JP5255748B2 - LIGHT EMITTING ELEMENT AND LIGHT EMITTING DEVICE - Google Patents

Description

  The present invention relates to a light-emitting element that emits light by passing a thin film containing a light-emitting substance between electrodes, a display device using the light-emitting element, and an electronic device using the light-emitting element.

  Development of a display using a self-luminous thin-film light-emitting element that emits light when an electric current flows is being actively promoted.

  These thin-film light-emitting elements emit light when an electrode is connected to a single-layer or multi-layer thin film formed using organic, inorganic, or both, and an electric current is applied. Such thin-film light emitting devices are expected to have low power consumption, space saving, visibility, and the like, and further expansion of the market is expected in the future.

  Among these, a light-emitting element having a multilayer structure can create an element that emits light more efficiently than before by dividing the function of each layer (see, for example, Non-Patent Document 1). .

A thin-film light-emitting element having a multilayer structure sandwiches a light-emitting laminate composed of a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and the like between an anode and a cathode. Yes. Among these, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer may include layers that are not used depending on the element structure.
C. W. Tan et al., Applied Physics Letters, Vol. 51, no. 12, 913-915 (1987)

  In the light emitting laminate as described above, the hole injection layer is made of a material that is relatively easy to inject holes from a metal electrode to a layer mainly composed of an organic substance, and the electron transport layer is made of a material having excellent electron transport properties. It is formed by selecting.

  However, there are very few materials whose main component is an organic material that can inject electrons from an electrode relatively easily, or materials whose main component is an organic material that can transport electrons with a certain degree of mobility. It has been. Further, as can be seen from the fact that the material is very limited, the injection of electrons from the electrode into the layer mainly composed of an organic substance hardly occurs. For this reason, the drive voltage has become high. Furthermore, an element with a high drive voltage tends to have a large increase in drive voltage over time according to experiments.

  Therefore, an object of the present invention is to provide a light-emitting element having a structure capable of relatively reducing a driving voltage. It is another object of the present invention to provide a light-emitting element having a structure with a small increase in drive voltage with time.

  It is another object of the present invention to provide a display device that can withstand long-term use with a small driving voltage and a small increase in driving voltage over time.

Another object is to improve the reliability of the light-emitting element.

  In the present invention, the layer in contact with the electrodes (first electrode, second electrode) in the light-emitting element is a layer that generates holes, such as a layer containing a P-type semiconductor or an organic compound layer containing an electron-accepting substance, and emits light. The layer is configured to be sandwiched between layers that generate holes, and a layer that generates electrons is formed between the hole-generating layer and the light-emitting layer on the second electrode side. As a result, the drive voltage can be suppressed. In addition, since the drive voltage is lowered, it is possible to suppress an increase in the drive voltage with time.

A light-emitting element that is one structure of the present invention includes a first electrode and a second electrode;
A first layer and a second layer comprising an organic material and an inorganic material;
A third layer containing a luminescent material;
A fourth layer for generating electrons,
The first layer is in contact with the first electrode, the second layer is in contact with the second electrode, and the third layer is interposed between the first electrode and the second electrode via the first layer and the second layer. And a fourth layer is provided between the third layer and the second layer.

  A light-emitting element having another structure includes a first electrode and a second electrode, a first layer and a second layer that generate holes, a third layer containing a light-emitting substance, an electron The first layer is in contact with the first electrode, the second layer is in contact with the second electrode, and the first layer is between the first electrode and the second electrode. A third layer is interposed between the third layer and the second layer, and a fourth layer is provided between the third layer and the second layer.

  A light-emitting element having another structure according to the present invention includes a first electrode and a second electrode, a first layer and a second layer containing a P-type semiconductor, a third layer containing a light-emitting substance, and an N-type. A first layer in contact with the first electrode, a second layer in contact with the second electrode, and a second layer between the first electrode and the second electrode. The third layer is sandwiched between the first layer and the second layer, and the fourth layer is provided between the third layer and the second layer.

  A light-emitting element having another structure according to the present invention includes a first electrode, a second electrode, a first layer including a first organic compound, and a first layer containing a substance exhibiting an electron accepting property with respect to the first organic compound. 2 layer, a third layer containing a light-emitting substance, and a fourth layer containing a second organic compound and a substance showing an electron donating property to the second organic compound. Is in contact with the first electrode, the second layer is in contact with the second electrode, and the third layer is sandwiched between the first electrode and the second electrode via the first layer and the second layer. In addition, a fourth layer is provided between the third layer and the second layer.

  In the above structure, the light-emitting element of the present invention has a molar ratio of a substance exhibiting electron acceptability to the first organic compound in the second layer and electron acceptability to the first organic compound in the first layer. The difference from the molar ratio of the substance is within 80% of the molar ratio of the substance exhibiting electron acceptability with respect to the first organic compound in the second layer and the electron acceptability with respect to the first organic compound in the first layer. Within 80% of the molar ratio of the substance to be exhibited, preferably within 40% of the molar ratio of the substance exhibiting electron acceptability to the first organic compound in the second layer, and to the electron with respect to the first organic compound in the first layer It should be within 40% of the molar ratio of the substance showing acceptability.

  In the light-emitting element of the present invention, the thickness of the first layer and the second layer is 30 nm to 1 μm in the above structure.

  In the above structure of the light-emitting element of the present invention, the thickness of the second layer is 50% to 150% of the thickness of the first layer, and the thickness of the first layer is the second layer. Within 50% to 150% of the film thickness.

  In the light emitting element to which the structure of the present invention is applied, the driving voltage can be lowered. Further, since the drive voltage is lowered, the rise in drive voltage with time can be suppressed to a low level.

  In addition, it is possible to provide a display device that can withstand long-term use in which the drive voltage and the increase in drive voltage with time are small.

In addition, stress on the light emitting layer can be relaxed. Therefore, the reliability of the light emitting element can be improved.

  Hereinafter, embodiments of the present invention will be described 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.

(Embodiment 1)
In this embodiment mode, a structure of a light-emitting element of the present invention will be described with reference to FIGS. In the light-emitting element of the present invention, a light-emitting layer 104 containing a light-emitting material and an electron-generating layer 105 are stacked, and the light-emitting layer 104 and the electron-generating layer 105 are combined with a first hole-generating layer 102 and a first hole 102. It is sandwiched between two holes 103 that generate holes. The first hole generating layer 102 is in contact with the first electrode, the second hole generating layer 103 is in contact with the second electrode, and the first hole generating layer 102 and the second hole The hole generating layer 103 is sandwiched between the first electrode 101 and the second electrode 106 and stacked on the insulator 100 such as a substrate or an insulating film. The first electrode 101, the first hole generating layer 102, the light emitting layer 104, the electron generating layer 105, and the second hole are sequentially stacked on the insulator 100 such as a substrate and an insulating film. Or the second electrode 106 in that order (FIG. 1), or the second electrode 106, the second hole generating layer 103, the electron generating layer 105, the light emitting layer 104, The layer 102 for generating one hole and the first electrode 101 are in this order (FIG. 2). Note that in this embodiment mode, when a voltage is applied so that the light emitting element emits light, the electrode having a higher potential is set as the first electrode, and the electrode having a lower potential is set as the second electrode. Let it be an electrode.

  The first hole-generating layer 102 and the second hole-generating layer 103 are formed using a hole-transporting material and an electron-accepting material that can receive electrons from the hole-transporting material. A layer including both, a layer of a P-type semiconductor, or a layer including a P-type semiconductor is formed using the same material. The thickness of the first hole generating layer 102 and the second hole generating layer 103 is preferably 30 nm to 1 μm. In addition, it is preferable that the thicknesses of the first hole generating layer 102 and the second hole generating layer 103 are approximately equal, and the second hole generating layer has a thickness of the first positive hole. It should not be thicker or thinner than 50% of the thickness of the layer that generates the holes. In addition, the thickness of the layer that generates the first holes is set to be 50% or more thicker than that of the layer that generates the second holes, or is not thin. That is, the thickness of the layer that generates the second hole is within 50% to 150% of the thickness of the layer that generates the first hole, and the thickness of the layer that generates the first hole. Is within 50% to 150% of the thickness of the layer generating the second hole. That is, assuming that the thickness of the first hole generating layer is X and the thickness of the second hole generating layer is Y, 0.5 ≦ (Y / X) ≦ 1.5 and 0 .5 ≦ (X / Y) ≦ 1.5.

The first hole-generating layer 102 and the second hole-generating layer 103 each have an electron-accepting property capable of receiving electrons from the hole-transporting material and the hole-transporting material. The material is preferably formed of the same material, and the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer and the first hole are generated. The difference between the molar ratio of the electron-accepting material to the hole-transporting material in the generating layer is the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer. It may be within 80% and within 80% of the molar ratio of the electron-accepting material to the hole-transporting material in the first hole generating layer. More preferably, the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer and the hole-transporting material in the first hole-generating layer The difference from the molar ratio of the electron-accepting material is within 40% of the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer, and The molar ratio of the electron-accepting material to the hole-transporting material in the hole generating layer is preferably within 40%.

That is, the molar ratio of the electron-accepting material to the hole-transporting material in the first hole-generating layer is A, and the hole-transporting material in the second hole-generating layer is When the molar ratio of the electron-accepting material is B, (−0.8 × A) ≦ B−A ≦ (0.8 × A) and (−0.8 × B) ≦ B−A ≦ (0. 8 × B).

Examples of the hole transporting material include 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD) and 4,4′-bis [N -(3-Methylphenyl) -N-phenyl-amino] -biphenyl (abbreviation: TPD) or 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviation: TDATA) 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenyl-amino] -triphenylamine (abbreviation: MTDATA) and 4,4′-bis (N- (4- ( N, N-di-m-tolylamino) phenyl) -N-phenylamino) biphenyl (abbreviation: DNTPD) and other aromatic amine-based compounds (that is, having a benzene ring-nitrogen bond) and phthalocyanines (abbreviation: H ₂ Pc), copper Futaroshia Emissions (abbreviation: CuPc), or vanadyl phthalocyanine (abbreviation: VOPc), and the phthalocyanine compound and the like can be used. Examples of the electron-accepting material that can receive electrons from these hole-transporting materials include molybdenum oxide, vanadium oxide, 7,7,8,8, -tetracyanoquinodimethane (abbreviation). : TCNQ), 2,3-dicyanonaphthoquinone (abbreviation: DCNNQ), 2,3,5,6-tetrafluoro-7,7,8,8, -tetracyanoquinodimethane (abbreviation: F4-TCNQ), etc. As an example, an electron-accepting material capable of accepting electrons is selected in combination with a hole-transporting material. As the P-type semiconductor, metal oxides such as molybdenum oxide, vanadium oxide, ruthenium oxide, cobalt oxide, nickel oxide, and copper oxide can be used.

Further, instead of the first hole generating layer 102 and the second hole generating layer 103, an organic compound such as the hole transporting material described above, zinc oxide, indium oxide Inorganic materials such as oxides, tin oxides, antimony oxides, tungsten oxides, indium nitrides, tin nitrides, antimony nitrides or tungsten nitrides, molybdenum nitrides, or two or more inorganic materials selected therefrom You may use the 1st layer and 2nd layer which were formed with the layer containing these. And it is preferable that the thickness of a 1st layer and a 2nd layer is 30 nm-1 micrometer. Further, it is preferable that the thicknesses of the first layer and the second layer are substantially equal, so that the thickness of the second layer is not more than 50% thicker or thinner than the thickness of the first layer. Further, the thickness of the first layer should be 50% or more thicker than the thickness of the second layer. That is, the thickness of the second layer is within 50% to 150% of the thickness of the first layer, and the thickness of the first layer is within 50% to 150% of the thickness of the second layer. And In addition, the first layer and the second layer are preferably formed of a layer containing the same hole transporting material and the same inorganic material, and exhibit an electron accepting property for the first organic compound in the second layer. The difference between the molar ratio of the substance and the molar ratio of the substance exhibiting electron acceptability to the first organic compound in the first layer is the mole of the substance exhibiting electron acceptability to the first organic compound in the second layer. The ratio is within 80% of the ratio and within 80% of the molar ratio of the substance showing the electron accepting property with respect to the first organic compound in the first layer. More preferably, the molar ratio of the substance exhibiting electron acceptability with respect to the first organic compound in the second layer and the molar ratio of the substance exhibiting electron acceptability with respect to the first organic compound in the first layer. The difference is within 40% of the molar ratio of the substance exhibiting electron accepting property to the first organic compound in the second layer and the molar ratio of the substance exhibiting electron accepting property to the first organic compound in the first layer. Keep it within 40%.

The electron generating layer 105 includes a layer including both an electron transporting material and an electron donating material capable of donating electrons to the electron transporting material, an N-type semiconductor layer, or an N-type semiconductor. Form with layers. Examples of the electron transporting material include tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), and bis (10-hydroxybenzo [h ] -Quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), etc. Can be used. In addition, bis [2- (2-hydroxyphenyl) benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ) and other materials such as metal complexes having an oxazole-based or thiazole-based ligand can also be used. In addition to 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-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- ( 4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2, 4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), and the like can be used. Examples of the electron donating material that can give electrons to these electron transporting materials 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. An electron donating material that can donate electrons is selected depending on the combination with an electron transporting material. In addition, a metal compound such as a metal oxide can be used as the N-type semiconductor, and zinc oxide, zinc sulfide, zinc selenide, titanium oxide, or the like can be used.

The light emitting layer 104 containing a light emitting material is roughly classified into two types. One is a layer containing a light emitting material as a light emission center dispersed in a layer made of a material having an energy gap larger than that of the light emitting substance, and the other is a layer that constitutes the light emitting layer with only the light emitting material. However, the former is a preferable configuration because concentration quenching hardly occurs. As a light-emitting substance serving as a luminescent center, 4-dicyanomethylene-2-methyl-6- (1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (abbreviation: DCJT), 4 -Dicyanomethylene-2-t-butyl-6- (1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran, perifrantene, 2,5-dicyano-1,4-bis ( 10-methoxy-1,1,7,7-tetramethyljulolidyl-9-enyl) benzene, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq _3), 9,9'-bianthryl, 9,10-diphenyl anthracene (abbreviation: DPA) and 9,10-bis (2-naphthyl) anthracene (abbreviation: DN ), 2,5,8,11-tetra -t- butyl perylene (abbreviation: TBP), and the like. As a base material for forming a layer in which the light emitting material is dispersed, an anthracene such as 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-BuDNA) is used. Derivatives, carbazole derivatives such as 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP), 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) pyridinato] zinc (abbreviation: Znpp ₂ ), bis [2- (2-hydro A metal complex such as xylphenyl) benzoxazolate] zinc (abbreviation: ZnBOX) can be used. As a material that can form the light-emitting layer 104 using only a light-emitting substance, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), And bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq).

  Further, the light-emitting layer 104 may be formed as a single layer or a plurality of layers, and the light-emitting layer 104 is formed between the layer in which the light-emitting material is dispersed in the light-emitting layer 104 and the layer 102 that generates first holes. An electron transport layer may be provided between the hole transport layer and the layer in which the light emitting material is dispersed in the light emitting layer 104 and the layer 105 that generates electrons. These layers may or may not be provided, and only one of them may be provided. The materials of the hole transport layer and the electron transport layer are the same as those of the hole transport layer in the hole generating layer and the electron transport layer in the electron generating layer. Is omitted. See each description.

The first electrode 101 is preferably formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a high work function (work function of 4.0 eV or more). Specific examples of the first electrode material include ITO (indium tin oxide), ITO containing silicon, and IZO (indium zinc oxide) in which indium oxide is mixed with 2 to 20% zinc oxide (ZnO). 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 metal material (TiN), or the like can be used. On the other hand, as the second electrode material used for forming the second electrode 106, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (work function of 3.8 eV or less) is used. preferable. Specific examples of the second electrode material include elements belonging to Group 1 or Group 2 of the element periodic rule, that is, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, and these In addition to alloys containing Mg (Mg: Ag, Al: Li) and compounds (LiF, CsF, CaF ₂ ), transition metals including rare earth metals can be used, but metals such as Al, Ag, and ITO ( It can also be formed by lamination with an alloy.

  The light-emitting element includes a first electrode 101, a layer 102 that generates first holes, a light-emitting layer 104, a layer 105 that generates electrons, a layer 103 that generates second holes, and a second electrode 106. In addition, a layer 107 (FIGS. 3 and 4) that generates third holes may be provided between the layer 102 that generates first holes and the light-emitting layer 104. At this time, the third hole generating layer 107 is formed of a material different from that of the first hole generating layer 102 and generates the first hole generating layer 102 and the second hole. The layer 103 to be formed is preferably formed using the same material. In addition, the thickness of the layer 103 that generates the second holes is set to be 50% or more thicker or thinner than the thickness of the layer 102 that generates the first holes. In addition, the thickness of the layer 102 that generates the first holes is set to be 50% or more thicker than that of the layer 103 that generates the second holes. That is, it is preferable that the thicknesses of the first hole generating layer 102 and the second hole generating layer 103 be approximately the same.

  In addition, regarding the material illustrated above, it is only an illustration to the last, and a practitioner can select suitably in the range which can maintain the effect of this invention.

  When a voltage is applied to the light-emitting element of the present invention having the above structure, holes are injected into the second electrode from the layer 103 that generates the second holes. Further, electrons are injected into the light emitting layer 104 from the layer 105 that generates electrons. Further, holes are injected into the light-emitting layer 104 from the first hole-generating layer 102, and the electrons and holes injected in the light-emitting layer are recombined, so that the excited light-emitting material returns to the ground state. Light emission is obtained. Here, in the light-emitting element of the present invention, there is no injection of electrons from the electrode to the layer containing organic material as the main component, and the injection of electrons is performed from the layer containing organic material as the main component to the other organic material layer. Is called. Electron injection from the electrode into the organic-based layer is unlikely to occur, and in conventional light-emitting devices, the drive voltage has increased during the injection of electrons from the electrode into the organic-based layer. Since the light-emitting element of the present invention does not have this process, it can be a light-emitting element with low driving voltage. In addition, since it is known from experiments that a light emitting element with a high driving voltage has a large increase in the driving voltage with time, the light emitting element of the present invention with a low driving voltage may be a light emitting element with a low driving voltage with time. It becomes possible.

In addition, since the light emitting element of the present invention is sandwiched between electrodes on both sides of the light emitting layer 104 through layers where the stress between the light emitting layer 104 and the electrode is about the same, the stress on the light emitting layer 104 can be relieved. Can do. And the reliability of a light emitting element can be improved.

In particular, it has a layer for generating holes on the electrode, further has a light emitting layer on it, further has a layer for generating holes on it, and further has an electrode on it, so that it is in contact with the electrode If the light emitting element has a structure in which a hole is generated and a light emitting layer is sandwiched between electrodes through the hole generating layer, the stress on both sides of the light emitting layer is offset and the reliability of the light emitting element is further improved. Will improve. Note that the hole generating layer is a layer containing an organic material and a metal oxide. For example, a layer containing a hole transporting material and molybdenum oxide, zinc oxide, or indium oxide described above, A layer containing a hole transporting material and two or more metal oxides selected from molybdenum oxide, zinc oxide and indium oxide is preferable. Note that another layer may be interposed between the hole-generating layer and the light-emitting layer.

(Embodiment 2)
Another embodiment of the present invention will be described. In this embodiment, an example in which the viewing angle characteristics of the light-emitting element and the display device are improved by appropriately adjusting the film thicknesses of the first hole generating layer 102 and the second hole generating layer 103 is described. explain. In this embodiment mode, the stacked structure and materials of the light-emitting element are the same as those in Embodiment Mode 1, and thus description thereof is omitted. Refer to Embodiment Mode 1. Note that also in this embodiment mode, when a voltage is applied so as to cause the light-emitting element to emit light, the electrode having a higher potential is set as the first electrode, and the electrode having a lower potential is set as the second electrode. Electrode.

  Light emitted from the light emitting element includes light emitted from the light emitting layer 104 and directly emitted, and light emitted after being reflected once or plural times. The directly emitted light and reflected and emitted light interfere with each other depending on the phase relationship, and the light emitted from the light emitting element is light synthesized as a result of the interference.

  Since the phase of light reflected when entering a large medium from a medium having a small refractive index is reversed, the first electrode 101, the second electrode 106, or the like in the light-emitting element having the structure described in Embodiment Mode 1 is used. Reflection at the interface between the electrode and the layer in contact with the electrode reverses the phase of the reflected light. When the light reflected by the electrode interferes with the light emitted from the light emitting layer, the optical distance (refractive index × physical distance) between the light emitting layer and the electrode is (2m−1) λ / 4 (m Is a natural number of 1 or more, and λ is the center wavelength of light emitted from the light emitting layer), the change in spectral shape that occurs depending on the angle at which the light emission surface is viewed can be reduced, and the current efficiency of the light emitting element Will also improve. The current efficiency represents how much luminance is obtained with respect to the flowed current, and the specified luminance can be obtained even with a small current as the efficiency is improved. Moreover, there is a tendency that the deterioration of the element is small.

  Since reflection is small between films with a small difference in refractive index, it can be ignored except for reflection that occurs at the interface between the electrode and the film in contact with the electrode, so in this embodiment, only reflection that occurs between the electrode and the film in contact with the electrode is considered. Focus on it.

  In the case of a light-emitting element that extracts light emission from the first electrode 101 side, reflection occurs at the second electrode 106. Therefore, in order to improve the current efficiency of the light emitting element and reduce the change in the spectral shape that occurs depending on the angle at which the light emission surface is viewed, the optical distance from the position where light emission occurs to the surface of the second electrode 106 The distance (refractive index × physical distance) may be (2m−1) λ / 4 (m is a natural number of 1 or more, and λ is the center wavelength of light emitted from the light emitting layer).

  The light-emitting layer 104 may be formed as a single layer including a light-emitting material, but may have a plurality of structures including a layer including an electron-transport layer and a hole-transport layer and a layer including a light-emitting material. The layer containing the light emitting material may be a layer in which the light emitting material serving as the light emission center is dispersed, or may be a layer formed only of the light emitting material.

A plurality of layers made of different materials are provided from the position where the light emission occurs to the second electrode 106. In this embodiment mode, the layer 105 generates electrons and the layer 103 generates second holes. In addition, a layer containing a light-emitting material can also be said to be a layer located between the position where light is emitted and the second electrode 106, with half the film thickness. Further, when the light emitting layer is formed of a plurality of layers, different layers may be included. In such a configuration, the optical distance from the position where light emission occurs to the second electrode 106 can be obtained by summing the product of the refractive index of each film and the film thickness. -1) λ / 4 (m is a natural number of 1 or more, and λ is the center wavelength of light emitted from the light emitting layer). That is, the layer containing the luminescent material is the layer between the second electrode 106 and the layer containing the luminescent material, where 1 is the layer containing the luminescent material and j is the second electrode 106 (j is an integer of 4 or more). When the refractive index n and the film thickness d are set to the refractive index and film thickness of the layer numbered with the same number (that is, n ₁ , the refractive index of the layer containing the light emitting material) , D _j is the thickness of the second electrode), and the following equation (1) is satisfied.

  Here, it is necessary to adjust the film thickness in order to satisfy the above formula (1). A layer containing an organic substance as a main component has a low electron mobility, and the driving voltage increases when the thickness of the layer 105 that generates electrons including an electron transporting material whose carriers are electrons is increased. Therefore, in this embodiment mode, the thickness of the layer 103 that generates the second hole with relatively high mobility in the layer mainly composed of an organic substance is adjusted to increase the driving voltage without significantly increasing the above formula (1). ) Can be satisfied.

  In the case of a light-emitting element that extracts light emission from the second electrode 106 side, reflection occurs at the first electrode 101. Therefore, in order to improve the current efficiency of the light-emitting element and reduce the change in spectral shape that occurs depending on the angle at which the light emission surface is viewed, the optical distance from the position where light emission occurs to the surface of the first electrode 101 The distance (refractive index × physical distance) may be (2m−1) λ / 4 (m is a natural number of 1 or more, and λ is the center wavelength of light emitted from the light emitting layer).

  The light-emitting layer 104 may be formed as a single layer including a light-emitting material, but may have a plurality of structures including a layer including an electron-transport layer and a hole-transport layer and a layer including a light-emitting material. The layer containing the light emitting material may be a layer in which the light emitting material serving as the light emission center is dispersed, or may be a layer formed only of the light emitting material. However, in any of the configurations exemplified here, the layer containing the light emitting material has a certain thickness, and there are an infinite number of light emission centers, so the position where light emission has occurred must be determined strictly. Therefore, in this embodiment mode, a position where light emission occurs is regarded as a position corresponding to half of the thickness of the layer including the light emitting material.

Now, several layers made of different materials are provided from the position where the light emission occurs to the first electrode 101. In this embodiment mode, the layer 102 generates a first hole. In addition, a layer containing a light-emitting material can also be said to be a layer in which half the film thickness is located between the position where light emission occurs and the first electrode 101. Further, when the light emitting layer is formed of a plurality of layers, different layers may be included. In such a configuration, the optical distance from the position where light emission occurs to the first electrode 101 can be obtained by adding the product of the refractive index of each film and the film thickness. That is, a layer containing a light emitting material is a layer existing between the layer containing the light emitting material and the first electrode 101, where 1 is the layer containing the light emitting material and j is the first electrode 101 (j is an integer of 4 or more). When the refractive index n and the film thickness d are set to the refractive index and film thickness of the layer numbered with the same number (that is, n ₁ , the refractive index of the layer containing the light emitting material) , D _j is the thickness of the first electrode), and the following equation (2) is satisfied.

  Here, it is necessary to adjust the film thickness in order to satisfy the above formula (2). In this embodiment mode, the above formula (2) is obtained without increasing the driving voltage by adjusting the film thickness of the layer 102 that generates the first hole having relatively high mobility in the layer mainly composed of an organic substance. It becomes possible to satisfy.

  In the case of a structure in which light is extracted from both the first electrode 101 and the second electrode 106, the above formulas (1) and (2) may be satisfied at the same time.

  When the light-emitting element has a structure as in this embodiment mode, it is possible to provide a light-emitting element in which a change in emission spectrum depending on an angle at which a light emission extraction surface is viewed is reduced.

  This embodiment can be used in combination with Embodiment 1.

(Embodiment 3)
In this embodiment mode, the display device of the present invention described in Embodiment Mode 1 or Embodiment Mode 2 will be described with reference to FIGS. Note that although an example of manufacturing an active matrix display device is described in this embodiment mode, it is needless to say that the light-emitting element of the present invention can be applied to a passive matrix display device.

  First, after the first base insulating layer 51a and the second base insulating layer 51b are formed over the substrate 50, a semiconductor layer is further formed over the second base insulating layer 51b. (Fig. 5 (A))

  As a material of the substrate 50, glass, quartz, plastic (polyimide, acrylic, polyethylene terephthalate, polycarbonate, polyacrylate, polyethersulfone, or the like) can be used. These substrates may be used after being polished by CMP or the like, if necessary. In this embodiment, a glass substrate is used.

  The first base insulating layer 51a and the second base insulating layer 51b prevent an element such as an alkali metal or an alkaline earth metal in the substrate 50 that adversely affects the characteristics of the semiconductor film from diffusing into the semiconductor layer. Provided for this purpose. As a material, silicon oxide, silicon nitride, silicon oxide containing nitrogen, silicon nitride containing oxygen, or the like can be used. In this embodiment mode, the first base insulating layer 51a is formed using silicon nitride, and the second base insulating layer 51b is formed using silicon oxide. In this embodiment mode, the base insulating layer is formed of the first base insulating layer 51a and the second base insulating layer 51b. However, the base insulating layer may be formed of a single layer or a multilayer of two or more layers. It doesn't matter. In addition, it is not necessary to provide a base insulating layer as long as the diffusion of impurities from the substrate does not matter.

  A semiconductor layer formed subsequently is obtained by laser crystallization of an amorphous silicon film in this embodiment mode. An amorphous silicon film is formed to a thickness of 25 to 100 nm (preferably 30 to 60 nm) over the second base insulating layer 51b. As a manufacturing method, a known method such as a sputtering method, a low pressure CVD method or a plasma CVD method can be used. Then, hydrogen treatment is performed at 500 ° C. for 1 hour.

  Subsequently, the amorphous silicon film is crystallized using a laser irradiation apparatus to form a crystalline silicon film. In the laser crystallization of the present embodiment, an excimer laser is used, and a laser beam oscillated is processed into a linear beam spot using an optical system and irradiated to an amorphous silicon film to form a crystalline silicon film. Used as a semiconductor layer.

  Other methods for crystallization of the amorphous silicon film include a method for crystallization only by heat treatment and a method for heat treatment using a catalyst element that promotes crystallization. Examples of elements that promote crystallization include nickel, iron, palladium, tin, lead, cobalt, platinum, copper, and gold. Compared to the case where crystallization is performed only by heat treatment by using such an element, Since crystallization is performed at a low temperature for a short time, there is little damage to the glass substrate. When crystallization is performed only by heat treatment, the substrate 50 may be a quartz substrate resistant to heat.

  Subsequently, in order to control the threshold value in the semiconductor layer as required, a small amount of impurity addition, so-called channel doping is performed. In order to obtain a required threshold value, N-type or P-type impurities (phosphorus, boron, etc.) are added by an ion doping method or the like.

  After that, as shown in FIG. 5A, the semiconductor layer is patterned into a predetermined shape, and an island-shaped semiconductor layer 52 is obtained. Patterning is performed by applying a photoresist to the semiconductor layer, exposing a predetermined mask shape, baking, forming a resist mask on the semiconductor layer, and etching using the mask.

Subsequently, a gate insulating layer 53 is formed so as to cover the semiconductor layer 52. The gate insulating layer 53 is formed of an insulating layer containing silicon with a thickness of 40 to 150 nm by plasma CVD or sputtering. In this embodiment mode, silicon oxide is used.

  Next, the gate electrode 54 is formed over the gate insulating layer 53. The gate electrode 54 may be formed of an element selected from tantalum, tungsten, titanium, molybdenum, aluminum, copper, chromium, and niobium, or an alloy material or a compound material containing the element as a main component. Alternatively, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. Further, an AgPdCu alloy may be used.

  Further, although the gate electrode 54 is formed as a single layer in this embodiment mode, a stacked structure of two or more layers such as tungsten in the lower layer and molybdenum in the upper layer may be used. Even in the case where the gate electrode is formed as a stacked structure, the materials described in the preceding stage may be used. Moreover, the combination may be selected as appropriate. The gate electrode 54 is processed by etching using a mask using a photoresist.

  Subsequently, a high concentration impurity is added to the semiconductor layer 52 using the gate electrode 54 as a mask. Thus, the thin film transistor 70 including the semiconductor layer 52, the gate insulating layer 53, and the gate electrode 54 is formed.

  Note that there is no particular limitation on the manufacturing process of the thin film transistor, and it may be changed as appropriate so that a transistor with a desired structure can be manufactured.

  In this embodiment mode, a top-gate thin film transistor using a crystalline silicon film crystallized by laser crystallization is used; however, a bottom-gate thin film transistor using an amorphous semiconductor film is used for a pixel portion. It is also possible. As the amorphous semiconductor, not only silicon but also silicon germanium can be used. When silicon germanium is used, the concentration of germanium is preferably about 0.01 to 4.5 atomic%.

  Alternatively, a microcrystalline semiconductor film (semi-amorphous semiconductor) in which crystals of 0.5 nm to 20 nm can be observed in an amorphous semiconductor may be used. Microcrystals capable of observing 0.5 nm to 20 nm crystals are also called so-called microcrystals (μc).

Semi-amorphous silicon (also referred to as SAS) which is a semi-amorphous semiconductor can be obtained by glow discharge decomposition of a silicide gas. A typical silicide gas is SiH ₄ , and in addition, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _{4 and the} like can be used. The formation of the SAS can be facilitated by diluting the silicide gas with one or plural kinds of rare gas elements selected from hydrogen, hydrogen and helium, argon, krypton, and neon. It is preferable to dilute the silicide gas at a dilution ratio in the range of 10 times to 1000 times. The reaction generation of the film by glow discharge decomposition may be performed at a pressure in the range of 0.1 Pa to 133 Pa. The power for forming the glow discharge may be high frequency power of 1 MHz to 120 MHz, preferably 13 MHz to 60 MHz. The substrate heating temperature is preferably 300 ° C. or less, and a substrate heating temperature of 100 to 250 ° C. is suitable.

The SAS formed in this way has a Raman spectrum shifted to a lower wavenumber than 520 cm ⁻¹ , and diffraction peaks of (111) and (220), which are considered to be derived from the Si crystal lattice in X-ray diffraction, are observed. Is done. At least 1 atomic% or more of hydrogen or halogen is contained as a neutralizing agent for dangling bonds. As an impurity element in the film, impurities of atmospheric components such as oxygen, nitrogen, and carbon are desirably 1 × 10 ²⁰ cm ⁻¹ or less, and in particular, the oxygen concentration is 5 × 10 ¹⁹ / cm ³ or less, preferably 1 × 10 ¹⁹ / cm ³ or less. When the TFT is used, the mobility μ is μ = 1 to 10 cm ² / Vsec.

  Further, this SAS may be further crystallized with a laser.

  Subsequently, an insulating film (hydrogenated film) 59 is formed of silicon nitride so as to cover the gate electrode 54 and the gate insulating layer 53. After the insulating film (hydrogenated film) 59 is formed, heating is performed at 480 ° C. for about 1 hour to activate the impurity element and hydrogenate the semiconductor layer 52.

  Subsequently, a first interlayer insulating layer 60 covering the insulating film (hydrogenated film) 59 is formed. As a material for forming the first interlayer insulating layer 60, silicon oxide, acrylic, polyimide, siloxane, an Iow-k material, or the like may be used. In this embodiment mode, the silicon oxide film is formed as the first interlayer insulating layer. (Fig. 5 (B))

  Next, a contact hole reaching the semiconductor layer 52 is opened. The contact hole can be formed by performing etching using a resist mask until the semiconductor layer 52 is exposed, and can be formed by either wet etching or dry etching. Note that etching may be performed once depending on conditions, or etching may be performed in a plurality of times. In addition, when etching is performed a plurality of times, both wet etching and dry etching may be used. (Fig. 5 (C))

Then, a conductive layer covering the contact hole and the first interlayer insulating layer 60 is formed. The conductive layer is processed into a desired shape, and the connection portion 61a, the wiring 61b, and the like are formed. This wiring may be a single layer of aluminum, copper, or the like, but in this embodiment mode, a multilayer structure of molybdenum / aluminum / molybdenum is formed from the bottom. The laminated wiring may have a structure of titanium / aluminum / titanium or titanium / titanium nitride / aluminum / titanium. (Fig. 5 (D))

  Thereafter, a second interlayer insulating layer 63 is formed so as to cover the connection portion 61a, the wiring 61b, and the first interlayer insulating layer 60. As a material for the second interlayer insulating layer 63, a coating film of acrylic, polyimide, siloxane or the like having self-flatness can be suitably used. In this embodiment mode, siloxane is used as the second interlayer insulating layer 63. (Fig. 5 (E))

  Subsequently, an insulating layer may be formed using silicon nitride or the like over the second interlayer insulating layer 63. This is formed to prevent the second interlayer insulating layer 63 from being etched more than necessary in the subsequent etching of the pixel electrode. Therefore, when the ratio of the etching rate between the pixel electrode and the second interlayer insulating layer is large, it may not be provided. Subsequently, a contact hole that penetrates through the second interlayer insulating layer 63 and reaches the connection portion 61a is formed.

  Then, after forming the light-transmitting conductive layer so as to cover the contact hole and the second interlayer insulating layer 63 (or insulating layer), the light-transmitting conductive layer is processed to form the first light-emitting element in the thin film light-emitting element. One electrode (an electrode for receiving electrons) 101 is formed. Here, the first electrode 101 is in electrical contact with the connecting portion 61a. As the material of the first electrode 101, it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a high work function (work function of 4.0 eV or more). For example, ITO (indium tin oxide), ITO containing silicon (ITSO), IZO (indium zinc oxide) in which 2 to 20% zinc oxide (ZnO) is mixed with indium oxide, zinc oxide, and zinc oxide with gallium. In addition to contained GZO (Galium Zinc Oxide), gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co) , Copper (Cu), palladium (Pd), or a nitride of metal (TiN) can be used. In this embodiment mode, ITSO is used as the first electrode 101 (FIG. 6A).

  Next, an insulating layer made of an organic material or an inorganic material is formed so as to cover the second interlayer insulating layer 63 (or the insulating layer) and the first electrode 101. Subsequently, the insulating layer is processed so that a part of the first electrode 101 is exposed, and a partition wall 65 is formed. As the material of the partition wall 65, a photosensitive organic material (acrylic, polyimide, or the like) is preferably used, but it may be formed of an organic material or an inorganic material that does not have photosensitivity. Further, a black pigment or dye such as titanium black or carbon nitride may be dispersed in the material of the partition wall 65 by using a dispersing material or the like, and the partition wall 65 may be made black to be used like a black matrix. It is desirable that the end face of the partition wall 65 facing the first electrode has a curvature and has a tapered shape in which the curvature continuously changes (FIG. 6B).

  Next, a light emitting laminate 66 that covers the first electrode 101 exposed from the partition wall 65 is formed. In this embodiment mode, the light-emitting stacked body 66 may be formed by an evaporation method or the like. The first hole generating layer 102, the light emitting layer 104, the electron generating layer 105, and the second hole generating layer. It is formed by laminating in the order of 103.

The first hole-generating layer 102 and the second hole-generating layer 103 are formed using a hole-transporting material and an electron-accepting material that can receive electrons from the hole-transporting material. A layer including both, a layer of a P-type semiconductor, or a layer including a P-type semiconductor is formed using the same material. Examples of the hole transporting material include 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD) and 4,4′-bis [N -(3-Methylphenyl) -N-phenyl-amino] -biphenyl (abbreviation: TPD) or 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviation: TDATA) 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenyl-amino] -triphenylamine (abbreviation: MTDATA) and 4,4′-bis (N- (4- ( N, N-di-m-tolylamino) phenyl) -N-phenylamino) biphenyl (abbreviation: DNTPD) and other aromatic amine-based compounds (that is, having a benzene ring-nitrogen bond) and phthalocyanines (abbreviation: H ₂ Pc), copper Futaroshia Emissions (abbreviation: CuPc), or vanadyl phthalocyanine (abbreviation: VOPc), and the phthalocyanine compound and the like can be used. Examples of the electron-accepting material that can receive electrons from these hole-transporting materials include molybdenum oxide, vanadium oxide, 7,7,8,8, -tetracyanoquinodimethane (abbreviation). : TCNQ), 2,3-dicyanonaphthoquinone (abbreviation: DCNNQ), 2,3,5,6-tetrafluoro-7,7,8,8, -tetracyanoquinodimethane (abbreviation: F4-TCNQ), etc. An electron-accepting material capable of accepting electrons is selected depending on the combination with a hole-transporting material. As the P-type semiconductor, molybdenum oxide, vanadium oxide, ruthenium oxide, cobalt oxide, nickel oxide, copper oxide, or the like can be used. It should be noted that the materials listed here are merely examples and can be appropriately selected by the practitioner. The mixing ratio of the material having hole transportability to the material having electron transportability to the material having hole transportability may be 0.5 or more in terms of molar ratio, and preferably 0.5-2. . The molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer and the electron-accepting to the hole-transporting material in the first hole-generating layer The difference from the molar ratio of the material having the property is within 80% of the molar ratio of the electron-accepting material to the hole-transporting material in the layer generating the second holes, and the first hole is The molar ratio of the electron-accepting material to the hole-transporting material in the generated layer is preferably within 80%. More preferably, the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer and the hole-transporting material in the first hole-generating layer The difference from the molar ratio of the electron-accepting material is within 40% of the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer, and The molar ratio of the electron-accepting material to the hole-transporting material in the hole generating layer is preferably within 40%. In the first hole generating layer and the second hole generating layer in this embodiment, electrons that can accept electrons from α-NPD and α-NPD as materials having an electron transporting property Molybdenum oxide (MoO ₃ ) is used as a receptive material, and vapor deposition is performed by a co-evaporation method so that α-NPD: MoO ₃ = 4: 1 (corresponding to 1 in molar ratio) by weight.

Note that a layer containing a plurality of materials can be formed by depositing each material at the same time, such as co-evaporation by resistance heating evaporation, co-evaporation by electron beam evaporation, resistance heating evaporation and electron beam. What is necessary is just to form combining the same kind and different methods, such as the co-evaporation method by vapor deposition, the film formation by resistance heating vapor deposition and sputtering, and the film formation by electron beam vapor deposition and 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.

The first hole generating layer and the second hole generating layer have a thickness of 30 nm to 1 μm, and the thickness of the second hole generating layer is set to generate the first hole. Do not be more than 50% thicker or thinner than the layer thickness. In addition, the thickness of the first hole generating layer is set to be 50% or more thicker or thinner than the thickness of the second hole generating layer. More preferably, the first hole generating layer and the second hole generating layer have the same thickness as in this embodiment. Note that in this embodiment mode, the thickness of the first hole generating layer is 50 nm, and the thickness of the second hole generating layer is 50 nm. The first hole-generating layer 102 and the second hole-generating layer 103 each have an electron-accepting property capable of receiving electrons from the hole-transporting material and the hole-transporting material. It is preferable to form a layer including both of the materials, and the molar ratio of the electron-accepting material to the hole-transporting material in the layer 103 that generates the second holes and the first holes are generated. The difference between the molar ratio of the electron-accepting material to the hole-transporting material in the layer 102 is that the molar ratio of the electron-accepting material to the hole-transporting material in the layer 103 that generates the second hole. The ratio may be within 80% of the ratio and within 80% of the molar ratio of the electron-accepting material to the hole-transporting material in the first hole-generating layer 102. More preferably, the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer 103 and the hole-transporting property in the first hole-generating layer 102 are the same. The difference from the molar ratio of the electron-accepting material to the material is within 40% of the molar ratio of the electron-accepting material to the hole-transporting material in the second hole-generating layer 103, and The molar ratio of the electron-accepting material to the hole-transporting material in the layer 102 that generates one hole is preferably within 40%.

In addition, as the first hole generating layer 102 and the second hole generating layer 103, the hole transporting material described above, zinc oxide, indium oxide, tin oxide, antimony, and the like can be used. A first layer and a second layer formed using layers containing an inorganic material such as oxide, indium nitride, tin nitride, antimony nitride, tungsten nitride, molybdenum nitride, or the like may be used. And it is preferable that the thickness of a 1st layer and a 2nd layer is 30 nm-1 micrometer. Further, it is preferable that the thicknesses of the first layer and the second layer are substantially equal, so that the thickness of the second layer is not more than 50% thicker or thinner than the thickness of the first layer. Further, the thickness of the first layer should be 50% or more thicker than the thickness of the second layer. That is, the thickness of the second layer is within 50% to 150% of the thickness of the first layer, and the thickness of the first layer is within 50% to 150% of the thickness of the second layer. To be. In addition, the first layer and the second layer 103 are preferably formed of a layer containing the same hole transporting material and the same inorganic material, and the electron accepting to the hole transporting material in the second layer. The difference between the molar ratio of the conductive material and the molar ratio of the electron-accepting material to the hole-transporting material in the first layer is the difference in electron-accepting property to the hole-transporting material in the second layer. It is preferable that the molar ratio of the material is within 80% and the molar ratio of the electron-accepting material to the hole-transporting material in the first layer is within 80%. More preferably, the molar ratio of the electron-accepting material to the hole-transporting material in the second layer and the molar ratio of the electron-accepting material to the hole-transporting material in the first layer The difference is within 40% of the molar ratio of the electron-accepting material to the hole-transporting material in the second layer and the mole of the electron-accepting material to the hole-transporting material in the first layer. It should be within 40% of the ratio.

The light emitting layer 104 becomes a light emission center when the light emitting layer 104 is formed as a layer containing a light emitting material serving as a light emission center dispersed in a layer made of a material having an energy gap larger than that of the light emitting substance. As the light-emitting substance, 4-dicyanomethylene-2-methyl-6- (1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (abbreviation: DCJT), 4-dicyanomethylene-2 -T-butyl-6- (1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran, periflanthene, 2,5-dicyano-1,4-bis (10-methoxy-1) , 1,7,7-tetramethyljulolidyl-9-enyl) benzene, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8- Quinolinolato) aluminum (abbreviation: Alq ₃ ), 9,9′-bianthryl, 9,10-diphenylanthracene (abbreviation: DPA), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), 2,5, 8,11-tetra-t-butylperylene (abbreviation: TBP), 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-) as a base material for dispersing the light-emitting material. Anthracene derivatives such as BuDNA), carbazole derivatives such as 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP), tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8) - quinolinolato) aluminum (abbreviation: Almq _3), bis (10-hydroxybenzo [h] - quinolinato) beryllium Abbreviation: BeBq _2), or bis (2-methyl-8-quinolinolato) -4-phenylphenolato - aluminum (abbreviation: BAlq), bis [2- (2-hydroxyphenyl) pyridinato] zinc (abbreviation: Znpp _2), It can be manufactured using a metal complex such as bis [2- (2-hydroxyphenyl) benzoxazolate] zinc (abbreviation: ZnBOX). In the case where the light-emitting layer 104 is formed using only a light-emitting substance, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), bis (2- A material such as methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq) is used.

  The light-emitting layer 104 may be formed as a single layer or a plurality of layers. The light-emitting layer 104 in which the light-emitting material is dispersed (or a layer made of the light-emitting material) and the first hole are generated. An electron transport layer may be provided between the hole transport layer and the layer 102 in which the light emitting material is dispersed in the light emitting layer 104 (or a layer made of the light emitting material) and the layer 105 that generates electrons. . These layers may or may not be provided, and only one of them may be provided. The materials of the hole transport layer and the electron transport layer are the same as those of the hole transport layer in the hole generating layer and the electron transport layer in the electron generating layer. Is omitted. See each description.

  In this embodiment mode, a hole transport layer, a layer in which a light-emitting material is dispersed, and an electron transport layer are sequentially formed as the light-emitting layer 104 over the layer 102 that generates holes. As a hole transport layer, α-NPD has a thickness of 10 nm. As a layer in which a light emitting material is dispersed, Alq and coumarin 6 have a weight ratio of 1: 0.005, a thickness of 35 nm. As an electron transport layer, Alq has a thickness of 10 nm. Vapor deposition is performed.

The electron generating layer 105 is formed of a layer containing both an electron transporting material and an electron donating material capable of donating electrons to the electron transporting material, an N-type semiconductor layer, or an N-type semiconductor. It is formed by the layer containing. Examples of the electron transporting material include tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), and bis (10-hydroxybenzo [h ] -Quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), etc. Can be used. In addition, bis [2- (2-hydroxyphenyl) benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ) and other materials such as metal complexes having an oxazole-based or thiazole-based ligand can also be used. In addition to 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-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- ( 4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2, 4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), and the like can be used. Examples of the electron donating material that can give electrons to these electron transporting materials 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. An electron donating material that can donate electrons is selected depending on the combination with an electron transporting material. As the N-type semiconductor, zinc oxide, zinc sulfide, zinc selenide, titanium oxide, or the like can be used.

  The mixing ratio of the electron transporting material and the material capable of donating electrons to the electron transporting material may be about 1: 0.5 to 1: 2, preferably 1: 1. In the layer for generating electrons in this embodiment, Alq is used as a material having an electron transporting property, lithium (Li) is used as an electron donating material capable of donating electrons to Alq, and Alq: Li by weight ratio. = 1: 0.01 Deposition is performed by a co-evaporation method. The film thickness is 10 nm.

  A light emitting element having a different emission wavelength band may be formed for each pixel to perform color display. Typically, a light emitting element corresponding to each color of R (red), G (green), and B (blue) is formed. In this case as well, by providing a filter (colored layer) that transmits light in the emission wavelength band on the light emission side of the pixel, the color purity is improved and the pixel portion is mirrored (reflected). Prevention can be achieved. By providing the filter (colored layer), it is possible to omit a circularly polarizing plate that has been conventionally required, and it is possible to eliminate the loss of light emitted from the light emitting element. Furthermore, a change in color tone that occurs when the pixel portion (display screen) is viewed obliquely can be reduced.

  In addition, the light-emitting element can have a structure that emits monochromatic or white light. In the case of using a white light emitting material, color display can be made possible by providing a filter (colored layer) that transmits light of a specific wavelength on the light emission side of the pixel.

To form a light emitting layer that emits white light, for _{example, Alq 3, Alq 3, Alq} 3 doped with Nile Red which is partly red light emitting pigment, p-EtTAZ, by TPD (aromatic diamine) evaporation A white color can be obtained by sequentially laminating.

  Furthermore, a triplet excitation material containing a metal complex or the like may be used for the light emitting layer in addition to a singlet excitation light emitting material. For example, among red light emitting pixels, green light emitting pixels, and blue light emitting pixels, a red light emitting pixel having a relatively short luminance half time is formed of a triplet excitation light emitting material, and the other A singlet excited luminescent material is used. The triplet excited luminescent material has a feature that the light emission efficiency is good, so that less power is required to obtain the same luminance. That is, when applied to a red pixel, the amount of current flowing through the light emitting element can be reduced, so that reliability can be improved. As a reduction in power consumption, a red light-emitting pixel and a green light-emitting pixel may be formed using a triplet excitation light-emitting material, and a blue light-emitting pixel may be formed using a singlet excitation light-emitting material. By forming a green light-emitting element having high human visibility with a triplet excited light-emitting material, power consumption can be further reduced.

  Examples of triplet excited luminescent materials include those using a metal complex as a dopant, and metal complexes having a third transition series element platinum as the central metal and metal complexes having iridium as the central metal are known. Yes. The triplet excited light-emitting material is not limited to these compounds, and a compound having the above structure and having an element belonging to group 8 to 10 in the periodic table as a central metal can also be used.

  A light-emitting element formed using the above materials emits light by being forward-biased. A pixel of a display device formed using a light-emitting element can be driven by a simple matrix method or an active matrix method. In any case, each pixel emits light by applying a forward bias at a specific timing, but is in a non-light emitting state for a certain period. By applying a reverse bias during this non-light emitting time, the reliability of the light emitting element can be improved. The light emitting element has a degradation mode in which the emission intensity decreases under a constant driving condition and a degradation mode in which the non-light emitting area is enlarged in the pixel and the luminance is apparently decreased. By performing a typical drive, the progress of deterioration can be slowed and the reliability of the light emitting device can be improved.

Subsequently, a second electrode 106 that covers the light-emitting stacked body 66 is formed. Thus, a light-emitting element 93 including the first electrode 101, the light-emitting stack 66, and the second electrode 106 can be manufactured. Note that in this embodiment mode, when a voltage is applied so that the light emitting element emits light, the electrode having a higher potential is set as the first electrode, and the electrode having a lower potential is set as the second electrode. Let it be an electrode. As the second electrode material used for forming the second electrode 106, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (work function of 3.8 eV or less) is preferably used. Specific examples of the second electrode material include elements belonging to Group 1 or Group 2 of the element periodic rule, that is, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, and these In addition to alloys containing Mg (Mg: Ag, Al: Li) and compounds (LiF, CsF, CaF ₂ ), transition metals including rare earth metals can be used, but metals such as Al, Ag, and ITO ( It can also be formed by lamination with an alloy. In this embodiment, aluminum is used as the second electrode.

  The light-emitting element having the above structure can be a light-emitting element having a low drive voltage and a small increase in drive voltage with time.

In addition, stress on the light-emitting layer can be relaxed and the reliability of the light-emitting element can be improved.

  In the present embodiment, the electrode that is in electrical contact with the connection portion 61 a is the first electrode 101, but the electrode that is in electrical contact with the connection portion 61 a is the second electrode 106. There may be. In this case, the stacking order of the light-emitting stacked body 66 is formed by stacking the layer 103 for generating the second hole, the layer 105 for generating the electron, the light-emitting layer 104, and the layer 102 for generating the first hole in this order. Then, the first electrode 101 may be formed on the light emitting stack 66.

Thereafter, a silicon oxide film containing nitrogen is formed as a second passivation film by a plasma CVD method. In the case of using a silicon oxide film containing nitrogen, a silicon oxynitride film manufactured from SiH ₄ , N ₂ O, NH ₃ by a plasma CVD method, or a silicon oxynitride film manufactured from SiH ₄ , N ₂ O, Alternatively, a silicon oxynitride film formed from a gas obtained by diluting SiH ₄ or N ₂ O with Ar may be formed.

Alternatively, a silicon oxynitride silicon film formed from SiH ₄ , N ₂ O, and H ₂ may be applied as the first passivation film. Needless to say, the first passivation film is not limited to a single layer structure, and another insulating layer containing silicon may be used as a single layer structure or a stacked structure. Further, a multilayer film of a carbon nitride film and a silicon nitride film, a multilayer film of styrene polymer, a silicon nitride film, or a diamond-like carbon film may be formed instead of the silicon oxide film containing nitrogen.

  Subsequently, the display portion is sealed in order to protect the electroluminescent element from a substance that promotes deterioration such as water. In the case where the counter substrate is used for sealing, bonding is performed with an insulating sealing material so that the external connection portion is exposed. A space between the counter substrate and the element substrate may be filled with an inert gas such as dry nitrogen, or a sealing material may be applied to the entire surface of the pixel portion to bond the counter substrate. It is preferable to use an ultraviolet curable resin or the like for the sealing material. The sealing material may contain a desiccant or particles for keeping the gap between the substrates constant. Subsequently, the display device is completed by attaching a flexible wiring board to the external connection portion.

  One example of the structure of the display device manufactured as described above will be described with reference to FIG. In addition, even if the shapes are different, parts showing similar functions are denoted by the same reference numerals, and explanations thereof are omitted. In this embodiment mode, the thin film transistor 70 having an LDD structure is connected to the light emitting element 93 through the connection portion 61a.

  FIG. 7A illustrates a structure in which the first electrode 101 is formed using a light-transmitting conductive film and light emitted from the light-emitting stack 66 is extracted to the substrate 50 side. Reference numeral 94 denotes a counter substrate, which is fixed to the substrate 50 by using a sealing material or the like after the light emitting element 93 is formed. Filling the counter substrate 94 with the light-transmitting resin 88 or the like between the elements and sealing them can prevent the light-emitting element 93 from being deteriorated by moisture. Further, it is desirable that the resin 88 has a hygroscopic property. Further, if a desiccant 89 having high translucency is dispersed in the resin 88, the influence of moisture can be further suppressed, which is a more desirable form.

  FIG. 7B illustrates a structure in which both the first electrode 101 and the second electrode 106 are formed using a light-transmitting conductive film, and light can be extracted to both the substrate 50 and the counter substrate 94. It has become. Further, in this configuration, by providing the polarizing plate 90 outside the substrate 50 and the counter substrate 94, it is possible to prevent the screen from being seen through, and visibility is improved. A protective film 91 may be provided outside the polarizing plate 90.

  Note that either an analog video signal or a digital video signal may be used for the display device of the present invention having a display function. When a digital video signal is used, the video signal is classified into one using a voltage and one using a current. When the light emitting element emits light, the video signal input to the pixel has a constant voltage and a constant current. When the video signal has a constant voltage, the voltage applied to the light emitting element is constant. And the current flowing through the light emitting element is constant. In addition, a video signal having a constant current includes a constant voltage applied to the light emitting element and a constant current flowing in the light emitting element. A constant voltage applied to the light emitting element is constant voltage driving, and a constant current flowing through the light emitting element is constant current driving. In constant current driving, a constant current flows regardless of the resistance change of the light emitting element. In the light emitting display device and the driving method thereof of the present invention, either a voltage video signal or a current video signal may be used, and either a constant voltage drive or a constant current drive may be used.

  The display device of the present invention which is formed by the method of this embodiment mode is a display device which has a low driving voltage and a small increase in the driving voltage with time. In addition, the display device is highly reliable.

(Embodiment 4)
In this embodiment, the appearance of a panel of a light-emitting device that corresponds to one embodiment of the present invention will be described with reference to FIGS. 8A is a top view of a panel in which a transistor and a light-emitting element formed over a substrate are sealed with a sealant formed between a counter substrate 4006 and FIG. 8B is a plan view of FIG. Corresponds to the cross-sectional view. In addition, the structure of the light-emitting element mounted on this panel is such that each layer in contact with the pair of electrodes including the first electrode and the second electrode generates holes, and the light-emitting layer has holes. The structure is sandwiched between layers that generate Further, a layer for generating electrons is provided between the layer for generating holes on the second electrode side of the light emitting element and the light emitting layer. Note that in this embodiment mode, when a voltage is applied so that the light emitting element emits light, the electrode having a higher potential is set as the first electrode, and the electrode having a lower potential is set as the second electrode. Let it be an electrode. The layers that generate holes are formed of the same material, and the thickness of the layer that generates holes formed on the counter substrate side is greater than the thickness of the layer that generates holes formed on the substrate side. Avoid being thicker or thinner than 50%. In addition, the thickness of the layer that generates holes formed on the substrate side is set to be 50% or more thicker or thinner than the thickness of the layer that generates holes formed on the counter substrate side. The thicknesses of the hole generating layer formed on the counter substrate side and the hole generating layer formed on the substrate side are both 30 nm to 1 μm.

  A sealant 4005 is provided so as to surround the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 which are provided over the substrate 4001. A counter substrate 4006 is provided over the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004. Therefore, the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 are sealed together with the filler 4007 by the substrate 4001, the sealant 4005, and the counter substrate 4006.

  The pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004 provided over the substrate 4001 include a plurality of thin film transistors. In FIG. 8B, the thin film transistor 4008 included in the signal line driver circuit 4003 is provided. And a thin film transistor 4010 included in the pixel portion 4002.

  The light emitting element 4011 is electrically connected to the thin film transistor 4010.

  The lead wiring 4014 corresponds to a wiring for supplying a signal or a power supply voltage to the pixel portion 4002, the signal line driver circuit 4003, and the scan line driver circuit 4004. The lead wiring 4014 is connected to the connection terminal 4016 via the lead wiring 4015a and the lead wiring 4015b. The connection terminal 4016 is electrically connected to a terminal included in a flexible printed circuit (FPC) 4018 through an anisotropic conductive film 4019.

  Note that as the filler 4007, in addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used, and polyvinyl chloride, acrylic, polyimide, epoxy resin, silicon resin, polyvinyl butyral, Alternatively, ethylene vinylene acetate can be used.

  Note that the display device of the present invention includes in its category a panel in which a pixel portion having a light-emitting element is formed and a module in which an IC is mounted on the panel.

  The panel and module configured as in the present embodiment are panels and modules that have a small driving voltage and a small increase in the driving voltage with time. Moreover, it is a highly reliable panel and module.

(Embodiment 5)
As an electronic device of the present invention on which a module whose example is shown in Embodiment 4 is mounted, a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproduction device (car audio component, etc.) A recording medium such as a computer, a game machine, a portable information terminal (mobile computer, cellular phone, portable game machine, electronic book, etc.), an image reproducing device (specifically Digital Versatile Disc (DVD)) equipped with a recording medium And a device having a display capable of reproducing and displaying the image). Specific examples of these electronic devices are shown in FIGS.

  FIG. 9A illustrates a light-emitting display device, such as a television receiver or a personal computer monitor. A housing 2001, a display portion 2003, a speaker portion 2004, and the like are included. The light-emitting display device of the present invention is a light-emitting display device in which the driving voltage of the display portion 2003 is small and the increase in driving voltage with time is small. In addition, the display portion 2003 is a light-emitting display device with high reliability. In order to increase the contrast in the pixel portion, a polarizing plate or a circular polarizing plate may be provided. For example, a film may be provided on the sealing substrate in the order of a 1 / 4λ plate, a 1 / 2λ plate, and a polarizing plate. Further, an antireflection film may be provided on the polarizing plate.

  FIG. 9B illustrates a mobile phone, which includes a main body 2101, a housing 2102, a display portion 2103, an audio input portion 2104, an audio output portion 2105, operation keys 2106, an antenna 2108, and the like. The cellular phone of the present invention is a cellular phone in which the drive voltage of the display portion 2103 is small and the increase in drive voltage with time is small. Further, the display portion 2103 is a light-emitting display device with high reliability.

  FIG. 9C illustrates a computer, which includes a main body 2201, a housing 2202, a display portion 2203, a keyboard 2204, an external connection port 2205, a pointing mouse 2206, and the like. The computer of the present invention is a computer in which the drive voltage of the display portion 2203 is small and the drive voltage rises with time. In addition, the display portion 2203 is a light-emitting display device with high reliability. Although a notebook computer is illustrated in FIG. 9C, the present invention can also be applied to a desktop computer in which a hard disk and a display portion are integrated.

  FIG. 9D illustrates a mobile computer, which includes a main body 2301, a display portion 2302, a switch 2303, operation keys 2304, an infrared port 2305, and the like. The mobile computer of the present invention is a mobile computer in which the driving voltage of the display portion 2302 is small and the increase in driving voltage with time is small. In addition, the display portion 2302 is a light-emitting display device with high reliability.

  FIG. 9E illustrates a portable game machine including a housing 2401, a display portion 2402, speaker portions 2403, operation keys 2404, a recording medium insertion portion 2405, and the like. The portable game machine of the present invention is a portable game machine in which the drive voltage of the display portion 2402 is small and the drive voltage rises with time. Further, the display portion 2402 is a light-emitting display device with high reliability.

  As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields.

(Embodiment 6)
FIG. 10 shows an example of bottom emission, double side emission, and top emission. A structure in which a manufacturing process is described in Embodiment 3 corresponds to the structure in FIG. 10A and 10B, the first interlayer insulating layer 900 in FIG. 10C is formed of a material having self-planarity, and wirings connected to the thin film transistor 901 and the first electrode 101 of the light-emitting element are provided. This is a configuration when formed on the same interlayer insulating layer. FIG. 10A illustrates a structure of bottom emission in which only the first electrode 101 of the light-emitting element is formed using a light-transmitting material and light is emitted toward the lower portion of the light-emitting device, and FIG. By forming a light-transmitting material such as ITSO or IZO as the second electrode 106, a light-emitting display device that emits light from both sides as shown in FIG. 10B can be obtained. . Note that although the film is non-light-transmitting when formed with a thick film such as aluminum or silver, the light-transmitting property is obtained when the film is thinned; Even if formed, double-sided light emission can be achieved. Note that in this embodiment mode, when a voltage is applied so that the light emitting element emits light, the electrode having a higher potential is set as the first electrode, and the electrode having a lower potential is set as the second electrode. Let it be an electrode.

(Embodiment 7)
In this embodiment, pixel circuits and protection circuits included in the panel and module described in Embodiment 4 and operations thereof will be described. Note that the cross-sectional views shown in FIGS. 5 and 6 are cross-sectional views of the driving TFT 1403 and the light emitting element 1405.

  In the pixel shown in FIG. 11A, a signal line 1410 and power supply lines 1411 and 1412 are arranged in the column direction, and a scanning line 1414 is arranged in the row direction. The pixel further includes a switching TFT 1401, a driving TFT 1403, a current control TFT 1404, a capacitor element 1402, and a light emitting element 1405.

  The pixel shown in FIG. 11C is different from the pixel shown in FIG. 11A in that the gate electrode of the driving TFT 1403 is connected to the power supply line 1412 arranged in the row direction. It is a configuration. That is, both pixels shown in FIGS. 11A and 11C show the same equivalent circuit diagram. However, in the case where the power supply line 1412 is arranged in the row direction (FIG. 11C) and in the case where the power supply line 1412 is arranged in the column direction (FIG. 11A), each power supply line has a different layer. It is formed of a conductive film. Here, attention is paid to the wiring to which the gate electrode of the driving TFT 1403 is connected, and FIGS. 11A and 11C are shown separately to show that the layers for manufacturing these are different.

  As a feature of the pixel shown in FIGS. 11A and 11C, a driving TFT 1403 and a current control TFT 1404 are connected in series in the pixel, and the channel length L (1403) and channel width W (1403) of the driving TFT 1403 are connected. ), The channel length L (1404) and the channel width W (1404) of the current control TFT 1404 satisfy L (1403) / W (1403): L (1404) / W (1404) = 5 to 6000: 1. It is good to set to.

  Note that the driving TFT 1403 operates in a saturation region and has a role of controlling a current value flowing through the light emitting element 1405, and the current control TFT 1404 operates in a linear region and has a role of controlling supply of current to the light emitting element 1405. . Both TFTs preferably have the same conductivity type in terms of manufacturing process, and in this embodiment mode, they are formed as n-channel TFTs. The driving TFT 1403 may be a depletion type TFT as well as an enhancement type. In the present invention having the above configuration, since the current control TFT 1404 operates in a linear region, a slight change in Vgs of the current control TFT 1404 does not affect the current value of the light emitting element 1405. That is, the current value of the light emitting element 1405 can be determined by the driving TFT 1403 operating in the saturation region. With the above structure, it is possible to provide a display device in which luminance unevenness of a light-emitting element due to variation in TFT characteristics is improved and image quality is improved.

  In the pixels shown in FIGS. 11A to 11D, the switching TFT 1401 controls input of a video signal to the pixel. When the switching TFT 1401 is turned on, the video signal is input into the pixel. Then, the voltage of the video signal is held in the capacitor element 1402. 11A and 11C illustrate the structure in which the capacitor 1402 is provided, the present invention is not limited to this, and the capacity for holding a video signal can be covered by a gate capacity or the like. In this case, the capacitor 1402 is not necessarily provided.

  The pixel shown in FIG. 11B has the same pixel structure as that shown in FIG. 11A except that a TFT 1406 and a scanning line 1415 are added. Similarly, the pixel illustrated in FIG. 11D has the same pixel structure as that illustrated in FIG. 11C except that a TFT 1406 and a scanning line 1415 are added.

  The TFT 1406 is controlled to be turned on or off by a newly arranged scanning line 1415. When the TFT 1406 is turned on, the charge held in the capacitor element 1402 is discharged, and the current control TFT 1404 is turned off. That is, the arrangement of the TFT 1406 can forcibly create a state where no current flows through the light-emitting element 1405. Therefore, the TFT 1406 can be called an erasing TFT. Accordingly, the configurations in FIGS. 11B and 11D can improve the duty ratio because the lighting period can be started simultaneously with or immediately after the start of the writing period without waiting for signal writing to all pixels. It becomes possible.

  In the pixel shown in FIG. 11E, a signal line 1410, a power supply line 1411 are arranged in the column direction, and a scanning line 1414 is arranged in the row direction. Further, the pixel includes a switching TFT 1401, a driving TFT 1403, a capacitor element 1402, and a light emitting element 1405. The pixel illustrated in FIG. 11F has the same pixel structure as that illustrated in FIG. 11E except that a TFT 1406 and a scanning line 1415 are added. Note that the duty ratio of the structure in FIG. 11F can also be improved by the arrangement of the TFT 1406.

  As described above, various pixel circuits can be employed. In particular, in the case where a thin film transistor is formed from an amorphous semiconductor film, it is preferable to increase the semiconductor film of the driving TFT 1403. In the case of increasing the size of the semiconductor film, the pixel circuit is preferably a top emission type in which light from the electroluminescent layer is emitted from the sealing substrate side.

  Such an active matrix light-emitting device is considered to be advantageous because it can be driven at a low voltage because a TFT is provided in each pixel when the pixel density is increased.

  In this embodiment mode, an active matrix light-emitting device in which each pixel is provided with each TFT has been described; however, a passive matrix light-emitting device in which a TFT is provided for each column can also be formed. A passive matrix light-emitting device has a high aperture ratio because a TFT is not provided for each pixel. In the case of a light-emitting device in which light emission is emitted to both sides of an electroluminescent layer, transmittance is increased when a passive matrix display device is used.

  The display device of the present invention further including such a pixel circuit can have a small driving voltage, a small increase in the driving voltage with time, and a display device having each characteristic.

  Next, a case where a diode is provided as a protective circuit in the scan line and the signal line is described using the equivalent circuit illustrated in FIG.

  In FIG. 12, a switching TFT 1401, a driving TFT 1403, a capacitor element 1402, and a light emitting element 1405 are provided in the pixel portion 1500. The signal line 1410 is provided with diodes 1561 and 1562. Like the switching TFT 1401 or the driving TFT 1403, the diodes 1561 and 1562 are manufactured based on the above embodiment mode and include a gate electrode, a semiconductor layer, a source electrode, a drain electrode, and the like. The diodes 1561 and 1562 operate as diodes by connecting a gate electrode and a drain electrode or a source electrode.

  Common potential lines 1554 and 1555 connected to the diode are formed in the same layer as the gate electrode. Therefore, in order to connect to the source electrode or the drain electrode of the diode, it is necessary to form a contact hole in the gate insulating layer.

  A diode provided in the scan line 1414 has a similar structure.

  Thus, according to the present invention, the protection diode provided in the input stage can be formed simultaneously. Note that the position where the protective diode is formed is not limited to this, and the protective diode can be provided between the driver circuit and the pixel.

The display device of the present invention having such a protection circuit has a low driving voltage, a small increase in the driving voltage with time, and a high reliability as a display device.

  In this example, measurement data of the light-emitting element of the present invention is shown.

  First, a method for manufacturing a light-emitting element in this example is described. The light-emitting element in this example conforms to the structure of the light-emitting element described in Embodiment Mode 1. In this embodiment, a glass substrate is used as the insulator 100. An ITO containing silicon was formed over the glass substrate by a sputtering method, whereby the first electrode 101 was formed. The first electrode 101 was formed to have a thickness of 110 nm.

Subsequently, molybdenum oxide (6) and α-NPD were co-evaporated on the first electrode 101 to form a layer 102 that generates first holes made of molybdenum oxide and α-NPD. Here, the thickness of the layer 102 that generates the first holes was set to 50 nm. The molar ratio of α-NPD and molybdenum oxide was set to 1: 1.

Next, the light-emitting layer 104 was formed over the layer 102 that generates the first holes. The light-emitting layer 104 has a three-layer structure, and is formed in this order from the first hole-generating layer 102 side: a hole transport layer, a layer in which a light-emitting material is dispersed, and an electron transport layer. The hole transport layer is formed by α-NPD so as to have a film thickness of 10 nm by a vacuum deposition method, and the layer in which the light emitting material is dispersed is formed by co-deposition of Alq ₃ and coumarin 6 to form Alq ₃ . A layer containing coumarin 6 was formed to a film thickness of 35 nm, and the electron transport layer was formed to have a film thickness of 10 nm only by Alq ₃ by vacuum deposition. The layer in which the light emitting material was dispersed was adjusted so that the ratio of Alq ₃ and coumarin 6 was 1: 0.005 by weight.

Subsequently, Alq ₃ and lithium were co-evaporated on the light-emitting layer 104 to form a layer 105 that generates electrons composed of Alq ₃ and lithium so as to have a thickness of 10 nm. The weight ratio of Alq3 and lithium was adjusted to be 1: 0.01.

Next, a layer 103 for generating second holes made of molybdenum oxide and α-NPD was formed on the layer 105 for generating electrons by co-evaporation of molybdenum oxide (6) and α-NPD. . Here, the thickness of the layer 102 for generating the second holes was set to 20 nm. The molar ratio of α-NPD to molybdenum oxide was set to 1: 1.

  A second electrode 106 made of aluminum was formed on the second hole generating layer 105. The film thickness was 100 nm.

  When a voltage is applied to the light-emitting element of the present invention having the above structure, holes are injected into the second electrode from the layer 103 that generates the second holes. Further, electrons are injected into the light emitting layer 104 from the layer 105 that generates electrons. Furthermore, holes are injected into the light-emitting layer 104 from the first hole-generating layer 102, and the electrons and holes injected in the light-emitting layer are recombined, and light emission is obtained from the coumarin 6.

  FIG. 13 shows voltage-luminance characteristics and FIG. 14 shows voltage-current characteristics of the light-emitting element manufactured in this manner. In FIG. 13, the horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m 2). In FIG. 14, the horizontal axis represents voltage (V) and the vertical axis represents current (mA).

  As described above, the light-emitting element in this example exhibits favorable characteristics.

In this embodiment, when a voltage is applied so that the light emitting element emits light, the electrode on which the higher potential is set is the first electrode, and the electrode on which the lower potential is set is the second electrode. And The light-emitting element in this embodiment has a structure in which a light-emitting layer 104 is sandwiched between a layer 102 that generates first holes in contact with a first electrode and a layer 103 that generates second holes in contact with a second electrode. The thickness of the layer 103 that generates the second hole is 50% or more thicker or thinner than the thickness of the layer 102 that generates the first hole, and the first hole is generated. The thickness of the layer 102 is not more than 50% thicker or thinner than the thickness of the layer 103 that generates the second hole. Moreover, each thickness is the range of 30 nm-1 micrometer. Further, the molar ratio of molybdenum oxide to α-NPD constituting the layer 103 generating the second hole is equal to the molar ratio of molybdenum oxide to α-NPD constituting the layer 102 generating the first hole. Difference between the molar ratio of molybdenum oxide to α-NPD constituting the second hole generating layer 103 and α-NPD in the layer 102 generating the first hole. It is within 80% of the molar ratio of the molybdenum oxide to the silicon oxide.

Therefore, the light-emitting element in this embodiment has high reliability because stress on the light-emitting layer is reduced.

  In this embodiment, four light-emitting elements, a light-emitting element (1), and a light-emitting element (where the mixing ratio of a hole-transporting substance and a substance that exhibits electron accepting property to the substance in the layer that generates holes are different. 2) A method for manufacturing the light-emitting element (3) and the light-emitting element (4), and characteristics of these elements will be described.

  First, a method for manufacturing a light-emitting element in this example is described. The light-emitting element in this example conforms to the structure of the light-emitting element described in Embodiment Mode 1. In this embodiment, a glass substrate is used as the insulator 100. An ITO containing silicon was formed over the glass substrate by a sputtering method, whereby the first electrode 101 was formed. The first electrode 101 was formed to have a thickness of 110 nm.

  Subsequently, a molybdenum oxide film was formed over the first electrode 101 by a vacuum evaporation method, and a layer 102 that generates holes made of a molybdenum oxide film was formed. Here, the film thickness was set to 5 nm.

Next, the light-emitting layer 104 was formed over the layer 102 that generates the first holes. The light-emitting layer 104 has a three-layer structure, and is formed in this order from the first hole-generating layer 102 side: a hole transport layer, a layer in which a light-emitting material is dispersed, and an electron transport layer. The hole transport layer is formed by depositing α-NPD so as to have a film thickness of 55 nm by vacuum deposition, and the layer in which the light emitting material is dispersed is formed by co-deposition of Alq ₃ and coumarin 6 to form Alq ₃ . A layer containing coumarin 6 was formed to a film thickness of 35 nm, and the electron transport layer was formed to have a film thickness of 10 nm only by Alq ₃ by vacuum deposition. The layer in which the light emitting material was dispersed was adjusted so that the ratio of Alq ₃ and coumarin 6 was 1: 0.005 by weight.

Subsequently, Alq ₃ and lithium were co-evaporated on the light-emitting layer 104 to form a layer 105 that generates electrons composed of Alq ₃ and lithium so as to have a thickness of 10 nm. The weight ratio of Alq3 and lithium was adjusted to be 1: 0.01.

Next, a layer 103 for generating second holes made of molybdenum oxide and α-NPD was formed on the layer 105 for generating electrons by co-evaporation of molybdenum oxide (6) and α-NPD. . Here, for the light emitting element (1), the molar ratio of NPB to molybdenum oxide was adjusted to 0.5 (= molybdenum oxide / NPB). For the light-emitting element (2), the molar ratio of NPB to molybdenum oxide was adjusted to 1.0 (= molybdenum oxide / NPB). For the light-emitting element (3), the molar ratio of NPB to molybdenum oxide was adjusted to 1.5 (= molybdenum oxide / NPB). For the light-emitting element (4), the molar ratio of NPB to molybdenum oxide was adjusted to 2.0 (= molybdenum oxide / NPB). In addition, the thickness of the layer 102 that generates the first holes was set to 20 nm.

  A second electrode 106 made of aluminum was formed on the second hole generating layer 105. The film thickness was 100 nm. In this embodiment, when a voltage is applied so that the light emitting element emits light, the electrode on which the higher potential is set is the first electrode, and the electrode on which the lower potential is set is the second electrode. And

  When a voltage is applied to the light-emitting element of the present invention having the above structure, holes are injected into the second electrode from the layer 103 that generates the second holes. Further, electrons are injected into the light emitting layer 104 from the layer 105 that generates electrons. Furthermore, holes are injected into the light-emitting layer 104 from the first hole-generating layer 102, and the electrons and holes injected in the light-emitting layer are recombined, and light emission is obtained from the coumarin 6.

FIG. 15 shows the voltage-luminance characteristics of the light emitting element of this example, FIG. 16 shows the current density-luminance characteristics, and FIG. 17 shows the voltage-current characteristics. In FIG. 15, the horizontal axis represents voltage (V) and the vertical axis represents luminance (cd / m 2). In FIG. 16, the horizontal axis represents current density (mA / cm 2), and the vertical axis represents luminance (cd
/ M2). In FIG. 17, the horizontal axis represents voltage (V), and the vertical axis represents current (mA). 15 to 17, the ▲ mark indicates the characteristics of the light emitting element (1), the ● mark indicates the characteristics of the light emitting element (2), the ◯ mark indicates the characteristics of the light emitting element (3), and the ■ mark indicates the characteristics of the light emitting element (4).

  15 to 17, it can be seen that any of the light-emitting elements operates well. In particular, in the light emitting elements (2) to (4) in which the molar ratio of NPB to molybdenum oxide (= NPB / molybdenum oxide) in the hole generating layer is 1 to 2, an arbitrary voltage is applied. It can be seen that the luminance obtained is high and the current value is large. Thus, by adjusting the molar ratio of NPB to molybdenum oxide (= NPB / molybdenum oxide) to be 1 to 2, a light-emitting element that operates at a low driving voltage can be obtained.

  Next, the results of performing a continuous lighting test on the light-emitting element of this example will be described. The continuous lighting test was performed as follows at normal temperature after sealing the light-emitting element manufactured as described above in a nitrogen atmosphere.

  As can be seen from FIG. 16, in the light emitting device of the present invention in the initial state, the current density necessary for emitting light with a luminance of 3000 cd / m 2 is 26.75 mA / cm 2. In this example, a current of 26.75 mA / cm 2 was kept flowing for a certain period of time, and a change with time of the voltage necessary to pass a current of 26.75 mA / cm 2 and a change with time of luminance were examined. The measurement results are shown in FIGS. In FIG. 18, the horizontal axis represents the elapsed time (hour), and the vertical axis represents the voltage (V) required to pass a current of 26.75 mA / cm 2. In FIG. 19, the horizontal axis represents elapsed time (hour), and the vertical axis represents luminance (arbitrary unit). Note that the luminance (arbitrary unit) is a relative value with respect to the initial luminance (value obtained by dividing the luminance at an arbitrary time by the initial luminance and multiplying by 100) with the initial luminance as 100.

  From FIG. 18, it can be seen that the voltage required to pass a current with a current density of 26.75 mA / cm 2 is only about 1 V higher than the initial state after 100 hours. From this, it can be seen that the light-emitting element of the present invention is a good element with little increase in voltage with time.

  In each of the light-emitting elements of Example 1 and Example 2, a layer that functions as a hole injection layer, a hole transport layer, an electron transport layer, or the like is formed in addition to a layer that functions as a light-emitting layer. However, these layers are not necessarily provided. Further, in both Example 1 and Example 2, after forming a layer that functions as a light emitting layer, a layer that generates electrons is formed, and then a layer that generates holes is formed. However, the manufacturing method of the light emitting element is not limited to this. For example, after forming a hole generating layer, an electron generating layer may be formed, and then a layer including a layer functioning as a light emitting layer may be formed.

FIG. 14 illustrates a light-emitting element of the present invention. FIG. 14 illustrates a light-emitting element of the present invention. FIG. 14 illustrates a light-emitting element of the present invention. FIG. 14 illustrates a light-emitting element of the present invention. The figure showing the creation process of the thin film light emitting element of this invention. The figure showing the creation process of the thin film light emitting element of this invention. The figure which illustrated the structure of the display apparatus. 2A and 2B are a top view and a cross-sectional view of a light-emitting device of the present invention. FIG. 10 illustrates an electronic device to which the present invention is applicable. The figure which illustrated the structure of the display apparatus. FIG. 14 illustrates an example of a pixel circuit of a display device. FIG. 11 illustrates an example of a protection circuit of a display device. 3 is a graph showing voltage-luminance characteristics of the element of Example 1. 3 is a graph showing voltage-current characteristics of the element of Example 1. 6 is a graph showing voltage-luminance characteristics of the element of Example 2. 6 is a graph showing current density-luminance characteristics of the element of Example 2. 6 is a graph showing voltage-current characteristics of the element of Example 2. 6 is a graph showing a change in voltage over time of the element of Example 2. 6 is a graph showing a change in luminance over time of the element of Example 2.

Explanation of symbols

100 Insulator 101 First Electrode 102 Layer 103 Layer 104 Light-Emitting Layer 105 Layer 106 Second Electrode 107 Layer 50 Substrate 51a Underlying Insulating Layer 51b Underlying Insulating Layer 52 Semiconductor Layer 53 Gate Insulating Layer 54 Gate Electrode 59 Insulating Film (Hydrogenated) film)
60 Interlayer insulating layer 61a Connection portion 61b Wiring 63 Interlayer insulating layer 65 Partition 66 Light emitting laminate 70 Thin film transistor 88 Resin 89 Desiccant 90 Polarizing plate 91 Protective film 93 Light emitting element 94 Counter substrate 900 Interlayer insulating layer 901 Thin film transistor 4001 Substrate 4002 Pixel unit 4003 Signal line driver circuit 4004 Scan line driver circuit 4005 Sealant 4006 Counter substrate 4007 Filler 4008 Thin film transistor 4010 Thin film transistor 4011 Light emitting element 4014 Wiring 4015a Wiring 4015b Wiring 4016 Connection terminal 4018 Flexible printed circuit (FPC)
4019 Anisotropic conductive film 2001 Case 2003 Display unit 2004 Speaker unit 2101 Main body 2102 Case 2103 Display unit 2104 Audio input unit 2105 Audio output unit 2106 Operation key 2108 Antenna 2201 Main body 2202 Case 2203 Display unit 2204 Keyboard 2205 External connection port 2206 Pointing mouse 2301 Main body 2302 Display unit 2303 Switch 2304 Operation key 2305 Infrared port 2401 Case 2402 Display unit 2403 Speaker unit 2404 Operation key 2405 Recording medium insertion unit 1401 Switching TFT
1402 Capacitor element 1403 Driving TFT
1404 Current control TFT
1405 Light Emitting Element 1406 TFT
1410 Signal line 1411 Power supply line 1412 Power supply line 1414 Scan line 1415 Scan line 1500 Pixel portion 1561 Diode 1554 Common potential line

Claims (3)

A first electrode, a second electrode, and a first layer to a fourth layer;
The first layer is in contact with the first electrode;
The second layer is in contact with the second electrode;
The third layer is sandwiched between the first electrode and the second electrode via the first layer and the second layer,
The fourth layer is in contact with the second layer and sandwiched between the third layer and the second layer;
The first layer and the second layer each include 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD), molybdenum oxide, The third layer includes a luminescent material;
Said fourth layer include tris (8-quinolinolato) aluminum (abbreviation: Alq ₃₎ and, seen containing lithium, a,
The light-emitting element does not contain 8-quinolinolato lithium (abbreviation: Liq) between the first electrode and the second electrode . A first electrode, a second electrode, and a first layer to a fourth layer;
The first layer is in contact with the first electrode;
The second layer is in contact with the second electrode;
The third layer is sandwiched between the first electrode and the second electrode via the first layer and the second layer,
The fourth layer is in contact with the second layer and sandwiched between the third layer and the second layer;
The first layer and the second layer are formed of a hole transporting material, molybdenum oxide, vanadium oxide, ruthenium oxide, cobalt oxide, nickel oxide, copper oxide, 7, 7, 8 , 8, -tetracyanoquinodimethane (abbreviation: TCNQ), 2,3-dicyanonaphthoquinone (abbreviation: DCNNQ) and 2,3,5,6-tetrafluoro-7,7,8,8, -tetracyanoquino Including any of dimethane (abbreviation: F4-TCNQ),
The third layer includes a luminescent material;
It said fourth layer is seen containing an electron transporting material, lithium, cesium, magnesium, calcium, erbium, ytterbium, zinc oxide, zinc sulfide, one of the zinc selenide and titanium oxide,
A light-emitting element which does not contain 8-quinolinolato lithium (abbreviation: Liq) between the first electrode and the second electrode .   A light-emitting device comprising the light-emitting element according to claim 1.