JPS59128581A - El display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (8.) Technical Field of the Invention The present invention relates to a switching system that integrates an electroluminescence (hereinafter abbreviated as EL) display element and a drive circuit to constitute a drive circuit that drives the EL display element. It relates to EL display devices with reduced breakdown voltage of transistor elements for
The present invention relates to an EL display device that prevents destruction of a transistor element for driving a display element when an L display element is locally destroyed.

(2) Background of the technology EEL display devices, which integrate EL display elements and drive circuits, utilize semiconductor manufacturing technology to fabricate a high-density array of multiple EL display elements. It has the advantage of being able to be manufactured integrally with a drive circuit, and is attracting attention as an alternative to display devices using cathode ray tubes, liquid crystals, and gas discharge. (0) Conventional technology and problems Figure 1 2 shows a circuit diagram for one pixel in an ELL display device having an integrated structure of an ELL display element and a drive circuit. In the figure, 1 is a KLL display element, with opposing t poles ia, t
A configuration f is adopted in which an EL layer IC is sandwiched between b and a dielectric layer (not shown). and one electrode 1 of the ELL display element 1
A multi-pulse alternating voltage from the power source 2 is applied to a. Further, the data line DL is connected to the drain of the transistor element Ql, the scanning line SL is connected to the gates of the transistor elements Q,l, the source of the transistor element Q1 is connected to the gate of the transistor element Q2, and the storage capacitor Connected to Cs. Also, transistor element Q2
The drain of is connected to the other electrode lbK of the ELL display element 1, and the source is connected to the ground potential serving as a reference potential point.

In such a configuration, when a pulse-like scanning signal with a predetermined width is supplied to the scanning line Sr and the IC with the data line L set to ``1'', the transistor element Q1 turns on and the capacitor Cs accumulates charges in response to the scanning signal. This turns on the transistor element Q2, causing the ELL display element 1 to emit light. Also, the data line DL
When the transistor element Q2 is turned off due to the discharge of the capacitor Cs due to the change in the state of ``0#b'', the EL display unit 1 does not emit light.

Now, in such an ELL display device, the ELL display element 1 is in a non-emitting state, that is, the switching transistor Q
2 is in the off state, approximately 2 of the pass/L/su voltage VA of the t source 2 is present between the drain and the drain of the transistor element Q2.
Double the voltage will be applied, and the transistor element Q
2 requires a material with extremely high withstand voltage. Therefore, the breakdown voltage in the off state of the transistor element Q2 is set on the difference plate between the light-emitting voltage value of the EL table display 1 and the non-light-emitting voltage value, and the voltage applied to both ends of the transistor element Q2 is set below the breakdown voltage of the transistor element Q2. It can be clamped to the
A device has been proposed that reduces the withstand voltage required for the transistor element Q2. According to this method, the emission voltage is 2001. When driving the KLL display element 1 with a non-emission voltage of 170V, the breakdown voltage of the transistor Q2 may be set to 30V, and a breakdown voltage of more than 30V is sufficient.

By the way, if local dielectric breakdown occurs in the dielectric layer or EL layer of the ELL display element 1, the transistor element Q2 may be destroyed. At this time, the destruction of the ELL display element 1 is limited to pinhole-like destruction in a minute area and does not result in a practical display defect, but the destruction of the transistor Q8 does not result in a display defect of one pixel and is fatal to the display. This is one of the causes of quality deterioration.

FIG. 2 shows a partial equivalent circuit of an E'L display device with a conventional drive circuit integrated structure, and FIG. 3 shows the electric waveforms of each part in FIG. The voltage waveform applied to the electrode 1a, (b) is the drain voltage waveform when the transistor Q2 is on, ((3) is the drain voltage waveform when the transistor Q, Q is off. In FIG. 2, Q2 is the transistor element, 1 is the ELL display element, 2 is the power supply, Rs is the internal impedance of the power supply 2, RON is the on-resistance of the transistor element Q2, 2 ROFF is the off-resistance of the transistor element part, and in this case, the off-resistance at the breakdown voltage VB shows.

Now, if the ELL display element 1 of FIG. 2 is locally destroyed during the period t shown in FIG. ) is applied. This voltage VPON is expressed by equation (1).

VPON =-one group-・VA・・・・・・・・・・・・・
(1) R3+ROM Then, when the voltage VPON exceeds the breakdown voltage BYON when the transistor element Q2 is turned on, the transistor element Q
B destroys it.

Further, when the transistor element Q2 is in the off state, an overvoltage VPOFF as shown in FIG. 8(C) is applied to the transistor element Q2, and the voltage VPOFFIF is
) is expressed by the formula.

Then, when this voltage VPOFF exceeds the breakdown voltage BVoyp when the transistor element Q2 is turned off, the transistor element Q2 is also destroyed. As a result, the ELL display element 1 becomes unable to display, resulting in poor display quality. It becomes a financial defect.

OBJECT OF THE INVENTION The present invention has been made in view of the above-mentioned points, and provides an EL display device which prevents destruction of switching transistor elements connected to the EL display element when the ELL display element is locally destroyed.
The object of the present invention is to provide an ELL display device having an integrated structure with a front display driver circuit.

(e) Structure of the Invention The ELL display device according to the present invention has two opposing! ELN between poles
For switching, the display element has an ELL display element provided with an ELL display element, in which an alternating voltage is applied to one electrode of the display element, and between the other electrode and a reference potential point to control whether or not the display element emits light. A transistor element is connected, and the breakdown voltage of the transistor element in the off state is set on the difference plate between the light-emitting voltage value and the non-light-emitting voltage value of the display element, and the voltage applied across the transistor element is set to the voltage applied to both ends of the transistor element. In the configuration configured to clamp the voltage below the breakdown voltage, the other electrode of the display element and the transistor element are connected by a protective resistance element consisting of a resistance connection body, and the above-mentioned E
The gist of this invention is to limit the voltage applied to the transistor element at the time of local breakdown to below the breakdown voltage of the transistor element.

(f) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a sectional view of a main part showing an example of the structure of one pixel of the ELL display device according to the present invention. In the figure, Q2 is a thin film polycrystalline silicon transistor element, 1 is an ELL display element, and these transistor element Q2 and ELL display element 1 are
is formed on a substrate 41 made of hard glass, ceramic, or the like. The transistor element Q2 is composed of a drain D and a source S formed on the surface layer of the polycrystalline silicon layer 42, and a conductive layer serving as the gate G disposed on the polycrystalline silicon M42 via a 5102 layer 43. .

The drain D and source S are made of polycrystalline silicon layer 42.
It consists of n10 regions in which, for example, phosphorus [F] is injected into the surface layer. The breakdown voltage VB of this transistor element Q2 is determined by controlling, for example, the distance between the source and drain (channel length), the amount of impurity doping of the semiconductor thin film 42, etc.
It is set to 0V.

In addition, the ELL display element 1 has an electrode 1a (transparent conductive film) and an electrode 1.
b (for example, an Al film) through a dielectric layer (not shown).
It can be constructed by sandwiching an L-layer IC.

A power source 2 is connected to the electrode 1a, and a Papnu-like alternating voltage is applied thereto. Also, the transistor element Ql! The source S of is connected to the ground potential, and the drain D and the electrode 1b are connected, but in the present invention, they are connected by a resistance connection body called a protective resistance element Ra. The resistance connection body R
For example, a is formed of a polycrystalline silicon layer to control the amount of doping with impurities such as phosphorus.

The resistance value can be set to a predetermined value by controlling the control.

In addition, in FIG. 4, the transistor elements Q and l in FIG.
Condenser Cs. Gator and scan line DT, and S
L is omitted from illustration. In such a configuration, the fiEL display element 1 is controlled by turning on and off the transistor element Q2.
0 emission/non-emission is controlled. At this time, the ELL display element 1
The light emitting area becomes a region W and defines one pixel. This pixel area W is set depending on the size of the window of the Sing film 48 provided on the electrode lb.

Next, FIG. 5 is a partial circuit diagram for one pixel of the ELL display device according to the present invention, and FIG. 6 shows voltage waveforms at various parts in FIG. (b) is the drain voltage waveform when transistor element QQ is on, and (C) is the drain voltage waveform when transistor element Q2 is off. Parts that are equivalent to those in Figure 3 are given the same symbols. As is clear from FIGS. 2 and 5, according to the present invention, the drains D of the transistor elements Q and g and the t
This differs from the conventional one in that it is connected to Wlb by a protective resistance element Pα consisting of a resistance connection body.

If the EL display element 1 shown in FIG. 5 is locally destroyed during the period t shown in FIG. 6(a), if the transistor element Q2 is in the on state, the transistor element Q2
An overvoltage V'PON as shown in FIG. 6 (to) is applied to. This voltage V'PON is determined by formula (8)% (3) When the transistor element Qw is in the off state, an overvoltage V'poFF as shown in FIG. 6(C) is applied to the transistor element Q2. The voltage V'POFF is expressed by equation (4).

0FF V'POFF! □・VA・・・・・・・・・(4)R
s + Ra + RoFy Therefore, as is clear from equations (1) and (2) and equations (8) and (4), the voltages V'PON', V
'POFF can be limited to a lower value than the voltages VPON and VPOFF by providing the protective resistance element Ra. The resistance value of the protective resistor element α is set so that the voltage V'pon is lower than the breakdown voltage BVou when the transistor element Q2 is turned on. Also the voltage 'V'PO
The resistance value of the protection resistance element Rd is set so that the breakdown voltage BVOFF of FF and the transistor element Q2 when turned off is also lower. Thus, according to the present invention, by arranging the protective resistance element Ha, even if local destruction occurs in the EL display element, it is possible to prevent destruction of the transistor element Q2. There is no fatal defect in the display due to the inability to display, and the display quality in practical use is not affected in any way.

Note that in the above embodiment, the drive circuit and the EL are provided on the insulating substrate 41.
Although the case where a display element is formed has been described, similar effects can be obtained even if the present invention is applied to an EL display device in which a drive circuit and an EL display element are integrated on a semiconductor substrate.

(2) Effects of the Invention As is clear from the above explanation, according to the present invention, even if an EL display element is locally destroyed, destruction of the transistor element for driving the display element can be prevented, and the transistor element can be prevented from being destroyed. It is possible to prevent fatal display defects due to destruction, and has the advantage of improving the manufacturing yield and reliability of EL display devices with integrated drive circuits (TT).
Its practical effects are great.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of an EL display device, Fig. 2 is a partial equivalent circuit diagram for one pixel of a conventional KL display device, Fig. 3 is a voltage waveform diagram of each part in Fig. 2, and Fig. 4 5 is a partial sectional view showing an example structure of one pixel of the EL display device according to the present invention, FIG. 5 is a partial equivalent circuit diagram of one pixel of the EL display device according to the present invention, and FIG. FIG. In the figure, 1 is an EL display element, 1a and 1b are electrodes, IC is a KL layer, Q, 1 and Q2 are switching transistor elements, R11 is a protective resistance element consisting of a resistance connection body, and 41 is a substrate.

Claims (2)

[Claims] (1) It has a KL display element in which ELs are provided between opposing electrodes, an alternating voltage is applied to one electrode of the display element, and between the other electrode and a reference potential point of the display element. A switching transistor element for controlling light emission/non-light emission is connected, and the breakdown voltage of the transistor element in the OFF state is set to be greater than or equal to the difference between the light emission voltage value and the non-light emission voltage value of the display element, and the transistor element is destroyed. In a configuration in which a voltage applied to both ends of the transistor element is clamped to a voltage below the voltage of the transistor element, a protective resistance element is interposed between the other electrode of the display element and the switching transistor element to produce the EL display. 1. An EL display device characterized in that a voltage applied to a transistor element at the time of local breakdown of the element is limited to a voltage equal to or lower than the breakdown voltage of the transistor element. (2) The protective resistance element is composed of a resistance connection body that connects the other electrode of the EL display element in the EL display element and the switching transistor element integrally formed on the substrate and the transistor element. A KL display device according to claim (1).