Reflection type liquid crystal display device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an active type display device, particularly an active type liquid crystal display device, and two thin film type insulated gate field effect transistors (hereinafter referred to as TFT) of P channel type and N channel type are complementary to each pixel. It relates to a reflection type electro-optical device and an electro-optical device which are provided to form pixels.

【0002】

[Conventional technology]

Conventionally, an active type liquid crystal display device using a TFT is known as an effective display device. In this case, an amorphous or polycrystalline semiconductor is used as the TFT, and only one of the P or N type conductive type TFTs is used for one pixel. That is, in general, N-channel TFTs (called NTFTs) are connected in series with pixels. A typical example is shown in FIG.

【0003】

Generally, an active matrix type liquid crystal display device has a very large number of pixels of 480 × 640 or 1260 × 960. In FIG. 8, they have the same meanings, and are shown in a 2 × 2 matrix array for the sake of simplicity. Multiple gate lines G_1,G₂And multiple data lines D_1,D₂Are arranged orthogonally to each other, and a pixel display element is provided at the intersection of the matrix. This pixel display element is composed of a liquid crystal unit 102 and a TFT unit 101. A signal is applied to each pixel from peripheral circuits 106 and 107 to selectively turn on or off a predetermined pixel for display.

【0004】

However, when these liquid crystal display devices are actually manufactured and displayed, the voltage V of the TFT output, that is, the input (called the liquid crystal potential) for the liquid crystal._LC100 often does not become "1" (High) when it should be "1" (High), and conversely 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 characteristics of the TFT are not symmetric. That is, there is a bias in electrical characteristics between the state of charging and the state of discharging the pixel electrodes. The liquid crystal 102 is inherently insulating in its operation, and also has a liquid crystal potential (V) when the TFT is off._LC) Is in a floating state. Since this liquid crystal 102 is equivalently a capacitor, V is generated by the electric charge accumulated therein._LCIs decided. This charge is R for the liquid crystal_LCIt becomes a relatively small resistance, it leaks due to the presence of dust and ionic impurities, and it is R due to the pinhole of the gate insulating film of the TFT._GSIf 105 occurs, the charge leaks from it and V_LCWill be in a half-finished state. 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.

【0005】

As the liquid crystal 102, a TN (twisted nematic) liquid crystal is generally used. A rubbing alignment film is provided on each electrode for the orientation of the liquid crystal. The static electricity generated by this rubbing process causes weak dielectric breakdown, which may cause a leak between the adjacent pixel or the adjacent lead wire, or the gate insulating film may be weak and leak. It ends up.

【0006】

[Problems to be Solved by the Invention]

In an active liquid crystal display device, it is extremely important to keep the liquid crystal potential at a predetermined level as the initial value for one frame. However, in reality, there are many malfunctions of the active element, and the actual situation is that the liquid crystal potential cannot always be maintained at a predetermined level as the same value as the initial value for one frame. In addition, when the voltage applied to the liquid crystal is biased to either + or-due to the applied signal in driving the liquid crystal or the like, electrolysis or the like occurs, and the liquid crystal material is decomposed and denatured so that the display can be sufficiently performed. Nothing happens. In this case, the applied signal is converted to AC so that the voltage applied to the liquid crystal material is not biased, but this AC signal is very complicated.

【0007】

The present invention solves the above-mentioned problems and makes the current matrix larger, that is, makes the response speed larger. Also, the potential of each pixel, that is, the liquid crystal potential V._LCIs fixed to "1" and "0" sufficiently stably so that the level does not drift in one frame.

【0008】

Further, due to the demand for colorization and high quality of the display device, gradation display is strongly required, but the driving method of gradation display is very complicated.

【0009】

[Means for solving problems]

The present invention has NTFT and PTFT as a complementary configuration with respect to a pixel, and connects the source (drain) portion of the NTFT to the first signal line of the pair of signal lines to form the source of the PTFT (the source of the PTFT. The drain) section is connected to the second signal line of the pair of signal lines, the gate electrodes of the NTFT and PTFT are commonly connected to the third signal line, and the drain (source) section of the NTFT and PTFT is connected. It is a method of driving a display device provided in connection with a pixel electrode, and is applied to the third signal line during a period in which a signal waveform is applied to the pair of first and second signal lines. On the other hand, this is a method of driving a display device that drives a thin film having a complementary configuration (hereinafter referred to as C / TFT) by applying a signal waveform 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.

【0010】

As a configuration of a display device to which the driving method of the present invention can be applied, two or more C / TFTs may be connected to one pixel to form one pixel. Further, one pixel may be divided into two or more, and one or more C / TFTs may be connected to each.

【0011】

BEST MODE FOR CARRYING OUT THE INVENTION

Typical examples of the configuration of the display device to which the drive method of the present invention can be applied are shown as circuit diagrams in FIGS. 2, 3, and 4. In addition, examples of actual pattern layouts (layouts) are shown in FIGS. 5, 6 and 7 corresponding to each. In order to simplify the explanation, a 2 × 2 matrix configuration will be used as an example. In the example of the 2 × 2 matrix shown in FIG. 2, the 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 the common output end of C / TFT. Is connected to the liquid crystal 15. Connect the input end (10 side) of NTFT to the first signal line 5 or 6 of the pair of signal lines in the X-axis direction, and connect the input end (20 side) of PTFT to the pair of signal lines in the X-axis direction. It is connected to our second signal line 8 or 7.

【0012】

In such a configuration, as shown in FIG. 1, the third signal line 3 is connected to the third signal line 3 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 the on signal waveform is applied, the liquid crystal potential (V)_LC) 14 is the voltage V applied to the first signal line_GG-Vth. Further, when the off signal waveform is applied between the pair of the first signal lines 5 and the second signal line 8, and the off signal waveform is applied to the third signal line 3, 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 during the period when the on signal waveform is applied between the pair of first signal lines 5 and the second signal line 8, the liquid crystal potential (V_LC) 14 also has no potential. As you can see, 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.

【0013】

Further, the counter electrode 16 has an offset voltage V._OFFSETIs applied, and the voltage actually applied to the liquid crystal 15 is V._GG+ V_OFFSET-Vth, or V_OFFSETIt becomes two values of. In the driving method of the present invention, the offset voltage V applied to the counter electrode_OFFSETCan be changed to turn the liquid crystal drive on and off as desired. In addition, since the threshold value when actually driving the liquid crystal differs depending on the liquid crystal material, this offset voltage V is used to match the value of the liquid crystal._OFFSETAny threshold can be adjusted simply by changing.

【0014】

In addition, when the voltage applied to the liquid crystal is biased to either + or-due to the applied signal when driving the liquid crystal or the like, electrolysis or the like occurs, and the liquid crystal material is decomposed and denatured so that the display is sufficient. In this case, the signal to be applied is converted to alternating current so that the voltage applied to the liquid crystal material is not biased. However, according to the driving method of the present invention, the offset voltage V applied to the counter electrode is V._OFFSETIt has a feature that an AC signal can be generated very easily only by inverting the polarity of the above and the logic of the selection signal added to the data signal line.

【0015】

In the example of FIG. 3, the four gate electrodes of NTFT13PTFT22 constituting the first C / TFT and NTFT24 and PTFT25 constituting the second C / TFT are commonly connected to the third signal line 3 in the Y direction. , The input terminals of NTFT13 and NTFT24 are shared and connected to the first signal line 5 in the X direction, and the input ends of PTFT22 and PTFT25 are shared and connected to the second signal line 8 in the X direction. Further, the outputs of the two C / TFTs are shared and connected to the pixel electrode 17, which is one electrode of one liquid crystal 15. In this way, even if one of the two NTFTs or the two PTFTs is slightly leaked, the pixels are in phase and can be driven.

【0016】

FIG. 4 shows two pixel electrodes 17 and 26 and two C / TFTs corresponding to each of the two pixel electrodes 17 and 26 in one pixel 23. Make the gate electrodes of the two C / TFTs common and make the first input. Further, the input of each NTFT and each PTFT of each C / TFT is 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 inoperable due to a defect such as a TFT leak. Further, even if the operation is delayed, the other operates normally, so that there is a feature that defects are not conspicuous in the matrix configuration operation.

【0017】

[Example]

[Example 1]

In this embodiment, an explanation will be given using a liquid crystal display device having a circuit configuration as shown in FIG. Fig. 5 shows the actual arrangement of electrodes and the like corresponding to this circuit configuration. For the sake of simplicity, only the part corresponding to 2 × 2 is described. The actual drive signal waveform is shown in FIG. For the sake of simplicity, this will also be explained using the signal waveform when a 4 × 4 matrix configuration is used.

【0018】

First, a method of manufacturing the liquid crystal display device used in this embodiment will be described with reference to FIG. In FIG. 13 (A), a silicon oxide film as a blocking layer 51 using a magnetron RF (radio frequency) sputtering method on a glass 50 that can withstand a heat treatment of 700 ° C or less, for example, about 600 ° C, which is not expensive, such as quartz glass. To a thickness of 1000-3000 Å. The process conditions were an atmosphere of 100% oxygen, a film formation temperature of 15 ° C, an output of 400 to 800 W, and a pressure of 0.5 Pa. The film formation rate using quartz or single crystal silicon for the target was 30 to 100 Å / min.

【0019】

A silicon film was formed on this by LPCVD (vacuum vapor phase) method, sputtering method or plasma CVD method. When formed by the vacuum gas phase method, disilane (Si) is formed at 450 to 550 ° C, which is 100 to 200 ° C lower than the crystallization temperature, for example, 530 ° C.₂H₆) Or trisilane (Si₃H₈) Was supplied to the CVD equipment to form a film. The pressure in the reactor was 30 to 300 Pa. The film formation rate was 50 to 250 Å / min. Boron is 1 × 10 using diborane to control the threshold voltage (Vth) of NTFT and PTFT almost the same.¹⁵~1×10¹⁸cm^-3May be added during film formation as the concentration of.

【0020】

When using the sputtering method, the back pressure before sputtering is 1 x 10^-5The setting was Pa or less, and the target was single crystal silicon, and the atmosphere was such that 20 to 80% of hydrogen was mixed with argon. For example, argon was 20% and hydrogen was 80%. The film formation temperature was 150 ° C, the frequency was 13.56 MHz, the sputtering output was 400 to 800 W, and the pressure was 0.5 Pa.

【0021】

When a silicon film is produced by the plasma CVD method, the temperature is set to, for example, 300 ° C, and monosilane (SiH) is used.₄) Or disilane (Si₂H₆) Was used. These were introduced into a PCVD apparatus and a high-frequency power of 13.56 MHz was applied to form a film.

【0022】

The film formed by these methods has 5 x 10 oxygen.²¹cm^-3The following is preferable. When this oxygen concentration is high, it is difficult to crystallize, and the thermal animation temperature must be high or the thermal animation time must be lengthened. If it is too small, the backlight will increase the leak current in the off state. Therefore, 4x10¹⁹~4×10²¹cm^-3The range was set to. Hydrogen is 4x10²⁰cm^-3And silicon 4x10²²cm^-3It was 1 atomic% when compared as. In addition, the oxygen concentration is 7 × 10 in order to promote crystallization more for the source and drain.¹⁹cm^-3Below, preferably 1 × 10¹⁹cm^-3The following is performed, and oxygen is implanted only in the channel-forming region of the TFT that constitutes the pixel by the ion implantation method.²⁰~5×10²¹cm^-3It may be added so as to become. At that time, since the TFTs constituting the peripheral circuits are not irradiated with light, it is effective to reduce the mixing of oxygen and to have a larger carrier mobility for high-frequency operation.

【0023】

Next, an amorphous silicon film is prepared to a thickness of 500 to 5000 Å, for example 1500 Å, and then heat-treated at a temperature of 450 to 700 ° C. for 12 to 70 hours at a medium temperature in a non-oxide atmosphere, for example, hydrogen. It was kept at a temperature of 600 ° C in an atmosphere. Since a silicon oxide film having an amorphous structure is formed on the surface of the substrate under the silicon film, no specific nuclei are present in this heat treatment, and the whole is uniformly heated and annealed. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed.

【0024】

Due to the anneal, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order in the state after the film formation of silicon tends to crystallize to become a crystalline state. However, since the silicon existing between these regions forms a bond with each other, the silicons pull each other. Single crystal silicon peak 522 cm as measured by Reza Raman spectroscopy^-1A peak shifted to the lower wavenumber side is observed. The apparent particle size of it is 50 to 500 Å when calculated from the half width, which is like a microcrystal, but in reality, there are many regions with high crystallinity and it has a cluster structure, and between each cluster. Was able to form a film with a semi-amorphous structure in which silicon was bonded (anchoring) to each other.

【0025】

As a result, the coating exhibits a state in which there is virtually no grain boundary (hereinafter referred to as GB). Carriers can easily move to each other through anchored locations between clusters, resulting in higher carrier mobility than so-called GB's well-existing polycrystalline silicon. That is, hole mobility (μh) = 10 to 200 cm²/ Vsec, electron mobility (μe) = 15 ~ 300cm²/ Vsec is obtained.

【0026】

On the other hand, when the coating is polycrystallized by a high-temperature animation of 900 to 1200 ° C instead of the medium-temperature animation as described above, solid-phase growth from the nucleus causes segregation of impurities in the coating, resulting in GB. Impurities such as oxygen, carbon, and nitrogen increase in the crystal, and the mobility in the crystal is large, but it creates a barrier in GB and hinders the movement of carriers there. As a result, 10 cm²The reality is that it is difficult to obtain mobility of / Vsec or higher. That is, in this embodiment, for this reason, a silicon semiconductor having a semi-amorphous or semi-crystal structure is used.

【0027】

In FIG. 13 (A), the silicon film was photoetched with a first photomask to prepare a region 22 for PTFT (channel width 20 μm) on the right side of the drawing and a region 13 for NTFT on the left side.

【0028】

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 the same condition as the production of the silicon oxide film as the blocking layer. A small amount of fluorine may be added during this film formation to immobilize sodium ions.

【0029】

After this, phosphorus is 1 ~ 5 × 10 on this upper side.²¹cm^-3Silicon film with the concentration of, or molybdenum (Mo), tungsten (W), MoSi on this silicon film₂Or WSi₂A multilayer film was formed with. 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, a channel length of 10 μm, lind-psilicon as a gate electrode was formed to a thickness of 0.2 μm, and molybdenum was formed therein to a thickness of 0.3 μm. In FIG. 13 (C), photoresist 57 is formed using a photomask, and boron is 1 to 5 × 10 with respect to the source 59 drain 58 for PTFT.¹⁵cm^-2The dose was added by the ion implantation method. Next, as shown in FIG. 13 (D), the photoresist 61 was formed using a photomask. Source 64 for NTFT, phosphorus as drain 62 1 ~ 5 × 10¹⁵cm^-2It was added by the ion implantation method in the dose amount of.

【0030】

These were performed through the gate insulating film 54. However, in FIG. 13B, silicon oxide on the silicon film may be removed using the gate electrodes 55 and 56 as masks, and then boron and phosphorus may be ion-implanted directly into the silicon film.

【0031】

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

【0032】

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

【0033】

In this example, the thermal animation was performed twice in FIGS. 13 (A) and 13 (D). However, the animation shown in FIG. 13 (A) may be omitted depending on the desired characteristics, and both may be combined with the animation shown in FIG. 13 (D) to shorten the manufacturing time. In FIG. 13 (E), the interlayer insulator 65 was formed into a silicon oxide film by the above-mentioned sputtering method. The LPCVD method, the optical CVD method, and the atmospheric pressure CVD method may be used to form the silicon oxide film. For example, it was formed to a thickness of 0.2 to 0.6 μm, and then a window 66 for an electrode was formed using a photomask. Further, aluminum is formed on all of them by a sputtering method, and after the leads 71 and 72 and the contacts 67 and 68 are prepared by using a photomask, the surface is coated with an organic resin 69 for flattening, for example, a translucent polyimide resin. The electrode was formed and the electrode was drilled again with a photomask.

【0034】

As shown in FIG. 13 (F), two TFTs have a complementary configuration, and the output end is connected to the electrode of one pixel of the liquid crystal device as a transparent electrode by the sputtering method. Membrane) was formed. It was etched with a photomask to form the electrode 70. This ITO was formed at room temperature to 150 ° C and was achieved by oxygen at 200 to 400 ° C or atmospheric air. In this way, PTFT22, NTFT13, and the transparent conductive film electrode 70 were made on the same glass substrate 50. The electrical characteristics of the obtained TFT are PTFT, and the mobility is 20 (cm).²/ Vsec), Vth is -5.9 (V), NTFT mobility is 40 (cm)²/ Vsec), Vth was 5.0 (V).

【0035】

A transparent electrode was provided on the entire surface of one substrate for a liquid crystal device and the other glass substrate manufactured according to the above method, and these substrates were laminated to form a liquid crystal cell, and a TN liquid crystal material was injected therein. .. FIG. 6 shows the arrangement of the electrodes and the like of this liquid crystal display device. The NTFT 13 is provided at the intersection of the first scanning line 5 and the data line 3, and the NTFT for other pixels 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, at the intersection of the other adjacent first scanning line 6 and the data line 3, NTFTs for other pixels are provided. We have provided a matrix configuration using such a C / TFT. The NTFT13 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.

【0036】

On the other hand, in the PTFT22, the input end of the drain 20 is connected to the second scanning line 8 via the contact, the gate 21 is connected to the data line 3, and the output end of the source 18 is connected to the second scanning line 8 via the contact. It is connected to the electrode 17. Thus, between the pair of scanning lines 5 and 8 (inside), a pixel 23 made of a transparent conductive film and a C / TFT form one pixel. By repeating such a structure left and right and up and down, a 2 × 2 matrix can be expanded into a large pixel liquid crystal display device such as 640 × 480 and 1280 × 960.

【0037】

The feature here is that two TFTs are provided in a complementary configuration on one pixel, so that the pixel electrode 17 has a liquid crystal potential V of three values._LCIs to be fixed to. The operation will be described with reference to FIGS. 9 and 10. FIG. 9 shows a circuit diagram of the present invention when displaying a liquid crystal in a 4 × 4 matrix configuration, and FIG. 10 shows a timing chart of a drive signal waveform.

【0038】

In the case of this embodiment, X_1aX_1b, X_2aX_2b, X_3aX_3b, X_4aX_4bEach functions as a pair of scanning signal lines. Also, Y₁, Y₂, Y₃, Y₄Is functioning as a data line. Further, AA, AB ... DD in FIG. 9 mean the addresses of the pixels at the corresponding positions.

【0039】

In the display of such a 4 × 4 configuration, the timing chart of the signal waveform, the liquid crystal potential, and the potential difference actually applied to the liquid crystal corresponding to the four pixels of the addresses AA, AB, BA, and BB is shown in FIG. .. In FIG. 10, the horizontal axis represents time. One frame is set between times T1 and T2, and the interval is divided into four, and four pairs of scanning lines are sequentially scanned to apply a scanning signal. X in the figure_1a, X_2a, X_3a, X_4aOnly listed, but actually X_1b, X_2b, X_3b, X_4bTo X_1a, X_2a, X_3a, X_4aThe same waveform with different polarity is applied. Also, Y₁, Y₂, Y₃, Y₄A data signal as shown in FIG. 10 is applied to the line, and during the time period T1 to T2, only the AA pixel is selected and turned on or off. That is, T₁From t₁Data line Y between₁A data signal is applied to the liquid crystal, and within this time, a voltage exceeding the threshold value is applied to the liquid crystal of the AA pixel to drive the liquid crystal. At this time, an offset voltage is applied to the counter electrode of the liquid crystal display device. In FIG. 10, the exact same signal waveform is applied to T2 to T3 at the next time, and AA is displayed.

【0040】

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

【0041】

Next, a signal that inverts the logic of the signal applied to the data line is applied to the time T6 to T8, and an offset voltage having a different polarity from the signal applied between the time T1 and T6 is applied to the counter electrode. Is applied, and an AC signal is applied to the liquid crystal. This AC signal can cancel the positively biased charge between times T1 and T6. That is, of the signals applied from time T2 to T4, Y₁, Y₂, Y₃, Y₄By inverting the logic of the line, that is, by exchanging the selected signal and the non-selected signal and exchanging the positive and negative of the offset voltage of the counter electrode, the AA pixel is selected in the first frame of the time T2 to T4, and the latter 1 It has become possible to drive the liquid crystal by applying an AC signal that does not select four pixels in the frame. As a result, the electric charge remaining in the pixel can be easily canceled.

【0042】

As described above, the potential difference actually applied to the liquid crystal is the voltage of the signal of the third signal line, in this embodiment, the potential of the pulse voltage of the data line and the offset voltage of the counter electrode minus the Vth of the TFT. is there. 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. As a result, gradation display can be performed. In particular, for a liquid crystal drive whose threshold value is not clear, that is, a distributed liquid crystal having a gentle threshold or the like, sufficient gradation display can be performed by a drive method particularly well suited.

【0043】

As described above, the liquid crystal display can be performed only by adding a pulse signal to the data line and the pair of scanning lines, which is very simple according to the driving of the present invention.

【0044】

In addition, as another gradation method, when displaying one screen by applying drive signals of a plurality of frames to the liquid crystal for one display screen, the selection signal added to a specific pixel is reduced from the total number of frames. Therefore, gradation display can be easily performed.

【0045】

In this 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 alignment films on both transparent conductive films, and rub them to form them.

【0046】

When using FLC (ferroelectric) liquid crystal as the liquid crystal material, the operating voltage is ± 20 V, the cell spacing is 1.5 to 3.5 μm, for example 2.3 μm, and an alignment film is provided only on the counter electrode 16 for rubbing treatment. Just give it.

【0047】

When a dispersed liquid crystal or a polymer-liquid crystal is used, an alignment film is not required and the switching speed is increased. Therefore, the operating voltage is set to ± 10 to ± 15 V, and the cell spacing is reduced to 1 to 10 μm.

【0048】

In particular, when a dispersed liquid crystal is used, since a polarizing plate is not required, the amount of light can be increased both as a reflective type and as a transmissive type. And since the liquid crystal does not have a threshold, by adopting a C / TFT type in which a clear threshold voltage is specified as in the present invention, a large contrast and a cross-talk (evil with the adjacent pixel) are adopted. Interference) could be eliminated.

【0049】

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

【0050】

[Example 2]

This embodiment was carried out using a liquid crystal display device having the configuration corresponding to FIGS. 3 and 7. As is clear from this drawing, the Y-line scanning line 3 is arranged in the center, and the portion of the pair of data lines sandwiched between the first data line 5 and the second data line 8 is defined as one pixel 23. .. One pixel is connected to two C / TFTs consisting of one transparent conductive film pixel 17 and two NTFT13, 24 and two PTFT22, 25. All gate electrodes are connected to scan line 3, two NTFTs are connected to the first data line 3, and two PTFTs are connected to the second data line 8. One of these two C / TFTs can operate as a pixel even if there is a leak between the gate electrode and the channel formation region and it is defective.

【0051】

The feature here is that two C / TFTs are provided in one pixel, so that the pixel electrode 17 has a liquid crystal potential V of three values._LCIs to be fixed to. The operation will be described with reference to FIGS. 9 and 11. FIG. 9 shows a circuit diagram of the present invention when displaying a liquid crystal having a 4 × 4 matrix configuration, and FIG. 11 shows a timing chart of a drive signal waveform.

【0052】

In the case of this embodiment, X_1aX_1b, X_2aX_2b, X_3aX_3b, X_4aX_4bEach functions as a pair of data lines. Also, Y₁, Y₂, Y₃, Y₄Functions as a scanning line. Further, AA, AB ... DD in FIG. 9 mean the addresses of the pixels at the corresponding positions.

【0053】

In the display of such a 4 × 4 configuration, FIG. 11 shows a timing chart of the signal waveform, the liquid crystal potential, and the potential difference actually applied to the liquid crystal corresponding to the four pixels of the addresses AA, AB, BA, and BB. .. In FIG. 11, the horizontal axis represents time. One frame is between time T1 and T2, and the interval is divided into four, and the scanning line Y₁, Y₂, Y₃, Y₄Scanning signals are applied to the lines by sequentially scanning. Also, X₁, X₂, X₃, X₄A data signal as shown in FIG. 11 is applied to the line. X in the figure_1a, X_2a, X_3a, X_4aOnly listed, but actually X_1b, X_2b, X_3b, X_4bTo X_1a, X_2a, X_3a, X_4aThe same waveform with different polarities is applied, and only AA pixels are selected and turned on or off during the time T1 and T2. That is, T₁From t₁A pair of data lines X between₁A data signal is applied to the liquid crystal, and within this time, a voltage exceeding the threshold value is applied to the liquid crystal of the AA pixel, and the liquid crystal is driven. At this time, an offset voltage is applied to the counter electrode of the liquid crystal display device. In FIG. 11, the exact same signal waveform is applied to T2 to T3 at the next time, and AA is displayed.

【0054】

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

【0055】

Next, at times T6 to T8, a signal that inverts the logic of the signal applied to the pair of data lines is applied, and the polarity of the counter electrode is different from that of the signal applied between times T1 and T6. An offset voltage is applied and an AC signal is applied to the liquid crystal. This AC signal can cancel the positively biased charge between times T1 and T6. In fact, a pair of X's of the signals applied from time T2 to T4₁, X₂, X₃, X₄By inverting the logic of the line, that is, exchanging the selected signal and the non-selected signal, and exchanging the positive and negative of the offset voltage of the counter electrode, the AA pixel is selected in the first half frame, and four pixels are not selected in the second half frame. It has become possible to apply an AC signal and drive the liquid crystal.

【0056】

As described above, the liquid crystal display can be performed only by adding a pulse signal to the data line and the pair of scanning lines, which is very simple according to the driving of the present invention. Further, as in the first embodiment, the gradation display can be performed by changing the signal voltage on the scanning line side.

【0057】

[Example 3]

This embodiment was carried out using a liquid crystal display device having the configuration corresponding to FIGS. 4 and 8. As is clear from this drawing, the Y-line data line 3 is arranged in the center, and the portion of the pair of scanning lines sandwiched between the first scanning line 5 and the second scanning line 8 is defined as one pixel 23. .. One pixel is composed of two transparent conductive film pixel electrodes 17 and 26. The pixel 17 is connected to NTFT13 and PTFT22, and the pixel 26 is connected to NTFT24 and PTFT25 as each C / TFT configuration. All gate electrodes are connected to data line 3, two NTFTs are connected to the first scan line 3, and two PTFTs are connected to the second scan line 8. One of these two C / TFTs can operate as a pixel even if there is a leak between the gate electrode and the channel formation region and it is defective. In this way, even if one pixel operates only halfway, the degree of deterioration of the gray scale can be reduced when the other pixel operates normally and is colored.

【0058】

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

【0059】

In the case of this embodiment, X_1aX_1b, X_2aX_2b, X_3aX_3b, X_4aX_4bEach functions as a pair of scanning signal lines. Also, Y₁, Y₂, Y₃, Y₄Is functioning as a data line. Further, AA, AB ... DD in FIG. 9 mean the addresses of the pixels at the corresponding positions.

【0060】

In the display of such a 4 × 4 configuration, the timing chart of the signal waveform, the liquid crystal potential, and the potential difference actually applied to the liquid crystal corresponding to the four pixels of the addresses AA, AB, BA, and BB is shown in FIG. I will. In FIG. 12, the horizontal axis represents time. One frame is set between times T1 and T2, and the interval is divided into 16, and four pairs of scanning lines are sequentially scanned to apply a scanning signal. X in the figure_1a, X_2a, X_3a, X_4aOnly listed, but actually X_1b, X_2b, X_3b, X_4bTo X_1a, X_2a, X_3a, X_4aThe same waveform with different polarity is applied. Also, Y₁, Y₂, Y₃, Y₄A data signal as shown in FIG. 12 is applied to the line, and the timing is from time T1 when the data signal is applied to the data line at a specific time divided into 16 in one frame according to the address of the selected pixel. During T2, only AA pixels are selected and turned on or off. That is, T₁From t₁Data line Y between₁A data signal is applied to the liquid crystal, and within this time, a voltage exceeding the threshold value is applied to the liquid crystal of the AA pixel to drive the liquid crystal. At this time, an offset voltage is applied to the counter electrode of the liquid crystal display device. Next, at times T2 to T3, a signal that does not select four pixels at all is applied.

【0061】

Next, for time T3 to T4, a signal that inverts the logic of the signal applied to the data line is applied, and an offset having a different polarity from the signal applied between time T1 and T3 is applied to the counter electrode. A voltage is applied and an AC signal is applied to the liquid crystal. With this AC signal, it is possible to cancel the charge that was positively biased between the times T1 and T3. That is, of the signals applied from time T1 to T2, Y₁, Y₂, Y₃, Y₄By inverting the logic of the line, that is, by exchanging the selected signal and the non-selected signal and exchanging the positive and 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 has become possible to drive the liquid crystal by applying an AC signal that does not select.

【0062】

As described above, the liquid crystal display can be performed only by adding a pulse signal to the data line and the pair of scanning lines, which is very simple according to the driving of the present invention. In this embodiment, scanning is performed with the scanning side as the Y line, but the scanning is not particularly limited to this configuration, and the X-ray side can be the scanning side. It is also possible to randomly apply a data signal to each data line to randomly select pixels. Other than that, what is not described here is the same as that described in Examples 1 and 2.

【0063】

[Effect of the invention]

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. In addition, since the drive capability of the C / TFT as an active element is high, the operating matrix can be expanded, and the peripheral drive circuits can be made simpler, which makes it possible to reduce the size of the display device and the manufacturing cost. effective. In addition, a very simple signal can be used for the three signal lines and the counter electrode to exert high drive capability.

【0064】

Even if there are some defective TFTs, they can be compensated to some extent because they have in-phase output.

【0065】

Furthermore, in order to prevent the liquid crystal material from being electrolyzed, the logic of the signal that applies the AC signal drive, which is indispensable for driving the liquid crystal, to the gate signal line of the C / TFT is inverted, and the polarity of the offset voltage applied to the counter electrode is inverted. It was achieved by the simple thing of doing.

【0066】

Further, if the voltage of the signal of the third signal line is arbitrarily changed, the potential difference actually applied to the liquid crystal can be changed accordingly. As a result, gradation display can be performed. In particular, for a liquid crystal drive whose threshold value is not clear, that is, a distributed liquid crystal having a gentle threshold, sufficient gradation display can be performed by a particularly well-suited drive method. As another gradation method, when displaying one screen 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. As a result, gradation display can be easily performed.

【0067】

As the display medium in the present invention, it can be used as a transmissive liquid crystal display device or a reflective liquid crystal display device. Further, as the liquid crystal material that can be used, the TN liquid crystal, the FLC liquid crystal, the dispersed liquid crystal, and the polymer type liquid crystal of the previous technique can be used. In addition, an ionic dopant is added to a guest-host type or dielectric anisotropic type nematic liquid crystal to apply an electric field to form a nematic liquid crystal, and an electric field is applied to a mixture with the cholesteric liquid crystal to form a nematic phase and cholesteric. It is also possible to use a phase transition liquid crystal that causes a phase change with the phase and realizes a transparent or cloudy display. In addition to the liquid crystal, it is also possible to use a so-called dispersion system for electrophoresis display in which pigment particles having a different color are dispersed in an organic solvent colored with a dye, for example.

【0068】

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

[Simple explanation of drawings]

[Figure 1]

The drive waveform of the present invention is shown.

[Figure 2]

A circuit diagram of an active display device using a complementary TFT is shown.

[Fig. 3]

A circuit diagram of an active display device using a complementary TFT is shown.

[Fig. 4]

A circuit diagram of an active display device using a complementary TFT is shown.

[Fig. 5]

The circuit diagram of the conventional active liquid crystal apparatus is shown.

[Fig. 6]

A plan view of one substrate of the liquid crystal display device corresponding to FIG. 2 is shown.

[Fig. 7]

A plan view of one substrate of the liquid crystal display device corresponding to FIG. 3 is shown.

[Fig. 8]

A plan view of one substrate of the liquid crystal display device corresponding to FIG. 4 is shown.

[Fig. 9]

The circuit diagram of the 4 × 4 active liquid crystal apparatus using the complementary TFT is shown.

[Fig. 10]

An example of the drive signal waveform of the present invention and its timing chart is shown.

[Fig. 11]

An example of the drive signal waveform of the present invention and its timing chart is shown.

[Fig. 12]

An example of the drive signal waveform of the present invention and its timing chart is shown.

[Fig. 13]

The manufacturing process diagram of the C / TFT used in this invention is shown.

[Explanation of symbols]

~ Process using photomask 1, 2 ... Peripheral circuit 3, 4 ... 3rd signal line 5, 6 ... 1st signal line 7, 8 ... 2nd signal line 13 ... NTFT 16 ... Opposite electrode 17 ... Pixel electrode 22 ... PTFT 23 ... pixels