JP3649927B2 - Electroluminescence display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescence display device including an electroluminescence element and a thin film transistor.
[0002]
[Prior art]
In recent years, an EL display device using an electroluminescence (hereinafter referred to as “EL”) element has attracted attention as a display device that replaces a CRT or an LCD, for example, as a switching element for driving the EL element. Research and development of an EL display device including a thin film transistor (hereinafter referred to as “TFT”) is also in progress.
[0003]
6 shows an equivalent circuit diagram of one display pixel of the organic EL display device, FIG. 7 shows a plan view showing one display pixel of the organic EL display device, and FIG. 8A shows a line AA in FIG. FIG. 8B shows a cross-sectional view along the line BB in FIG.
[0004]
As shown in FIGS. 6 and 7, display pixels are formed in a region surrounded by the gate signal line 51 and the drain signal line 52. A first TFT 130 serving as a switching element is provided in the vicinity of the intersection of both signal lines, and the source 13s of the TFT 130 serves as a capacitor electrode 55 that forms a capacitance with a later-described storage capacitor electrode line 54, and is also organic. It is connected to the gate 41 of the second TFT 140 that drives the EL element. The source 43s of the second TFT 140 is connected to the anode 61 of the organic EL element, and the other drain 43d is connected to the drive power supply line 53 that drives the organic EL element.
[0005]
In addition, a storage capacitor electrode line 54 is disposed in the vicinity of the TFT in parallel with the gate signal line 51. The storage capacitor electrode line 54 is made of chromium or the like, and forms a capacitor by accumulating electric charges between the capacitor electrode 55 connected to the TFT source 13 s through the gate insulating film 12. The storage capacitor 160 is provided to hold a voltage applied to the gate electrode 41 of the second TFT 140.
[0006]
First, the first TFT 130 which is a switching TFT will be described.
[0007]
As shown in FIG. 8A, a gate signal also serving as a gate electrode 11 made of a refractory metal such as chromium (Cr) or molybdenum (Mo) on an insulating substrate 10 made of quartz glass, non-alkali glass or the like. A line 51 and a drain signal line 52 made of Al are provided, and a drive power supply line 53 made of Al, which is a drive power supply for the organic EL element, is arranged.
[0008]
Subsequently, an active layer 13 composed of a gate insulating film 12 and a p-Si film is formed in this order, and the active layer 13 is provided with a so-called LDD (Lightly Doped Drain) structure. That is, the low concentration region 13LD is provided on both sides of the gate electrode 11, and the source 13s and the drain 13d of the high concentration region are provided outside thereof.
[0009]
An interlayer insulating film 15 in which an SiO ₂ film, an SiN film, and an SiO ₂ film are stacked in this order is provided on the entire surface of the gate insulating film 12, the active layer 13, and the stopper insulating film 14, and provided corresponding to the drain 13d. A drain electrode 16 is provided by filling the contact hole with a metal such as Al. Further, a planarizing insulating film 17 made of, for example, an organic resin and flattening the surface is provided on the entire surface.
[0010]
Next, the second TFT 140 that is a TFT for driving the organic EL element will be described.
[0011]
As shown in FIG. 8B, a gate electrode 41 made of a refractory metal such as Cr or Mo is provided on an insulating substrate 10 made of quartz glass, non-alkali glass or the like, and the gate insulating film 12 and p- An active layer 43 made of a Si film is formed in order, and the active layer 43 is subjected to ion doping on both sides of the channel 43c on both sides of the channel 43c that is intrinsic or substantially intrinsic above the gate electrode 41. A source 13s and a drain 13d are provided.
[0012]
Then, an interlayer insulating film 15 in which an SiO ₂ film, an SiN film, and an SiO ₂ film are stacked in this order is formed on the entire surface of the gate insulating film 12 and the active layer 43, and contact holes provided corresponding to the drains 43d are formed. A drive power supply line 53 filled with a metal such as Al and connected to the drive power supply 50 is disposed. Further, a planarization insulating film 17 made of, for example, an organic resin and flattening the surface is formed on the entire surface, a contact hole is formed at a position corresponding to the source 43s of the planarization insulating film 17, and the source is connected through this contact hole. A transparent electrode made of ITO (Indium Thin Oxide) in contact with 13 s, that is, an anode 61 of an organic EL element is provided on the planarizing insulating film 17.
[0013]
The organic EL element 160 includes an anode 61 made of a transparent electrode such as ITO, a first hole transport layer 62 made of MTDATA (4,4-bis (3-methylphenylphenylamino) biphenyl), TPD (4,4,4-tris ( Light emission comprising a second hole transport layer 63 comprising 3-methylphenylphenylamino) triphenylanine), a light-emitting layer 64 comprising Bebq2 (10-benzo [h] quinolinol-beryllium complex) containing a quinacridone derivative, and an electron transport layer comprising Bebq2. The element layer 65 and the cathode 66 made of a magnesium / indium alloy are stacked in this order. The cathode 66 is provided on the entire surface of the substrate 10 forming the organic EL display device shown in FIG.
[0014]
In the organic EL element, holes injected from the anode and electrons injected from the cathode are recombined inside the light emitting layer, and excitons are generated by exciting organic molecules forming the light emitting layer. Light is emitted from the light emitting layer in the process of radiation deactivation of the excitons, and this light is emitted from the transparent anode through the transparent insulating substrate to emit light.
[0015]
Here, FIG. 3 shows characteristics of the second TFT.
[0016]
The horizontal axis represents the gate voltage Vgs based on the potential at the intersection 173 of the drive power supply line 53 and the storage capacitor 170 in FIG. 6, and the vertical axis represents the drain current Ids.
[0017]
When the cathode is not above the channel of the second TFT, the characteristics shown by the solid line in FIG. 3 are exhibited. Further, when the cathode is formed on the entire surface of the organic EL display device, that is, for example, when the cathode has a potential of −10 V, the TFT characteristics change as indicated by a broken line in FIG.
[0018]
This is because a voltage is applied to the cathode 66 of the organic EL element 160 provided above the channel 43c, but a back channel is generated with respect to the channel 43c by the voltage. That is, as shown in FIG. 5B, the organic EL display device has a structure in which the second TFT 140 is formed on the substrate 10 and the organic EL element 160 is further provided thereon. This is because, since the cathode 66 has a structure formed on the entire surface, when a voltage is applied to the cathode 66, an electric field is generated by an electric field generated by the voltage, and a so-called back channel is generated.
[0019]
[Problems to be solved by the invention]
However, the second TFT 140 has a function of supplying current to the organic EL element 60 by controlling the current from the power source for driving the organic EL element 160 according to the voltage applied to the gate 41 of the second TFT 140. However, the amount of characteristic fluctuation (ΔV) due to the cathode potential is determined by the film thickness and film quality of the stopper insulating film and the planarizing insulating film on the channel, and when these fluctuate within the display surface, ΔV is easily Will fluctuate. The variation in ΔV causes the current flowing in the EL light emitting element layer to fluctuate. Therefore, there is a disadvantage in that the display luminance varies for each display pixel and the display is uneven.
[0020]
Accordingly, the present invention has been made in view of the above-described conventional disadvantages, and eliminates fluctuations in the characteristics of the second TFT, supplies current that should be supplied to the EL element, and does not cause display unevenness. An object is to provide an apparatus.
[0021]
[Means for Solving the Problems]
The EL display device of the present invention includes an electroluminescence element having a light emitting layer between an anode and a cathode, an active layer made of a non-single crystal semiconductor film, a drain connected to a drain signal line, and a gate connected to a gate signal line. The first thin film transistor and the drain of the active layer made of a non-single-crystal semiconductor film are connected to the driving power source of the electroluminescence element, and the gate provided below the channel of the active layer is connected to the source of the first thin film transistor. An electroluminescence display device including the second thin film transistor, wherein a conductor covering the channel is provided above the channel provided in the active layer of the second thin film transistor.
[0022]
Further, the conductor of the above-described EL display device is an electroluminescence display device in which a drive power supply line connected to the drive power supply is provided to extend above the channel.
[0023]
Furthermore, the conductor of the above-described EL display device is an electroluminescence display device in which the gate signal line is provided to extend above the channel.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The EL display device of the present invention will be described below.
<First Embodiment>
FIG. 1 is a plan view showing one display pixel when the present invention is applied to an organic EL display device, FIG. 2A is a cross-sectional view taken along line AA in FIG. b) shows a cross-sectional view along the line BB in FIG.
[0025]
As shown in FIG. 1, display pixels are formed in a region surrounded by the gate signal line 51 and the drain signal line 52. A first TFT 30 is provided in the vicinity of the intersection of both signal lines. The source 13 s of the TFT 30 also serves as a capacitor electrode 55 that forms a capacitance with the storage capacitor electrode line 54, and the gate 41 of the second TFT 40. It is connected to the. The source 43s of the second TFT is connected to the anode 61 of the organic EL element 60, and the other drain 43d is connected to a drive power supply line 53 that drives the organic EL element.
[0026]
In addition, a storage capacitor electrode line 54 is disposed in the vicinity of the TFT in parallel with the gate signal line 51. The storage capacitor electrode line 54 is made of chromium or the like, and forms a capacitor by accumulating electric charges between the capacitor electrode 55 connected to the TFT source 13 s through the gate insulating film 12. This storage capacitor is provided to hold the voltage applied to the gate electrode 41 of the second TFT 40.
[0027]
In this manner, display pixels including the organic EL element 60 and the TFTs 30 and 40 are arranged in a matrix on the substrate 10 to form an organic EL display device.
[0028]
As shown in FIG. 2, the organic EL display device is formed by sequentially laminating TFTs and organic EL elements on a substrate 10 such as a substrate made of glass or synthetic resin, a conductive substrate, or a semiconductor substrate. However, when a conductive substrate and a semiconductor substrate are used as the substrate 10, an insulating film such as SiO ₂ or SiN is formed on the substrate 10, and then a TFT and an organic EL display device are formed.
[0029]
In the present embodiment, both the first and second TFTs 30 and 40 are so-called bottom-gate TFTs in which gate electrodes are provided below the active layer 13, and polycrystalline silicon (Poly-Silicon, hereinafter) is used as the active layer. , Referred to as “p-Si”). The case where the gate electrodes 11 and 41 are TFTs having a double gate structure is shown. The first TFT 30 which is a switching TFT has the same structure as the conventional first TFT 140 as shown in FIG.
[0030]
Next, the second TFT 40 that is a TFT for driving the organic EL element 60 will be described.
[0031]
As shown in FIG. 2B, a gate electrode 41 made of a refractory metal such as Cr or Mo is formed on an insulating substrate 10 made of quartz glass, non-alkali glass or the like.
[0032]
A gate insulating film 12 and an active layer 43 made of a p-Si film are sequentially formed.
[0033]
In the active layer 43, an intrinsic or substantially intrinsic channel 43c is provided above the gate electrode 41, and a source 13s and a drain 13d are ion-doped on both sides of the channel 43c.
[0034]
Then, an interlayer insulating film 15 in which an SiO ₂ film, an SiN film, and an SiO ₂ film are stacked in this order is formed on the entire surface of the gate insulating film 12 and the active layer 43, and Al is formed in the contact hole provided corresponding to the drain 43d. A drive power supply line 53 connected to the drive power supply 50 is formed by filling the metal such as. Further, a planarizing insulating film 17 made of, for example, an organic resin and flattening the surface is formed on the entire surface. Then, a contact hole is formed at a position corresponding to the drain 43d of the planarization insulating film 17, and the drive power supply line 53 made of Al is formed in contact with the drive power supply line 53 through the contact hole. At this time, a conductor 56 is formed so as to extend a part of the drive power supply line 53 on the channel 43c. Further, a contact hole is formed at a position corresponding to the source 43s of the planarization insulating film 17, and the transparent electrode made of ITO, that is, the anode 61 of the organic EL element, which is in contact with the source 13s through the contact hole, is planarized and insulated. It is formed on the film 17.
[0035]
Since the structure of the organic EL element 60 is the same as that described in the prior art, the description thereof is omitted.
[0036]
As described above, by forming the conductor 56 formed of a part of the drive power supply 53 above the channel 43c of the second TFT 40, a back channel caused by an electric field due to a voltage applied to the cathode 66 can be suppressed. That is, the original TFT characteristics can be maintained without being affected by variations in the electric field due to the cathode potential and the film quality and thickness of the channel. Accordingly, it is possible to prevent display unevenness caused by fluctuations in the electric field due to the potential of the cathode, the film quality of the channel upper part, the film thickness, and the like.
[0037]
Further, if the second TFT 40 is a p-type channel TFT having an active layer having a source and a drain doped with p-type impurities, a region saturated in the Id-Vd characteristics can be widened. Id becomes difficult to change according to Vd, that is, variation in drain current value according to the change in drain voltage is reduced, so that the light emission luminance of the organic EL element can be made uniform with good reproducibility. Can be easily obtained.
[0038]
In particular, in a polycrystalline silicon TFT, as described in the section of the prior art, a crystal grain boundary exists, a potential barrier is formed by electrons trapped at the grain boundary, and a depletion layer is expanded. For this reason, a strong electric field is applied to the grain boundary at the edge of the drain electrode, and an impact ionization phenomenon in which the accelerated electrons collide with the lattice occurs. This phenomenon is more significant in the case of the p-type channel than in the case of the n-type channel TFT. Since the drain current shows a region where the drain current is saturated and good saturation characteristics can be obtained, it is preferable to use a p-type channel TFT as the second TFT.
<Second Embodiment>
FIG. 4 is a plan view of the vicinity of the display pixel of the EL display device of the present invention, and FIG. 5 is a cross-sectional view taken along the line CC in FIG.
[0039]
This embodiment is different from the first embodiment in that the conductor 56 provided above the channel 43c of the second TFT 40 is part of the gate electrode 41 of the second TFT 40 as shown in FIG. This is a point that extends.
[0040]
As shown in FIGS. 4 and 5, the second TFT includes an active layer made of p-Si provided on the gate electrode 41 and the gate insulating film 12 stacked. The active layer includes a source 43s and a drain 43d doped with impurities.
[0041]
A conductor 56 in contact with the gate electrode 41 through a contact hole provided in the gate insulating film 12 and the interlayer insulating film 15 is provided so as to extend above the channel 43c. That is, the conductor 56 having the same potential as that of the gate electrode 41 is provided.
[0042]
As described above, by providing the conductor 56 having the same potential as that of the gate electrode 41, the back channel that has conventionally occurred can be suppressed.
[0043]
For this reason, since the current that should be supplied to the organic EL element 60 is supplied to emit light, there is no variation in light emission luminance among the display pixels, and an organic EL display device in which display unevenness does not occur can be obtained.
[0044]
Further, the second TFT is a TFT having a p-type channel as in the first embodiment, so that the variation in drain current with respect to the drain voltage is small and the light emission luminance of the organic EL element is made uniform with good reproducibility. Thus, an organic EL display device capable of obtaining a good gradation display can be obtained.
[0045]
In each of the above embodiments, the p-Si film is used as the active layer, but a microcrystalline silicon film or an amorphous silicon film may be used.
[0046]
Further, in each of the above-described embodiments, the organic EL display device has been described. However, the present invention is not limited thereto, and can be applied to an inorganic EL display device in which the light emitting layer is made of an inorganic material. Similar effects can be obtained.
[0047]
【The invention's effect】
Since the EL display device of the present invention includes the first TFT with high-speed writing and holding characteristics and the second TFT with good current controllability, an EL display device capable of good gradation display is provided. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view showing a first embodiment of an EL display device of the present invention.
FIG. 2 is a cross-sectional view showing a first embodiment of an EL display device of the present invention.
FIG. 3 is a characteristic diagram of a TFT provided in the EL display device of the present invention.
FIG. 4 is a plan view showing a second embodiment of an EL display device of the present invention.
FIG. 5 is a sectional view showing an EL display device according to a second embodiment of the present invention.
FIG. 6 is an equivalent circuit diagram of an EL display device.
FIG. 7 is a plan view of a conventional EL display device.
FIG. 8 is a cross-sectional view of a conventional EL display device.
[Explanation of symbols]
11, 41 Gate 13s, 43s Source 13d, 43d Drain 13c, 43c Channel 13s, 43s LDD region 30 First TFT
40 Second TFT
50 drive power supply 56 conductor 60 organic EL element

Claims (2)

An electroluminescent device having a light emitting layer between an anode and a cathode;
A first thin film transistor in which a drain of an active layer made of a non-single-crystal semiconductor film is connected to a drain signal line and a gate is connected to a gate signal line;
A second thin film transistor in which a drain of an active layer made of a non-single crystal semiconductor film is connected to a driving power source of the electroluminescence element, and a gate provided below a channel of the active layer is connected to a source of the first thin film transistor; An electroluminescence display device comprising:
Above the channel provided in the active layer of the second thin film transistor, a drive power supply line connected to the drive power supply is extended to the upper side of the channel , and a conductor covering the channel is provided, 1. An electroluminescence display device, wherein a conductor covering the channel is not provided on the opposite side of the channel of one thin film transistor to the gate. An electroluminescent device having a light emitting layer between an anode and a cathode;
A first thin film transistor in which a drain of an active layer made of a non-single-crystal semiconductor film is connected to a drain signal line and a gate is connected to a gate signal line;
A second thin film transistor in which a drain of an active layer made of a non-single crystal semiconductor film is connected to a driving power source of the electroluminescence element, and a gate provided below a channel of the active layer is connected to a source of the first thin film transistor; An electroluminescence display device comprising:
Above the channel provided in the active layer of the second thin film transistor, the channel is electrically connected to the gate of the second thin film transistor through a contact hole and extends to the upper side of the channel. An electroluminescence display device, wherein a conductor covering the channel is provided, and a conductor covering the channel is not provided on a side opposite to the gate of the channel of the first thin film transistor.

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