JP2006058814A - Display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent changes in the characteristics of a circuit element due to light irradiation on a lower layer than an organic EL (electroluminescence) element and to improve the picture quality in a display apparatus of a top emission system using an organic EL element. <P>SOLUTION: The display apparatus 1 comprises a driving circuit mounted on a substrate 2, an interlayer insulating film 5 provided on the substrate 2 to cover the driving circuit, and organic EL elements EL arranged on the interlayer insulating film 5, and has a structure that the emission light h of the organic EL element EL is extracted through the opposite side to the substrate 2. The organic EL element EL is connected to the driving circuit through a contact hole 5a formed in the interlayer insulating film 5, and comprises a lower electrode 6 made of a light shielding material, an organic layer 8 and an upper electrode 9 successively layered on the lower electrode 6. A thin film transistor Tr constituting the driving circuit is selectively laid only below the lower electrode 6 and below an auxiliary line 6a comprising the same layer as the lower electrode 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device using an organic EL element as a light emitting element, and more particularly to a top emission type display device that extracts emitted light from a side opposite to a substrate on which organic EL elements are arranged.

  An organic EL element using electroluminescence (hereinafter referred to as EL) of an organic material has an organic layer formed by laminating an organic hole transport layer and an organic light emitting layer between a lower electrode and an upper electrode. Thus, color tone is obtained by controlling the current value flowing through the organic EL element. Among display devices using such organic EL elements, in an active matrix display device, a pixel circuit including a thin film transistor and a capacitor element is provided for each pixel, and the organic EL element is driven by the pixel circuit. It has been broken.

  FIG. 11 is a cross-sectional view showing the layer structure of the active matrix display device as described above. As shown in this figure, the active matrix display device 100 is provided with a thin film transistor Tr and a capacitor element Cs that constitute a pixel circuit at positions corresponding to the respective pixels 101a on the substrate 101. In addition, a pixel circuit is configured by wiring using a conductive layer constituting each element. An organic EL element EL is formed on the interlayer insulating film 103 covering these pixel circuits. Each organic EL element EL includes a lower electrode (for example, an anode electrode) 104, an organic layer 105, and an upper electrode (for example, a cathode electrode) 106, which are sequentially stacked from the lower layer side. Among these, the lower electrode 104 is patterned as a pixel electrode, and is connected to the drive transistor Tr through a connection hole 103 a formed in the interlayer insulation 103. The upper electrode 106 is formed as a solid film covering all the pixels 101a, 101a,.

  An active matrix display device having the above-described layer structure is effective in securing the aperture ratio of the organic EL element 101 by adopting a so-called top emission method in which light is extracted from the side opposite to the substrate 101. . Further, with such a top emission method, the aperture ratio of the organic EL element EL does not depend on the layout of the thin film transistor Tr constituting the pixel circuit. Therefore, a pixel circuit using a plurality of thin film transistors Tr and capacitive elements Cs can be laid out in correspondence with each pixel 101a.

  In the case of such a top emission type display device, a conductive material having a high light transmittance is used for the upper electrode 106 on the side from which the emitted light h is extracted. Such a material has a high resistance value. . On the other hand, the lower electrode 104 on the substrate 101 side is configured using a metal having high reflectivity. For this reason, the auxiliary electrode 104a is provided in the same layer as the lower electrode 104, and the upper electrode 106 is connected to the auxiliary wire, thereby reducing the resistance of the upper electrode 106 (see, for example, Patent Document 1 below).

JP 2002-318556 A

  However, in the active matrix type display device having the above-described layer configuration, a pixel circuit is disposed below the organic EL element, and the circuit element constituting the pixel circuit includes a lower electrode constituting the organic EL element and In some cases, the auxiliary wiring is formed so as to protrude from the lower part of the same layer as the lower electrode. In this case, in the case of a top emission type display device, light incident from the display surface side passes through the upper electrode that covers the entire display area, and further leaks into the lower layer through the gap between the lower electrode and the auxiliary wiring. Will be irradiated to the circuit element of the pixel circuit arranged in the lower layer.

  In general, a transistor, which is one of circuit elements, changes its characteristics when exposed to light. For example, as shown in the VI characteristic of the transistor in FIG. 12, the transistor with light irradiation shown by the broken line in the figure shows an off-region compared to the transistor without light irradiation shown by the solid line in the figure. Leakage characteristics deteriorate. And deterioration of the image quality is caused by the deterioration of the leak characteristic due to such light.

  Accordingly, an object of the present invention is to improve the image quality in a top emission type display device using an organic EL element by preventing characteristic fluctuations of circuit elements due to light irradiation to a lower layer than the organic EL element.

  In order to achieve such an object, a display device of the present invention includes a driving circuit provided on a substrate, an interlayer insulating film provided on the substrate in a state of covering the driving circuit, and the interlayer insulating film And an organic EL element arranged in an array, and the light emitted from the organic EL element is extracted from the side opposite to the substrate. Among these, the organic EL element is connected to the driving circuit through a connection hole formed in the interlayer insulating film and has a lower electrode made of a light shielding material, an organic layer sequentially stacked on the lower electrode, and An upper electrode is provided. In particular, the circuit elements constituting the drive circuit are selectively disposed only on the lower electrode of the organic EL element and the lower part of the wiring composed of the same layer.

  In the display device having such a configuration, the external light incident from the display surface side of the display device passes through the upper electrode layer and reaches the lower electrode layer, and the external light transmitted through the lower electrode arrangement portion is further transmitted. The drive circuit is irradiated. However, in the configuration of the present invention, the thin film transistor that constitutes the drive circuit is selectively disposed only at the lower portion of the lower electrode and the wiring composed of the same layer as the lower electrode, so that the lower electrode layer is made of a light shielding material. As a result, the lower electrode layer becomes wrinkled, and irradiation of external light to the thin film transistor is prevented. Accordingly, characteristic fluctuations and malfunctions of the thin film transistor due to light irradiation are prevented.

  As described above, according to the display device of the present invention, it is possible to prevent characteristic fluctuations and malfunctions due to light irradiation of the thin film transistor disposed in the lower layer of the organic EL element. Therefore, in the top emission type display device using the organic EL element. It becomes possible to improve the image quality.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a main configuration of a display device according to an embodiment, and is a cross-sectional view of two pixels in a display region in which pixel portions are arranged.

  A display device 1 shown in this figure is a top emission type display device using an organic EL element, and a thin film transistor Tr and a capacitor element Cs that constitute a pixel circuit on a substrate 2 and further illustration is omitted here. A resistive element is arranged. These thin film transistors Tr and capacitive elements Cs are arranged corresponding to the respective pixels 2 a on the substrate 2. A source electrode line 4s and a drain electrode line 4d connected to the thin film transistor Tr are provided above the interlayer insulating film 3 covering these elements Tr and Cs. Further, another wiring (not shown) constituting the pixel circuit is formed by the conductive layer constituting each element Tr, Cs and the conductive layer constituting the source electrode line 4s and the drain electrode line 4d.

  Further, an upper interlayer insulating film 5 is provided in a state of covering the layers of the source electrode line 4 s and the drain electrode line 4 d, and the organic EL element EL is provided on the interlayer insulating film 5.

  Each organic EL element EL includes a lower electrode 6 connected to the drain electrode line 4 d of the thin film transistor Tr through a connection hole 5 a provided in the interlayer insulating film 5. The lower electrode 6 is used as an anode electrode (or a cathode electrode), for example, and is patterned as a pixel electrode. Each lower electrode 6 is covered with an insulating film pattern 7 so that only the central portion is widely exposed. A portion where the lower electrode 6 is exposed from the insulating film pattern 7 is a light emitting portion, for example, a portion corresponding to the pixel 2a here.

  An organic layer 8 having at least a light emitting layer is laminated on the exposed portion of each lower electrode 6 in a patterned state. The light emitting layer provided in the organic layer 8 is made of an organic material that emits light by recombination of holes and electrons injected into the light emitting layer. An upper electrode 9 is disposed and formed above each organic layer 8 and the insulating film pattern 7 patterned in this manner in a state in which insulation is maintained between the lower electrode 6. The upper electrode 9 is used as a cathode electrode (or an anode electrode), and is formed as an electrode common to each organic EL element EL.

  An auxiliary wiring 6a is formed in the same layer as the lower electrode 6 on the interlayer insulating film 5 provided with the organic EL element EL having the above-described structure, and the upper electrode 9 is in contact with the auxiliary wiring 6a. Is provided.

  FIG. 2 is a plan view showing an example of the layout of the lower electrode 6 and the auxiliary wiring 6a. As shown in this figure, the lower electrodes 6 are arranged in a matrix corresponding to the arrangement of the pixels. Then, an auxiliary wiring 6 a composed of the same layer as the lower electrode 6 is wired between the lower electrodes 6.

  Here, the display device 1 shown in the figure is a top emission type in which the emitted light h is extracted from the side opposite to the substrate 2, so that the lower electrode 6 is made of a material having a high light shielding property and a high reflectance. Suppose that On the other hand, the upper electrode 9 is configured using a material having high light transmittance. The lower electrode 6 and the upper electrode 9 may be formed of a material appropriately selected from an anode electrode material or a cathode electrode material so that at least the layer in contact with the organic layer 8 is formed. In some cases, it may be composed of a laminated structure having a light transmitting property or a light transmitting property.

  In the substrate 2, a light shielding metal layer 10 is provided on the surface opposite to the side where the transistor Tr and the organic EL element EL are disposed for light leakage and temperature diffusion.

  A particularly characteristic configuration in the present embodiment is a layout in which the thin film transistors Tr constituting the pixel circuit are disposed only below the lower electrode 6 and the auxiliary wiring 6a having a light shielding property. Is where you are. Thereby, as shown in FIG. 2, the thin film transistor Tr is not arranged in the gap between the lower electrode 6 and the auxiliary wiring 6a when seen in a plan view. In this gap, a wiring portion of a pixel circuit configured using the thin film transistor Tr is disposed. It is important that the channel portion (portion where the gate electrode g is laminated) of the thin film transistor Tr is disposed only below the lower electrode 6 and the auxiliary wiring 6a. The extended wiring portion may be disposed in a gap between the lower electrode 6 and the auxiliary wiring 6a.

  In the display device 1 configured as described above, the external light H incident from the display surface (upper electrode 9) side of the display device 1 is transmitted through the layer of the upper electrode 9 having light transmittance and has a light shielding property. The layer of the lower electrode 6 is reached. Then, the external light H reaching the layer of the lower electrode 6 leaks further into the lower layer through the gap between the lower electrode 6 and the auxiliary wiring 6a, and is irradiated to the pixel circuits arranged in these lower layers. However, since the thin film transistor Tr (particularly the channel portion of the thin film transistor) constituting the pixel circuit is selectively disposed only under the lower electrode 6 and the auxiliary wiring 6a formed of the same layer as the lower electrode 6, The auxiliary wiring 6a becomes a saddle and the thin film transistor Tr is prevented from being irradiated with external light H.

  As a result, characteristic fluctuations and malfunctions of the thin film transistor Tr due to light irradiation are prevented, and the image quality in the display device 1 can be improved.

  In the embodiment described with reference to FIG. 1, the configuration in which the thin film transistor Tr constituting the pixel circuit is provided below the lower electrode 6 and the auxiliary wiring 6a formed of the same layer as the lower electrode 6 has been described. However, the present invention may have a configuration in which the thin film transistor Tr is disposed only under the lower electrode 6 as shown in FIG. Although illustration is omitted here, the thin film transistor Tr may be arranged only in the lower part of the auxiliary wiring 6a made of the same layer as the lower electrode 6 and other wirings, and the same effect can be obtained. .

  Furthermore, the thin film transistors constituting the peripheral circuit provided around the display area where the organic EL elements are arranged are also selectively arranged only in the lower part of the wiring composed of the same layer as the lower electrode made of a light shielding material. Thus, the same effect can be obtained. In other words, thin film transistors that make up peripheral circuit scanners and selectors are also selectively placed only under the wiring made of the same layer as the lower electrode made of a light-shielding material. Can be prevented. Thereby, the malfunction of a display apparatus can be prevented.

  FIG. 4 is a block diagram illustrating an outline of a display device to which the above-described configuration is applied. This display device has a pixel array unit 22 in which pixels (pixel circuits) 21 including organic EL elements are arranged in m columns and n rows in a matrix. Here, in order to simplify the drawing, a case where the pixel array unit 22 has a pixel arrangement of 3 columns and 2 rows is shown as an example.

  In the pixel array unit 22, a scanning line 23 is wired for each row of each pixel 21, and a data line 25 is wired for each column. Around the pixel array section 22, a writing scanning circuit 26 for driving the scanning line 23 and a data line driving circuit 28 for supplying a data signal corresponding to the luminance information to the data line 25 are arranged.

  FIG. 5 is a circuit diagram showing an example of a pixel circuit (unit pixel circuit) in an active matrix organic EL display device. As shown in this figure, the pixel circuit in this display device includes, for example, an organic EL element EL whose cathode electrode is connected to the ground potential GND, a drain connected to the anode electrode of the organic EL element EL, and a source which is a positive power supply potential. A p-channel drive transistor Tr1 connected to Vcc, a capacitive element Cs connected between the gate of the drive transistor Tr1 and the positive power supply potential Vcc, a source to the gate of the drive transistor Tr1, and a gate to the scanning line 23 In addition, the n-channel write transistor Tr2 has a drain connected to the data line 25, respectively. Note that the connection state of the source and the drain of the write transistor Tr2 may be reversed depending on the voltage setting.

  FIG. 6 is a timing chart for explaining the operation of such a pixel circuit. As shown in this figure (timing chart), in the pixel circuit of FIG. 5, the write signal WS is applied to the selected scanning line 23 and the gate potential of the write transistor Tr2 is controlled to be applied to the data line 25. The signal voltage thus written is written to the gate of the drive transistor Tr1. At this time, the gate potential of the driving transistor Tr1 is stably held by the capacitive element Cs for one field (1f) period until the next scanning line 23 is selected. During this time, a current corresponding to the gate-source voltage of the drive transistor Tr1 flows to the organic EL element EL, and the organic EL element EL continues to emit light with a luminance corresponding to the current value.

  In the display device laid out in this way, the anode electrode of the organic EL element EL is configured to have a light shielding property as the lower electrode shown in FIG. 1, and the auxiliary wiring of the cathode electrode is configured in the same layer as this anode electrode. To do. Then, the drive transistor Tr1 and the write transistor Tr2 are disposed only below the anode electrode and the auxiliary wiring.

  As a result, the anode electrode and the auxiliary wiring become traps even for incident light from the light emitting side, and the drive transistor Tr1 and the write transistor Tr2 are shielded from light. And the change of the leak characteristic by the light of each transistor Tr1, Tr2 does not arise, it becomes possible to perform a homogeneous display, and it becomes possible to maintain a stable uniformity.

  Heretofore, in the display device having the pixel circuit shown in FIG. 5, when the leak characteristic is deteriorated due to, for example, light irradiation on the writing transistor Tr2, so-called vertical crosstalk has occurred. That is, as shown in FIG. 7, when the central portion of the window A is the black display area A1, a gray display area A2 is generated along the black display area A1.

  However, as described above, the drive transistor Tr1 and the write transistor Tr2 are arranged only under the anode electrode and the auxiliary wiring, so that such deterioration can be prevented. As a result, display characteristics can be improved.

  FIG. 8 is a block diagram showing an outline of a second display device to which the configuration of the embodiment is applied. This display device includes a pixel array unit 32 in which pixels (pixel circuits) 31 including organic EL elements that emit light of red (R), green (G), and blue (B) are arranged in a matrix of m columns and n rows. have. Here, for simplification of the drawing, a case where the pixel array section 32 has a pixel array of 6 columns and 2 rows is shown as an example.

  In the pixel array section 32, a scanning line 33 and a first drive line 34 are wired for each row of each pixel 31, and a second drive line 35 is wired for each pixel of the same emission color in each row. In addition, an auto-zero line 36 is wired for each row for each pixel 31, and a data line 37 is wired for each column. Around the pixel array section 32, a write scanning circuit 38 for driving the scanning line 33, a first driving scanning circuit 39 for driving the first driving line 34, and a second driving scanning for driving the second driving line 35 are provided. A circuit 40, an auto zero circuit 41 for driving the auto zero line 36, and a data line driving circuit 42 for supplying a data signal corresponding to the luminance information to the data line 37 are arranged. In this example, the writing scanning circuit 38 and the first driving scanning circuit 39 are arranged on one side (right side in the figure) across the pixel array section 32, and the second driving scanning circuit 40 and the auto zero circuit 41 are arranged on the opposite side. It has been configured.

  FIG. 9 is a circuit diagram of a pixel circuit (unit pixel circuit) in the active matrix organic EL display device. As shown in this figure, the pixel circuit 31 in this display device has a configuration in which, in addition to the organic EL element EL, a drive transistor Tr1, capacitors (pixel capacitors) Cs1 and Cs2, and switching transistors Tr2 to Tr6 are provided as circuit elements. ing. The drive transistor Tr1 and the switching transistors Tr2 to Tr6 are N-channel field effect transistors, for example, N-channel TFTs (thin film transistors).

  The organic EL element EL has a cathode electrode connected to the first power supply potential (in this example, the ground potential GND). The drive transistor Tr1 is a drive transistor that drives the organic EL element EL to emit light, and the drain is connected to the second power supply potential (in this example, the positive power supply potential Vcc) and the source is connected to the anode electrode of the organic EL element EL. As a result, a source follower circuit is formed. The capacitive element Cs1 is a pixel capacitor, and one end is connected to the gate of the drive transistor Tr1, and the other end is connected to a connection node N11 between the source of the drive transistor Tr1 and the anode electrode of the organic EL element EL.

  The transistor Tr2 has a source connected to the data line 37 and a gate connected to the scanning line 33. One end of the capacitive element Cs2 is connected to the drain of the transistor Tr2, and the other end is connected to a connection node N12 between the gate of the driving transistor Tr1 and one end of the capacitive element Cs1. The transistor Tr3 has a drain connected to the connection node N11, a source connected to the third power supply potential Vss (for example, the ground potential GND), and a gate connected to the first drive line 34. Note that a negative power supply potential may be used as the third power supply potential Vss.

  The transistor Tr4 has a drain connected to the power supply potential Vcc, a source connected to the drain of the drive transistor Tr1, and a gate connected to the second drive line 35. The transistor Tr5 has a drain connected to the connection node N13 between the drain of the drive transistor Tr1 and a source of the transistor Tr4, a source connected to the connection node N12, and a gate connected to the auto-zero line 36. The transistor Tr6 has a drain connected to the predetermined potential Vofs, a source connected to the drain of the transistor Tr2, and a gate connected to the auto-zero line 36. Of the above transistors, the transistors Tr2, Tr5, Tr6 may have the source and drain connected in reverse depending on the voltage setting.

  FIG. 10 is a timing chart for explaining the operation of such a pixel circuit. The pixel circuit of FIG. 9 drives the lines 33 to 36 as shown in the timing chart by driving the circuits 38 to 41. As a result, the gate-source potential Vgs of the drive transistor Tr1 is kept constant at Vgs = Vini + Vth. For this reason, the electric current which flows into the organic EL element EL does not change. Therefore, even if the IV characteristic of the organic EL element EL deteriorates, the constant current Ids always flows, so that the luminance of the organic EL element EL does not change. Further, the threshold voltage Vth of the drive transistor Tr1 is canceled by the action of the transistor Tr5 during the threshold cancellation period, and a constant current Ids that is not affected by the variation of the threshold voltage Vth can be flowed, so that a high-quality image is obtained. be able to.

  In the display device laid out in this way, the anode electrode of the organic EL element EL is configured to have a light shielding property as the lower electrode shown in FIG. 1, and the auxiliary wiring of the cathode electrode is formed in the same layer as the anode electrode. Configure. Then, the transistors Tr1 to Tr6 are arranged only below these anode electrodes and auxiliary wiring.

  As a result, the anodes and the auxiliary wiring also act as a trap for the incident light from the light emitting side to shield the transistors Tr1 to Tr6. And the change of the leak characteristic by the light of each transistor Tr1-Tr6 does not arise, it becomes possible to perform a homogeneous display, and it becomes possible to maintain the stable uniformity.

  Here, in the conventional display device having the pixel circuit shown in FIG. 9, in addition to the occurrence of vertical crosstalk due to light leakage, for example, display unevenness via the transistor Tr5 and black floating due to a decrease in contrast become problems. . However, as described above, since the drive transistors Tr1 to Tr6 are arranged only below the anode electrode and the auxiliary wiring, light leakage is prevented. Therefore, such vertical crosstalk, display unevenness, and contrast are prevented. It is possible to suppress the black float caused by the decrease in the level.

It is sectional drawing which shows the structure of the display apparatus of embodiment. It is a layout diagram of the lower electrode of the organic EL element and the auxiliary wiring in the display device of the embodiment. It is sectional drawing which shows the other structure of the display apparatus of embodiment. 1 is a block diagram illustrating a schematic configuration of a display device according to a first embodiment. 3 is a circuit diagram illustrating a pixel circuit of the display device of Example 1. FIG. 3 is a timing chart illustrating the operation of the pixel circuit in the display device according to the first exemplary embodiment. It is a figure explaining the vertical crosstalk in the conventional display apparatus which has a pixel circuit equivalent to Example 1. FIG. FIG. 6 is a block diagram illustrating a schematic configuration of a display device according to a second embodiment. 6 is a circuit diagram illustrating a pixel circuit of a display device according to Example 2. FIG. 6 is a timing chart illustrating an operation of a pixel circuit in the display device according to the second embodiment. It is sectional drawing which shows the structure of the conventional display apparatus. It is a graph explaining the subject in the conventional display apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 2 ... Board | substrate, 5 ... Interlayer insulation film, 5a ... Connection hole, 6 ... Lower electrode, 6a ... Auxiliary wiring, 8 ... Organic layer, 9 ... Upper electrode, EL ... Organic EL element, h ... Light emission , Tr ... Transistor

Claims (5)

A driving circuit provided on the substrate; an interlayer insulating film provided on the substrate in a state of covering the driving circuit; and an organic EL element arrayed on the interlayer insulating film. In a display device configured to extract light emitted from the element from the side opposite to the substrate,
The organic EL element is connected to the driving circuit through a connection hole formed in the interlayer insulating film and is made of a light shielding material, and an organic layer and an upper electrode sequentially stacked on the lower electrode. With
The display device, wherein the thin film transistor that constitutes the driving circuit is selectively disposed only in the lower electrode and a lower portion of a wiring that is formed in the same layer as the lower electrode. The display device according to claim 1,
The lower electrode is made of a light shielding material. A display device, wherein: The display device according to claim 1,
The drive circuit includes a pixel circuit provided in each pixel in which the organic EL element is arranged, and a peripheral circuit provided in the periphery of a display area in which the organic EL element is arranged,
Both the thin film transistor that constitutes the pixel circuit and the thin film transistor that constitutes the peripheral circuit are selectively disposed only below the lower electrode and the wiring formed in the same layer as the lower electrode. Display device. The display device according to claim 1,
The display device is characterized in that the wiring composed of the same layer as the lower electrode is an auxiliary wiring connected to the upper electrode. The display device according to claim 1,
The lower electrode is used as an anode electrode,
The display device, wherein the upper electrode is used as a cathode electrode.

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