JPH0695080A - Image display method of liquid crystal display - Google Patents

Abstract

PURPOSE:To provide the gradation display system which is precise and is less affected by the variations among elements as the gradation display of the liquid crystal display device. CONSTITUTION:Ferroelectric or antiferroelectric liquid crystals or polymer liquid crystals formed by utilizing these liquid crystals are used as the liquid crystal materials for the active matrix type electrooptical display device. Pulses are periodically impressed to the control electrodes thereof and the time when the voltage is impressed to picture elements is arbitrarily controlled while impressing a voltage to the other ends of input/output terminals or turning off the voltage, by which the visual gradation display is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display method in a liquid crystal display device using a thin film transistor (hereinafter referred to as a TFT) as a switching element for driving, and more particularly, a gradation display method for obtaining an intermediate color tone or shade expression. It is about. The present invention particularly relates to so-called completely digital gradation display that performs gradation display without applying any analog signal from the outside to the active element, and the liquid crystal material used is a strong high speed responsiveness. Display method of liquid crystal display device characterized by limiting to dielectric liquid crystal or antiferroelectric liquid crystal, or so-called polymer liquid crystal (also referred to as dispersed liquid crystal) in which they are dispersed in a polymer compound (polymer) Regarding

[0002]

2. Description of the Related Art Liquid crystal compositions have different permittivities in the horizontal and vertical directions with respect to the molecular axis because of their material properties, and therefore they can be aligned horizontally or vertically with respect to an external electric field. It can be done easily. The liquid crystal electro-optical device utilizes the anisotropy of the dielectric constant to control the amount of transmitted light or the amount of scattered light, thereby performing ON / OFF, that is, bright / dark display. Liquid crystal materials include TN (Twinstead Nematic) liquid crystal, STN (Super Twinsteaded Nematic) liquid crystal, ferroelectric or antiferroelectric liquid crystal, and recently, nematic liquid crystal, ferroelectric or antiferroelectric liquid crystal. There is known a material called polymer liquid crystal (also referred to as dispersion type liquid crystal) in which a functional liquid crystal is dispersed in a polymer material. It is known that liquid crystal does not respond to an external voltage in an infinitely short time, but it takes a certain time to respond. The value is unique to each liquid crystal material, and is 1 in the case of TN liquid crystal.
0 msec, several hundred msec for STN liquid crystal,
In the case of a ferroelectric liquid crystal, it is several tens of μsec, and in the case of a dispersion type or polymer liquid crystal using nematic liquid crystal, it is several tens of msec.

Among electro-optical devices using liquid crystals, the one which can obtain the most excellent image quality is one using the active matrix system. In a conventional active matrix type liquid crystal electro-optical device, a thin film transistor (TFT) is used as an active element, an amorphous or polycrystalline semiconductor is used for the TFT, and P is used for one pixel.
The TFT of only one of the N type and the N type was used. That is, in general, N-channel TFT
(Referred to as NTFT) is connected in series to the pixel. Then, a signal voltage is applied to the signal lines of the matrix, and when signals are applied from both sides to the TFTs provided at the orthogonal positions of the respective signal lines, the TFTs are turned on. It was to control OFF individually. By controlling the pixels by such a method, a liquid crystal electro-optical device having a large contrast can be realized.

[0004]

However, in such an active matrix system, it is extremely difficult to perform gradation display such as brightness and color tone. Conventionally, a method of utilizing the fact that the light transmittance of the liquid crystal changes depending on the magnitude of the applied voltage has been studied for gradation display. This is, for example, the source of the TFT in the matrix
By supplying an appropriate voltage from the peripheral circuit between the drains and applying a signal voltage to the gate electrode in that state,
It was intended to apply a voltage of that magnitude to the liquid crystal pixels.

However, in such a method, the voltage applied to the liquid crystal pixel actually varies from pixel to pixel by at least several percent due to, for example, the non-uniformity of the TFT and the non-uniformity of the matrix wiring. Oops. On the other hand, for example, the voltage dependence of the light transmittance of liquid crystal is extremely non-linear, and the light transmittance changes abruptly at a certain voltage. It could be significantly different. Therefore, actually, it was a limit to achieve 16 gradations. For example, in a TN liquid crystal material, the so-called transition region where the light transmittance changes is
In order to achieve 16 gradations with a width of only 1.2V, it is necessary to control a voltage as small as 75 mV, and therefore the manufacturing yield is remarkably low.

The difficulty of gradation display is extremely disadvantageous in that the liquid crystal display device competes with the CRT (cathode ray tube) which is a conventional general display device. An object of the present invention is to propose a completely new method for realizing gradation display which has been difficult in the past.

[0007]

As described above, it is possible to control the light transmissivity of the liquid crystal by controlling the voltage applied to the liquid crystal in an analog manner. It has been found that the gradation can be visually obtained by controlling the time when voltage is applied to the liquid crystal.

For example, in the case of using TN (twisted nematic) liquid crystal which is a typical liquid crystal material,
For example, although various pulse waveforms are shown in FIG. 1, it has been found that the brightness can be changed by applying such a waveform voltage to the liquid crystal pixels. That is, "1", "2", ... In FIG.
The brightness can be gradually increased in the order of "15". That is, in the example of FIG. 1, 16 gradations can be displayed. At this time, with "1", a pulse having a length of 1 unit is applied. Further, at "2", a pulse having a length of 2 units is applied. At "3", a pulse of 1 unit and a pulse of 2 units are applied, and as a result, a pulse of a length of 3 units is applied. At "4", a pulse with a length of 4 units is applied. At "5", 1 unit pulse and 4 unit pulse are applied, and at "6", 2 unit pulse and 4 unit pulse are applied. Furthermore, by providing a pulse length of 8 units, a pulse length of 15 units can be obtained as a result.

That is, by appropriately combining four types of pulses of 1 unit, 2 units, 4 units, and 8 units, it is possible to display 2 ⁴ = 16 gradations. Furthermore, 1
By preparing many pulses, such as 6 units, 32 units, 64 units, and 128 units, respectively,
High gradation display of 32 gradations, 64 gradations, 128 gradations and 256 gradations is possible. For example, in order to obtain 256 gradation display, eight kinds of pulses may be prepared.

Further, in the example of FIG. 1, the duration of the voltage applied to the pixel is first T ₁ , second 2T ₁ , and then 4T.
An example of arranging so as to increase in a geometric progression such as ₁ has been shown.
_1, then 8T _1, the following 2T _1, finally may be 4T _1. By arranging in this way, the load on the device for transmitting data to the display device can be reduced.

However, when the TN liquid crystal is used, as a result, the applied voltage is required to have the same accuracy as in the conventional analog gradation display system. That is, when 5V is applied to the pixel as the ON voltage and "10" in FIG. 1 is displayed, the ON voltage is 5.
By applying a voltage of 1 V, it looks darker by about 2% than the case where the same "10" is displayed. That is, in such a digital gradation display system, it is required that there is no variation in TFT as in the conventional analog gradation display system.

The drawback is that the TN liquid crystal changes the light transmittance depending on the effective voltage. The same was true for STN liquid crystals or dispersion type liquid crystals using nematic liquid crystals, which are the basic materials of these. On the other hand, the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal shows a very high-speed response and does not substantially respond to the effective value voltage. Therefore, when the digital gradation display as described above is performed, T
It has been clarified that uniform gradation display is possible regardless of the characteristics of FT. That is, the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal shows the same light transmittance at 5 V and 5.1 V when the ON voltage of 1 msec or more is applied.

Similar effects were observed in a material in which a ferroelectric liquid crystal or an antiferroelectric liquid crystal was dispersed in a polymer.

To implement the present invention, for example, a matrix circuit using thin film transistors as shown in FIG. 4 may be assembled. The circuit shown in FIG. 4 is the same as the circuit used in a conventional active matrix type display device using TFTs.

Since the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal has a memory property itself, the auxiliary capacitance (capacity inserted in parallel with the pixel capacitance) required for the conventional active matrix is obtained. Even if the pixel electrode is discharged, the ON state can be maintained. However, such a material having a strong ferroelectricity (or antiferroelectricity) is liable to cause a phenomenon called "burning" and lacks reliability. On the other hand, a material with low ferroelectricity (or antiferroelectricity) has few display defects such as "burning", but the pixel capacitance is discharged severely and a voltage sufficient to sustain display cannot be maintained. In this case, it becomes difficult to maintain the ON state (or OFF state). Therefore, the auxiliary capacitance is required as usual.

Of course, if the discharge of the pixel is sufficiently small, such an artificial capacitor may be omitted. In particular, the presence of an excessive auxiliary capacity is not desirable in the practice of the present invention because the charging or discharging operation takes time. In order to reduce the pixel discharge, for example, it is necessary to sufficiently increase the OFF resistance of the thin film transistor, reduce the leak current, and sufficiently increase the interelectrode resistance of the pixel itself such as liquid crystal. Particularly for the latter purpose, it is effective to coat the pixel electrode with an insulating material such as tantalum oxide or aluminum oxide such as silicon nitride or silicon oxide.

In such a circuit, by controlling the gate voltage and the source-drain voltage of each thin film transistor, the voltage applied to the pixel is turned on / off.
It is possible to control OFF. In this example, the matrix is 640 × 480 dots, but for simplicity, only the vicinity of the nth row and the mth column is shown. If you expand the same thing up, down, left and right, you can get the perfect one. An operation example using this circuit is shown in FIG.

The signal lines X _1, X _{2, ..} X _n, X _{n + 1, ..} X ₄₈₀ (hereinafter collectively referred to as X-rays) are connected to the gate electrodes of the respective TFTs. Then, as shown in FIG. 2, rectangular pulse signals are sequentially applied. On the other hand, the signal lines Y _1, Y _{2 ,.
m,} Y _{m + 1, ..} Y ₆₄₀ (hereinafter collectively referred to as Y line) is a TF
Although it is connected to the source (or drain electrode) of T, a signal composed of a plurality of pulses is still applied to this. This pulse train contains 640 pieces of information in one unit of time T ₁ .

In the following, four pixels Z _{n, m} , Z _{n + 1, m} ,
Focusing on Z _{n, m + 1} and Z _{n + 1, m + 1} , the leak current of the pixel is sufficiently small and the voltage of the pixel does not change unless a signal comes to both the gate electrode and the source electrode. Therefore, regarding these four pixels, it suffices to pay attention to the signal lines X _n, X _{n + 1} and Y _m, Y _{m + 1} .

Consider the case where a rectangular pulse is applied to X _n , as shown. Now four pixels Z _{n, m} ,
If attention is paid to Z _{n, m + 1} , Z _{n + 1, m} , and Z _{n + 1, m + 1} , attention is paid to the current states of Y _m and Y _{m + 1} . At this time, since there is a signal in Y _m and no signal in Y _{m + 1} , the pixel Z _{n, m} is in the voltage state and Z _{n, m + 1} is in the non-voltage state in the end. Then, by cutting off the pulse of the X-ray earlier than the voltage applied to the Y-line, the voltage state of the pixel is maintained by the pixel capacitor, so that the pixel Z
_{n and m} maintain the voltage state. After that, basically, the state of each pixel continues until the signal is applied to X _n next time.

Next, a pulse is applied to X _{n + 1} . As shown in the figure, since Y _m is in the non-voltage state and Y _{m + 1} is in the voltage state at that time, the pixel Z _{n + 1, m} is in the non-voltage state and the pixel Z _{n + 1, m + 1} is in the non-voltage state. Becomes a voltage state, and continues to maintain each state as described above.

Next, when the pulse is applied to X _n first and then the second pulse is applied to the signal line X _n after the time T ₁ , Y _m and Y _{m + 1} are respectively non-voltage. state, since the voltage state, the pixel Z _{n, m} in the non-voltage state, the pixel Z _{n, m + 1} is the voltage state, respectively, state changes. Further, a pulse is applied to X _{n + 1} . As shown in the figure, since both Y _m and Y _{m + 1} are in the voltage state at that time, the pixels Z _{n + 1, m} and Z _{n + 1, m + 1} are in the voltage state. At this time, the pixel Z _{n + 1, m + 1} continues to be in the voltage state.

Then, after a time 2T ₁ , a third signal is applied to X _n . At that time, since both Y _m and Y _{m + 1} are in the voltage state, the pixel Z _{n, m} changes from the non-voltage state to the voltage state, and the pixel Z _{n, m + 1} continues the voltage state. Further, a pulse is applied to X _{n + 1} . At that time, since both Y _m and Y _{m + 1} are in the non-voltage state, the pixel Z _{n + 1, m}
Also Z _{n + 1, m + 1} becomes a non-voltage state, and the voltage state is terminated in both cases.

Then, after a lapse of time 4T ₁ , a fourth signal is applied to X _n . At that time, since both Y _m and Y _{m + 1} are in the non-voltage state, both the pixel Z _{n, m} and the pixel Z _{n, m + 1} change from the voltage state to the non-voltage state. Further, a pulse is applied to X _{n + 1} , but since Y _m and Y _{m + 1} are also in the non-voltage state, the pixels Z _{n + 1, m} and Z _{n + 1, m + 1} are in the non-voltage state. It remains.

In this way, one frame is completed.
During this time, four pulses are applied to each X-ray, and an information signal of 3 × 480 = 1440 is applied to each Y-line. Also, the time of this one frame is 7T ₁ , and T ₁
For example, 10 nsec to 10 msec is suitable. Then, focusing on each pixel, the pixel Z _{n, m}
, The pulse of time T _{1 and} the pulse of 4T ₁ are applied, and visually the same effect as that of the pulse of 5T ₁ is obtained. That is, a brightness of "5" is obtained. Similarly, in the pixels Z _{n, m + 1} , the pixels Z _{n + 1, m} , and Z _{n + 1, m + 1} , brightness of “2”, “6”, and “3” is finally obtained.

In the above example, display of 8 gradations is possible, but higher gradations are possible by adding more pulse signals. For example, by applying a pulse five times to each X-ray and applying an information signal of 3840 to each Y-line in one frame, it is possible to achieve high-gradation display of 256 gradations.

Further, if high gradation display is to be performed, extremely high speed switching is required, as is apparent from FIG. For example, in order to realize 256 gradations, it is necessary to feed out 30 or more moving images per second, so 256T ₁ <30 msec. Therefore, T ₁ <1
It is 00 μsec. Therefore, for example, when the X-ray (connected to the gate electrode) has 480 columns, the width is 20
A pulse of 0 nsec or less needs to be applied. Figure 3
In the above example, only the NMOS TFT is used, but a circuit having a CMOS circuit may be connected to the pixel for the purpose of increasing the operation speed. For example, the speed can be increased by using a CMOS transfer gate circuit or the like.

In the above description, the signals are clearly distinguished as a non-voltage state and a voltage state in order to make the explanation easy to understand. However, this is below the substantial threshold voltage of the liquid crystal or TFT. , Or more, it doesn't have to be zero.

Further, it is possible to change the substantial voltage applied to the pixel material by applying an appropriate bias voltage to the counter electrode of the pixel. For example, by applying an appropriate voltage to the counter electrode of the pixel, it is possible to take both positive and negative directions of the voltage applied to the pixel material.

[0030]

【Example】

Example 1 In this example, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. Further, the TFT at that time was made of polycrystalline silicon using laser annealing.

First, a method for manufacturing the liquid crystal panel used in this embodiment will be described with reference to FIG. In FIG. 6A, a silicon oxide film as a blocking layer 2 is formed on a glass 1 that can withstand a heat treatment at 700 ° C. or lower, for example, about 600 ° C. by using a magnetron RF (radio frequency) sputtering method.
It is made to a thickness of 0 to 3000Å. The process conditions are an oxygen 100% atmosphere, a film forming temperature of 15 ° C., and an output of 400 to 800.
W and pressure were 0.5 Pa. Synthetic quartz was used to reduce impurities in the target. Deposition rate is 30 to 10
It was 0Å / min.

A silicon film was formed thereon by plasma CVD to form a silicon film 3. The film forming temperature is 250 ° C to 350
C., and in this embodiment 320.degree. C., monosilane
(SiH ₄ ) was used. Not only monosilane (SiH ₄ ) but also disilane
(Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) may be used. These were introduced into the PCVD apparatus at a pressure of 3 Pa, and 13.5
A high frequency power of 6 MHz was applied to form a film. At this time, a high frequency power of 0.02 to 0.10 W / cm ² is suitable,
In this example, 0.055 W / cm ² was used. The flow rate of monosilane (SiH ₄ ) was 20 SCCM, and the film formation rate at that time was about 120 Å / min. The silicon film may be a pure intrinsic semiconductor, or boron may be added during the film formation using diborane at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ . Further, not only the plasma CVD but also the sputtering method or the low pressure CVD method may be used for forming the silicon layer to be the channel region of the TFT. The method will be briefly described below.

When the sputtering method is used, the back pressure before sputtering is set to 1 × 10 ^-5 Pa or less, the single crystal silicon is used as the target, and the atmosphere is mixed with 20-80% of hydrogen in argon. For example, argon is 20% and hydrogen is 80%.
The film forming temperature was 150 ° C., the frequency was 13.56 MHz, the sputter output was 400 to 800 W, and the pressure was 0.5 Pa.

When formed by the reduced pressure vapor phase method, it is 450 to 550 ° C., which is 100 to 200 ° C. lower than the crystallization temperature, for example, 5
Disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) was supplied to a CVD apparatus at 30 ° C. to form a film. The reactor pressure is 30 ~
It was set to 300 Pa. The film forming rate was 50 to 250 Å / min.

The film formed by these methods is
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. In order to promote crystallization, the oxygen concentration is 7 × 10 ¹⁹ cm ^-3 or less,
It is preferable that the size is 1 × 10 ¹⁹ cm ^-3 or less,
If the amount is too small, the leak current in the off state increases due to the backlight, so this concentration was selected. If the oxygen concentration is high, it is difficult to crystallize, and the laser annealing temperature must be high or the laser annealing time must be long. Hydrogen is 4 × 10 ²⁰ cm ^-3 and silicon is 4 × 10 ²²
It was 1 atom% when compared as cm ^-3 .

In order to further promote crystallization of the source and drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ^-3 or less, preferably 1 × 10 ¹⁹ cm ^-3 or less, and the TF for forming a pixel is set.
Oxygen may be added only to the channel forming region of T by the ion implantation method so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .
By the above method, an amorphous silicon film is formed into 500
The film was formed to a thickness of ˜5000 Å, 1000 Å in this example.

Then, a pattern was formed in which only the source / drain regions were opened using the photoresist 4 as a mask. A silicon film 5 to be an n-type active layer was formed thereon by the plasma CVD method. The film forming temperature is 250 ° C. to 35
The temperature is set to 0 ° C., and in this embodiment, it is set to 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) 3%
The one with the concentration was used. These were introduced into the PCVD apparatus at a pressure of 5 Pa, and high frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is 0.05 to 0.20.
W / cm ² is suitable, and in this embodiment, 0.120 W /
cm ² was used.

The specific conductivity of the n-type silicon layer produced by this method was about 2 × 10 ^-1 [Ωcm ^-1 ]. The film thickness was 50Å. In this way, FIG.
Got Thereafter, the lift-off method was used to remove the resist 4 and form the source / drain regions 6 and 7. Thus, FIG. 6B was obtained.

After that, as shown in FIG. 6C, XeCl
Using an excimer laser, the source / drain / channel regions were laser-annealed and simultaneously the active layer was laser-doped. The laser energy at this time has a threshold energy of 130 mJ / cm ² , and 220 mJ / cm ² is required for crystallization of the entire film thickness.
However, when the energy of 220 mJ / cm ² or more is applied from the beginning, the hydrogen contained in the film is rapidly released, so that the film is broken. Therefore, it is necessary to first drive out hydrogen with low energy and then melt it. After performing the flush hydrogen in the first 150 mJ / cm ² in the present embodiment was subjected to crystallization at 230 mJ / cm ^2.

Then, the silicon film 3 was removed by etching using a mask to form the N-channel type thin film transistor island region 10. Further, the silicon oxide film 8 is used as a gate insulating film on the surface of 500 to 2000Å, for example
It was formed to a thickness of 000Å. This was performed under the same conditions as the production of the silicon oxide film as the blocking layer. During this film formation, a small amount of fluorine may be added to immobilize sodium ions.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 concentration silicon film or this silicon film with molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned using a third photomask to obtain a gate electrode 9 for NTFT (FIG. 6 (D)). The size of the gate electrode is, for example, 7 μm in channel length, and the gate electrode is made of phosphorus-doped silicon having a thickness of 0.2 μm and molybdenum having a thickness of 0.3 μm.

Besides the above materials, for example, aluminum (Al) can be used as the gate electrode material. When aluminum is used, the self-aligning method can be applied by patterning this with a third photomask and then anodizing its surface.
Since the source / drain contact hole can be formed at a position closer to the gate, the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

In this way, a C / TFT can be manufactured without applying a temperature above 400 ° C. in all steps. Therefore, an expensive substrate such as quartz does not have to be used as the substrate material, and it can be said that the process is extremely suitable for the large-screen liquid crystal display device of the present invention.

Further, the interlayer insulator 11 was formed as a silicon oxide film by the above-mentioned sputtering method. The silicon oxide film may be formed by using the LPCVD method, the photo CVD method, or the atmospheric pressure CVD method. For example, it is formed to have a thickness of 0.2 to 0.6 μm, and then a window 13 for an electrode is formed using a fourth photomask. After that, aluminum was further formed on the entire surface to a thickness of 0.3 μm by a sputtering method, and a lead 12 and a contact 14 were manufactured using a fifth photomask. Thus, FIG. 6E was obtained.

After that, an organic resin 15 for flattening, for example, a translucent polyimide resin was applied and formed on the surface, and another hole for the electrode was formed by using a sixth photomask. Further, ITO (Indium Tin Oxide) was formed on the whole of the above to have a thickness of 0.1 μm by the sputtering method, and the pixel electrode 16 was formed using the seventh photomask. This ITO is room temperature ~ 15
The film was formed at 0 ° C. and was accomplished by oxygen at 200 to 400 ° C. or annealing in the atmosphere. Thus, FIG. 6F was obtained.

The electrical characteristics of the TFT obtained as described above are mobility 80 (cm ² / Vs) and Vth 5.0 (V).
Met. It was possible to obtain one substrate for a liquid crystal electro-optical device manufactured according to the method as described above. By repeating this structure horizontally and vertically, 640 × 48
The liquid crystal display device can have a large pixel size of 0,1280 × 960. In this embodiment, the size is 1920 × 400. Thus, the first substrate was obtained.

A method for manufacturing the other substrate is shown in FIG. A polyimide resin in which a black pigment is mixed with polyimide is formed on a glass substrate to a thickness of 1 μm by a spin coating method,
Black stripe 41 using the eighth photomask
Was produced. After that, a polyimide resin mixed with a red pigment was formed into a film with a thickness of 1 μm by a spin coating method, and a red filter 82 was manufactured using a ninth photomask. Similarly, using the masks (circle numbers 10 and 11), the green filter 43 and the blue filter 44 were produced. After making these, each filter was baked at 350 ° C. in nitrogen for 60 minutes. After that, the leveling layer 45 was made of transparent polyimide by using the spin coating method.

After that, ITO (indium tin oxide) was formed on the whole of the above to have a thickness of 0.1 μm by a sputtering method to form a common electrode 46. This ITO is room temperature to 150 ° C
Then, a film was formed and the film was completed by oxygen at 200 to 300 ° C. or an anneal in the atmosphere to obtain a second substrate.

A polyimide precursor was printed on the substrate by the offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere such as nitrogen. Then, a known rubbing method was used to modify the surface of the polyimide, and a means for orienting liquid crystal molecules in a certain direction was provided at least in the initial stage.

After that, a liquid crystal display device is constituted by the first substrate and the second substrate, and a T on the lead on the substrate.
PC with AB-shaped drive IC, common signal, and potential wiring
B was connected and a polarizing plate was attached to the outside to obtain a transmissive liquid crystal electro-optical device. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves, to complete a wall-mounted TV. Compared with the conventional CRT type TV, the device has a planar shape, so that it can be installed on a wall or the like. It has been confirmed that the operation of this liquid crystal television is capable of 8-gradation display by applying a signal substantially equal to that shown in FIG. 2 to the liquid crystal pixels. At this time, T ₁ = 4 msec, X-ray and Y
The line pulse width (or minimum pulse width) is
It was set to 5 μsec and 8 μsec.

[Embodiment 2] In this embodiment, a wall-mounted television is manufactured by using a liquid crystal display device having a circuit configuration as shown in FIG. 4, which will be described. Also T at that time
FT was polycrystalline silicon using laser annealing.

In the following, a method of manufacturing the TFT portion will be described with reference to FIG. In FIG. 7A, 70
A silicon oxide film as the blocking layer 21 is formed on the glass 20 that can withstand a heat treatment of 0 ° C. or lower, for example, about 600 ° C., by using a magnetron RF (radio frequency) sputtering method.
The thickness is 3000 Å. Process condition is oxygen 10
0% atmosphere, film forming temperature 15 ° C., output 400 to 800 W,
The pressure was 0.5 Pa. The deposition rate using quartz for the target was 30 to 100Å / min.

On top of this, a silicon film 2 is formed by a plasma CVD method.
2 was produced. The film forming temperature is 250 ° C. to 350 ° C.
In this embodiment, the temperature is 320 ° C. and monosilane (SiH ₄ ) is used. Not limited to monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) may be used. PCVD these
The film was introduced into the apparatus at a pressure of 3 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is 0.
02 to 0.10 W / cm ² is suitable, and 0.055 W / cm ² was used in this example. In addition, monosilane (SiH
The flow rate of ₄ ) is 20 SCCM, and the film formation speed at that time is about 1
It was 20Å / min. This silicon film may be an intrinsic semiconductor, or boron may be added to diborane at 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ^−3.
It may be added during the film formation as a concentration of.

In order to further promote crystallization of the source and drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ^-3 or less, preferably 1 × 10 ¹⁹ cm ^-3 or less, and the TF for forming a pixel is set.
Oxygen may be added only to the channel forming region of T by the ion implantation method so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .
By the above method, an amorphous silicon film is formed into 500
The film was formed to a thickness of ˜5000 Å, 1000 Å in this example.

After that, the photoresist 23 was used as a mask to form a pattern in which only the regions to be the source / drain regions of the NTFT were opened. And the resist 2
By using 3 as a mask, phosphorus ions are ion-implanted,
2 × 10 ^{14 to} 5 × 10 ¹⁶ cm ⁻² , preferably 2 × 10 ¹⁶
Only cm ^{−2 was} implanted to form an n-type impurity region 24.
After that, the resist 103 was removed.

Thereafter, as shown in FIG. 7B, a thickness of 50 to 300 nm, for example 100 nm, is formed on the silicon film 22.
The silicon oxide film 25 of was formed by the RF sputtering method described above. Then, the source / drain / channel regions were crystallized and activated by laser annealing using a XeCl excimer laser. After the laser annealing was completed, the silicon oxide film 25 was removed.

In addition, this crystallization can be performed by a thermal annealing method. In that case, 45
Temperature of 0 to 700 degrees C, preferably 550 to 600 degrees C
The heat treatment may be performed at a temperature of 12 to 70 hours, for example, 24 hours, in a non-oxidizing atmosphere, for example, a hydrogen or nitrogen atmosphere.

After that, an island-shaped NTFT region 28 was formed by a photomask. A silicon oxide film 26 is formed thereon as a gate insulating film to a thickness of 500 to 2000Å, for example 1000Å. This was performed under the same conditions as the production of the silicon oxide film as the blocking layer.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 concentration silicon film or this silicon film with molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This is patterned with a third photomask, and as shown in FIG.
A gate electrode 27 for FT was formed. For example, the channel length is 7 μm, and the gate electrode is 0.2 μm of phosphorus-doped silicon.
m, and molybdenum was formed thereon to a thickness of 0.3 μm.

Further, in FIG. 7E, the inter-layer insulator 29 was formed as a silicon oxide film by the above-mentioned sputtering method. This silicon oxide film is formed by the LPCVD method, light C
VD method or atmospheric pressure CVD method may be used. For example 0.2 ~
It was formed to a thickness of 0.6 μm, and then a window 31 for an electrode was formed using a fourth photomask. After that, aluminum is further formed on the entire surface by a sputtering method to a thickness of 0.3 μm to form a lead 30 and a contact 32 using a fifth photomask, and then the surface is flattened with an organic resin 34, for example, an organic resin 34. A translucent polyimide resin was applied and formed, and another electrode hole was formed using a sixth photomask. Further, ITO (Indium Tin Oxide) was formed on the whole of these by a sputtering method to a thickness of 0.1 μm, and a pixel electrode 33 was formed by using a seventh photomask.
This ITO film is formed at room temperature to 150 ° C.
Achieved by oxygen at ℃ or anneal in air. The electric characteristics of the TFT obtained as described above were a mobility of 90 (cm ² / Vs) and a Vth of 4.8 (V).

It was possible to obtain one substrate for a liquid crystal electro-optical device manufactured by the above method. Since the method for manufacturing the other substrate is the same as that in the first embodiment, it will be omitted.
After that, a liquid crystal display device is configured by the first substrate and the second substrate, and a TAB-shaped drive IC and a PCB having a common signal and potential wiring are connected to leads on the substrate.
A polarizing plate was attached to the outside to obtain a transmissive liquid crystal electro-optical device. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves, to complete a wall-mounted TV. Compared to the conventional CRT television,
Since it is a flat device, it can be installed on a wall. It was confirmed that the operation of this liquid crystal television can display 128 gradations by applying a signal substantially equal to that shown in FIG. 2 to the liquid crystal pixel.

[0062]

According to the present invention, in contrast to the conventional analog type gradation display using a nematic liquid crystal, a digital type gradation display using a ferroelectric or antiferroelectric liquid crystal material or a polymer liquid crystal material thereof. It is characterized by performing. As an effect, if a liquid crystal electro-optical device having a number of pixels of 640 × 400 dots is assumed, it is very difficult to manufacture the characteristics of all 256,000 TFTs in total without variations. In consideration of mass productivity and yield, 16 gradation display is considered to be the limit, whereas as in the present invention, gradation display is performed by purely digital control without adding any analog signal. By doing so, gradation display of 256 gradations or more became possible. Since it is a completely digital display, T
The gradation ambiguity due to the variation in FT characteristics is completely eliminated, and therefore, even if there is a slight variation in TFT, extremely uniform gradation display was possible. Therefore, in the past, the yield was extremely low in order to obtain a TFT with less variation, but since the yield of the TFT was not so much a problem according to the present invention, the yield of the TFT was improved and the manufacturing cost was significantly suppressed. did it.

For example, 256,0 of 640 × 400 dots
When normal analog gradation display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square,
Since there is about ± 10% variation in TFT characteristics, 1
6 gradation display was the limit. However, when the digital gray scale display according to the present invention is performed, it is possible to display up to 256 gray scales because it is hardly affected by the characteristic variation of the TFT element, and the color display is 16,777,2.
A wide variety of 16 colors and subtle colors can be displayed. When displaying software such as a television image, for example, even "rocks" of the same color have slightly different shades due to their fine depressions. If you try to display something close to the natural color,
16 gradations are difficult. The gradation display according to the present invention makes it possible to impart these minute color tone changes.

[Brief description of drawings]

FIG. 1 shows an example of drive waveforms according to the present invention.

FIG. 2 shows an example of drive waveforms according to the present invention.

FIG. 3 shows an example of drive waveforms according to the present invention.

FIG. 4 shows an example of a matrix configuration according to the present invention.

FIG. 5 shows a process of a color filter according to an embodiment.

FIG. 6 shows a process of a TFT according to an example.

FIG. 7 shows a process of a TFT according to an example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Takemura 398 Hase, Atsugi, Kanagawa Prefecture Semiconductor Energy Research Institute Co., Ltd.

Claims (1)

[Claims] 1. N signal lines X _1, X _2, ..X _n, ..X _N and M signal lines Y _1, Y _2, ..Y _m, ..Y _M orthogonal thereto. And a pixel Z provided in the intersection region of each signal line and at least one N-channel thin film transistor or P-channel thin film transistor in the intersection region of each matrix
_, Z ₁₂ , ... Z _mn , ... Z _MN , one of the source or drain of each thin film transistor is connected to one of the electrodes constituting each pixel, and the gate electrode of the thin film transistor is scanned. The first line is connected to the lines X _1, X ₂ , ..X _n, ..X _N , and the other one of the source and the drain is connected to the signal lines Y _1, Y _2, ..Y _m, ..Y _M. A substrate and a second substrate on which a transparent conductive film is formed.
It is applied to an arbitrary signal line X _n in a liquid crystal display device in which a ferroelectric liquid crystal or an antiferroelectric liquid crystal, or a fine mixture thereof with a high molecular compound is sandwiched between them facing each other at intervals of μm or less. Of the pulse
The image display method of the electro-optical device, wherein the interval of the +1) th pulse is represented by 2 ^i-1 T ₁ (i is a finite natural number and T ₁ is a constant).