JP3062299B2 - Electro-optical device image display method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of displaying an image in a liquid crystal electro-optical device using a thin film transistor (hereinafter referred to as a TFT) as a driving switching element, and particularly to a gradation display for obtaining an intermediate color tone or light and shade. It is about the method. The present invention particularly relates to a so-called full digital gradation display for performing gradation display without applying any analog signal to an active element from the outside.

[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, that is, displays light and dark by controlling the amount of transmitted light or the amount of scattering of light using the anisotropy of the dielectric constant. As liquid crystal materials, TN (twisted nematic) liquid crystal, STN (super
Materials known as "twisted nematic" liquid crystal, ferroelectric liquid crystal, polymer liquid crystal or dispersion type liquid crystal are known. It is known that a liquid crystal does not respond to an external voltage in an infinitely short time, but takes a certain time to respond. The value is specific to each liquid crystal material. In the case of a TN liquid crystal, the value is several tens of msec.
The time is several hundred msec for N liquid crystal, several hundred μsec for ferroelectric liquid crystal, and several tens msec for dispersion type or polymer liquid crystal.

[0003] Among electro-optical devices using liquid crystals, the one that can obtain the best image quality is the one using the active matrix system. In a conventional active matrix type liquid crystal electro-optical device, a thin film transistor (TFT) is used as an active element, an amorphous or polycrystalline semiconductor is used for the TFT, and P
In this case, a TFT of only one of the N-type and the N-type was used. That is, in general, an N-channel TFT
(Referred to as NTFT) is connected in series to the pixel. Then, a signal voltage is applied to the signal lines of the matrix, and when signals are applied from both sides to the TFTs provided at the orthogonal portions of the respective signal lines, the ON / OFF state of the liquid crystal pixels is utilized by utilizing the fact that the TFTs are turned ON. OFF was individually controlled. By controlling the pixels by such a method, a liquid crystal electro-optical device having a high contrast can be realized.

[0004]

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

However, in such a method, for example, due to the inhomogeneity of the TFT and the inhomogeneity of the matrix wiring, the voltage actually applied to the liquid crystal pixels differs by at least several% depending on each pixel. Oops. On the other hand, for example, the voltage dependence of the light transmittance of the liquid crystal is extremely non-linear, and the light transmittance changes rapidly at a specific voltage. In some cases it was significantly different. Therefore, in practice, achieving 16 gradations has been the limit.

[0006] As described above, the difficulty of gradation display is extremely disadvantageous in that the liquid crystal display device competes with a conventional general display device such as a cathode ray tube (CRT).

An object of the present invention is to propose a completely new method for realizing a gradation display which has been difficult in the past.

[0008]

[Means for Solving the Problem] As mentioned above, it is possible to control the light transmittance of the liquid crystal by controlling the voltage applied to the liquid crystal in an analog manner. It has been found that gradation can be visually obtained by controlling the time during which voltage is applied to the liquid crystal.

For example, when a TN (twisted nematic) liquid crystal, which is a typical liquid crystal material, is used,
For example, it has been found that the brightness can be changed by applying various pulses shown in FIG. 1 to the liquid crystal pixels. That is, "1" in FIG.
Brightness can be gradually increased in the order of “2”,..., “15”. That is, in the example of FIG. 1, display of 16 gradations is possible. At this time, at "1", a pulse having a length of one unit is applied. In the case of "2", a pulse having a length of 2 units is applied. At “3”, one unit pulse and two unit pulses are applied, and as a result, a pulse having a length of three units is applied. At "4", a pulse having a length of 4 units is applied. At "5", a pulse of 1 unit and 4 units of pulses are applied. At "6", a pulse of 2 units and 4 units of pulses are applied. You. Further, by preparing a pulse having a length of 8 units, a pulse having a maximum length of 15 units can be obtained.

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

Further, in the example of FIG. 1, the duration of the voltage applied to the pixel, the first _{T 1,} the following is 2T _1, the following 4T
An example is shown in which are arranged to increase geometric progression manner as that _1, which is for example, as shown in FIG. 3, the first T _1,
Next, 8T ₁ , then 2T ₁ , and finally 4T ₁ may be used. By arranging in this manner, the load on the device transmitting data to the display device can be reduced.

In order to carry out the present invention, TN liquid crystal, STN liquid crystal, ferroelectric liquid crystal, and dispersion (polymer) liquid crystal are suitable as the liquid crystal material. Further, the pulse width of one unit slightly varies depending on which liquid crystal material is selected, but in the case of a TN liquid crystal material, 10 nsec or more is suitable.

In order to further implement the present invention, for example, a matrix circuit using TFTs as shown in FIG. 4 may be assembled. The circuit shown in FIG. 4 is different from that used in the conventional active matrix, and is a modification of the CMOS buffer circuit used for the switching element.

FIG. 4 illustrates four modified buffer circuits. Each deformation buffer circuit includes at least two NTFTs and at least two PTFTs.
The number of TFTs may be further increased in case of a defect. In this circuit, first, a set of NTFT and PTFT of the gate electrode of the central portion is connected, further connected to a signal line X _n, also one of the source or Doruin the NTFT and PTFT are connected to each other, which is the pixel Connected to the electrodes of _{Zn, m} . This state is the same as that of a normal complementary field effect device (CMOS). This N
The other source or drain of the TFT and PTFT is connected to the source or drain of the second PTFT and NTFT, respectively. Also, this second PT
FT, the other of the source or drain of the NTFT are respectively connected to the signal line _{Y m} and _{Y m + 1.} Further, the second PTFT, the gate electrode of the NTFT are respectively connected to the signal line _{Y m + 1} and _{Y m.} Hereinafter, the signal lines X1 _. X _{2,. . XN} are collectively or individually referred to as X-rays, and signal lines Y1 _{, Y2,. .} Y _M
Collectively or individually called Y lines.

Also, in the figure, a capacitor is artificially inserted in parallel with the capacitor of the pixel. The capacitor inserted at this time has a function of suppressing a drop in the voltage of the pixel due to spontaneous discharge of the pixel. Since the falling speed of the voltage of the pixel is determined by the variation of the pixel, in particular, as in the present invention, in the case of performing the gradation display assuming that the voltage applied to the pixel is constant, the image quality is reduced. Invite. However, by inserting the capacitor in parallel with the pixel as described above, the voltage effect due to the variation of the pixel can be significantly suppressed, and high image quality can be obtained.

Further, by incorporating an organic ferroelectric material such as tetrafluoroethylene or polyvinylidene fluoride into a pixel such as a liquid crystal cell, the capacitance of the pixel is increased, and thus the time constant of the discharge of the pixel is increased. , It is also possible to obtain high image quality without making such an artificial capacitor.

Of course, if the discharge of the pixel is sufficiently small, such an artificial capacitor is unnecessary. In particular, the presence of an excessive capacitance takes time for the charging / discharging operation, which is not desirable in practicing the present invention. In order to reduce the discharge of the pixel, for example, the O
It is necessary to increase the FF resistance to reduce the leak current and to sufficiently increase the inter-electrode resistance of a pixel such as a liquid crystal. In particular, for the latter purpose, it is effective to cover the pixel electrode with an insulating material such as silicon nitride, silicon oxide, tantalum oxide, and aluminum oxide.

In such a circuit, ON / OFF of the voltage applied to the pixel can be controlled by controlling the gate voltage and the source / drain voltage of each TFT. In the example of FIG. 4, the matrix is 480
Although it is × 640 dots, only the vicinity of n rows and m columns are shown to avoid complexity. If you expand the same thing up, down, left and right, you will get a complete one. FIG. 2 shows an operation example of this circuit. As shown in FIG. 2, rectangular pulse signals are sequentially applied to the Y line. On the other hand, X-ray
A signal consisting of a plurality of pulses is applied. This pulse train, in a unit of time T _1, which contains 480 information.

In the following, four pixels Zn _{, m} , Z
_{Focus on n, m + 1} , Zn _{+ 1, m} , Zn _{+ 1, m + 1} . For these pixels, taking Zn _{, m} as an example,
X _n is a positive potential, or if using a more general representation, a high potential state _{(V H),} and, if _{Y m} be the _{V H,} the pixel electrode becomes _{V H.} On the other hand, if _Ym is _VL , no change occurs in the pixel regardless of the state of _Xn . Therefore, for these four pixels,
Signal lines _{X n} and _{X n + 1,} and may be of interest to _{Y n} and _{Y m + 1.}

As shown in the figure, the rectangular pulse is applied to the Y _m, consider the case where becomes V _H state. Since attention is now focused on four pixels, attention should be paid to the current state of _Xn and _{Xn + 1} . At this time, _Xn is _VH , X
_{Since n + 1} is _VL , the pixel Zn _{, m} eventually has _VH ,
The pixel Zn _{+ 1, m} becomes _VL . Then, if the Y line is set to _VL before the next signal is applied to the X line, the voltage state of the pixel is maintained by the capacitor of the pixel, so that the pixel Zn _{, m} maintains _VH . Thereafter, until the next Y _m is V _H, basically, the state of each pixel is sustained.
Next, a pulse is applied to _{Yn + 1} . As shown in the figure, then _Xn is _VL and _{Xn + 1} is _VH
Therefore, pixel Zn _{, m + 1} is V _L , pixel Z
_{n + 1 and m + 1} become _VH . Then, as described above, each state is maintained.

Next, after being previously pulses applied to the _{Y m,} after time _{T 1,} again, when a pulse is applied to _{Y m} is, _{X n} is _{V L,} since _{X n + 1} is a _{V H,} The state of the pixel Zn _{, m} changes to _VL , and the state of the pixel Zn _{+ 1, m} changes to _VH . Further, a pulse is applied to _{Ym + 1} . At this time, as shown in FIG, X _n be X
Since _{n + 1} is also at _{V H,} pixel _{Z n, m + 1} also pixel Z
_{n + 1 and m + 1} also become _VH . At this time, the pixel Z
_{n + 1 and m + 1} continue _VH .

[0022] Then, after a time 2T _1, 3-time pulse is applied to the _{Y m.} At that time, since it is _{X n} be _{X n + 1} is also _{V H,} pixel _{Z n, m} varies from _{V L} to _{V H,} pixel _{Z n + 1, m} is decided to continue the _{V H.} Further, a pulse is applied to _{Ym + 1} . At that time,
Since both _Xn and _{Xn + 1} are _VL , the pixels Zn _{, m + 1} and the pixels Zn _{+ 1, m + 1} also have _VL .

[0023] Then, after a time 4T _1, 4-time pulse is applied to the _{Y m.} At that time, since both _Xn and _{Xn + 1} are _VL , the pixels Zn _{and m} are also the pixels Zn _{+ 1 and mVL.}
Becomes Further, although a pulse is applied to Y _{m + 1} , since X _n and X _{n + 1} are also _VL , the pixel Z
_{The n and m + 1} pixels Zn _{+ 1 and m + 1} also remain at _VL .

Thus, one cycle is completed. During this time, four pulses are applied to each Y line, and 3 × 640 = 1920 information signals are applied to each X line. Also,
Time of one cycle is 8T _1, as the _{T 1,} for example, 10Nsec～10msec are suitable. Then, Come to focusing on each pixel, pixel Z _n, the _m, the pulse application of the pulse and 4T ₁ time T _1, the visual has the same effect as pulse 5T ₁ is applied can get.
That is, a brightness of “5” is obtained. Similarly, pixel Z
_{n + 1, m} , pixel Zn _{, m + 1} , pixel Zn _{+ 1, m + 1}
After all, the brightness of "2", "6", and "3" is obtained.

In the above example, eight gradations can be displayed, but by adding more pulse signals,
Higher gradation is possible. For example, during one cycle, five pulses are further applied to the Y line, and 8 × 640 is applied to each X line.
By applying an information signal of = 5120, a high gradation display of as many as 256 gradations can be achieved.

If a high gradation display is to be performed, as shown in FIG. 2, extremely high-speed switching is required. For example, to achieve a 256 gray level, since video has to be fed more than 30 frames per second, 256T ₁
<30 msec _o Therefore, T ₁ <100 μsec. Therefore, when the number of Y lines is 640, a pulse having a width of 150 nsec or less needs to be applied to the Y lines. Since such operation performance is required, it is necessary to use a CMOS buffer circuit, unlike the related art.

In the above description, the counter electrode of the pixel has not been described at all for the sake of easy understanding. Voltage can be changed. For example, the counter electrode of the pixel, by applying an appropriate voltage, the direction of the voltage applied to the pixel material varied V _L and V _H, can also be adapted can take both positive and negative. Such an operation is necessary for a ferroelectric liquid crystal, for example.

Further, in order to make the explanation easy to understand,
The signal zero level and voltage level have been clarified.
It is not necessary to be absolutely zero because it is only a matter of whether or not it is above. Also, since the voltage is a relative physical quantity with reference to the potential at an arbitrary point, in the above example,
It will be clear that the pulses can be of opposite polarity.

Further, in the above example, although the method of line by line scanning, for example, first _{Y 1, Y 3, Y 5} ,. _.
And then Y ₂ , Y ₄ , Y
_{6 ,. .} Needless to say, a method of so-called interlaced scanning in which scanning is performed is also possible.

[0030]

[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. 5 shows an actual arrangement of electrodes and the like corresponding to this circuit configuration for one pixel. First, a method for manufacturing a liquid crystal panel used in this embodiment will be described with reference to FIGS. In order to carry out the present invention, two NTFTs and two PTFTs are required for one pixel.
Although a total of four TFTs are shown in the figure, for simplicity, the numbers are given to only one of the NTFT and PTFT. FIG.
In (A), a silicon oxide film as a blocking layer 51 is formed on a glass 50 that can withstand a heat treatment at an inexpensive temperature of 700 ° C. or less, for example, about 600 ° C.
It is made to a thickness of 0 °. The process conditions were a 100% oxygen atmosphere, a film formation temperature of 15 ° 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 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 during the film formation at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane. 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 the 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 by 100 to 200 ° C. than the crystallization temperature, for example,
At 30 ° C., disilane (Si ₂ H ₆ ) or trisilane (S
i ₂ 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 dolin, 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, the photoresist 53 is masked with a mask P1.
Was used to form a pattern in which only the source / drain regions were opened. A silicon film 54 serving as an n-type active layer was formed thereon by a plasma CVD method. Film formation temperature is 250 ° C
In this example, the temperature was set to 320 ° C., and monosilane (SiH ₄ ) and monosilane-based phosphine (PH ₃ ) having a concentration of 3% were used. These are PCV
The film was introduced at a pressure of 5 Pa in the D apparatus, 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 was removed by a lift-off method to form an n-type impurity region 55.

Using the same 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.
, And a high frequency power of 13.56 MHz was applied to form a film. At this time, the high frequency power is 0.05 to 0.2
0 W / cm ² is suitable, and in this embodiment, 0.120 W
/ 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 °. Thereafter, a p-type impurity region 59 was formed by using 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.

After that, using a XeCl excimer laser, the source / drain / channel regions were laser-annealed, 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 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 , 23 mJ /
Crystallization was performed in cm ² .

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.

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. 6D. 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. At the same time, as shown in FIG. 7 (A), the gate wiring and the wiring arranged in parallel to it 68 was also patterned.

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 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. 6E, a silicon oxide film was formed on the interlayer insulator 69 by the above-mentioned sputtering method. This silicon oxide film is formed by LPCVD, optical CVD
Or a normal pressure CVD method. For example, 0.2-0.
6 μm thick, and then a fifth photomask P
5 was used to form an electrode window 79. Thereafter, aluminum was further formed on the entire surface to a thickness of 0.3 μm by a sputtering method, and leads 74 and contacts 73 and 75 were formed using a sixth photomask P6. There was thus obtained 6 (E) and FIG. 7 (B). After that, the surface is coated with an organic resin 77 for flattening, for example, a translucent polyimide resin, and a hole is formed again in the seventh photomask P.
7 was performed. Further, ITO (indium tin oxide) was formed on the entire surface by sputtering to a thickness of 0.1 μm, and a pixel electrode 71 was formed using an eighth photomask P8. This ITO is deposited at room temperature to 150 ° C.
This was achieved by annealing at 400 ° C. oxygen or in air.

Thus, FIGS. 6F and 7C are obtained. The sectional view of the A-A 'in FIG. 7 (C) shown in FIG. 7 (D). Actually, a counter electrode is provided with a liquid crystal material interposed therebetween, and a capacitance is generated between the counter electrode and the electrode 71 as shown in the figure. At the same time, capacitance also occurs between the wiring 68 and the electrode 71. Then, by keeping the wiring 68 at the same potential as the counter electrode, a circuit in which a capacitor is inserted in parallel with the liquid crystal pixel is formed as shown in FIG. In particular, by arranging as in the present embodiment, the wiring 68 is parallel to the gate wiring 65, so that the parasitic capacitance between the two wirings is small, and therefore, there is an effect of reducing attenuation and delay of a signal transmitted through the gate wiring.

The wiring 68 thus formed is
Can be used as a ground line of a protection circuit provided at the end of each matrix when used with ground. The protection circuit is provided between the peripheral driving circuit and the pixel as shown in FIG. 10 and refers to a circuit as shown in FIGS. 11 and 12 . In any case, when an excessive voltage is applied to the wiring of the pixel, it is turned on, and has a function of removing the voltage. These protection circuits are formed using a doped or undoped semiconductor material such as silicon, a transparent conductive material such as ITO, or a normal wiring material. Therefore, it can be formed at the same time when the circuit of the pixel is formed. .

[0048] This can, for example, C each protection circuit of Figure 11, the combined NTFT and PTFT, or they
/ TFT. Although the TFT is not used in the protection circuit shown in FIG. 12 , the diode is constituted by, for example, a PIN junction.
It is obvious that it has a structure such as IN, PIP, NPN or PNP, and can be manufactured by using the manufacturing method shown in this embodiment without need to explain each time.

The electrical characteristics of the TFT thus obtained are PTFT and the mobility is 40 (cm ² / V).
s), Vth was -5.9 (V), the mobility was NT (80 (cm ² / Vs), and Vth was 5.0 (V) for NTFT.

One substrate for a liquid crystal electro-optical device manufactured according to the above method was obtained. FIG. 5 shows the arrangement of the electrodes and the like of the liquid crystal display device.
Complementary TFT constituting deformation buffer according to the present invention
(C / TFT) is between the signal line _{Y 1} and _{Y 2,} and _Y between ₂ and _{Y 3,} is provided in parallel to the signal lines _X 1, _{X 2.} A matrix configuration using such a C / TFT is provided. By repeating such a structure left and right and up and down, a liquid crystal display device having a large pixel size of 640 × 480 or 1280 × 960 can be obtained. In this embodiment, 19
20 × 400. Thus, a first substrate was obtained.

FIG. 8 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. After that, a film of a polyimide resin mixed with a red pigment was formed to a thickness of 1 μm using a spin coating method,
Red filter 8 using tenth photomask P10
3 was produced. Similarly, a green filter 85 and a blue filter 86 were manufactured using the masks P11 and P12. During the production, each filter was fired at 350 ° C. in nitrogen for 60 minutes. After that, the leveling layer 89 was formed using transparent polyimide also by using the spin coating method.

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 thirteenth photomask P13. This ITO is deposited at room temperature to 150 ° C.
This was achieved by annealing in oxygen or atmosphere at 0 to 300 ° C. 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, 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 common signals and potential wiring were connected to leads on the substrate, and a polarizing plate was adhered 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 liquid crystal television was confirmed by applying signals substantially equivalent to those shown in FIGS. 1 and 2 to the liquid crystal pixels.

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

[0056] The following describes in accordance with FIG. 9, the manufacturing method of a TFT portion. 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) of the PTFT and the NTFT to be substantially the same, boron is used to diborane to 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³
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 method is used, 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 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.
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 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 using the mask P2, a pattern was formed in which only the area to be the source / drain area of the PTFT was opened. Then, using the resist 105 as a mask, the p-type impurity region 106 is formed.
Was formed. As an impurity, boron is used, and also by ion implantation, 2 × 10 ^{14 to} 5 × 10 ¹⁶ cm
⁻² , preferably 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 . Further, after the end of the laser annealing, the silicon oxide film 107 was removed.

Thereafter, an NTFT region 111 and a PTFT region 112 in the shape of an island were formed using the 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.

After that, 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. Although not shown in the figure, a gate wiring and a wiring parallel to the gate wiring were also formed as in the case of the first embodiment.

As a material for the wiring, for example, aluminum (Al) can be used in addition to the above materials. When aluminum is used, after patterning it with a fourth photomask P4 and then anodizing the surface thereof, the self-alignment method can be applied. Therefore, the contact hole of the source / toluin is located closer to the gate. Since it can be formed, the characteristics of the TFT can be further improved by reducing the mobility and the threshold voltage.

[0068] 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.

After that, further, aluminum is formed on the whole by a sputtering method to a thickness of 0.3 μm, and leads 116 and contacts 114 and 115 are formed using a sixth photomask P6. A resin 119, for example, a translucent polyimide resin is applied and formed,
The electrode drilling was performed again using the seventh photomask P7. Furthermore, ITO (indium tin oxide)
Was formed 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 formed at room temperature to 150 ° C.
This was achieved by annealing in oxygen or air.

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 common signals and potential wiring were connected to leads on the substrate, and a polarizing plate was adhered 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 liquid crystal television was confirmed to be capable of displaying 128 gradations by applying signals substantially equivalent to those shown in FIGS. 1 and 2 to the liquid crystal pixels.

[0072]

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 idea of the present invention, an electro-optical device using a liquid crystal, particularly a display device has been 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 a driving waveform according to the present invention.

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

FIG. 5 shows a planar structure of a device according to an example.

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

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

FIG. 8 shows a process of a color filter according to an example.

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

FIG. 10 shows a connection example of a protection circuit in the embodiment.

FIG. 11 shows an example of a protection circuit in the embodiment.

FIG. 12 shows an example of a protection circuit in the embodiment.

Continuation of the front page (56) References JP-A-5-281925 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133

Claims (1)

(57) [Claims] 1. N signal lines X ₁ , X ₂ ,.
And X _N (N is a natural number), the signal lines X _1, X _2, · · ·, the M orthogonal to X _N Shin
Line _{Y 1, Y 2, ···,} Y M (M is a natural number) are provided, wherein (n is an integer, 1 ≦ n ≦ N) signal line X _n and the signal
At the intersection of line Y _m (m is an integer and 1 ≦ m ≦ M), the first and
A second N-channel thin film transistor and first and second
P-channel type thin film transistor and pixel electrode provided
It is the source of the first N-channel thin film transistor Oyo
By connecting one of a one and the first source and drain of the P-channel type thin film Trang <br/> Soo other fine drain connected before <br/> Symbol pixel electrode, the first N-channel Type thin film transistor source and
And the other of the source and the drain of the second P-channel thin film transistor is connected to the source and the drain of the first P-channel thin film transistor.
And the second N-channel type thin film transistor
Connect one of the source and drain of the register, the source of the second P-channel type thin film transistor Oyo
The other micro drain connected to the signal line Y _m, the source of the second N-channel thin film transistor Oyo
Provided the other fine drains next to the signal line Y _m
Connected to signal Line Y _{m + 1,} the gate electrodes of the first P-channel type thin film transistor and said first N-channel thin film transistor
Connected to signal Line X _n, to connect the gate electrode of the second P-channel type thin film transistor to the signal line Y _{m + 1,} the gate electrode of the second N-channel thin film transistor
In the electro-optical device connected to the signal line Y _m and in one period of the pulse signal applied to the signal line Y _m,
The following path from any pulse is applied to the signal line Y _m
Time 2 _^i-1 T ¹ until pulse is applied (i is finite natural number, T ₁ is a fixed time), and the signal during the period in which by applying a pulse to the signal line Y _m
When a pulse is applied to the line _Xn , the pixel electrode is in a high potential state
To become the signal during the period in which by applying a pulse to the signal line Y _m
When no pulse is applied to the line _Xn , the pixel electrode is in a low potential state.
Becomes state, the signal in the period in which by applying a pulse to the signal line Y _m
Line Y _{m + 1} to the signal line pulses and reverse being applied to the Y _m
The image display method for an electro-optical device comprising that you apply a pulse phase.