KR100659053B1 - Organic electro-luminescent display device - Google Patents

Abstract

An object of the present invention is to provide a capacitor capable of increasing a capacitor capacity, thereby reducing a capacitor size, and increasing an aperture ratio, and a flat panel display device having the same. The present invention provides a thin film transistor comprising a semiconductor thin film, a gate electrode opposing the semiconductor thin film to be insulated from the semiconductor thin film, and a source and a drain electrode connected to the semiconductor thin film; An organic electroluminescent device having a pixel electrode electrically connected to the thin film transistor, an opposite electrode facing the pixel electrode, and an organic light emitting layer interposed between the pixel electrode and the opposite electrode; And a capacitor having at least two electrodes facing each other so as to be insulated from each other, wherein one of the electrodes is formed on the same layer as the pixel electrode and made of the same material as the pixel electrode. Provide the device.

Description

Organic electro-luminescent display device

1 is a plan view illustrating one pixel of a conventional active matrix organic electroluminescent display.

FIG. 2 is a cross-sectional view of one pixel of a conventional active matrix organic electroluminescent display taken along the line II ′ of FIG. 1.

3 is a plan view illustrating one pixel of the active matrix organic electroluminescent display of the present invention.

FIG. 4 is a cross-sectional view of one pixel of the active matrix organic electroluminescent display of the present invention taken along line II-II 'of FIG. 3.

5 is a simplified cross-sectional view of the capacitor portion of FIG. 4.

Explanation of symbols on the main parts of the drawings

Ts ... switching thin film transistor

Cst ... Capacitor

Td ... Drive Thin Film Transistor

OLED ... organic electroluminescent element

308 ... first electrode

313 ... second electrode

323 ... third electrode

440 ... fourth electrode

321 ... 7th contact hole

425 ... 8th Contact Hole

403 gate insulating film

405 ... interlayer insulation film

407 ... passivation film

317 ... pixel electrode

445 organic electroluminescent film

445 ... counter electrode

The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device having a capacitor having an improved capacity.

Elements used in integrated circuits and flat panel displays include passive elements such as resistors and capacitors, and active elements such as thin film transistors (TFTs), diodes, and MOSFETs.

Among these capacitors, the integration degree of the integrated circuit device is increased, and as the speed increases, the demand for high capacity is gradually increased. In addition, in flat panel display devices such as liquid crystal display devices, organic electroluminescent display devices, or inorganic electroluminescent display devices, in order to improve the display screen quality, signals applied through data lines are stored for a predetermined period of time until the next frame. At least one terrain capacitor is installed, and as the number of thin film transistors installed in each pixel increases, the demand for higher capacity is gradually increased.

1 is a plan view illustrating one pixel of a conventional active matrix organic electroluminescent display.

First, there is a data line 101, a scan line 103, and a power supply line 105 that define a pixel. The scan line 103 is connected to the gate electrode 107 of the switching thin film transistor Ts, the data line 101 is connected to the source electrode 104 of the switching thin film transistor Ts, and the source electrode 104 is connected. Is connected to the source region (not shown) of the active layer of the switching thin film transistor Ts through the first contact hole 109, and the drain electrode 106 is connected to the switching thin film transistor Ts through the second contact hole 102. It is connected to the drain region (not shown) of the active layer of. In addition, the drain electrode 106 of the switching thin film transistor Ts is connected to the first electrode 108 of the capacitor Cst through the third contact hole 111. The power line 105 is connected to the source electrode 112 of the driving thin film transistor Td and the second electrode 113 of the capacitor Cst. The second electrode 113 is positioned to overlap the upper portion of the first electrode 108, and an insulating film (not shown) is interposed between both electrodes to form a capacitor Cst. The source electrode 112 of the driving thin film transistor Td is connected to the source region (not shown) of the active layer of the driving thin film transistor Td through the fourth contact hole 115 and the drain electrode of the driving thin film transistor Td. 116 is connected to the drain region (not shown) of the active layer of the driving thin film transistor Td through the fifth contact hole 118. In addition, the drain electrode 116 is connected to the pixel electrode 117 through the sixth contact hole 119.

FIG. 2 is a cross-sectional view of one pixel of a conventional active matrix organic electroluminescent display taken along the line II ′ of FIG. 1.

The buffer layer 203 is formed on the substrate 201, and the switching thin film transistor Ts, the driving thin film transistor Td, and the capacitor Cst are formed on the buffer layer 203. First, the thin film transistors Ts and Td will be described. The active layers 220 and 230 are formed on the buffer layer 203, and the gate insulating layer 205 is formed on the active layers 220 and 230. Next, gate electrodes 107 and 114 are formed on the gate insulating film 350, and an interlayer insulating film 207 is formed on the gate electrodes 107 and 114. Next, source electrodes 112 and 112 and drain electrodes 106 and 116 are formed on the interlayer insulating film 207. Meanwhile, the capacitor Cst is formed between the thin film transistors Ts and Td. As shown in the drawing, a first electrode 108 is formed on the gate insulating film 205, an interlayer insulating film 207 is formed on the first electrode 108, and a second electrode 113 is formed on the interlayer insulating film 207. ) Is formed. The interlayer insulating film 207 functions as a dielectric. The capacitor Cst is formed by the first electrode 108 and the second electrode 113 and the interlayer insulating film 207 interposed therebetween. The first electrode 108 may be made of the same material as the gate electrode, and the second electrode 113 may be made of the same material as the source and drain electrodes.

According to the related art, in order to increase the capacitance of the capacitor, the area of the electrode should be increased, but this has a problem in that the aperture ratio is lowered because the area of the pixel area of the organic EL device is reduced.

Meanwhile, the liquid crystal display device disclosed in Korean Laid-Open Publication No. 2000-0034034 includes a capacitor using only a pixel electrode and a gate electrode.

Although the capacitor is formed using the same material as the pixel electrode, it may be inefficient in that other electrodes are not used. Therefore, there is a limit to increasing the capacity of the capacitor.

Therefore, in view of the high capacity of the capacitor and the improvement of the aperture ratio, the above-described conventional technologies are deficient.

The present invention has been made to solve the above problems, by using a pixel electrode An object of the present invention is to provide a flat panel display device having a capacitor capable of increasing the capacitor capacity, thereby reducing the capacitor size and increasing the aperture ratio.

In order to achieve the above object, the present invention provides a thin film transistor comprising a semiconductor thin film, a gate electrode opposed to be insulated from the semiconductor thin film, and a source and a drain electrode connected to the semiconductor thin film; An organic electroluminescent device having a pixel electrode electrically connected to the thin film transistor, an opposite electrode facing the pixel electrode, and an organic light emitting layer interposed between the pixel electrode and the opposite electrode; And a capacitor having at least two electrodes facing each other to be insulated from each other, wherein one of the electrodes is formed of the same material as the pixel electrode on the same layer as the pixel electrode. Provide a display device.

According to another aspect of the present invention, any one of the electrodes of the capacitor may be formed of the same material as the semiconductor thin film of the thin film transistor.

According to another feature of the invention, the semiconductor thin film may be made of polysilicon.

According to another feature of the invention, any one of the electrodes of the capacitor may be provided with the same material as the gate electrode of the thin film transistor.

According to another feature of the invention, any one of the electrodes of the capacitor may be formed of the same material as the source and drain electrodes of the thin film transistor.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

3 is a plan view illustrating one pixel of the active matrix organic electroluminescent display of the present invention.

First of all, there are a data line 301, a scan line 303, and a power line 305 that define a pixel. The scan line 303 is connected to the gate electrode 307 of the switching thin film transistor Ts, the data line 301 is connected to the source electrode 304 of the switching thin film transistor Ts, and the source electrode 304 Is connected to the source region (not shown) of the active layer of the switching thin film transistor Ts through the first contact hole 309, and the drain electrode 306 is connected to the switching thin film transistor Ts through the second contact hole 302. It is connected to the drain region (not shown) of the active layer of. In addition, the drain electrode 306 of the switching thin film transistor Ts is connected to the first electrode 308 of the capacitor Cst through the third contact hole 311. The power line 305 is connected to the source electrode 312 of the driving thin film transistor Td and the second electrode 313 of the capacitor Cst. Meanwhile, the first electrode 308 is connected to the third electrode 323 through the seventh contact hole 321. In the relationship between the first electrode 308 and the third electrode 323, the second electrode 313 overlaps the first electrode 308, and the third electrode 313 is disposed on the second electrode 313. 323 are located overlapping. In addition, although not shown in FIG. 3, there may be a fourth electrode connected to the second electrode 313 by a contact hole and positioned below the first electrode. The first electrode and the third electrode are connected to be one electrode, and the second electrode and the fourth electrode are connected to be another electrode. An insulating film (not shown) is interposed between the electrodes to form a capacitor Cst. The first electrode may be made of the same material as the gate electrode of the thin film transistor, and the second electrode may be made of the same material as the source and drain electrodes of the thin film transistor. The third electrode may be made of the same material as the pixel electrode on the same layer as the pixel electrode, and the fourth electrode may be made of the same material as the semiconductor thin film of the thin film transistor. The semiconductor thin film may be formed of polysilicon. The source electrode 312 of the driving thin film transistor Td is connected to the source region (not shown) of the active layer of the driving thin film transistor Td through the fourth contact hole 315 and the drain electrode of the driving thin film transistor Td. 316 is connected to the drain region (not shown) of the active layer of the driving thin film transistor Td through the fifth contact hole 318. In addition, the drain electrode 316 is connected to the pixel electrode 317 through the sixth contact hole 319.

The operating principle is that when a voltage is applied to the gate electrode 307 of the switching thin film transistor Ts through the scan line 303, the switching thin film transistor Ts is turned on. When the data signal is input to the switching thin film transistor Ts through the data line 301, the data signal is stored in the capacitor Cst via the drain electrode 306 of the switching thin film transistor Ts. The data signal is transmitted to the gate electrode 314 of the driving thin film transistor Td to operate the driving thin film transistor Td. Accordingly, a signal is applied to the pixel electrode 317 through the drain electrode 316 of the driving thin film transistor Td, thereby emitting light from the organic light emitting layer (not shown).

FIG. 4 is a cross-sectional view of one pixel of the active matrix organic electroluminescent display of the present invention taken along line II-II 'of FIG. 3.

A buffer layer 403 is formed on an insulating substrate 401 made of glass, and a thin film transistor and a capacitor Cst are formed on the buffer layer 403. As shown in FIG. 4, a switching thin film transistor Ts and a driving thin film transistor Td are formed. First, the buffer layer 403 may be formed of SiO ₂ , and may be deposited to about 3000 GPa by PECVD, APCVD, LPCVD, ECR, or the like. The substrate 401 may be formed of a plastic material. In this case, the buffer layer may be omitted.

The switching thin film transistor Ts and the driving thin film transistor Td may include active layers 420 and 430 formed on a buffer layer, a gate insulating film 405 and a gate electrode formed on the gate insulating film 405 on the active layers 420 and 430. 307 and 314 and source electrodes 304 and 312 and drain electrodes 306 and 316 connected to the active layer.

The active layers 420 and 430 may be formed of an inorganic semiconductor or an organic semiconductor, and are formed at about 100 GPa. When the active layer is formed of polysilicon in the inorganic semiconductor, after the amorphous silicon is formed, it can be polycrystallized by various crystallization methods. This active layer has a channel region therebetween if it has a source and drain region heavily doped with N-type or P-type impurities.

Silicon oxide (SiO ₂ ) on top of the active layer The gate insulating film 405 is provided, and the gate electrodes 307 and 314 are formed of a conductive metal film such as MoW, Al, Cr, Al / Cu, and the like on a predetermined region of the gate insulating film 405. The material forming the gate electrodes 307 and 314 is not limited thereto, and various conductive materials such as conductive polymers may be used as the gate electrodes 307 and 314. The region where the gate electrodes 307 and 314 are formed corresponds to the channel region of the active layer.

An interlayer insulating layer 407 is formed on the gate electrodes 307 and 314 by using silicon oxide (SiO ₂₎ or silicon nitride (SiNx). The source electrodes 304 and 312 and the drain electrodes 306 and 316 are formed on the interlayer insulating film 407 in the state where the contact holes are drilled in the interlayer insulating film 407 and the gate insulating film 405. As the source electrodes 304 and 312 and the drain electrodes 306 and 316, a conductive metal film such as MoW, Al, Cr, Al / Cu, or a conductive polymer may be used.

A passivation film 409 made of silicon nitride (SiNx) or the like is formed on the source electrodes 304 and 312 and the drain electrodes 306 and 316. A pixel definition layer 435 made of acryl, polyimide, or the like may be formed on the passivation layer 409.

The structure of the thin film transistor as described above is not necessarily limited thereto, and the structure of the conventional general thin film transistor may be adopted as it is.

Referring to the capacitor Cst, the capacitor Cst is formed between the switching thin film transistor Ts and the driving thin film transistor Td. A buffer layer 403 is formed on the substrate 401, and a fourth electrode 440 is formed on the buffer layer 403 using the same material as that of the polysilicon 420 and 430 of the thin film transistor. Next, a gate insulating film 405 is formed to insulate the gate electrodes 307 and 314 of the thin film transistor, and a first electrode 308 is formed on the gate insulating film 405 with the same material as the gate electrodes 307 and 314 of the thin film transistor. do. Next, an interlayer insulating film 407 is formed over the gate electrodes 307 and 314. Next, an eighth contact hole 425 is formed to connect with the fourth electrode 440. The second electrode 313 is formed of the same material as the source electrodes 304 and 312 and the drain electrodes 306 and 316 of the thin film transistor in the region where the eighth contact hole 425 is formed. Next, a passivation film 409 is formed on the second electrode 313. A seventh contact hole 321 penetrating the passivation film 409 is formed to connect the second electrode 313, and a third electrode 323 is formed on the same material as the pixel electrode 317. do. That is, the first electrode 308 overlaps the fourth electrode 440, the second electrode 313 overlaps the first electrode 308, and the second electrode 313 overlaps the second electrode 313. The three electrodes 323 overlap each other. In addition, the fourth electrode 440 and the second electrode 313 are connected through the eighth contact hole 425 to become one electrode constituting the capacitor Cst, and the first electrode 308 and the third electrode ( 323 is connected through the seventh contact hole 321 to become another electrode constituting the capacitor Cst. The gate insulating film 405, the interlayer insulating film 407, and the passivation film 409 positioned between each electrode function as a dielectric constituting the capacitor Cst.

In the organic light emitting diode display, an organic light emitting diode OLED is connected to the drain electrode 316 of the driving thin film transistor Td, and may be connected to a pixel electrode 317 of the organic light emitting diode OLED. . The pixel electrode 317 may be formed on the passivation film 409, and a pixel definition film 435 may be formed on the pixel electrode 317, and a predetermined opening may be formed in the pixel definition film 435. Thereafter, an organic light emitting diode (OLED) may be formed.

The organic light emitting diode OLED emits red, green, and blue light according to the flow of current to display predetermined image information, and is connected to and connected to the drain electrode 316 of the driving thin film transistor Td. A pixel electrode 317 receiving positive power, an opposite electrode 455 provided to cover all pixels, and supplying negative power, and disposed between the pixel electrode 317 and the opposite electrode 455 to emit light It may be composed of an organic light emitting film.

The pixel electrode 317 may be formed of a transparent electrode such as ITO or a reflective electrode of Al / ITO, and the counter electrode 455 may be entirely deposited by Al / Ca or the like in the case of a bottom emission type for implementing an image toward a substrate. In the case of a top emission type for forming an image toward the counter electrode 455, a transparent electrode may be formed of Mg-Ag / ITO. The counter electrode 455 does not necessarily have to be entirely deposited, and of course, may be formed in various patterns. Of course, the pixel electrode 317 and the counter electrode 455 may be stacked on opposite sides of each other.

The organic film may be a low molecular or polymer organic film. When the low molecular organic film is used, a hole injection layer (HIL), a hole transport layer (HTL), an organic emission layer (EML), and an electron transport layer (ETL) may be used. : Electron Transport Layer (EIL), Electron Injection Layer (EIL), etc. can be formed by stacking single or complex structure. Usable organic materials are also copper phthalocyanine (CuPc), N, N-D (Naphthalen-1-yl) -N, N'-diphenyl-benzidine (N, N'-Di (naphthalene-1-yl) -N, N'-diphenyl-benzidine: NPB), tris-8-hydroxy Various applications are possible, including quinoline aluminum (tris-8-hydroxyquinoline aluminum) (Alq3). These low molecular weight organic films can be formed by a vacuum deposition method.

In the case of the polymer organic film, it may have a structure generally provided with a hole transport layer (HTL) and a light emitting layer (EML), wherein PEDOT is used as the hole transport layer (HTL), and poly-phenyleneylene (PPV) and polyflu as the light emitting layer. Polymer organic materials such as polyfluorene are used and can be formed by screen printing or inkjet printing.

The structure of the organic light emitting diode OLED is not necessarily limited thereto, and various modifications may be applied thereto.

5 is a simplified cross-sectional view of the capacitor portion of FIG. 4.

The first electrode 308, the second electrode 313, and the third electrode 323 are sequentially formed on the fourth electrode 440, and the fourth electrode 440 and the second electrode 313 are connected to each other. The first electrode 308 and the third electrode 323 are connected. The connection structure between the fourth electrode 440 and the second electrode 313 is a 'c' shape, and becomes one electrode constituting the capacitor Cst. In addition, the connection structure between the first electrode 308 and the third electrode 323 is also a 'C' shape, and is the other electrode constituting the capacitor Cst. A dielectric is formed between the electrodes. The capacitor Cst is formed in a form of a combination of '-shaped' electrodes.

The capacitance of the capacitor Cst is proportional to the relative dielectric constant and the area of the electrode constituting the capacitor Cst, and is inversely proportional to the distance between the electrodes of the capacitor Cst. Therefore, in the trend of increasing the capacity of the capacitor Cst, there are efforts to increase the area of the electrode, reduce the distance between the electrodes, or use a material having a high dielectric constant as the dielectric. In the present invention, the capacitor Cst has a four-layer electrode structure in a way to increase the capacitance of the capacitor Cst by increasing the area of the capacitor Cst electrode. Each electrode has a form of staggered coupling. As shown in the drawing, the first common area 501 between the fourth electrode 440 and the first electrode 308, and the second common area 503 of the first electrode 308 and the second electrode 313. The area of the capacitor Cst electrode is increased by the sum of the third common area 505 of the second electrode 313 and the third electrode 323. Therefore, the capacitor (Cst) capacity is greatly increased. In the present invention, the fourth electrode 440 is made of the same material as the polysilicon of the thin film transistor, the first electrode 308 is made of the same material as the gate electrode of the thin film transistor, and the second electrode 313 is a source electrode of the thin film transistor and The third electrode 323 is made of the same material as the drain electrode, and the third electrode 323 is made of the same material as the pixel electrode. Therefore, in the process of producing the organic electroluminescent device, it is possible to simply implement the capacitor (Cst) having increased capacity by using the materials used in each process. In the organic electroluminescent device, especially in the bottom emission type organic electroluminescent device, the aperture ratio tends to depend on the size of the capacitor Cst. The aperture ratio may be improved by reducing the size of the capacitor Cst and simultaneously increasing the pixel area. However, if the size of the capacitor Cst is reduced, the capacity of the capacitor Cst is reduced, which is a problem. According to the present invention, since the overlapped area of the electrode of the capacitor Cst can be increased by the four-layer structure, the capacity of the capacitor Cst can be increased regardless of the size of the capacitor Cst. In addition, it is possible to reduce the size of the capacitor (Cst) within the limit to obtain the desired capacity of the capacitor (Cst). Therefore, since the pixel area can be relatively increased, the four-layer structure of the present invention can be of great help in improving the aperture ratio, particularly in the bottom emission type organic electroluminescent device.

According to the present invention as described above, the following effects can be obtained.

First, the capacitor is formed in a four-layer structure using the pixel electrode, and the first electrode and the second electrode connected in a 'c' shape are alternately coupled to increase the area of the capacitor electrode, thereby increasing the capacity of the capacitor.

Second, due to the increased capacitor capacitance, the area of the source electrode and the drain electrode can be reduced, so that the area of the pixel region can be relatively large, particularly in a bottom emission type organic light emitting display device, thereby improving the aperture ratio.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art various modifications and variations of the present invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (5)

A thin film transistor including a semiconductor thin film, a gate electrode facing the semiconductor thin film so as to be insulated from the semiconductor thin film, and a source and a drain electrode connected to the semiconductor thin film; An organic electroluminescent device having a pixel electrode electrically connected to the thin film transistor, an opposite electrode facing the pixel electrode, and an organic light emitting layer interposed between the pixel electrode and the opposite electrode; And A first electrode formed on the same layer as the gate electrode, a second electrode formed on the same layer as the source and drain electrodes, a third electrode formed of the same material as the pixel electrode on the same layer as the pixel electrode, and the semiconductor A stacked type capacitor having a fourth electrode formed on the same layer as the thin film, The capacitor includes an organic light emitting display device in which the first electrode and the third electrode are connected by a contact hole, and the second electrode and the fourth electrode are connected by a contact hole. The method of claim 1, And the fourth electrode of the capacitor is formed of the same material as the semiconductor thin film of the thin film transistor. The method of claim 2, And the semiconductor thin film is made of polysilicon. The method of claim 1, And the first electrode of the capacitor is formed of the same material as the gate electrode of the thin film transistor. The method of claim 1, The second electrode of the capacitor is formed of the same material as the source and drain electrodes of the thin film transistor.

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