JP2754293B2 - Driving method of 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 electro-optical device and, more particularly, to an image display method for an active liquid crystal electro-optical device. According to the present invention, a pulse voltage (digital signal) is applied to one input terminal of an active element and a control signal voltage (digital signal) is applied to another input terminal at an arbitrary timing, and thereafter, a pulse signal is applied. By applying a signal voltage in a state where no voltage is applied, a state in which a voltage is applied to a pixel of the electro-optical device for an arbitrary time is realized, so that a visually-clear gradation level can be set. Display method.

[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. 3 shows the electro-optical characteristics of a nematic liquid crystal, which is a typical liquid crystal material. Low applied voltage V
At a (point A), the amount of transmitted light is almost 0%, at Vb (point B), about 20%, at Vc (point C), about 70%, and at Vd (point D).
In this case, the amount of transmitted light changes with the voltage, such as 100%. In other words, if only points A and D are used, black and white 2
If the gradation display uses the rising part of the electro-optical characteristic as at points B and C, an intermediate gradation display becomes possible.

Conventionally, in the case of gradation display of a liquid crystal electro-optical device using a TFT, in an active matrix type liquid crystal electro-optical device, a thin film transistor (TFT) is used as an active element and a gate applied voltage of the TFT or a voltage between a source and a drain is applied. The voltage applied to the liquid crystal is adjusted in an analog manner by changing the applied voltage to perform gradation display.

[0005]

However, when actually manufacturing such a liquid crystal electro-optical device, a TFT
Characteristic is remarkably large, and the conventional gradation display method has a limit of 16 gradations. Therefore, a completely new gradation method has been demanded.

[0006]

In view of the above, the present invention proposes a gradation display method completely different from the conventional concept of gradation display. That is, by controlling two input signals to the active element, a state in which a voltage is applied to a pixel is controlled. The present inventors have found that even when a certain voltage is applied to the pixel, the brightness looks different if the time is different. The present invention utilizes the characteristics of the present invention positively, and is a completely innovative one which has never been seen before.

FIG. 2 shows an example of an active matrix circuit of a liquid crystal display device necessary for implementing the present invention.
In the present invention, since the active element is required to respond in a short time of 100 nsec or less, it is necessary to form a circuit that operates at high speed. For this purpose, switching is not performed by using only an N-channel thin film transistor (NTFT) or a P-type thin film transistor (PTFT) as in the related art, but as shown in FIG.
It is necessary to use a modified transfer gate type circuit configuration in which T operates in a complementary manner.

In this example, a matrix of N rows and M columns is configured, but for the sake of simplicity, FIG. 2 shows only the vicinity of elements of n rows and m columns in the matrix. If you expand the same thing up, down, left and right, you will get a complete one.

[0009] As shown in the figure, four modified transfer gates are depicted, and the source of each modified transfer gate is connected to _Ym or Ym _{+ 1} (hereinafter collectively referred to as Y line). Deformation transfer
The gate of the gate is connected to _Xn or _{Xn + 1} (hereinafter collectively referred to as X-ray). The drains of the modified transfer gate are liquid crystal pixels Zn _{, m} , Z
_{n, m + 1} , Zn _{+ 1, m} , Zn _{+ 1, m + 1} . NTF at the modified Tonsfar Gate
Since T and PTFT are symmetric, their positions may be interchanged. Although not shown in the figure, a capacitor may be artificially inserted in parallel with the capacitor of the pixel. At this time, the inserted capacitor has an effect of suppressing a decrease in voltage due to spontaneous discharge. The capacitance of the capacitor is desirably several times to approximately 100 times the capacitance of the pixel, and preferably 10 times or less. The reason for this is that the existence of an excessive capacity prevents the high-speed operation, which is the object of the present invention and is a feature of the present invention.

Next, an example of operation of a circuit using such a circuit will be described with reference to FIG. Hereinafter, V _Ym , V
The _{Xn, respectively,} means the potential applied to the Y m, _{X n, also, V Zn,} and _m, the liquid crystal pixel _{Z n} shown in FIG. _2, means the TFT side of the potential of the _m. For simplicity, if the potential of the counter electrode of the liquid crystal pixel is set to 0 V, V
_{Zn, m} means a voltage applied to a liquid crystal pixel.

[0011] First, the _{Y 1} line, applying a rectangular pulse as shown in FIG. Then, while this pulse continues, each X-ray is provided with a pulse signal (hereinafter, referred to as a bipolar pulse) whose polarity is inverted as shown in the figure.
Is intentionally applied at an arbitrary timing.

At this time, the liquid crystal pixels Zn _{, m} , Z
Looking at _{n, m + 1} , Zn _{+ 1, m} , and Zn _{+ 1, m + 1} , it is understood that no voltage is applied to any of the pixels. This voltage also Y _{m + 1} to Y _m is because not supplied. At this stage, the pixels to which any voltage may be applied are the pixels in the first column, that is, Z ₁₁ , Z ₂₁ ,. . Z _N1 . Then Y ₂
A similar rectangular pulse is applied to each X-ray,
Also, a bipolar pulse is applied. At this time, a voltage is applied to the pixels in the second column, and an image in the second column is obtained.

In this way, voltages are applied one after another,
Eventually, the rectangular pulse is applied to the Y _m. Then, a bipolar pulse is applied to the X-ray. At this time, the timing (start time) of the pulse applied to each X-ray is not the same. For example, _Xn has X
_A pulse is applied earlier than _{n + 1} . At the moment the pulse is applied, the capacitor of the pixel is charged and the pixel is energized. As a result, a voltage is applied to the pixel Zn _{, m} before the pixel Zn _{+ 1, m} . here,
Although the time required to charge the capacitor of the liquid crystal pixel is neglected, the time constant of the TFT and the capacitor is actually several nsec at most, whereas the width of the bipolar pulse is several hundred nsec. Can be ignored. Took state of voltage to the pixels, after the rectangular pulse of the Y _m is turned off, is interrupted by the bipolar pulse is applied to all the X-ray. That is, at this time, since no voltage is applied to any of the Y lines,
The electric charge stored in the pixel is released, and the voltage of the pixel becomes zero.

Next, a pulse voltage is applied to _{Ym + 1} .
Then, a bipolar pulse is applied to the X-ray. At that time, since a voltage is applied to Y _{m + 1} , the pixels Zn _{, m + 1} and Z
_Electric charges are accumulated in _{n + 1 and m + 1,} and the voltage state continues for a certain time, respectively.

[0015] In this way, the voltage until Y _M is Yuki is applied in sequence, one screen (also referred to as frame) is formed. At this time, it should be noted that the images are displayed in a so-called dynamic mode in which the images appear one after another in each column, and disappear when the image in the next column appears. However, by connecting a diode in series with the transfer gate, for example, it is possible to prevent loss of charge and consequently to a static mode, such as a normal active matrix. Also, for example, in parallel with the liquid crystal pixels,
It is also possible to connect a capacitor made of a ferroelectric material and retain the charge of the liquid crystal pixel by utilizing the hysteresis of the electrostatic characteristics of the ferroelectric material.

As is apparent from the above example, gradation display can be performed. The gradation accuracy is obtained by dividing the time width of the signal voltage applied to the Y line by the width of the bipolar pulse. It is considered to be about the same. The time required to form one screen is usually about 30 msec. In the example of FIG. 1, since a voltage is applied to the Y ₁ is a single screen of the time,
Y _M voltage is applied to, again, a time until a voltage is applied to the Y _1. 30 msec for one screen,
In the case of a display device having M = 480, ie, 480 rows of lines, the bipolar pulse must be 250 nsec to achieve 256 gray levels.

In the above description, for simplicity, the zero level and the voltage level of the signal are clarified. However, the signal level is equal to or lower than the threshold voltage of an electro-optical material such as a liquid crystal or a TFT. It is not absolutely necessary that the voltage be zero, since only the question of Also,
In the above description, since the voltage is a relative physical quantity with reference to the potential at an arbitrary point, it is apparent that the pulse may have an opposite polarity. Further, an appropriate offset voltage may be applied to the counter electrode of the pixel. Further, in the above example, the screen is scanned in order of one line at a time. However, first, the first line, the third line, the fifth line, and the like are scanned, and then the second line, the fourth line, and the sixth line are scanned. Needless to say, a so-called interlaced scanning method in which scanning is performed like eyes is also possible.

[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 TF at that time
T is polycrystalline silicon using laser annealing.

FIG. 4 shows an actual arrangement of electrodes and the like corresponding to this circuit configuration for one pixel. First, FIG. 5 Contact a manufacturing method of a liquid crystal panel used in this embodiment
This will be described with reference to FIG. In FIG. 5 (A), a non- expensive material other than quartz glass is 700 ° C. or less, for example, about 60 ° C.
Magnetron R on glass 50 that can withstand heat treatment at 0 ° C.
A silicon oxide film as the blocking layer 51 is formed to a thickness of 1000 to 3000 ° by using F (high frequency) sputtering. Process conditions are 100% oxygen atmosphere, film formation temperature 1
The temperature was 5 ° C., the output was 400 to 800 W, and the pressure was 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
At 0 ° C., the temperature was set to 320 ° C. in this embodiment, and monosilane (S
iH ₄ ) was used. Not limited to monosilane (SiH ₄ )
Disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ )
May be used. These were introduced into a PCVD apparatus at a pressure of 3 Pa, and high-frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is 0.02 to 0.10 W /
cm ² is appropriate, and in this embodiment, 0.055 W / cm
² was used. The flow rate of monosilane (SiH ₄ ) is 2
At 0 SCCM, the deposition rate at that time was about 120 ° / min. In order to control the threshold voltage (Vth) of the PTFT and the NTFT substantially the same, boron may be added at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane during the film formation. The plasma CVD is used to form a silicon layer to be a channel region of a TFT.
In addition, a sputtering method or a low pressure CVD method may be used, 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, and single crystal silicon is used as a target in an atmosphere in which hydrogen is mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%. The deposition temperature is 150 ° C., the frequency is 13.56 MHz,
The sputter output was 400-800 W and the pressure was 0.5 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. 5B, 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 was from 250 ° C. to 350 ° C. In this example, the film formation temperature was 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,
A film was formed by applying a high frequency power of 13.56 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 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. 5 (C))

Using a similar process, a p-type active layer was formed. The gas introduced at that time is monosilane (Si
H ₄ ) and monosilane-based diborane (B ₂ H ₆ ) 5%
Concentrations were used. These are placed in a PCVD apparatus at 4 Pa.
Was introduced at a pressure of, it was formed by adding 13.56MHz high frequency power. At this time, the high frequency power is 0.05 to 0.20.
W / cm ² is appropriate, and in this embodiment, it is 0.120 W / cm ^2.
cm ² was used. The specific conductivity of the p-type silicon layer completed by this method was about 5 × 10 ⁻² [Ωcm ⁻¹ ]. The film thickness was 50 °. (FIG. 5 (C)) Thereafter, source / drain regions 59 and 60 were formed by a 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. (Figure
5 (D))

After that, using a XeCl excimer laser, the source / drain / channel regions were laser-annealed, and at the same time, the active layer was laser-doped. At this time, the laser energy has a threshold energy of 130 mJ / cm ² and is 220 220 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, so that 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
/ Cm ² was crystallized.

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 top of this, a silicon oxide film 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. 5E)

When aluminum (Al) is used as a gate electrode material, the aluminum is used as a fourth photomask 69.
After patterning in, by anodizing the surface,
Since the self-alignment method can be applied, the source and drain contact holes can be formed at positions closer to the gate, so that the mobility and threshold voltage can be further reduced, and the characteristics of the TFT can be further improved.

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 . 6A, a silicon oxide film was formed on the interlayer insulator 68 by the above-described sputtering method. This silicon oxide film is formed by LPCVD, optical CVD
Or a normal pressure CVD method. For example, 0.2-0.
6 μm thick, and then a fifth photomask P
5 was used to form an electrode window 79. (FIG. 6 (A))
Then, further, 0.3 μm of aluminum
After forming a lead 74 and contacts 73 and 75 using a sixth photomask P6 with a thickness of m (FIG. 6B) , the surface is flattened by an organic resin 7 for planarization.
7 For example, a translucent polyimide resin was applied and formed, and the electrode drilling was performed again using the seventh photomask P7. (FIG. 6
(C)) Further, an ITO (indium tin oxide) is formed on the entire surface to a thickness of 0.1 μm by a sputtering method.
The pixel electrode 71 was formed using the photomask P8.
This ITO is formed at room temperature to 150 ° C.
Fulfilled by annealing in oxygen at 0 ° C or in air. (Figure
6 (D))

The electrical characteristics of the obtained TFT are PTFT
And the mobility is 40 (cm ² / Vs) and the 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 manufactured according to the above method was obtained.

FIG. 4 shows the arrangement of the electrodes and the like of the liquid crystal display device. N-channel type thin film transistor and P
The channel type thin film transistor is connected to the first signal line 3 and the second signal line.
At the intersection with the signal line 4. A matrix configuration using such a C / TFT is provided. NT
The FT is connected to the second terminal through the contact at the input terminal of the drain 10.
And the gate 9 is connected to the first signal line 3. The output terminal of the source 12 is connected to the pixel electrode 17 via a contact.

On the other hand, in the PTFT, the input terminal of the drain 20 is connected to the second signal line 4 via a contact, the gate 21 is connected to the signal line 3, and the output terminal of the source 18 is connected to the pixel via the contact in the same manner as the NTFT. It is connected to the electrode 17.
By repeating such a structure left and right, up and down, 640
A liquid crystal display device having a large pixel size such as × 480 or 1280 × 960 can be obtained. In this embodiment, 1920 × 40
0 was set. Thus, a first substrate was obtained.

FIG. 7 shows a method for manufacturing the other substrate. A polyimide resin obtained by mixing a black pigment with polyimide is formed on a glass substrate to a thickness of 1 μm using a spin coating method,
Black stripe 8 using ninth photomask P9
1 was produced. (FIG. 7A) 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 83 was manufactured using a tenth photomask P10. (FIG. 7B) Similarly, using the masks P11 and P12, the green filter 85 is used.
And a blue filter 86 were produced. During the production, each filter was fired at 350 ° C. in nitrogen for 60 minutes. (FIG. 7 (C)) Thereafter, the leveling layer 89 was formed using a transparent polyimide, also by using the spin coating method. (FIG. 7 (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. 7E)

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. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves to complete a wall-mounted TV. Compared to a conventional CRT system television, the device has a flat shape, so that it can be installed on a wall or the like. The operation of this LCD TV is shown in FIG.
Were confirmed by applying a signal substantially equivalent to that shown in FIG.

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

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. FIG. 4 shows the arrangement of the active elements on the substrate of the liquid crystal display device used in this embodiment, and FIG.
FIG. 8 illustrates a manufacturing process showing a section taken along the line -B '.

[0046] In FIG. 8 (A), the inexpensive, 700 ° C. or less, for example, a silicon oxide film as a blocking layer using magnetron RF (radio frequency) sputtering method on the glass 50 capable of withstanding heat treatment at about 600 ° C. 1000 to 3000Å
To a thickness of 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 deposition rate using quartz or single crystal silicon as the target was 30 to 100 ° / min.

On this, a silicon film was formed by LPCVD (low pressure gas phase), sputtering or plasma CVD. 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 was 20% and hydrogen was 80%. The deposition temperature is 150 ° C., the frequency is 13.56 MHz,
The sputter output was 400-800 W and the pressure was 0.5 Pa.

When a silicon film is formed by a 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 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, 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 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, no specific nucleus is present in 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 that can be said to be 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, if the film is polycrystallized by annealing at a high temperature of 900 to 1200 ° C. instead of annealing at the medium temperature as described above, segregation of impurities in the film occurs due to solid phase growth from nuclei. 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.

[0055] In FIG. 8 (A), the subjected to photo-etching silicon film at a first photomask, the A-A 'cross-sectional side region 13 (channel width 20 [mu] m) figures for NTFT, area for PTFT No. 22 was formed on the BB 'cross section side.

On this, a silicon oxide film 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.

After this, 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 8 (B). Gate electrode 9 for NTFT, PTF
A gate electrode 21 for T was formed. In this embodiment, NT
The channel length for FT is 10 μm, the channel length for PTFT 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.

[0058] In FIG. 8 (C), the source 18 for the PTFT, to drain 20, 1~5 × ^{10 15} boron
It was added by ion implantation at a dose of cm ⁻² .

[0059] As next of FIG. 8 (D), the photoresist 6
1 was formed using a photomask. Source 10 for NTFT, 1 to 5 × ^{10 15} phosphorus as drain 12
It was added by ion implantation at a dose of cm ⁻² .

When aluminum (Al) is used as a gate electrode material, after patterning it with a second photomask and then anodic oxidizing the surface, 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.

[0063] Thermal annealing in this embodiment FIG. 8 (A), the
(D) was performed twice. However omitted by annealing obtaining characteristics of FIG. 8 (A), the both may be shortened in doubles by annealing manufacturing time in FIG. 8 (D) a. In FIG. 8 (E), was performed as formation of a silicon oxide film by a sputtering method with the interlayer insulator 65. 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 66 for an electrode was formed using a photomask. Further, as shown in FIG. 8 (F), aluminum is formed on the whole by sputtering, and leads 71 and contacts 72 are formed using a photomask.
The surface was coated with an organic resin 69 for flattening, for example, a translucent polyimide resin, and the electrode was drilled again using a photomask.

An ITO (indium tin oxide film) was formed by a sputtering method so that the two TFTs had a complementary structure, and their output terminals were connected 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 atmosphere. 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. 8
(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).

One substrate for a liquid crystal device was manufactured according to the method described above. FIG. 4 shows the arrangement of the electrodes and the like of the liquid crystal display device. A matrix configuration using such a C / TFT is provided.

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 by 2000 ° on a blue plate glass by a sputtering method. 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 by 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.

The operation of this liquid crystal display device was confirmed by signal driving substantially equivalent to that shown in FIG.

For example, 384 × 128 dots 49, 15
Two sets of TFTs are placed in a 50 mm square (36 mm from a 300 mm square substrate).
When a normal analog gray scale display is performed on a liquid crystal electro-optical device prepared in a multi-panel display, 16 gray scale display is the limit because there is about ± 10% variation in TFT characteristics. . 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, and in the color display, 2,097,152 colors are various and delicate. Color display has been realized.

In the case of displaying software such as a television 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. 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.

Example 3 In this example, a wall-mounted television was manufactured using a liquid crystal display device having a circuit configuration as shown in FIG. 2, and a description thereof will be given. Also T at that time
FT was polycrystalline silicon using laser annealing.

Hereinafter, a method for manufacturing a TFT portion will be described with reference to FIG. In FIG. 9 (A), the following 700 ° C. less expensive such as quartz glass, for example, about 600 ° C.
Magnetron RF on glass 100 that can withstand heat treatment
A silicon oxide film as the blocking layer 101 is formed to a thickness of 1000 to 3000 ° by using (high frequency) sputtering. Process conditions are 100% oxygen atmosphere, film formation temperature 1
The temperature was 5 ° C., the output was 400 to 800 W, and the pressure was 0.5 Pa.
The deposition rate using quartz or single crystal silicon as the target was 30 to 100 ° / min.

A silicon film 102 was formed thereon by a plasma CVD method. Film formation temperature is 250 ° C-3
In this example, the temperature was set to 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) between 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.

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 in which hydrogen was mixed with 20 to 80% of argon. For example, argon was 20% and hydrogen was 80%. The deposition temperature is 150 ° C., the frequency is 13.56 MHz,
The sputter output was 400-800 W and the pressure was 0.5 Pa.

In the case of forming by a reduced pressure gas phase method, 450 to 550 ° C. lower by 100 to 200 ° C. than the crystallization temperature, for example, 5
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 used to form 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 further 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 °.

After that, the photoresist 103 is
Using No. 1, a pattern was formed in which only the region to be the source / drain region of the NTFT was opened. Using the resist 103 as a mask, phosphorus ions are implanted by ion implantation at a dose of 2 × 10 ^{14 to} 5 × 10 ¹⁶ cm ⁻² , preferably 2 × 10 ¹⁶ cm ⁻² to form the n-type impurity region 104. . After that, the resist 103 was removed.

Similarly, a resist 105 was applied, and a pattern was formed using a mask P3 in which only the regions to be the source / drain regions of the PTFT were opened. Then, using the resist 105 as a mask, a p-type impurity region was formed. As an impurity, boron is used, and an ion implantation method is used, and 2 × 10 ^{14 to} 5 × 10 ¹⁶ cm ⁻² ,
Preferably, an impurity is introduced only by 2 × 10 ¹⁶ cm ⁻² . Like this. To give 9 a (B).

After that, a thickness of 50 to 3
00 nm, for example, 100 nm silicon oxide film 107
Was formed by the above-mentioned RF sputtering method. And
Using a XeCl excimer laser, the source, drain and channel regions are crystallized by laser annealing.
Activated. At this time, the threshold energy of the laser energy is 130 mJ / cm ² , and 220 mJ / cm ² is required to melt the entire film thickness. However, when an energy of 220 mJ / cm ² or more is irradiated from the beginning, 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
After purging hydrogen at 50 mJ / cm ² , 23
Crystallization was performed at 0 mJ / cm ² . (FIG. 9 (C))
Et al., After the end of laser annealing was removed silicon oxide film 107 is.

Thereafter, an NTFT region 111 and a PTFT region 112 in an island shape were formed using a photomask P3. On this, a silicon oxide film 108 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 is patterned in the fourth photomask P4 was obtained FIG 9 (D). A gate electrode 109 for NTFT,
A gate electrode 110 for PTFT was formed. For example, a channel length is 7 μm, and phosphorus-doped silicon is used as a gate electrode in 0.1 μm.
2 μm, and molybdenum was formed thereon with a thickness of 0.3 μm.

In the case where aluminum (Al) is used as the gate electrode material, it is used as the fourth photomask P4.
After patterning in, by anodizing the surface,
Since the self-alignment method can be applied, the source and drain contact holes can be formed at positions closer to the gate, so that the mobility and threshold voltage can be further reduced, and the characteristics of the TFT can be further improved.

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.

[0086] In FIG. 9 (E), was performed as formation of a silicon oxide film by a sputtering method with the interlayer insulator 113. This silicon oxide film is formed by LPCVD, optical CVD
Or a normal pressure CVD method. For example, 0.2-0.
6 μm thick, and then a fifth photomask P
5 was used to form a window 117 for an electrode. Thereafter, aluminum was further formed to a thickness of 0.3 μm on the whole by sputtering, and leads 116 and contacts 114 and 115 were formed using a sixth photomask P6 . As after, for planarizing the surface organic resin 119, for example, a light-transmitting polyimide resin is formed by coating, was electrodes drilling again in a seventh photomask P7. Furthermore, ITO (indium tin oxide) was formed on the entire surface to a thickness of 0.1 μm by a sputtering method, and a pixel electrode 118 was formed using an eighth photomask P8. 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. (FIG. 9 (F))

The electrical characteristics of the obtained TFT are PTFT
And the mobility is 35 (cm ² / Vs) and the Vth is −5.9.
(V), the mobility of NTFT is 90 (cm ² / Vs),
Vth was 4.8 (V).

One substrate for a liquid crystal electro-optical device manufactured according to the above method was obtained. The method for fabricating the other substrate is the same as that in the first embodiment, and will not be described.
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 a potential wiring were connected to leads on the substrate, and a polarizing plate was adhered on the outside to obtain a transmissive liquid product electro-optical device. This was connected to a rear lighting device in which three cold cathode tubes were arranged, and a tuner for receiving TV radio waves to complete a wall-mounted TV. Compared to a conventional CRT system television, the device has a flat shape, so that it can be installed on a wall or the like. The operation of this LCD television is the same as that shown in FIG.
This was confirmed by applying substantially equivalent signals to the liquid crystal pixels.

[0089]

The present invention is characterized in that digital gray scale display is performed in contrast to the conventional analog gray scale display. As an effect, assuming a liquid crystal electro-optical device having a number of pixels of 640 × 400 dots, for example, it is very difficult to manufacture all the 256,000 TFTs without variation in characteristics. In consideration of mass productivity and yield, 16-gradation display is considered to be the limit. However, as in the present invention, gradation display is performed purely by digital control without adding analog signals at all. By doing so, gray scale display of 256 gray scale display or more is possible. Since it is a complete digital display,
The ambiguity of the gradation due to the variation in the characteristics of the FT was completely eliminated. Therefore, even if the variation in the TFT was slight, a very uniform gradation display was possible. Therefore, while the yield has been extremely low in order to obtain a TFT having a small variation, the yield of the TFT is no longer a problem according to the present invention. Was completed.

For example, 256,0 of 640 × 400 dots
When a normal analog gradation display is performed on a liquid crystal electro-optical device in which 00 sets of TFTs are formed in a 300 mm square,
Since there is about ± 10% variation in TFT characteristics,
Six gradation display was the limit. 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.
A variety of 16 colors can be displayed in subtle colors. 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. If you try to display something close to the colors of nature,
Difficulty is required for 16 gradations. With the gradation display according to the present invention, it is possible to impart these minute color changes.

In the embodiment of the present invention, T using silicon is used.
The explanation has been added focusing on FT.
FT can be used as well. In particular, the electron mobility of single crystal germanium is 3600 cm ² / Vs and the hole mobility is 1800 cm ² / Vs, which is the value of single crystal silicon (1350 cm ² / Vs in electron mobility and 480 c in hole mobility).
m ² / Vs), which is an extremely excellent material for implementing the present invention that requires high-speed operation. In addition, 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.

In order to explain the technical concept of the present invention, an electro-optical device using liquid crystal, particularly a display device has been mainly described as an example. However, in order to apply the idea of the present invention, no display device is required. It is not necessary to use a so-called projection type television, another optical switch, or an optical shutter. Further, it is apparent that the present invention can be applied to electro-optical materials that are not limited to liquid crystals, as long as optical characteristics change due to electric influences such as electric fields and voltages.

[Brief description of the drawings]

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

FIG. 2 shows an example of a driving waveform according to the present invention.

FIG. 3 shows an example of gradation display characteristics of a liquid crystal according to the present invention.

FIG. 4 shows an example of a planar structure of a device according to the present invention.

FIG. 5 shows a TFT process according to an embodiment.

FIG. 6 shows a TFT process according to an embodiment.

FIG. 7 shows a process of a color filter according to an example.

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

FIG. 9 shows a TFT process according to an embodiment.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-43435 (JP, A)

Claims (4)

(57) [Claims] And 1. A substrate, a plurality of signal lines from the X ₁ that is provided on the substrate to X _{N (N} is an integer) and (X-ray), is provided on the substrate, intersecting the X-ray Te, Z _(the M integer) Y _M from Y ₁ constituting a matrix and a plurality of signal lines to (Y-rays), from Z ₁₁ arranged in matrix on the substrate
A plurality of pixel electrodes up to _NM (N and M are integers, N ≧ 1, M ≧ 1), a capacitor provided in parallel with the pixel electrode, and a plurality of thin film transistors provided on the substrate. The thin film transistor provided at the intersection of an arbitrary signal line X _n (n is an integer and 1 ≦ n ≦ N) and an arbitrary signal line Y _m (m is an integer and 1 ≦ m ≦ M) , A P-channel thin film transistor and an N-channel thin film transistor. One of a source and a drain of the N-channel and P-channel thin film transistors is connected to a pixel electrode Z _nm provided at the intersection, and the other is a signal line Y _m. to, to the gate electrode signal line X _n, relates to a drive method for an electro-optical device are connected, comprising the steps of applying a rectangular pulse only to the signal line Y _m, sustained by that period of the rectangular pulse , The process of applying the steps of applying a bipolar pulse in each of the X-rays from X ₁ to X _N, the period during which any rectangular pulse to Y lines is not applied, simultaneously bipolar pulses to all the X-rays And a driving method of the electro-optical device. 2. The method according to claim 1, wherein a nematic liquid crystal material is provided on the pixel electrode. 3. An electro-optical device according to claim 1, wherein an electro-optical device having another substrate facing the pixel electrode and having a layer of a liquid crystal material therebetween is used. Method. The sustained period of 4. A reference signal, the scanning lines other than Y _m, the driving method of claim 1 an electro-optical device, wherein the any signal is also not applied.