JPS5821863A - liquid crystal display device - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active matrix substrate for a display using a metal-insulator-semiconductor transistor array.

Conventional display panels using an active matrix can have a much larger matrix size than the dynamic method, and are attracting attention as a method that can realize large panels with a large number of dots. Particularly in light-receiving devices such as liquid crystals, there is a limit to the driving duty of the dynamic method, and active matrix applications are being considered for television displays and the like.

FIG. 1 shows one cell of a conventional active matrix. The address line X is input to the date of the transistor 2, and the transistor is turned on to cause the signal on the data line Y to be stored in the holding capacitor 3 as a charge. Until data is written again, this capacitor 3 is used to hold the data, and at the same time drives the liquid crystal 4. Here, VC is a common electrode signal. Since liquid crystal leakage is very low, it is sufficient to hold charge for a short period of time.

The manufacturing of the transistor and capacitor 1 here is a normal T,
The process is exactly the same as C.

FIG. 2 is an example in which the cell shown in FIG. 1 is produced by a silicon gate process. A transistor 10 and a capacitor 11 are constructed on a single crystal silicon wafer. address line x
and the upper electrode 11 of the capacitor are made of polycrystalline silicon (polysilicon), and the data line Y and the liquid crystal drive electrode 13 are made of AA, and the contact holes 7, 8, and 9 connect the substrate, At1 polysilicon, and At, respectively. Connected.

Matrix substrates according to this type of conventional IC process have the following major drawbacks.

One is that the manufacturing process of the matrix substrate is the same as that of IC, so the process is complicated and the process cost is high, and at the same time, the yield decreases due to junction leakage with the substrate silicon.
Total cost is high. In particular, the junction between the silicon substrate and the diffusion layer that becomes the source/drain is considerably affected by crystal defects in the single crystal, and in a normal cell, this leakage current can be reduced to 100P.
It has to be less than A, and it is difficult to suppress leakage in all tens of thousands of cells with this structure. The junction leak generated here discharges the charge accumulated in the capacitor 3,
Reduces contrast.

Second, the light incident on the silicon substrate through the gap between the Aja electrodes generates electron-hole pairs and is diffused to generate a photocurrent and discharge the charge in the capacitor 6, resulting in a decrease in contrast.

The purpose of the present invention is to provide a method for improving this drawback, and the present invention is constructed using glass or quartz.

Alternatively, a thin film transistor having a silicon thin film as a channel is constructed on a silicon wafer, and a specific example will be explained below.

Figure 3 shows a 7-trix cell used in the present invention, and the difference from the conventional one in Figure 1 is that a CHD wiring with a capacitance of 18 is newly provided, and the basic data writing and retention are the same. It is. In this case, the GND potential means a constant bias voltage, regardless of the bias level or signal level. XX can also be used.

Also, input the display data as data, 191 Y is the sample.
As the holding capacitor, a capacitor 21 between the data line Y and the GND line or a capacitor 22 between the address MX is used.

An example of the cell structure is shown based on the plan view of the cell in FIG. 4(A) and the sectional view taken along line A-E in FIG. 4(B). A silicon thin film 28 that forms the source, drain, and channel of the transistor on the transparent substrate 33 and a silicon thin film that forms the gate line that becomes the gate of the transistor, or a wiring layer 26 simultaneously therewith.
and GND line 27, and a transparent low resistance material such as Bn.
A data line 25 and a liquid crystal drive electrode 31 made of a metal film or the like having a thickness of several hundred times or less are formed.

Further, the overlapped portion of the GND line 27 and the liquid crystal drive electrode becomes a charge holding capacitor (FIG. 3-18). N+ diffusion (P
If it is a channel, P+) is formed, and a channel 30 exists below the gate electrode 38 with a gate insulating film 36 interposed therebetween.

FIG. 5 shows a manufacturing process for the active matrix substrate shown in FIG. 4. On the transparent substrate 40, a transparent conductive film such as Nesa film, 2O3 film, or a very thin metal film is formed as an electrode material for the gate so that the area of the capacitor can be increased, and after patterning, the gate electrode 41 is formed. Next, a gate insulating film 42 is formed on the gate electrode.

The method for forming the gate insulating film is to form the oxide of the gate electrode, for example, by anodic oxidation, thermal oxidation, plasma oxidation, etc., or by nitriding SiO, AA203, etc., Si3N, etc. by OVD method, etc. It is a thing. (The example shown in FIG. 5 is an oxidation method of the gate electrode.) These insulators are transparent.

Next, a silicon thin film that will form the transistor channel is deposited and buttered to form the source, drain, and
A silicon layer 46 constituting a channel is formed. (5th
In this state, a negative resist 44 is applied to the upper surface and patterned to form a mask portion 45 for doping impurities into the source and drain portions except for the channel portion. (FIG. 5 (c)) When impurity ions are implanted using this resist 45 as a mask, the ions are implanted into the source/drain region 46 to form a low resistance layer, but the ions are not implanted into the lower part of the resist 45 and the channel It remains as layer 47. (Fig. 5 (c)) Next, a transparent conductive film is deposited and patterned to form data lines 48 and drive electrodes 49, and the source/drain 46 of the transistor is connected to the insulating film and further to the insulating part. Make contact without opening a contact hole.

Further, the capacitor can be formed by sandwiching the same material as the gate insulating film 42 between the gate electrode 41 and the drive electrode 49 made of a transparent conductive film.

The advantage of this method is that although it forms a transparent capacitor, the process is simple.

In FIG. 4, the intersection of the data 11J25 and the gate line 26 needs to be insulated from each other, but if the gate electrode is placed at the bottom and the channel is placed at the top as in the present invention, a special insulating film is used. Even if it is not present, the gate insulator is naturally insulated using the same material as the gate insulator, so the process of attaching an insulating film and the process of opening a contact hole in the insulating film, which were used only for insulation, as in the past, are not necessary. Furthermore, the disadvantage that the light transmittance of a transparent capacitor decreases due to the special insulating film can be prevented.

Another advantage of the present invention is that the capacitor is made using a transparent conductive film made of the same material as the gate electrode, a transparent conductive film that becomes the liquid crystal drive electrode, and a gate insulating film as a dielectric film. No extra steps are required. Furthermore, when using a TN mode liquid crystal using a transparent substrate, the liquid crystal drive part needs to be transparent, but in the present invention, the capacitor is also transparent, so the capacitor can occupy most of the area below the liquid crystal drive electrode. Therefore, the capacitance of the capacitor can be increased. Therefore, the tolerance for OFF' leakage of the transistor can be widened, yield can be improved, and reliability can also be improved.

As described above, the present invention provides an active matrix having silicon transistors and silicon capacitors on a substrate, and has the following advantages over the prior art.

The manufacturing process is simple; the conventional bulk silicon type requires 6 photoetching steps, but the method of the present invention requires only 4 photoetching steps, and the process cost is low, as well as the ability to cut P-N junctions like bulk silicon. Since the area is very small, there is little junction leakage, and an improvement in yield can be expected.

In addition, more than 90% of the light incident from above passes through, and the diffusion length of carriers in the silicon thin film is short, so almost no photocurrent is generated, and the leakage value for light is 1 even under 10,000 lux. ．． The OPA was below A, and it was possible to prevent the display image from disappearing due to the incidence of light.

Furthermore, if a transparent liquid crystal drive is used for a transparent substrate, it is possible to use an FE type liquid crystal with the highest fundus resistance, and the brightness of the screen can also be improved, making it possible to dramatically improve display quality.

At the same time, using glass or a similar material for the substrate makes it easier to assemble the panel, improving the assembly yield and simplifying the process compared to the conventional bulk silicon type.

The active matrix panel made according to the present invention enables an inexpensive portable liquid crystal television with low power consumption, and can produce drawings with very high contrast, especially outdoors in strong sunlight.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a cell used in a conventional active matrix, Fig. 2 is a plan view of a cell using bulk silicon, Fig. 3 is a cell diagram of the present invention, and Fig. 4 (A), (
B) is a plan view and a cross-sectional view of an example of its realization, and Figures 5(A) to 5
) is its manufacturing process. 11... Polysilicon upper electrode 10 of capacitor 3... Polysilicon gate 7.8.9... Contact hole 13...
・Drive electrode 33.40 by AA...Transparent substrate 38.41...Gate electrode 36.42...Gate insulating film 3.4, 35.46...・Source Φ drain 30
．． 47... Channel 25, 31.48... Transparent conductive film 45...
...Register or above Applicant Suwa Seikosha Co., Ltd. Agent Patent Attorney Tsutomu Mogami αυ Y (shi^TA) Figure 1 Figure 3\6

Claims (1)

[Claims] (1) In an active matrix substrate in which display data is written to a charge holding capacitor from a data line to an arbitrary series selected by a gate of a transistor via a data line and a source/drain of a transistor, the active matrix substrate is transparent. The transistor is configured on a substrate, and further includes a gate electrode facing downwardly,
1. An active matrix substrate having a structure in which a channel is formed upward, and wherein the charge retention capacitor is constituted by a gate insulator constituting the gate electrode and a liquid crystal driving electrode.