JP2009059640A - Organic electroluminescent display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To alleviate brightness unevenness of emission of organic EL elements by lowering resistance values of power wirings without raising manufacturing cost. <P>SOLUTION: A reflecting layer 101, a first transparent electrode 104, organic EL light-emitting layers 105, 106, and a second transparent electrode 107 are laminated in that order, emission light from the organic EL light-emitting layers 105, 106 is reflected toward a front face of the display device with the reflecting layer 101. The reflecting layer 101, formed of a material capable of conducting electricity, is connected with electric wires. Further, the reflecting layer 101 is electrically insulated from the first transparent electrode 104 by an insulating layer 102 provided on the surface of a first transparent electrode 104 side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic EL display device in which light emitted from an organic compound layer is reflected by a reflective layer to the front surface of the display device.

  In recent years, display devices using organic electroluminescence (organic EL, OLED) have been actively developed. The methods for turning on the organic EL elements are roughly classified into a passive matrix driving method and an active matrix driving method.

  In the passive matrix driving method, wiring of a matrix is performed for all the pixels configured by the organic EL elements in the display device, and a desired pixel is turned on by selecting a wiring of this matrix and flowing a current.

  On the other hand, in the active matrix driving method, an active element such as a low-temperature polycrystalline silicon transistor (hereinafter referred to as TFT) is arranged and driven in each pixel to light a desired pixel.

  Here, in the display device of the passive matrix driving system, since the matrix wiring is arranged in the display device, the pixel and the wiring occupy the space in the display device, and the pixel space corresponds to the space for the wiring. The space is narrow. That is, in the passive matrix driving method, the area of the pixel is reduced due to the influence of the wiring.

  In contrast, in an active matrix drive type display device using TFTs, a TFT is used for each pixel, and an organic EL element is stacked on the upper surface or the lower surface of the TFT, thereby providing a display device having a high pixel aperture ratio. can do. In this manner, the active matrix driving method can be suitably used for a high-definition display device because pixels can be reduced by increasing the aperture ratio. Therefore, the active matrix driving method is mainstream in high-definition display devices using organic EL.

  In the wiring connection using the TFT, the source electrode of the TFT is connected to the first power wiring, the anode of the organic EL element is connected to the drain of the TFT, and the common second power wiring is connected to the cathode of the organic EL element. . Then, by selectively turning on / off the TFT, a current from the first power wiring flows through the TFT to the organic EL element, and the current returns to the power source through the second power wiring. Here, when a plurality of pixels are turned ON at the same time, a voltage drop occurs due to the current for the plurality of pixels passing through the resistance of the power wiring. Then, the power supply voltage is lowered by the voltage drop generated in the first power wiring and the second power wiring, and a desired current does not flow through the organic EL element. Therefore, luminance unevenness is caused in the light emission of the organic EL element.

  Therefore, a technique for reducing the resistance value of the power wiring has been developed (see Patent Document 1).

  A conventional organic EL display device described in Patent Document 1 will be described with reference to FIGS. 8 and 9 are cross-sectional views of a pixel region constituting a conventional organic EL display device. 8 and 9, the cross-sectional directions are different.

  In the figure, 801 is a storage capacitor, 802 is a substrate, 803 is a channel region, 804 is a source, 805 is a drain, 806 is an electric signal wiring, 807 and 808 are relay conductive layers, 809 is an anode conductive film, 810 is a contact hole, Reference numeral 811 denotes a cathode conductive film (auxiliary conductive layer). Reference numeral 812 denotes a first capacitor electrode, 813 denotes a second capacitor electrode, 814 denotes a protective insulating layer, 815 denotes a gate insulating layer, 816 denotes a first interlayer insulating layer, 817 denotes a semiconductor layer, 818 denotes a gate electrode, and 819 denotes an element electrode. , 820 denotes a hole transport layer, 821 denotes a light emitting layer, and 822 denotes a common cathode.

  As shown in FIGS. 8 and 9, the conventional organic EL display device described in Patent Document 1 is provided with a plurality of scanning lines and a plurality of electric signal wirings 806 extending perpendicularly to these scanning lines. It has been. A region surrounded by the scanning lines and the electric signal wiring 806 corresponds to an element region. A switching TFT is provided at this intersection, and a storage capacitor 801 is connected between the gate and the source. In addition, the drain of the TFT is connected to the element electrode 819 through the contact hole 810. The element electrode 819 is connected to the hole transport layer 820, the hole transport layer 820 is connected to the light emitting layer 821, and the cathode of the organic functional layer including the hole transport layer 820 and the light emitting layer 821 serves as the common cathode 822. It is connected. The common cathode 822 is connected to the cathode conductive film (auxiliary conductive layer) 811.

  In the conventional organic EL display device described in Patent Document 1, an interlayer insulating film is disposed on the first power wiring, and a second power wiring is disposed on the interlayer insulating film, thereby providing a first power. The wiring and the second power wiring are connected through a contact hole. And by setting it as such a structure, the resistance value parasitic on a power wiring is reduced.

JP 2005-215354 A

  However, the conventional organic EL display device described in Patent Document 1 requires a process step for forming an interlayer insulating film that insulates the first power wiring and the second power wiring, and the interlayer insulating film Process steps for creating contact holes are required. Therefore, in the conventional organic EL display device described in Patent Document 1, a process step has to be added in order to reduce the power wiring resistance, and there is a problem that the manufacturing cost increases.

  The present invention has been proposed in view of the above-described circumstances, and can reduce the luminance unevenness of light emission of the organic EL element by reducing the resistance value of the power wiring without increasing the manufacturing cost. The purpose is to provide.

  The organic EL display device of the present invention has the following features in order to achieve the above-described object. That is, in the organic EL display device of the present invention, the reflective layer, the first transparent electrode, the organic compound layer, and the second transparent electrode are laminated in this order, and light emitted from the organic compound layer is reflected from the front surface of the display device. It is the structure which reflects toward. The reflective layer is formed of an electrically conductive material and connected to the electrical wiring. Furthermore, the reflective layer is electrically insulated from the first transparent electrode by providing an insulating layer on the surface on the first transparent electrode side.

  According to the organic EL display device of the present invention, the function of the power wiring is shared with the reflective layer for guiding the light emitted from the organic compound layer, which is an organic EL element, to the outside, so that the interlayer insulating film and the contact hole can be formed. No need to create a process. For this reason, it becomes possible by using the existing process to reduce the resistance value of the power wiring without increasing the manufacturing cost.

  In addition, since a desired current flows through the organic EL element by lowering the resistance value of the power wiring, a high-quality organic EL display device with no luminance unevenness can be obtained.

  Hereinafter, embodiments of the organic EL display device of the present invention will be described with reference to the drawings.

<First Embodiment>
First, the organic EL display device according to the first embodiment of the present invention will be described.

  1, 2, and 3 show an organic EL display device according to a first embodiment of the present invention, FIG. 1 is a plan view of the organic EL display device, and FIG. 2 is a direction A in FIG. 1. FIG. 3 is a longitudinal sectional view in the direction B in FIG.

  In the figure, reference numeral 101 denotes a reflective layer, 103 denotes a contact hole for connecting the reflective layer and a lower electrical wiring, and 105 and 106 denote organic EL light emitting layers which are organic compound layers. In the figure, 102 is an insulating layer made of a metal oxide film, 104 is a first transparent electrode, 107 is a second transparent electrode, 108 is a planarizing film, 109 is an element isolation film for separating pixels, and 110 is an organic EL light emitting device. A TFT for driving the layers 105 and 106 is shown.

  In the organic EL display device according to the first embodiment of the present invention, as shown in FIGS. 1 to 3, the source (S) of the TFT 110 is connected to a power source. One side of the first transparent electrode 104 is connected to the drain (D) of the TFT 110, and one side of the organic EL light emitting layers 105 and 106, which are organic compound layers, is connected to the other side of the first transparent electrode 104. Further, the second transparent electrode 107 is connected to the other side of the organic EL light emitting layers 105 and 106 which are organic compound layers, and the second transparent electrode 107 is connected to the GND of the power source.

  By driving the TFT 110, a current flows through the organic EL light emitting layers 105 and 106 that are organic compound layers, and the organic EL light emitting layers 105 and 106 emit light. Here, when the light emitted from the organic EL light emitting layers 105 and 106 which are organic compound layers is directly emitted toward the second transparent electrode 107, the light passes through the first transparent electrode 104 in the opposite direction and passes through the first transparent electrode 104. In some cases, the light is reflected and emitted upward in FIGS. 2 and 3.

  The wiring resistance in the organic EL display device having such a configuration will be described. FIG. 5 is a drive circuit diagram of the TFT. In the figure, reference numeral 501 denotes a storage capacitor, 502 denotes a wiring resistance, and 503 denotes a GND wiring resistance.

  As shown in FIG. 5, when the wiring resistance 502 is generated in the power supply line of the TFT 110, the potential of the source (S) of the TFT 110 is lowered due to the voltage drop. Then, the gate-source voltage VGS of the TFT 110 is lowered, and a desired current does not flow to the organic EL light emitting layer 105.

  In order to avoid such a phenomenon, the wiring resistance of the power supply line may be reduced. That is, by reducing the wiring resistance of the power supply line, the gate-source voltage VGS of the TFT 110 can be prevented from being lowered, and a desired current can be output to the organic EL light emitting layer 105.

  Here, a voltage drop occurs due to the GND wiring resistance 503 at the cathode of the organic EL light emitting layer 105. The influence is compensated by the drain-source voltage VDS of the TFT 110, and a desired current is continuously output to the organic EL display device. .

  In the organic EL display device according to the first embodiment of the present invention, a method for reducing the wiring resistance of the power supply line is as follows.

  That is, the reflective layer 101 and the metal wiring are connected by a contact hole so that power is shared between adjacent elements, and the insulating layer 102 is formed by oxidizing the surface of the reflective layer 101 on the first transparent electrode side. Thereby, the reflective layer 101 can be used as an electrical wiring. Note that the electrical wiring means a power supply and a GND wiring or an electric signal wiring.

  Here, any method may be used to insulate the reflective layer 101. For example, the reflective layer 101 can be electrically insulated by oxidizing or nitriding the surface of the reflective layer 101.

The reflective layer 101 is made of an electrically conductive material, and examples of such a material include a material mainly composed of Cr or Al. In addition, the material which has Cr or Al as a main component is a Cr simple substance, Al simple substance, and the material which made these contain Si, Cu, etc. The insulating layer 102 can be formed by oxidizing the surface of the reflective layer 101 with oxygen or nitriding with nitrogen. Specifically, when the reflective layer 101 is formed of Cr alone or a material containing Cr, Si, Cu or the like, the surface thereof is oxidized or nitrided to obtain Cr ₂ O ₃ , CrN, SiO ₂ , An insulating layer 102 such as SiN, CuO, or CuN can be formed. Further, in the case of forming a reflective layer 101 on the Al alone or Al Si, the material containing Cu or the like, by oxidizing or nitriding the _{surface, ALO 2, ALN, SiO 2} , SiN, CuO, CuN Or the like. By this insulating layer 102, the reflective layer 101 and the first transparent electrode 104 are electrically insulated.

  Next, power wiring of the organic EL display device according to the first embodiment of the present invention will be described. FIG. 6 is a schematic diagram of an organic EL display device using conventional power wiring, and FIG. 7 is a schematic diagram of the power wiring of the organic EL display device according to the first embodiment of the present invention.

  FIG. 7 shows the organic EL display device in a simplified manner and does not show all the light emitting element regions. However, in the actual organic EL display device, the light emitting element regions are arranged in an array. FIG. 6 shows the positional relationship between the power lines and the pixels of the organic EL display device.

  In the figure, 600 is an organic EL display device, 601, 602, and 603 are power lines, 604 is a pixel portion, and 605 and 606 are external electrode portions (PAD). In the figure, reference numerals 701 and 702 denote power wirings.

  In the organic EL display device according to the first embodiment of the present invention, as shown in FIG. 7, power lines are connected to external electrode portions (PAD) 605 and 606, respectively, and the external electrode portions 605 and 606 are connected to the counter electrode. The power wiring is extended to the end of the position to be connected, and each is connected in common.

  As shown in FIG. 6, in the conventional organic EL display device, the resistance values parasitic on the power wirings 601 and 602 are R1 and R2, respectively, and the resistance value parasitic on the power wiring 603 up to the pixel portion 604 is R3. . Here, the total resistance value parasitic up to the pixel portion 604 can be expressed as R1 // R2 + R3.

  In the organic EL display device according to the first embodiment of the present invention, as shown in FIG. 7, the reflective layer 101 is used as the power wiring, and the power wiring resistance can be represented by R4 // R5.

  Here, an approximate power wiring resistance value is calculated assuming an organic EL display device for mobile use in which the panel is 3 inches and the pixel is located in the center.

  In the conventional organic EL display device shown in FIG. 6, the sheet resistance value of the Al power wiring is 50 mΩ / □, the number of sheets of the power wirings 601 and 602 is 80 sheets, and the number of sheets of the power wiring 603 is 1150 sheets. Approximate the wiring resistance value.

  In this case, the power wiring resistance value is (80/80 + 1150) × 50 mΩ / □ = 59.5Ω.

  Assuming that the current flowing per element of the organic EL is 100 nA and the total number of elements is QVGA (320 columns × 240 rows × RGB), the voltage drop due to the wiring resistance can be expressed as the following formula (1).

    100 nA × 320 × 240 × 3 × 59.5 = 1.37 V (1)

  This voltage drop reduces the gate-source voltage VGS of the TFT.

  Here, when the current flowing through the organic EL element is defined as IEL and calculated using the relational expression of the current / voltage of the TFT, the following expression (2) is obtained.

IEL = β / 2 · (VGS−Vth) ² (2)

  Β is the shape of the TFT, and is a value determined from the gate film thickness and carrier mobility. Vth is a gate-source voltage VGS at which a current starts to flow when a voltage is gradually applied between the gate and source of the TFT.

  The current IEL ′ of the organic EL element due to the power wiring resistance can be expressed by the following formula (3) from the formulas (1) and (2).

IEL ′ = β / 2 · (VGS−1.37−Vth) ² (3)

  From the expressions (2) and (3), the degree of influence of the IEL due to the power wiring resistance can be expressed by the following expression (4).

(IEL′−IEL) / IEL = {voltage drop / (VGS−Vth)} ² −2 · voltage drop / (VGS−Vth) (4)

  Here, when VGS−Vth is set to 2.5 v, the value of the following formula (5) is obtained from the formula (4).

(1.37 / 2.5) ² −2 · 1.37 / 2.5 = −20.4% (5)

  From the above formula (5), when the power wiring has a resistance value of 59.5Ω, the current flowing through the organic EL element is reduced by 20.4%, and the light emission luminance of the organic EL element is reduced by 20.4%. .

  Similarly, in the organic EL display device according to the first embodiment of the present invention shown in FIG. 7, the sheet resistance value of the Al power wiring is 50 mΩ / □, the sheet resistance value of the reflective layer 101 is 50 mΩ / □, The number of sheets of the wirings 701 and 702 is two. In this case, the approximate value of the power wiring resistance value is 2/2/2 × 50 mΩ / □ = 50 mΩ, and the voltage drop due to the power wiring resistance value is 100 nA × 320 × 240 × 3 × 50 m = 1.152 mV.

  Substituting this voltage drop into equation (4) gives the value of equation (6) below.

(1.152 m / 2.5) ² -2.1.152 m / 2.5 = -0.09% (6)

  From the above formula (6), when the power wiring resistance is 50 mΩ, the current flowing through the organic EL element is reduced by 0.09%, and the light emission luminance of the organic EL element is reduced by 0.09%. That is, the light emission luminance of the organic EL element, which has been reduced by 20.4% in the conventional organic EL display device, is reduced to 0.09% in the organic EL display device according to the first embodiment of the present invention.

  As described above, in the organic EL display device according to the first embodiment, since the power wiring is laid out so as to cover the element region and the impedance of the wiring is low, resistance to external noise is increased. For example, when electrostatic noise flows from the outside, the electrostatic noise flows away to the power supply terminal having a low impedance, and does not destroy the TFT constituting the pixel.

  In addition, the organic EL display device according to the first embodiment also has high resistance to internal noise. For example, even when inductive noise occurs due to current fluctuation, it is possible to prevent noise from flowing into the power supply terminal with low impedance and flowing into the TFT.

  Further, the reflective layer 101 is not limited to being used as a power wiring, but may be used as an electric signal wiring. For example, when the sheet resistance of the wiring is 50 mΩ / □ and the sheet resistance of the reflective layer 101 is 50 mΩ / □, the wiring and the reflective layer 101 are overlapped, so that the sheet resistance is 50 mΩ / □ //. 50 mΩ / □ = 25 mΩ / □.

<Second Embodiment>
Next, an organic EL display device according to a second embodiment of the present invention will be described.

  FIG. 4 is a plan view of an organic EL display device according to the second embodiment of the present invention. In FIG. 4, portions having the same functions as those of the above-described first embodiment are described with the same reference numerals.

  In the first embodiment, as shown in FIG. 7, the power wiring is shared in the horizontal direction of the reflective layer 101. On the other hand, in the second embodiment, as shown in FIG. 4, the power supply wiring is also shared in the vertical direction of the reflective layer 401 in order to further reduce the resistance value of the power wiring.

  Here, when the number of sheets of Al power wiring is roughly estimated as 0.65 sheets, the power wiring resistance value is 0.65 // 0.65 × 50 mΩ / □ = 16.25 mΩ.

  The voltage drop due to the power wiring resistance value is 100 nA × 320 × 240 × 3 × 16.25 m = 0.374 mV.

  When this voltage drop is substituted into the above equation (4), the value of the following equation (7) is obtained.

(0.374 m / 2.5) ² −2 · 0.374 m / 2.5 = −0.01% (7)

  From the above formula (7), when the power wiring resistance is 50 mΩ, the current flowing through the organic EL element is reduced by 0.01%, and the light emission luminance of the organic EL element is reduced by 0.01%. It can be seen that it is further reduced than the decrease of 0.09%.

<Specific effects>
As described above, according to the organic EL display device of the present invention, the function of the power wiring is shared with the reflective layer that guides the light emitted from the organic compound layer to the outside, thereby increasing the power without increasing the manufacturing cost. The resistance value of the wiring can be lowered. For this reason, it becomes a high-quality organic EL display device with no luminance unevenness.

Here, when the wiring resistance value of the existing power wiring is R _kizon and the wiring resistance value of the reflective layer is R _hansyametaru , the total resistance value R _souteikou of the power wiring is expressed as R _souteikou = R _kizon // R _hansyametaru be able to. Therefore, in the organic EL display device of the present invention, the total power wiring resistance value can be reduced as compared with the wiring resistance value R _kizon of the existing power wiring.

  And the voltage drop of the power wiring part produced by the electric current which flows into an organic EL element can be reduced by reducing the resistance value of a power wiring.

  Further, the wiring impedance is lowered by connecting the reflective layer to a power source or GND and using it as a power wiring. For this reason, even if noise flows from the outside, this noise flows to the power supply or GND via the reflective layer, so that active / passive elements such as TFTs and capacitors in the lower layer can be protected. Further, even if noise occurs when the lower TFT is switched, the noise flows to the power supply or GND via the reflective layer, so that noise emission outside the display device can be prevented.

1 is a plan view of an organic EL display device according to a first embodiment of the present invention. 1 is a longitudinal sectional view of an organic EL display device according to a first embodiment of the present invention. 1 is a longitudinal sectional view of an organic EL display device according to a first embodiment of the present invention. It is a top view of the organic electroluminescence display concerning a 2nd embodiment of the present invention. It is a drive circuit diagram of TFT. It is a schematic diagram of the organic electroluminescence display using the conventional power wiring. It is a schematic diagram of the electric power wiring of the organic electroluminescence display which concerns on the 1st Embodiment of this invention. It is sectional drawing of the pixel area | region which comprises the conventional organic EL display apparatus. It is sectional drawing of the pixel area | region which comprises the conventional organic EL display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101,401 Reflective layer 102 Insulating layer 104 1st transparent electrode 105,106 Organic electroluminescent light emitting layer 107 2nd transparent electrode 600 Organic electroluminescent display device 601,602,603,701,702, Power wiring 605,606 External electrode part (PAD) )
806 Electrical signal wiring

Claims (5)

An organic EL display device in which a reflective layer, a first transparent electrode, an organic compound layer, and a second transparent electrode are laminated in this order, and light emitted from the organic compound layer is reflected by the reflective layer toward the front surface of the display device. Because
The reflective layer is formed of an electrically conductive material and connected to an electrical wiring, and an insulating layer is provided on the surface of the first transparent electrode to be electrically insulated from the first transparent electrode. An organic EL display device characterized by comprising:   The organic EL display device according to claim 1, wherein the electrical wiring is a power supply and a GND wiring.   The organic EL display device according to claim 1, wherein the electrical wiring is an electrical signal wiring.   4. The organic EL display device according to claim 1, wherein the reflective layer is made of a material containing Cr as a main component. 5.   4. The organic EL display device according to claim 1, wherein the reflective layer is formed of a material containing Al as a main component. 5.

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