JP2676092B2 - Electro-optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active type liquid crystal electro-optical device, and more particularly to an active type liquid crystal electro-optical device, in which a clear gradation level can be set.

[0002]

2. Description of the Related Art Liquid crystal compositions have different dielectric constants in a horizontal direction and a vertical direction with respect to a molecular axis due to their material properties. Therefore, liquid crystal compositions may be horizontally or vertically aligned with an external electric field. Can be easily done. The liquid crystal electro-optical device displays ON / OFF by controlling the amount of transmitted light or the amount of dispersion by utilizing the anisotropy of the dielectric constant.

FIG. 1 shows the electro-optical characteristics of nematic liquid crystals. When the applied voltage is small Va (point A 101),
When the transmitted light amount is almost 0% and Vb (point B 102), 3
About 0%, about 80% in the case of Vc (C point 103),
In the case of Vd (D point 104), it is about 100%. In other words, if only the points A and D are used, black and white two-gradation display is possible, and if the rising portion of the electro-optical characteristic is used like points B and C, intermediate gradation display is possible. As specific voltages confirmed by the present inventors, Va = 2.0 V, Vb =
2.18 V, Vc = 2.3 V, and Vd = 2.5 V.

Conventionally, in the case of a gray scale display of a liquid crystal electro-optical device using a TFT, the gray scale display is performed by changing the voltage applied to the gate of the TFT or the voltage applied between the source and drain to adjust the voltage in an analog manner. I was

[0005]

A more detailed description will be given of a gradation display method for a liquid crystal electro-optical device using a TFT. An n-channel thin film transistor used in a conventional liquid crystal electro-optical device has a voltage-current characteristic as shown in FIG. The voltage-current characteristics shown in FIG. 2 are characteristics 201 of an n-channel thin film transistor using amorphous silicon and characteristics 202 of an n-channel thin film transistor using polysilicon.

By controlling the voltage applied to the gate electrode in an analog manner, the drain current can be controlled, and consequently the resistance value between the source and drain can be changed. As a result, the magnitude of the electric field applied to the liquid crystals connected in series can be arbitrarily changed by the resistance division. Thereby, gradation display is possible. There is also a method of connecting the gate electrode to the scanning-side signal line and changing the source-drain voltage to control the electric field applied to the liquid crystal arbitrarily.

In either case, there is no difference that the analog gray scale display system largely depends on the characteristics of the TFT. However, it is difficult to make a large number of TFT elements in a matrix configuration so as to have uniform characteristics. In particular, fine adjustment of an intermediate voltage required for gradation display requires extremely difficulties with the present technology. That is the current situation. As can be seen from the electro-optical characteristics of the nematic liquid crystal shown in FIG. 2, 0.32 from around 2.08 V which is the boundary value in the dark state to around 2.40 V which is the boundary value in the bright state.
All gradation display must be performed between Vs. When 16 gradations are processed, it is necessary to control at an average 0.02V interval.

If point A 101 and point D 104 shown in FIG.
When the voltage is controlled in a portion where the liquid crystal is completely turned on / off as described above, the voltage difference can be set to 0.5 V or more, so that the in-plane characteristic variation of the TFT is sufficiently reduced. Using a plurality of write frames, for example, 1
By turning on (2.5 V) 6 frames out of 0 frames and turning off (2.0 V) the remaining 4 frames,
The writing average voltage is 2.3 V, and a halftone display is possible.

However, in this case, since a plurality of frames are used, 30H which can be visually confirmed by humans is used.
There is a risk that the display becomes z or less, and this may cause display failure such as flicker depending on conditions. As a method for preventing this, increasing the driving frequency has been proposed, but the data transfer speed of the driver IC is also reduced to 20M.
There was a limit of about Hz, which required difficulty.

[0010]

Therefore, the present invention proposes means for supplying a clear gradation display level to a liquid crystal by performing digital gradation display instead of the conventional analog gradation display. At that time, the method does not simply increase the drive frequency to perform gradation display as conventionally proposed, but makes the data transfer frequency and the gradation display frequency independent to change the frame frequency. It is characterized in that the digital gradation display is performed in a state where the image is not displayed.

In the active matrix type liquid crystal electro-optical device, the gradation display of the electro-optical device using the display driving method having the display timing related by the unit time t for writing in any pixel and the time F for writing one screen is performed. The signal during the writing time of the time t is time-divided without changing the time F, whereby the average value of the electric field applied to the liquid crystal of the pixel at the time t is changed according to the division ratio, and the gradation is changed. It is characterized by making it possible to display.

4 × 4 as shown in FIG. 3 for detailed explanation.
Is used. FIG. 4 shows drive waveforms for driving the matrix shown in FIG. In the case of the conventional electro-optical device, as shown in FIG. 3, signal lines 301 to 30 in the data direction are provided.
The strength of the electric field of No. 4 determines the electric field applied to the pixel electrode as indicated by 305 to 308, and the transmittance of the liquid crystal is determined by the electric field. Needless to say, the reference numerals in FIGS. 3 and 4 correspond to each other.

In the present invention, such analog gradation control is not performed, but as shown in FIG. 5, the signal during the writing time of the unit time t501 for writing to an arbitrary pixel is time-divided, and the division number is set. The gradation of minutes can be displayed. At that time, electric field changes 503, 505, 5 during writing time
When 07 changes as shown in FIG. 1, average values 504, 506, and 508 are obtained in the non-writing time, and clear gradation display is possible.

As for the data transfer speed on the information signal side, for example, in the case of a 1920 × 400 dot liquid crystal electro-optical device, a clock frequency of 5.76 MHz is required for 8-bit parallel transfer. On the other hand, when the conventional multiple frame method is used, if 10 frames are used, a clock frequency of 57.6 MHz is simply required. However, in the case of the present invention, since the clock frequency for gray scale display is independently set, it is possible to display up to about 166 gray scales when using an IC having a drive capability of a maximum of 8 MHz. With a drive IC of 12.3 MHz, the value can be up to 256 gradation display which is said to be necessary for visual use, which is significantly superior to the conventional analog and multi-frame digital gradation display. Sexuality occurs. A more detailed description will be given below with reference to examples.

The liquid crystal composition of the present invention has a ferroelectric property, a nematic liquid crystal as a main component, a cholesteric liquid crystal as a main component, and a nematic liquid crystal as a mixture dispersed in an organic resin. It is possible to use one in which a cholesteric liquid crystal is dispersed in an organic resin and one in which a smectic liquid crystal is dispersed in an organic resin.

[0016]

【Example】

Example 1 In this example, a liquid crystal electro-optical device having a circuit configuration as shown in FIG. 6 was used to fabricate a wall-mounted television as an image display device, which will be described. The TFT at that time was a staggered type made of polycrystalline silicon using laser annealing.

In FIG. 6, reference numeral 700 is a gate electrode,
701 is a source, 702 is a drain, and 703 is an NMOS
TFT and 704 represent pixel electrodes.

FIG. 7 shows the actual arrangement of electrodes and the like corresponding to this circuit structure. For simplicity, only portions corresponding to 2 × 2 (or less) are described. The same reference numerals are given to the parts corresponding to those in FIG. 705 is a lead contact, and 706
Indicates a pixel contact. Further, an actual drive signal waveform is shown in FIG. This is also 2x2 to simplify the explanation
The description will be made with reference to the signal waveforms in the case of the matrix configuration.

First, a method of manufacturing the liquid crystal panel used in this embodiment will be described with reference to FIG. In FIG. 8A, a silicon oxide film as a blocking layer 801 is formed on a glass 800, such as quartz glass, which can withstand a heat treatment at 700 ° C. or less, for example, about 600 ° C., which is not expensive, by using a magnetron RF (radio frequency) sputtering method. Produce to a thickness of ~ 3000Å. Process conditions are 100% oxygen atmosphere, film forming temperature 15 ° C., output 400 to 800 W, pressure 0.5 Pa.
And The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film was formed on this by a plasma CVD method. The film formation temperature is 250 ° C to 350 ° C
In this example, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) was used. Monosilane is not limited to (SiH _4), disilane (Si ₂ H ₆₎
Alternatively, trisilane (Si ₃ H ₈ ) may be used. These are PC
It was introduced into the VD apparatus at a pressure of 3 Pa, and high frequency power of 13.56 MHz was applied to form a film. At this time, an appropriate high frequency power is 0.02 to 0.10 W / cm ² , and in this example, 0.055 W / cm ² was used. Also, monosilane
The flow rate of (SiH ₄ ) was 20 SCCM, and the film formation rate at that time was about 120 ° / min.

The threshold voltage of the NTFT (Vt
To control h), use 1 x 10 of boron with diborane.
A concentration of ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ may be added during film formation. In addition, not only the plasma CVD but also a sputtering method and a low pressure CVD method may be used for forming the silicon layer to be a channel region of the TFT, and the method will be briefly described below.

When the sputtering method is used, the back pressure before the 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 argon and hydrogen of 20 to 80%. For example, argon was 20% and hydrogen was 80%.
The film formation 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 gas phase method, 450 to 550 ° C. lower by 100 to 200 ° C. than the crystallization temperature, for example,
Disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) was supplied to the CVD apparatus at 30 ° C. to form a film. The reactor pressure is 30 ~
It was set to 300 Pa. The deposition rate was 50-250 ° / min.

The coatings formed by these methods are:
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. In order to promote crystallization, the oxygen concentration should be 7 × 10 ¹⁹ cm ⁻³ or less,
Preferably, it is desirable to be 1 × 10 ¹⁹ cm ⁻³ or less,
If the amount is too small, the leakage current in the off state increases due to the backlight, so this concentration was selected. If the oxygen concentration is high, crystallization is difficult, and the laser annealing temperature must be increased or the laser annealing time must be increased. Hydrogen is 4 × 10 ²⁰ cm ⁻³ and silicon 4 × 10 ²²
When compared with cm ^-3 , it was 1 atomic%.

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 T channel formation region by ion implantation so as to have a concentration of 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ .

According to the above method, the silicon film 802 in an amorphous state is formed to a thickness of 500 to 5000 Å, 100 in this embodiment.
The film was formed to a thickness of 0 °.

After that, as shown in FIG. 7B, a pattern was formed in the photoresist 803 by using the mask 1 and only the source / drain regions were opened. A silicon film 804, which will be an n-type active layer, is formed thereon by a plasma CVD method. The film was formed at a temperature of 250 ° C. to 350 ° C. In this embodiment, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) having a concentration of 3% were used. These are introduced into the PCVD apparatus at a pressure of 5 Pa, and 13.56
The film was formed by applying a high frequency power of MHz. At this time, the high-frequency power is suitably 0.05~0.20W / cm ^2, in this embodiment using 0.120W / cm ^2.

The specific conductivity of the n-type silicon layer produced by this method was about 2 × 10 ^-1 [Ωcm ^-1 ]. The film thickness was 50 °. After that, the source / drain regions 805 and 806 were formed by using the lift-off method.
After that, an N-channel thin film transistor island region 807 was formed using the mask P2.

Then, using a XeCl excimer laser, the source / drain / channel regions were laser-annealed and at the same time, the active layer was laser-doped. The laser energy at this time has a threshold energy of 130 mJ / cm ² , and 220 for melting the entire film thickness.
mJ / cm ² is required. However, 220m from the beginning
When energy of J / cm ² or more is irradiated, hydrogen contained in the film is rapidly released, and the film is destroyed. For this purpose, it is necessary to first displace hydrogen and then melt it with low energy. In this embodiment, first 150 m
After purging hydrogen at J / cm ² , 230mJ
The crystallization was carried out at / cm ² .

The annealing causes the silicon film to shift from an amorphous structure to a highly ordered state, and a part thereof exhibits a crystalline state. In particular, a region having a relatively high order in a state after the formation of silicon is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When measured by laser Raman spectroscopy, a single crystal silicon peak 522 is obtained.
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size is 50 to 5 when calculated from the half width.
Although the area is 00 °, there are actually a large number of regions having high crystallinity and a cluster structure, and a film having a structure in which each cluster is bonded to each other by silicon (anchoring) can be formed. .

As a result, the coating is in a state in which it can be said that it is substantially free of grain boundaries (hereinafter referred to as GB). Since the carriers can easily move between the clusters through the anchored portions, the carrier mobility is higher than that of polycrystalline silicon in which so-called GB is clearly present. That is, electron mobility (μe) = 15 to 300 cm ² / V
Sec was obtained.

A silicon oxide film 808 is formed thereon as a gate insulating film to a thickness of 500 to 2000Å, for example 1000Å. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During this film formation, a small amount of fluorine is added,
Sodium ions may be immobilized.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned with the third photomask 69 to obtain FIG. 8 (E). A gate electrode 809 is formed, for example, a channel length is 7 μm, a gate electrode is formed of 0.2 μm of phosphorus-doped silicon, and molybdenum is formed thereon to a thickness of 0.3 μm.

When aluminum (Al) is used as the gate electrode material, the self-alignment method can be applied by patterning this with the third photomask 3 and then anodizing the surface. Since the source / drain contact holes can be formed at positions closer to the gate, the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

Thus, a C / TFT can be manufactured without applying a temperature to 400 ° C. or more in all steps. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and it can be said that the process is very suitable for the large-screen liquid crystal display device of the present invention.

In FIG. 8F, an interlayer insulator 810 was formed as a silicon oxide film by the above-mentioned sputtering method. This silicon oxide film is formed by LPCVD, optical CVD
Or a normal pressure CVD method. For example, 0.2-0.
It is formed to a thickness of 6 μm, and then the fourth photomask 4
Was used to form a window 811 for the electrode. After that, aluminum is further formed on the entire surface to a thickness of 0.3 μm by a sputtering method to form a lead 812 and a contact 813 by using a fifth photomask 5, and then an organic resin 814 for flattening the surface is used. A translucent polyimide resin was applied and formed, and another electrode hole was formed using the sixth photomask 6.

Further, ITO (Indium Tin Oxide) was formed on the whole of the above to have a thickness of 0.1 μm by a sputtering method, and a pixel electrode 815 was formed using the seventh photomask 7. This ITO is deposited at room temperature to 150 ° C.
It was accomplished by oxygen at 400 ° C or by annealing in air.

The electric characteristics of the obtained TFT were mobility 80 (cm ² / Vs) and Vth 5.0 (V). One substrate for a liquid crystal electro-optical device manufactured according to such a method was obtained.

A method for manufacturing the other substrate is shown in FIG. A polyimide resin in which a black pigment was mixed with polyimide was formed on a glass substrate 900 to a thickness of 1 μm by a spin coating method, and a black stripe 901 was formed using the first photomask 11. Thereafter, a polyimide resin mixed with a red pigment was formed into a film having a thickness of 1 μm by spin coating, and a red filter 902 was manufactured using the second photomask 12. Similarly, the third photomask 1
3 was used, and a blue filter 904 was manufactured using the green filter 903 and the fourth photomask 14. During the production of these filters, each filter was heated to 60 ° C in nitrogen at 350 ° C.
Minutes were fired. After that, the leveling layer 905 was formed using a transparent polyimide, also by using the spin coating method.

After that, ITO (Indium Tin Oxide) was formed on the entire surface by sputtering to a thickness of 0.1 μm, and the common electrode 906 was formed using the fifth photomask 15. This ITO is deposited at room temperature to 150 ° C.
Fulfilled by oxygen at ~ 300 ° C. or in air, a second substrate was obtained.

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

Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. A drive IC having a TAB shape and a PCB having a common signal and potential wiring were connected to leads on the substrate, and a polarizing plate was attached on the outside to obtain a transmissive liquid crystal electro-optical device.

FIG. 10 is a schematic structural diagram of the electro-optical device according to this example. Liquid crystal panel 100 obtained in the above process
0 was installed in combination with a rear illumination device 1001 in which three cold cathode tubes are arranged. Thereafter, a tuner 1002 for receiving television waves was connected to complete the electro-optical device. Compared with the conventional CRT type electro-optical device,
Since it is a flat device, it can be installed on a wall.

Next, a peripheral circuit of the liquid crystal electro-optical device for completing the present invention will be described with reference to FIG. The drive circuit 1103 is connected to the information signal side wirings 1101 and 1102 connected to the matrix circuit of the liquid crystal electro-optical device. The drive circuit 1103 is composed of two parts when divided by the drive frequency system. One is a data latch circuit system 1104 which is similar to the conventional driving system, and is mainly composed of basic clocks CLK1 and 1106 for sequentially transferring data 1105.
Bit parallel processing is performed. The other one is a component according to the present invention, which is composed of clocks CLK2 and 1107, a flip-flop circuit 1108, and a counter 1109 according to the ratio of division necessary for gradation display. The counter 1109 produces a pulse corresponding to the gradation display data sent from the data latch system 1104.

What is characteristic of the present invention is exactly these portions, and by adopting two kinds of driving frequencies, the number of frames for screen rewriting is not changed,
This is to enable clear digital gradation display. It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

On the other hand, signal lines 1110 and 1111 on the scanning side
The drive circuit 1112 connected to the
The transferred potential is controlled by the flip-flop circuit 1115 of the clock CLK 1114, and a selection signal is added.

The TFT according to this embodiment has a mobility of 80.
Since it could be (cm ² / Vs), the driving frequency could be increased up to about 1 MHz. For this reason,

[0048]

(Equation 1)

It is possible to display up to 42 gradations which can be calculated by.

When analog gradation display is performed, TF
The 16-gradation display was the limit due to the T characteristic variation. However, when the digital gradation display according to the present invention is performed, it is possible to display up to 42 gradations and 7 in color display because it is hardly affected by the characteristic variation of the TFT element.
A wide variety of 4,088 colors and subtle colors can be displayed.

[Embodiment 2] In this embodiment, a viewfinder for a video camera using a liquid crystal electro-optical device having a diagonal of 1 inch was manufactured and the present invention was carried out.

In this embodiment, a viewfinder is constructed by forming an element using an amorphous TFT by a low temperature process with a construction of 387 × 128 pixels.
A method for manufacturing the liquid crystal display device used in this embodiment will be described with reference to FIGS. In FIG. 12A, a silicon oxide film as a blocking layer 1201 is formed on an inexpensive glass 1200 such as soda lime glass by a magnetron RF (radio frequency) sputtering method to a thickness of 1000 to 3000 Å. Process conditions are 100% oxygen atmosphere, film formation temperature 15
° C, output 400-800W, pressure 0.5Pa. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned with the first photomask 21 to form a gate electrode 1202, and FIG. 12A was obtained. In this embodiment, the channel length is 10 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.

When aluminum (Al) is used as the gate electrode material, this is patterned by the first photomask 21 and then the surface thereof is anodized to form an insulating film or a channel on the gate electrode. No hillocks or voids are generated in the region, and the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

A silicon oxide film is formed on the gate insulating film 120.
As No. 3, it was formed to a thickness of 500 to 2000Å, for example 1000Å. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix the sodium ions.

An amorphous silicon film was formed on this by the plasma CVD method. When the silicon film is formed by the plasma CVD method, the temperature is set to 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a high-frequency power of 13.56 MHz was applied to form a film.

The film formed by this method preferably has oxygen of 5 × 10 ²¹ cm ⁻³ or less. If this oxygen concentration is high, the mobility will decrease, and if it is too low, the backlight will increase the leak current in the off state.
Therefore, the range was set to 4 × 10 ¹⁹ to 4 × 10 ²¹ cm ⁻³ . Hydrogen was 4 × 10 ²⁰ cm ^-3 , which was 1 atom% when compared with silicon 4 × 10 ²² cm ^-3 . According to the above method, a silicon film in an amorphous state is formed in a thickness of 500 to 5000 Å, for example 1500 Å
It was manufactured to a thickness of.

After that, a resist 1204 for forming a contact region is formed by the lift-off method using the second photomask 22, and a silicon film 1205 to be an n-type active layer is formed on the resist 1204 by the plasma CVD method. . The film forming temperature is 250 ° C. to 350 ° C., and in this embodiment 320
℃ and was used as monosilane (SiH ₄₎ and monosilane based phosphine (PH ₃₎ 1% concentration. In addition, hydrogen (H ₂ ) was added at a ratio of 5: 3: 20 to the PC.
It was introduced at a pressure of 5 Pa in the VD apparatus, and a high frequency electric field of 13.56 MHz was applied to form a film. At this time, the high-frequency power is suitably 0.05~0.20W / cm ^2, in this embodiment using 0.120W / cm ^2.

The specific conductivity of the silicon film 1205, which becomes the n-type active layer by this method, is 2 × 10 ^-1 [Ωcm.
^-1 ]. The film thickness was 50 °. Then, Al is used as a lead and a contact electrode by sputtering 3
A 000Å film was formed 1206, and then an excess portion was removed by a lift-off method to form a source 1207 and a drain 1208 region.

After that, after forming individual TFTs 1209 on the island by the third mask 23, as shown in FIG.
As shown in (D), an organic resin 1210 for flattening the surface was applied and formed, for example, a translucent polyimide resin, and re-drilling of electrodes was performed with a photomask 24.

In order to connect the output end to the electrode of one pixel of the liquid crystal device as a transparent electrode, I is formed by the sputtering method.
A TO (indium tin oxide film) was formed. It was etched with the photomask 25 to form the electrode 1211. This ITO film is formed at room temperature to 150 ° C.
Fulfilled by oxygen or anneal in the atmosphere at 00-400 ° C. In this way, the NTFT 1209 and the transparent conductive film electrode 1211 were formed on the same glass substrate 1200. The mobility of the electrical characteristics of the obtained TFT is 0.2.
(Cm ² / Vs) and Vth were 5.3 (V).

Next, a color filter and a transparent conductive film ITO were formed on the insulating substrate by the same method as in "Example 1".
1000 Å was deposited 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. Thereafter, the surface of the polyimide was modified using a known rubbing method, and at least initially, means for aligning the liquid crystal molecules in a certain direction was provided to obtain first and second substrates.

Thereafter, the nematic liquid crystal composition was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. Since the pitch of the leads on the substrate was as fine as 46 μm, they were connected using the COG method. In this embodiment, a method is used in which gold bumps provided on an IC chip are connected with an epoxy-based silver-palladium resin, and the IC chip and the substrate are filled and fixed with an epoxy-modified acrylic resin for the purpose of fixing and sealing. Was. Thereafter, a polarizing plate was attached on the outside to obtain a transmission type liquid crystal display device.

Since the TFT according to this embodiment can have a mobility of 0.2 (cm ² / Vs) even in the amorphous state, the driving frequency can be increased up to about 100 KHz. For this reason,

[0066]

(Equation 2)

It is possible to display up to 13 gradations, which can be calculated by. For example, 49,152 of 384 × 128 dots
When a normal analog gradation display is performed on a liquid crystal electro-optical device in which a set of TFTs is formed in 50 mm square (36 multiple cuts from a 300 mm square substrate), an amorphous TF is displayed.
Since there is a variation of about 10% in the characteristics of T, 8-gradation display is the limit. However, when the digital gradation display according to the present invention is performed, it is possible to display more than 13 gradations because it is not easily affected by the characteristic variation of the TFT element, and in the color display, there are 2,207 colorful and delicate colors. The display of is realized.

[Embodiment 3] In this embodiment, a projection type image display device as shown in FIG. 13 was produced, and therefore, description will be added.

In this embodiment, three liquid crystal electro-optical devices 13 are used.
00 is used to assemble the projection unit for the projection type image display device. Each one is 640 x 480
It has a dot configuration, and 307,20 in 4 inch diagonal
0 pixels were produced. The size per pixel was 127 μm square.

As a configuration of the projection type image display device, a liquid crystal electro-optical device 1300 is divided and installed for the three primary colors of light: red, green and blue. A red filter 1301, a green filter 1302 and a blue filter 1 are provided.
303, a reflector 1304, a 150W metal halide light source 1307, and a focusing optical system 1308.

The substrate of the liquid crystal electro-optical device used in the electro-optical device of this example was a substrate having a matrix circuit of NMOS structure. A device using a high-mobility TFT was formed by a low-temperature process to form a projection type liquid crystal electro-optical device. A method for manufacturing the liquid crystal display device used in this embodiment will be described with reference to FIGS. In FIG. 14A, a silicon oxide film as a blocking layer 1401 is formed on a glass 1400 that can withstand a heat treatment at 700 ° C. or less, for example, about 600 ° C., which is not expensive, such as quartz glass by a magnetron RF (radio frequency) sputtering method as a blocking layer 1401. ~ 3000
Make it to the thickness of Å. The process conditions are a 100% oxygen atmosphere, a film forming temperature of 15 ° C., an output of 400 to 800 W, and a pressure of 0.
5 Pa was set. The film formation rate using quartz or single crystal silicon as a target was 30 to 100 ° / min.

A silicon film was formed thereon by LPCVD (Low Pressure Vapor Phase) method, sputtering method or plasma CVD method. When formed by the reduced pressure gas phase method, the temperature is 1
450-550 ° C lower by 00-200 ° C, for example 530 ° C
CVD of disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ )
The film was supplied to the apparatus to form a film. Reactor pressure is 30 ~ 300
Pa. The deposition rate was 50-250 ° / min.
Threshold voltage (Vt) between PTFT and NTFT
In order to control substantially the same as in h), boron may be added at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ during film formation using diborane.

In the case of the sputtering method, the back pressure before sputtering was set to 1 × 10 ^-5 Pa or less, the single crystal silicon was used as the target, and the atmosphere was mixed with hydrogen of 20 to 80% in argon. For example, argon was 20% and hydrogen was 80%.
The film formation 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 a silicon film is formed by the plasma CVD method, the temperature is, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a high-frequency power of 13.56 MHz was applied to form a film.

The coating formed by these methods is
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. If the oxygen concentration is high, it is difficult to crystallize, and the heat annealing temperature must be increased or the heat annealing time must be increased.
If the amount is too small, the lamp is turned off by the backlight.
Current increases. Therefore, 4 × 10 ¹⁹ to 4 × 10 ²¹
The range was cm ⁻³ . Hydrogen is 4 × 10 ²⁰ cm ^-3 and silicon 4
It was 1 atomic% when compared with × 10 ²² cm ⁻³ .

By the above method, a silicon film in an amorphous state is formed to a thickness of 500 to 5000 Å, for example 1500 Å, and then a heat treatment at a medium temperature in a non-oxide atmosphere at a temperature of 450 to 700 ° C. for 12 to 70 hours, For example, it was held at a temperature of 600 ° C. in a hydrogen atmosphere. Since a silicon oxide film having an amorphous structure is formed on the surface of the substrate under the silicon film, no specific nucleus is present in this heat treatment, and the whole is annealed uniformly. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein.

The annealing causes the silicon film to shift from an amorphous structure to a highly ordered state, and a part thereof assumes a crystalline state. In particular, a region having a relatively high order in a state after the formation of silicon is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When measured by laser Raman spectroscopy, a single crystal silicon peak 522 is obtained.
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size is 50 to 5 when calculated from the half width.
Although it is a microcrystal with a size of 00Å, there are actually a large number of regions with high crystallinity and a cluster structure, and a semi-amorphous structure film in which each cluster is bonded to each other by silicon (anchoring). Could be formed.

As a result, the coating film is in a state in which it can be said that there is substantially no grain boundary (hereinafter referred to as GB). Since the carriers can easily move between the clusters through the anchored portions, the carrier mobility is higher than that of polycrystalline silicon in which so-called GB is clearly present. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² /
VSec, electron mobility (μe) = 15 to 300 cm ² / V
Sec is obtained.

On the other hand, when the film is polycrystallized by a high temperature anneal at 900 to 1200 ° C. instead of the anneal at the medium temperature as described above, the segregation of impurities in the film occurs due to the solid phase growth from the nucleus. , GB have a large amount of impurities such as oxygen, carbon, and nitrogen, and have a large mobility in the crystal, but they form a barrier in GB and hinder the movement of carriers there. As a result, a mobility of 10 cm ² / Vsec or more cannot be easily obtained. That is, in this embodiment, the silicon semiconductor having the semi-amorphous or semi-crystal structure is used for the reason as described above.

In FIG. 14A, the silicon film was photoetched using the first photomask 31 to form a TFT region 1402 (channel width 20 μm).

A silicon oxide film is formed on the gate insulating film 140.
As No. 3, it was formed to a thickness of 500 to 2000Å, for example 1000Å. This was made under the same conditions as those for forming the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix the sodium ions.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
^-3 silicon film or molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned using the second photomask 32 to form a gate electrode 1404 as shown in FIG. In this embodiment, the channel length is 10 .mu.m and the gate electrode is made of phosphorus-doped silicon.
2 μm, and molybdenum was formed thereon with a thickness of 0.3 μm. In FIG. 14C, as a source 1405 and a drain 1406, phosphorus is added by an ion implantation method at a dose amount of 1 to 5 × 10 ¹⁵ cm ^-2 .

When aluminum (Al) is used as the gate electrode material, the self-alignment method can be applied by patterning this with the second photomask 32 and then anodizing the surface. Since the source / drain contact holes can be formed at positions closer to the gate, the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

Next, heating anneal was performed again at 600 ° C. for 10 to 50 hours. Source 1405, drain 140
6 impurities were activated and produced as N ⁺ . A channel forming region 1407 is formed as a semi-amorphous semiconductor below the gate electrode 1404.

In this way, it is possible to fabricate an NTFT without applying a temperature above 700 ° C. in all steps, even though it is a self-aligned method. Therefore, it is not necessary to use an expensive substrate such as quartz as the substrate material,
This process is extremely suitable for the large-pixel liquid crystal display device of the present invention.

In this embodiment, the thermal anneal is as shown in FIG.
It was performed twice in (C). However, the anneal of FIG. 14 (A) is omitted depending on the desired characteristics, and both are omitted.
The manufacturing time may also be reduced by using a tool. FIG.
In (D), an interlayer insulator 1408 was formed as a silicon oxide film by the above-described sputtering method. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, it is formed to have a thickness of 0.2 to 0.6 μm, and then a window 1 for an electrode is formed using a photomask 33.
409 was formed. Further, as shown in FIG. 14E, aluminum is formed on the entire surface by a sputtering method, a lead 1410 and a contact 1411 are formed by using a photomask 34, and then the surface of the organic resin 1 for flattening
412 For example, a translucent polyimide resin was applied and formed, and the photomask 35 was used to re-drill the electrode.

Since the output terminal is connected to the electrode of one pixel of the liquid crystal device as a transparent electrode, the I electrode is formed by the sputtering method.
A TO (indium tin oxide film) was formed. It was etched with a photomask 36 to form an electrode 1413. This ITO film is formed at room temperature to 150 ° C.
Fulfilled by oxygen or anneal in the atmosphere at 00-400 ° C. Thus, the NTFT 1402 and the transparent conductive film electrode 1413 were formed on the same glass substrate 1400. The mobility of the electric characteristics of the obtained TFT is 120.
(Cm ² / Vs), Vth was 5.0 (V).

FIG. 15 shows a schematic structure. 15 on the substrate
00, a fumaric acid polymer resin and nematic liquid crystal
A mixture dissolved in xylene, which is a common solvent, in a ratio of 5:35 was formed into a thickness of 10 μm by a die casting method. Thereafter, the solvent was removed in a nitrogen atmosphere at 120 ° C. for 180 minutes to form a liquid crystal dispersion layer 1501. in this case,
It was found that when the pressure was slightly reduced from the atmospheric pressure, the tact time could be reduced.

After that, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode 212. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, using a printing method, a translucent silicone resin was applied to a thickness of 30 μm, and baked at 100 ° C. for 30 minutes to obtain a liquid crystal electro-optical device.

The functional configuration of the driving IC used in this embodiment is the same as that in "Embodiment 1". 3 of 640 x 480 dots
When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 07,200 sets of TFTs are formed in a 300 mm square, 16 gray scale displays are performed because there is about ± 10% variation in TFT characteristics. It was the limit. T according to the present embodiment
Since the driving frequency of FT could be increased up to 2.5MHz,

[0091]

(Equation 3)

It is possible to display up to 86 gradations which can be calculated with.

Therefore, when the digital gradation display according to the present embodiment is performed, it is possible to display up to 64 gradations because it is hardly affected by the characteristic variation of the TFT element. Yes, subtle color display can be realized.

In the case of displaying software such as a television image, for example, even "rock" of the same color has a slightly different shade due to the adjustment of the light hitting the minute depressions. When an attempt is made to display a color close to the natural colors, it is difficult to perform the display with 16 gradations, and it is not suitable for expressing these subtle depressions. With the gradation display according to the present invention, it is possible to impart these minute color changes.

This liquid crystal electro-optics can be used not only for the front type projection television shown in FIG. 13 but also for the rear type projection television.

[0096]

[Embodiment 4] In this embodiment, an electro-optical device for a portable computer using a reflection type liquid crystal dispersion type display device as shown in FIG.

As the first substrate used in this example, the one prepared in the same process as in "Example 1" was used. This embodiment will be described using the liquid crystal electro-optical device shown in FIG. Fumaric acid-based polymer resin and black dye 1 on the substrate 1500
A nematic liquid crystal mixed with 5% was dissolved in xylene which is a common solvent at a ratio of 65:35 to form a mixture having a thickness of 10 μm by a die casting method, and then the solvent was heated at 120 ° C. for 180 minutes in a nitrogen atmosphere for 180 minutes. Liquid crystal dispersion layer 1 removed
501 was formed.

Here, since a black dye is used, a flat panel display, which has been difficult with a dispersion type liquid crystal display, shows black when light is scattered (when no electric field is applied) and white when transmitted (when an electric field is applied). It can be displayed, and it is possible to display it like the letters written on paper.

As an opposite structure, it is also possible to express a white color when scattering and a black color when transmitting without mixing a black dye. However, in this case, the back side shown below needs to be black. This is also possible to display like characters written on paper.

After that, ITO (indium tin oxide film) was formed by a sputtering method to obtain a counter electrode 1502. This ITO was formed at a temperature from room temperature to 150 ° C. Thereafter, using a printing method, a white silicon resin was applied to a thickness of 55 μm and baked at 100 ° C. for 90 minutes to obtain a liquid crystal electro-optical device.

[0101]

According to the present invention, in contrast to the conventional analog gray scale display, digital gray scale display is performed using two independent driving frequencies. As an effect, for example, when assuming a liquid crystal electro-optical device having a pixel number of 640 × 400 dots, a total of 256,0
It is very difficult to fabricate the characteristics of all the 00 TFTs without variation. In reality, considering the mass productivity and the yield, 16 gradation display is considered to be the limit. In order to clarify the level, the reference voltage value is input as a signal from the controller side instead of an analog value, and the timing of connecting the reference signal to the TFT is controlled by a digital value, so that the voltage applied to the TFT is reduced. The present invention is characterized in that the present invention employs a method of controlling the characteristic variation of the TFT by controlling, so that clear digital gradation display is possible.

Further, by adopting two kinds of drive frequencies, it is possible to perform clear digital gradation display without changing the number of frames for screen rewriting.
It is possible to avoid the occurrence of flicker and the like due to the decrease in the number of frames.

When the digital gradation display according to the present invention is performed, it is possible to achieve up to about 64 gradations because it is not easily affected by the characteristic variation of the TFT element. Color display is realized. When projecting software like TV images,
For example, even a “rock” made of the same color has a slightly different color due to its fine dents and the like. If an attempt is made to perform a display close to natural colors, it is difficult to achieve 1696 gradations of 4096 colors. With the gradation display according to the present invention, it is possible to impart these minute color changes.

[Detailed Description of Drawings]

FIG. 1 shows the electro-optical properties of nematic liquid crystals.

FIG. 2 T with polysilicon and amorphous silicon
4 shows the electrical characteristics of FT.

FIG. 3 shows a matrix circuit according to a conventional example.

FIG. 4 shows a drive waveform according to a conventional example.

FIG. 5 shows drive waveforms according to the present invention.

FIG. 6 shows a matrix circuit according to this embodiment.

FIG. 7 shows a planar structure of a device according to this example.

FIG. 8 shows a process of a TFT according to this example.

FIG. 9 shows a process of forming a counter electrode according to this embodiment.

FIG. 10 shows a configuration of a liquid crystal display device (TV) according to this embodiment.

FIG. 11 shows a system configuration of a drive circuit according to the present embodiment.

FIG. 12 shows a process of a TFT according to this example.

FIG. 13 shows the structure of a projection type liquid crystal electro-optical device according to the present embodiment.

FIG. 14 shows a process of a TFT according to this example.

FIG. 15 is a sectional view of a liquid crystal electro-optical device according to an example.

FIG. 16 shows a configuration of a portable computer according to this embodiment.

[Explanation of symbols]

 501 unit time 503 electric field change 505 electric field change 507 electric field change

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01L 29/786 (56) Reference JP-A-2-16596 (JP, A) Actual development Sho 60- 154996 (JP, U)

Claims (7)

(57) [Claims] 1. A signal line having a matrix structure on a substrate and an n-channel thin film transistor is provided for each pixel electrode, one of the input and output sides of the thin film transistor is the pixel electrode, and the other one has the matrix structure. A first substrate having an electric circuit connected to a first signal line of a pair of signal lines, and a gate of the thin film transistor connected to a second signal line of the signal line having the matrix structure; and an electrode on the substrate In a liquid crystal display device in which at least a liquid crystal composition or a mixture containing a liquid crystal composition is sandwiched between a second substrate having a lead and a lead , data transfer with a period for writing one frame as a cycle
Number of frequency generation means and unit time to write in any one pixel required for gradation display
The gradation display frequency is generated with the time division
Electro-optical device characterized by having a means for raw. 2. The electro-optical device according to claim 1, wherein the liquid crystal composition exhibits ferroelectricity. 3. The electro-optical device according to claim 1, wherein the liquid crystal composition mainly comprises a nematic liquid crystal. 4. The electro-optical device according to claim 1, wherein the liquid crystal composition is mainly composed of a cholesteric liquid crystal. 5. An electro-optical device according to claim 1, wherein the mixture containing the liquid crystal composition has nematic liquid crystal dispersed in an organic resin. 6. The electro-optical device according to claim 1, wherein the mixture containing the liquid crystal composition has a cholesteric liquid crystal dispersed in an organic resin. 7. The electro-optical device according to claim 1, wherein the mixture containing the liquid crystal composition has smectic liquid crystals dispersed in an organic resin.