JPH0830799B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a TFT (Thin Fi)
lm Trs) and the like, the present invention relates to a protection circuit for preventing destruction of the elements constituting the matrix due to static electricity or the like.

[0002]

2. Description of the Related Art In a TFT, since a transistor is formed on an insulating substrate, it is difficult to monolithically form a protection circuit for preventing element destruction due to static electricity or noise. The reason for this is that there is no common substrate for absorbing current when static electricity or the like enters from the terminals of the circuit composed of TFTs. Moreover, the TF is a protection circuit which has been used in ordinary ICs and LSIs formed on a single crystal silicon substrate and has a high degree of technical perfection and a proven track record.
One of the reasons is that it cannot be adopted in T.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a protection circuit which protects an active matrix composed of TFTs and the like formed on a broken substrate from destruction due to static electricity or the like.

[0004]

The present invention provides a pair of insulating substrates.
A liquid crystal is enclosed between the substrates, and one of the substrates or both substrates are
A matrix of scan electrodes and signal electrodes on a plate
Formed in the shape of a circle, near the intersection of each scan electrode and each signal electrode.
In a liquid crystal display device in which a pixel electrode is formed,
The element electrodes form a display part, and the entire outer circumference or the outer circumference 1 of the display part
/ 2 is a conductive wire, and the conductive wire is a GND wire.
Connected between the scan electrodes and the conductive lines and
The source region and the gate are short-circuited between the signal electrode and the conductive line.
MOS transistor and gate and drain regions
Is connected in series with the MOS transistor
It is characterized by becoming.

[0005]

According to the present invention, the active matrix terminal
Source area connected in series when static electricity is input to
MOS transistor with shorted gate and gate, and gate
Via a MOS transistor in which the drain region is shorted
Then, static electricity, etc. is poured into the conductive wire.
Does not cause element destruction.

[0006]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 shows a conventional TFT active matrix. Each X line (X1, X2 ... Xn) has electrodes at both ends for connecting to an external circuit, and between the electrodes at both ends, as is apparent from FIG. 1, it is connected to the gate of each TFT. Each Y line (Y1, Y ... Ym) also has electrodes for connecting to an external circuit at both ends, and the electrodes between the both ends are connected to the source of each TFT as is apparent from FIG. In the process of assembling an active matrix as shown in FIG. 1 as a panel, static electricity is often input from the X and Y line terminals of the active matrix. For example, if static electricity is input from the left terminal of the X1 line in FIG.
Voltage is sequentially applied from the gate of T11 to the gate of T1m while changing the input waveform according to the wiring resistance of one line. When the electrostatic input voltage is low, T1
After the electrostatic waveform propagates to the gate of m, X1
The entire line becomes a certain potential, and the static electricity is discharged due to surface leakage or the like with the lapse of time, and the potential gradually decreases.

Even if static electricity is input, when the static electricity is discharged in the above process, the TFT is not damaged in any way.

However, when the static electricity voltage input from the left end of the X1 line is sufficiently high and exceeds the gate breakdown voltage of the TFT, when the static electricity reaches the gate portion of T11, the gate oxide film of T11 is destroyed. Sometimes.
In such a case, the TFT will be permanently damaged.

Therefore, an object of the present invention is to provide a protection circuit in which the TFT is not destroyed even if static electricity is input to the terminals of the active matrix. An embodiment of the present invention is shown in FIG. As is apparent from FIG. 2, the point of the present invention is that a conductive line is wired outside the active matrix (hereinafter referred to as a wiring A), and two MOSs are provided between the wiring A and each X and Y line. Type transistors are connected in series. The two MOS type transistors are TX11, TX12, ... Tn1, TX.
n2, TY11, TY12, ... TYm1, TYm2. Of the two MOS transistors tangential to the X line, the gate of the MOS transistor closer to the X line (TX11, TX21, ... TXn1) is connected to each X line, which is also connected to the Y line. Of the two MOS-type transistors to be connected, whichever is closer to the Y line
OS type transistors (TY11, TY21, ... TY)
The gate of m1) is connected to each Y line. Meanwhile X
MOS connected differently from the line and Y line
Type transistors (TX12, ... TX12, TY12 ...
The gate of TYm2) is connected to the wiring A provided outside the active matrix. Therefore, the protection circuit according to the present invention includes the wiring A and the wiring A as shown in FIG.
And two MOS type transistors inserted between the X and Y lines.

The reason why the active matrix having the protection circuit according to the present invention shown in FIG. 2 is strong against static electricity is that the static electricity input is applied to the gate of the TFT constituting the active matrix by increasing the current path. This is because the effective potential decreases. The two solid MOS type transistors newly added to each of the X to Y lines are turned on and the other is turned off in response to the positive or negative of the applied static electricity. Part of static electricity is off
The current flows to the wiring A due to the breakdown between the source and drain of the MOS type transistor. When the active matrix of FIG. 2 is in the process of assembly, the wiring A is floating. Therefore, the ratio of the static electricity flowing to the wiring A is determined by the floating potential of the wiring A and the capacitance of the wiring.

The larger the capacity of the wiring A, the greater the effect of preventing the destruction due to the generation of power. Specifically, the wiring width of the wiring A is increased, and the wiring A shown in FIG. 2 is laid on the outer periphery 1/2 of the active matrix. It should be larger. When the active matrix is connected to a peripheral circuit or the like and assembly is completed, the wiring A is also preferably connected to the GND potential. In this case, the protection circuit of the present invention is useful not only for static electricity but also for surges input through peripheral circuits.

The method of connecting two MOS type transistors inserted between each X to Y line and the wiring A is necessary for the active matrix to operate normally.
For the operation of the active matrix, at least the potential of the Y line needs to swing both positive and negative with respect to the GND potential. There is also an active matrix in which both X and Y potentials swing positively and negatively. With respect to the normal X and Y potentials of the two MOS type transistors, one of them is always OFF, and the X and Y potentials are secured, so that the operation of the active matrix is guaranteed.

FIG. 3 shows another protection circuit according to the present invention.
Resistors (RX1, RY1) are additionally inserted in each line as compared with FIG. The resistor plays a role of blunting the applied waveform of static electricity or the like, and the element breakdown is more effectively prevented. The basic operation of the protection circuit is similar to that described with reference to FIG.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional active matrix.

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

Claims (1)

[Claims] 1. A liquid crystal is sealed between a pair of insulating substrates,
A plurality of scan electrodes on one or both substrates of the plate and
A plurality of signal electrodes are formed in a matrix and each scanning electrode
And a pixel electrode is formed near the intersection of each signal electrode
In the liquid crystal display device, the pixel electrode forms a display portion,
Conductive wires are provided on the entire outer circumference or the outer circumference 1/2 of the display section.
The conductive line is connected to the GND potential,
Between the inspection electrode and the conductive line and between the signal electrode and the conductive line
Is a MOS transistor in which the source region and the gate are short-circuited
And a MOS type transistor in which the gate and drain regions are short-circuited.
Liquid, characterized by being connected in series with a transistor
Crystal display device.