JP5201827B2 - Light emitting device - Google Patents

Description

The present invention relates to a configuration of a display device for increasing a contrast ratio.

Development of a so-called flat panel display, which is much thinner and lighter than conventional cathode-ray tubes, is being developed. Flat panel displays are competing with liquid crystal display devices with liquid crystal elements as display elements, display devices with self-luminous elements, FED (field emission display) using electron sources, etc. Therefore, low power consumption and high contrast are required.

In a general liquid crystal display device, one polarizing plate is provided on each substrate, and the contrast ratio is increased. By making the black display darker, the contrast ratio can be increased, and high display quality can be provided when an image is viewed in a dark room like a home theater.

For example, in order to increase the contrast ratio, a first polarizing plate is provided on the outside of the substrate on the viewing side of the liquid crystal cell, and a second polarizing plate is provided on the outside of the substrate opposite to the viewing side. When the light from the auxiliary light source is polarized through the second polarizing plate and passes through the liquid crystal cell, a configuration is proposed in which a third polarizing plate is provided to increase the degree of polarization (see Patent Document 1). As a result, it is possible to improve display non-uniformity and contrast ratio caused by insufficient polarization degree and polarization degree distribution of the polarizing plate.

As a flat panel display similar to a liquid crystal display device, there is a display device having an electroluminescence element. The electroluminescence element is a self-luminous element, can eliminate the need for light irradiation means such as a backlight, and can reduce the thickness of the display device. Furthermore, a display device having an electroluminescence element has advantages such as a faster response speed and less viewing angle dependency than a liquid crystal display device.

A configuration in which a polarizing plate and a circularly polarizing plate are provided is also proposed for a display device having such an electroluminescence element (see Patent Documents 2 and 3).

As a structure of a display device having an electroluminescent element, light emitted from a light emitting element sandwiched between light-transmitting substrates can be observed as light on the anode substrate side and light on the cathode substrate side. (See Patent Document 4).
International Publication No. 00/34821 Japanese Patent No. 2761453 Japanese Patent No. 3174367 JP-A-10-255976

However, the demand for increasing the contrast ratio is not limited to liquid crystal display devices, but is also required for display devices having electroluminescent elements. In particular, in the case of an electroluminescence element that can be observed from both sides of the display, a high contrast in a bright place such as under external light is required.

In view of the above problems, the present invention is characterized in that each of the light-transmitting substrates arranged so as to face each other has a plurality of polarizing plates. The plurality of polarizing plates can be a polarizing plate having a laminated structure.

The polarizing plates facing each other through the light-transmitting substrate are arranged so as to be crossed Nicols. In addition, the plurality of polarizing plates stacked on one side of the translucent substrate are arranged so as to be in parallel Nicols. Here, the crossed Nicol is an arrangement in which the transmission axes of the two polarizing plates are shifted by 90 °. Parallel Nicol is arranged such that the deviation between the transmission axes of the two polarizing plates is 0 °. An absorption axis is provided so as to be orthogonal to the transmission axis of the polarizing plate, and crossed Nicols and parallel Nicols are defined in the same manner even when the absorption axis is used.

According to another aspect of the display device of the present invention, the first light-transmitting substrate and the second light-transmitting substrate are disposed so as to face each other, and the first light-transmitting substrate is provided between the opposed substrates. A light emitting element that emits light in both directions of the substrate and the second translucent substrate, a stacked first linearly polarizing plate disposed outside the first translucent substrate, and the second And a laminated second linearly polarizing plate disposed outside the translucent substrate.

In another display device of the present invention, the first light-transmitting substrate and the second light-transmitting substrate are disposed so as to face each other, and are provided between the opposed substrates. A light-emitting element that emits light in both directions of the light-transmitting substrate and the second light-transmitting substrate; the stacked first linearly polarizing plates disposed outside the first light-transmitting substrate; A laminated second linearly polarizing plate disposed outside the second translucent substrate, and the transmission axes of the laminated first linearly polarizing plates are parallel Nicols It is set as the structure arrange | positioned so that the transmission axes of the laminated | stacked 2nd linear polarizing plate may become parallel Nicols.

In another display device of the present invention, the first light-transmitting substrate and the second light-transmitting substrate are disposed so as to face each other, and are provided between the opposed substrates. A light emitting element that emits light in both directions of the translucent substrate and the second translucent substrate, and a laminated first linear polarizing plate disposed outside the first translucent substrate, A laminated second linearly polarizing plate disposed outside the second translucent substrate, and the transmission axes of the laminated first linearly polarizing plates are parallel Nicols The transmission axes of the stacked second linear polarizing plates are arranged in parallel Nicols, the transmission axis of the stacked first linear polarizing plates, and the stacked second linear polarizing plates It is set as the structure arrange | positioned so that it may become crossed Nicol with the transmission axis of a linearly-polarizing plate.

In another display device of the present invention, the first light-transmitting substrate and the second light-transmitting substrate are disposed so as to face each other, and are provided between the opposed substrates. A light emitting element that emits light in both directions of the translucent substrate and the second translucent substrate, and a laminated first linear polarizing plate disposed outside the first translucent substrate, A second linearly polarizing plate disposed outside the second translucent substrate, and the transmission axes of the laminated first linearly polarizing plates are disposed so as to be parallel Nicols. The transmission axis of the laminated first linear polarizing plate and the transmission axis of the second linear polarizing plate are arranged to be crossed Nicols.

In the configuration of the present invention, the first linear polarizing plate or the second linear polarizing plate is configured such that the first linear polarizing plates or the second linear polarizing plates are in contact with each other. It may be.

Moreover, in the structure of this invention, a display element is a light emitting element. As a light emitting element, there are an element using electroluminescence (electroluminescence element), an element using plasma, and an element using field emission. An electroluminescence element can be distinguished from an organic EL element or an inorganic EL element depending on a material to be applied. A display device having such a light-emitting element is also referred to as a light-emitting device.

With a simple structure such as providing a plurality of polarizing plates, the contrast ratio of a display device having a light-emitting element can be increased.

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

(Embodiment 1)
In this embodiment mode, the concept of the display device of the present invention will be described. In this embodiment mode, description is made using an electroluminescence element as a light-emitting element.

As shown in FIG. 1, a layer 100 having an electroluminescent element is sandwiched between a first light-transmitting substrate 101 and a second light-transmitting substrate 102 which are arranged so as to face each other. 1A is a cross-sectional view of the display device of the present invention, and FIG. 1B is a perspective view of the display device of the present invention.

In FIG. 1B, light from the electroluminescent element can radiate light emitted to the first light-transmitting substrate 101 side and the second light-transmitting substrate 102 side (in the direction of the dotted arrow). is there. As the light-transmitting substrate, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, or the like can be used. In addition, a substrate formed of a plastic typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or a flexible synthetic resin such as acrylic can be used.

A stacked polarizing plate is provided on the outer side of the first light-transmitting substrate 101 and the second light-transmitting substrate 102, that is, on the side not in contact with the layer 100 having an electroluminescent element. Light emitted from the electroluminescence element is linearly polarized by the polarizing plate. That is, the laminated polarizing plate can be described as a laminated linearly polarizing plate. The laminated polarizing plate refers to a state in which two or more polarizing plates are laminated. In this embodiment, a display device in which two polarizing plates are stacked is illustrated, and the two polarizing plates to be stacked are stacked in contact with each other as illustrated in FIG.

A first polarizing plate (A) 111 and a second polarizing plate (A) 112 are sequentially provided on the outer side of the first light-transmitting substrate 101. The transmission axis (A) of the first polarizing plate (A) 111 and the transmission axis (A) of the second polarizing plate (A) 112 are arranged in parallel. That is, the first polarizing plate (A) 111 and the second polarizing plate (A) 112, that is, the stacked polarizing plates are arranged so that the transmission axes of the polarizing plates are parallel Nicols.

In addition, a first polarizing plate (B) 121 and a second polarizing plate (B) 122 are sequentially provided on the outer side of the second light-transmitting substrate 102. The transmission axis (B) of the first polarizing plate (B) 121 and the transmission axis (B) of the second polarizing plate (B) 122 are arranged in parallel. That is, the first polarizing plate (B) 121 and the second polarizing plate (B) 122, that is, the stacked polarizing plates are arranged so that the transmission axes of the polarizing plates are parallel Nicols.

Then, the transmission axis (A) of the stacked polarizing plates provided on the first light transmitting substrate 101 and the transmission axis (A) of the stacked polarizing plates provided on the second light transmitting substrate 102 are provided. It is characterized by being orthogonal to B). That is, the laminated polarizing plate (A) and the laminated polarizing plate (B), that is, the opposing polarizing plates are arranged so that the transmission axes of the polarizing plates form crossed Nicols.

These polarizing plates can be formed from a known material. For example, an adhesive surface, a TAC (triacetyl cellulose), a mixed layer of PVA (polyvinyl alcohol) and iodine, and a structure in which TAC are sequentially stacked are used from the substrate side. Can do. The degree of polarization can be controlled by a mixed layer of PVA (polyvinyl alcohol) and iodine. Moreover, a polarizing plate may be called a polarizing film from the shape.

Note that, due to the characteristics of the polarizing plate, there is an absorption axis in the direction orthogonal to the transmission axis. Therefore, even when the absorption axes are parallel to each other, it can be called parallel Nicol.

The stacked polarizing plates are stacked so that the transmission axes of the stacked polarizing plates are parallel Nicols, and the opposing polarizing plates are disposed so as to be crossed Nicols. By having such a laminated polarizing plate, light leakage can be reduced as compared with a configuration in which the polarizing plate single layers are simply arranged in crossed Nicols. For this reason, the contrast ratio of the display device can be increased.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 2)
In this embodiment mode, a concept of a display device using stacked polarizing plates and one polarizing plate will be described.

As shown in FIG. 2, a layer 100 having an electroluminescence element is sandwiched between a first light-transmitting substrate 101 and a second light-transmitting substrate 102 which are arranged so as to face each other. 2A is a cross-sectional view of the display device of the present invention, and FIG. 2B is a perspective view of the display device of the present invention.

In FIG. 2B, light from the electroluminescence element can emit light emitted from the first light-transmitting substrate 101 side and the second light-transmitting substrate 102 side (in the direction of the dotted arrow). is there. As the light-transmitting substrate, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, or the like can be used. In addition, a substrate made of a plastic such as polyethylene-terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or a synthetic resin having flexibility such as acrylic can be used.

On the outside of the first light-transmitting substrate 101 and the second light-transmitting substrate 102, that is, the side not in contact with the layer 100 having an electroluminescent element, a stacked polarizing plate and a single-layer polarizing plate are provided. ing. Light emitted from the electroluminescence element is linearly polarized by the polarizing plate. That is, the laminated polarizing plate can be described as a laminated linearly polarizing plate. The laminated polarizing plate refers to a state in which two or more polarizing plates are laminated. A single-layer polarizing plate refers to a state where one polarizing plate is provided. In this embodiment mode, a display device in which two polarizing plates are stacked on one side emitting light and a single-layer polarizing plate is provided on the other side emitting light is illustrated and stacked. The two polarizing plates are assumed to be in contact with each other as shown in FIG.

A first polarizing plate (A) 111 and a second polarizing plate (A) 112 are sequentially provided on the outer side of the first light-transmitting substrate 101. The transmission axis (A) of the first polarizing plate (A) 111 and the transmission axis (A) of the second polarizing plate (A) 112 are arranged in parallel. That is, the first polarizing plate (A) 111 and the second polarizing plate (A) 112, that is, the stacked polarizing plates are arranged so that the transmission axes of the polarizing plates are parallel Nicols.

A first polarizing plate (B) 121 is provided outside the second light-transmitting substrate 102.

Then, the transmission axis (A) of the stacked polarizing plates provided on the first light-transmitting substrate 101 and the transmission axis of the polarizing plate having a single layer structure provided on the second light-transmitting substrate 102. It is characterized by being orthogonal to (B). That is, the laminated polarizing plate (A) and the polarizing plate (B) having a single layer structure, that is, the opposing polarizing plates are arranged so that the transmission axes of the polarizing plates form crossed Nicols.

These polarizing plates can be formed from a known material. For example, an adhesive surface, a TAC (triacetyl cellulose), a mixed layer of PVA (polyvinyl alcohol) and iodine, and a structure in which TAC are sequentially stacked are used from the substrate side. Can do. The degree of polarization can be controlled by a mixed layer of PVA (polyvinyl alcohol) and iodine. Moreover, a polarizing plate may be called a polarizing film from the shape.

Note that, due to the characteristics of the polarizing plate, there is an absorption axis in the direction orthogonal to the transmission axis. Therefore, even when the absorption axes are parallel to each other, it can be called parallel Nicol.

Thus, among the polarizing plates arranged so as to face each other, a polarizing plate provided in one direction or the other direction is used as a laminated polarizing plate, and the transmission axes of the opposing polarizing plates are crossed Nicols. Also by arranging in this way, light leakage in the transmission axis direction can be reduced. As a result, the contrast ratio of the display device can be increased.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 3)
In this embodiment mode, a concept of a display device having a polarizing plate in which three or more polarizing plates are stacked by increasing the number of opposing polarizing plates will be described.

As shown in FIG. 3, a layer 100 having an electroluminescent element is sandwiched between a first light-transmitting substrate 101 and a second light-transmitting substrate 102 that are arranged to face each other. 3A is a cross-sectional view of the display device of the present invention, and FIG. 3B is a perspective view of the display device of the present invention.

In FIG. 3B, light emitted from the electroluminescent element can be emitted from the first light-transmitting substrate 101 side and the second light-transmitting substrate 102 side (in the direction of the dotted arrow). is there. As the light-transmitting substrate, for example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a quartz substrate, or the like can be used. In addition, a substrate formed of a plastic typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or a flexible synthetic resin such as acrylic can be used.

A stacked polarizing plate is provided on the outer side of the first light-transmitting substrate 101 and the second light-transmitting substrate 102, that is, on the side not in contact with the layer 100 having an electroluminescent element. Light emitted from the electroluminescence element is linearly polarized by the polarizing plate. That is, the laminated polarizing plate can be described as a laminated linearly polarizing plate. The laminated polarizing plate refers to a state in which two or more polarizing plates are laminated. In this embodiment mode, a display device in which three polarizing plates are stacked is illustrated, and the three polarizing plates to be stacked are stacked in contact with each other as illustrated in FIG. Of course, a configuration in which four or more polarizing plates are laminated may be used.

A first polarizing plate (A) 111, a second polarizing plate (A) 112, and a third polarizing plate (A) 113 are provided in this order on the outside of the first light-transmitting substrate 101. The transmission axis (A) of the first polarizing plate (A) 111, the transmission axis (A) of the second polarizing plate (A) 112, and the transmission axis (A) of the third polarizing plate (A) 113 Are arranged in parallel. That is, the first polarizing plate (A) 111, the second polarizing plate (A) 112, and the third polarizing plate (A) 113, that is, the stacked polarizing plates have a transmission axis of the polarizing plate of parallel Nicol. It is arranged to become.

In addition, a first polarizing plate (B) 121, a second polarizing plate (B) 122, and a third polarizing plate (B) 123 are provided in this order on the outer side of the second light transmitting substrate 102. The transmission axis (B) of the first polarizing plate (B) 121, the transmission axis (B) of the second polarizing plate (B) 122, and the transmission axis (B) of the third polarizing plate (B) 123 Arranged to be parallel. That is, the first polarizing plate (B) 121, the second polarizing plate (B) 122, and the third polarizing plate (B) 123, that is, the stacked polarizing plates have a transmission axis of the polarizing plate of parallel Nicol. It is arranged to become.

Then, the transmission axis (A) of the stacked polarizing plates provided on the first light transmitting substrate 101 and the transmission axis (A) of the stacked polarizing plates provided on the second light transmitting substrate 102 are provided. It is characterized by being orthogonal to B). That is, the laminated polarizing plate (A) and the laminated polarizing plate (B), that is, the opposing polarizing plates are arranged so that the transmission axes of the polarizing plates form crossed Nicols.

These polarizing plates can be formed from a known material. For example, an adhesive surface, a TAC (triacetyl cellulose), a mixed layer of PVA (polyvinyl alcohol) and iodine, and a structure in which TAC are sequentially stacked are used from the substrate side. Can do. The degree of polarization can be controlled by a mixed layer of PVA (polyvinyl alcohol) and iodine. Moreover, a polarizing plate may be called a polarizing film from the shape.

Note that, due to the characteristics of the polarizing plate, there is an absorption axis in the direction orthogonal to the transmission axis. Therefore, even when the absorption axes are parallel to each other, it can be called parallel Nicol.

As described above, the polarizing plates arranged so as to face each other are made into three or more laminated polarizing plates, and the transmission axes in the direction of the transmission axis are also arranged so that the transmission axes of the opposing polarizing plates are crossed Nicols. Light leakage can be reduced. As a result, the contrast ratio of the display device can be increased.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 4)
In this embodiment mode, a cross-sectional view of the display device of the present invention is illustrated with reference to FIG.

A thin film transistor is formed over a substrate (hereinafter referred to as an insulating substrate) 201 having an insulating surface with an insulating layer interposed therebetween. A thin film transistor (also referred to as a TFT) is connected to a semiconductor layer processed into a predetermined shape, a gate insulating layer covering the semiconductor layer, a gate electrode provided on the semiconductor layer through the gate insulating layer, and an impurity layer in the semiconductor layer Source electrode or drain electrode. The material used for the semiconductor layer is a semiconductor material containing silicon, and the crystalline state may be any of an amorphous state, a microcrystalline state, and a crystalline state. For the insulating layer typified by the gate insulating film, an inorganic material is preferably used, and silicon nitride or silicon oxide can be used. The gate electrode, the source electrode, or the drain electrode may be formed using a conductive material, and includes tungsten, tantalum, aluminum, titanium, silver, gold, molybdenum, copper, and the like. The display device can be broadly divided into a pixel portion 215 and a driver circuit portion 218. The thin film transistor 203 provided in the pixel portion 215 is used as a switching element, and the thin film transistor 204 provided in the driver circuit portion is used as a CMOS circuit. In order to be used as a CMOS circuit, it is composed of a P-channel TFT and an N-channel TFT. The thin film transistor 203 can be controlled by a CMOS circuit provided in the driver circuit portion 218.

An insulating layer having a stacked structure or a single layer structure is formed so as to cover the thin film transistor. The insulating layer can be formed from an inorganic material or an organic material. As the inorganic material, silicon nitride or silicon oxide can be used. As the organic material, polyimide, acrylic, polyamide, polyimide amide, resist, benzocyclobutene, siloxane, or polysilazane can be used. Siloxane has a skeletal structure composed of a bond of silicon (Si) and oxygen (O), and an organic group containing at least hydrogen (such as an alkyl group or aromatic hydrocarbon) is used as a substituent. A fluoro group may be used as a substituent. Alternatively, an organic group containing at least hydrogen and a fluoro group may be used as a substituent. Polysilazane is formed using a liquid material containing a polymer material having a bond of silicon (Si) and nitrogen (N) as a starting material. When formed using an inorganic material, the surface is in a state of following the unevenness on the lower side. When formed using an organic material, the surface is flattened. For example, in the case where flatness is required in the insulating layer 205, an organic material may be used. In addition, even if it is an inorganic material, flatness can be provided by thickening.

The source electrode or the drain electrode is manufactured by forming a conductive layer in an opening provided in the insulating layer 205 or the like. At this time, a conductive layer functioning as a wiring over the insulating layer 205 can be formed. The capacitor 214 can be formed using the conductive layer of the gate electrode, the insulating layer 205, and the conductive layer of the source or drain electrode.

Then, a first electrode 206 connected to any one of the source electrode and the drain electrode is formed. The first electrode 206 is formed using a light-transmitting material. Examples of the light-transmitting material include indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide added with gallium (GZO). Alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof (calcium fluoride, In addition to calcium nitride), even non-transparent materials such as rare earth metals such as Yb and Er can be made translucent by having a very thin film thickness. May be used for the first electrode 206.

An insulating layer 210 is formed so as to cover the end portion of the first electrode 206. The insulating layer 210 can be formed in a manner similar to that of the insulating layer 205. An opening is provided in the insulating layer 210 to cover the end portion of the first electrode 206. The end face of the opening may have a taper shape, and a layer formed thereafter can be prevented from being disconnected. For example, when a non-photosensitive resin or a photosensitive resin is used for the insulating layer 210, the side surface of the opening can be tapered depending on the exposure conditions.

Thereafter, an electroluminescent layer 207 is formed in the opening of the insulating layer 210. The electroluminescent layer has a layer having each function, specifically, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer. Moreover, the boundary of each layer is not necessarily clear, and some of them may be mixed.

As a specific example of the material for forming the light emitting layer, when red light emission is desired, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetra Methyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyljulolidine-9- Yl) ethenyl] -4H-pyran (abbreviation: DCJT), 4-dicyanomethylene-2-tert-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTB), periflanthene, 2,5-dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] Benze , Bis [2,3-bis (4-fluorophenyl) Kinokisarinaito] iridium (acetylacetonate) (abbreviation: Ir _[Fdpq] 2 acac), or the like can be used. However, the present invention is not limited to these materials, and a substance exhibiting light emission having an emission spectrum peak from 600 nm to 700 nm can be used.

When green light emission is desired, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), or the like is used for the light emitting layer. Can do. However, the present invention is not limited to these materials, and a substance exhibiting light emission having an emission spectrum peak from 500 nm to 600 nm can be used.

In order to obtain blue light emission, 9,10-bis (2-naphthyl) -tert-butylanthracene (abbreviation: t-BuDNA), 9,9′-bianthryl, 9,10-diphenyl is used in the light-emitting layer. Anthracene (abbreviation: DPA), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-gallium (abbreviation: BGaq), bis ( 2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq) or the like can be used. However, the present invention is not limited to these materials, and a substance exhibiting light emission having an emission spectrum peak from 400 nm to 500 nm can be used.

When white light emission is desired, TPD (aromatic diamine), 3- (4-tert-butylphenyl) -4-phenyl-5- (4-biphenylyl) -1,2,4-triazole (abbreviation) : TAZ), tris (8-quinolinolato) aluminum (abbreviation: _Alq 3), can be used a configuration in which laminated by the _Alq 3, Alq ₃ doped with Nile red which is a red light emitting pigment deposition method.

After that, the second electrode 208 is formed. The second electrode 208 can be formed in a manner similar to that of the first electrode 206. A light-emitting element 209 including the first electrode 206, the electroluminescent layer 207, and the second electrode 208 can be formed.

At this time, since the first electrode 206 and the second electrode 208 have a light-transmitting property, light can be emitted from the electroluminescent layer 207 in both directions. Such a display device capable of emitting light in both directions can be referred to as a dual emission type display device.

After that, the insulating substrate 201 and the counter substrate 220 are bonded to each other with the sealing material 228. In this embodiment, since the sealing material 228 is provided over part of the driver circuit portion 218, a narrow frame can be achieved. Needless to say, the arrangement of the sealing material 228 is not limited to this, and may be provided outside the drive circuit portion 218.

A space formed by the bonding is filled with an inert gas such as nitrogen or filled with a resin material having a light-transmitting property and a high hygroscopic property. As a result, intrusion of moisture or oxygen that is a cause of deterioration of the light-emitting element 209 can be prevented. In order to maintain a distance between the insulating substrate 201 and the counter substrate 220, a spacer may be provided or the spacer may be hygroscopic. The spacer has a spherical or columnar shape.

The counter substrate 220 can be provided with a color filter or a black matrix. The color filter enables full color display even when a monochromatic light emitting layer, for example, a white light emitting layer is used. Even when each of the RGB light emitting layers is used, by providing a color filter, the wavelength of the emitted light can be controlled and a beautiful display can be provided. Further, the black matrix can reduce reflection of external light due to wiring or the like.

Thereafter, the first polarizing plate (A) 216 and the second polarizing plate (A) 217 are formed outside the insulating substrate 201, and the first polarizing plate (B) 226 and the second polarizing plate are formed outside the counter substrate 220. A plate (B) 227 is provided. That is, stacked polarizing plates are provided on the outer sides of the insulating substrate 201 and the counter substrate 220, respectively. As a result, black can be sunk and the contrast ratio can be increased.

In this embodiment mode, the driving circuit portion is also formed integrally on the insulating substrate 201. However, the driving circuit portion may be an IC circuit formed from a silicon wafer. In that case, a video signal or the like from the IC circuit can be input to the switching thin film transistor 203 through a connection terminal or the like.

Note that although an active display device is described in this embodiment mode, a stacked polarizing plate can be provided even in a passive display device. As a result, the contrast ratio can be increased.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 5)
In this embodiment mode, a structure of a display device including a pixel portion and a driver circuit of the present invention will be described.

FIG. 5 is a block diagram illustrating a state where the scan line driver circuit 723 and the signal line driver circuit 722 are provided around the pixel portion 700.

The pixel portion 700 includes a plurality of pixels, and each pixel is provided with a light emitting element and a switching element.

The scan line driver circuit 723 includes a shift register 701, a level shifter 704, and a buffer 705. A signal is generated based on the start pulse (GSP) and the clock pulse (GCK) input to the shift register 701 and input to the buffer 705 via the level shifter 704. In the buffer 705, the signal is amplified and input to the pixel portion 700. The pixel portion 700 is provided with a light-emitting element and a switching element for selecting the light-emitting element, and a signal from the buffer 705 is input to a gate line included in the switching element. Then, a switching element of a predetermined pixel is selected.

The signal line driver circuit 722 includes a shift register 711, a first latch circuit 712, a second latch circuit 713, a level shifter 714, and a buffer 715. A start pulse (SSP) and a clock pulse (SCK) are input to the shift register 711, a data signal (DATA) is input to the first latch circuit 712, and a latch pulse (LAT) is input to the second latch circuit 713. ) Is entered. DATA is input to the second latch circuit 713 based on SSP and SCK. The second latch circuit 713 holds DATA for one row and inputs it to the pixel portion 700 all at once.

The signal line driver circuit 722, the scan line driver circuit 723, and the pixel portion 700 can be formed using semiconductor elements provided over the same substrate. For example, the thin film transistor can be formed using the thin film transistor provided over the insulating substrate described in the above embodiment mode.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 6)
In this embodiment, an equivalent circuit diagram of a pixel included in the display device is described with reference to FIGS.

FIG. 6A illustrates an example of an equivalent circuit diagram of a pixel. A signal line 6114, a power supply line 6115, a scanning line 6116, a light-emitting element 6113, transistors 6110 and 6111, and a capacitor element 6112 in an intersection region thereof. Have A video signal (also referred to as a video signal) is input to the signal line 6114 by a signal line driver circuit. The transistor 6110 can control supply of the potential of the video signal to the gate of the transistor 6111 in accordance with a selection signal input to the scan line 6116. The transistor 6111 can control supply of current to the light-emitting element 6113 in accordance with the potential of the video signal. The capacitor 6112 can hold a voltage between the gate and the source of the transistor 6111 (referred to as a gate-source voltage). Note that although the capacitor 6112 is illustrated in FIG. 6A, the capacitor 6112 is not necessarily provided when it can be covered by the gate capacitance of the transistor 6111 or other parasitic capacitance.

FIG. 6B is an equivalent circuit diagram of a pixel in which a transistor 6118 and a scan line 6119 are newly provided in the pixel illustrated in FIG. The transistor 6118 can make the gate and the source of the transistor 6111 have the same potential and can forcibly prevent a current from flowing to the light-emitting element 6113; The length of the period can be shortened.

FIG. 6C is an equivalent circuit diagram of a pixel in which a transistor 6125 and a wiring 6126 are newly provided in the pixel illustrated in FIG. The potential of the gate of the transistor 6125 is fixed by the wiring 6126. The transistor 6111 and the transistor 6125 are connected in series between the power supply line 6115 and the light-emitting element 6113. Therefore, in FIG. 6C, the value of the current supplied to the light-emitting element 6113 is controlled by the transistor 6125, and the presence or absence of the current supplied to the light-emitting element 6113 can be controlled by the transistor 6111.

Note that the pixel circuit included in the display device of the present invention is not limited to the structure shown in this embodiment mode. For example, the pixel circuit having a current mirror may be configured to perform analog gradation display.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

(Embodiment 7)
As electronic devices according to the present invention, portable information such as a television device (also simply referred to as a television or a television receiver), a digital camera, a digital video camera, a cellular phone device (also simply referred to as a cellular phone or a cellular phone), a PDA Examples include a terminal, a portable game machine, a computer monitor, a computer, an audio playback device such as a car audio, and an image playback device equipped with a recording medium such as a home game machine. A specific example will be described with reference to FIG.

A portable information terminal device illustrated in FIG. 7A includes a main body 9201, a display portion 9202, and the like. The display device of the present invention can be applied to the display portion 9202. As a result, a portable information terminal device with a high contrast ratio can be provided.

A digital video camera shown in FIG. 7B includes a display portion 9701, a display portion 9702, and the like. The display device of the present invention can be applied to the display portion 9701. As a result, a digital video camera with a high contrast ratio can be provided.

A cellular phone shown in FIG. 7C includes a main body 9101, a display portion 9102, and the like. The display device of the present invention can be applied to the display portion 9102. As a result, a mobile phone with a high contrast ratio can be provided.

A portable television device illustrated in FIG. 7D includes a main body 9301, a display portion 9302, and the like. The display device of the present invention can be applied to the display portion 9302. As a result, a portable television device with a high contrast ratio can be provided. In addition, the present invention can be applied to a wide variety of television devices, from a small one mounted on a portable terminal such as a cellular phone to a medium-sized one that can be carried and a large one (for example, 40 inches or more). The display device can be applied.

A portable computer illustrated in FIG. 7E includes a main body 9401, a display portion 9402, and the like. The display device of the present invention can be applied to the display portion 9402. As a result, a portable computer with a high contrast ratio can be provided.

A television device illustrated in FIG. 7F includes a main body 9501, a display portion 9502, and the like. The display device of the present invention can be applied to the display portion 9502. As a result, a television device with a high contrast ratio can be provided.

As described above, the display device of the present invention can provide an electronic device with a high contrast ratio.

  Note that this embodiment mode can be freely combined with the description in other embodiment modes and embodiments in this specification.

In this example, the result of optical calculation using stacked polarizing plates will be described. The contrast ratio was the ratio of white transmittance to black transmittance (white transmittance / black transmittance), and the black transmittance and white transmittance were calculated to calculate the contrast ratio.

An optical system of black transmittance is shown in FIG. Since the black display in the electroluminescent element is a non-light emitting state, the first light transmitting substrate and the second light transmitting substrate including the light emitting layer of the electroluminescent element are not provided between the polarizing plate crossed Nicols. In addition, a backlight is disposed instead of the external light on the side where the external light is incident in the non-light emitting state. As for the arrangement of the transmission axes of the polarizing plates, the transmission axes of the opposing polarizing plates shown in FIG. 8 are arranged in a crossed Nicols arrangement, and the polarizing plates to be laminated are parallel Nicols. In the optical system arranged in this way, the light transmittance from the backlight on the viewing side opposite to the backlight was calculated as the black transmittance. At this time, the calculation was performed by changing the number of polarizing plates to be laminated.

An optical system of white transmittance is shown in FIG. A backlight was used instead of light emission from the electroluminescence element. Therefore, as shown in FIG. 9, the polarizing plate was not disposed in crossed Nicols, but was disposed on the backlight. The polarizing plate to be laminated was parallel Nicol. In the optical system thus arranged, the transmittance for the backlight on the viewing side opposite to the backlight was calculated as the white transmittance. At this time, the calculation was performed by changing the number of polarizing plates.

The calculation in this example uses an optical calculation simulator LCD MASTER (manufactured by Shintech Co., Ltd.) for liquid crystal. When calculating the transmittance with respect to the wavelength using the LCD MASTER, the 2 × 2 matrix optical calculation algorithm that does not consider multiple interference between elements is used, and the light source wavelength is set at 10 nm intervals from 380 nm to 780 nm. Asked. When the refractive index n is n = n ′ + in ″, the polarizing plate has n ′ = n ′ and n ″ = 3.22e−5 at the wavelength of 550 nm, respectively. A polarizing plate in which n ′ and n ″ of the absorption axis are n ′ = 1.5 and n ″ = 2.21e-3, respectively, was used, and the thickness of the polarizing plate was 180 μm. In addition, a D65 light source was used as the backlight, and the polarization state was set to mixed circular polarization.

FIG. 10 shows the calculation result of the contrast ratio when the number of polarizing plates is changed. BL \ 2 × 1 in the figure represents the calculation of black transmittance when the number of polarizing plates on the backlight (BL) side is two and the number of polarizing plates on the viewing side is one in FIG. It means that you are using the result. Similarly, BL \ 1 × 1, BL \ 2 × 2, BL \ 1 × 2, BL \ 3 × 1, etc. mean the number of backlights, the number of polarizing plates on the backlight side, and the number of polarizing plates on the viewing side. .

Further, the white transmittance when indicated as BL \ 2 × 1 in the figure means that the calculation result of one polarizing plate in FIG. 9 is used, and the last number is white. The number of polarizing plates for transmittance is shown. Similarly, for BL \ 1 × 1, BL \ 2 × 2, BL \ 1 × 2, BL \ 3 × 1, etc., the last number indicates the number of polarizing plates with white transmittance.

The contrast (white transmittance / black transmittance) of the white transmittance that is the transmittance of the sample arranged as shown in FIG. 9 and the black transmittance that is the transmittance of the sample arranged as shown in FIG. Calculations were made considering the ratio.

FIG. 10A shows that the contrast ratio increases as the number of polarizing plates increases by one on each side. Further, FIG. 10B shows that the contrast ratio increases even if the number of polarizing plates is increased by one on one side. Compared to the case where the number of all polarizing plates is the same and the number of polarizing plates on either the backlight side or the viewing side is different, such as BL \ 1 × 2, BL \ 2 × 1, the black transmittance is the same, but white The transmittance is higher when the number of viewing side polarizing plates is smaller. For this reason, the contrast ratio increases as the number of viewing-side polarizing plates decreases. From FIG. 10C, when the total number of polarizing plates is the same, such as BL \ 2 × 2, BL \ 3 × 1, the contrast ratio is larger when the number of polarizing plates on each side is two or more.

From the above results, by arranging the transmission axes of the polarizing plates to be stacked to be parallel Nicols, light leakage can be reduced, so that the contrast ratio can be improved. When the number of polarizing plates is an odd number, it can be seen that the smaller the number of polarizing plates on the viewing side, the greater the contrast ratio. When the number of polarizing plates is equal, the contrast ratio becomes larger when the number of polarizing plates on each side is two or more.

In this example, the results of an experiment conducted in the case of increasing the number of polarizing plates on both sides in the contents of the optical calculation of Example 1 will be described.

FIG. 11 shows a measurement system in actual measurement. As shown in FIG. 11, a polarizing plate 1102 was placed on a backlight 1101, and transmitted light was measured with a color luminance meter 1103 (BM-5A manufactured by Topcon Technohouse).

As shown in FIG. 8, in the optical system for measuring black luminance, two pairs of polarizing plates opposed to the backlight were arranged in a crossed Nicol arrangement, and the transmission axes of the laminated polarizing plates were arranged in a parallel Nicol arrangement. Then, the luminance when the transmitted light intensity on the viewing side when the number of polarizing plates is changed is measured with a color luminance meter is defined as black luminance.

An optical system for measuring white luminance is shown in FIG. The polarizing plate transmission axis laminated on the backlight is arranged in parallel Nicols, and the luminance when the transmitted light intensity on the viewing side when the number of polarizing plates is changed is measured with a color luminance meter is defined as white luminance. The ratio between white luminance and black luminance (white luminance / black luminance) was calculated as the contrast ratio.

The polarizing plate used was NPF-EG1425DU (Nitto Denko). At this time, the polarizing plate was laminated in a state of being attached to the glass substrate. Note that the transmittance of the glass substrate is high and does not affect the results of this experiment.

FIG. 12A shows the measurement result of white luminance, FIG. 12B shows the measurement result of black luminance, and FIG. 12C shows the result of contrast ratio. In FIG. 12A, BL \ 2 means that two polarizing plate transmission axes are arranged in parallel on the backlight (BL). In FIGS. 12B and 12C, BL \ 2 × 2 has two polarizing plates (numbers in the foreground) arranged in parallel Nicol on the backlight (BL), and two opposing polarizing plates (at the end) Numbers) also indicate that the polarizing plates to be laminated are arranged in parallel Nicols, and the polarizing plates facing the backlight-side polarizing plates are arranged in crossed Nicols. Therefore, the white luminance calculated in FIG. 12C uses the result when the number of polarizing plates is the last number.

From FIG. 12A, the white luminance gradually decreases as the number of polarizing plates increases by one. On the other hand, the black luminance shown in FIG. 12B decreases sharply as the number of polarizing plates increases from BL \ 1 × 1 to BL \ 2 × 2, and BL \ 3 × 3 and BL \ 4 × 4 are Compared with BL \ 2 × 2, the brightness was slightly reduced, but almost the same result was obtained. Therefore, as shown in FIG. 12 (C), the contrast ratio is higher when the number of polarizing plates is increased to BL \ 2 × 2, BL \ 3 × 3, BL \ 4 × 4 than BL \ 1 × 1. I understood. However, in the case of BL \ 4 × 4, the reduction ratio of black luminance was smaller than the reduction ratio of white luminance compared to BL \ 3 × 3, so the contrast ratio was low.

That is, when comparing FIG. 12A and FIG. 12B, the decrease in black luminance is much more significant than the decrease in white luminance caused by stacking a plurality of polarizing plates. large. Therefore, as shown in FIG. 12C, the contrast ratio is higher in the configuration in which a plurality of polarizing plates are provided. This result was different from the expectation that the use of a plurality of polarizing plates reduces both the white luminance and the black luminance, and there is no significant difference in the increase or decrease of the contrast ratio. In the present invention, the difference between the decrease in white luminance and black luminance due to the provision of the plurality of polarizing plates is extremely large, and as a result, the contrast ratio can be increased.

From the above, it can be seen that the contrast ratio increases as the number of polarizing plates increases on each side. However, in BL \ 3 × 3 and BL \ 4 × 4, the contrast ratio of BL \ 3 × 3 is higher, so it can be said that the contrast ratio is saturated when three polarizing plates are provided on both sides.

When the polarizing plates facing each other are crossed Nicols, the polarizing plates having a single layer structure are arranged so as to be crossed Nicols by arranging the transmission axes of the polarizing plates to be parallel Nicols. Light leakage can be reduced compared to a polarizing plate. As a result, the contrast ratio of the light emitting device can be increased. The number of laminated polarizing plates is preferably three.

It is the figure which showed the display apparatus of this invention It is the figure which showed the display apparatus of this invention It is the figure which showed the display apparatus of this invention It is the figure which showed the display apparatus of this invention It is the block diagram which showed the display apparatus of this invention FIG. 6 is a diagram illustrating a pixel circuit included in a display device of the present invention. It is the figure which showed the electronic device of this invention It is the figure which showed the measurement system of the black transmittance of the example It is the figure which showed the measurement system of the white transmittance of the example It is the figure which showed the measurement result of Example 1. It is the figure which showed the measurement system of Example 2. It is the figure which showed the measurement result of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Layer 101 with electroluminescent element 1st translucent board | substrate 102 2nd translucent board | substrate 111 1st polarizing plate (A)
112 Second polarizing plate (A)
113 Third polarizing plate (A)
121 First polarizing plate (B)
122 Second polarizing plate (B)
123 Third polarizing plate (B)
201 Insulating substrate 203 Thin film transistor 204 Thin film transistor 205 Insulating layer 206 Electrode 207 Electroluminescent layer 208 Electrode 209 Light emitting element 210 Insulating layer 214 Capacitor element 215 Pixel portion 216 First polarizing plate (A)
217 Second polarizing plate (A)
218 Drive circuit unit 220 Counter substrate 226 First polarizing plate (B)
227 Second polarizing plate (B)
228 Sealant 700 Pixel portion 701 Shift register 704 Level shifter 705 Buffer 711 Shift register 712 Latch circuit 713 Latch circuit 714 Level shifter 715 Buffer 722 Signal line driver circuit 723 Scan line driver circuit 1101 Backlight 1102 Polarizer 1103 Color luminance meter 6110 Transistor 6111 Transistor 6112 Capacitor element 6113 Light emitting element 6114 Signal line 6115 Power line 6116 Scan line 6118 Transistor 6119 Scan line 6125 Transistor 6126 Wiring 9101 Main body 9102 Display portion 9201 Main body 9202 Display portion 9301 Main body 9302 Display portion 9401 Main body 9402 Display portion 9501 Main body 9502 Display portion 9701 Display unit 9702 Display unit

Claims (2)

A first linear polarizing plate;
A second linear polarizer on the first linear polarizer;
A third linear polarizer on the second linear polarizer;
A first translucent substrate on the third linearly polarizing plate;
A light emitting element on the first translucent substrate;
A second translucent substrate on the light emitting element;
A fourth linearly polarizing plate on the second translucent substrate;
A fifth linear polarizer on the fourth linear polarizer;
A sixth linear polarizing plate on the fifth linear polarizing plate,
The transmission axis of the first linear polarizing plate and the transmission axis of the second linear polarizing plate are arranged to be parallel Nicols,
The transmission axis of the second linear polarizing plate and the transmission axis of the third linear polarizing plate are arranged to be parallel Nicols,
The transmission axis of the third linearly polarizing plate and the transmission axis of the fourth linearly polarizing plate are arranged to be crossed Nicols,
The transmission axis of the fourth linearly polarizing plate and the transmission axis of the fifth linearly polarizing plate are arranged to be parallel Nicols,
The light emitting device, wherein the transmission axis of the fifth linearly polarizing plate and the transmission axis of the sixth linearly polarizing plate are arranged in parallel Nicols. Oite to claim 1,
A light-emitting device comprising a spacer having a hygroscopic property between the first light-transmitting substrate and the second light-transmitting substrate.

Images