oxide is 238 nm, 178 nm, and 126 nm in order from the light-emitting element exhibiting red, green, and blue. The light extraction efficiency η _opt can be improved by varying the film thickness of the mixed layer containing molybdenum oxide for each color.

FIG. 8B shows a simulation result of the light extraction efficiency η _opt when titanium nitride is used as the reflective electrode with respect to the viewing angle. The film thickness of the mixed layer containing molybdenum oxide is 226 nm, 172 nm, and 126 nm in order from the light emitting element exhibiting red, green, and blue. The light extraction efficiency η _opt can be improved by varying the film thickness of the mixed layer containing molybdenum oxide for each color.

8A and 8B, the light extraction efficiency when titanium nitride, which is a refractory metal material, is used as a reflective electrode at all viewing angles is greater than the light extraction efficiency when aluminum is used as a reflective electrode. It turns out that it is low.

From the above, it can be seen that when titanium nitride is used, the contact resistance with the mixed layer containing molybdenum oxide is improved and a sufficient current can flow, but the light extraction efficiency is low because of the low reflectance. .

Incidentally, the luminance I _{ext of the} light emitting element is expressed by the following equation.
I _ext (cd / cm ² ) = η _ext (cd / A) × J (current density: mA / cm ² )
η _ext indicates that if the configuration of the light emitting element is constant, it is proportional to the light extraction efficiency. Therefore, if the light extraction efficiency is η _opt , I _ext ∝η _opt (cd / A) × J
It becomes.

Therefore, the relative luminance when aluminum and titanium nitride are used for the reflecting electrode can be obtained from the current value when a voltage of 6 V is applied and the simulation result of FIG. FIGS. 9A and 9B show the relative luminance when 6 V is applied in the case where aluminum and titanium nitride are each used as a reflective electrode. FIG. 9A shows the luminance when aluminum is used as the reflective electrode with respect to the viewing angle, and FIG. 9B shows the luminance when titanium nitride is used as the reflective electrode with respect to the viewing angle. 9A and 9B, the mixed layer having molybdenum oxide is made different for each light emitting element exhibiting each emission color so as to have the same film thickness as that in FIG.

9 (A) and 9 (B), it can be seen that the luminance I _ext when titanium nitride, which is a refractory metal material, is used as a reflective electrode is higher than the luminance when aluminum is used as a reflective electrode at all viewing angles. .

Therefore, in the present invention, a reflective electrode in which titanium nitride having a film thickness of 1 to 20 nm is provided on aluminum provides good contact resistance with a mixed layer containing molybdenum oxide, and at the same time, reflection of light to the reflective electrode. The light emitting element with high brightness was realized by suppressing the decrease of the rate, that is, maximizing the reflectance.

Below, the experimental result which shows the effect using the reflective electrode of this invention is shown.

In the light-emitting element shown in FIG. 7, the current value when 6 V was applied to a 2 × 2 mm light-emitting element using a reflective electrode in which titanium nitride was formed to 10 nm on aluminum was 8.05 (mA / cm ² ). That is, it can be seen that when a reflective electrode in which titanium nitride is formed to 10 nm on aluminum is used, contact resistance with a mixed layer having molybdenum oxide equivalent to titanium nitride can be obtained. This current value is larger than the value obtained when the titanium nitride single layer is used for the reflective electrode, and it is preferable to use a laminate of aluminum and titanium nitride for the reflective electrode rather than the titanium nitride single layer.

FIG. 10 shows a simulation result for obtaining the light extraction efficiency when a reflective electrode in which 5 nm of titanium nitride is formed on aluminum is used. Compared with the case of aluminum shown in FIG. 8A, the light extraction efficiency is lowered. However, it can be seen that the light extraction efficiency is significantly improved as compared with the titanium nitride single layer shown in FIG.

Using this result and the current value when 6 V is applied as 8.05 (mA / cm ² ), the luminance I when relative to 6 V when used as a reflective electrode in which 5 nm of titanium nitride is deposited on aluminum is used. _ext can be calculated. The result is as shown in FIG. 11, and it can be seen that a significant increase in luminance can be expected as compared with the aluminum and titanium nitride single layer.

As described above, the present invention in which a thin titanium nitride of about 1 to 20 nm is provided on aluminum can obtain a good contact resistance with molybdenum oxide, and at the same time, suppress a decrease in the reflectance of light with respect to the reflective electrode, thereby improving the luminance. A light-emitting element with high brightness could be realized.

It is the figure which showed the light emitting element of this invention. It is the figure which showed the light emitting element of this invention. It is sectional drawing which showed the pixel which has a light emitting element of this invention. It is sectional drawing which showed the pixel which has a light emitting element of this invention. It is a figure showing a pixel circuit having a light emitting element of the present invention. It is a figure showing an electronic device having a light emitting element of the present invention It is the figure which showed the light emitting element of this invention used for simulation It is a graph which shows a simulation result It is a graph which shows a simulation result It is a graph which shows a simulation result It is a graph which shows a simulation result It is a figure showing a pixel circuit having a light emitting element of the present invention. It is sectional drawing which showed the pixel which has a light emitting element of this invention. It is sectional drawing which showed the pixel which has a light emitting element of this invention.

Claims (11)

A first electrode having a laminated structure;
An electroluminescent layer provided on the first electrode;
A second electrode provided on the electroluminescent layer,
The electroluminescent layer includes a mixed layer having a metal oxide on the side in contact with the first electrode,
The light emitting device, wherein the first electrode includes a refractory metal material on a side in contact with the mixed layer including the metal oxide. A first electrode having a laminated structure;
An electroluminescent layer provided on the first electrode;
A second electrode provided on the electroluminescent layer, which is a reflective material and is thinned so as to have translucency,
The electroluminescent layer includes a mixed layer having a metal oxide on the side in contact with the first electrode,
The first electrode has a refractory metal material on a side in contact with the mixed layer having the metal oxide,
The light emitting device, wherein the second electrode has a film thickness that transmits light emitted from the electroluminescent layer. A first electrode having a laminated structure;
An electroluminescent layer provided on the first electrode;
A second electrode provided on the electroluminescent layer; and a light emitting element exhibiting red, green, and blue, respectively.
The electroluminescent layer includes a mixed layer having a metal oxide on the side in contact with the first electrode,
The first electrode has a refractory metal material on a side in contact with the mixed layer having the metal oxide,
In the light-emitting element exhibiting red, green, and blue, the first electrode has the same film thickness, and the mixed layers having the metal oxide have different film thicknesses. . A semiconductor film formed on an insulating substrate;
An electrode connected to the impurity region in the semiconductor film;
A first electrode having a laminated structure connected to the electrode;
An electroluminescent layer provided on the first electrode;
A second electrode provided on the electroluminescent layer,
The electroluminescent layer includes a mixed layer having a metal oxide on the side in contact with the first electrode,
The light emitting device, wherein the first electrode includes a refractory metal material on a side in contact with the mixed layer including the metal oxide. In claim 4,
The light-emitting device, wherein the impurity region is a p-type impurity region. In any one of Claims 1 thru | or 5,
The metal oxide includes vanadium oxide, molybdenum oxide, niobium oxide, rhenium oxide, tungsten oxide, ruthenium oxide, titanium oxide, chromium oxide, zirconium oxide, hafnium oxide, and tantalum oxide. A light-emitting device characterized by being any one of the above. In any one of Claims 1 thru | or 6,
A light-emitting device, wherein light from the electroluminescent layer is emitted from the second electrode. In any one of Claims 1 thru | or 7,
The first electrode has a laminated structure of the refractory metal material and a reflective material. In any one of Claims 1 thru | or 8,
A light-emitting device using titanium nitride as the refractory metal material. In any one of Claims 1 thru | or 8,
A light-emitting device using titanium, tungsten, molybdenum, or a compound including these as the refractory metal material. In any one of Claims 8 thru | or 10,
The light-emitting device, wherein the reflective material is aluminum, silver, an alloy containing aluminum, or an alloy containing silver.

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