JP4926427B2 - Method for manufacturing light emitting device - Google Patents

Description

The present invention comprises an element having a structure in which an anode, a cathode, and a thin film that emits light by a phenomenon called electroluminescence (hereinafter referred to as “EL”) are sandwiched between the anode and the cathode. The present invention belongs to a technical field related to a light emitting device.

An EL element is an element that emits light by forming a thin film or a crystal containing an organic compound or an inorganic compound between a cathode and an anode and energizing between the anode and the anode. In recent years, an EL element in which a thin film (hereinafter referred to as an organic thin film) containing an organic compound as a main component (hereinafter referred to as an organic thin film) is installed between a cathode and an anode, that is, an organic EL element has been actively developed.

The organic EL element is expected to be applied in various fields, and is considered to be used from a simple lighting device to a display used in a mobile phone or a personal computer. Some of them have been put to practical use in displays for in-vehicle displays and small electric appliances.

However, the organic EL device still has some problems regardless of the application. One of them is a display defect caused by the manufacturing process. Specifically, referring to FIG. 1A, an organic EL element is a device in which a thin film containing an organic compound is placed between two electrodes, in which electrons are transferred from one electrode and holes are transferred from the other electrode. Is injected and driven. Then, holes and electrons recombine in the thin film to form a compound responsible for light emission, that is, an excited state of the light emitter. Light emission is obtained when this excited state returns to the ground state by the radiation process. That is, the organic EL element is a light emitting element that is driven only when a current flows. Therefore, if the current does not flow to the pixel, or if the two electrodes are short-circuited and a uniform current cannot flow to the pixel, light emission as an element cannot be obtained.

In particular, a short circuit between the electrodes is a serious problem. Several causes of the short circuit have been considered, but the main causes are crystallization of the material in the film and the electric field concentration derived from the unevenness of the electrode surface, that is, the surface roughness of the electrode surface. The former cause can be solved by selecting a material that is difficult to crystallize, but the latter cause is caused by the manufacturing process, and thus cannot be solved only by the contrivance of the material. For example, when minute dust is generated during the manufacturing process of the substrate and the first electrode is formed with the dust attached (FIG. 1B), a convex portion is formed on this electrode. When an EL element is formed on a pixel electrode having such a rough surface, the electric field concentrates on this convex part, and a current necessary for light emission cannot flow to other regions, so that the pixel emits light. Spots appear. If the electric field concentration further progresses, the element is destroyed and the two electrodes are short-circuited. As a result, this pixel cannot emit light in almost any region.

For example, when an organic EL element is applied as a high-definition display, an EL element is manufactured for each pixel on either a simple matrix type (hereinafter referred to as passive matrix) or active matrix type substrate. Display is possible by controlling the current to each pixel with an external circuit. At this time, when a pixel is short-circuited due to the problem caused by the above-described process, the pixel is recognized as a black spot (hereinafter referred to as a dark spot) on the screen, and display quality is greatly deteriorated.

Considering application of the organic EL element as illumination, since the substrate manufacturing process is relatively simple, dust generated during the process can be removed relatively easily. However, when considering the application of a display, the manufacturing process of an active matrix substrate is particularly complicated, and it is not easy to completely remove minute dust generated in the process. In particular, when the panel size is increased, the influence of slight dust greatly affects the yield. Therefore, it is an urgent task to develop an EL element formation method that is not affected by the surface roughness of the pixel electrode caused by dust.

In the conventional pixel structure shown in FIG. 2A, 201 is a data signal line, 202 is a gate signal line, 203 is a power supply line, 204 is a switching TFT, 205 is a capacitor, 206 is a driving TFT, and 207 is a driving TFT. A drain electrode 208 is a pixel electrode connected to the drain electrode of the driving TFT, and the pixel electrode 208 functions as an anode of the light emitting element.

FIG. 2B shows a drawing corresponding to the cut surface at A-A ′ at this time. The substrate 210 has a driving TFT 206 and is patterned in a lattice pattern so as to cover at least the driving TFT and the switching TFT, and an end portion of the pixel electrode 208 formed so as to be connected to the driving TFT 206. An insulator 209 is provided.

In FIG. 2, there is no dust under the pixel electrode, and the pixel electrode 208 with high flatness is provided. Therefore, the light emitting layers 211a to 211c formed on the pixel electrode 208 do not have to be thickly formed. At this time, the thickness of the light emitting layer is 10 nm to 40 nm, and even when it is thick, it is about 100 nm. A cathode 212 is formed thereon.

On the other hand, FIG. 3A shows a schematic diagram in the case where dust caused by a process exists under the pixel electrode and the flatness of the pixel electrode is lost. In FIG. 3A, reference numeral 300 denotes a substrate, and reference numerals 301a to 301c denote pixel electrodes. It schematically shows that process-related dust 302 exists below the pixel electrode 301a. Since the dust 302 has not been completely removed, the flatness of the pixel electrode 301a formed in this pixel portion is lost, and a large convex portion is formed.

The film thickness of the EL element is 0.1 μm to 0.2 μm, and even when it is thick, it is about 0.5 μm. Therefore, when an EL element is manufactured by a normal method on an anode having a convex portion, light emitting layers 303b and 303c having high flatness are formed on the pixel electrodes 301b and 301c as shown in FIG. However, the flatness of the light emitting layer 303a formed on the pixel electrode 301a is lost, and a large convex portion is formed. A cathode 304 is further formed on the light emitting layer thus manufactured. When each pixel is energized, light emission can be obtained from the light emitting region where the pixel electrodes 301b and 301c exist, but the pixel electrode 301a exists. In the region, electric field concentration is likely to occur in the convex portion, and the reliability of such a pixel is remarkably lowered, and light emission cannot be actually obtained from this pixel. That is, this pixel area is recognized as a dark spot.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a light-emitting element in which defects due to dust and the like are reduced and a manufacturing method thereof.

One of the light-emitting elements of the present invention is formed on a first electrode, a first layer containing an organic compound formed on the first electrode, and having conductivity, and the first layer. And a second layer having a hole transporting property, a light emitting layer formed on the second layer, and a second electrode formed on the light emitting layer. It is characterized by.

In other words, the first layer provided in contact with the first electrode and the second layer provided in contact with the first layer between the first electrode and the second electrode. The light emitting layer is provided between the second layer and the second electrode. The first electrode, the second electrode, the first layer, the second layer, and the light emitting layer are formed so that the first layer is the first layer and the second layer is the second layer. Are stacked. Here, the first layer is a layer containing an organic compound. Among organic compounds, an organic compound having conductivity is preferable. The second layer is a layer containing an inorganic compound. Among inorganic compounds, an electron-accepting inorganic compound is particularly preferable.

Further, one of the light-emitting elements of the present invention includes a first electrode, an insulating layer formed on the first electrode, an end of the insulating layer, an organic compound, A first layer having conductivity, a second layer formed on the first layer, containing an inorganic compound and having a hole transporting property, and a light emitting layer formed on the second layer And a second electrode formed on the light emitting layer,
It is characterized by having.

According to one method for manufacturing a light-emitting element of the present invention, a first electrode is formed over a substrate, an insulating film is formed over the first electrode, an opening is formed in the insulating layer, and the opening The first electrode is exposed to form a first layer so as to cover the first electrode, and the first electrode and the first layer are superimposed on the first layer. A second layer is selectively formed at a site to be etched, and the first layer is etched using the second layer as a mask.

That is, after the first electrode is formed, the first layer is formed on the first electrode, and the second layer is selectively formed on the first layer and overlapping with the first electrode. Forming a layer. Then, the method includes a step of etching the first layer using the second layer as a mask. Here, the first layer is a layer containing an organic compound. Among organic compounds, an organic compound having conductivity is preferable. The second layer is a layer containing an inorganic compound. Among inorganic compounds, an electron-accepting inorganic compound is particularly preferable.

By thickly forming a highly conductive material, the surface roughness of the pixel electrode can be remarkably reduced, and an organic layer can be formed on a flat surface. Thereby, partial electric field concentration can be suppressed, and as a result, occurrence of pixel defects recognized as dark spots can be prevented.

Further, a protective film having etching resistance and carrier transporting property, preferably hole transporting property is formed on the pixel portion, and etching is performed thereafter, so that the pixel portion is not etched and is formed on an insulator. Only the conductive film formed can be selectively removed. Since this protective film also functions as a carrier injection or transport layer, more specifically as a hole injection or transport layer, with respect to the light emitting layer, it is not necessary to remove the protective film. Therefore, if a light emitting layer is formed on this protective film, an EL element can be manufactured, and the occurrence of dark spots and the crosstalk phenomenon can be suppressed without complicating the process.

Hereinafter, one embodiment of the present invention will be described. 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 the embodiment.

(Embodiment 1)
Although FIG. 1 describes the case where an EL element is formed on a substrate provided with a circuit for active matrix driving, the present invention is not limited to the form of the substrate, and is for passive matrix driving. A substrate provided with the above circuit or a substrate having only a single pixel may be used.

First, since it is necessary to extract emitted light in an organic EL element, at least one of the anode and the cathode needs to be transparent. Hereinafter, a light-emitting element capable of forming a transparent anode on a substrate and taking out light emission from the anode side will be described. However, the present invention is not limited to this structure. For example, the present invention can be applied to a structure in which only the cathode is transparent, or a structure in which both the cathode and anode are transparent to obtain light emission from above and below the element.

  Next, the light emitting device of the present invention will be described. Note that in FIG. 1A, reference numeral 412 denotes a base including a transistor 410 and the like that perform active matrix driving. The transistor 410 is electrically connected to the first electrode 400 of the light-emitting element through the connection portion 411. As the substrate 412, a glass substrate, a quartz substrate, a plastic substrate, or other translucent substrate can be used.

In the present invention, first, a thick conductive layer 401 is formed using a highly conductive material over the first electrode 400 exposed from the insulating layer 402 having an opening (FIG. 1B). The conductive layer 401 is preferably formed to have a thickness of 0.1 μm to 2 μm, and particularly preferably has a thickness of 0.2 μm to 1.5 μm.

The conductive materials that can be used here are roughly classified into high-molecular materials and low-molecular materials. As the high-conductivity polymer material, camphorsulfonic acid, toluenesulfonic acid, poly (styrenesulfonic acid) -doped polyaniline derivative, polythiophene derivative, or the like is preferable. In particular, as a polythiophene derivative, poly (3,4-ethylenedioxythiophene) is easy to inject holes due to its very low oxidation potential, and the drive voltage hardly increases even when it is formed thick. This is advantageous because of its merit. Since these polymer materials cannot be formed into a film by a dry method such as vapor deposition, a wet method such as a spin coat method or a spray method is used.

As a low molecular conductive material, a mixture of a donor compound and an acceptor compound is suitable. These two compounds are co-evaporated. Alternatively, the mixed solution may be deposited by a wet method. As the donor compound, a sulfur-containing compound such as tetrathiafulvalene or an aromatic amine compound is preferable. On the other hand, as an acceptor compound, a compound having an electron withdrawing group such as tetracyanoquinodimethane, particularly a quinone derivative is suitable.

However, the conductive layer 401 is preferably formed by a wet method using a polymer material. This is based on the following reason. When a low molecular weight compound is formed by a wet method, in many cases, aggregation and crystallization are likely to occur, and it is difficult to form an amorphous film. Therefore, it is better to form a film by a dry method such as a vacuum evaporation method. However, it is inherently difficult to form a film with a number of μm by vapor deposition. On the other hand, although a polymer material cannot be formed by a dry method, a uniform amorphous layer can be easily formed by adopting a wet method, and the thickness can be easily controlled. . For these reasons, in order to achieve the present invention, it is better to form a polymer material thicker by a wet method.

Note that the first electrode 400 is preferably formed using a conductive film that is transparent to visible light so that light emitted from the light emitter can pass through, such as ITO (compound of indium oxide and tin oxide) or indium oxide. It is preferable to use an oxide conductive film such as a compound of zinc oxide. These conductive metal oxide films are usually formed by sputtering, but may be formed by applying a sol-gel method or the like. In addition, a metal having a high work function such as gold can be used as a material other than the metal oxide. However, in this case, an ultrathin film is formed in consideration of light transmittance.

Next, a conductive layer 401 is formed in the pixel portion. In the present invention, when a thick conductive film is formed on the substrate, the conductive layer 401 is patterned in a lattice pattern so as to cover the driving TFT and the switching TFT. There is a possibility that the conductive layer 401 is also formed over the insulating layer 402. In particular, when the conductive layer 401 is formed by a wet method such as a spin coating method or a spray method, the conductive layer 401 may be formed over the insulating layer 402 in some cases. In order to suppress crosstalk between pixels, it is preferable to remove the conductive film coated also on the insulator, and this is performed by etching. However, it is necessary to prevent the portion of the conductive layer 401 stacked with the first electrode 400 from being removed by etching. Therefore, first, as a protective layer against etching, a protective layer 403 containing an inorganic compound having etching resistance and carrier transporting property, preferably hole transporting property is provided on the pixel (FIG. 1C). At this time, it is preferable that the protective layer 403 be selectively formed in a portion overlapping with the first electrode 400 by a vapor deposition method using a shadow mask or the like. In addition, damage to the conductive layer 401 can be prevented by using a vapor deposition method. Specific examples of the protective layer 403 include transition metal oxides such as cobalt oxide, titanium oxide, niobium oxide, nickel oxide, neodymium oxide, vanadium oxide, molybdenum oxide, lanthanum oxide, ruthenium oxide, and rhenium oxide. Alternatively, various metal-containing compounds can be used. For example, a transition metal oxide, nitride, or halide of Group 4 to Group 7 may be used. These metal oxides, nitrides, halides, and the like are expected to have higher etching resistance than organic compounds, and thus the protective layer exists in the pixel portion even after etching described later. Since this layer has carrier transport properties, particularly hole transport properties, carriers are injected into the protective layer from the conductive film, and carriers, particularly holes, are injected into the light emitting layer formed on the protective layer. be able to.

The transition metal oxides, nitrides, and halides described above can be used for hole injection alone, but this causes an electron transfer reaction at the interface where these materials are in contact with the light emitting layer, so-called charge transfer complexes. It is for forming. Therefore, these materials may be doped with an appropriate donor to positively form a charge transfer complex. Examples of the donor include electron-rich organic compounds such as tetrathiafulvalene and carbazole derivatives. Aromatic amines that are classified as so-called hole transport and injection materials in organic EL devices are also good examples. Specifically, 4,4′-bis [N- (3-methylphenyl) -N-phenyl-amino] -biphenyl (TPD) and 4,4′-bis [N- (1-naphthyl) -N— Phenyl-amino] -biphenyl (NPB) and the like.

After the protective layer 403 is formed in this way, etching is performed using the protective layer 403 as a mask, and the conductive layer 401 formed over the insulating layer 402 is removed. Etching is roughly classified into dry etching and wet etching, but any method may be used (FIG. 1D). Here, the etched conductive layer 401 preferably covers an end portion of the insulating layer 402.

Thus, the conductive layer 401 and the protective layer 403 capable of carrier transport are selectively formed in the pixel portion. Next, the light-emitting layer 404 is formed over the protective layer 403 (FIG. 1E). The light emitting layer 404 is mainly formed using an organic compound, but may be formed using a single composition thin film. For example, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: BeBq) ₂ ), bis (2-methyl-8-quinolinolato)-(4-hydroxy-biphenylyl) -aluminum (abbreviation: BAlq), bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn) (BOX) ₂ ), and typical metal complexes such as bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ). Alternatively, hydrocarbon compounds such as 9,10-diphenylanthracene and 4,4′-bis (2,2-diphenylethenyl) biphenyl are also suitable.

Further, the light emitting layer 404 may be a mixed layer of a plurality of materials. Luminous efficiency can be increased by mixing a small amount of a fluorescent dye or a phosphorescent dye (hereinafter referred to as a dopant) into the above-described phosphor. Examples of the fluorescent material include coumarin derivatives, quinacridone derivatives, acridone derivatives, pyrene derivatives, perylene derivatives, anthracene derivatives, and pyrone derivatives. Examples of phosphorescent dyes include triplet light-emitting materials. Examples of triplet light-emitting materials include tris (2-phenylpyridine) iridium (hereinafter referred to as “Ir (ppy) ₃ ”), 2, 3, 7, 8 , 12, 13, 17, 18-octaethyl-21H, 23H-porphyrin-platinum (hereinafter referred to as “PtOEP”), and transition metal complexes such as Ir, Ru, Rh, Pt, or rare earth metals.

On the other hand, the light emitting layer 404 may be a laminated film. When it is difficult to control the injection balance of electrons and holes in the light emitting layer having the single composition or the mixed light emitting layer described above, a plurality of materials are laminated to improve the light emission. Efficiency can be improved. For example, in addition to the light-emitting layer having the single composition or the mixed composition described above, a hole transport layer that efficiently transports injected holes to the light-emitting layer, and an electron transport layer that efficiently transports injected electrons to the light-emitting layer It is good to provide. A material suitable for the hole transport layer is a compound containing an aromatic amine (that is, a compound having a benzene ring-nitrogen bond). Widely used materials include TPD and its derivatives NPB, 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine, 4,4 ′, 4 ″ -tris And starburst aromatic amine compounds such as [N- (3-methylphenyl) -N-phenyl-amino] -triphenylamine. Examples of suitable materials for the electron transport layer include the above-mentioned typical metal compounds, but 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1 Triazole derivatives such as 2,2,4-triazole, and phenanthroline derivatives such as bathophenanthroline and bathocuproin may be used.

The light emitting layer 404 may be formed not only by a vacuum deposition method but also by a so-called wet method such as a spin coating method, a dip coating method, or a spray method.

Moreover, although the above-mentioned dopant is mixed in a small amount in a hole transport layer, an electron transport layer, or the like, the dopant is not limited to one kind, and two or more kinds of dopants may be used simultaneously. For example, if two types of dopants whose emission colors are complementary to each other are used, it is also possible to obtain white emission.

Further, by forming a layer that promotes electron injection on the light emitting layer 404 formed in this manner, the EL can be driven at a lower voltage. As a material suitable for the electron injection layer, first, a metal having a small work function and a metal compound thereof are included. For example, there are Mg—Ag alloy, Al—Li alloy, Mg—Li alloy, Ca ₃ N ₂ , Mg ₃ N ₂ and the like. In addition to metals, organic semiconductors doped with donors can be used. A preferable example of the organic semiconductor here is a compound having an acceptor property, and an electron-transporting material often used in a light-emitting element may be used. For example, typical metal complexes represented by Alq, phenanthroline derivatives, triazine derivatives, oxazole derivatives, quinoline derivatives, quinoxaline derivatives, and the like can be given. Also, electron-accepting compounds such as tetracyanoquinodimethane, tetracyanoethylene, and tetrachloroquinone are good examples. Other examples include condensed aromatic hydrocarbons such as rubrene and perylene derivatives. Further, a conductive material such as graphite can also be used. Furthermore, conjugated polymers such as polyphenylene vinylene, polyphenylene ethynylene, and polypyridine can also be used. As a donor for doping an organic semiconductor, a metal having a small work function such as an alkali metal or an alkaline earth metal is preferable. Alternatively, an electron excess type organic compound such as tetrathiafulvalene may be used. However, it is essential that the acceptor property of the organic semiconductor is strong. This is because the donor property of the electron-rich organic compound is smaller than that of the alkali metal or alkaline earth metal. Examples other than organic semiconductors include alkali metals, alkaline earth metals, rare earth metals, and compounds having these. Specific examples include calcium fluoride, lithium oxide, lithium chloride, lithium fluoride, magnesium fluoride, and barium oxide.

A second electrode 405 is formed over the light-emitting layer 404 (FIG. 1E). As the second electrode 405, a metal having a low work function and a metal compound thereof can be given. For example, Mg—Ag alloy, Al—Li alloy, Mg—Li alloy and the like. However, when an electron injection layer is used, since an electron injection barrier is reduced, Al which is a metal having a small work function may be used.

In the element manufactured in this manner, when current is passed between the pixel electrodes, electrons are injected from the second electrode 405 to the light-emitting layer 404 and holes are injected from the first electrode 400 to the light-emitting layer 404 to emit light. It reaches. Since the surface roughness of the anode due to dust mixed during the substrate manufacturing process is eliminated by the thick conductive film, uniform light emission can be obtained from the entire pixel and the occurrence of dark spots can be suppressed. .

(Embodiment 2)
Since the light-emitting element of the present invention has few defects due to dust or the like, by using the light-emitting element of the present invention for a pixel or the like, a light-emitting device free from a display defect due to a defect of the light-emitting element can be obtained.

  In this embodiment mode, a circuit configuration and a driving method of a light-emitting device including the light-emitting element of the present invention and having a display function will be described with reference to FIGS.

  FIG. 4 is a schematic view of a light emitting device to which the present invention is applied as viewed from above. In FIG. 4, a pixel portion 6511, a source signal line driver circuit 6512, a write gate signal line driver circuit 6513, and an erase gate signal line driver circuit 6514 are provided over a substrate 6500. The source signal line drive circuit 6512, the write gate signal line drive circuit 6513, and the erase gate signal line drive circuit 6514 are each an FPC (flexible printed circuit) 6503 which is an external input terminal via a wiring group. Connected. The source signal line driver circuit 6512, the writing gate signal line driver circuit 6513, and the erasing gate signal line driver circuit 6514 receive a video signal, a clock signal, a start signal, a reset signal, and the like from the FPC 6503, respectively. . A printed wiring board (PWB) 6504 is attached to the FPC 6503. Note that the driver circuit portion is not necessarily provided over the same substrate as the pixel portion 6511 as described above. For example, an IC chip mounted on an FPC on which a wiring pattern is formed (TCP) or the like is used. It may be used and provided outside the substrate.

  In the pixel portion 6511, a plurality of source signal lines extending in the column direction are arranged side by side in the row direction. In addition, current supply lines are arranged side by side in the row direction. In the pixel portion 6511, a plurality of gate signal lines extending in the row direction are arranged side by side in the column direction. In the pixel portion 6511, a plurality of pixel circuits including light-emitting elements are arranged.

  FIG. 5 is a diagram showing a circuit for operating one pixel. The circuit illustrated in FIG. 5 includes a first transistor 901, a second transistor 902, and a light-emitting element 903.

  Each of the first transistor 901 and the second transistor 902 is a three-terminal element including a gate electrode, a drain region, and a source region, and has a channel region between the drain region and the source region. Here, since the source region and the drain region vary depending on the structure and operating conditions of the transistor, it is difficult to limit which is the source region or the drain region. Therefore, in this embodiment, regions functioning as a source or a drain are referred to as a first electrode and a second electrode, respectively.

  The gate signal line 911 and the writing gate signal line driving circuit 913 are provided so as to be electrically connected or disconnected by a switch 918. The gate signal line 911 and the erasing gate signal line driver circuit 914 are provided so as to be electrically connected or disconnected by a switch 919. The source signal line 912 is provided so as to be electrically connected to either the source signal line driver circuit 915 or the power source 916 by the switch 920. The gate of the first transistor 901 is electrically connected to the gate signal line 911. The first electrode of the first transistor 901 is electrically connected to the source signal line 912, and the second electrode is electrically connected to the gate electrode of the second transistor 902. The first electrode of the second transistor 902 is electrically connected to the current supply line 917, and the second electrode is electrically connected to one electrode included in the light-emitting element 903. Note that the switch 918 may be included in the write gate signal line driver circuit 913. The switch 919 may also be included in the erase gate signal line driver circuit 914. Further, the switch 920 may also be included in the source signal line driver circuit 915.

  There is no particular limitation on the arrangement of transistors, light-emitting elements, and the like in the pixel portion. For example, they can be arranged as shown in the top view of FIG. In FIG. 6, the first electrode of the first transistor 1001 is connected to the source signal line 1004, and the second electrode is connected to the gate electrode of the second transistor 1002. The first electrode of the second transistor 1002 is connected to the current supply line 1005, and the second electrode is connected to the electrode 1006 of the light emitting element. Part of the gate signal line 1003 functions as a gate electrode of the first transistor 1001.

  Next, a driving method will be described. FIG. 7 is a diagram for explaining the operation of a frame over time. In FIG. 7, the horizontal direction represents the passage of time, and the vertical direction represents the number of scanning stages of the gate signal line.

  When image display is performed using the light emitting device of the present invention, the screen rewriting operation and the display operation are repeatedly performed during the display period. The number of rewrites is not particularly limited, but is preferably at least about 60 times per second so that a person viewing the image does not feel flicker. Here, a period during which one screen (one frame) is rewritten and displayed is referred to as one frame period.

As shown in FIG. 7, one frame period is time-divided into four subframe periods 501, 502, 503, and 504 including a writing period 501a, 502a, 503a, and 504a and a holding period 501b, 502b, 503b, and 504b. ing. A light emitting element to which a signal for emitting light is given is in a light emitting state in the holding period. The ratio of the length of the holding period in each subframe period is as follows: first subframe period 501: second subframe period 502: third subframe period 503: fourth subframe period 504 = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1 As a result, 4-bit gradation can be expressed. However, the number of bits and the number of gradations are not limited to those described here. For example, eight subframe periods may be provided to enable 8-bit gradation.

  An operation in one frame period will be described. First, in the subframe period 501, the write operation is performed in order from the first row to the last row. Therefore, the start time of the writing period differs depending on the row. From the row in which the writing period 501a ends, the storage period 501b is started in order. In the holding period, the light-emitting element to which a signal for emitting light is given is in a light-emitting state. Further, the processing proceeds to the next subframe period 502 in order from the row in which the holding period 501b ends, and the writing operation is performed from the first row to the last row in the same manner as in the subframe period 501. The operation as described above is repeated until the holding period 504b of the subframe period 504 is completed. When the operation in the subframe period 504 is completed, the process proceeds to the next frame period. Thus, the accumulated time of the light emission in each subframe period is the light emission time of each light emitting element in one frame period. Various display colors having different brightness and chromaticity can be formed by changing the light emission time for each light emitting element and combining them in various ways within one pixel.

  Like the subframe period 504, when it is desired to forcibly end the holding period in the row that has already finished writing and shifted to the holding period before the writing up to the last row is completed, the holding period 504b It is preferable to provide an erasing period 504c later and control to forcibly turn off light. Then, the row that is forcibly set to the non-light-emitting state is kept in the non-light-emitting state for a certain period (this period is referred to as a non-light-emitting period 504d). Then, as soon as the writing period of the last row ends, the next (or frame period) writing period starts in order from the first row. Note that in order to perform writing in pixels in a certain row in this way and to input an erasing signal for making the pixels non-light-emitting in pixels in a certain row, two horizontal periods are provided as shown in FIG. And one period is used for writing and the other period is used for erasing. Each gate signal line 911 is selected within the divided horizontal period, and a corresponding signal is input to the source signal line 912 at that time. For example, in one horizontal period, the i-th row is selected in the first half and the j-th row is selected in the second half. Then, in one horizontal period, it is possible to operate as if two rows were selected at the same time. That is, signals are written to the pixels in the writing periods 501a to 504a using the writing period of one horizontal period. In this case, no pixel is selected in the erase period of one horizontal period. Further, the signal written to the pixel in the erasing period 504c is erased using another erasing period of one horizontal period. At this time, no pixel is selected in the writing period of one horizontal period. Accordingly, a display device having a pixel with a high aperture ratio can be provided, and the yield can be improved.

  In this embodiment, the subframe periods 501 to 504 are arranged in order from the longest holding period. However, the subframe periods 501 to 504 are not necessarily arranged as in this embodiment, and are arranged in order from the shortest holding period, for example. Alternatively, the long holding period and the short holding period may be arranged at random. Further, the subframe period may be further divided into a plurality of frame periods. That is, the gate signal line may be scanned a plurality of times during the period when the same video signal is applied.

  Here, the operation of the circuit shown in FIG. 6 in the writing period and the erasing period will be described.

  First, the operation in the writing period will be described. In the write period, the i-th (i is a natural number) gate signal line 911 is electrically connected to the write gate signal line drive circuit 913 via the switch 918, and the erase gate signal line drive circuit 914 Is disconnected. The source signal line 912 is electrically connected to the source signal line driver circuit 915 through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the i-th row, and the first transistor 901 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 912 in each column are independent from each other. A video signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, on / off of the second transistor 902 is controlled by a signal input to the gate electrode of the second transistor 902. When the second transistor 902 is turned on, a voltage is applied to the light-emitting element 903, and a current flows through the light-emitting element 903. That is, light emission or non-light emission of the light-emitting element 903 is determined by a signal input to the gate electrode of the second transistor 902. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 emits light by inputting a low level signal to the gate electrode of the second transistor 902. On the other hand, in the case where the second transistor 902 is an n-channel transistor, the light-emitting element 903 emits light when a high level signal is input to the gate electrode of the second transistor 902.

  Next, the operation in the erasing period will be described. In the erasing period, the gate signal line 911 in the j-th row (j is a natural number) is electrically connected to the erasing gate signal line driving circuit 914 via the switch 919, and is connected to the writing gate signal line driving circuit 913. Not connected. The source signal line 912 is electrically connected to the power source 916 through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the j-th row, and the first transistor 901 is turned on. At this time, the erase signal is simultaneously input to the source signal lines from the first column to the last column. The erase signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, the second transistor 902 is turned off by the erase signal input to the gate electrode of the second transistor 902 and current supply from the current supply line 917 to the light-emitting element 903 is blocked. Then, the light emitting element 903 is forced to emit no light. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 does not emit light when a high level signal is input to the gate electrode of the second transistor 902. On the other hand, in the case where the second transistor 902 is an n-channel transistor, the light emitting element 903 does not emit light by inputting a low level signal to the gate electrode of the second transistor 902.

  In the erasing period, a signal for erasing the j-th row is input by the operation as described above. However, as described above, the j-th row may be an erasing period, and the other rows (i-th row) may be a writing period. In such a case, it is necessary to input a signal for erasure to the j-th row and a signal for writing to the i-th row by using the source signal line in the same column, and will be described below. It is preferable to perform such an operation.

  The gate signal line 911 and the erasing gate signal line drive circuit 914 are immediately disconnected after the light emitting element 903 in the j−1th row does not emit light by the operation in the erasing period, and the switch 920 And the source signal line 912 and the source signal line driver circuit 915 are connected. Then, the source signal line 912 and the source signal line driver circuit 915 are connected, and the switch 918 is switched to connect the gate signal line 911 and the writing gate signal line driver circuit 913. Then, a signal is selectively input from the write gate signal line driver circuit 913 to the gate signal line 911 in the i-th row, the first transistor 901 is turned on, and the source signal line driver circuit 915 supplies one column. A video signal for writing is input to the source signal line 912 from the first to the last column. By this video signal, the i-th light emitting element 903 emits light or does not emit light.

  Immediately after the writing period for the i-th row is completed as described above, the erasing period for the j-th row is started. For this purpose, the switch 918 is switched to disconnect the gate signal line and the write gate signal line drive circuit 913, and the switch 920 is switched to connect the source signal line to the power source 916. In addition, the gate signal line 911 and the write gate signal line drive circuit 913 are disconnected, and the gate signal line 911 is switched to the erasure gate signal line drive circuit 914 by switching the switch 919. Then, a signal is selectively input from the erasing gate signal line driver circuit 914 to the gate signal line 911 in the j-th row to turn on the first transistor 901 and an erasing signal is input from the power supply 916. Then, the light emitting element 903 is forcibly turned off by the erase signal. In this way, immediately after the erasing period of the j-th row is finished, the writing period of the (i + 1) -th row is started. Thereafter, similarly, the erasing period and the writing period may be repeated until the erasing period of the last row is operated.

  In this embodiment, the mode in which the writing period of the i-th row is provided between the erasing period of the (j−1) -th row and the erasing period of the j-th row has been described. An i-th writing period may be provided between the period and the (j + 1) -th erasing period.

  In this embodiment, in the case where the non-light emission period 504d is provided as in the subframe period 504, the erase gate signal line driver circuit 914 and a certain gate signal line are brought into a non-connected state, and writing is performed. The operation of connecting the gate signal line driving circuit 913 and the other gate signal lines is repeated. Such an operation may be performed particularly in a frame period in which a non-light emitting period is not provided.

(Embodiment 3)
Since a light-emitting device including the light-emitting element of the present invention can display a good image, an electronic device that can provide excellent images can be obtained by applying the light-emitting device of the present invention to a display portion of an electronic device. it can.

  One embodiment of an electronic device mounted with a light emitting device to which the present invention is applied is shown in FIG.

  FIG. 8A illustrates a personal computer manufactured by applying the present invention, which includes a main body 5521, a housing 5522, a display portion 5523, a keyboard 5524, and the like. A personal computer can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 8B illustrates a telephone manufactured by applying the present invention, which includes a main body 5552, a display portion 5551, an audio output portion 5554, an audio input portion 5555, operation switches 5556 and 5557, an antenna 5553, and the like. . A telephone can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 8C illustrates a television set manufactured by applying the present invention, which includes a display portion 5531, a housing 5532, a speaker 5533, and the like. A television receiver can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  As described above, the light-emitting device of the present invention is very suitable for use as a display portion of various electronic devices.

  Note that although a personal computer, a telephone, and a television receiver are described in this embodiment mode, a light-emitting device having the light-emitting element of the present invention may be mounted on a navigation device, a lighting device, or the like.

8A and 8B illustrate a method for manufacturing a light-emitting device of the present invention. 10A and 10B illustrate a light-emitting element of a conventional technique. 10A and 10B illustrate a light-emitting element of a conventional technique. 4A and 4B illustrate a light-emitting device to which the present invention is applied. FIG. 6 illustrates a circuit included in a light-emitting device to which the present invention is applied. The top view of the light-emitting device to which this invention is applied. 4A and 4B illustrate a frame operation of a light-emitting device to which the present invention is applied. The figure of the electronic device to which this invention is applied. The figure explaining the method of selecting a plurality of gate signal lines simultaneously in one horizontal period

Explanation of symbols

400 First electrode 401 Conductive layer 402 Insulating layer 403 Protective layer 404 Light emitting layer 405 Second electrode 410 Transistor 411 Connection portion 412 Base body

Claims (4)

Forming a plurality of transistors on a substrate;
Forming a plurality of first electrodes electrically connected to each of the plurality of transistors;
An insulating layer having a plurality of openings is formed between the plurality of first electrodes so as to cover only end portions of the plurality of first electrodes, respectively.
A continuous conductive layer is formed on the insulating layer and the plurality of first electrodes so as to have a thickness covering an upper surface of the insulating layer,
Forming a plurality of second layers selectively on the conductive layers, covering the plurality of openings and end portions of the insulating layer, and selectively overlapping with the plurality of first electrodes;
Using the plurality of second layers as a mask , etching the conductive layer so that the surface of the insulating layer is exposed , thereby forming a plurality of first layers,
Forming a plurality of light emitting layers respectively provided on the plurality of openings and covering side surfaces of the plurality of second layers and side surfaces of the plurality of first layers;
A method for manufacturing a light-emitting device, comprising forming a second electrode so as to be in contact with the plurality of light-emitting layers and to cover side surfaces of the plurality of light-emitting layers . In claim 1,
The method for manufacturing a light-emitting device, wherein the plurality of first layers include an organic compound and have conductivity. In claim 1 or 2,
The method for manufacturing a light-emitting device, wherein the plurality of second layers are layers containing an inorganic compound and having a hole transporting property. In any one of Claims 1 thru | or 3,
The method for manufacturing a light-emitting device, wherein the conductive layer is formed by a wet method.

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