JP2000221907A - Electroluminescence display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EL display device having no display irregularities generated by supplying a current to be supplied originally to an EL element, by suppressing a characteristic change of a second TFT for driving the EL element. SOLUTION: In this organic EL display device equipped with a first TFT for switching, a second TFT for driving an organic EL element, and the organic EL element comprising an anode 61, a cathode 66, and a luminous element layer 65 interposed between both electrodes, a back channel generated by a voltage applied on the cathode 66 is suppressed, and display irregularities are reduced, by installing a conductor 56 formed by extending a part of driving power supply wire for supplying a current to the organic EL element 60, on the upper part of a channel 43c of the second TFT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent display device having an electroluminescent element and a thin film transistor.

[0002]

2. Description of the Related Art In recent years, electroluminescence (Elec)
tro Luminescence: Hereinafter, referred to as “EL”. An EL display device using an element has attracted attention as a display device replacing a CRT or an LCD. For example, a thin film transistor (Th) is used as a switching element for driving the EL element.
in Film Transistor: Hereinafter, referred to as “TFT”. Research and development of an EL display device having ()) are also in progress.

FIG. 6 is an equivalent circuit diagram of one display pixel of the organic EL display device, FIG. 7 is a plan view showing one display pixel of the organic EL display device, and FIG. FIG. 8B is a cross-sectional view taken along a line BB in FIG. 7.

As shown in FIGS. 6 and 7, a display pixel is formed in a region surrounded by a gate signal line 51 and a drain signal line 52. A first TFT 130 serving as a switching element is provided near the intersection of the two signal lines, and a source 13 s of the TFT 130 also serves as a capacitance electrode 55 forming a capacitance with a storage capacitance electrode line 54 described later, and an organic TFT. 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 for driving the organic EL element.
It is connected to the.

Further, a gate signal line 5 is provided near the TFT.
A storage capacitor electrode line 54 is arranged in parallel with the storage capacitor electrode line 1. The storage capacitor electrode line 54 is made of chromium or the like, and forms a capacitor by storing charge between the capacitor electrode 55 connected to the source 13s of the TFT via 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.

First, the first TFT, which is a switching TFT, is used.
The TFT 130 will be described.

As shown in FIG. 8A, a gate electrode 11 made of a high melting point metal such as chromium (Cr) or molybdenum (Mo) is formed on an insulating substrate 10 made of quartz glass, non-alkali glass or the like. A gate signal line 51 and a drain signal line 52 made of Al are provided, and a drive power line 53 made of Al, which is a drive power source for the organic EL element, is provided.

Subsequently, a gate insulating film 12 and p-Si
An active layer 13 composed of a film is formed in 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 the low concentration region 13LD.

An SiO ₂ film and a Si film are formed on the entire surface of the gate insulating film 12, the active layer 13 and the stopper insulating film 14.
An interlayer insulating film 15 laminated in the order of the N film and the SiO ₂ film is provided, and a contact hole provided corresponding to the drain 13 d is filled with a metal such as Al to form a drain electrode 16. Further, a flattening insulating film 17 made of, for example, an organic resin and flattening the surface is provided on the entire surface.

Next, the second TFT 140 which is a TFT for driving the organic EL element will be described.

As shown in FIG. 8B, Cr, Cr, and the like are placed on an insulating substrate 10 made of quartz glass, non-alkali glass, or the like.
A gate electrode 41 made of a high melting point metal such as Mo is provided,
Gate insulating film 12 and active layer 43 made of p-Si film
In the active layer 43, an intrinsic or substantially intrinsic channel 43c is formed above the gate electrode 41, and both sides of the channel 43c are subjected to ion doping on both sides to form a source 13s and a drain 13d. Is provided.

The gate insulating film 12 and the active layer 43
On the entire upper surface, an interlayer insulating film 15 laminated in the order of a SiO ₂ film, a SiN film and a SiO ₂ film is formed, and a drain 43d is formed.
Are filled with metal such as Al, and a drive power supply line 53 connected to a drive power supply 50 is arranged. Further, a flattening 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 No. 7, and a transparent electrode made of ITO (Indium Thin Oxide) contacting the source 13s via this contact hole, that is, the anode 61 of the organic EL element is formed on the planarizing insulating film 17 Provided above.

The organic EL element 160 includes an anode 61 made of a transparent electrode such as ITO, and an MTDATA (4,4-bis (3-methy).
lphenylphenylamino) biphenyl), the first hole transport layer 62, TPD (4,4,4-tris (3-methylphenylphenyla
Second hole transport layer 6 composed of mino) triphenylanine)
3. Beb containing quinacridone derivatives
q2 (10-benzo [h] quinolinol-beryllium complex)
A light emitting element layer 65 made of an electron transport layer made of Bebq2, and a 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. 7, that is, on the entire surface of the paper.

In the organic EL device, holes injected from the anode and electrons injected from the cathode are recombined inside the light emitting layer, and excite the organic molecules forming the light emitting layer to generate excitons. Light is emitted from the light emitting layer during the process of radiation deactivation of the excitons, and the light is emitted from the transparent anode to the outside through the transparent insulating substrate to emit light.

FIG. 3 shows the characteristics of the second TFT.

The horizontal axis indicates the gate voltage Vgs based on the potential at the intersection 173 between the drive power supply line 53 and the storage capacitor 170 in FIG. 6, and the vertical axis indicates the drain current Ids.

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 shown by the broken line in FIG.

This is because a voltage is applied to the cathode 66 of the organic EL element 160 provided above the channel 43c, and the voltage generates a back channel with respect to the channel 43c. That is, as shown in FIG. 5B, the organic EL display device includes the second TFT 1 on the substrate 10.
40, and the organic EL element 160 is further provided thereon. Since the cathode 66 of the organic EL element 160 is formed on the entire surface, when a voltage is applied to the cathode 66, the This is because electric charges are generated by an electric field generated by a voltage and a so-called back channel is generated.

[0019]

However, the second TF
T140 has a function of controlling the current from a power supply for driving the organic EL element 160 in accordance with the voltage applied to the gate 41 of the second TFT 140 and supplying the current to the organic EL element 60. The amount of characteristic variation due to potential (Δ
V) is determined by the thickness and quality of the stopper insulating film and the planarizing insulating film on the channel, and when these change within the display surface, ΔV easily changes. Since the variation of ΔV changes the current flowing in the EL light emitting element layer, there is a disadvantage that the emission luminance varies for each display pixel and the display becomes uneven.

Accordingly, the present invention has been made in view of the above-mentioned conventional disadvantages, and eliminates fluctuations in the characteristics of the second TFT and supplies a current which should be supplied to the EL element, thereby causing display unevenness. It is an object of the present invention to provide an EL display device that does not use such a display device.

[0021]

According to an EL display device of the present invention, an electroluminescent element having a light emitting layer between an anode and a cathode, and a drain of an active layer formed of a non-single-crystal semiconductor film are connected to a drain signal line. A first thin film transistor having a gate connected to a gate signal line, a drain of an active layer made of a non-single-crystal semiconductor film serving as a drive power source for the electroluminescent element, and a gate provided below a channel of the active layer being provided as a gate. An electroluminescent display device comprising: a second thin film transistor connected to a source of a first thin film transistor; and a conductor covering the channel provided above a channel provided in an active layer of the second thin film transistor. It is provided.

Further, the conductor of the above-mentioned 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.

Further, the above-mentioned conductor of the EL display device is an electroluminescence display device provided with the gate signal line extending above the channel.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An EL display device according to 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, and FIG.
FIG. 2A is a sectional view taken along the line AA in FIG.
FIG. 2B is a sectional view taken along line BB in FIG.

As shown in FIG. 1, a display pixel is formed in a region surrounded by a gate signal line 51 and a drain signal line 52. The first TFT 30 is provided near the intersection of the two signal lines, and the source 13 s of the TFT 30 also functions as the capacitance electrode 55 that forms a capacitance with the storage capacitance 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 the organic EL element 6
The other drain 43d is connected to a drive power supply line 53 for driving the organic EL element.

The gate signal line 5 is located near the TFT.
A storage capacitor electrode line 54 is arranged in parallel with the storage capacitor electrode line 1. The storage capacitor electrode line 54 is made of chromium or the like, and forms a capacitor by storing charge between the capacitor electrode 55 connected to the source 13s of the TFT via the gate insulating film 12. This storage capacitor is connected to the gate electrode 4 of the second TFT 40.
1 is provided to hold the voltage applied to the switch 1.

As described above, the organic EL element 60 and the TFT 3
An organic EL display device is formed by arranging display pixels including 0 and 40 on the substrate 10 in a matrix.

As shown in FIG. 2, the organic EL display device comprises:
A TFT and an organic EL element are sequentially laminated on a substrate 10 such as a substrate made of glass or synthetic resin, a conductive substrate, or a semiconductor substrate. However, substrate 1
In the case where a substrate having conductivity and a semiconductor substrate are used as 0, a TFT and an organic EL display device are formed after forming an insulating film such as SiO ₂ or SiN on the substrate 10.

In this embodiment, both the first and second TFTs 30 and 40 are so-called bottom gate type TFTs in which a gate electrode is provided below the active layer 13, and the active layer is made of polycrystalline silicon (Poly-Si). Silicon, hereafter "p
-Si ". ) Shows the case where a film is used. Also, a case is shown where the gate electrodes 11 and 41 are TFTs having a double gate structure. First TFT that is a switching TFT
Reference numeral 30 denotes a conventional first TFT as shown in FIG.
Since the structure is the same as 140, the description is omitted.

Next, a TFT for driving the organic EL element 60
The second TFT 40 will be described.

As shown in FIG. 2B, on an insulating substrate 10 made of quartz glass, non-alkali glass or the like, Cr,
A gate electrode 41 made of a high melting point metal such as Mo is formed.

A gate insulating film 12 and an active layer 43 made of a p-Si film are sequentially formed.

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 provided on both sides of the channel 43c by ion doping on both sides. I have.

Then, the gate insulating film 12 and the active layer 43
On the entire upper surface, an interlayer insulating film 15 laminated in the order of a SiO ₂ film, a SiN film and a SiO ₂ film is formed, and a contact hole provided corresponding to the drain 43d is filled with a metal such as Al to drive a driving power supply 50. To form a drive power supply line 53 connected to the power supply line. Further, a flattening 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 planarizing insulating film 17, and the drive power supply line 53 is contacted through the contact hole to form a drive power supply line 53 made of Al. At this time, at the same time, a conductor 56 is formed to extend and cover a part of the drive power supply line 53 on the channel 43c. In addition, a contact hole is formed at a position corresponding to the source 43s of the planarizing insulating film 17, and the ITO contacted with the source 13s through this contact hole.
, Ie, the anode 61 of the organic EL element is formed on the flattening insulating film 17.

The structure of the organic EL element 60 is the same as the structure described in the prior art, and the description is omitted.

As described above, by forming the conductor 56 which is a part of the driving power supply 53 above the channel 43c of the second TFT 40, the back channel generated by the electric field due to the voltage applied to the cathode 66 can be suppressed. Can be. That is, the original TFT characteristics can be maintained without being affected by the electric field due to the potential of the cathode and the fluctuation of the film quality, film thickness, and the like above the channel. Therefore, it is possible to prevent display unevenness due to an electric field due to the potential of the cathode, a change in film quality, film thickness, and the like above the channel.

Further, if the second TFT 40 is a p-type channel TFT having an active layer having a source and a drain doped with a p-type impurity, a region saturated in the Id-Vd characteristics can be widened. V
Id is less likely to change in accordance with d, that is, the variation in drain current value in accordance with 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, so that good gradation display can be achieved. Can be easily obtained.

In particular, in a polycrystalline silicon TFT, as described in the section of the prior art, a crystal grain boundary exists, and a potential barrier is formed by electrons trapped in the grain boundary, so that a depletion layer spreads. For this reason, a strong electric field is applied to the grain boundary at the edge of the drain electrode, and this causes a collision ionization phenomenon in which accelerated electrons collide with the lattice. This phenomenon is more significant in the case of the p-type channel than in the case of the n-type channel TFT. It is preferable to use a p-type channel TFT as the second TFT because the drain current shows a region where the drain current is saturated and good saturation characteristics can be obtained since the drain current is extremely small. <Second Embodiment> FIG. 4 is a plan view showing the vicinity of a display pixel of an EL display device according to the present invention, and FIG. 5 is a cross-sectional view taken along line CC in FIG.

This embodiment is different from the first embodiment in that, as shown in FIG. 4, a conductor 56 provided above a channel 43c of the second TFT 40 is connected to a gate electrode 41 of the second TFT 40. It is a point that a part is provided to extend.

As shown in FIGS. 4 and 5, the second TFT
Has an active layer made of p-Si provided on a stack of the gate electrode 41 and the gate insulating film 12. And
The active layer has a source 4 doped with impurities.
3s and a drain 43d.

A conductor 56 which is in contact with the gate electrode 41 via the contact holes provided in the gate insulating film 12 and the interlayer insulating film 15 is provided to extend above the channel 43c. That is, the conductor 56 having the same potential as the gate electrode 41 is provided.

As described above, by providing the conductor 56 having the same potential as the gate electrode 41, the back channel which has conventionally occurred can be suppressed.

As a result, 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 in each display pixel, and an organic EL display device without display unevenness can be obtained.

Further, since the second TFT is a TFT having a p-type channel similarly to the first embodiment, the variation of the drain current with respect to the drain voltage is small, and the emission luminance of the organic EL element is uniform with good reproducibility. And an organic EL display device capable of obtaining good gradation display can be obtained.

Although the p-Si film is used as the active layer in each of the above embodiments, a microcrystalline silicon film or an amorphous silicon film may be used.

Further, in each of the above-described embodiments, the organic EL display device has been described. However, the present invention is not limited to this, and is applicable to an inorganic EL display device in which the light emitting layer is made of an inorganic material. And the same effect can be obtained.

[0047]

As described above, the EL display device of the present invention includes the first TFT having good writing and holding characteristics at high speed and the second TFT having good current controllability, so that good gradation display is possible. An EL display device 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 sectional view showing a first embodiment of the 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 the EL display device of the present invention.

FIG. 5 is a cross-sectional view showing a second embodiment of the EL display device of the present invention.

FIG. 6 is an equivalent circuit diagram of the EL display device.

FIG. 7 is a plan view of a conventional EL display device.

FIG. 8 is a 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 Driving power source 56 Conductor 60 Organic EL device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 33/26 H01L 29/78 617N F-term (Reference) 3K007 AB17 BA06 CC00 DA01 DB03 EB00 EC03 FA01 GA04 5C058 AA12 AB01 AB06 BA35 5C094 AA04 AA06 AA07 AA09 AA13 AA48 AA54 BA03 BA09 BA12 BA27 CA19 CA24 CA25 DA13 DB04 EA01 EA04 EA07 EA10 FA01 FB12 FB14 FB16 5F110 AA18 AA30 BB20 CC07 CC08 DD02 DD03 DD30 GG13 EE14 GG14 EE14 NN23 NN24 NN27 NN44 NN72 QQ19

Claims (3)

[Claims] An electroluminescent device having a light emitting layer between an anode and a cathode, and a first electrode 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, respectively. The thin-film transistor and the drain of an active layer made of a non-single-crystal semiconductor film are connected to the drive power supply of the electroluminescent element, and the gate provided below the channel of the active layer is connected to the source of the first thin-film transistor. An electroluminescent display device comprising: a second thin film transistor; and a conductor covering the channel provided above the channel provided in the active layer of the second thin film transistor. . 2. The electroluminescent display device according to claim 1, wherein the conductor is provided with a drive power supply line connected to the drive power supply extending to above the channel. 3. The electroluminescent display device according to claim 1, wherein the conductor is provided so as to extend the gate signal line above the channel.