JP3431875B2 - Active matrix display - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a high light transmittance and can present a large amount of information, and is considered to be applied to a reflection type display, a projection type display or the like which does not require a backlight. To be

[0002]

2. Description of the Related Art As a conventional liquid crystal display device, a TN type or STN type using a nematic liquid crystal has been widely put into practical use. Recently, a liquid crystal using a ferroelectric liquid crystal is also known. All of these devices required a polarizing plate and the liquid crystal had to be regularly oriented in a certain direction in the device. On the other hand, without the need for these polarizing plates and orientation,
Dispersion type liquid crystal with a bright screen and good contrast is known. The dispersed liquid crystal is a liquid crystal having a translucent solid phase polymer holding nematic, cholesteric, or smectic liquid crystals in a granular or spongy form. As a method for producing this liquid crystal device, it is known that a liquid crystal is dispersed in a polymer by encapsulating the liquid crystal and the polymer is formed as a thin film on a film or a substrate. Here, gelatin, gum arabic, polyvinyl alcohol and the like have been proposed as the encapsulating substance.

In these techniques, liquid crystal molecules encapsulated with polyvinyl alcohol are aligned in the direction of the electric field in the presence of an electric field if they have a positive dielectric anisotropy in a thin film. However, when the refractive index of the liquid crystal and the refractive index of the polymer are equal, transparency is exhibited. On the other hand, when there is no electric field, the liquid crystal does not align in a specific direction and faces various directions, so the refractive index of the liquid crystal deviates from the refractive index of the polymer, and light is scattered and obstructs the transmission of light. It becomes cloudy. In addition to the above-mentioned examples, there are some known polymers or thin films obtained by dispersing the encapsulated liquid crystal in the polymer. For example, a liquid crystal material dispersed in an epoxy resin, a liquid crystal material utilizing phase separation between a liquid crystal and a photo-curing substance, and a liquid crystal impregnated in a three-dimensionally linked polymer are known. . In the present invention, these liquid crystal electro-optical devices are collectively referred to as dispersion type liquid crystal.

[0004]

As one of the factors that determine the characteristics of the dispersed liquid crystal device, the existence region of the liquid crystal,
For example, in the case of the capsule type, it is the degree of dispersion of the capsule, and in the type using a polymer, the degree of dispersion of the space portion. Here, if these variations are large,
The steepness of the average electro-optical characteristics of the liquid crystal composition is deteriorated, and a so-called threshold for driving is not clearly defined. FIG. 14 shows the above-mentioned typical electro-optical characteristics of the dispersion type liquid crystal.

As a means for solving this, there is a determination of a threshold value by a thin film transistor called an active element, which has been indispensable.

Conventionally, as a thin film transistor used for a dispersion type liquid crystal, an N channel type thin film transistor is usually the mainstream, but when driven by only one of an N channel type thin film transistor and a P channel type thin film transistor, Since the leak current at the time of OFF cannot be suppressed small, it is necessary to form an independent capacitive element in parallel with the capacitive component of the liquid crystal element. FIG. 15 shows a structural diagram of a liquid crystal device using a typical single-channel thin film transistor.

Further, in general, an active matrix type liquid crystal display device is 480 × 640 or 1260 × 960.
And has so many pixels. In FIG. 5, the same meanings are shown, and in order to simplify the description, a 2 × 2 matrix arrangement is shown. Multiple gate lines G _1, G ₂
And a plurality of data lines D _{1 and} D ₂ are arranged orthogonally to each other, and a pixel display element is provided at a matrix-shaped intersection. This pixel display element is composed of a liquid crystal section 102 and a TFT section 101. Peripheral circuits 106, 1 for each pixel
A signal is added from 07 to selectively turn on or off predetermined pixels to perform display.

However, when these liquid crystal display devices are actually manufactured and displayed, the output of the TFT, that is, the voltage V _LC 100 of the input to the liquid crystal (referred to as liquid crystal potential) is often ∧1 "(High). It does not become ∧1 "(High) when it should be, and it does not become ∧0" (Low) when it should be ∧0 "(Low). This occurs because the switching element that applies a signal to the pixel, that is, the TFT has no symmetry. That is, the state of charging and the state of discharging of the pixel electrode has a bias in terms of electrical characteristics. The liquid crystal 102 is essentially insulating in its operation, and T
When the FT is off, the liquid crystal potential (V _LC ) is in a floating state.
Since this liquid crystal 102 is equivalently a capacitor, V _LC is determined by the charges accumulated therein. When the liquid crystal has a relatively small resistance at R _LC , leaks due to the presence of dust or ionic impurities, or causes R _GS 105 due to the pinhole of the gate insulating film of the TFT, this charge is generated. The electric charge leaks from there, and V _LC becomes halfway. Therefore, in a liquid crystal display device having 200,000 to 5 million pixels in one panel, there is a problem that a high yield cannot be achieved.

[0009]

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, the reality is that there are many defects and they are not always fulfilled.

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 and the liquid crystal material is decomposed or denatured to display. In this case that something that can not be done enough occurs
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 increases the current margin, that is, the response speed. Further, the potential of the pixel in each pixel, that is, the liquid crystal potential V _LC is fixed to ∧1 "and ∧0" sufficiently stably so that the level does not drift during one frame.

Further, as described above, since it is very difficult to uniformly disperse the liquid crystal in the large area substrate with the dispersion type liquid crystal, the threshold for driving is gentle, and therefore the active element works to drive the liquid crystal. The threshold is secured.

[0013]

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 gate electrode of the NTFT and the PTFT is commonly connected to a third signal line, and a drain (source) portion of the NTFT and the PTFT is connected to a pixel electrode.
It is a liquid crystal electro-optical device that has a liquid crystal material and a light-transmissive solid substance between the substrate and a second substrate provided with electrodes and leads.

As a driving method thereof, a signal waveform is applied to the third signal line while a signal waveform is applied to the pair of first and second signal lines. As a result, the thin film transistor of the above-mentioned complementary structure (hereinafter referred to as C / TFT) is driven to turn on or off the display of the pixel.

As a constitution of a liquid crystal electro-optical device to which the present invention can be applied, one pixel has two or more C / Ts.
The FTs may be concatenated to form one pixel.
Divide one pixel into two or more,
One or a plurality of C / TFTs may be connected to each.

The dispersion type liquid crystal material in the present invention includes a transparent solid substance (translucent solid phase polymer or polymer forming monomer) and nematic, cholesteric or smectic liquid crystal, and these liquid crystals are granular or It is spongy and is retained. As the light-transmitting solid-phase polymer, polyethylene, polymethacrylic acid ester, polystyrene, polyvinyl chloride, polyacrylonitrile, polyvinyl alcohol, polyester, polyamide resin, polyethylene terephthalate resin, fluororesin, silicone resin, etc. may be used alone or in a mixture. To be

As the dispersion type liquid crystal constituent material, a polymer-forming monomer and a liquid crystal material or a solid phase polymer and a liquid crystal material dissolved in a common solvent are used. In the former case, the mixture is applied on a substrate by a coating method and then irradiated with heat or light to form a light control layer. On the other hand, in the latter, a dissolved liquid material is applied to form a liquid medium layer, and then the solvent is removed to obtain a dispersed liquid crystal.

As the solvent, ketones, alcohols,
Unsaturated hydrocarbons such as benzene and toluene and water can be used. These are selected appropriately according to the coating method and used alone or as a mixture. Depending on the shape and characteristics of the liquid crystal material, the coating method may be a doctor knife, roll coater,
A method such as a curtain coater, a knife coater, spray coating, spin coating, screen printing or offset printing can be adopted.

A typical example of the configuration of a liquid crystal electro-optical device to which the present invention can be applied is shown as a circuit diagram in FIGS. 1, 2 and 3. Further, examples of actual pattern layouts (arrangement diagrams) are shown in FIGS. 6, 7, and 8 correspondingly. 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. 1, NT
Gates of FT and PTFT are connected to each other, and further connected to the third signal line 3 or 4 in the Y-axis direction, and C / TF
The common output terminal of T 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, and the input end (2
The (0 side) 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.
When the off signal waveform is applied to the third signal line 3 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, the liquid crystal potential (V _LC ) 14 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 likewise 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. You can

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 . In 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 varies depending on the liquid crystal material, the offset voltage V _OFFSET is adjusted to match the value of the liquid crystal.
Can be adjusted to any threshold value by simply changing.

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, and the liquid crystal material is decomposed or modified to display. In this case that something that can not be done enough occurs
The applied signal is converted into an alternating current so that the voltage applied to the liquid crystal material is not biased, but according to the driving method of the present invention, the polarity of the offset voltage V _OFFSET applied to the counter electrode and the logic of the selection signal applied to the data signal line. Just flip
It has a feature that an alternating signal can be generated very easily.

In the example of FIG. 2, the four gate electrodes of the NTFT13PTFT22 constituting the first C / TFT and the NTFT24 and PTFT25 constituting the second C / TFT are commonly used 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. Also, the output of the two C / TFTs is made common and one liquid crystal 1
5 is connected to the pixel electrode 17 which is one electrode.
Thus, even if either one of the two NTFTs or the two PTFTs is leaked to some extent, the pixel can be driven because the phase is the same.

In FIG. 3, 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. Also, the input of each NTFT of each C / TFT and each PTFT is connected to the first signal line 5 and the second signal line 8 respectively.
It is connected to. 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.

[0025]

DETAILED DESCRIPTION OF THE INVENTION

[Embodiment 1] In this embodiment, description will be made using a liquid crystal display device having a circuit configuration as shown in FIG. FIG. 6 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. Also, 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 for 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, film forming temperature 15 ° C., output 400 to 800 W, pressure 0.5 Pa.
And The film formation rate using quartz or single crystal silicon 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 more than the crystallization temperature.
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 30-300
It was Pa. The film forming rate was 50 to 250 Å / min.
Threshold voltage (Vt) between NTFT and PTFT
In order to control the concentration to be substantially the same as that of h), boron may be added during the film formation with diborane at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ .

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

When 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 coatings formed by these methods are
5 × 10 oxygen^{twenty one}cm^-3The following is preferable. This acid
When the elemental concentration is high, it is difficult to crystallize and the thermal annealing temperature is
Higher or longer thermal anneal times must be provided.
If it is too small, the backlight will turn off the light.
The current will increase. Therefore 4 × 10¹⁹~ 4 x 10 ^{twenty one}
cm^-3And the range. 4 × 10 for hydrogen²⁰cm^-3And silicon 4
× 10^{twenty two}cm^-3Was 1 atom%. Also,
To promote crystallization of the source and drain
Therefore, the oxygen concentration is 7 × 10¹⁹cm^-3Below, preferably 1 × 10¹⁹
cm^-3The following is to form the channel of the TFT that makes up the pixel
5 × 10 oxygen only in the region by ion implantation²⁰~ 5 x 10
^{twenty one}cm^-3You may add so that it may become. Then the peripheral circuit
This TFT does not emit light because it does not emit light.
With less carrier and higher carrier mobility
Squeezing is effective in accumulating high frequency operation.
It

Next, a silicon film in an amorphous state is formed into 500
~ 5,000 Å, for example, 1500 Å after making, 4
Medium temperature heat treatment in a non-oxide atmosphere at a temperature of 50 to 700 ° C. for 12 to 70 hours, for example, 600 in a hydrogen atmosphere.
Hold at a temperature of ° 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.

By annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part thereof assumes a crystalline state. In particular, a region having a relatively high degree of ordering after the film formation of silicon tends to be crystallized and become a crystalline state. However, since silicon existing between these regions is bonded to each other, the silicon members pull each other. A single crystal silicon peak 522 measured by laser Raman spectroscopy
A peak shifted to the lower wave number side than cm ^-1 is observed. The apparent particle size is 50 to 5 when calculated from the full width at half maximum.
Although it is a microcrystal like 00Å, in reality, there are many highly crystalline regions with a cluster structure, and each cluster has a semi-amorphous structure in which silicon is bonded (anchoring) with each other. Could be formed.

As a result, the coating is in a state in which it may be said that it is substantially free of grain boundaries (hereinafter referred to as GB). Since the carriers can easily move between the clusters through the anchored portions, the carrier mobility is higher than that of polycrystalline silicon in which so-called GB is clearly present. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² /
VSec, electron mobility (μe) = 15 to 300 cm ² / V
Sec is obtained.

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

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

On this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000Å, for example 1000Å. 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.
^-3 concentration silicon film or this silicon film with molybdenum (Mo), tungsten (W), MoSi ₂ or
A multilayer film with WSi ₂ was formed. This was patterned with a second photomask to obtain FIG. 13 (B). A gate electrode 55 for PTFT and a gate electrode 56 for NTFT were formed. For example, the channel length is 10 .mu.m, the gate electrode is 0.2 .mu.m of phosphorus-doped silicon, and molybdenum is 0.2 .mu.m.
It was formed to a thickness of 3 μm. In FIG. 13C, a photoresist 57 is formed using a photomask, and P
1 source of boron for the source 59 drain 58 for the TFT
It was added by the ion implantation method in a dose amount of ˜5 × 10 ¹⁵ cm ⁻² . Next, as shown in FIG. 13D, the photoresist 61
Was formed using a photomask. Source for NTFT
1 to 5 × 10 ¹⁵ cm ^-2 for phosphorus as the drain 64 and drain 64
Was added by the ion implantation method.

These are performed through the gate insulating film 54. However, in FIG. 13B, the gate electrodes 55, 5
Silicon oxide on the silicon film may be removed using 6 as a mask, and then boron and phosphorus may be directly ion-implanted into the silicon film.

Next, heating anneal 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. Also gate electrode 5
Channel formation regions 60 and 63 are formed as semi-amorphous semiconductors below 5 and 56.

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

In this embodiment, the thermal anneal is as shown in FIG.
Done twice in (D). However, the anneal of FIG. 13 (A) is omitted depending on the desired characteristics, and both are omitted.
The manufacturing time may be shortened depending on the requirements. FIG.
In (E), the 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, it is formed to have a thickness of 0.2 to 0.6 μm, and then a window 66 for an electrode is 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. 13 (F), 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 NTF
The same glass substrate 50 is used for T13 and the electrode 70 of the transparent conductive film.
Made above. The electrical characteristics of the obtained TFT are PTF.
Mobility is 20 (cm ² / Vs) at T, Vth is -5.9 (V)
With NTFT, the mobility is 40 (cm ² / Vs) and Vth is 5.0.
(V).

A photocurable modified acrylic resin (World Lock 880K1) and a nematic liquid crystal composition (E) were formed on one substrate for a liquid crystal device manufactured by the above method.
44) as a uniform solution and printed to a thickness of 10 μm by a screen printing method, and the other glass substrate provided with a transparent electrode on the entire surface is laminated under reduced pressure with these substrates, and 2 kg / cm ² is applied from above. A liquid crystal cell was formed by applying pressure and simultaneously irradiating ultraviolet light from below. FIG. 6 shows how the electrodes and the like of this liquid crystal display device are arranged. NTF
T13 is provided at the intersection of the first scanning line 5 and the data line 3, and NTFTs for other pixels are similarly provided at the intersection of the first scanning line 5 and the data line 4. On the other hand, PTFT
Are provided at the intersections of the second scanning lines 8 and the data lines 3. Also, the other adjacent first scanning line 6 and data line 3
NTFTs for other pixels are provided at the intersections with and. 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 terminal of the source 12 is connected to the pixel electrode 1 through a contact.
It is linked to 7.

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 via a contact like an NTFT. Is connected to the pixel electrode 17. Thus, one pixel is constituted by the pixel 23 made of the transparent conductive film and the C / TFT between the pair of scanning lines 5 and 8 (inside). 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 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 Fig. 10. In FIG.
The horizontal axis represents time. One frame is time T
It is divided into 4 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. 10.
Is applied, and the pixel of AA between time T1 and T2
Only selected and turned on or off. That is, T₁From
t₁Data line Y between₁Apply a data signal to
Then, within this time, the liquid crystal of the AA pixel exceeds the threshold value.
Voltage is applied to drive the liquid crystal. At this time, the liquid crystal display
An offset voltage is applied to the counter electrode of the device. Figure
In 10, the same signal waveform is obtained from the next time T2 to T3.
It is applied and AA is displayed.

Next, at times T3 to T4 and T4 to T5, signals for not selecting four pixels at all are applied.
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 an offset having a polarity different from that of the signal applied from time T1 to T6 is applied to the counter electrode. A voltage is 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, among the signals applied from time T2 to T4, the logic of the Y ₁ , Y ₂ , Y ₃ , and Y ₄ lines is inverted, that is, the selection signal and the non-selection signal are exchanged,
By switching the positive and negative of the offset voltage of the counter electrode, an AA pixel is selected in the first half frame of time T2 to T4, and four pixels are not selected in the second half frame, and an AC signal can be applied to drive the liquid crystal. It has become possible. 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, which causes
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, a gray level display can be performed by a driving method that is particularly well suited for a liquid crystal driving threshold that is not clear, that is, a dispersion type liquid crystal having a gentle threshold.

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.

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 invention, no polarizing plate is required, the operating voltage is ± 10 to ± 15 V and the cell interval is about 1 to 20 μm in order to increase the switching speed of the liquid crystal.

In particular, in the present invention using the dispersion type liquid crystal, since the polarizing plate is not necessary, the light quantity can be increased both as the reflection type and the transmission type. Since the liquid crystal does not have a threshold, a C / TFT type in which a clear threshold voltage is defined as in the present invention provides a large contrast and crosstalk (bad interference with adjacent pixels). ) Could be excluded.

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

Example 2 This example is shown in FIGS.
This example was carried out by using a liquid crystal display device having a structure corresponding to. As is clear from this drawing, Y
The scanning line 3 of the lines 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 includes one transparent conductive film pixel 17 and two NTFTs 13 and 24,
The two PTFTs 22 and 25 are connected to two C / TFTs. All the gate electrodes are connected to the scanning line 3, two NTFTs are connected to the first data line 3, and two PTFTs are connected to the second data line 8. Even if one of these two C / TFTs 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 / Ts are provided for one pixel.
Since the FT is provided, 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 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 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 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 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 Fig. 11. In Figure 11
The horizontal axis represents time. One frame is time T
The interval between 1 and T2 is divided into four, and the scan line
Y₁, Y₂, Y₃, Y_FourScan the lines sequentially to scan signals
It is applying. Also, X ₁, X₂, X₃, X_FourFigure on line
A data signal such as 11 is applied. In the figure
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_4aWhen
The same waveforms with different polarities are applied, and from time T1
During T2, only AA pixels are selected and turned on or off.
Be done. Ie T₁To t₁A pair of data lines X between₁
A data signal is applied to the AA image within this time.
A voltage exceeding the threshold is applied to the elementary liquid crystal.
Then the liquid crystal is driven. At this time, the counter voltage of the liquid crystal display device
Offset voltage is applied to the poles. In Figure 11
Apply exactly the same signal waveform from time T2 to T3, and
Is displayed.

Next, at times T3 to T4 and T4 to T5, signals for selecting no four pixels are applied.
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 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. Actually, from time T2 to T4
Of the signals applied to the pair of X ₁ , X ₂ ,
X _3, inverts the logic of X _4-wire, i.e. interchanged selection signal and a non-selection signal, by replacing the positive and negative offset voltage of the counter electrode, in the first half of the frame to select the pixels of AA, 4 in the second half of the frame It is possible to apply an alternating signal that does not select one pixel 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, similarly to the first embodiment, it is possible to perform gradation display by changing the signal voltage on the scanning line side.

[Embodiment 3] This embodiment is shown in FIGS.
This example was carried out by using a liquid crystal display device having a structure corresponding to. As is clear from this drawing, Y
A line data line 3 is arranged in the center, and a portion sandwiched between a first scanning line 5 and a second scanning line 8 of a pair of scanning lines is one pixel 23. One pixel is composed of two transparent conductive film pixel electrodes 17 and 26.
FT13 and PTFT22 are connected, and pixel 26 has NT
The FT 24 and the PTFT 25 are each connected in a C / TFT configuration. The gate electrodes are all connected to the data line 3, and the two NTFTs are connected to the first scan line 3 and 2
One PTFT is connected to the second scan line 8. Even if one of these two C / 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,
It was possible to reduce the degree of deterioration of the gray scale.

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 having a polarity different from that of the signal applied from time T1 to T3 is applied to the counter electrode. A voltage is 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 T3. That is, among the signals applied from time T1 to T2, the logics of the Y ₁ , Y ₂ , Y ₃ , and Y ₄ lines are inverted, that is, the selection signal and the non-selection signal are exchanged,
By switching the positive / negative of the offset voltage of the counter electrode, it is possible to apply an AC signal that selects AA pixels in the first half frame and does not select four pixels in the second half frame, and it is possible to drive the liquid crystal.

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. In this embodiment,
The scanning is performed with the Y-ray as the scanning side, but the configuration is not particularly limited to this configuration, 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.

[0070]

As described above, according to the structure of the present invention, it is possible to display and drive a large area and a large number of large capacity elements even in the case of the dispersion type liquid crystal which has a large threshold variation and the liquid crystal material is not steep. As a result, the display capacity can be increased as compared with the conventional dispersion type liquid crystal electro-optical element.

Further, according to the structure of the present invention, since the liquid crystal potential is not floated, stable display can be performed. Further, since the driving capability of the C / TFT as an active element is high, the operation margin can be expanded, and the peripheral driving circuit can be further simplified, which is effective in downsizing the display device and reducing the manufacturing cost. There is. 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 some defective TFTs are in-phase output, the compensation can be performed to some extent.

Furthermore, in order to prevent the liquid crystal material from being electrolyzed, the AC signal drive which is indispensable for driving the liquid crystal is C / TF.
This could be achieved simply by inverting the logic of the signal applied to the T gate signal line 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. In particular, a gray level display can be performed by a driving method that is particularly well suited for a liquid crystal driving threshold that is not clear, that is, a dispersion type liquid crystal having a gentle threshold. Further, as another gradation method, when one screen is displayed by applying drive signals of a plurality of frames to a liquid crystal for one display screen, the selection signal added 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. As the liquid crystal material that can be used, the above-mentioned nematic liquid crystal, cholesteric liquid crystal, or smectic liquid crystal can be used.

[Brief description of drawings]

FIG. 1 shows a circuit diagram of an active display device using complementary TFTs.

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 drive waveforms of the present invention.

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.

FIG. 14 shows electro-optical characteristics of a conventional dispersion type liquid crystal.

FIG. 15 shows a vertical cross-sectional view of a liquid crystal electro-optical device using a conventional TFT.

[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) Reference JP-A-2-58336 (JP, A) JP-A-1-156725 (JP, A) JP-A-62-159126 (JP, A) JP-A-58- 199564 (JP, A) JP 62-147759 (JP, A) JP 60-154660 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/13-1 / 141 G09F 9/30 H01L 29/786

Claims (6)

(57) [Claims] 1. An active matrix type display device having a thin film transistor formed on an insulating surface, wherein a flattening film is formed on the thin film transistor, and a source of the thin film transistor is formed on the flattening film. a pixel electrode connected to the drain is formed, the oxygen concentration of the source and drain regions of the thin film transistor Ri der 7 × 10 ¹⁹ cm ^-3 or less, the oxygen concentration in the channel formation region of the thin film transistor
5 × 10 ²⁰ to 5 active matrix display device which is a × 10 ²¹ cm ^-3. 2. An active matrix type display device having a thin film transistor having a silicon film formed on an insulating surface, wherein the silicon film has a boron concentration of 1 × 10 ¹⁵ cm ⁻³ to 1 × 10.
¹⁸ cm ⁻³ , a flattening film is formed on the thin film transistor, a pixel electrode connected to a source or a drain of the thin film transistor is formed on the flattening film, and a source of the thin film transistor is formed. And the oxygen concentration of the drain region is 7 × 10 ¹⁹ cm ⁻³ or less, and the oxygen concentration of the channel forming region of the thin film transistor is
5 × 10 ²⁰ to 5 active matrix display device which is a × 10 ²¹ cm ^-3. 3. An active matrix display device having a thin film transistor formed on an insulating surface, wherein a flattening film is formed on the thin film transistor, and a source of the thin film transistor or a source of the thin film transistor is formed on the flattening film. A pixel electrode connected to the drain is formed, the oxygen concentration of the source and drain regions of the thin film transistor is 7 × 10 ¹⁹ cm ⁻³ or less, and the oxygen concentration of the channel forming region of the thin film transistor is
5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ , and the electron mobility of the thin film transistor is 15 to 300 cm.
² / Vs and Hall mobility is 10 to 200 cm ² / V
s is an active matrix type display device. 4. An active matrix display device having a thin film transistor having a silicon film formed on an insulating surface, wherein the silicon film has a boron concentration of 1 × 10 ¹⁵ cm ⁻³ to 1 × 10.
¹⁸ cm ⁻³ , a flattening film is formed on the thin film transistor, a pixel electrode connected to a source or a drain of the thin film transistor is formed on the flattening film, and a source of the thin film transistor is formed. And the oxygen concentration of the drain region is 7 × 10 ¹⁹ cm ⁻³ or less, and the oxygen concentration of the channel forming region of the thin film transistor is
5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ , and the electron mobility of the thin film transistor is 15 to 300 cm.
² / Vs and Hall mobility is 10 to 200 cm ² / V
s is an active matrix type display device. 5. The active matrix type display device according to claim 1, wherein the flattening film is an organic resin film. 6. The active matrix type display device according to claim 5, wherein the organic resin is polyimide.