JPH03233431A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE:To reduce Cgs and to prevent a CD voltage component from being generated on a display panel by making the drain electrode opposite to source electrode of a thin film transistor(TFT) to be arranged in a U or L shape. CONSTITUTION:A gate electrode 1 of Cr is sputtered and deposited on a glass substrate 8 and then patterned. Then a SiN layer 7 which becomes a gate insulating film an a-Si layer 4 as a semiconductor layer, and an n0a-Si layer 6 as an ohmic contact layer are laminated in order, and then the source electrode 3 and drain electrode 2 are formed. At this time, the drain electrode 2 is opposed to the source electrode 3 to be formed the U shape surrounding the source electrode 3. Consequently, the channel part of the TFT is formed in a U shape, as well. Thus, the driving ability for picture element electrode is increased and the generation of the DC voltage component by Cgs can be suppressed small.

Description

[Detailed description of the invention]

(Industrial Application Field 1) The present invention relates to a thin film transistor (TPT) using hydrogenated amorphous silicon (a-5i:H) and a liquid crystal display panel using the same.

[Conventional technology]

In liquid crystal display panels using thin film transistors, as described in Japanese Patent No. 63-095574, it is known that a DC voltage component due to the capacitance Cgs between the gate and source of the thin film transistor is applied to the liquid crystal, which adversely affects the characteristics of the display panel. ing. In order to increase the drive capability of a thin film transistor, it is sufficient to increase the W/L of the transistor, but there is a problem in that an increase in W/L leads to an increase in Cgs. The above-mentioned known example describes a method of canceling out this DC component by installing an additional capacitor. However, this method has drawbacks such as the need for a special gate pulse waveform, and there has been a demand for simpler measures to reduce the DC component. Another known example is JP-A-62-165368 (Sharp Thin Film Transistor). This invention focuses on the above-mentioned variations in DC voltage and describes methods for suppressing variations due to pattern deviation. However, there was no mention of reducing the DC voltage itself, and problems still remained. In addition, as a publicly known example regarding the TPT shape, the public utility model published in 1986
There is 0-54171 (Sanyo liquid crystal display W). This invention was made to reduce the area occupied by the transistor, and the pixel electrode is U-shaped. Therefore, this is different from the gist of the present invention.

[Problem to be solved by the invention]

An object of the present invention is to reduce Cgs by changing the structure of the TPT, and to suppress the generation of DC voltage components on the display panel. Another object of the invention is an effective increase in the transconductance of the TPT and a reduction in the amplitude of the opening gate voltage. [Means for Solving the Problems] In order to achieve the above object, the drain electrode (source electrode) of a thin film transistor is arranged in a U-shape or an L-shape so as to face the source electrode (drain electrode). [Function] The drain electrode arranged in a U-shape or L-shape with respect to the source electrode effectively uses the area around the source electrode, which contributes to increasing the W/L of the thin film transistor. On the other hand, since the shape of the source electrode does not change, Cgs does not increase. In thin film transistors on display panels, signal electrodes formed in a U-shape or L-shape relative to pixel electrodes can increase W/L and reduce Cgs, thereby keeping the DC voltage component of the display panel low and preventing deterioration of panel characteristics. does not bring about

【Example】

The present invention will be explained below using examples. FIG. 1 shows an embodiment of the present invention. This figure shows the pixels on the TPT substrate side of the liquid crystal display panel.
A signal voltage is supplied to a pixel electrode 9 made of an O transparent electrode. A gate pulse is applied to the gate bus line 10, the transistor 12 is activated, and a signal is transmitted from the signal bus line 11 to the pixel through the electrode 2. A liquid crystal is inserted between the TPT substrate and a color filter substrate provided opposite to the TPT substrate. Although an AC voltage is applied to the liquid crystal, a DC voltage is induced in the liquid crystal by the capacitance Cgs formed between the gate electrode 1 and the pixel electrode 3. However, since the effective W/L of transistor E2 is large, the driving gate voltage can be kept low, and since Cgs is relatively small, this induced voltage component can be kept low. This has the effect of significantly reducing the problems of display panel characteristic deterioration, such as burn-in and shortened liquid crystal life, which occur when Cgs is large. The TFT section of the embodiment shown in FIG. 1 will be explained in more detail with reference to FIGS. 2 and 3. Figure 2 (a) is its plan view, and Figure 2 (b) is (a
) is shown. A gate electrode 1 of Cr is formed on a glass substrate 8 by patterning using a sputter deposition machine. Next, a plasma CVD method is used to deposit S, which will become the gate insulating film.
iN layer7. A-5i layer 4 which is a semiconductor layer, and n which is an ohmic contact layer. The a-Si layers 6 are sequentially laminated. Then, a source electrode 3 and a drain electrode 2 are formed. The metal is a double layer of Cr/AQ, which is patterned after sputter deposition. At this time, as shown in FIG. 3A, a U-shaped pattern is formed so that the drain electrode faces the source electrode and surrounds it. As a result, the channel portion of the TPT is also formed into a U-shape. The effect of this embodiment becomes clear when compared with the conventional example shown in FIG. Although the transistor area in FIG. 3 is almost the same as that in FIG. 2, W/L in FIG. On the other hand, in the transistor shown in FIG. 2, which is an embodiment of the present invention, the area around the electrode 3 is effectively used as a TPT channel, so the channel is formed in a U shape, and its effective W/L is W/L=5, and its Cgs is 174, assuming that the conventional example shown in FIG. 2 is 1. In other words, Cgs was significantly reduced with the same W/L. Conversely, if Cgs is kept constant, W/L has effectively increased by more than four times. This is equivalent to increasing the mutual conductance or mobility by more than four times, and the effect is very large. In this case, what should be noted is that the electrode 3 is connected to the pixel electrode 9 (see the first drawing), and the reason why the gate pulse drop-in is greatly reduced is because of the parasitic capacitance Cg s of the electrode connected to the pixel electrode. This is because it is small. FIG. 3 shows another embodiment of the invention. The drain electrode is arranged in an L-shape opposite to the source electrode. In this case as well, an increase in effective W/L is achieved with Cgs constant. In this case, W/L is ~3. In other words, this is equivalent to triple the effective mobility while Cgs remains constant. Of course, in this case the electrode 3 is connected to the pixel electrode 9 in the drawing. Further, the electrode 2 is connected to a signal bus line (FIG. 1) 11, and the gate electrode 1 is connected to a gate bus line 10 shown in FIG. 1, thereby operating as a liquid crystal display panel. Although the TPT structure shown in FIG. 4 has a smaller increase in effective W/L than the TPT shown in FIG. 2, it becomes an effective means when the bus line spacing becomes small. Although the present invention has been described above based on embodiments, the gist of the present invention is not limited only to the above embodiments. The electrode and channel shapes referred to as U-shaped and L-shaped may be any shape having approximately the same shape. In other words, in a U-shape, the left and right branches may have slightly different lengths, and even if it is an L-shape, the corners do not necessarily have to be at right angles. The process may also result in rounded corners. U
The character shape and the L shape are merely approximate shapes. The electrode 3 is also rod-shaped, and although the example in which the lengths of each side of the channel forming portion are approximately equal has been shown, it does not depart from the gist of the present invention even if the lengths of each side are different. In addition, although the structure of the TFT was explained using a-5i (amorphous silicon) as an example, it is also possible to use other materials such as CdSe,
Te, poly-Si, etc. may be used, and the gate insulating film is not limited to SiN either. Effects of the Invention According to the present invention, Cgs of a thin film transistor can be reduced without reducing W/L. Therefore, when this transistor is used in a liquid crystal display panel, it has the effect of increasing the opening ability of the pixel liquid crystal and suppressing the generation of a DC voltage component due to Cgs. This has a great effect in preventing characteristic deterioration of the liquid crystal panel. When Cgs is kept constant, the opening ability of the transistor is greatly improved. This makes it possible to improve the voltage writing rate. On the other hand, increasing the opening capability also makes it possible to reduce the opening gate pulse amplitude. In the above embodiment, the amplitude of the opening gate pulse voltage can be reduced to about half. Since the magnitude of the DC voltage component is proportional to the gate voltage amplitude, a small Cgs and a low gate voltage act as a double effect, and have the effect of preventing the panel characteristics from deteriorating. In other words, it has effects such as improving the reliability of the liquid crystal and reducing burn-in.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention in a display panel. Figure 2 is a plan view (a) of the thin film transistor section in Figure 1.
3 is a plan view showing a conventional thin film transistor, and FIG. 4 is a plan view showing another embodiment of the present invention. Explanation of symbols 1...Gate electrode, 2...Drain electrode, 3...
Source electrode, 4...a-8i, 5... Gate-source capacitance, 6... Ohmic contact layer, 7... Gate insulating film, 8... Substrate, 9... Pixel electrode, ↓O・・・
・Gate bus line, 11...Signal line bus line, 1
2...Thin film transistor. 4 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. It has a plurality of gate bus lines and a plurality of signal bus lines formed on a substrate, and has a thin film transistor and a pixel electrode provided at the intersection of these bus lines, and the above-mentioned In a liquid crystal display panel having a configuration in which the gate electrode of the thin film transistor is connected to the gate bus line and two electrodes (source and drain electrodes) through which drain current flows, one is connected to the signal bus line and the other is connected to the pixel electrode. A liquid crystal display panel characterized in that the planar shape of an electrode connected to a signal bus line of a thin film transistor and the planar shape of a channel of the thin film transistor are U-shaped or L-shaped. 2. The liquid crystal display panel according to item 1, wherein the semiconductor layer of the thin film transistor is made of amorphous silicon.