JPH06123896A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To decrease an ON-resistance in a video signal write switching thin film transistor and to shorten a write time and to reduce the number of divisions of a video signal by connecting plural thin film transistors hydroprocessed in parallel and keeping individual channel width within the range of a specific value. CONSTITUTION:Plural display pixel parts 4 formed two-dimensionally on the same substrate are controlled by forming the drive circuit of a shift regist 1, a buffer 2 and the video signal write switching thin film transistor 3, etc., on the substrate. The switching thin film transistor is driven point-sequentially. At this time, in the video signal writing thin film transistor 3, plural thin film transistors hydroprocessed are connected in parallel, and the individual channel width is kept in 1-30mum. Then, perfect hydroprocess is performed, and the dispersion of the process is reduced. Thus, the on resistance in the video signal write thin film transistor 3 is reduced, and the write time is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a drive circuit integrated active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, since liquid crystal display devices have the great advantages of thinness, light weight, and low power consumption, various liquid crystal display devices have been used for OA equipment such as liquid crystal televisions, Japanese word processors and desktop personal computers. ing. The active matrix type liquid crystal display device integrated with a drive circuit capable of high quality display is also required to have higher quality display characteristics.

FIG. 7 shows a partial circuit diagram of a conventional active matrix type liquid crystal display device integrated with a drive circuit. In a conventional active matrix type liquid crystal display device integrated with a drive circuit, a drive circuit such as a shift register 1, a buffer 2 and a video signal write switch thin film transistor 3 is formed on a substrate by using a thin film transistor made of polycrystalline silicon. The switching thin film transistor 5 for controlling a plurality of display pixel portions 4 formed two-dimensionally on the same substrate is driven in a dot-sequential manner. In addition, 6 is a signal line, 7 is a gate line, and 8 is a gate scanning line drive circuit. Here, the thin film transistor 3 for video signal write switch is designed so that a video signal can be written within a required writing time by forming a wide channel width and reducing on-resistance. Its channel width is usually 3
Although it is 00 to 400 μm, if the channel width is made wider, the punch-through voltage due to the capacitance between the gate and drain of the thin film transistor 3 for video signal write switch increases (SID'90 DIGEST P315), so the width is also limited. is there.

On the other hand, in the polycrystalline silicon thin film transistor, a drain leak current is apt to occur on the off side of the transistor operation which causes a decrease in contrast of the liquid crystal display device. Also, the mobility must be increased in order to improve the characteristics of the polycrystalline silicon thin film. For this reason, polycrystalline silicon thin film transistors are usually subjected to hydrogenation treatment in order to reduce drain leakage current and increase mobility. This hydrogenation treatment is related to the channel width, and since the effect of the hydrogenation treatment becomes smaller as the channel width becomes wider, there is disclosed a method of forming a slit in the channel portion to form an opening (JP-A-62-62). -268161).

[0005]

However, when the current television broadcasting (NTSC) standard is changed to the high-definition broadcasting standard, and the quality of image display is improved by the interlace drive to the non-interlace drive, video signal writing is performed. There is a problem that writing time of the video signal to the switching thin film transistor 3 becomes short, and writing becomes difficult in the case of the dot sequential driving method.

A shift register and a means for dividing the video signal can be considered as means for lengthening the video signal writing time, but it is difficult to increase and adjust the external drive circuit for the division of the video signal. Therefore, it is desirable to reduce the number of divisions of the video signal, or to lower the on-resistance of the video signal write switch thin film transistor 3 so that the division is not necessary. However, as described above, the channel width is also limited, and The method of performing a hydrogenation process after forming a slit in a channel part and forming an opening also has the following problems. When a narrow opening is formed in the channel part and the opening pattern width is formed by etching, it is difficult to form the opening itself by rounding the corners of the square opening. In addition, if the width of the opening is narrow, the withstand voltage of the gate electrode at the end of the active layer becomes poor.

Further, when a liquid crystal display device integrated with a drive circuit is subjected to a hydrogenation process, a thin film transistor thin film transistor, a buffer circuit and a protective MOS are formed as a pattern in which a channel width of a thin film transistor is narrow in a shift register or the like.
Since the thin film transistor of a diode exists as a wide pattern, if the hydrogenation process is performed for an optimal time for the channel width of the thin film transistor for video signal writing, the hydrogenation process becomes excessive in the shift register and the depletion phenomenon of the thin film transistor in the drive circuit section occurs. Occurs, leakage current at the time of off increases, power consumption also increases, and problems such as heat generation occur.

The present invention has been made to solve such a problem, and in a drive circuit integrated type liquid crystal display device, the ON resistance of a thin film transistor for a video signal writing switch is lowered, the writing time is shortened, and an image is displayed. An object of the present invention is to provide a liquid crystal display device capable of reducing the number of signal divisions.

[0009]

A liquid crystal display device according to the present invention comprises a substrate, a plurality of display pixel portions formed two-dimensionally on the substrate, and a plurality of switching pixels for controlling the display pixel portions. In a liquid crystal display device including a thin film transistor and a drive circuit unit including a signal line scanning circuit and a gate line scanning circuit for sequentially driving the thin film transistor on a substrate, the signal line scanning circuit includes a video signal processing unit and a video signal processing unit. A video signal writing thin film transistor for writing a video signal from the signal processing unit to a signal scanning line is provided, and a plurality of thin film transistors formed by hydrogenating the video signal writing thin film transistor are connected in parallel, and are connected in parallel. Each thin film transistor has a channel width of 1 μm or more and 30 μm or less.

In the liquid crystal display device according to the present invention, a plurality of thin film transistors each having a channel width of 1 μm or more and 30 μm or less are connected in parallel with a thin film transistor for video signal writing, a thin film transistor of a buffer circuit and a protection MOS diode having a wide channel width. Good.

In the liquid crystal display device of the present invention, the entire display pixel portion of the substrate having the above-mentioned display pixel portion, driving circuit portion, etc. is aligned with the counter substrate at a predetermined interval, and liquid crystal is injected into the gap portion, It constitutes a liquid crystal cell. Then, the exterior assembly is formed to obtain the liquid crystal display device of the present invention.

[0012]

By connecting a plurality of thin film transistors having a narrow channel width in parallel, the hydrogenation process can be more completely performed. Further, since the channel width has a perfect stripe shape between the source and drain regions, the hydrogenation treatment can be performed without variation.

Furthermore, since the channel widths of the thin film transistors formed on the same substrate including the drive circuit portion and the pixel portion are substantially the same, the hydrogenation treatment and the like can be performed in the same step. Therefore, in particular, it is possible to reduce the ON resistance of the thin film transistor for video signal writing switch, shorten the writing time, and reduce the number of divisions of the video signal.

[0014]

Embodiments of the present invention will be described with reference to FIGS. FIG. 4 shows transistor characteristics before and after hydrogenation treatment of the polycrystalline silicon thin film transistor. By performing the hydrogenation treatment, mobility is increased, threshold voltage is reduced, and the like, so that leakage current at the time of off can be reduced. Here, the polycrystalline silicon thin film transistor shown in FIG. 4 preferably has an LDD (Lightly Doped Drain) structure in which the source and drain portions have an n − region. The LDD structure forms a drain junction or the like by gradually changing the charge distribution in the vicinity of the drain portion or the like. Since the charge distribution gradually changes, the junction electric field at the junction also gradually changes and abnormal leakage current does not flow. This is because in the case of a polycrystalline silicon thin film transistor, unless the LDD structure is used, the leak current increases in the region where the gate bias is negative, and if the leak current increases, the video signal holding characteristic within one gate scanning time cannot be secured.

FIG. 5 shows the channel width dependence of the mobility and threshold voltage characteristics of a polycrystalline silicon thin film transistor after hydrogenation treatment. From FIG. 5, in the polycrystalline silicon thin film transistor, when the hydrogenation treatment is performed under the same conditions, the wider the channel width is, the insufficient hydrogenation is caused, the mobility is lowered, and the threshold voltage is increased. on the other hand,
If the channel width is too narrow, it becomes difficult for the drain current to flow, and the number of thin film transistors connected in parallel will be too large. For this reason, the channel width in the present invention is
It is important that the thickness is 1 μm or more and 30 μm or less.

Note that FIG. 6 shows that when hydrogenation treatment of a polycrystalline silicon thin film transistor is performed for a long time, hydrogen acts as a donor and the transistor characteristics change from an enhancement type to a depletion type. .

FIG. 1 is a partial circuit diagram of an active matrix type liquid crystal display device integrated with a drive circuit, which is composed of a polycrystalline silicon thin film transistor according to the present invention. FIG. 2 is a plan view of the thin film transistor 3 for video signal write switch. In FIG. 1, drive circuits such as a shift register 1, a buffer 2, and a thin film transistor 3 for a video signal write switch are formed on a substrate to control a plurality of display pixel portions 4 which are two-dimensionally formed on the same substrate. The switching thin film transistor 5 is driven in a dot-sequential manner. Here, the video signal write switch thin film transistor 3 is formed by connecting a plurality of thin film transistors in parallel,
In addition, each thin film transistor connected in parallel has a channel width of about 8 μm. By connecting 40 thin film transistors in parallel, the on resistance of the video signal write switch thin film transistor 3 was 500Ω or less when writing the video signal.

Since the video signal line wiring capacitance is usually about 10 pF, the frequency characteristics (f = 1 /
A frequency of about 30 MHz can be obtained from (2πRC)). As a result, the high-definition video signal band can be performed without division, and the load on the external circuit can be reduced.

FIG. 3 is another partial circuit diagram of an active matrix type liquid crystal display device integrated with a drive circuit, which is composed of a polycrystalline silicon thin film transistor according to the present invention. In FIG. 3, a thin film transistor 3 for video signal write switch
At the same time, the thin film transistor of the buffer circuit 2 also has a structure in which a plurality of thin film transistors having a channel width of about 8 μm are connected in parallel. An inverter circuit having a large channel width is used as the buffer circuit 2. By using thin film transistors of this buffer circuit in a parallel connection structure,
The hydrogenation was completed, and the hydrogenation was possible in the same manufacturing process.

Similarly, the protection MOS diode formed in the input protection circuit section as a countermeasure against static electricity has a high resistance if hydrogenation is insufficient and causes a deterioration in the original function, but a plurality of thin film transistors are shown in FIG. Thus, by connecting them in parallel, it was possible to achieve low resistance.

[0021]

According to the liquid crystal display device of the present invention, a plurality of thin film transistors for which a video signal writing thin film is hydrogenated are connected in parallel, and each thin film transistor connected in parallel has a channel width of 1 μm or more.
Since the width is made as small as μm or less, it is possible to perform a complete hydrogenation process and reduce variations in the hydrogenation process. Therefore, the on-resistance of the thin film transistor for video signal writing switch can be reduced, and the writing time can be shortened. Further, it is possible to reduce the leak current at the time of off and suppress power consumption and heat generation. Therefore, a liquid crystal display device having high-quality image display with excellent contrast can be obtained.

Further, since the thin film transistors formed on the same substrate have substantially the same channel width, the hydrogenation process and the like can be performed in the same manufacturing process, so that the manufacturing process can be simplified, and the liquid crystal The reliability of the display device is improved.

[Brief description of drawings]

FIG. 1 is a partial circuit diagram of a liquid crystal display device of the present invention.

FIG. 2 is a plan view of a thin film transistor 3 for a video signal write switch in a liquid crystal display device of the present invention.

FIG. 3 is another partial circuit diagram of the liquid crystal display device of the present invention.

FIG. 4 is a diagram showing transistor characteristics before and after hydrogenation treatment of a polycrystalline silicon thin film transistor.

FIG. 5 is a diagram showing channel width dependence of mobility and threshold voltage characteristics of a polycrystalline silicon thin film transistor after hydrogenation.

FIG. 6 is a diagram showing transistor characteristics when a polycrystalline silicon thin film transistor is hydrogenated for a long time.

FIG. 7 is a partial circuit diagram of a conventional liquid crystal display device.

FIG. 8 is a partial circuit diagram of a protection MOS diode in an input protection circuit section of the liquid crystal display device of the present invention.

[Explanation of symbols]

1 ......... Shift register, 2 ......... Buffer, 3 ...
Thin film transistor for video signal writing switch, 4 ...
Display pixel portion, switching thin film transistor, signal line, gate line, gate scanning line drive circuit.

Claims (1)

[Claims] 1. A substrate, a plurality of display pixel portions formed two-dimensionally on the substrate, a plurality of switching thin film transistors for controlling the display pixel portions, and a signal for sequentially driving the thin film transistors. In a liquid crystal display device having a drive circuit unit including a line scanning circuit and a gate line scanning circuit on the substrate, the signal line scanning circuit performs a signal scanning of a video signal processing unit and a video signal from the video signal processing unit. A thin film transistor for writing a video signal for writing in a line, the thin film transistor for writing the video signal is connected in parallel to a plurality of thin film transistors, and the individual channel widths of the thin film transistors connected in parallel are 1 μm or more 30
A liquid crystal display device characterized by having a size of less than μm.