KR100639010B1 - Light emission display and the manufacturing method thereof - Google Patents

Abstract

A light emitting display device and a manufacturing method thereof are provided to reduce contraction of pixels by reducing a discharge amount of gas emitted from an acryl unit. A light emitting display device includes plural light emitting elements(OLEDR,OLEDB,OLEDG) and plural pixel circuits(120). Different light emitting elements represent different colors. The pixel circuits are electrically connected to the light emitting element and include at least two TFTs and at least one capacitor. The TFT(Thin Film Transistor) supplies current to the light emitting elements. One of a passivation layer and a planarizing layer is selectively formed on the TFT according to the color of the light emitting element.

Description

Light emitting display device and manufacturing method thereof

Figure 1a is a graph showing the amount of outgas discharge according to the acrylic planarization film thickness.

1B is a graph showing the amount of outgas discharged over time.

2 is a circuit diagram of a light emitting display device according to an embodiment of the present invention.

3 is a partially enlarged circuit diagram of FIG. 1 in which two pixels each including three subpixels are shown.

4 is a partial side cross-sectional view according to the red subpixel disclosed in FIG. 3.

5 is a partial side cross-sectional view taken along the blue subpixel illustrated in FIG. 3.

FIG. 6 is a partial side cross-sectional view taken along the green subpixel illustrated in FIG. 3.

♣ Reference numerals for main components ♣

300, 400, 500: substrate 310, 410, 510: buffer layer

320, 420, 520: semiconductor layer 330, 430, 530: gate insulating film

340, 440, 540: thin film transistors 350, 450, 550: passivation film

560: planarization film 370, 470, 580: light emitting element

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting display device and a method of manufacturing the same, and more particularly, to a light emitting display device and a method of manufacturing the same which can reduce pixel shrinkage.

Recently, various flat panel display devices having a lighter weight and a smaller volume than a cathode ray tube have been developed. In particular, a light emitting display device having excellent luminous efficiency, brightness, viewing angle, and fast response speed has been attracting attention. The light emitting display device has a back light emitting structure which emits light emitted from the light emitting display element toward the substrate side, and a front light emitting structure which emits light emitted to the cathode electrode side of the light emitting display element.

In general, to implement a high resolution of the light emitting display device, it is preferable to adopt a front light emitting structure. The top light emitting structure includes a thin film transistor formed on the substrate, a planarization film formed on the thin film transistor, and a light emitting display device electrically connected to the thin film transistor through a contact hole formed in the planarization film. The planarization film used for the front light emitting structure usually uses an acrylic planarization film. When the planarization film is formed using acrylic, a gas, such as benzaldehyde, may be formed in the acrylic itself according to the thickness and time of the acrylic planarization film. Outgases such as toluene, xylene, and benzoquinone are emitted. The emissions of these outgass are explained using the graph below.

Figure 1a is a graph showing the amount of outgas discharge according to the thickness of the acrylic planarization film, Figure 1b is a graph showing the amount of outgas discharge with time. Referring to FIG. 1A, the horizontal axis represents the thickness of the acrylic planarization film (1.1 μm to 1.8 μm), and the vertical axis represents the outgas discharged from the acrylic planarization film. In this figure, the emission level according to the outgas emissions is indicated. As shown in the graph, when the thickness of the planarization is 1.1 mu m, the out gas is not discharged, and when the thickness is 1.3 mu m, the out gas discharge level is 1, and when the thickness is 1.6 mu m, the out gas discharge level is 3. 1B, the horizontal axis represents time and the vertical axis represents outgas discharge level. As shown in the graph, it can be seen that a large amount of outgas is emitted over time.

As a result, it can be seen that the thicker the planarization film thickness and the more time elapses, the larger the amount of outgas discharged. When the outgassing increases, there is a disadvantage in that a pixel shrinkage phenomenon, namely, pixel shrinkage, in which the size of each pixel is reduced after a predetermined time elapses, is expressed. In order to solve this disadvantage, it is devised to reduce the thickness of the planarization film.

However, when the acrylic planarization film thickness is formed to be less than or equal to a predetermined thickness (for example, 1 μm or less), there is a problem that the flatness is poor, which may cause a defect of the light emitting display device itself. Furthermore, the luminous ability of the luminous means is different for each color, and in particular, in the case of green, since the luminous efficiency is relatively good compared to red and blue, it will cause more mura than the luminous elements of other colors (red and blue). Has the problem that it can.

Accordingly, the present invention has been made to solve the above-mentioned problems, and relates to a light emitting display device and a method of manufacturing the same, which can reduce pixel shrinkage by reducing the thickness of the acrylic planarization film formed on the thin film transistor.

Further, another object of the present invention is to provide a light emitting display device and a method of manufacturing the same, which can improve light emission efficiency by configuring different pixel circuits for each color of light emitting devices.

In order to achieve the above object, according to an aspect of the present invention, the light emitting display device includes a plurality of light emitting elements for displaying different colors; A plurality of pixel circuits electrically connected to the light emitting device, the plurality of pixel circuits including at least two thin film transistors for supplying current to the light emitting device, and at least one capacitor, the upper portion of the thin film transistor according to the color of the light emitting device. At least one of a passivation film and a planarization film is selected.

Preferably, the light emitting device is provided to have one or more colors of red (R), green (G), blue (B).

A planarization film is formed below the green light emitting device, and a passivation film is formed below the planarization film formed below the green light emitting device. The planarization film formed under the green light emitting device is an acrylic planarization film. The pixel circuit electrically connected to the green light emitting device further includes a threshold voltage compensation circuit for compensating a threshold voltage of one of the thin film transistors. The pixel circuit electrically connected to the green light emitting device further includes a voltage drop compensating circuit for compensating a voltage drop of the first power supplied to the recycling circuit.

A passivation film is formed under the red and blue light emitting devices. The passivation film formed under the red and blue light emitting devices is a silicon nitride film. The pixel circuit electrically connected to the red and green light emitting devices is formed so as not to cover the light emitting area of each light emitting device.

Meanwhile, according to another aspect of the present invention, a method of manufacturing a light emitting display device includes forming a plurality of thin film transistors including a gate electrode, a source, and a drain electrode on a substrate, and a capacitor electrically connected to the thin film transistors. step; Forming at least one of a passivation film and a planarization film on the thin film transistor; And forming a light emitting device electrically connected to the thin film transistor and displaying different colors according to the passivation film and the planarization film formed on the thin film transistor.

Hereinafter, with reference to the drawings according to an embodiment of the present invention, the present invention will be described in more detail.

FIG. 2 is a circuit diagram of a light emitting display device according to an exemplary embodiment of the present invention, and FIG. 3 is a partially enlarged circuit diagram of FIG. 1, and two pixels each including three subpixels are shown.

Referring to FIG. 2, the light emitting display device 100 includes an image display unit 110 including a plurality of pixels 120 displaying an image, and an image display unit 110 through a plurality of scan lines S1, S2, and Sn. ) And a scan driver 130 to transmit a selection signal to the image display unit 110, and a data driver 140 to transmit a data signal to the image display unit 110 through a plurality of data lines D1, D2, D3, and Dm.

The image display unit 110 includes a plurality of pixels 120 displaying red (R), green (G), and blue (B). Each pixel 120 includes a scan line Sn to which a selection signal such as a scan signal is applied, a first power voltage line 150 to supply a data line Dm and a first power voltage EL VDD to which a data signal is applied. And a second power supply voltage line 160 for supplying a second power supply voltage EL VSS.

In FIG. 3, two pixels each including three subpixels are illustrated. Hereinafter, one pixel will be described. Referring to FIG. 3, the pixel 120 includes three subpixels, a red subpixel 120R, a green subpixel 120G, and a blue subpixel 120B.

The red subpixel 120R includes two thin film transistors M11 and M12, one storage capacitor Cst1, and a red light emitting diode OLED R. One thin film transistor M11 constituting the red subpixel 120R is a driving thin film transistor, and the other thin film transistor M12 is a switching thin film transistor. Here, the second thin film transistor M12 is electrically connected to the scan line Sn-1 and the first data line Dm-1, and the capacitor Cst1 is connected to the second thin film transistor M12, so that the first thin film transistor M12 is electrically connected to the second thin film transistor M12. The voltage corresponding to the first data signal applied from the data line D1 is charged. In the first thin film transistor M11, a gate is connected to the capacitor Cst1, and one electrode is electrically connected to the red light emitting diode OLED R.

By the configuration of the red sub-pixel 120R, the red light emitting element 120R emits full light according to the following driving principle. First, when the second thin film transistor M12 is turned on by the scan signal applied through the scan line Sn-1, the red light emitting diode OLED R receives the data signal through the first data line Dm-1. Is passed. At this time, the capacitor Cst1 stores a voltage obtained by subtracting the voltage level of the red light emitting device power supply and the voltage level of the data signal. The voltage stored in the capacitor Cst1 is applied to the gate electrode of the first thin film transistor M1 so that a constant current flows from the source electrode of the first thin film transistor M11 toward the drain electrode. An electric current flows in 120R, and the red light emitting element 120R emits light. The red subpixel 120R constituting the pixel 120 has a cross-sectional structure as shown in FIG. 3.

The blue subpixel 120B includes two thin film transistors M31 and M32, one storage capacitor Cst3, and a blue light emitting device OLED B. One thin film transistor M31 constituting the blue subpixel 120B is a driving thin film transistor, and the other thin film transistor M32 is a switching thin film transistor. In order to avoid duplication, descriptions of the same components as the red subpixel 120R and the operation principle thereof will be omitted, and the cross-sectional structure of the blue subpixel 120B constituting the pixel 120 will be described with reference to FIG. 4. do.

Meanwhile, the green subpixel 120G includes a first thin film transistor M21 which is a driving thin film transistor, a second thin film transistor M22 which is a switching thin film transistor, a storage capacitor Cst2 and a light emitting device OLED G. In addition, a threshold voltage compensation circuit I for compensating the threshold voltage of the driving thin film transistor M22 is further included. The threshold voltage compensating circuit I includes a third thin film transistor M23, a fourth thin film transistor M24, a fifth thin film transistor M25, and a sixth thin film transistor M26. The first to sixth thin film transistors M21, M22, M23, M24, M25, and M26 may include a gate electrode, a source electrode, and a drain electrode, and the storage capacitor Cst2 may include a first electrode and a second electrode.

The gate electrode of the second thin film transistor M22 is connected to the n-th scan line Sn- 1, the source electrode is connected to the data line D2, and the drain electrode is connected to the first node A. Therefore, the data signal is transmitted to the first node A by the n-th scan signal input through the n-th scan line Sn-1. The source electrode of the first thin film transistor M21 is connected to the first node A, the drain electrode is connected to the third node C, and the gate electrode is connected to the second node B. Therefore, when the potentials of the second node B and the third node C are the same by the operation of the fourth thin film transistor M24, the first thin film transistor M21 is diode-coupled and the first node ( The data signal transmitted to A) reaches the second node B through the first thin film transistor M21. When the pixel power is delivered to the first node A, current flows from the source electrode through the drain electrode in response to the voltage applied to the gate electrode. That is, the amount of current flowing by the potential of the second node B is determined.

The gate electrode of the third thin film transistor M23 is connected to the nth scan line Sn and the drain electrode is connected to the second node B. Therefore, the n th scan signal input through the n th scan line Sn is transmitted to the second node B. FIG. The gate electrode of the fourth thin film transistor M24 is connected to the n-1 scan line Sn-1, the source electrode is connected to the third node C, and the drain electrode is connected to the second node B. . Therefore, the potentials of the second node B and the third node C are equalized by the n-1 scan signal input through the n-1 scan line Sn-1. The source electrode of the fifth thin film transistor M25 is connected to the pixel power line EL VDD, the drain electrode is connected to the first node A, and the gate electrode is connected to the emission control line En. Accordingly, the pixel power is selectively transmitted to the first thin film transistor M21 according to the emission control signal transmitted through the emission control line En.

The source electrode of the sixth thin film transistor M26 is connected to the third node C, the drain electrode is connected to the green light emitting diode OLED G, and the gate electrode is connected to the emission control line En. Therefore, the current is selectively transmitted to the green light emitting device according to the light emission control signal transmitted through the light emission control line En. The first electrode of the storage capacitor Cst2 is connected to the pixel power line EL VDD and the second electrode is connected to the second node B. Accordingly, when the initialization signal is connected to the second node B by the third thin film transistor M23, the initialization signal is transferred to the storage capacitor Cst2 so that the storage capacitor Cst2 stores the initialization voltage and the second thin film transistor M22. When the data signal is transferred to the first thin film transistor M21 by the fourth thin film transistor M24, the voltage corresponding to the data signal is charged. The storage capacitor Cst2 transfers the stored voltage to the second node B so that the voltage stored in the storage capacitor Cst2 is applied to the gate electrode of the first thin film transistor M21.

Since the green light emitting device OLED G has good luminous efficiency, the green light emitting device OLED G contributes to various kinds of Mura. In contrast, in the case of the red or blue light emitting devices OLED R and B, mura is also relatively weak since the luminous efficiency is lower than that of the green light emitting devices OLED G. Accordingly, as shown in FIG. 2, the threshold voltage compensation circuit I including a plurality of thin film transistors is applied to the green subpixel 120G, but a separate compensation is applied to the red or blue subpixel 120R and 120B. Do not apply circuits.

4 through 6 are partial side cross-sectional views of the red subpixel, the blue subpixel, and the green subpixel disclosed in FIG. 3.

Referring to FIG. 4, the cross-sectional structure of the subpixel 120R first includes a buffer layer 310 formed of a nitride film or an oxide film on an insulating substrate 300 such as glass. The buffer layer 310 is formed to prevent diffusion of impurities such as metal ions into the semiconductor layer to be described later.

Next, an amorphous silicon layer is formed on the buffer layer 310 through CVD, sputtering, or the like, and the semiconductor layer 320 is formed by crystallizing the amorphous silicon layer. In this case, the lower electrode 325a of the storage capacitor Cst1 is also formed together with the semiconductor layer 320. The semiconductor layer 320 may be formed by depositing and patterning a polysilicon layer directly on the buffer layer 310 in addition to the method of forming the amorphous silicon layer by crystallization.

The gate insulating layer 330 is formed on the semiconductor layer 320, and the gate electrode 340a is formed on the gate insulating layer 330. In this case, the upper electrode 325b of the storage capacitor Cst1 is formed together with the gate electrode 340a. Thereafter, source and drain regions (not shown) are formed by implanting impurities using the gate electrode 340a as a mask. Here, the semiconductor layer 320 under the gate electrode 340a becomes a channel region (not shown).

An interlayer insulating layer 340 is formed on the gate insulating layer 330 and the gate electrode 340a, and a plurality of contact holes (not shown) and upper electrodes 325b of the capacitor exposing the source and drain regions in the interlayer insulating layer 340. ) Is also formed with other contact holes (not shown). Next, source and drain electrodes 340b are formed to be electrically connected to the source and drain regions through the plurality of contact holes. The upper electrode 325b of the storage capacitor Cst1 is connected through another contact hole.

Next, a passivation film 350 having a predetermined thickness is formed on the source and drain electrodes 340b. The passivation film 350 includes a contact hole 350a exposing one of the source and drain electrodes 340b. In this case, the passivation film 350 is formed using an organic material, for example, an organic film such as silicon nitride. A light emitting device OLED R 370 including a first electrode 370a, a light emitting layer 370b, and a second electrode 370c is formed on the passivation film 350.

Referring to FIG. 5, the blue subpixel 120B may be described in detail. Since the blue subpixel 120B has the same structure as the red subpixel 120R except for the light emitting layer 470b of the light emitting device OLED B 470, the description of the same components will be omitted. Omit.

6 illustrates a cross-sectional structure of the green subpixel 120G in detail. Most of the components are the same as the green subpixel 120G, also the red subpixel 120R and the blue subpixel 120B, and the role thereof is also the same. Therefore, the description of the same components as the red subpixel 120R and the blue subpixel 120B will be omitted. Referring to FIG. 6, a passivation film 550 is formed on the source and drain electrodes 540b. The passivation film 550 is generally an organic film using an organic material (for example, silicon nitride). The planarization film 560 is formed on the passivation film 550. In general, the planarization layer 560 is formed to remove the step due to the pattern bending of each layer. The planarization layer 560 uses benzocyclobutene (BCB), acryl, polyimide, etc., and generally uses acryl. A contact hole 550a exposing the source and drain electrodes 540b is formed in the planarization layer, and electrically connects the light emitting element OLED 580 and the source and drain electrodes 540b through the contact hole 550a. .

As described above, the red and blue subpixel structures 120R and 120B described with reference to FIGS. 3, 4, and 5 have passivation films 350 and 450 using silicon nitride on the source and drain electrodes 340b and 440b. Only formed. In this case, the passivation film (350, 450) thickness is preferably formed to a predetermined thickness or more in order to eliminate the step caused by the pattern bending of each layer. In addition, it can be seen that the red and blue subpixel structures 120R and 120B include a pixel circuit including two thin film transistors M11 and M12 and one capacitor Cst1. That is, planarization films made of acryl or the like are not formed in the red and blue subpixel structures 120R and 120B. Accordingly, the pixel circuits 2TR and 1Cap are not disposed under the light emitting devices OLED R and OLEDB constituting the red and blue subpixel structures 120R and 120B.

     On the other hand, the passivation film 550 using silicon nitride is formed on the source and drain electrodes 540b of the green subpixel structure 120G. The planarization film 560 having a predetermined thickness is formed. The planarization film 560 is generally made of acryl, and preferably formed to have a thickness of about 1.2 μm. When the thickness of the acrylic flattening film 560 exceeds 1.2 μm, the amount of outgas discharged from the acrylic itself increases, thereby degrading the performance of the light emitting device OLED. Because. In addition, a compensation circuit for compensating threshold voltages of the pixel circuits of 2TR and 1Cap is further formed in the green subpixel 120G, which is a green light emitting device having better luminous efficiency than other light emitting devices OLED R and OLED B. In order to reduce the ura of OLED G), the pixel circuit and the compensation circuit constituting the green subpixel 120G are formed under the green light emitting device OLED G.

According to this structural feature, since the acrylic planarization film 560 is formed only in the green subpixel 120G, as a result, the acrylic planarization film 560 is entirely red, blue, and green subpixels 120R, 120B, and 120G. Since the amount of acrylic used is about one third of that of the conventional light emitting display device, the amount of outgas emitted from the acrylic planarization film can be significantly reduced. Accordingly, pixel shrinkage due to outgas emitted from acrylic can be significantly reduced. In addition, in the case of the green subpixel 120G, since the planarization film 560 having a predetermined thickness is formed, even if a pixel circuit including a plurality of thin film transistors and capacitors is disposed below the planarization film 560, the front emission is affected. Does not have

In the above-described embodiment, the passivation film and the planarization film are formed under the green light emitting device. However, the present invention is not limited thereto, and only the planarization film may be formed under the green light emitting device. Further, in the above-described embodiment, only the threshold voltage compensation circuit for compensating the threshold voltage is disclosed in the pixel circuit of the green light emitting device. Alternatively, a voltage drop compensation circuit for dropping the voltage of the first power supply may be disclosed. to be.

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

As described above, according to the present invention, by reducing the amount of acrylic used in the light emitting display device, it is possible to significantly reduce the amount of outgas discharged from the acrylic itself, thereby reducing the pixel reduction phenomenon.

In addition, by configuring a different pixel circuit for each color of the light emitting device, it is possible to improve the luminous efficiency.

Claims (18)

A plurality of light emitting devices displaying different colors; A plurality of pixel circuits electrically connected to the light emitting device and including at least two thin film transistors and at least one capacitor for supplying current to the light emitting device And at least one of a passivation film and a planarization film formed on the thin film transistor according to the color of the light emitting device. The method of claim 1, The light emitting device is provided with one or more colors of red (R), green (G), blue (B). The method of claim 2, And a flattening film formed under the green light emitting device. The method of claim 3, And a passivation film formed under the planarization film formed under the green light emitting device. The method of claim 4, wherein And a planarization film formed under the green light emitting device is an acrylic planarization film. The method of claim 4, wherein And the pixel circuit electrically connected to the green light emitting device further comprises a threshold voltage compensation circuit configured to compensate for a threshold voltage of one of the thin film transistors. The method of claim 4, wherein And the pixel circuit electrically connected to the green light emitting device further comprises a voltage drop compensating circuit for compensating a voltage drop of the first power supplied to the recycling circuit. The method of claim 2, A passivation film is formed under the red and blue light emitting devices. The method of claim 8, A passivation film formed under the red and blue light emitting devices is a silicon nitride film. The method of claim 9, And a pixel circuit electrically connected to the red and green light emitting devices so as not to cover the light emitting area of each light emitting device. Forming a plurality of thin film transistors including a gate electrode, a source and a drain electrode on a substrate, and a capacitor electrically connected to the thin film transistors; Forming at least one of a passivation film and a planarization film on the thin film transistor; And Forming a light emitting device electrically connected to the thin film transistor and displaying different colors according to the passivation layer and the planarization layer formed on the thin film transistor; Method of manufacturing a light emitting display device comprising a. The method of claim 11, And the light emitting device has one or more colors of red (R), green (G), and blue (B). The method of claim 12, When the planarization layer is formed on the thin film transistor, the green light emitting device including a pixel electrode is formed on the planarization layer. The method of claim 13, And the planarization film is an acrylic planarization film. The method of claim 13, And a threshold voltage compensating circuit electrically connected to the green light emitting device and compensating the threshold voltage of one of the thin film transistors. The method of claim 13, And a voltage drop compensation circuit electrically connected to the green light emitting device and compensating for the voltage drop of the first power supplied to the recycling circuit. The method of claim 12, When only a passivation layer is formed on the thin film transistor, any one of the red and blue light emitting elements is formed on the passivation layer. The method of claim 17, The passivation layer is formed of silicon nitride.

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