JP2754290B2 - Electro-optical device and driving method thereof - 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 electro-optical device, and more particularly to an active-type liquid-crystal electro-optical device, wherein a clear gradation level can be set.

[0002]

2. Description of the Related Art Liquid crystal compositions have different dielectric constants in the horizontal and vertical directions with respect to the molecular axis due to their material properties. 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. 2 shows the electro-optical characteristics of a nematic liquid crystal. When the applied voltage is small at Va (point A), the transmitted light amount is almost 0%, and when Vb (point B), the transmitted light amount is about 20%.
In the case of c (point C), it is about 70%, and in the case of Vd (point D), 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.

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]

The method of displaying a gradation of a liquid crystal electro-optical device using a TFT will be further described. An N-channel thin film transistor conventionally used for a liquid crystal electro-optical device has a voltage-current characteristic as shown in FIG. The voltage-current characteristics shown in FIG. 3 are the characteristics of an N-channel thin film transistor using amorphous silicon and the characteristics 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 the magnitude of the electric field applied to the liquid crystal can be changed. Thereby, gradation display is possible.

However, assuming a liquid crystal electro-optical device having a pixel number of 640 × 400 dots, for example, it is very difficult to manufacture the characteristics of all 256,000 TFTs without variation. In reality, considering the mass productivity and the yield, 16 gradation display is considered to be the limit.

Further, the gate voltage is set to a constant value,
A method of performing gray scale display by controlling only N / OFF and controlling the source / drain voltage is considered, but it is considered that the limit is about 16 gray scales due to instability of characteristics. Analog gradation display control largely depends on the characteristics of the TFT, and clear display requires difficulty.

As another method, a method of gradation display using a plurality of frames has been proposed. This means that, as shown in FIG. 12, for example, when gradation display is performed using 10 frames, the pixel A transmits two frames out of 10 frames,
20% on average by making the remaining 8 frames non-transparent
And can be displayed. Similarly, the pixel B can display 70% transmission, and the pixel C can display 50% transmission.

However, when such a display is performed, the number of frames is substantially reduced, so that flickering and the like and display damage have occurred. To solve this, increasing the frame frequency has been devised.
This technology has limitations because it is difficult to increase power consumption with an increase in drive frequency or to increase the speed of an IC.

[0011]

Therefore, in the present invention, in order to clarify the applied voltage level, a reference voltage value which is not an uncertain analog value but is repeated at a constant cycle is input from the controller as a signal. The present invention employs a method of controlling the voltage applied to the TFT by controlling the timing at which the reference signal is connected to the TFT with a digital value, thereby controlling variations in the characteristics of the TFT. And

That is, a signal used for selecting an arbitrary pixel drive for gradation display of an electro-optical device using a display drive method having a display timing related to a time F for writing one screen and a time t for writing one pixel. The time t on one of the lines
Applying a selection signal to the reference signal having a voltage change having a period of and a signal line at an arbitrary timing within the time t;
It is characterized in that a voltage applied to the liquid crystal is determined and a gray scale can be displayed without changing the time F by actually applying a voltage to the pixel. In addition, this timing does not depend on data transfer, but a high-speed clock is applied to the driver IC itself mounted on the liquid crystal electro-optical device, and processing is performed in a signal processing portion. It is characterized in that high-speed control not limited to several tens of MHz, which was the limit of the above, can be performed.

FIG. 1 specifically shows a driving waveform of the electro-optical device according to the present invention. FIG. 1 shows an example in which the present drive waveform is inserted in a 2 × 2 active matrix circuit using a so-called transfer gate element shown in FIG. Here, a half sine wave is used as the reference signal waveform. Signal lines Y ₁ 303 and Y ₂ 304 corresponding to the scanning line direction
Sine waves as shown in FIG. 1 V _DD1 and V _DD2 are applied to the signal lines X ₁ 301 and X ₂ 30 corresponding to the information line direction.
2, two-polarity (hereinafter, referred to as "bipolar") signals whose polarities are inverted as shown by V _GG1 and V _GG2 in FIG. By selecting the timing of applying the bipolar signal, the voltage applied to each pixel can be arbitrarily controlled.

That is, when a bipolar signal is added,
The pixel is charged with a sinusoidal voltage. For example, if a bipolar signal is added when the sine wave signal is almost 0,
The voltage stored in the capacitor of the pixel is almost 0, and when the bipolar signal is applied when the sine wave signal takes the maximum value, the voltage of the pixel becomes the same value as the maximum value of the sine wave signal. When the timing for applying the bipolar signal is intermediate, an intermediate voltage is applied to the pixel.

By changing the timing of the bipolar signal and using an appropriate scanning technique for selecting each pixel in this manner, the signals are accumulated in the four liquid crystal pixel electrodes A to D in FIG. The charge amount and the potential are determined, and the magnitude of the electric field applied to the pixels and the liquid crystal is determined by arbitrarily setting the potential of the counter electrode.

If the potential of the opposing electrode is set to 0 V, the voltages applied to the pixels A to D can take any values as shown in FIG. 1, and gray scale display can be performed. In FIG. 1, for simplicity, an extremely simple matrix of 2.times.2 has been described. Also, PTFT
And the NTFT may be interchanged.

The timing at which the bipolar signal is applied is not determined by the transfer speed of the information signal, but is limited by the basic clock input to the driver IC directly connected to the liquid crystal electro-optical device in the configuration according to the present invention . Mark to Examples below, addition of a more detailed description.

[0018]

[Embodiment 1] In this embodiment, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. The TFT at that time was made of polycrystalline silicon using laser annealing. FIG. 6 shows an actual arrangement of electrodes and the like corresponding to this circuit configuration. These are 2x for simplicity of explanation
Only the part corresponding to 2 (or less) is described. FIG. 1 shows an actual drive signal waveform. For the sake of simplicity, the description will be made using signal waveforms in the case of a 2 × 2 matrix configuration.

[0019] First, a manufacturing method of a liquid crystal panel used in this embodiment using FIGS. FIG.
(A) Inexpensive 700 ° C. other than quartz glass
Hereinafter, for example, a glass 50 that can withstand a heat treatment at about 600 ° C.
Using a magnetron RF (high frequency) sputtering method, a silicon oxide film as a blocking layer
It is manufactured to a thickness of 00 mm. Process condition is 100% oxygen
The atmosphere, film forming temperature, 150 ° C., output, 400 to 800 W, pressure, 0.5 Pa. The deposition rate using quartz or single crystal silicon as the target was 30 to 100 ° / min.

A silicon film 52 was formed thereon by a plasma CVD method. The film formation temperature is from 250 ° C to 35
In this example, the temperature was set at 320 ° C., and monosilane (SiH ₄ ) was used. Not only monosilane (SiH ₄ ) but also disilane (Si ₂ H ₆ ) and trisilane (Si ₃ H
₈ ) may be used. These are placed in a PCVD apparatus at 3 Pa.
And a 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 appropriate, and in this embodiment, 0.055 W / cm ²
cm ² was used. The flow rate of monosilane (SiH ₄ ) was set to 20 SCCM, and the deposition rate at that time was about 120 ° /
Minutes. In order to control the threshold voltage (Vth) of the PTFT and the NTFT to be substantially the same, boron is used in a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ by using diborane.
May be added during the film formation. The plasma C is used for forming a silicon layer to be a channel region of the TFT.
Not only VD but also a sputtering method and a low pressure CVD method may be used, and the method will be briefly described below.

When the sputtering is performed, the back pressure before the sputtering is set to 1 × 10 ⁻⁵ Pa or less, and the single crystal silicon is used as a target in an atmosphere containing 20 to 80% of hydrogen mixed with argon. For example, argon 20%, hydrogen 8
0%. The film forming temperature is 150 ° C. and the frequency is 13.56.
MHz, sputter output 400-800W, pressure 0.
It was 5 Pa.

In the case of forming by a reduced pressure gas phase method, 450 to 550 ° C. lower than the crystallization temperature by 100 to 200 ° C., for example, 5 to 50 ° C.
At 30 ° C., disilane (Si ₂ H ₆ ) or trisilane (S
i ₃ H ₈ ) was supplied to a CVD apparatus to form a film. The pressure in the reactor was 30 to 300 Pa. Film formation rate is 50-25
0 ° / min. In order to control the threshold voltage (Vth) of the PTFT and the NTFT to be substantially the same, boron is changed to 1 × 10 ¹⁵ to 1 × 10 ¹⁸ c using diborane.
It may be added during film formation as a concentration of m- ³ .

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
It is desirable to be ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less. However, if the amount is too small, the off-state leakage current increases due to the backlight.
This concentration was chosen. If the oxygen concentration is high, crystallization is difficult, and the laser annealing temperature must be increased or the laser annealing time must be lengthened. Hydrogen is 4 × 1
It was 0 ²⁰ cm ⁻³ , which was 1 atomic% as compared with silicon 4 × 10 ²² cm ⁻³ .

In order to promote crystallization of the source and the drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ^−3.
Hereafter, preferably, it is set to 1 × 10 ¹⁹ cm ⁻³ or less, and oxygen is ion-implanted only in a channel formation region of a TFT forming a pixel to 5 × 10 ^{20 to} 5 × 10 ²¹ cm ^−3.
You may add so that it may become. By the above method, a silicon film in an amorphous state was formed to a thickness of 500 to 5000 °, in this example, 1000 °.

Thereafter, as shown in FIG. 7B, a pattern was formed by opening only the source / drain regions of the photoresist 53 using the mask P1. A silicon film 54 serving as an n-type active layer was formed thereon by a plasma CVD method. The film formation temperature is from 250 ° C. to 350 ° C. In this embodiment, the film formation temperature is 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) having a concentration of 3% are 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 suitably 0.05~0.20W / cm ^2, in this embodiment using 0.120W / cm ^2.

The specific conductivity of the n-type silicon layer formed by this method was about 2 × 10 ⁻¹ [Ωcm ⁻¹ ]. The film thickness was 50 °. Thereafter, the resist 53 is removed by a lift-off method, and the source / drain region 5 is removed.
5, 56 were formed. (FIG. 7 (C))

Using the same process, a p-type active layer 57 was formed on the resist 58. The gas introduced at that time is
Monosilane (SiH ₄ ) and monosilane-based diborane (B ₂ H ₆ ) having a concentration of 5% were used. These are PCV
Introduced into the D device at a pressure of 4 Pa, 13.56 MHz
The film was formed by applying high frequency power of 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 p-type silicon layer completed by this method is 5 × 10 ^−2.
[Ωcm ^-1 ]. The film thickness was 50 °.
(FIG. 7 (C)) Thereafter, source / drain regions 59 and 60 were formed by the lift-off method as in the case of the N-type region.
Thereafter, the silicon film 52 was removed by etching using the mask P3 to form an N-channel type thin film transistor island region 63 and a P-channel thin film transistor island region 64.

Thereafter, the source, drain and channel regions were laser-annealed using a XeCl excimer laser 61, and simultaneously the active layer was laser-doped. At this time, the laser energy has a threshold energy of 130 mJ / cm ² , and is 2
20 mJ / cm ² is required. However, 22 from the beginning
When energy of 0 mJ / 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, the first 150
After purging hydrogen at mJ / cm ² , 230
Crystallization was performed at mJ / cm ² . (FIG. 7 (D))

By the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film 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. Single crystal silicon peak 522 measured by laser Raman spectroscopy
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size, calculated from the half width, is 5
However, in practice, there are a number of regions having high crystallinity, each having a cluster structure, and a film having a structure in which each cluster is bonded to each other by silicon (anchoring) is formed. did it.

As a result, the coating exhibits a state substantially free of grain boundaries (hereinafter referred to as GB). Carriers can easily move from one cluster to another through the anchored locations between the clusters, so-called GB
Carrier mobility higher than that of polycrystalline silicon that clearly exists. That is, hole mobility (μh) = 10 to 200 cm
² / VSec, electron mobility (μe) = 15-300 cm
² / VSec is obtained.

On this, a silicon oxide film 65 was formed as a gate insulating film to a thickness of 500 to 2000 {for example, 1000}. 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.

Thereafter, 1 to 5 × 10
A silicon film having a concentration of ²¹ cm ⁻³ or a multilayer film of the silicon film and molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ was formed thereon. This was patterned using a fourth photomask P4 to obtain FIG. Gate electrode 66 for NTFT, P
A gate electrode 67 for a TFT was formed. For example, a channel length is 7 μm, and phosphorus-doped silicon is 0.2 μm as a gate electrode.
m, and molybdenum was formed thereon to a thickness of 0.3 μm. (FIG. 7E)

When aluminum (Al) is used as the gate electrode material, it is used as a fourth photomask P4.
After patterning in, by anodizing the surface,
Since the self-alignment method can be applied, the source / drain contact holes can be formed closer to the gate, so that the characteristics of the TFT can be further improved from the reduction of 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. 8 (A), the was performed as formation of a silicon oxide film by a sputtering method with the interlayer insulator 68. This silicon oxide film may be formed by an LPCVD method, a photo CVD method, or a normal pressure CVD method. For example, it was formed to a thickness of 0.2 to 0.6 μm, and then a window 79 for an electrode was formed using the fifth photomask P5. (FIG. 8A)

Thereafter, aluminum is further formed on the entire surface to a thickness of 0.3 μm by sputtering, and leads 74 and contacts 73 and 75 are formed using a sixth photomask P6 (FIG. 8B). The surface was coated with an organic resin 77 for flattening, for example, a translucent polyimide resin, and an electrode hole was formed again using a seventh photomask P7. (FIG. 8 (C))

Further, an ITO (indium tin oxide) was formed on the whole to a thickness of 0.1 μm by a sputtering method, and a pixel electrode 71 was formed using an eighth photomask P8. This ITO is deposited at room temperature to 150 ° C.
Fulfilled by annealing at 00 ° C. oxygen or air.
(FIG. 8D) The electrical characteristics of the obtained TFT are PTF
At T, the mobility is 40 (cm ² / Vs), and Vth is −5.9.
(V), the mobility of NTFT is 80 (cm ² / Vs),
Vth was 5.0 (V).

One substrate for a liquid crystal electro-optical device could be obtained by manufacturing according to the method described above. FIG. 6 shows the arrangement of the electrodes and the like of the liquid crystal display device. An N-channel thin film transistor and a P-channel thin film transistor are provided at the intersection of the first signal line 3 and the second signal line 4. Such C / TF
A matrix configuration using T was provided. NTFT13
Is connected to the second signal line 4 via a contact at the input end of the source 10, and the gate 9 is connected to the first signal line 3. The output terminal of the drain 12 is connected to the pixel electrode 17 via a contact.

On the other hand, the PTFT 22 has an input terminal of a source 20 connected to the second signal line 4 via a contact, a gate 21 connected to the signal line 3, and an output terminal of the drain 18 connected to the pixel via a contact, similarly to the NTFT. It is connected to the electrode 17. By repeating such a structure left, right, up and down, 6
A liquid crystal display device having a large pixel size of 40 × 480 or 1280 × 960 can be obtained. In this embodiment, 1920 ×
400. Thus, a first substrate was obtained.

FIG. 13 shows a method for manufacturing the other substrate. A 1 μm-thick polyimide film obtained by mixing a black pigment with polyimide was formed on a glass substrate by spin coating, and a black stripe 81 was formed using a ninth photomask P9. (FIG. 13 (A)) Thereafter, a polyimide resin mixed with a red pigment was applied to the polyimide resin by spin coating.
A film was formed to a thickness of μm, and a red filter 83 was manufactured using the tenth photomask P10. (FIG. 13 (B))

Similarly, a green filter 85 and a blue filter 86 were manufactured using the masks P11 and P12. During these fabrications, each filter was fired at 350 ° C. in nitrogen for 60 minutes. (FIG. 13 (C)) Thereafter, the leveling layer 8 was formed using a re-spin coating method.
9 was produced using transparent polyimide. (FIG. 13
(D))

Thereafter, ITO (indium tin oxide) was formed on the entire surface to a thickness of 0.1 μm by sputtering, and a common electrode 90 was formed using a fifth photomask P13. This ITO is deposited at room temperature to 150 ° C.
This was achieved by annealing in oxygen or air at ~ 300 ° C to obtain a second substrate. (FIG. 13E)

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.

FIGS. 9 and 10 are schematic structural views of the electro-optical device according to the present embodiment. The rear lighting device 22 in which the three liquid crystal panels 220 obtained in the above steps are arranged with three cold cathode tubes
Installation was performed in combination with 1. Thereafter, a tuner 223 for receiving a television wave was connected to complete the electro-optical device. Compared to a conventional CRT-type electro-optical device, the device has a planar shape, so that it can be installed on a wall or the like.

[0045] in order to then complete the present invention is added to the description of the peripheral circuits of the liquid crystal electro-optical device with reference to FIG. The configuration is such that a drive circuit 352 is connected to the information signal side wirings 350 and 351 connected to the matrix circuit of the liquid crystal electro-optical device. The drive circuit 352 has two parts when divided in a drive frequency system. One is a data latch circuit system 353 similar to the conventional driving method, which is a basic clock CLK 355 for sequentially transferring data 356.
The main configuration is 1-bit to 12-bit parallel processing.

The other is a component according to the present invention, which comprises a clock 357, a flip-flop circuit 358, and a counter 360 according to the division ratio required for gradation display. The counter 360 generates a bipolar pulse generation timing corresponding to the gradation display data sent from the data latch system 353. Further, RO of Δt → sinθ conversion is provided between the exit of the latch circuit and the data line 361.
It has been found that the use of the M table makes it easier to control the gradation display data more finely. The features of the present invention are exactly these parts. By taking two types of driving frequencies, clear digital gradation display is possible without changing the number of frames for screen rewriting. is there. Furthermore, it is possible to avoid the occurrence of flicker due to a decrease in the number of frames.

The driving circuit 364 connected to the signal lines 363 and 362 on the scanning side controls the sine wave transmitted from the sine wave oscillating circuit 365 by the flip-flop circuit 366 of the clock CLK 367 and adds a selection signal. In this manner, grayscale display is enabled by digitally voltage-controlling the timing of cutting off the sine wave on the scanning line side by the bipolar pulse on the information line side.

For example, 768 of 1920 × 400 dots,
When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 000 sets of TFTs are formed in a 300 mm square, the 16 gray scale display is limited because the variation in TFT characteristics is about ± 10%. there were. However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the variation in the characteristics of the TFT elements, it is possible to display up to 64 gradations. The display has been realized.

Embodiment 2 In this embodiment, a viewfinder for a video camera using a liquid crystal electro-optical device having a diagonal width of 1 inch is manufactured and the present invention is implemented. In the description of the reference numerals of the drawings in the present embodiment, the same parts as those of the embodiment indicate the same parts as those of the first embodiment. In this embodiment, a viewfinder was formed by forming a device using a high mobility TFT by a low-temperature process with a configuration of 387 × 128 pixels. The liquid crystal display device A-A 'cross section of the illustrated view 14 in FIG. 14 and the state of arrangement of the active devices on the substrate that used in this embodiment B-
FIG. 15 illustrates a manufacturing process showing a B ′ cross section.

In FIG. 15 (A), inexpensive 700 ° C.
Hereinafter, for example, a glass 50 that can withstand a heat treatment at about 600 ° C.
A silicon oxide film as a blocking layer is formed thereon by using a magnetron RF (high frequency) sputtering method to a thickness of 1000 to 3000.
Make it to the thickness of Å. The process conditions were a 100% oxygen atmosphere, a film formation temperature of 150 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The deposition rate using quartz or single crystal silicon as the target was 30 to 100 ° / min.

A silicon film was formed thereon by an LPCVD (low pressure gas phase) method, a sputtering method or a 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
With disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H
₈ ) was supplied to a CVD apparatus to form a film. The pressure in the reactor was 30 to 300 Pa. The deposition rate is 50-250 ° /
Minutes. In order to control the threshold voltage (Vth) of the PTFT and the NTFT to be substantially the same, boron is used in a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ by using diborane.
May be added during the film formation.

In the case of performing the sputtering method, the back pressure before the sputtering was set to 1 × 10 ⁻⁵ Pa or less, and a single crystal silicon was used as a target in an atmosphere containing 20 to 80% of hydrogen mixed with argon. For example, argon 20%, hydrogen 8
0%. The film forming temperature is 150 ° C. and the frequency is 13.56.
MHz, sputter output 400-800W, pressure 0.
It was 5 Pa.

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

The coatings formed by these methods are:
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. If the oxygen concentration is high, crystallization is difficult, and the thermal annealing temperature must be increased or the thermal annealing time must be increased. If the amount is too small, the leakage current in the off state increases due to the backlight. Therefore 4 × 10
The range was ¹⁹ to 4 × 10 ²¹ cm ⁻³ . Hydrogen is 4x
It was 10 ²⁰ cm ⁻³ , which was 1 atomic% as compared with silicon 4 × 10 ²² cm ⁻³ .

After a silicon film in an amorphous state is formed to a thickness of 500 to 5000 °, for example, 1500 ° by the above method, heat treatment is performed at a temperature of 450 to 700 ° C. for 12 to 70 hours in a non-oxide atmosphere at a medium temperature. For example, it was kept at a temperature of 600 ° C. in a hydrogen atmosphere. Since a silicon oxide film having an amorphous structure is formed on the substrate surface below the silicon film, a specific crystal nucleus is not formed by this heat treatment, and the whole is uniformly heat-annealed. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein.

By the annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film 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. Single crystal silicon peak 522 measured by laser Raman spectroscopy
A peak shifted to a lower frequency side than cm ⁻¹ is observed. Its apparent particle size, calculated from the half width, is 5
Although it is like a microcrystal having a size of 0 to 500 °, there are actually a large number of regions having high crystallinity and a cluster structure, and a semi-amorphous structure in which each cluster is bonded to each other by silicon (anchoring). Could be formed.

As a result, the coating exhibits a state substantially free of grain boundaries (hereinafter referred to as GB). Carriers can easily move from one cluster to another through the anchored locations between the clusters, so-called GB
Carrier mobility higher than that of polycrystalline silicon that clearly exists. That is, hole mobility (μh) = 10 to 200 cm
² / VSec, electron mobility (μe) = 15-300 cm
² / VSec is obtained.

On the other hand, when the film is polycrystallized by high-temperature annealing at 900 to 1200 ° C. instead of annealing at the above-mentioned medium temperature, segregation of impurities in the film occurs due to solid phase growth from nuclei, and GB Impurities such as oxygen, carbon, and nitrogen increase, and the mobility in the crystal is large. However, a barrier (barrier) is formed in GB to 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, a silicon semiconductor having a semi-amorphous or semi-crystalline structure is used for such a reason.

[0059] In FIG. 15 (A), subjected to photo-etching silicon film at a first photomask, the region for NTFT 141 (channel width 20 [mu] m) to the drawings of A-A '
On the cross-section side, a PTFT region 142 was formed on the BB 'cross-section side. On this, a silicon oxide film is used as a gate insulating film.
It was formed to a thickness of 00 to 2000 °, for example, 1000 °. 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.

Thereafter, 1 to 5 × 10
A silicon film having a concentration of ²¹ cm ⁻³ or a multilayer film of the silicon film and molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ was formed thereon. This is patterned in the second photomask was obtained FIG 15 (B). Gate electrode 9 for NTFT, PT
A gate electrode 21 for FT was formed. In this embodiment,
The NTFT channel length is 10 μm, the PTFT channel length is 7 μm, and phosphorus-doped silicon is 0.2
μm, and molybdenum was formed thereon to a thickness of 0.3 μm.

In FIG. 15C , boron is applied to the PTFT source 18 and drain 20 by 1 to 5 × 10 ^15.
It was added by ion implantation at a dose of cm ⁻² .
Then as shown in FIG. 15 (D), and the photoresist 61 is formed using a photomask. Source 10 for NTFT,
Phosphorous was added as the drain 12 by ion implantation at a dose of 1 to 5 × 10 ¹⁵ cm ⁻² .

In the case where aluminum (Al) is used as a gate electrode material, after patterning it with a second photomask and then anodizing the surface thereof, the self-alignment method can be applied. Since the drain contact hole can be formed at a position closer to the gate, the characteristics of the TFT can be further improved from the reduction of the mobility and the threshold voltage.

Next, heat annealing was performed again at 600 ° C. for 10 to 50 hours. The source 10 and the drain 12 of the NTFT and the source 18 and the drain 20 of the PTFT were formed as P ⁺ and N ⁺ by activating impurities. Channel formation regions 19 and 11 are formed below the gate electrodes 21 and 9 as semi-amorphous semiconductors.

In this way, a C / TFT can be manufactured without applying a temperature to 700 ° C. or more in all steps, even though it is a self-aligned system. Therefore, it is not necessary to use an expensive substrate such as quartz as a substrate material, and this is a process very suitable for the large pixel liquid crystal display device of the present invention.

[0065] Thermal annealing in this embodiment FIG. 15 (A), the
(D) was performed twice. However annealing 15 (A) is omitted due to the characteristics of obtaining both may be shortened in Fig. 15 annealed by doubles production time of (D) a. Figure 1
In 5 (E), it was performed as formation of a silicon oxide film by a sputtering method with the interlayer insulator 65. This silicon oxide film is formed by an LPCVD method, a photo CVD method, a normal pressure CVD method.
Method may be used. For example, it is formed to a thickness of 0.2 to 0.6 μm, and thereafter, a window 7 for an electrode is
9 was formed. Further, as shown in FIG. 15 (F), aluminum is formed on the whole of these by sputtering, and leads 74 and contacts 75 are formed using a photomask. The resin was applied and formed, and the electrode drilling was performed again using a photomask.

An ITO (indium tin oxide film) was formed by a sputtering method in order to make the two TFTs complementary and to connect the output terminals thereof to the electrodes of one pixel of the liquid crystal device as transparent electrodes. It was etched using a photomask to form the electrode 17. This I
TO was formed at room temperature to 150 ° C. and achieved by annealing at 200 to 400 ° C. in oxygen or air. In this manner, the NTFT 13, the PTFT 22, and the electrode 17 of the transparent conductive film were formed on the same glass substrate 50. (FIG. 15
(G)) The electrical characteristics of the obtained TFT are PTFT, the mobility is 20 (cm ² / Vs), and the Vth is −5.9 (V).
In the NTFT, the mobility is 40 (cm ² / Vs), and Vth
Was 5.0 (V).

According to the method as described above, one substrate for a liquid crystal device was manufactured. FIG. 14 shows the arrangement of the electrodes and the like of the liquid crystal display device. NTFT13 and PTF
T22 is provided at the intersection of the first signal line 3 and the second signal line 4. A matrix configuration using such a C / TFT is provided. The NTFT 13 is connected to the second signal line 4 via a contact at the input end of the drain 10, and the gate 9 is connected to the signal line 3 on which a multilayer wiring is formed. The output terminal of the source 12 is connected to the pixel electrode 17 via a contact.

On the other hand, the PTFT 22 has an input terminal of the drain 20 connected to the second signal line 4 via a contact, a gate 21 connected to the signal line 3, and an output terminal of the source 18 connected to the pixel via a contact in the same manner as the NTFT. It is connected to the electrode 17. The present embodiment is configured by repeating such a structure left, right, up and down.

Next, as a second substrate, an ITO (indium tin oxide film) was formed also by a sputtering method on a substrate in which a silicon oxide film was laminated on a blue glass plate by a sputtering method at 2000 °. This ITO is between room temperature and 15
A film was formed at 0 ° C. and achieved by annealing at 200 to 400 ° C. in oxygen or air. A color filter was formed on this substrate using the same method as in "Example 1" to obtain a second substrate. A polyimide precursor was printed on the substrate using an offset method, and baked at 350 ° C. for 1 hour in a non-oxidizing atmosphere, for example, 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.

FIG. 16 shows driving waveforms used in this embodiment. A ramp waveform was used instead of the sine wave used in the first embodiment. The ramp wave has a simple structure, and the gradation data
It has an advantage in that conversion to t is easy. In FIG. 16 , similarly to FIG. 1, the analog voltage applied to the pixel can be digitally obtained. For example, although the voltage is low at the pixel A, the time during which the voltage is applied to the pixel is long.
Although a high voltage is applied, the time is shorter than that of the pixel A. Therefore, visually, the difference in density between the pixel A and the element B may be smaller than expected.

In order to overcome this difficulty, as shown in FIG. 17 , the time during which no voltage is applied to both V _DD1 and V _DD2 may be made longer than the time during which the voltage is applied.
For example, if the time is the same as the time for applying a voltage, the maximum time for applying a voltage to each pixel is theoretically three times as long as the minimum time, and is actually about twice. Furthermore, the figure
Assuming that the time during which no voltage is applied to both V _DD1 and V _DD2 is twice as long as the time during which the voltage is applied, as in 17 , for example, the pixel A is applied with a voltage 40% longer than the pixel B. It's just Accordingly, the visual density error caused by the voltage applied to the pixel, besides the voltage of the pixel, can be greatly improved.

FIG. 18 shows a configuration diagram of the viewfinder according to the present embodiment. In this example, the liquid crystal electro-optical device 370 manufactured by the above method was used. For example, 38
4 × 128 dots of 49,152 sets of TFTs are 50 mm
When a normal analog gradation display is performed on a liquid crystal electro-optical device formed on a corner (36 sheets from a 300 mm square substrate), the variation in TFT characteristics is about ± 10%.
Due to its existence, 16 gradation display was the limit. However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the characteristic variation of the TFT element, it is possible to display up to 128 gradations.
A variety of 097 and 152 colors can be displayed in subtle colors.

[0074] In "Example 3" This example is added and a description is therefore to produce a projection type image display apparatus as shown in FIG. 19. In this embodiment, three liquid crystal electro-optical devices 20 are used.
1 is used to assemble a projection unit for a projection type image display device. Each of them has a configuration of 640 x 480 dots, and 307,200 in 4 inch diagonal.
A pixel was produced. The size per pixel was 127 μm square.

As a configuration of the projection type image display device, the liquid crystal electro-optical device 201 is composed of three primary colors of light, red and red.
It is installed separately for green and blue, and red filter 2
02, green filter 203, blue filter 204
, Reflector 205, prism mirrors 206, 207 and 1
A 50 W metal halide light source 208 and a focusing optical system 209 are provided.

The substrate of the liquid crystal electro-optical device used in the electro-optical device of the present embodiment was a substrate having a matrix circuit of a C / MOS configuration by using the same process as that manufactured in “Embodiment 2”. . FIG. 20 shows the outline of the structure. On the substrate 210, a fumaric acid-based polymer resin and a nematic liquid crystal
A mixture dissolved in xylene as a common solvent at a ratio of 5:35 was formed to a thickness of 10 μm by die casting. Thereafter, the solvent was removed in a nitrogen atmosphere at 120 ° C. for 180 minutes to form a liquid crystal dispersion layer 211. In this case, it was found that when the pressure was slightly reduced from the atmospheric pressure, the tact time could be reduced.

Thereafter, an 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.

FIG. 21 shows the functional configuration of the driving IC used in this embodiment. The configuration on the information electrode side is the same as in "Example 1". The drive circuit 400 connected to the scan-side wirings 406 and 407 outputs the ramp wave transmitted from the ramp wave oscillation circuit 405 to the flip-flop circuit 4 of the clock CLK 408.
03 and 404, and a selection signal is added. In this manner, gradation display is enabled by digitally controlling the voltage at which the ramp wave on the scanning line side is cut off by the bipolar pulse on the information line side.

For example, 307 × 2 of 640 × 480 dots
When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square, 16 gray scale displays are limited due to a variation in TFT characteristics of about ± 10%. there were. However, when the digital gradation display according to the present invention is performed, the display is hardly affected by the variation in the characteristics of the TFT elements, so that it is possible to display up to 256 gradations.
The display of various and subtle colors of 7,216 colors can be realized.

In the case of displaying software such as a telescopic image, for example, even a "rock" of the same color has a slightly different color due to the degree of light corresponding to the minute depressions. In the case where a display close to natural colors is to be performed, 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. The liquid crystal electro-optics, 19
It can be used not only for the front type projection TV shown in (1) but also for the rear type projection TV.

[0081] In "Example 4" This embodiment uses a reflective-type liquid crystal dispersion type display device as shown in FIG. 22, added and a description is therefore to produce a portable computer for an electro-optical device. The first substrate used in this example was manufactured in the same process as in "Example 1". A mixture obtained by dissolving a nematic liquid crystal in which a fumaric acid-based polymer resin and a black pigment were mixed at a ratio of 15% in xylene, which is a common solvent, in a ratio of 65:35 on the substrate 210 by a die casting method was 10 μm.
m at a temperature of 120 ° C. in a nitrogen atmosphere.
The solvent was removed for 0 minutes to form a liquid crystal dispersion layer 211.

Here, a flat display, which was difficult in the dispersion type liquid crystal display due to the use of a black dye, appears black when scattering light (when there is no electric field) and white when transmitting (when applying an electric field). It can be displayed and can be displayed like characters written on paper. In addition, as the reverse structure, it is possible to express white when scattered and express black when transmitted without mixing a black pigment. However, in this case, the back side shown below needs to be black. This is also possible to display like characters written on paper.

Thereafter, an 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 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.

[0084]

According to the present invention, digital gray scale display is performed in contrast to conventional analog gray scale display. The effect is, for example, 640 × 40
Assuming a liquid crystal electro-optical device having a pixel number of 0 dots, it is extremely difficult to manufacture all the characteristics of all 256,000 TFTs without variation, and in reality, mass production and yield Considering that the 16 gray scale display is considered to be the limit, in order to clarify the applied voltage level, not the analog value but the reference voltage value is input as a signal from the controller side, and the reference signal is input to the TFT.
Is controlled by a digital value, thereby controlling the voltage applied to the TFT, thereby obtaining the TF.
The present invention is characterized in that a method for covering the variation in the characteristics of T is adopted, and therefore, a clear digital gradation display is possible.

Another advantage is that by using two driving frequencies, clear digital gradation display is possible 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. For example, 640 × 400 dots 256,
When a normal analog gray scale display is performed on a liquid crystal electro-optical device in which 000 sets of TFTs are formed in a 300 mm square, the 16 gray scale display is limited because the variation in TFT characteristics is about ± 10%. there were.

However, when the digital gradation display according to the present invention is performed, since it is hard to be affected by the variation in the characteristics of the TFT elements, it is possible to display up to 256 gradations, and in the color display, a variety of 16,777,216 colors can be obtained. Thus, a subtle color display can be realized. In the case of displaying software such as television images, for example, even a “rock” made of the same color has a slightly different color due to its minute dents and the like. In the case where a display close to natural colors is to be performed, difficulties are required at 16 gradations. With the gradation display according to the present invention, it is possible to impart these minute color changes.

The present invention is characterized in that 64 gray scales, 256 gray scales or more gray scales can be displayed without changing the number of frames. This does not mean that the number of frames is limited to 30 to 60 frames. Obviously, increasing the number of frames to improve the image quality is not contrary to the intention of the present invention.

Further, in the embodiments of the present invention, description has been made mainly on a TFT using silicon, but a TFT using germanium can be used similarly. In particular, the electron mobility of the single crystal germanium 3600 cm ² / Vs, the Hall mobility and 1800 cm ² / Vs, the single crystal silicon value of (1350 cm ² / Vs in electron mobility, 480 cm ² / Vs in hole mobility) Because of its superior properties, it is a very excellent material for implementing the present invention that requires high-speed operation.

Further, germanium has a lower transition temperature from an amorphous state to a crystalline state than silicon, and is suitable for a low-temperature process. In addition, the nucleation rate during crystal growth is low, and therefore, generally, large crystals are obtained when polycrystals are grown. Thus, germanium has characteristics comparable to those of silicon.

[Brief description of the drawings]

FIG. 1 shows a driving waveform according to the present invention.

FIG. 2 shows electro-optical characteristics of a nematic liquid crystal.

FIG. 3 shows current-voltage characteristics of a TFT made of polysilicon and amorphous silicon.

FIG. 4 shows a matrix configuration according to the invention.

FIG. 5 shows a matrix circuit according to an embodiment.

FIG. 6 shows a planar structure of a device according to an example.

FIG. 7 illustrates a TFT process according to an embodiment.

FIG. 8 illustrates a TFT process according to an embodiment.

FIG. 9 shows a structure of a liquid crystal display device (television) according to the embodiment.

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

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

FIG. 12 shows a frame gradation display according to a conventional example.

FIG. 13 shows a process of a color filter according to an example.

FIG. 14 shows a planar structure of a device according to an example.

FIG. 15 illustrates a TFT process according to an embodiment.

FIG. 16 shows another driving waveform according to the present invention.

FIG. 17 shows another driving waveform according to the present invention.

FIG. 18 shows the structure of a viewfinder according to an embodiment.

FIG. 19 shows a structure of a front projection television according to an embodiment.

FIG. 20 shows a liquid crystal electro-optical device according to an example.

FIG. 21 shows a system configuration of a drive circuit according to an embodiment.

FIG. 22 shows a configuration of a portable personal computer according to an embodiment.

[Explanation of symbols]

 Reference Signs List 50 glass substrate 51 silicon oxide film 52 silicon film 53 resist 54 N-type silicon film 55 NTFT source region 56 NTFT drain region 57 P-type silicon film 58 resist 59 PTFT source region 60 PTFT drain region 65 silicon oxide film 66 gate electrode of NTFT 67 gate electrode of PTFT 68 interlayer insulating film 79 window for electrode 74 lead 73.75 contact 77 organic resin for planarization 17, 71 pixel electrode 13 NTFT 22 PTFT 10 source of NTFT 9 gate of NTFT 12 NTFT 20 PTFT source 21 PTFT gate 18 PTFT drain 141 NTFT region 142 PTFT region

Claims (5)

(57) [Claims] And 1. A substrate, a plurality of scanning from X ₁ provided on the substrate X _{N (N} is an integer) and a plurality of information lines to, from Y ₁ provided on the substrate to Y _M A line (M is an integer), a plurality of pixel electrodes provided in a matrix on the substrate, and a plurality of thin film transistors provided on the substrate, and any of the information lines X _n (n is The thin film transistor provided at the intersection of an integer, 1 ≦ n ≦ N) and any of the scanning lines Y _m (m is an integer, 1 ≦ m ≦ M) includes a P-channel thin film transistor and an N-channel thin film transistor. from it, one of a source and a drain of the n-channel and P-channel type thin film transistor, to one of the pixel electrodes provided in the crossing portion, the other scanning lines Y _m, the gate electrode is in the information line X _n Connected to each other Relates to a drive method for an electro-optical device are the steps of applying a reference signal having a reference voltage value to the voltage changes at a constant period only to the scanning line Y _m, In the above process, each of the information line from X ₁ to X _N Applying a bipolar signal to the electro-optical device. 2. A substrate, a plurality of scanning from X ₁ provided on the substrate X _{N (N} is an integer) and a plurality of information lines to, from Y ₁ provided on the substrate to Y _M A line (M is an integer), a plurality of pixel electrodes provided in a matrix on the substrate, and a plurality of thin film transistors provided on the substrate, and any of the information lines X _n (n is The thin film transistor provided at the intersection of an integer, 1 ≦ n ≦ N, and any of the scanning lines Y _m (m is an integer, 1 ≦ m ≦ M) includes a P-channel thin film transistor and an N-channel thin film transistor. from it, one of a source and a drain of the n-channel and P-channel type thin film transistor, to one of the pixel electrodes provided in the crossing portion, the other scanning lines Y _m, the gate electrode is in the information line X _n Connected to each other During relates to a drive method for an electro-optical device are, the only scanning lines Y _m, during the application time, the step of applying a reference signal whose level varies, for the reference signal to the scan line Y _m is applied To
The bipolar signal information lines from X ₁ to X _N, the steps of applying at a timing corresponding to the magnitude of the voltage applied to the pixel electrode provided on the intersections of the information lines X _n and the scan line Y _m A method for driving an electro-optical device, comprising: Wherein on the pixel electrode, Nemachiikku liquid crystal, a driving method of distributed electro-optical device according to any claim 1 liquid crystal material is provided in乃<br/> optimal 2 wherein the liquid crystal. 4. The reference signal is a sine wave, a cosine wave, a triangular wave,
3. The driving method for an electro-optical device according to claim 1, wherein the driving method is one of a ramp wave. 5. The electro-optical device according to claim 1, further comprising another substrate facing the pixel electrode, and an electro-optical device having a liquid crystal material layer therebetween. Drive method.