JPS62151897A - Thin film transistor array - 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 Field of Industrial Application This invention relates to a thin film transistor array used in active matrix liquid crystal displays and the like.

Conventional technology Conventional transistor arrays used for this purpose include:
For example, as shown in Japanese Unexamined Patent Publication No. 59-47623, a configuration as shown in FIG. 2 is common. In other words, thin film transistors (hereinafter referred to as TPT) have gate electrodes connected to scanning lines
) 11, whose drain electrode is the pixel electrode 2
6.

A liquid crystal 13 is inserted between the picture element electrode and the counter ground electrode to constitute an independent picture element 14. The liquid crystal functions equivalently as a capacitor, but in some cases an auxiliary capacitor may be added in parallel.

The movement of TPT will be explained with reference to FIG. Scanning line X,,X
, , X, ,... are provided with selection pulses P as shown in FIG.
++ pg, P:1. ... are applied respectively.

When a specific scanning line, e.g. A signal line voltage is applied. When X is switched to non-selection, the TPT becomes non-conductive, so the voltage applied to the picture element maintains the previous value until Xl is selected in the next frame. In this way, a liquid crystal display using a TPT array is attracting attention because it is capable of accurately and independently transmitting the necessary signal voltage to each picture element, allowing display with a high contrast ratio without crosstalk.

Problems to be Solved by the Invention However, when the number of scanning lines and signal lines increases in such a configuration, it becomes extremely difficult to manufacture all TPTs as good products. In particular, TPT has a gate 21, a source 22, and a drain 2, as shown in FIG. 4, an example of its cross-sectional structure.
3 are stacked with at least an insulating film 24 interposed between them, so pinholes and other problems in the process may cause gate damage.
There is a risk of a short circuit between sources or between gate and drain. In particular, a gate-source short circuit causes abnormal operation of all TPTs on the scanning line and signal line connected thereto, resulting in a serious defect called a line defect. This is because the voltage waveforms externally supplied to the signal lines and scanning lines change significantly due to a short circuit between the gate and source.

The present invention has been made in view of the above problems, and an object thereof is to provide a transistor array having a structure in which picture element defects ('a defects and point defects) do not occur even if some transistors are defective. The purpose is

Means for Solving the Problems In order to solve the above problems, the present invention makes the resistance of the connection between the source of each transistor and the signal line sufficiently larger than the resistance of the scanning line and the signal line, and It is characterized in that the product (time constant) of the capacitance of the connected picture element and the resistance of the source connection portion is made sufficiently shorter than the selection pulse width of the scanning line.

According to the present invention, even if a short circuit occurs between the gate and source of a transistor due to process trouble, the resistance of the short circuit path is set to be greater than the resistance of the signal line and scanning line related to the short circuit point. Therefore, the voltage waveforms externally supplied to the signal line and scanning line do not change much due to a short circuit. Therefore, even if there is a short circuit between the gate and source of the TPT, this can be prevented from leading to serious defects such as line defects.

Embodiment FIG. 1 shows the basic configuration of the present invention, where l is the resistance at the connection between the signal line and the source of the TPT. The value of this resistance is better if it is larger than the resistance of the signal line and scanning line in order to avoid the influence of short circuit between source and gate, but the degree depends on the required display quality, type of display, panel configuration, etc. It is best to decide on a case-by-case basis so that there is no practical problem. On the other hand, the value of the above resistance is TPT
From the viewpoint that the information on the signal line must be transmitted to the picture element within the selection pulse width time during which the line becomes conductive, it is not preferable to make it too large. That is, the resistance of the connection part is Rc, the capacitance of the picture element is Cp, and the selection pulse width is 77M (M
If T is the total number of scanning lines and T is the rewriting period of the screen, then Rc-Cp<77M is required at least. A typical example is Cp −I PP, T = 16.7n+se
If c, M = 1000, the above request is Rc<16M
becomes Ω. If the resistance of the signal line and scanning line were 10Ω, again a typical example, then in this example the IO
It is sufficient to set Rc that satisfies KΩ<Rc<16MΩ, but in order to obtain a higher quality display, for example, set Rc to 10
It can be selected from OKΩ to LMΩ.

This resistor may be made using any material and construction method as long as it satisfies the above values, but TPT, which is more efficient,
If an array substrate manufacturing process is required, it is desirable to use materials conventionally used in that process.

Usually, as shown in FIG. 4, a doped layer 28 is interposed between the semiconductor film 25 and the source electrode 230 to ensure ohmic contact. Amorphous silicon is often used as a semiconductor film, and in this case, a thin amorphous silicon doped with n-type impurities is usually used for the doped layer. The sheet resistance of this doped layer is typically on the order of 10 7 Ω/hole, so it is suitable for achieving any required value of Rc.

Therefore, if the connection between the signal line and the source is made using this doped layer instead of the conventional source electrode material, the array substrate of the present invention can be fabricated using the same conventional process and simply changing the mask. It is possible to create .

Effects of the Invention As detailed above, the present invention provides a means for greatly improving the yield of active matrix substrates through extremely simple improvements, and has great practical value.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram showing a thin film transistor array according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of a conventional thin film transistor array, and FIG. 3 is a selection pulse waveform diagram of a scanning line.
FIG. 4 is a cross-sectional view of the thin film transistor array. 1...Resistance of connection part, 11...Thin film transistor, 13...Liquid crystal, 14...
Picture element, 22...Drain, 23...Source, 25...Semiconductor film, 26...Picture element electrode, 28...Dope N. Agent's name: Patent attorney Toshio Nakao 1 person 7 --- Mu) Morning at E-Seong (circle 11 --- TFT 26 --- T & xl, x2.Xa -- shot 4)' t, and 2. Ys - Signal East tl --- TFT /3 --- i item t4 --- # East 2nd figure 26-Transfer to Xr 2. 3-scanning lines YI, Yl, Y3=-signal section

Claims (3)

[Claims] (1) A plurality of scanning lines, a plurality of signal lines crossing these, a plurality of switch thin film transistors installed corresponding to the intersection points, and a plurality of picture elements driven by the transistors, The source of the above transistor is connected to the corresponding signal line via a resistor, and the above resistor is
A thin film transistor array characterized in that the resistance is greater than the resistance of the signal line and the scanning line, and the product of the capacitance of the picture element connected to the drain of the transistor and the resistance of the connection part is shorter than the selection pulse width of the scanning line. (2) the source is made of the same material as the signal line;
The thin film transistor array according to claim 1, wherein the source and the signal line are connected to each other through a high resistance material. (3) Claim (2) characterized in that the high-resistance material is an amorphous silicon film doped with impurities.
The thin film transistor array described in .