JP2005242323A - Display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device, its driving method and an element substrate that can make high in image quality and can improve deterioration of a light emitting element. <P>SOLUTION: Provided is a display device which has a plurality of pixels arranged in matrix and is characterized in that the plurality of pixels each have a light emitting element, a transistor, and a bypass element for AC driving, the light emitting element and transistor are connected in series, and the bypass element for AC driving and transistor are connected in parallel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a display device having a self-luminous element and a driving method thereof. The present invention also relates to an element substrate having elements on an insulating surface.

In recent years, research and development of a display device having a self-luminous element typified by an EL (Electro Luminescence) element has been advanced, and the thinness due to the high image quality, wide viewing angle, and no need for a backlight due to the self-luminous type. Utilizing advantages such as light weight, it is expected to be widely used. In general, the value of current flowing through the EL element and the luminance of the EL element are in a proportional relationship. For this reason, a pixel configuration that is different from that of an LCD that controls luminance with a voltage value has been proposed. For example, a pixel configuration that controls luminance with a current value has been proposed (see Patent Document 1).
International Publication No. 01/06484 Pamphlet

  As an example of the defect of the light emitting element, there is a defect in which a short portion is generated between both electrodes of the light emitting element. This defect is due to dust, protrusions, etc. on the pixel electrode during the formation of the light emitting element, resulting in a defect in the formation of the electroluminescent layer, and the two electrodes of the light emitting element contacting each other without going through the electroluminescent layer. Caused by. As described above, when a short-circuit portion is generated between both electrodes of the light-emitting element, current flows through the entire surface of the light-emitting element in a state where a forward bias is applied to the light-emitting element. A current that passes between the electrodes flows. The current that flows through the short circuit does not contribute to light emission.

  In addition, as an example of a defect in a light-emitting element, a defect in which the thickness of the electroluminescent layer becomes thin due to adhesion of dust or the like in the light-emitting element deposition process can be given. In this case, although light is emitted in the initial stage, the portion with a small film thickness is more stressed than the peripheral portion, and eventually a defect similar to the short portion described above occurs. This defect may not be dealt with by the initial aging process or the like because it is a progressive defect with the actual driving time.

  In view of the above circumstances, it is an object of the present invention to provide a display device that can realize high image quality and can improve deterioration of a light-emitting element, a driving method thereof, and an element substrate.

  As a method for solving the above-described problems of the prior art, the present invention uses a method of applying a reverse bias to the light emitting element as one means for improving the reliability of the light emitting element. When a reverse bias is applied to the light emitting element, the light emitting element has a rectifying property like a diode as an electrical characteristic. Therefore, although current does not flow in the reverse direction, current flows through the short-circuited portion. Therefore, repair that burns out the short-circuited portion can be performed by supplying current in a concentrated manner.

  The display device of the present invention includes a plurality of pixels arranged in a matrix, and each of the plurality of pixels includes a light emitting element, a transistor, and an AC drive bypass element, and the light emitting element and the transistor Are connected in series, and the AC drive bypass element and the transistor are connected in parallel.

  The display device includes a current source, and the transistor outputs a current depending on a magnitude of a signal current supplied from the current source to the light emitting element.

  The display device of the present invention includes a plurality of pixels arranged in a matrix, and each of the plurality of pixels includes a light emitting element, a first transistor, a second transistor, a third transistor, a fourth transistor, It has a storage capacitor element and an AC drive bypass element.

  The gate terminal of the third transistor is connected to a third wiring, one of the source and drain terminals of the third transistor is connected to the first wiring, and the other is the gate terminal of the second transistor. One of the source and drain terminals of the second transistor is connected to the second wiring, the other is connected to the gate terminal of the second transistor, and the gate terminal of the fourth transistor is the fourth terminal. One of the source and drain terminals of the fourth transistor is connected to the gate terminal of the second transistor, and the other is connected to the gate terminal of the first transistor. One of the source / drain terminals of the light-emitting element is connected to the second wiring, the other is connected to the first electrode of the light-emitting element, and the second electrode of the light-emitting element is connected to the counter power source, One terminal of the storage capacitor element is connected to the second wiring, the other terminal is connected to the gate terminal of the first transistor, and one terminal of the AC drive bypass element is connected to the second wiring. The other is connected to the first electrode of the light emitting element.

  The gate terminal of the third transistor is connected to a third wiring, one of the source / drain terminals of the third transistor is connected to the first wiring, and the other is connected to the source / drain of the second transistor. Connected to one of the drain terminals, the other of the source and drain terminals of the second transistor is connected to a second wiring, the gate terminal of the fourth transistor is connected to a fourth wiring, and One of the source and drain terminals of the transistor 4 is connected to a connection point between one of the source and drain terminals of the second transistor and one of the source and drain terminals of the third transistor, and the other is connected to the first transistor. One of the source and drain terminals of the first transistor is connected to the connection point between the gate terminal of the transistor and the gate terminal of the second transistor. The other electrode is connected to the first electrode of the light emitting element, the second electrode of the light emitting element is connected to a counter power source, and one terminal of the storage capacitor element is connected to the second wiring. The other is connected to the gate terminal of the first transistor, one terminal of the AC driving bypass element is connected to the second wiring, and the other is connected to the first electrode of the light emitting element. And

  Further, the AC drive bypass element is a diode, a transistor having a gate terminal and a drain terminal connected to each other.

  The light-emitting element is characterized in that one of the first electrode and the second electrode has a light-transmitting property and the other has a reflecting property. In addition, the first electrode and the second electrode of the light-emitting element have a light-transmitting property.

  In addition, the present invention provides an element substrate in a state where the pixel electrode of the light emitting element is formed in the display device having the above structure. More specifically, the element substrate is a state where a transistor and a pixel electrode connected to the transistor are formed on an insulating surface, and corresponds to a state where an electroluminescent layer and a counter electrode are not formed.

  The present invention having the above structure can provide a display device which can suppress the influence due to the characteristic variation of the transistor, in particular, the influence due to the characteristic variation of the driving TFT and realize high image quality. In addition, deterioration of the light-emitting element can be improved and a highly reliable display device can be provided.

  Embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below. Note that in the structures of the present invention described below, the same reference numerals are used in common in different drawings.

  The structure of the display device of the present invention will be described. In the display device of the present invention, a plurality of source lines S1 to S1 (l is a natural number) from which signals are output from the source driver circuit 402, and first gate lines Ga1 to Ga1 to which signals are output from the first gate driver circuit 403. The display area 401 includes Gam (m is a natural number) and second gate lines Gb1 to Gbn (n is a natural number) from which signals are output from the second gate driving circuit 404 (see FIG. 4). . The display region 401 includes a source line Sx (x is a natural number, 1 ≦ x ≦ l), a first gate line Gy (y is a natural number, 1 ≦ y ≦ m), and a second gate line Gz (z is a natural number). 1 ≦ z ≦ n) includes a plurality of pixels 400 including a plurality of elements in a region intersecting with an insulator.

The pixel 400 includes a light emitting element 113, a switching TFT 103, a holding TFT 104, a driving TFT 101, a conversion TFT 102, an AC driving bypass element 115, and a holding capacitor 112 (see FIG. 1).
The gate electrode of the switching TFT 103 is connected to the first gate line 107, one of the source electrode and the drain electrode is connected to the source line 105, and the other is connected to the gate electrode of the conversion TFT 102. One of the source electrode and the drain electrode of the conversion TFT 102 is connected to the power supply line 110 and the other is connected to the gate electrode of the conversion TFT 102. The gate electrode of the holding TFT 104 is connected to the second gate line 108, one of the source electrode and the drain electrode is connected to the gate electrode of the conversion TFT 102, and the other is connected to the gate electrode of the driving TFT 101. One of the source electrode and the drain electrode of the driving TFT 101 is connected to the power supply line 110, and the other is connected to the first electrode of the light emitting element 113. Further, the second electrode of the light emitting element 113 is connected to the second power source 114. The storage capacitor 112 is connected between the gate electrode of the driving TFT 101 and the power supply line 110, and the AC driving bypass element 115 is connected between the first electrode of the light emitting element 113 and the power supply line 110. A current source 106 controlled in accordance with luminance information is connected to the source line 105, and a first power source 111 is connected to the power line 110.

  The conductivity type of the switching TFT 103 and the holding TFT 104 is not limited, and may be either N-type or P-type. Further, the conductivity types of the driving TFT 101 and the conversion TFT 102 are not limited, but both must be the same conductivity type. If the polarity of the light-emitting element 113 is the forward direction in which current flows from the first electrode to the second electrode, it is desirable that the driving TFT 101 and the conversion TFT 102 be P-type as shown in FIG. In the case where the current flows from the second electrode to the first electrode in the forward direction, the driving TFT 101 and the conversion TFT 102 are desirably N-type.

  The AC drive bypass element 115 may be turned off when a forward bias is applied to the light emitting element 113 and may be turned on when a reverse bias is applied to the light emitting element 113. For example, as shown in FIG. 2A, the diode 201 may be configured, and the diode 201 may have any configuration. Further, a transistor 202 having a diode connection (a gate terminal and a drain terminal are connected) as shown in FIG. 2B may be used, or a PN junction diode, a PIN junction diode, or the like may be used. Further, a TFT 203 may be used as shown in FIG. The gate terminal of the TFT 203 may be controlled from the outside of the pixel 400 by the control line 204 and may be turned on only when a reverse bias is applied to the light emitting element 113.

  An operation of the pixel 400 illustrated in FIG. 1 will be described. The operation of the pixel 400 can be divided into a programming period, a light emission period, and a reverse bias application period (see FIG. 3). First, in the programming period shown in FIG. 3A, an H level signal is input to the first gate line 107 and the second gate line 108, the switching TFT 103 and the holding TFT 104 are turned on, and the current source 106 By connecting the conversion TFT 102, a signal current Idata corresponding to the luminance information flows between the source and drain of the conversion TFT 102. At this time, since the gate electrode and the drain electrode of the conversion TFT 102 are connected to each other, the conversion TFT 102 operates in a saturation region, and the gate / drain necessary for the signal current Idata to flow between the source and drain of the conversion TFT 102. A source-to-source voltage is stored in the storage capacitor 112. Thereafter, an L level signal is input to the first gate line 107 and the second gate line 108, the switching TFT 103 and the holding TFT 104 are turned off, the programming period ends, and the light emission period starts. At this time, it is preferable that an L level signal is output to the second gate line 108 before the first gate line 107 and the holding TFT 104 is turned off before the switching TFT 103.

  In the light emission period shown in FIG. 3B, a current Idriv is supplied to the light emitting element 113 by the driving TFT 101 in accordance with the potential difference stored in the storage capacitor 112 in the programming period. However, it is necessary to control the second power supply 114 so that the driving TFT 101 operates in a saturation region. At this time, if the mobility and threshold value of the driving TFT 101 and the conversion TFT 102 are the same, the current value Idriv supplied to the light emitting element 113 is the signal current Idata, the channel width of the driving TFT 101 and the conversion TFT 102. The channel length of the driving TFT 101 is L1, the channel width is W1, the channel length of the conversion TFT 102 is L2, and the channel width is W2. It is represented by (1).

  Idriv = (W1 / L1) / (W2 / L2) · Idata (1)

  As described above, even if the TFT characteristics vary among the pixels 400 in the display region 401, each of the adjacent TFTs (the driving TFT 101 and the conversion TFT 102) has no variation in mobility and threshold value. Since the current supplied to the light emitting element of the pixel 400 depends only on the signal current Idata supplied from the current source 106, high-quality display without variation in light emission luminance is possible.

  Next, in the reverse bias application period shown in FIG. 3C, the relationship between the potentials of the first power supply 111 and the second power supply 114 is reversed from the programming period and the light emission period. In the programming period and the light emission period, the potential of the first power supply 111 is higher than that of the second power supply 114, the light emitting element 113 is forward-biased, and no current flows through the AC drive bypass element 115. To do. On the other hand, in the reverse bias application period, the potential of the second power source 114 is set higher than that of the first power source 111, and the AC drive bypass element 115 is turned on, whereby a reverse bias is applied to the light emitting element 113. Normally, no current flows even if a bias is applied in the reverse direction in the light emitting element 113, but when there is a short part in the light emitting element 113, the current concentrates in the short part, so the short part is burned out and the light emitting element 113 Deterioration can be reduced and reliability can be increased. In the present invention, not only the initial short-circuited portion but also the progressive short-circuited portion can be burned out, so that deterioration of the light emitting element 113 can be reduced and reliability can be improved.

  Although this embodiment has been described using the circuit configuration of the pixel illustrated in FIG. 1 as a representative example, the circuit configuration is not limited to that illustrated in FIG. For example, the connection position of the holding TFT 104 may be changed as shown in FIG.

  In the present invention having the above-described configuration, the AC driving bypass element 115 connected in parallel to the driving TFT 101 for supplying current to the light emitting element 113 is provided, so that the reverse bias application period is different from the light emitting period. Apply directional bias. When there is a short-circuited portion in the light emitting element, current can easily flow through the short-circuited portion, and the short-circuited portion can be easily burned out. In addition, the present invention can provide a display device with high image quality and high reliability regardless of TFT variations.

  A structure of a light emitting element which is a constituent element of the present invention will be described. The light-emitting element corresponds to a stacked body of a conductive layer, an electroluminescent layer, and a conductive layer provided over one surface of a substrate having an insulating surface such as glass, quartz, metal, or an organic substance. The light emitting element may be any of a stacked type in which the electroluminescent layer is composed of a plurality of layers, a single layer type in which the electroluminescent layer is composed of one layer, and a mixed type in which the electroluminescent layer is composed of a plurality of layers but the boundary is not clear. Good. In addition, the laminated structure of the light emitting element includes a stacked structure in which a conductive layer corresponding to the anode from the bottom \ electroluminescent layer \ conductive layer corresponding to the cathode is stacked, and a conductive layer corresponding to the cathode from the bottom \ electroluminescent layer \ anode. Although there is a reverse stacking structure in which conductive layers corresponding to the above are stacked, an appropriate structure may be selected according to the direction of light emission.

  The electroluminescent layer is formed of a charge injecting and transporting material containing an organic compound or an inorganic compound and a light emitting material. From the number of molecules thereof, a low molecular weight organic compound or a medium molecular weight organic compound (having no sublimation property and having a molecular number of 20 or less, or an organic compound having a chain molecule length of 10 μm or less), including one or a plurality of layers selected from high molecular weight organic compounds, and having an electron injection / transport property or a hole injection / transport property You may combine with an inorganic compound.

Among the charge injecting and transporting materials, materials having a particularly high electron transporting property include, for example, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (5-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), Bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), quinoline skeleton or benzoquinoline Examples thereof include metal complexes having a skeleton. As a substance having a high hole-transport property, for example, 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD), 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) (ie, benzene ring-nitrogen) And a compound having a bond of

Among the charge injecting and transporting materials, materials having particularly high electron injecting properties include alkali metals or alkaline earths such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ) and the like. Metal compounds can be mentioned. In addition, a mixture of a substance having a high electron transport property such as Alq ₃ and an alkaline earth metal such as magnesium (Mg) may be used.

In a low molecular weight organic light emitting material, 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 (abbreviation: DPA), 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-diphenylanthracene (abbreviation: DPA) and 9,10-bis (2-naphthyl) anthra Sen (abbreviation: DNA) or the like can be used. Other substances may also be used.

On the other hand, the high molecular organic light emitting material has higher physical strength than the low molecular weight material, and the durability of the device is high. In addition, since the film can be formed by coating, the device can be manufactured relatively easily. The structure of the light emitting element using the high molecular weight organic light emitting material is basically the same as that when the low molecular weight organic light emitting material is used, and is cathode / organic light emitting layer / anode. However, when forming a light emitting layer using a high molecular weight organic light emitting material, it is difficult to form a laminated structure as in the case of using a low molecular weight organic light emitting material. . Specifically, the structure is cathode / light-emitting layer / hole transport layer / anode.

  Since the light emission color is determined by the material for forming the light emitting layer, a light emitting element exhibiting desired light emission can be formed by selecting these materials. Examples of the polymer electroluminescent material that can be used for forming the light emitting layer include polyparaphenylene vinylene, polyparaphenylene, polythiophene, and polyfluorene.

  Examples of the polyparaphenylene vinylene include poly (paraphenylene vinylene) [PPV] derivatives, poly (2,5-dialkoxy-1,4-phenylene vinylene) [RO-PPV], poly (2- (2′- Ethyl-hexoxy) -5-methoxy-1,4-phenylenevinylene) [MEH-PPV], poly (2- (dialkoxyphenyl) -1,4-phenylenevinylene) [ROPh-PPV] and the like. Examples of polyparaphenylene include derivatives of polyparaphenylene [PPP], poly (2,5-dialkoxy-1,4-phenylene) [RO-PPP], poly (2,5-dihexoxy-1,4-phenylene). ) And the like. Polythiophene series includes polythiophene [PT] derivatives, poly (3-alkylthiophene) [PAT], poly (3-hexylthiophene) [PHT], poly (3-cyclohexylthiophene) [PCHT], poly (3-cyclohexyl). -4-methylthiophene) [PCHMT], poly (3,4-dicyclohexylthiophene) [PDCHT], poly [3- (4-octylphenyl) -thiophene] [POPT], poly [3- (4-octylphenyl) -2,2 bithiophene] [PTOPT] and the like. Examples of the polyfluorene series include polyfluorene [PF] derivatives, poly (9,9-dialkylfluorene) [PDAF], poly (9,9-dioctylfluorene) [PDOF], and the like.

  Note that when a hole-transporting polymer-based organic light-emitting material is sandwiched between an anode and a light-emitting polymer-based organic light-emitting material, hole injection properties from the anode can be improved. In general, an acceptor material dissolved in water is applied by spin coating or the like. In addition, since it is insoluble in an organic solvent, it can be stacked with the above-described light-emitting organic light-emitting material. Examples of the hole-transporting polymer organic light emitting material include a mixture of PEDOT and camphor sulfonic acid (CSA) as an acceptor material, a mixture of polyaniline [PANI] and polystyrene sulfonic acid [PSS] as an acceptor material, and the like. .

  Further, the electroluminescent layer may be configured to perform color display by forming a light emitting layer having a different emission wavelength band for each pixel. Typically, a light emitting layer 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 polarized plate that has been considered necessary in the past, and it is possible to eliminate the loss of light emitted from the light emitting layer. Furthermore, a change in color tone that occurs when the pixel portion (display screen) is viewed obliquely can be reduced.

  Alternatively, the electroluminescent layer may be configured to emit 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 the electroluminescent layer that emits white light, for example, Alq _3, Alq ₃ partially doped with Nile red that is a red light emitting pigment, Alq _3, p-EtTAZ, evaporation method TPD (aromatic diamine) The white color can be obtained by laminating sequentially. In the case where the EL is formed by a coating method using spin coating, it is preferable that baking is performed by vacuum heating after coating. For example, a poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) that acts as a hole injection layer is applied and baked on the entire surface, and then a luminescent center dye (1, 1,4,4-tetraphenyl-1,3-butadiene (TPB), 4-dicyanomethylene-2-methyl-6- (p-dimethylamino-styryl) -4H-pyran (DCM1), Nile Red, Coumarin 6 Etc.) A doped polyvinyl carbazole (PVK) solution may be applied to the entire surface and fired.

  The electroluminescent layer can be formed as a single layer, and an electron transporting 1,3,4-oxadiazole derivative (PBD) may be dispersed in hole transporting polyvinyl carbazole (PVK). Further, white light emission can be obtained by dispersing 30 wt% PBD as an electron transporting agent and dispersing an appropriate amount of four kinds of dyes (TPB, coumarin 6, DCM1, Nile red). In addition to the light-emitting element that can emit white light as shown here, a light-emitting element that can obtain red light emission, green light emission, or blue light emission can be manufactured by appropriately selecting the material of the light-emitting layer.

  Note that when a hole-transporting polymer-based organic light-emitting material is sandwiched between an anode and a light-emitting polymer-based organic light-emitting material, hole injection properties from the anode can be improved. In general, an acceptor material dissolved in water is applied by spin coating or the like. In addition, since it is insoluble in an organic solvent, it can be stacked with the above-described light-emitting organic light-emitting material. Examples of the hole-transporting polymer organic light emitting material include a mixture of PEDOT and camphor sulfonic acid (CSA) as an acceptor material, a mixture of polyaniline [PANI] and polystyrene sulfonic acid [PSS] as an acceptor material, and the like. .

  Further, for the electroluminescent layer, a triplet excitation material containing a metal complex or the like may be used in addition to the singlet excitation luminescent 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.

  In addition, the substance which forms the light emitting layer mentioned above is an example, and functions, such as a positive hole injection transport layer, a positive hole transport layer, an electron injection transport layer, an electron transport layer, a light emitting layer, an electron block layer, a hole block layer, etc. A light-emitting element can be formed by appropriately stacking each of the properties. Moreover, you may form the mixed layer or mixed junction which combined these each layer. The layer structure of the light-emitting layer can be changed, and instead of having a specific electron injection region or light-emitting region, it is possible to provide a modification with an electrode for this purpose or a dispersed light-emitting material. Can be permitted without departing from the spirit of the present invention.

  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 light 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. However, alternating current that applies a bias in the forward and reverse directions. By performing a typical drive, the progress of deterioration can be slowed, and the reliability of the light emitting device can be improved.

  The direction in which the light emitting element emits light can be classified into the following three types: one is when the light emitting element emits light on the substrate side (lower surface emission), and one is the counter substrate side facing the substrate One is a case where light is emitted from the substrate side and the opposite substrate side, that is, a case where light is emitted from one surface of the substrate and the opposite surface (double-side emission). In the case of performing dual emission, it is essential that the substrate and the counter substrate have translucency. The light emitted from the light emitting element includes light emission (fluorescence) when returning from the singlet excited state to the ground state and light emission (phosphorescence) when returning from the triplet excited state to the ground state. One or both of them can be used.

  The light-emitting element realizes a wide viewing angle, thinness and lightness by not requiring a backlight, and is suitable for displaying moving images because of its high response speed. By using a display device using such a light emitting element, higher functionality and higher added value are realized. This embodiment can be freely combined with the above embodiment modes.

  A panel including a display region and a driver circuit, which is one embodiment of the display device of the present invention, will be described with reference to FIGS. Over the substrate 405, a display region 401 including a plurality of pixels each including a light-emitting element, a source driver circuit 402, first and second gate driver circuits 403 and 404, a connection terminal 415, and a connection film 407 are provided (FIG. A)). The connection terminal 415 is connected to the connection film 407 through anisotropic conductive particles or the like. The connection film 407 is connected to the IC chip.

  FIG. 5B is a cross-sectional view taken along the line A-A ′ of the panel, and shows the driving TFT 101 provided in the display region 401 and the CMOS circuit 414 provided in the source driving circuit 402. In addition, a conductive layer 411, an electroluminescent layer 412, and a conductive layer 413 provided in the display region 401 are shown. The conductive layer 411 is connected to the source electrode or the drain electrode of the driving TFT 101. In addition, the conductive layer 411 functions as a pixel electrode, and the conductive layer 413 functions as a counter electrode. A stacked body of the conductive layer 411, the electroluminescent layer 412, and the conductive layer 413 corresponds to a light-emitting element.

  A sealant 408 is provided around the display region 401 and the drive circuits 402 to 404, and the light-emitting element is sealed with the sealant 408 and the counter substrate 406. This sealing process is a process for protecting the light emitting element from moisture. Here, a method of sealing with a cover material (glass, ceramics, plastic, metal, etc.) is used, but thermosetting resin or ultraviolet light curing is used. A method of sealing with a functional resin or a method of sealing with a thin film having a high barrier ability such as a metal oxide or a nitride may be used.

  The element formed over the substrate 405 is preferably formed using a crystalline semiconductor (polysilicon) having favorable characteristics such as mobility as compared with an amorphous semiconductor. Realized. Since the number of external ICs to be connected is reduced, the panel having the above configuration can be made small, light, and thin.

  5B, the conductive layer 411 is formed using a light-transmitting transparent conductive film, and the conductive layer 413 is formed using a reflective film having reflectivity. Therefore, light emitted from the electroluminescent layer 412 passes through the conductive layer 411 and is emitted to the substrate 405 side as indicated by an arrow. Such a configuration is generally called a bottom emission method.

  In contrast, when the conductive layer 411 is formed using a reflective film and the conductive layer 413 is formed using a transparent conductive film, light emitted from the electroluminescent layer 412 can be emitted from the counter substrate 406 side as illustrated in FIG. A configuration in which the light is emitted from the light source is also possible. Such a configuration is generally called a top emission method.

  Further, the source or drain electrode of the driving TFT 101 and the conductive layer 411 are stacked in the same layer without an insulating layer interposed therebetween, and are directly connected by overlapping of films. Therefore, since the formation region of the conductive layer 411 is a region excluding the region where the driving TFTs 101 and the like are disposed, a reduction in aperture ratio is unavoidable due to high definition of pixels and the like. Therefore, as shown in FIG. 6B, an interlayer film 416 is added, a pixel electrode is provided in an independent layer, and a top emission method is used, so that a region where a TFT or the like is formed can be effectively used as an issue region. Can be used. At this time, depending on the film thickness of the electroluminescent layer 412, a short circuit between the conductive layer 411 and the conductive layer 413 may occur in the contact region between the conductive layer 411 and the source electrode or the drain electrode of the driving TFT 101. A configuration in which a bank 417 or the like is provided to prevent a short circuit is desirable.

  Further, as shown in FIG. 8, the conductive layer 411 and the conductive layer 413 are both formed of a transparent conductive film, whereby light emitted from the electroluminescent layer 412 is extracted to both the substrate 405 side and the counter substrate 406 side. Configuration is also possible. Such a configuration is called a double-sided emission method.

  In the case of FIG. 8, the light emission areas on the top emission side and the bottom emission side are substantially equal, but as described above, the aperture ratio on the top emission side can be increased by adding an interlayer film to increase the area of the pixel electrode. Needless to say.

  Note that when the electroluminescent layer 412 included in the light-emitting element is separately formed corresponding to each color of RGB, light emitted from the light-emitting element can be divided into red, blue, and green to perform full-color display. However, as a method for performing full color display, the electroluminescent layer 412 may be formed corresponding to blue or white without forming the electroluminescent layer 412, and color filters or color conversion layers 454 and 455 may be provided (FIG. 6). (See (A) and (B)).

  In the case where the dual emission method of FIG. 8 is employed, polarizing plates 450 and 452 may be provided over both the substrate 405 and the counter substrate 406. As described above, when the polarizing plates 450 and 452 are attached, the panel itself is not transparent, so that the surroundings are not seen through. The polarizing plates 450 and 452 can block outside light by being arranged so that their polarization directions intersect. The intersecting angle may be 40 to 90 degrees, preferably 70 to 90 degrees, and more preferably 90 degrees. With the above configuration, since the display is performed in a region other than the display region, the background is not seen through from either side. In other words, the arrangement of the polarizing plates 450 and 452 allows only the light emitted from the light emitting element to pass through without transmitting external light to the double-sided display panel, thereby improving the contrast. In addition, the polarizing plates 450 and 452 can change the transmittance of the panel itself by adding a means for rotating one or both of them and changing the intersecting angle. That is, a dimming function can be added. Further, by providing antireflection films or antireflection films 451 and 453 outside the polarizing plates 450 and 452 to reduce the reflectance, display quality can be improved. In addition, a half-wave plate or a quarter-wave plate (or the film) may be added. By adding the optical functional film in this way, display quality can be improved, and in particular, black smearing can be improved.

  In addition, this invention is not restrict | limited to said Example. For example, the display region 401 in FIG. 5A may be configured by a TFT using an amorphous semiconductor (amorphous silicon) formed over an insulating surface as a channel portion, and the driver circuits 402 to 404 may be configured by an IC chip. Good. The IC chip may be bonded onto the substrate by a COG method, or may be bonded to a connection film connected to the substrate. An amorphous semiconductor can be formed over a large-area substrate by using a CVD method, and a crystallization step is unnecessary, so that an inexpensive panel can be provided. At this time, if a conductive layer is formed by a droplet discharge method typified by an ink jet method, a cheaper panel can be provided. This embodiment can be freely combined with the above embodiment modes and embodiments.

  As electronic devices having a display area including a light emitting element, a television device, a digital camera, a digital video camera, a mobile phone device (mobile phone), a personal digital assistant such as a PDA, a portable game machine, a monitor, a notebook computer, a car Examples thereof include an audio reproduction device such as an audio, and an image reproduction device including a recording medium such as a home game machine. Specific examples will be described below.

  FIG. 7A illustrates a portable information terminal, which includes a main body 9201, a display portion 9202, and the like. FIG. 7B illustrates a digital video camera, which includes a display portion 9701, a main body 9702, and the like. FIG. 7C illustrates a portable terminal, which includes a main body 9101, a display portion 9102, and the like. FIG. 7D illustrates a portable television device including a main body 9301, a display portion 9302, and the like. FIG. 7E illustrates a portable computer, which includes a main body 2202, a display portion 2203, and the like. FIG. 7F illustrates a television device which includes a main body 2001, a display portion 2003, and the like. The present invention is applied to a configuration of a display device including a display unit. By applying the present invention, a display screen that realizes high image quality and high reliability can be provided; therefore, an electronic device that realizes high functionality and high added value can be provided. This embodiment can be freely combined with the above embodiment modes and embodiments.

The figure explaining embodiment of this invention. The figure explaining embodiment of this invention. The figure explaining embodiment of this invention. FIG. 6 illustrates a structure of a display device of the present invention. The figure explaining Example 2 of this invention. The figure explaining Example 2 of this invention. The figure explaining Example 3 of this invention. The figure explaining Example 2 of this invention. The figure explaining embodiment of this invention.

Claims (8)

Having a plurality of pixels arranged in a matrix;
Each of the plurality of pixels includes a light emitting element, a transistor, and an AC driving bypass element,
The light emitting element and the transistor are connected in series,
The AC drive bypass element and the transistor are connected in parallel. The display device according to claim 1 has a current source,
The display device, wherein the transistor outputs a current depending on a magnitude of a signal current supplied from the current source to the light emitting element. Having a plurality of pixels arranged in a matrix;
Each of the plurality of pixels includes a light emitting element, a first transistor, a second transistor, a third transistor, a fourth transistor, a storage capacitor element, and an AC driving bypass element.
The gate terminal of the third transistor is connected to a third wiring, one of the source / drain terminals of the third transistor is connected to the first wiring, and the other is connected to the gate terminal of the second transistor. And
One of the source and drain terminals of the second transistor is connected to the second wiring, and the other is connected to the gate terminal of the second transistor,
The gate terminal of the fourth transistor is connected to a fourth wiring, one of the source and drain terminals of the fourth transistor is connected to the gate terminal of the second transistor, and the other is connected to the first transistor. Connect to the gate terminal,
One of the source and drain terminals of the first transistor is connected to the second wiring, the other is connected to the first electrode of the light emitting element,
A second electrode of the light emitting element is connected to a counter power source;
One terminal of the storage capacitor is connected to the second wiring, and the other terminal is connected to the gate terminal of the first transistor;
One terminal of the AC drive bypass element is connected to the second wiring, and the other terminal is connected to the first electrode of the light emitting element. Having a plurality of pixels arranged in a matrix;
Each of the plurality of pixels includes a light emitting element, a first transistor, a second transistor, a third transistor, a fourth transistor, a storage capacitor element, and an AC driving bypass element.
The gate terminal of the third transistor is connected to a third wiring, one of the source / drain terminals of the third transistor is connected to the first wiring, and the other is the source / drain terminal of the second transistor. Connected to one of the
The other terminal of the source / drain terminals of the second transistor is connected to the second wiring,
The gate terminal of the fourth transistor is connected to a fourth wiring, and one of the source / drain terminals of the fourth transistor is one of the source / drain terminals of the second transistor and the source of the third transistor. The drain terminal is connected to a connection point with one of the drain terminals, and the other is connected to a connection point between the gate terminal of the first transistor and the gate terminal of the second transistor;
One of the source and drain terminals of the first transistor is connected to the second wiring, and the other is connected to the first electrode of the light emitting element,
A second electrode of the light emitting element is connected to a counter power source;
One terminal of the storage capacitor is connected to the second wiring, and the other terminal is connected to the gate terminal of the first transistor;
One terminal of the AC drive bypass element is connected to the second wiring, and the other terminal is connected to the first electrode of the light emitting element. In any one of Claims 1 thru | or 4,
A display device, wherein the AC drive bypass element is a diode. In any one of Claims 1 thru | or 4,
The display device, wherein the AC drive bypass element is a transistor having a gate terminal and a drain terminal connected to each other. In any one of Claims 1 thru | or 4,
In the light-emitting element, one of the first electrode and the second electrode has a light-transmitting property and the other has a reflecting property. In any one of Claims 1 thru | or 4,
The display device is characterized in that the first electrode and the second electrode of the light-emitting element have a light-transmitting property.

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