JPS58114453A - Liquid-crystal display device - Google Patents

Abstract

PURPOSE:To prevent the degradation of the contrast of a picture by a method wherein a Schottky barrier is formed to the path of discharge currents having capacitance between a liquid-crystal driving electrode and a transparent electode in the reverse direction, reverse resistance is applied between source-drain in case of OFF and the resistance section of a time constant is increased. CONSTITUTION:A gate electrode 6 in NiCr is formed onto a glass plate 5, and a SiO2 gate film 7 and an amorphous Si film 8 are stacked. A Pt film 19 for the Schottky barrier is evaporated, a source electrode 9 in Al, a drain electrode 10, a Y selective line 2 and the liquid-crystal driving electrode 4 are formed, and coated with a SiO2 protective film 11, and a NiCr light-shielding film 12 is attached. Accordingly, when a Schottky and the Schottky barrier is formed between the amorphous Si 8 and the drain electrode 10 through negative pulse drive, the resistor R having a discharge time constant can be increased easily, the display of the picture can be held for the scan of one picture, and contrast can be improved with excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a liquid crystal display device comprising a liquid crystal and a thin film transistor matrix array, and particularly relates to a display screen control device.
Regarding improvement of strikes.

(2) Background of the technology Figure M1 is a plan view showing a liquid crystal display device with a thin film transistor matrix play, in which pairs of thin film transistors 3 and liquid crystal drive electrodes 4 are arranged in a matrix by X selection lines 1 and Y selection lines 2. are doing. Figure 2 is A of Figure 1.
-A' is a sectional view, and the thin film transistor has a gate on a glass substrate 5, a gate insulating film 7, a morphous silicon group 8, a source electrode 9, a drain 11, an L pole 10, a pudge vane film 11, and a light shielding film 12. The gate electrode 6 is connected to the X selection line 1, the source electrode 9 is connected to the Y selection line 2, and the drain electrode 10 is connected to the liquid crystal drive electrode 4ζ. - 10,000, a transparent electrode 15 is coated on the other glass substrate 5, and this transparent electrode 15
Both glass substrates 5 and 14 are combined so that the liquid crystal drive electrodes 4 and 4 face each other with a narrow parallel gap. The narrow parallel gap is filled with liquid crystal 17 to form a liquid crystal display. Note that 13 and 16 in FIG. 2 are polyimide or polyvinyl alcohol films for orienting the liquid crystal, and one liquid crystal drive electrode corresponds to one pixel.

The above is a clarification of the basic structure of a typical liquid crystal display device including a conventionally known thin film transistor matrix display, but if we draw an equivalent circuit for 11i11 elements of this configuration at once, it will be as shown in Figure 3. Become.

In the same figure, 1.2. and 3 are the aforementioned X selection line, X
selection line, and thin film transistor, C and R'
are the liquid crystal drive electrode 4 and transparent electrode 1 when filled with liquid crystal 17
The capacitance and leakage resistance between 5 and 5. 18 is an X selection line or a pulse power source for driving the X selection line;
l is 1l when the charge stored in the static capacity 1kc is in the OFF state
jl) is the radiation 'l1ILIt current when discharging through the drain and source of the transistor. The discharge current also flows due to the leakage resistance R' of the liquid crystal and the leakage resistance R' of the gate insulating metal, but their values are extremely small compared to the discharge current, so their discussion will be omitted here.

In a liquid crystal display device including a thin film transistor matrix array as described above, there are many X:s fold lines and many Y
A method is adopted in which the -s fold lines are sequentially switched and a large number of pixels are scanned from one end of the screen to the other to display an entire screen. In this scheme, some pixels are normally not driven when other pixels are selected. Therefore, if the display is not maintained by some means after scanning is completed until the next screen is driven, the contrast of the screen will deteriorate.

As this holding means, the above-mentioned capacitance C (#!3 shown in figure)
A method is known that utilizes the electric charge stored in However, since this charge is gradually reduced by the above-mentioned discharge current process, the following relationship is required between the discharge time constant OR and the scanning time T of one cycle.

OR≧T Here, C is the capacitance mentioned above, and B is the electrical resistance of the path through which the discharge current I flows, in other words, the OF of the thin film transistor
It approximately matches the source-drain resistance ROFF at F.

Therefore, if 50 frames per second are displayed on the jiii screen, T will be 20 m5, and the size of the liquid crystal drive electrode will be 20
0μmX200μm1 If the inter-electrode gap is 10μm, 0 is approximately 0.4PF, so Royy is 5X10I0
Ω or more is required.

(Step 4) The fourth factor in the prior art is an example of the change in the source-drain resistance with respect to the gate voltage Vo when the source-drain voltage V suppression is IOV.When the gate voltage VG is zero, The value when the gate voltage Vo is high, that is, when the transistor is ON, is the value between the source and drain. There is almost no variation in resistance, O
There is a very large variation when it comes to FF, and as a practical matter, it is extremely difficult to achieve the above-mentioned value of 5×10100 or more with good reproducibility. As can be seen from the conditional expression for the discharge time constant CI-L, there is a way to increase the capacitance C, and one possible way to do this is to add a thin film capacitor in each floor. In some cases, the structure of the liquid crystal display device becomes complicated, and it is extremely difficult to obtain a thin film capacitor with good characteristics, as in the case of improving Royy with good reproducibility.

(4) Purpose of the invention The purpose of the invention is that even if there is variation in the source-drain resistance ROFF during OFF as described above, the above-mentioned The object of the present invention is to provide a means within the liquid crystal display device that satisfies the conditions for the discharge time constant and prevents a decrease in screen contrast.

(5) Structure of the Invention The present invention provides a blind lattice barrier which is in the opposite direction to the current flow in the path of the current flow, and the resistance between the source and drain when OFF is set to The objective is to be achieved by adding directional resistance and increasing the resistance R of the discharge time constant OR. Specifically, when the pulse power supply 18 (illustrated in figure #g3) generates a negative pulse, an amorphous silicon barrier is formed between the amorphous silicon film and the drain electrode, and when a positive pulse is generated, an amorphous silicon barrier is formed between the amorphous silicon film and the drain electrode. A shield barrier is formed between the gate electrode 6 and the source electrode. This 71 key barrier is formed by inserting a thin film of platinum or gold between the amorphous silicon film and a source or drain electrode such as aluminum, or by making the electrode itself platinum or gold. do.

(6) Embodiment of the Invention FIG. 5 shows an embodiment in which a Schittky barrier is formed between the amorphous silicon film 8 and the drain electrode 10 by negative pulse driving. First, Ni0r is vapor-deposited at about 100 dX on the glass substrate 5, patterned to form an IE electrode, and then Sin is deposited at about 100 dX.
Approximately 500 OA of amorphous silicon was continuously deposited using the plasma OVD method, and then buttered all at once.
A gate insulating film 7 and a 7-morphous silicon M8 are formed. Next, platinum is vacuum-deposited at about 100 dX, and patterned to form a platinum film 19 for the Schitt key barrier.Next, A is vacuum-deposited at about 200X, and the pattern is y-g, source electrode 9 and drain electrode 10. ．． A Y selection line 2 and a liquid crystal drive electrode 4 are formed. Next, 8i0 or Sin, 50
0OA-1, am vacuum evaporated, patterned and patterned. Finally, about 100OA of Ni0r is vacuum-deposited and patterned to form a light-shielding film 1.
The purpose of the last light shielding film 2 is to prevent the electric resistance of the amorphous silicon film from changing due to external light. Note that the distance between the source and drain is 30×m×200 μm, the width of the drain electrode is 200 μm, and the size of the liquid crystal drive electrode is 200 μm×200 Am. The vEG diagram is an electrically equivalent open circuit of this example, and compared to the equivalent circuit of FIG. They are the same except that the current flowing through the electric current is in the opposite direction. ji7
As shown in FIG. 8(1), approximately 2000 μm of Ta (M) is deposited on a glass substrate 5 by vacuum evaporation.

An electrode 22 is formed thereon, and an aluminum-Tsass silicon film 8 and a platinum 31
19 and an aluminum Ecum electrode 22 are formed.

The electrode size is also 2004n% in length according to the example.
0 μm so that this characteristic is considered to be the same as that of a Schittky barrier formed on a thin film transistor. Therefore, the characteristics of the above embodiment are as follows.
It is considered that the characteristic is the sum of the resistance value of J and the resistance value in this figure. In this figure, Rf is the forward direction characteristic and Bbl is the reverse direction characteristic. Therefore, the minimum resistance when the thin film transistor is OFF is 108Ω (see Figure 4) and the reverse resistance of the switch key diode is 101Ω! If Ω or more is added, the required condition is 5.
X10''Ω or more is satisfied for the light component.On the other hand, the current required to switch the liquid crystal is 10-Ω in the case of the above embodiment.
'A or more, and the drive pulse applied to the source is IOV
The sum of the ON resistance of the thin film transistor and the forward resistance of the Schittky diode is required to be 1080 or less. In this example, the voltage between the source and drain is 5V to I.
Since the source-drain resistance hardly changes between OV, as shown in Figures 4 and 7 (711), the gate voltage is
At around OV, the voltage drop of the Shiso-Dottky diode is 1.5V.
It is clear that the above requirements are fully satisfied in this respect. Incidentally, the variation in the reverse resistance of the Schottky diode can be easily and significantly reduced compared to the variation in the resistance between the source and the drain when the thin film transistor is OFF, so there is no problem due to the variation in the reverse resistance of the Schottky diode. There isn't.

In this embodiment, we have described the case in which the Schitt key barrier is formed on the drain side using negative pulse driving, but a similar process can be used to form the Schitt Φ- barrier on the source side using positive pulse driving. Similar characteristics can be obtained. Further, instead of forming the Schittky barrier by inserting a platinum thin film between the 7-morphous silicon film and the source or drain electrode, the same characteristics can be obtained even if these electrode materials are made of platinum. However, in this case, since it is an electrode, the thickness of the platinum film must be approximately 2000 Å, which has the disadvantage of increasing the cost of electrode materials. In addition, metals that form a shield barrier against amorphous silicon include gold in addition to platinum, and are not limited to platinum; the gist of the present invention is simply to add a barrier during shielding. It's about doing.

In addition, Rh in Fig. 1Ii7 is added to the ga-th structure (like Shu, in the above embodiment) with a thickness of about 40X and 8i0. j
This is the reverse resistance characteristic when i[23 is inserted between the amorphous silicon film 8 and the platinum film 19. By doing so, the reverse direction characteristics are further improved and it is effective.

Note that the forward characteristic in this case is 8i0. The characteristics of Fig. 8 (Maro) without a film, that is, the characteristics are almost the same as those of Fig. 7 Rf.

Further, 8i0*J[ used here may be other insulating films such as Tie. Also, 840. When the film thickness is less than 10X, the effect is not small, and when it is more than 50X, the forward characteristics deteriorate.

(7) Effects of the invention According to the FIA of the present invention, as mentioned above, it is possible to easily increase the resistance R, and it is possible to maintain the pixel display during scanning of one screen, resulting in good reproducibility and contrast. It is possible to measure the improvement in

Particularly, the present invention is effective when the pixel density is increased in order to improve the resolution, since the above-mentioned capacitance 0 becomes small.

[Brief explanation of the drawing]

Figures 1 to 4 show conventional examples, where the first section is a plan view of a liquid crystal display device including a transistor matrix array, the second section is a partial sectional view of the same device, and the third section is an electrical diagram of the same device. The equivalent circuit shown in FIG. 4 is the source-drain resistance characteristic of the same device. Figure 5. Figure 6, Rf and Rb3 in Figure 7, and Figure 8 (it) are diagrams showing an embodiment of the present invention;
) is a diagram showing another embodiment. Here l is the X selection line,
2 is a Y selection line, 3 is a thin film transistor, 4 is a liquid crystal drive electrode, 5 and 14 are glass substrates, 6 is a gate electrode, 7 is a gate insulating film, 8 is an amorphous silicon film, 9 is a source electrode, IO is a drain 11UIi , 11 is Batsushibe
12j' [light film, 13 and 16 are polyimide AT or polyvinyl alcohol JJ, 15 is transparent 11L pole, 17 is liquid crystal, 18 is pulse power supply, 19 is platinum film, 20 is button key Diode, 21 is Ta1
1 pole, 22 is the human j% pole, and 23 is SiO, il. Figure 1 Figure 2 Figure 3 Figure 4 - Figure 50 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] In a liquid crystal display device including a matrix layer of a thin film transistor in which a gate electrode, a source electrode, and a drain electrode are added to an amorphous silicon film, either the source electrode or the drain/electrode has 10,000 electrodes and the amorphous silicon film. This is a liquid crystal display device with a patented feature that provides a shutter key barrier between the silicon and the liquid crystal display.