JP3380794B2 - Electro-optical device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active type display device, and more particularly to an active type liquid crystal display device.
The present invention relates to an electro-optical device in which each pixel is provided with two P-channel type and N-channel type thin film type insulated gate field effect transistors (hereinafter referred to as TFTs) in a complementary manner to form a pixel.

[0002]

2. Description of the Related Art Conventionally, T is one of the effective display devices.
An active type liquid crystal display device using FT is known. In this case, a semiconductor having an amorphous or polycrystalline structure is used for the TFT, and a TFT having only one of P-type and N-type conductivity is used for one pixel. That is, generally, an N-channel TFT (referred to as NTFT) is connected in series to a pixel. A representative example thereof is shown in FIG.

In general, an active matrix type liquid crystal display device has a very large number of pixels of 480 × 640 or 1260 × 960. In FIG. 8, the same meanings are shown, and in order to simplify the description, a 2 × 2 matrix arrangement is shown. A plurality of gate lines G _{1 and} G ₂ and a plurality of data lines D _{1 and} D ₂ are arranged orthogonally to each other, and pixel display elements are provided at intersections of the matrix. This pixel display element is composed of a liquid crystal section 102 and a TFT section 101. Peripheral circuits 106, 10 for each pixel
A signal is added from 7 to selectively turn on or off a predetermined pixel for display.

However, these liquid crystal display devices are actually manufactured.
When manufactured and displayed, the output of the TFT, that is, the liquid crystal
Input voltage (called liquid crystal potential) V_LC100 is
Often when it should be "1" (High)
On the contrary, if it goes to "0" (Low) when it should go to "0" (Low)
Absent. This is a switching element that applies a signal to the pixel,
That is, it occurs because the TFT characteristics do not have symmetry.
That is, the state of charging and discharging of the pixel electrode is
This is because there is a characteristic bias. And the liquid crystal 10
2 is inherently insulating in its operation, and TF
When T is off, liquid crystal potential (V_LC) Is in a floating state. This
Since the liquid crystal 102 is equivalently a capacitor,
V due to the charge stored in_LCCan be decided. This charge
Is liquid crystal R _LCWith relatively small resistance, dust,
Leakage due to the presence of ionic impurities, and TFT
R by the pinhole of the gate insulating film of_GS105 has occurred
In some cases, charge leaks from it, and V_LCIs halfway
turn into. Therefore, 200,000 to 500 in one panel
High yields for liquid crystal display devices with 10,000 pixels
There was a problem that Mari could not be fulfilled.

The liquid crystal 102 is generally a TN (twisted nematic) liquid crystal. A rubbing alignment film is provided on each electrode for the alignment of the liquid crystal. The static electricity generated due to this rubbing process causes weak dielectric breakdown, which may cause leakage between adjacent pixels or adjacent conductive lines, or the gate insulating film is weak and may leak. I will end up.

[0006]

In the active type liquid crystal display device, it is extremely important to keep the liquid crystal potential at the same level as the initial value for one frame to keep a predetermined level. However, in reality, there are many malfunctions of the active element, and the liquid crystal potential cannot always be kept at a predetermined level with the same value as the initial value during one frame. When the voltage applied to the liquid crystal is biased to either + or-depending on the applied signal when driving the liquid crystal or the like, electrolysis or the like occurs, and the liquid crystal material is decomposed or denatured to perform sufficient display. It happens that there is nothing. in this case,
The applied signal is converted into an alternating current so that the voltage applied to the liquid crystal material is not biased, but the alternating signal is very complicated.

The present invention solves the above problems and
Increase the current margin, that is, increase the response speed.
It In addition, the pixel potential in each pixel, that is, the liquid crystal
Potential V _LCIs fixed to "1", "0" with sufficient stability and 1 frame
To prevent the level from drifting during
It

Further, due to demands for colorization and high quality of the display device, gradation display has been strongly demanded, but the driving method of gradation display was very complicated.

[0009]

According to the present invention, an NTFT and a PTFT are complementary to a pixel, and the NT
The source (drain) portion of the FT is connected to the first signal line of the pair of signal lines, and the source (drain) portion of the PTFT is connected to the second signal line of the pair of signal lines,
A method of driving a display device, wherein the gate electrodes of the NTFT and PTFT are commonly connected to a third signal line, and the drain (source) parts of the NTFT and PTFT are connected to pixel electrodes. By applying a signal waveform to the third signal line while the signal waveform is being applied to the pair of first and second signal lines, the complementary thin film transistor (hereinafter referred to as C / TFT). That is, the display device is driven to turn on or off the display of pixels. In addition, the potential difference applied to the liquid crystal is changed according to the level of the voltage of the signal applied to the third signal line to enable gradation display.

As a structure of a display device to which the driving method of the present invention can be applied, one pixel has two or more C / s.
One pixel may be formed by connecting TFTs. Further, one pixel may be divided into two or more, and one or a plurality of C / TFTs may be connected to each.

A typical example of the configuration of a display device to which the driving method of the present invention can be applied is shown in FIG. 2, FIG. 3, and FIG. 4 as circuit diagrams.
In addition, examples of actual pattern layouts (arrangement diagrams) are shown in FIGS. 5, 6 and 7, respectively. To simplify the description, a 2 × 2 matrix configuration will be described here as an example. In the example of the 2 × 2 matrix of FIG. 2,
Gates of NTFT and PTFT are connected to each other, further connected to the third signal line 3 or 4 in the Y-axis direction, and a common output terminal of C / TFT is connected to the liquid crystal 15. The input end (10 side) of the NTFT is connected to the first signal line 5 or 6 of the pair of signal lines in the X-axis direction,
The input end (20 side) of T is connected to the second signal line 8 or 7 of the pair of signal lines in the X-axis direction.

In such a configuration, as shown in FIG. 1, the third signal is applied during the period when the ON signal waveform is applied between the pair of the first signal line 5 and the second signal line 8. When an ON signal waveform is applied to the line 3, the liquid crystal potential (V _LC ) 1
4 is the voltage V _GG -Vth applied to the first signal line. In addition, the third signal line 3 is applied during the period when the off signal waveform is applied between the pair of the first signal line 5 and the second signal line 8.
Liquid crystal potential (V _LC ) 1 when a signal waveform of OFF is also applied
4 has no potential. Furthermore, when the ON signal waveform is not applied to the third signal line 3 while the ON signal waveform is applied between the pair of the first signal line 5 and the second signal line 8, the liquid crystal potential The (V _LC ) 14 also has no potential. As described above, the liquid crystal potential (V _LC ) 14 is given according to the voltage applied to the third signal line, and the potential difference applied to the liquid crystal can be arbitrarily changed by changing the voltage of the signal applied to this signal line. can do.

Further, the counter electrode 16 has an offset voltage V
_{Since OFFSET} is applied, the voltage actually applied to the liquid crystal 15 has two values of V _GG + V _OFFSET −V th or V _OFFSET . According to the driving method of the present invention, the offset voltage V _OFFSET applied to the counter electrode can be varied to arbitrarily change the ON / OFF of liquid crystal driving. Further, since the threshold value at the time of actually driving the liquid crystal is different depending on the liquid crystal material, this offset voltage V is adjusted to match the value of the liquid crystal.
The threshold can be adjusted to any threshold value by simply changing _OFFSET .

When the voltage applied to the liquid crystal is biased to either + or-depending on the applied signal in driving the liquid crystal or the like, electrolysis or the like occurs to decompose the liquid crystal material,
In this case, there is a possibility that the display cannot be sufficiently performed due to the modification. In this case, the applied signal is converted into an alternating current so that the voltage applied to the liquid crystal material is not biased. It has a feature that an AC signal can be generated very easily only by inverting the polarity of the offset voltage V _OFFSET and the logic of the selection signal applied to the data signal line.

In the example of FIG. 3, the four gate electrodes of the NTFT 13 PTFT 22 which constitutes the first C / TFT and the NTFT 24 and PTFT 25 which constitute the second C / TFT are shared by the third signal line 3 in the Y direction. To N,
The input ends of the TFT 13 and the NTFT 24 are made common to the first signal line 5 in the X direction, and the input ends of the PTFT 22 and PTFT 25 are made common to be connected to the second signal line 8 in the X direction. In addition, the outputs of the two C / TFTs are commonly connected to the pixel electrode 17 which is one electrode of one liquid crystal 15. Thus, two NTFTs or two PTFTs
Even if either one of them is slightly leaked, the pixel can be driven because it is in phase.

In FIG. 4, in one pixel 23, two pixel electrodes 17 and 26 and C / T corresponding to each of them are provided.
Two FTs are provided. The gate electrodes of the two C / TFTs are made common, and the first input is performed. The inputs of the respective NTFTs and the respective PTFTs of the respective C / TFTs are connected to the first signal line 5 and the second signal line 8. By doing so, one of the two pixels of one pixel does not become inoperative due to a defect such as a leak of the TFT. Further, even if the operation is delayed, the other one operates normally, so that the defect is less noticeable in the matrix forming operation.

[0017]

[Embodiment 1] In this embodiment, description will be made using a liquid crystal display device having a circuit configuration as shown in FIG. FIG. 5 shows an actual arrangement configuration of electrodes and the like corresponding to this circuit configuration. For simplicity of description, only the portion corresponding to 2 × 2 is shown. Further, the actual drive signal waveform is shown in FIG. In order to simplify the explanation, the explanation will also be made on the signal waveform in the case of the 4 × 4 matrix configuration.

First, a method of manufacturing the liquid crystal display device used in this embodiment will be described with reference to FIG. In FIG. 13A, a silicon oxide film as a blocking layer 51 is formed on a glass 50, such as quartz glass, which can withstand a heat treatment at 700 ° C. or less, for example, about 600 ° C., which is not expensive, by using a magnetron RF (radio frequency) sputtering method. Produce to a thickness of ~ 3000Å. Process conditions are 100% oxygen atmosphere,
Deposition temperature 15 ° C, output 400-800W, pressure 0.5P
a. The film formation rate using quartz or single crystal silicon for the target was 30 to 100 Å / min.

A silicon film was formed thereon by LPCVD (Low Pressure Vapor Phase) method, sputtering method or plasma CVD method. When forming by the reduced pressure vapor phase method, it is 1
450-550 ° C, which is low by 00-200 ° C, for example, 530 ° C
CVD of disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ )
The film was supplied to the apparatus to form a film. The reactor pressure is 30 to 30
It was set to 0 Pa. The film forming rate was 50 to 250 Å / min. In order to control the threshold voltage (Vth) of the NTFT and the PTFT to be approximately the same, boron may be added during film formation using diborane at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ^-3. .

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

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

The coating formed by these methods is
It is preferable that oxygen is 5 × 10 ²¹ cm ⁻³ or less. If the oxygen concentration is high, it is difficult to crystallize and the thermal annealing temperature must be high or the thermal annealing time must be long. On the other hand, if it is too small, the leak current in the off state increases due to the backlight. Therefore, 4 × 10 ¹⁹ ~
The range was 4 × 10 ²¹ cm ^-3 . Hydrogen was 4 × 10 ²⁰ cm ^-3 , which was 1 atom% when compared with silicon 4 × 10 ²² cm ^-3 . In order to further promote crystallization of the source and drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ^-3 or less, preferably 1 × 10 ¹⁹ cm ^-3 or less, and a channel forming region of a TFT constituting a pixel is formed. 5 × 10 ²⁰ oxygen only by ion implantation
You may add so that it may become -5 * 10 < ²¹ > cm < ^-3 >. At that time,
Since the TFTs constituting the peripheral circuit are not irradiated with light, it is effective to reduce the mixing of oxygen and have a higher carrier mobility in order to operate at high frequency.

Next, a silicon film in an amorphous state is formed into 500
~ 5,000 Å, for example, 1500 Å after making, 4
Heat treatment at a temperature of 50 to 700 ° C. for 12 to 70 hours at a medium temperature in a non-oxide atmosphere, for example, 60 in a hydrogen atmosphere.
Hold at a temperature of 0 ° C. Since the amorphous silicon oxide film is formed on the surface of the substrate below the silicon film, no specific nuclei are present in this heat treatment, and the whole is uniformly annealed. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein.

The annealing causes the silicon film to shift from an amorphous structure to a highly ordered state, and a part thereof exhibits a crystalline state. In particular, a region having a relatively high degree of ordering after the film formation of silicon particularly tends to be crystallized to become a crystalline state. However, since silicon is bonded to each other by the silicon existing between these regions, the silicon members pull each other. When measured by laser Raman spectroscopy, a peak shifted to a lower frequency side than the peak 522 cm ^-1 of single crystal silicon is observed. The apparent grain size is 50 to 500 Å, which is similar to that of microcrystals, calculated from the half-width. However, in reality, there are many regions with high crystallinity and they have a cluster structure. Was able to form a film having a semi-amorphous structure in which silicon was bonded to each other (anchoring).

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

On the other hand, when the film is polycrystallized by a high temperature anneal of 900 to 1200 ° C. instead of the anneal at the medium temperature as described above, the segregation of impurities in the film occurs due to the solid phase growth from the nucleus. , GB have a large amount of impurities such as oxygen, carbon, and nitrogen, and have a high mobility in the crystal, but they form a barrier in the GB and hinder the movement of carriers there. As a result, it is difficult to obtain a mobility of 10 cm ² / Vsec or more. That is, in this embodiment, a silicon semiconductor having a semi-amorphous or semi-crystal structure is used for the reason as described above.

In FIG. 13 (A), a silicon film is photoetched using a first photomask, and a region 22 (channel width 20 μm) for PTFT is shown on the right side of the drawing.
A region 13 for FT was made on the left side.

On this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000 Å, for example, 1000 Å. This was performed under the same conditions as the production of the silicon oxide film as the blocking layer. During this film formation, a small amount of fluorine may be added to immobilize sodium ions.

After this, 1-5 × 10 ²¹ cm of phosphorus is placed on the upper side.
A silicon film having a concentration of ⁻³ , or a multilayer film of this silicon film and molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ was formed thereon. This was patterned with a second photomask to obtain FIG. 13 (B). PTFT
A gate electrode 55 for the gate and a gate electrode 56 for the NTFT are formed. For example, the channel length was 10 μm, the gate electrode was made of 0.2 μm of phosphorus-doped silicon, and molybdenum was formed thereon to a thickness of 0.3 μm. In FIG. 13 (C),
Forming a photoresist 57 using a photomask,
Boron was added to the source 59 drain 58 for the PTFT by an ion implantation method at a dose amount of 1 to 5 × 10 ¹⁵ cm ^-2 . Next, as shown in FIG. 13D, the photoresist 6
1 was formed using a photomask. Source 64 for NTFT, phosphorus 1-5 × 10 ¹⁵ cm as drain 62
^It was added by the ion implantation method at a dose amount of ^-2 .

These are performed through the gate insulating film 54. However, in FIG. 13B, the gate electrode 55,
56 is used as a mask to remove silicon oxide on the silicon film,
After that, boron or phosphorus may be directly ion-implanted into the silicon film.

Next, heating annealing was performed again at 600 ° C. for 10 to 50 hours. The source 59 of the PTFT, the source 64 of the drain 58 and the drain 62 of the NTFT were produced as P ⁺ and N ⁺ by activating impurities. Channel forming regions 60 and 63 are formed as semi-amorphous semiconductors under the gate electrodes 55 and 56.

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

In this embodiment, the thermal anneal is as shown in FIG.
It carried out twice in (A) and (D). However, the anneal shown in FIG.
The anneal of (D) may also serve to shorten the manufacturing time. In FIG. 13E, an interlayer insulator 65 was formed as a silicon oxide film by the above-described sputtering method. The silicon oxide film may be formed by using the LPCVD method, the photo CVD method, or the atmospheric pressure CVD method. For example, 0.2 to 0.6μ
It was formed to a thickness of m, and then a window 66 for an electrode was formed using a photomask. Further, aluminum is formed on all of them by a sputtering method, and the leads 71, 72 and the contacts 67, 68 are formed by using a photomask, and then the surface is coated with an organic resin 69 for flattening, for example, a translucent polyimide resin. After formation, re-drilling of electrodes was performed with a photomask.

As shown in FIG. 13F, two TFTs have a complementary structure, and the output terminal thereof is connected to the electrode of one pixel of the liquid crystal device as a transparent electrode. Therefore, ITO (indium) is formed by a sputtering method. -Tin oxide film) was formed. Etching it with a photomask, the electrode 7
Configured 0. This ITO was formed into a film at room temperature to 150 ° C. and accomplished by oxygen at 200 to 400 ° C. or an anneal in the atmosphere. In this way, PTFT22 and NT
The FT 13 and the transparent conductive film electrode 70 are formed of the same glass substrate 5.
0 made on. The electrical characteristics of the obtained TFT are PT
FT, mobility is 20 (cm ² / Vs), Vth is -5.9.
At (V), the mobility was 40 (cm ² / Vs) in NTFT and Vth was 5.0 (V).

Transparent electrodes are provided on the entire surface of one substrate and the other glass substrate for a liquid crystal device manufactured according to the method as described above, and these substrates are bonded together to form a liquid crystal cell.
A liquid crystal material of TN was injected into this. FIG. 6 shows how the electrodes and the like of this liquid crystal display device are arranged. NTFT1
3 is provided at the intersection of the first scanning line 5 and the data line 3, and an NTFT for another pixel is similarly provided at the intersection of the first scanning line 5 and the data line 4. On the other hand, the PTFT is provided at the intersection of the second scanning line 8 and the data line 3. Further, an NTFT for another pixel is provided at the intersection of another adjacent first scanning line 6 and data line 3. A matrix structure using such C / TFT is provided. The NTFT 13 is connected to the first scanning line 5 via the contact at the input end of the drain 10, and the gate 9 is connected to the data line 3 in which the multilayer wiring is formed.
The output end of the source 12 is connected to the pixel electrode 17 via a contact.

On the other hand, in the PTFT 22, the input end of the drain 20 is connected to the second scanning line 8 via a contact,
The gate 21 is connected to the data line 3, and the output end of the source 18 is connected to the pixel electrode 17 via a contact like the NTFT. Thus, the pixel 23 made of the transparent conductive film and the C / TFT are provided between the inner side of the pair of scanning lines 5 and 8.
And made up one pixel. By repeating this structure horizontally and vertically, a 2 × 2 matrix can be used as a large pixel liquid crystal display device such as 640 × 480 or 1280 × 960.

The feature here is that two TFs are provided for one pixel.
By providing T in a complementary configuration, the pixel electrode 17 is fixed to the liquid crystal potential V _LC of three values. The operation will be described with reference to FIGS. 9 and 10. FIG. 9 shows a circuit diagram of the present invention when performing liquid crystal display with a 4 × 4 matrix structure, and FIG. 10 shows a timing chart of drive signal waveforms.

In this embodiment, X _1a X _1b , X _2a X _2b , X
_3a X _3b and X _4a X _4b each function as a pair of scanning signal lines. Also, Y ₁ , Y ₂ , Y ₃ , and Y ₄ function as data lines. Further, AA, AB, ..., DD in FIG. 9 mean addresses of pixels at corresponding positions.

In the display of such a 4 × 4 structure,
It corresponds to four pixels of dresses AA, AB, BA and BB.
Signal potential, liquid crystal potential, and potential actually applied to the liquid crystal
A timing chart of the difference is shown in FIG. Smell in Figure 10
The horizontal axis represents time. One frame is time T1
To T2, this space is divided into four, and a pair of scans is performed.
Four pairs of lines are sequentially scanned to apply a scanning signal. In the figure
X_1a, X_2a, X_3a, X_4aOnly listed, but actually
Is X_1b, X_2b, X_3b, X_4bX_1a, X_2a, X_3a, X_4a
The same waveform with different polarity is applied. Also,
Y₁, Y₂, Y₃, Y _FourThe line shows the data signal as shown in Fig. 10.
Signal is being applied, and during time T1 to T2,
Only pixels are selected and turned on or off. That is, T₁
To t₁Data line Y between₁Apply data signal to
Then, within this time, a threshold value is set on the liquid crystal of the AA pixel.
Voltage is applied to drive the liquid crystal. At this time, the liquid crystal table
An offset voltage is applied to the counter electrode of the shown device.
In FIG. 10, exactly the same signal wave is generated from the next time T2 to T3.
A shape is applied and AA is displayed.

Next, times T3 to T4 and T4 to T5
In, a signal is applied that does not select four pixels at all. Further, from time T5 to T6, the signal for selecting the pixel AA is applied again.

Next, from time T6 to T8, a signal obtained by inverting the logic of the signal applied to the data line is applied, and the polarity of the signal applied during the time T1 to T6 is applied to the counter electrode. Different offset voltages are applied and an alternating signal is applied to the liquid crystal. By this alternating signal,
It is possible to cancel the charges that are positively biased between the times T1 and T6. That is, of the signal which has been applied from time T2 to _{T4, Y 1, Y 2,} Y 3, inverts the logic of Y _4-wire, i.e., interchanged selection signal and a non-selection signal, the offset voltage of the counter electrode By exchanging positive and negative, A in the first half frame from time T2 to T4
It is possible to drive the liquid crystal by selecting the pixel A and applying the alternating signal which does not select the four pixels in the latter half frame. This makes it possible to easily cancel the charges remaining in the pixels.

As described above, the potential difference actually applied to the liquid crystal is determined by the voltage of the signal of the third signal line, in this embodiment, the pulse voltage of the data line and the Vset voltage of the counter electrode from the V of the TFT.
It is the potential obtained by subtracting th. That is, if the pulse voltage of the data line is arbitrarily changed, the potential difference actually applied to the liquid crystal can be changed accordingly. Thereby, gradation display can be performed. In particular, sufficient gradation display can be performed by a driving method that is particularly well suited for liquid crystal driving whose threshold value is not clear, that is, dispersion type liquid crystal having a gentle threshold.

As described above, according to the driving of the present invention, the liquid crystal display can be performed by simply applying the pulse signal to the data line and the pair of scanning lines.

As another gradation method, when one screen is displayed by applying drive signals of a plurality of frames to the liquid crystal for one display screen, a selection signal to be added to a specific pixel is applied to all the frames. By further reducing the number, gradation display can be easily performed.

In the present embodiment, if TN liquid crystal is used as the liquid crystal material, it is necessary to set the substrate spacing of the liquid crystal container to about 10 μm, provide an alignment film on both transparent conductive films, and rub it to form an alignment film. .

When FLC (ferroelectric) liquid crystal is used as the liquid crystal material, the operating voltage is ± 20 V and the cell spacing is
The thickness is 1.5 to 3.5 μm, for example 2.3 μm, and an alignment film may be provided only on the counter electrode 16 and a rubbing treatment may be performed.

When the dispersion type liquid crystal or polymer liquid crystal is used, the alignment film is unnecessary and the switching speed is high. Therefore, the operating voltage is ± 10 to ± 15 V and the cell interval is 1
Thinned to ~ 10μm.

In particular, when the dispersion type liquid crystal is used, since the polarizing plate is unnecessary, it is possible to increase the light quantity of both the reflection type and the transmission type. Since the liquid crystal has no threshold, a C / TFT type in which a clear threshold voltage is regulated as in the present invention is used, so that a large contrast and crosstalk (impairment with adjacent pixels) can be obtained. Interference) could be eliminated.

Further, as the semiconductor of the TFT used in this embodiment, materials other than those used in this embodiment can be used.

[0050]

[Embodiment 2] This embodiment is carried out by using a liquid crystal display device having a structure corresponding to FIGS. 3 and 7. As is apparent from this drawing, the scanning line 3 of the Y line is arranged in the center, and the portion sandwiched between the first data line 5 and the second data line 8 of the pair of data lines is one pixel 23. . One pixel is one transparent conductive film pixel 1
7 and 2 NTFTs 13 and 24 and 2 PTFTs
It is connected to two C / TFTs 22 and 25. All gate electrodes are connected to scan line 3 and two N
The TFT is connected to the first data line 3 and the two PTFTs are connected to the second data line 8. These two C / T
Even if one of the FTs is defective due to a leak between the gate electrode and the channel formation region, it can operate as a pixel.

The feature here is that two C /
Since the TFT is provided, the pixel electrode 17 has three
The liquid crystal potential V _LC of one value is fixed. The operation will be described with reference to FIGS. 9 and 11. FIG. 9 shows a circuit diagram of the present invention when performing liquid crystal display with a 4 × 4 matrix structure, and FIG. 11 shows a timing chart of drive signal waveforms.

In this embodiment, X _1a X _1b , X _2a X _2b , X
_3a X _3b and X _4a X _4b each function as a pair of data lines. Further, Y ₁ , Y ₂ , Y ₃ , and Y ₄ function as scanning lines. Further, AA, AB, ..., DD in FIG. 9 mean addresses of pixels at corresponding positions.

In such a 4 × 4 configuration display,
It corresponds to four pixels of dresses AA, AB, BA and BB.
Signal potential, liquid crystal potential, and potential actually applied to the liquid crystal
A timing chart of the difference is shown in FIG. Smell of Figure 11
The horizontal axis represents time. One frame is time T1
To T2, this space is divided into four, and the scanning line
Y₁, Y₂, Y₃, Y_FourScan the line to scan signal sequentially
Is being applied. Also, X₁, X₂, X₃, X_FourOn the line
, A data signal as shown in FIG. 11 is applied. In the figure
Is X_1a, X_2a, X_3a, X_4aOnly listed but actually
Is X_1b, X_2b, X_3b, X _4bX_1a, X_2a, X_3a, X_4a
The same waveform with different polarity is applied, and the time T1
Between T2 and T2, only AA pixel is selected to turn on or off
To be done. That is, T₁To t₁A pair of data lines between
X₁Apply a data signal to AA within this time
A voltage exceeding the threshold is applied to the liquid crystal of the pixel of
Then, the liquid crystal is driven. At this time, the liquid crystal display device
Offset voltage is applied to the anti-electrode. In Figure 11
The same signal waveform is applied from the next time T2 to T3,
AA is displayed.

Next, times T3 to T4 and T4 to T5
In, a signal is applied that does not select four pixels at all. Further, from time T5 to T6, the signal for selecting the pixel AA is applied again.

Next, from time T6 to T8, a signal obtained by inverting the logic of the signal applied to the pair of data lines is applied, and the signal applied between the counter electrodes during the time T1 to T6. Offset voltages with different polarities are applied,
An alternating signal is applied to the liquid crystal. By this alternating signal, it is possible to cancel the charges that are positively biased between the times T1 and T6. In fact, from time T2 to T
Of the signals added to the signal _{No. 4} , a pair of X ₁ , X ₂ , X
₃ , by inverting the logic of the X ₄ line, that is, by exchanging the selection signal and the non-selection signal and exchanging the positive / negative of the offset voltage of the counter electrode, the AA pixel is selected in the first half frame, and the four pixels are selected in the second half frame. It is possible to apply an alternating signal that does not select pixels and drive the liquid crystal.

As described above, according to the driving method of the present invention, the liquid crystal display can be performed by simply applying the pulse signal to the data line and the pair of scanning lines. Further, as in the first embodiment, gradation display can be performed by changing the signal voltage on the scanning line side.

[0057]

[Embodiment 3] This embodiment is carried out by using the liquid crystal display device having the structure corresponding to FIGS. 4 and 8. As is clear from this drawing, the Y data line 3
Is arranged in the center, and the first scanning line 5 and the second scanning line of the pair of scanning lines are arranged.
The portion sandwiched between the scanning lines 8 is one pixel 23. One pixel is composed of two transparent conductive film pixel electrodes 17 and 26.
The TFT 22 is connected, and the pixel 26 has an NTFT 24,
The PTFTs 25 are each connected in a C / TFT configuration. All gate electrodes are connected to data line 3 and 2
Two NTFTs on the first scan line 3 and two PTFTs
Are connected to the second scan line 8. These two C /
Even if one of the TFTs is defective due to a leak between the gate electrode and the channel formation region, it can operate as a pixel. Thus, even if one pixel operates only halfway, when the other pixel operates normally and is colored, the degree of deterioration of the gray scale can be reduced.

The operation will be described with reference to FIGS. 9 and 12. FIG. 9 shows a circuit diagram of the present invention when performing liquid crystal display with a 4 × 4 matrix structure, and FIG. 12 shows a timing chart of drive signal waveforms.

In the case of this embodiment, X _1a X _1b , X _2a X _2b , X
_3a X _3b and X _4a X _4b each function as a pair of scanning signal lines. Also, Y ₁ , Y ₂ , Y ₃ , and Y ₄ function as data lines. Further, AA, AB, ..., DD in FIG. 9 mean addresses of pixels at corresponding positions.

In the display of such a 4 × 4 structure,
It corresponds to four pixels of dresses AA, AB, BA and BB.
Signal potential, liquid crystal potential, and potential actually applied to the liquid crystal
The timing chart of the difference is shown in Figure 12. In Figure 12
The horizontal axis represents time. One frame is time T
It is divided into 16 between 1 and T2, and a pair of
Four pairs of scanning lines are sequentially scanned to apply a scanning signal. Figure
Then X_1a, X_2a, X_3a, X_4aOnly listed but actually
X_1b, X_2b, X_3b, X_4bX_1a, X_2a, X _3a, X
_4aThe same waveform with different polarity is applied. Also, Y
₁, Y₂, Y₃, Y_FourThe data signal on the line is as shown in Fig. 12.
Is applied and the timing is
Responding to 16 specific times in one frame
The data signal is applied to the data line at time T1 to T
During 2, only the AA pixel is selected and turned on or off.
ing. That is, T₁To t₁Data line Y between₁Against
And apply the data signal, and within this time, the liquid of the pixel of AA
A voltage exceeding the threshold is applied to the crystal and the liquid crystal is driven.
It At this time, an offset voltage is applied to the counter electrode of the liquid crystal display device.
Is being applied. Next, from time T2 to T3, four
A signal is applied that does not select any pixels.

Next, from time T3 to T4, a signal obtained by inverting the logic of the signal applied to the data line is applied, and
An offset voltage having a polarity different from that of the signal applied between times T1 and T3 is applied to the counter electrode, and an alternating signal is applied to the liquid crystal. By this alternating signal, it is possible to cancel the charges that are positively biased between the times T1 and T3. That is, from time T1 to T2
Of the signals added to Y ₁ , Y ₂ , Y ₃ , Y ₄
By inverting the logic of the line, that is, by exchanging the selection signal and the non-selection signal and exchanging the positive and negative of the offset voltage of the counter electrode, the pixel of AA is selected in the first half frame, and the four pixels are selected in the second half frame. It became possible to apply an alternating signal without selecting and drive the liquid crystal.

As described above, according to the driving method of the present invention, the liquid crystal display can be performed by simply applying the pulse signal to the data line and the pair of scanning lines. In this embodiment,
Although the scanning is performed with the Y-line as the scanning side, the configuration is not particularly limited to this, and the X-ray side may be the scanning side. It is also possible to apply a data signal at random to each data line to randomly select pixels. Others that are not described here are the same as those described in Examples 1 and 2.

[0063]

As described above, according to the driving method of the present invention, since the liquid crystal potential is not floated, stable display can be performed. Further, since the driving capability of C / TFT as an active element is high, the operation margin can be expanded, and further the peripheral drive circuit can be made simpler, and the display device can be downsized and the manufacturing cost can be reduced. effective. Further, it is possible to exhibit high driving ability with a very simple signal on the three signal lines and the counter electrode.

Even if there are some defective TFTs, since they are in-phase output, the compensation can be performed to some extent.

Further, in order to drive the liquid crystal in order to prevent the liquid crystal material from being electrolyzed, it is necessary to drive the AC signal, which is indispensable.
This could be achieved simply by inverting the logic of the signal applied to the gate signal line of the FT and inverting the polarity of the offset voltage applied to the counter electrode.

If the voltage of the signal on the third signal line is arbitrarily changed, the potential difference actually applied to the liquid crystal can be changed accordingly. Thereby, gradation display can be performed. Especially, if the threshold for driving the liquid crystal is not clear,
That is, for a dispersion type liquid crystal or the like having a gentle threshold, sufficient gradation display can be performed by a driving method particularly well suited. As another gradation method, when one screen is displayed by applying drive signals of a plurality of frames to the liquid crystal for one display screen, the selection signal applied to a specific pixel is reduced from the total number of frames. Thus, gradation display can be easily performed.

The display medium in the present invention may be used as a transmissive liquid crystal display device or a reflective liquid crystal display device. The liquid crystal material that can be used is TN of the previous operation.
Liquid crystal, FLC liquid crystal, dispersion type liquid crystal, polymer type liquid crystal can be used. Further, by adding an ionic dopant to a guest-host type or dielectric-anisotropic nematic liquid crystal and applying an electric field, an electric field is applied to a mixture of the nematic liquid crystal and the cholesteric liquid crystal, and the nematic phase and the cholesteric liquid crystal are mixed. It is also possible to use a phase transition liquid crystal which causes a phase change between the phases and realizes a transparent or cloudy display. In addition to liquid crystals, a so-called electrophoretic display dispersion system in which pigment particles of different colors are dispersed in an organic solvent colored with a dye may be used.

In the present invention, when liquid crystal is used as the display medium, the output of the C / TFT is the liquid crystal potential. In addition, since a medium other than liquid crystal may be used, in that case,
It may be replaced with the output voltage of the C / TFT.

[Brief description of drawings]

FIG. 1 shows a drive waveform of the present invention.

FIG. 2 shows a circuit diagram of an active display device using complementary TFTs.

FIG. 3 shows a circuit diagram of an active display device using complementary TFTs.

FIG. 4 shows a circuit diagram of an active display device using complementary TFTs.

FIG. 5 shows a circuit diagram of a conventional active type liquid crystal device.

6 shows a plan view of one substrate of the liquid crystal display device corresponding to FIG.

7 is a plan view of one substrate of the liquid crystal display device corresponding to FIG.

8 is a plan view of one substrate of the liquid crystal display device corresponding to FIG.

FIG. 9 shows a circuit diagram of a 4 × 4 active liquid crystal device using complementary TFTs.

FIG. 10 shows an example of a drive signal waveform of the present invention and a timing chart thereof.

FIG. 11 shows an example of a drive signal waveform of the present invention and a timing chart thereof.

FIG. 12 shows an example of a drive signal waveform of the present invention and a timing chart thereof.

FIG. 13 shows a manufacturing process diagram of a C / TFT used in the present invention.

[Explanation of symbols] ~ ... Process using photomask 1, 2 ... Peripheral circuit 3, 4 ... Third signal line 5, 6 ... First signal line 7, 8 ... Second signal line 13 ... NTFT 16 ... Counter electrode 17 ... Pixel electrode 22 ... PTFT 23 ... Pixel

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-337399 (JP, A) JP-A-53-144297 (JP, A) JP-A-1-156725 (JP, A) JP-A 64-- 30272 (JP, A) JP 57-141684 (JP, A) JP 2-58336 (JP, A) JP 60-154660 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1368 G09F 9/30 H01L 29/786

Claims (3)

(57) [Claims] 1. A substrate having an insulating surface, and a plurality of thin film transistors including a P-channel type thin film transistor and an N-channel type thin film transistor formed on the insulating surface, the P-channel type thin film transistor and the N-channel type thin film transistor. Is the source region, drain region,
And a silicon film having a channel formation region, a gate insulating film, and a gate electrode. The silicon film has a crystal of silicon, and the apparent grain size of the crystal calculated from the half-width of Raman spectrum is 5 nm.
To 50 nm, and the oxygen concentration of the source region and the drain region is
In 1 × 10 ¹⁹ cm ^-3 or less, the oxygen concentration of the channel formation region, 5 × 10 ²⁰ cm ^-3 to Ri Ah <br/> at 5 × 10 ²¹ cm ^-3, the silicon film of the P-channel thin film transistor And the silicon film of the N-channel thin film transistor contains boron. 2. The electro-optical device according to claim 1, wherein the gate electrode of the P-channel type thin film transistor and the gate electrode of the N-channel type thin film transistor include molybdenum, tungsten, MoSi ₂ or WSi ₂ . 3. The electro-optical device according to claim 1, wherein the P-channel type thin film transistor and the N-channel type thin film transistor form a complementary type thin film transistor.