KR19990037504A - Driving method of liquid crystal device, spatial light modulating device and driving method thereof - Google Patents

Abstract

By using an electrical signal having a DC asymmetric waveform or so-called monopole waveform according to the present invention, a first period, i.e., a period of applying the electrical signal to select one of two states and a second period following the first period There is provided a liquid crystal driving method in which a period for maintaining a selected state is provided, i.e., without applying an electric signal or by applying an electric signal that neither of the two states is selected by the memory characteristics of the liquid crystal. A pulse signal having bipolar or negative polarity with respect to the reference level is used essentially as an electrical signal for selecting one of two states, and another pulse signal having a polarity opposite to this pulse signal as an electrical signal for selecting another state. Used essentially. As the reference level, the potential of the first electrode or the second electrode is usually used. Typically, a pulse signal and another pulse signal are each substantially implemented as a single pulse signal.

Description

Driving method of liquid crystal device, spatial light modulating device and driving method thereof

The present invention relates to a method for driving a liquid crystal element such as a liquid crystal spatial light modulation display device or a liquid crystal modulator, wherein a first substrate having a first electrode and a second substrate having a second electrode are provided to face each other. And a predetermined gap is sandwiched between the first electrode and the second electrode, and the ferroelectric liquid crystal or the antiferroelectric liquid crystal is placed in the gap so that the liquid crystal element is in accordance with the electrical signal applied between the first electrode and the second electrode. State, that is, one of the ON state and the OFF state can be substantially selected. Examples of ON and OFF states include light transmission and non-transmission states, light reflection and non-reflection states, light polarization and non-polarization states, and light rotation and non-rotation states. In addition, the present invention is in accordance with the electrical signal applied to the surface electrode of the spatial light modulation unit of the spatial light modulation device, that is, the light transmission and non-transmission state, the light reflection and non-reflection state, optical polarization and non-polarization state And a spatial light modulator such as a liquid crystal spatial light modulation display device capable of substantially selecting ON and OFF states such as light rotation and non-rotation states.

Liquid crystal display (LCD) devices used in display units using liquid crystals are characterized by low power consumption, small thickness and low weight. By these characteristics, to mention a few, the use of LCDs such as clocks, calculators, computer display units and television receivers is increasing in number.

Research and development on the use of FLC (ferroelectric liquid crystal), such as liquid crystal of the LCD device is being actively carried out. As for FLC, ferroelectric liquid crystals were first synthesized by Meyer in 1975, and in 1980 Clark and Ragawall invented surface-stabilized ferroelectric liquid crystals whose domains were reversible by electric fields.

FLC has a permanent dipole moment in each of its molecules itself, oriented perpendicular to the vertical axis of the molecule, and exhibits spontaneous polarization. The FLC display device having this advantage provided by the FLC is excellent in that the device has the following three characteristics.

1. The switching speed has a dimension value of μs. The FLC display device reacts at a speed 1,000 times the switching speed of the TN (twist nematic) liquid crystal display device, and therefore, the response thereof is excellent in that it is very fast.

2. It does not have a twist structure in its molecular arrangement, resulting in less dependence on the angle of view.

3. The picture is retained due to its ability to memorize the picture even when the power supply is interrupted. Simple matrix drive technology can be adopted even for more than 1,000 scan lines, which are in keeping with the high-vision display unit.

Accordingly, the FLC display device is a display device capable of pursuing high performance such as high resolution, low cost, and the possibility of keeping up with a large screen.

As shown in Fig. 37, in a ferroelectric liquid crystal display device such as a surface-stabilized ferroelectric liquid crystal display device, the direction of the liquid crystal molecules M is in two states, namely, in response to an externally applied electric field E (or spontaneous polarization Ps). Switch between state 1 and state 2. When the liquid crystal element is placed between two orthogonal polarizers, this change in the molecular direction appears as a change in the light transmission rate. As shown in Fig. 38, as the threshold voltage V _th crossing in the applied electric field increases, the light transmission rate suddenly changes from 0% to 100%.

The ferroelectric liquid crystal device operating in the bistable mode is stable only in two states. As a result, unlike TN liquid crystal displays, it is difficult to adjust the ferroelectric liquid crystal display to produce a toned display performance.

That is, the ferroelectric liquid crystal display device adjusts the light rays passing through the device by abruptly changing the amount of light emission as described above, which makes it difficult to achieve a toned display performance. As a measure to solve this problem, a technique called an area toning method has been proposed, whereby the toned display performance has appeared as a result of image adjustment by providing a sub-pixel. However, according to this area color rendering method, the color rendering is not expressed in the pixel. Thus, it causes problems of insufficient coloration performance and high cost for very small pixels such as spatial light modulators.

In order to solve the above problems, a method of implementing digitally colored display performance while maintaining excellent contrast has been invented, so that a spatial light modulator or a so-called on \ off type spatial light modulator is similar to a ferroelectric liquid crystal display. It is used to select one of two states: light reflecting state and non-reflecting state or light transmitting state and non-light transmitting state.

This method uses a spatial light modulator to modulate the light intensity of the light source and to select one of the two states described above, namely the light reflection state and the light non-reflective state or the light transmission state and the light non-transmission state. By combining the electric field continuous method, in principle, it is an intrinsic display technology that makes the display performance leading to continuous tonality visible to the human eye. This method is disclosed by the inventors of the present invention in Japanese Patent Laid-Open Nos. Hei 5-347576 and Hei 7-212686.

In the case of a reflective spatial light modulator using a ferroelectric liquid crystal, a reflection layer for reflecting light rays generated by a light source, a ferroelectric liquid crystal layer serving to modulate light rays, and ferroelectric liquid crystals driving opposite electrodes to each other are provided on the driving layer. Is provided.

In the first case, when a light source with a constant light intensity is used, in order to express an 8-bit color tone (or 0 to 255 hue), 16.7 ms by simple division into 0 to 255 hue that can be represented by 8 bits You need to display the frame. Thus, the ferroelectric liquid crystal should be fully driven within about 65.5 μs. In the case of a 10-bit display operation, the drive time is about 16.3 μs. In view of the response speed of modern ferroelectric liquid crystals, these values are difficult to realize. To obtain them, the applied voltage is set to a large value.

However, by using a light source capable of modulating the intensity of the generated light rays, the drive time of the time division of the ferroelectric liquid crystal can be substantially extended. Assume that 8-bit modulation on the intensity of the light beam can be performed to express the 8-bit toning as shown in FIG. 39. In such a case, a sufficiently satisfactory operation can be obtained when the ferroelectric liquid crystal can be fully driven within about 2.08 ms. In the case of a 10-bit display operation, the drive time is about 1.67 ms. In view of the response speed of modern ferroelectric liquid crystals, these values are values that allow driving of the ferroelectric liquid crystals to be actually implemented. Here, an image including one hue bit is called a bit plane, and the display time of the bit plane is known as the bit plane time. In this case, to express the 8-bit toning as shown in FIG. 39, the number of bit planes is 8, and the total bit plane time of the 8-bit plane is equal to the time of one frame.

In recent years, the development of a digital display device in the plasma display panel field is in progress. It is desirable to have a general purpose or high quality digital display device. An 8-bit display with digitally toned display capability is said to be sufficient as a minimally toned display. However, as high quality display performance, this is said to be insufficient.

In addition, in digitally toned displays, the problem of false contours is encountered.

False contours contribute to long bit plane display times that experience time division during field sequential (time division) driving. False contour is a phenomenon caused by improper stimulation provided to the retina. When the eye follows the light emission point, the time shift of the light emission pattern is converted to space shift, causing stimulation or the like. The effect of this phenomenon can be reduced by shortening the bit plane time.

Naturally, if the bit plane time is shortened indefinitely, the false contour is resolved. However, this will cause problems such as device structure, power consumption and data transfer rate to the light valve. Considering the elimination of false contours and the compromise in the current state of semiconductor technology between these problems, it has been found to be desirable to set the display time of a 1-bit plane to at least 100 μs. From the peak of the drive voltage and the actual response time of the ferroelectric liquid crystal using the active device, it is preferable to cover 50 µs for the switching completion time of the liquid crystal, and configure the frame with a 36 bit plane x 3 primary color.

However, depending on the driving voltage set to 10 Vp-p and 50 µs used as the switching completion time of the ferroelectric liquid crystal, the number of available driving waveforms is limited. In other words, since complex drive waveforms for reducing the number of burning and hysteresis phenomena cannot be used, a simple dipole waveform or the like is left as the only possible.

In addition, the display performance of all liquid crystal display devices is degraded due to the ions in the panel. In some cases, the ions in the panel are introduced during the synthesis of the liquid crystal, during the manufacture of the liquid crystal alignment film, or during the injection process of the liquid crystal. In the current state of the art, it may be difficult or impossible to control the number of ions after the liquid crystal is produced into the device.

Therefore, when DC (pulse waveform) asymmetry is introduced into the drive waveform, it is thought that ions are mis-distributed and deterioration will occur in the liquid crystal material. Common sense in which an electric neutral state is indispensable for a driving waveform is common in the liquid crystal industry. For more information on this common sense, see N.A. "FERROELECTRIC LIQUID CRYSTALS: Principles, Properties and Applications" by Clark and ST Ragawall, Vol. 7, pp. 409-461, Philadelphia: "Ferroelectrics" by Gordon & Breach, 1991, W. Hartman, Vol. 122, pp. 1-26 (1991) and "Ferroelectrics" by Y. Inabara, Vol. 85, pp. 255-264 (1988).

In order to prevent the DC element from occurring in the signal, the following driving technique is adopted:

1. A plurality of pulse signals are combined. The pulse signal includes a pulse signal for selecting a state and a pulse signal having a polarity opposite to the state for selecting a pulse signal for canceling the state for selecting the pulse signal. The state in which the pulse signal is selected and the pulse signal for canceling the state in which the pulse signal is selected are referred to as a black-display pulse signal and a white-display pulse signal, respectively. An example of a pulse signal combination is shown in FIG. 40.

2. After a predetermined write signal W (white) or B (black) has been applied for a fixed period, it has the same voltage and duration as each of these write signals W (white) or B (black), but with opposite polarity to it. An electrical signal -W or -B is applied to remove the DC element of the signal. An example of such a technique is shown in FIG. 41.

However, when the signal waveform of the first driving technique is used, the signal waveform becomes complicated, which complicates the driving circuit. Also, while the signal for removing the DC element is applied, the state is invalid. As a result, the period is shortened while the selected state is effective. In other words, the display time of the bit plane is shortened in the digitally toned display. Moreover, in the case of a signal that is applied only for a limited period of time, the pulse width of the write signal is narrowed because part of the period must be used for an invalid pulse for removing the DC element of the signal. For this reason, there is a need for liquid crystal materials having a high response speed.

In addition, when the signal waveform of the second driving technique is used, an invalid signal for removing the DC element is applied for the same period as that of the write signal. Thus, the period in which the selected state prevails is reduced by half. As a result, the display darkens due to the fact that the display time of the bit plane in the digitally toned display is also reduced by half.

It is therefore an object of the present invention to provide a very simple high performance liquid crystal drive method which can prevent degradation in liquid crystals without the need for DC neutralization to remove the DC elements as described above.

Another object of the present invention is to provide a method for driving a spatial light modulator as well as providing a spatial light modulator that is suitable for the liquid crystal driving method and capable of operating at high speed.

The inventors of the present invention have repeatedly conducted active research on a DC asymmetric driving method that is not constrained by common sense, such as the removal of a DC element by the DC symmetric waveform provided by the first and second driving techniques. As a result, the present inventors have led to the present invention by driving a ferroelectric liquid crystal by using a specific DC asymmetric waveform without causing deterioration of the liquid crystal, in addition, reducing the possibility of burning and hysteresis.

1A to 1E are diagrams showing single-pole pulse waveforms that can be applied to the driving method provided by the present invention, respectively.

Fig. 2 is a diagram specifically showing the drive waveform of the TFT type.

3 is a view showing another driving waveform specifically used in a linear sequential driving method of a VLSI type.

Fig. 4 is a diagram showing the driving waveform used in the block sequential driving method of VLSI type in detail.

Fig. 5 is a diagram showing the other drive waveforms used in the batch sequential driving method of the VLSI type specifically.

Fig. 6 is a diagram showing an equivalent circuit of a pixel of a conventional liquid crystal element using a twist-nematic liquid crystal (TN crystal).

7 shows an equivalent circuit of a pixel of a liquid crystal element using ferroelectric liquid crystal (FLC).

8 shows another equivalent circuit of a pixel of a liquid crystal element using ferroelectric liquid crystal (FLC).

FIG. 9 shows another equivalent circuit of a pixel of a liquid crystal element using ferroelectric liquid crystal (FLC). FIG.

FIG. 10 shows another equivalent circuit of a pixel of a liquid crystal element using ferroelectric liquid crystal (FLC). FIG.

FIG. 11 shows an equivalent circuit used to explain the operation of the pixel shown in FIG. 9; FIG.

12A-12C are timing diagrams of operations.

Fig. 13A is a diagram showing a cross section of the structure of a VLSI type ferroelectric liquid crystal spatial light modulation display device in a simple and clear manner.

Fig. 13B shows a perspective view of a partial cross section of the same ferroelectric liquid crystal spatial light modulation display of the VLSI type in a simple and clear manner;

14A is a partial perspective view of a partial cross section of another exemplary structure of the same ferroelectric liquid crystal spatial light modulation display;

FIG. 14B shows a partial perspective view of a partial cross section of another exemplary structure of the same ferroelectric liquid crystal spatial light modulation display; FIG.

FIG. 15A is a partial perspective view of a partial cross section of a typical structure of another ferroelectric liquid crystal spatial light modulation display; FIG.

FIG. 15B is a partial perspective view of a partial cross section of another exemplary structure of another ferroelectric liquid crystal spatial light modulation display; FIG.

Fig. 16A is a diagram showing a perspective view of a partial cross section of the structure of a TFT light transmission type ferroelectric liquid crystal spatial light modulation display device in a simple and clear manner;

FIG. 16B partially illustrates a perspective view of a partial cross section of another exemplary structure of the same ferroelectric liquid crystal spatial light modulation display; FIG.

17 shows DC asymmetric monopole pulse drive waveforms provided by an embodiment of the present invention, respectively.

18 shows a different DC symmetric dipole pulse, respectively, for comparison purposes.

19 shows another DC symmetric dipole pulse, respectively, for comparison purposes.

20A shows a result showing the dependence of the light transmission rate on the number of white display times per frame not exceeding 36 and the number of white display times for the DC symmetric drive waveform shown in FIG.

FIG. 20B shows a result showing the dependence of the light transmission rate on the number of black display times per frame not exceeding 36 and the number of black display times for the DC symmetric drive waveform shown in FIG. 17.

FIG. 21A shows a result showing the dependence of the light transmission rate on the number of white display times per frame not exceeding 36 and the number of white display times for the DC symmetric drive waveform shown in FIG. 18; FIG.

FIG. 21B shows a result showing the dependence of the light transmission rate on the number of black display times per frame not exceeding 36 and the number of black display times for the DC symmetric drive waveform shown in FIG. 18; FIG.

FIG. 22A shows a result showing the dependence of the light transmission rate on the number of white display times per frame not exceeding 36 and the number of white display times for the DC symmetric drive waveform shown in FIG. 19. FIG.

FIG. 22B shows a result showing the dependence of the light transmission rate on the number of black display times per frame not exceeding 36 and the number of black display times for the DC symmetric drive waveform shown in FIG. 19. FIG.

FIG. 23 is a graph showing a change in white level over time obtained as a result of driving a ferroelectric liquid crystal by continuously using a DC asymmetric unipolar pulse waveform for one week. FIG.

Fig. 24 is a diagram showing a combination of pulses of a drive waveform used for observing hysteresis phenomenon.

FIG. 25 shows a curve showing observation results for the ferroelectric liquid crystal material CS-1022 provided by the present invention. FIG.

FIG. 26 shows a curve showing observation results for the ferroelectric liquid crystal material CS-1016 provided by the present invention. FIG.

FIG. 27 shows a curve showing the observation results for the ferroelectric liquid crystal material CS-1017 provided by the present invention. FIG.

FIG. 28 is a view showing a change in light transmittance indicating hysteresis phenomenon for the ferroelectric liquid crystal material CS-1017 provided by the present invention. FIG.

Fig. 29 shows curves each showing the dependence of hysteresis on the pulse voltage for the ferroelectric liquid crystal material CS-1017 provided by the present invention at the ratio of 34 white displays to 2 black displays.

30 shows curves each showing the dependence of hysteresis on memory time for the ferroelectric liquid crystal material CS-1022 provided by the present invention at a ratio of 34 white displays to 2 black displays.

FIG. 31 shows curves each showing the dependence of hysteresis on memory time for the ferroelectric liquid crystal material CS-1016 provided by the present invention at a ratio of 34 white displays to 2 black displays. FIG.

32 shows curves each showing the dependence of hysteresis on memory time for the ferroelectric liquid crystal material CS-1017 provided by the present invention at a ratio of 34 white displays to 2 black displays.

Fig. 33 shows the amount of contrast of the ferroelectric liquid crystal CS-1022 obtained with a DC offset overlapping with the common electrode.

34 shows waveforms with the shape of an applied pulse corruption;

FIG. 35 shows a graph showing a relationship between a interruption time and a threshold of a corrupted waveform having a shape of a third order function for a liquid crystal display; FIG.

FIG. 36 is a graph showing a relationship between a interruption time and a threshold value of a trapezoidal shaped waveform for a liquid crystal display; FIG.

37 shows a bistable model of a ferroelectric liquid crystal display.

38 shows the V-T curve or threshold value of a conventional ferroelectric liquid crystal.

Fig. 39 is an explanatory diagram used for showing the weight in one frame of the liquid crystal display device of the light intensity modulation type in a simple and clear manner.

40 shows a drive waveform comprising a combination of a plurality of pulse signals comprising a write pulse signal and pulse signals each having a polarity opposite to the write pulse signal for canceling the write pulse signal;

Fig. 41 is a view showing a driving waveform in which an electric signal having the same voltage and period as the write signal but having the opposite polarity is applied to remove the DC element of the signal after the predetermined write signal is applied for a fixed time.

* Explanation of symbols on the main parts of the drawing

1a: glass substrate

2a: VLSI silicon circuit board

1b: common electrode

2b: drive electrode

3: spacer

4: ferroelectric liquid crystal

7: control circuit

8: control gate device

9: capacitor

11: Ferroelectric Liquid Crystal Spatial Light Modulator

The present invention provides a liquid crystal element driving method, also referred to as a driving method provided by the present invention, wherein a first substrate having a first electrode and a second substrate having a second electrode are provided so as to face each other, and the first A predetermined gap is sandwiched between the electrode and the second electrode, and a ferroelectric liquid crystal (FLC) or an antiferroelectric liquid crystal (AFLC) is placed in the gap so that the liquid crystal element is in accordance with an electrical signal applied between the first electrode and the second electrode. By substantially selecting one of two states, an ON state and an OFF state such as a light transmission and non-transmission state, a light reflection and non-reflection state, an optical polarization and non-polarization state, and an optical rotation and non-rotation state:

The first period of application of the electrical signal to select one of the two states and the application of the electrical signal not to select either state without the application of the electrical signal or by the memory characteristics of the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal (Hereinafter interpreted as an application of an electric field smaller than the switching threshold of the liquid crystal or an electric field which does not cause switching by the liquid crystal), a second period of maintaining the selected state is provided in the unit pixel selection period;

A pulse signal having a polarity with respect to a reference level is used essentially as an electrical signal for selecting one of two states;

A pulse signal having negative polarity relative to the reference level is used essentially as an electrical signal for selecting another state.

The driving method provided by the present invention is that the method uses an electrical signal having a DC asymmetric waveform or so-called monopole waveform:

A first period, i.e., a period of applying an electric signal to select one of two states, and a second period following the first period, i.e., without application of an electric signal or by the memory characteristics of the liquid crystal. A period for maintaining the selected state by applying an electrical signal for not selecting either side is provided in the unit pixel selection period, that is, the bit plane;

A pulse signal having bipolar or negative polarity with respect to the reference level is used essentially as an electrical signal for selecting one of two states, and another pulse signal having a polarity opposite to this pulse signal as an electrical signal for selecting another state. Used essentially;

As the reference level, the potential of the first electrode or the second electrode is usually used;

Typically, a pulse signal and another pulse signal are each substantially implemented as a single pulse signal.

The inventors of the present invention compare the result obtained by applying a plurality of types of DC asymmetric driving waveforms to the ferroelectric liquid crystal spatial light modulation display device and the result obtained by applying a DC asymmetric driving waveform. It has been found that it has minimal electro-optic deterioration.

Moments driven by the application of an asymmetric monopole pulse and moments driven by a counter electric field caused by spontaneous polarization generated after switching of the ferroelectric liquid crystals cause ions that are mis-distributed to sustain the pulse width while the counter electric field is generated. By making the time and duration asymmetrical to each other, the inventors thought that conditions for the possibility of neutralization would exist. It should be understood that the electric field generated by spontaneous polarization is always in the opposite direction to the applied pulse. For this reason, this electric field is called the opposite electric field. The period during which the counter electric field is generated is sometimes referred to as memory time.

Embodiments of the present invention will be described with reference to the following figures.

By making the counter electric field induced by spontaneous polarization of the ferroelectric liquid crystal or antiferroelectric liquid crystal in equilibrium with the counter electric field generated by the accumulated charge of ions in the liquid crystal induced by spontaneous polarization during each unit pixel selection period, In other words, by adopting the driving method provided by the present invention to neutralize the charge, the driving method without the need for DC neutralization can be implemented. The driving method provided by the present invention including such a mechanism is described in detail as follows.

As a driving method that can be suitably applied to the driving method provided by the present invention, the length of the first period is set to a value of at least 1 μs, which is a length of time sufficient to reverse spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. In addition, the ratio of the length of the first period to the length of the second period (the length of the first period / the length of the second period) is based on the spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal and the number of ions in the liquid crystal cell. It is set to a value less than or equal to 1 by using as a parameter to prevent the burning phenomenon from occurring in the selected state.

As an example of such a drive waveform, an electrical signal such as shown in FIGS. 1A-1E is provided. For each waveform, the ratio of the length of time sufficient to reverse the spontaneous polarization to the length of the memory time, i.e. the neutralization time (length of pulse application time / length of memory time), is a value of 1 or less, for example 1 Is set to / 2. Typically, the length of the pulse application time and the length of the memory time can be set to 50 μs and 100 μs, respectively.

The drive method provided by the present invention will be practiced when the drive waveform is conceptually a monopole pulse waveform. Examples of such drive waveforms include the rectangular waveform shown in FIG. 1A, the trapezoidal waveform of FIG. 1B caused by the use of a slow speed circuit, and the third order functional pulse and the exponential pulse shown in FIG. 1C. Another example is a selection signal shown in 1D as a pulse having a shortened duration and the same polarity, a pulse having a polarity opposite to the selection signal shown in Fig. 1E and a shortened duration, and a combination thereof.

FIG. 2 is a diagram showing a typical waveform generated by an active matrix driven by using the TFT structures of FIGS. 16A and 16B to be described later, that is, a typical driving waveform of a TFT type linear sequential driving method. Assume that data Dn is input to the n-th pixel positive in the display devices shown in FIGS. 16A and 16B. The pixels Pn (m-1), Pnm and Pn (m + 1) in the (m-1) th to (m + 1) th lines encountered during the electrode scanning process are given as examples in the following description. The scanned electrode is effective for the scan line selection period. When a signal is applied to the data line during this period, a voltage is applied to the pixel driving the ferroelectric liquid crystal (FLC). However, during the non-selection period, no signal from the data line is applied to the FLC.

3 is a view showing a typical drive waveform used in the VLSI type linear sequential driving method. Like the TFT type, the voltage is applied only to the selected pixel. Therefore, unnecessary voltage is not applied to the FLC during the non-selection period.

FIG. 4 is a diagram showing a typical driving waveform used in the block sequential driving method using a VLSI type structure using a memory device as shown in FIGS. 15A and 15B to be described later. As shown in FIG. 4, after data is transferred to the driving circuits of the blocks B _n-1 and B _n selected from the plurality of blocks in which all the pixels are divided, the pixel PB _n-1 (n, m) of the blocks is above all. FLCs corresponding to all of them are driven simultaneously. Then, by scanning the blocks, all the pixels are driven.

FIG. 5 is a diagram showing typical driving waveforms used in a VLSI type batch sequential driving method using a memory device as shown in FIGS. 15A and 15B. The operation is similar to that shown in FIG. However, in this case, after the data of all the pixels are transferred, the FLCs are all driven simultaneously in accordance with the data transmitted to each pixel.

The data is typically adjusted by using the control circuit 7 shown in FIG. 13B. In the driving method shown in Figs. 4 and 5, a memory device is used for each pixel. Thus, the pixels or all the pixels in one block can be driven simultaneously, resulting in high speed and excellent operation. The details of this will be described later.

In general, ions are misdistributed in the liquid crystal panel in the process of driving the liquid crystal due to the applied waveform. Possible parameters of ion motion include the polarity of the applied waveform, the applied voltage and the application time.

However, the inventors of the present invention thought that spontaneous polarization itself induces ions in the liquid crystal panel in the case of a liquid crystal of a type in which the molecules of the liquid crystal itself react to an electric field such as ferroelectric liquid crystal or antiferroelectric liquid crystal. .

In addition, an electric field causing the opposite spontaneous polarization generated in response to an applied electric field always has a polarity opposite to that of the applied electric field. For this reason, this electric field is also referred to as an opposite electric field below. As a matter of course, the intensity of the opposite electric field depends on the value of spontaneous polarization, the thickness of the liquid crystal aligning film, the electrical conductivity of the film and the layer thickness of the liquid crystal, and has a value of about half (1/2) of the voltage of the applied pulse. .

For example, when the voltage of the selected pulse is V _s , the strength of the generated counter electric field is about V _s / 2. Thus, by setting the memory time that no signal is applied to 2Tw when Tw is the width of the selected pulse, the condition for electrical neutralization can be seen to be satisfied for the ions in the liquid crystal panel. The only signal generated from the external source is the signal pulse applied in this way, i.e., + Vs + Tw. Thus, only one DC volt is applied during the period of 3Tw, ie for the time of one bit-plane.

The inventors of the present invention provide for the movement of ions driven by a DC asymmetric driving pulse during a first period of time and the movement of ions driven by an opposite electric field caused by spontaneous polarization of the ferroelectric liquid crystal or antiferroelectric liquid crystal generated during the second period. It is in equilibrium, which is presented by the present invention.

Thus, the memory time is set according to the counter electric field generated by this spontaneous polarization in order to introduce the proposed drive waveform having the property of preventing the burning phenomenon from occurring in the selected one of the two states.

The counter electric field generated by the spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal is applied during the period of selecting the unit pixel or unit scan line (1 bit plane) to neutralize the charge by adopting the driving method provided by the present invention as described above. By bringing into equilibrium with the counter electric field generated by the accumulated charge of ions in the liquid crystal induced by such spontaneous polarization, it is possible to implement a driving technique that does not require any DC neutralization conditions. As a result, the driving method becomes very simple, which makes it possible to design various devices such as a liquid crystal spatial light modulator and a liquid crystal spatial light modulator. It also has the effect of no longer having to pursue the strict accuracy of the voltage applied to the common electrode.

It was recognized that the hysteresis phenomenon appeared in the ferroelectric liquid crystal device used in the present invention. Hysteresis is a phenomenon in which the white or black display of the current bit plane is not only affected by the white or black display of the immediately preceding bit plane, but also by the white or black display of dozens of preceding bit planes. To clarify this, if the display of the immediately preceding bit plane is black, determining whether the color of the currently displayed bit plane is black or white only with the black or white display of the bit plane preceding the immediately preceding bit plane is black. impossible.

To avoid hysteresis, the voltage of the electrical signal used to select one of the two states prevents the burning phenomenon from occurring among the selected states, as will be described later in the description of the third embodiment. It is preferably set to a value.

Next, the configuration of the liquid crystal is explained by its pixels.

Fig. 6 is a diagram showing an equivalent circuit of a pixel of a conventional liquid crystal element using a twist-nematic liquid crystal (TN crystal). As shown in the figure, each pixel drives a TN liquid crystal having an auxiliary capacitive element by using a TFT (thin film transistor), and its gate is controlled by a scanning line.

On the other hand, as shown in Figs. 7 to 10, there are mainly four types of pixels of liquid crystal which can be driven by the driving method provided by the present invention.

FIG. 7 is a diagram showing an equivalent circuit of a pixel of a liquid crystal element using a ferroelectric liquid crystal (FLC) driven by a TFT or a MOSFET (metal oxide field effect transistor), the gate of which is controlled by a scanning line. Since the FLC has memory characteristics, the auxiliary capacitive element required for the TN liquid crystal is not necessary.

8 is a diagram showing another equivalent circuit of the pixel of the liquid crystal element using the ferroelectric liquid crystal. In comparison with the circuit shown in Fig. 7, the auxiliary capacitive element is connected to the FLC element, thereby extending the driving time.

FIG. 9 is a diagram showing another equivalent circuit of the pixel of the liquid crystal element using the ferroelectric liquid crystal. FIG. As shown in the figure, an equivalent circuit includes a capacitor composed of memory cells of a DRAM (dynamic random access memory) in addition to the MOSFET for driving the MOSFET and the FLC liquid crystal. The gate of the MOSFET for driving the FLC liquid crystal is connected to the data setting control line. However, similarly to the equivalent circuit shown in Fig. 7, since FLC has memory characteristics, an auxiliary capacitive element required for TN liquid crystal is required.

FIG. 10 is a diagram showing another equivalent circuit of a pixel of a liquid crystal element using a ferroelectric liquid crystal similar to that shown in FIG. However, compared with the circuit shown in FIG. 9, the auxiliary capacitive element is connected to the FLC liquid crystal to extend the driving time.

As mentioned above, the equivalent circuits shown in FIGS. 9 and 10 include MOSFETs and capacitors constituting memory devices, i.e., memory cells of DRAM, which are all pixels or one block shown in FIGS. 4 and 5. The fact that the pixels within can be driven simultaneously provides the advantage of high speed operation.

To clarify this, the data from the data line is stored once in the memory device. By adjusting the gate of the MOSFET for driving the FLCs by using the control line, data stored in the memory device can be transferred to the FLC device of all pixels or pixels of the selected block at the same point in time of the display operation.

This operation is described with reference to FIG. 11, which is a diagram showing an equivalent circuit used to explain the operation of the pixel shown in FIG. In the operation for reading data, firstly, the MOSFET for driving the FLC is turned off. On the other hand, the MOSFET of the memory device is turned on to accumulate data in the cell capacitor. Subsequently, the MOSFET for driving the FLC is turned on, during which the MOSFET of the memory cell is turned off to supply the FLC liquid crystal by the MOSFET for driving the FLC as the driving potential with the charge accumulated in the cell capacitor.

The driving potential can be applied to the FLC liquid crystal only during the first period of the bit plane as the pulses shown in FIGS. 1A-1E. Immediately after the application of a pulse, the MOSFET of the memory device is turned back on by the gate of the MOSFET to drive the FLC while keeping it active. In this state, the charge of the applied potential is momentarily discharged to the data line by all of the MOSFETs during the second period of the bit plane shown in Figs. 1A to 1E.

Therefore, the pixel structure shown in Figs. 9 and 10 not only operates at high speed, but also easily generates driving waveforms as shown in Figs. 1A to 1E. As a result, a very convenient driving method can be implemented.

12A-12C illustrate timing diagrams of the operation of FIG. 11 in clear terms.

Based on the above, the present invention is based on the electrical signal applied to the surface electrode of the spatial light modulation unit of the spatial light modulation element, that is, light transmission and non-transmission state, light reflection and non-reflection state, optical polarization And one of an ON state and an OFF state such as a non-polarization state and an optical rotation and a non-rotation state, wherein the memory unit and the spatial light modulation unit of the memory unit for electrically storing one of the above states can be selected. A state setting unit for setting a state stored in the memory unit at the surface electrode provides a spatial light modulator provided for each pixel.

In addition, the present invention is in accordance with the electrical signal applied to the surface electrode of the spatial light modulation unit of the spatial light modulation device, that is, the light transmission and non-transmission state, the light reflection and non-reflection state, optical polarization and non-polarization state And one of an ON state and an OFF state such as a light rotating and non-rotating state, wherein a memory unit and a state setting unit are provided for each pixel:

The memory unit is used for electrically storing one of the states;

The state setting unit provides a method of driving a spatial light modulator, which is used to set the state stored in the memory unit at the surface electrode of the spatial light modulator.

According to the spatial light modulator of the present invention and its driving method, a memory unit (typically implemented by a memory cell of a DRAM shown in FIG. 9) is used for electrically storing one of two states;

A state setting unit (typically implemented by the MOSFET shown in Fig. 9) is used to set the state stored in the memory unit at the surface electrode of the spatial light modulator (typically implemented by the FLC above). As a result, one block of pixels or all the pixels can be operated simultaneously.

Further, by discharging the charge accumulated in the state setting unit to the discharge line by the memory unit, the discharge waveform provided by the present invention as shown in Figs. 1A to 1E can be easily generated.

In this case, there are two states, i.e., light transmission and non-transmission states, depending on the electrical signal applied between the first electrode provided on the first substrate of the spatial light modulator and the second electrode provided on the second substrate of the apparatus. , One of the ON state and the OFF state such as the light reflection and non-reflection state, the light polarization and non-polarization state, and the light rotation and non-rotation state can be substantially selected, provided that the first substrate and the second substrate face each other. And sandwiching a predetermined gap between the first electrode and the second electrode, and placing the ferroelectric liquid crystal or the antiferroelectric liquid crystal element within this gap:

A first period of application of the electrical signal to select one of the two states and an electrical signal not to select either of the two states without the application of the electrical signal or by the memory characteristics of the ferroelectric liquid crystal or the antiferroelectric liquid crystal A second period for maintaining the selected state by applying is provided in the unit pixel selection period;

A pulse signal having a polarity with respect to a reference level is used essentially as an electrical signal for selecting one of two states;

It is desirable to provide a spatial light modulator in which a pulse signal having a negative polarity with respect to a reference level is essentially used as an electrical signal for selecting another state.

Further, each of the pulse signal having bipolarity and the pulse signal having negative polarity is substantially realized by a single pulse signal, and the accumulated charge of ions in the liquid crystal cell is neutralized by spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. It is preferable.

Furthermore, setting the length of the first period to a value of at least 1 μs;

The ratio of the length of the first period to the length of the second period (the length of the first period / the length of the second period) determines the number of ions in the liquid crystal cell and the spontaneous polarization of the ferroelectric liquid crystal or antiferroelectric liquid crystal from one of two states. Setting the value to 1 or less by using it as a parameter for preventing burning in the state;

The voltage of the pulse signal for selecting one of the two states is preferably set to prevent the burning phenomenon from occurring in the selected one of the two states.

Although the spatial light modulator and the driving method thereof provided by the present invention are suitable for FLC liquid crystals, the characteristics of the pixel structure indicate that the apparatus and method can be applied to other liquid crystals such as TN liquid crystals. Also, TFTs can be used in place of MOSFETs.

Typical structures of liquid crystal devices or spatial light modulators that can be used in the present invention are shown in FIGS.

FIG. 13A is a diagram showing a cross section of a structure of an FLC display device used as a liquid crystal element such as an antiferroelectric liquid crystal spatial light modulation display in a simple and clear manner, and FIG. 13B is a same antiferroelectric liquid crystal spatial light modulation in a simple and clear manner. It is a figure which shows the perspective view of the structure of a display apparatus. As shown in the figure, in the structure of the liquid crystal element used as the antiferroelectric liquid crystal spatial light modulator 11 on a transparent glass substrate 1a such as Corning 7059 having a thickness of 0.7 mm, it has a resistance of 100? / Cm ² . A transparent electrode 1b, typically made of ITO (indium tin oxide) and used as a common electrode, is produced by painting everything over the entire surface. As shown in Figs. 14A and 14B, on a silicon VLSI circuit (very large integrated circuit) substrate 2a, an aluminum film 2b which acts as both the other substrate facing the substrate 1a, the reflective film and the display electrode is matrixed. It is laid out for each pixel to form.

On the common electrode and the drive electrodes 1b and 2b, SiO lozenge deposition films 1c and 2c are generated to act as liquid crystal aligning films, respectively. SiO lozenge films 1c and 2c are not shown in Figs. 14A to 14B. In the production of these SiO rhombic films 1c and 2c, the glass substrate and the silicon VLSI circuit boards 1a and 2a are formed such that a straight line in the orthogonal direction forms an angle of 85 ° with a typical straight line of these substrates 1a and 2a. In a vertical manner from the SiO deposition source. After vacuum deposition of SiO at a substrate temperature of 100 ° C., the baking process is carried out at a temperature of 200 ° C. for 2 hours.

The glass substrate and the VLSI silicon circuit boards 1a and 2a, respectively, having the liquid crystal aligning film prepared as described above are directed to surfaces whose orientation processing directions on the sides of the common electrode 1b and the driving electrode 2b face each other. Assembled in a way that is parallel to each other in reverse. In this embodiment, the glass substrate and the VLSI silicon circuit boards 1a and 2a are assembled in such a way that the orientation directions are set in reverse parallel to each other. However, these substrates may be assembled such that the directions are set parallel to each other. Glass beads whose thickness is determined by a gap thickness of Sincere Sphere or the like as a spacer 3 between the glass substrate and the VLSI silicon circuit boards 1a and 2a having a diameter in the range of 0.6 to 3.0 μm manufactured by Catalyst Chemical Synthesis Corporation. Is commonly used.

The manufacturing method of the spacer 3 is determined by the size of the glass substrate and the VLSI silicon circuit boards 1a and 2a. In the case of substrates 1a and 2a having a small area, the spacer 3 is typically produced by diffusing Sincere Sphere particles with a sealant to fix the circumferences to each other at about 0.3% by weight. As the sealing material, an ultraviolet cured adhesive such as Photoleck manufactured by Sekisui Fine Chemicals Corporation is typically used. In this way, the thickness of the gap between the glass substrate and the silicon VLSI circuit boards 1a and 2a can be adjusted. On the other hand, in the case of substrates 1a and 2a with large areas, the spacer 3 is produced by dispersing Sincere Sphere particles over the substrates 1a and 2a, typically at an average density of 100 pieces / mm ² . . Then, a gap is set, and the injection holes of the liquid crystal are held to fix the circumferences to each other by the sealing material.

For example, a ferroelectric liquid crystal 4, such as CS-1022, CS-1016, CS-1017 or CS1025, manufactured by Chisso Corporation, is injected into the gap between the glass substrate and the pair of VLSI silicon circuit boards 1a and 2a. The ferroelectric liquid crystal, which is a composite, is injected under reduced pressure while exhibiting fluidity such as isotropic phase temperature or chiral nematic phase temperature. After injection of the liquid crystal, the temperature is gradually lowered. Subsequently, after the liquid crystal on the substrates around the injection hole is removed, the gap is sealed with an epoxy-based adhesive to produce the ferroelectric liquid crystal spatial light modulator 11.

As shown in Fig. 37, in a ferroelectric liquid crystal display device such as a surface stabilized ferroelectric liquid crystal display device, the direction of the liquid crystal molecules M reacts in two states, namely, in response to an externally applied electric field E (or spontaneous polarization Ps). , Switch between state 1 and state 2. This change in molecular orientation appears as a change in light transmission when the liquid crystal device is placed between two orthogonal polarizers. As shown in FIG. 38, as the applied electric field crosses the threshold voltage V _th , the light transmission rate suddenly changes from 0% to 100%.

As shown in Figs. 13A, 13B, 14A, and 14B, the pixels of the ferroelectric liquid crystal spatial light modulator 11 are disposed on a two-dimensional plane. In practice, these pixels can be arranged along a straight line. Further, as shown in Fig. 13B, the incident light 5 is reflected by the layer 2b serving as both the drive electrode and the reflective film. The light transmission rate of the ferroelectric liquid crystal (FLC) 4 provided on the light path varies with the electric field generated between the common electrode and the drive electrodes 1b and 2b as shown in FIG. In other words, the intensity of the reflected light 6 is modulated by the intensity of the electric field generated between the common electrode and the drive electrodes 1b and 2b. The state of reflecting light rays or the state of not reflecting light rays is selected for each pixel.

As shown in Fig. 13B, the application of the signal to the drive electrode 2b is controlled by the control circuit 7 outside the ferroelectric liquid crystal spatial light modulator 11 for each pixel. However, it should be appreciated that the control circuit embedded in the silicon VLSI circuit board 2a may be used instead of the external control circuit 7. The voltage may be applied to each pixel, to each of the plurality of pixels through scanning, or to all the pixels at the same time.

According to the application of a signal controlled by a circuit embedded in the silicon VLSI circuit board 2a, in order to design the pixel shown in FIG. 7, a MOS or dipole transistor is integrated therein as shown in FIG. Or a switch device) 8 to each pixel. Since the liquid crystal 4 exhibits memory characteristics after switching, the control gate device 8 does not require a storage capacitive element. On the other hand, to design the pixels shown in FIG. 8, the capacitor 9 is incorporated as an auxiliary capacitive element as shown in FIG. 14B to extend the driving time.

In order to design the pixel shown in FIG. 9, a memory device 10 connected to the control gate device 8 can be embedded in the silicon VLSI circuit board 2a as shown in FIG. 15A. As the memory device 10, memory cells of dynamic RAM (random access memory) or static RAM are typically used. The capacitor 9 is connected to the control gate device 8 as an auxiliary capacitive element as shown in Fig. 15B.

The present invention may be applied to the liquid crystal element 21 of the light transmission type shown in Figs. 16A and 16B.

The transmission device is basically different from the reflecting devices shown in Figs. 13A and 13B, and in the former case, the drive electrode is made of transparent ITO 12b provided on the glass substrate 2a. The drive circuit is driven by a TFT (thin film transistor) which serves as the control gate device 18 for each pixel. By turning the signal voltage on and off, the incident light 15 can pass through or be shielded as transmitted light 16. The auxiliary capacitive element can be connected to the control gate device 18.

Further, in the transfer apparatus shown in Figs. 16A and 16B, by connecting a memory device such as a DRAM memory cell to the control gate apparatus 18, the transfer apparatus can be driven to perform the operation shown in Fig. 11.

In the present invention, it should be recognized that antiferroelectric liquid crystals (AFLC) can be used as the liquid crystal instead of the ferroelectric liquid crystal. In the semiferroelectric liquid crystal, all permanent dipole moments on the layer are oriented in the same direction. However, the permanent dipole moments on the layer are all oriented in the opposite direction to the orientation direction of the permanent dipole moments on the adjacent layer. As a result, the polarization of the layer erases it of the adjacent layer, resulting in no spontaneous polarization with any mark. Like ferroelectric liquid crystals, spontaneous polarization is oriented perpendicular to the vertical axis of the molecule and parallel to the layer.

Antiferroelectric liquid crystals are transferred to ferroelectric liquid crystals by applying an electric field having an intensity at least equal to a certain threshold. In other words, by applying such an electric field, each dipole moment oriented in a direction opposite to the direction of the applied electric field is reversed, which causes the anti-ferroelectric liquid crystal to change the ferroelectric phase in which all dipole moments are oriented in the direction of the applied electric field. It can be introduced.

The antiferroelectric liquid crystal (AFLC) display has similar characteristics to the FLC display. The AFLC display panel is manufactured under the same conditions as the FLC display panel. An antiferroelectric liquid crystal (AFLC) display device such as CS-4000 manufactured by Chisso Corporation can be manufactured in the same manner as the FLC display device except that its liquid crystal is changed to an antiferroelectric liquid crystal.

The present invention will become more apparent by careful study of the following detailed description of some preferred embodiments in which the present invention is applied to ferroelectric liquid crystal displays, respectively.

Example 1

Tantalum boat containing SiO powder of 99.99% purity produced by Furuuchi Chemicals Corporation on a glass substrate having a transparent ITO film having a thickness of 40 nm and a surface resistance of 100 Ω / cm ² , prepared by using a sputtering method. (Manufactured by Japan Backs Metals Corporation) is heated by Joule's heat to produce an SiO lozenge deposition film having a thickness of 50 nm as a liquid crystal aligning film during the vacuum deposition process at a temperature of 80 ° C. At this point, a vacuum deposition process is performed whereby the lines typical for the glass substrate form an 85 ° angle with the line orthogonal to the deposition source. After the vacuum deposition process, the burning process in air at a temperature of 200 ° C. is carried out to obtain good orientation.

The two glass substrates having completed the above processes were then stuck together by an ultraviolet curing adhesive in such a way that the deposition direction of the SiO lozenge deposition film was reversed parallel to each other through spacers having a diameter of 1.6 μm, and then assembled into hollow. Produces a liquid crystal cell. As spacers, Sincere Sphere manufactured by Catalyst Chemical Synthesis Corporation was used, and Photoleck manufactured by Sekisui Fine Chemicals Corporation was used as ultraviolet curing adhesive. Ferroelectric liquid crystals have been introduced into gaps within cells to produce FLC displays, ie, liquid crystal displays comprising one pixel. As the ferroelectric liquid crystal, CS-1022 manufactured by Chisso Corporation was used.

The relationship between the applied voltage and the light transmission rate for this liquid crystal display (ie, liquid crystal panel) was investigated. In detail, a DC asymmetric driving waveform is applied to the liquid crystal display under orthogonal nicol. The DC asymmetric drive waveform includes a signal / bit plane with an applied pulse width of 50 μs and a memory time of 200 μs as shown in FIG. 17. 17 illustrates a case where the number of white (W) display times is increased. On the other hand, the lower diagram of Fig. 17 shows the case of increasing the number of black (B) display times. In both cases, after the same pulse signal is applied many times, pulse signals having opposite polarities are applied once. More specifically, in the case shown in the upper figure, after the white pulse signal W is applied for many hours, the black pulse signal B having the opposite polarity to this W pulse is applied once. On the other hand, in the case shown in the upper figure, after the black pulse signal B is applied many times, the white pulse signal W having the opposite polarity to that of the B pulse is applied once. This technique is also applied to the drive signal shown in FIGS. 18 and 19 for comparison purposes. 20A and 20B show the results obtained by monitoring the light transmission intensity according to the display technique of FIG. 17, respectively. As shown in FIGS. 20A and 20B, the magnitude of the change at the white and black levels is about 5% or less.

Comparative Example 1

DC symmetric driving waveforms as shown in FIGS. 18 and 19 were applied to the liquid crystal cell prepared in the same manner as in Example 1 in the same experiment as in Example 1 for the purpose of comparison.

FIG. 21A shows an experimental result showing the dependence of the light transmission rate on the number of white display times for the DC symmetric drive waveform shown in FIG. 18, and FIG. 21B is a diagram for the black display time for the DC symmetric drive waveform shown in FIG. 18. A diagram showing experimental results showing the dependence of optical transmission on number. On the other hand, FIG. 22A shows an experimental result showing the dependence of the light transmission rate on the number of white display times on the DC symmetric drive waveform shown in FIG. 19, and FIG. 22B is black on the DC symmetric drive waveform shown in FIG. 19. A diagram showing experimental results showing the dependence of the light transmission rate on the number of display times. When the DC symmetric driving voltage shown in FIG. 18 or 19 is used, the degree to which the white level change becomes high as shown in FIG. 21A or 22A, respectively, clearly indicates that a burning phenomenon occurs. In other words, as the number of white display times increases, the white level also rises. On the other hand, when the time for which the black pulse signal is applied increases, the white level drops as shown in Figs. 21B and 22B.

The comparison with Example 1 shows that in the case of the drive waveforms shown in Figs. 18 and 19, in particular, for the increased number of white display times, the magnitude of the increase in the white level is more than four times that of Example 1. On the other hand, for the increased number of black display times, the magnitude of the decrease in white level is more than six times that of Example 1. Thus, the drive waveforms shown in Figs. 18 and 19 show a large dependence on the number of white or black display times. Since each of the drive waveforms is a DC symmetric waveform or dipole waveform that includes a signal pulse followed by a pulse having a polarity opposite to that applied immediately after the signal pulse in the bit plane, the opposite electric field of spontaneous polarization is the bit-plane time. It is thought to contribute to the fact that during the subsequent memory time, it does not equilibrate with the counter electric field of ions.

The above results indicate that the DC asymmetrical drive waveform as shown in Fig. 17 burns contrary to the general belief that such a drive waveform can easily move ions and increase the amount of accumulated charge, and thus is easy to cause burning. It proves to be suitable to drive without causing phenomenon.

The above results allow the inventors to think of how the movement of ions caused by pulse (voluntary polarization) is in harmony with the movement of ions caused by opposite charge due to spontaneous polarization after switching of the ferroelectric liquid crystal. . In general, the intensity of the charge caused by spontaneous polarization is said to be less than half that of the applied charge. In the case of a pulse application time of 50 mu s, the period during which the opposite electric field is generated needs to be at least twice the pulse application time, i.e. at least 100 mu s. Regarding the amount of accumulated charge caused by the ions, the travel time is considered as a parameter. As a result, spontaneous polarization of the liquid crystal material is in equilibrium with the number of ions contained in the liquid crystal panel.

The degradation of the liquid crystal was investigated according to the same DC asymmetric waveform used to drive the liquid crystal provided by Example 1 continuously. To clarify this, as one frame is set to include the application of a 36 bit plane, i.e. 35 white pulse signals and one black pulse signal, the change in the white light transmission rate over time was measured.

FIG. 23 is a graph showing a change in white level over time obtained as a result of driving a ferroelectric liquid crystal by continuously using a DC asymmetric unipolar pulse waveform for one week. As shown in the figure, even after such a waveform is continuously applied for one week, it is evident that the change in the white level over time is stabilized with the changes observed during the first hour of the week. Thus, no degradation of the liquid crystal composite due to the accumulation of ions occurs.

Example 3

According to the ferroelectric liquid crystal materials CS-1022, CS-1016 and CS1017 injected into the liquid crystal cell prepared in the same manner as in Example 1, a hysteresis phenomenon was observed. These ferroelectric liquid crystal materials were all manufactured by Chisso Corporation.

In order to observe the hysteresis phenomenon, the drive waveform shown in Fig. 17 was used. FIG. 24 is a diagram showing a combination of pulses of a drive waveform used to observe the hysteresis phenomenon. Considering the fact that one frame includes a 36 bit plane of one primary color, the white level is now monitored at a predetermined position of a combination of 36 white and black bit planes including the displayed bit plane as shown in FIG. It should be recognized that 72 combinations exist. The pulse immediately before this position may be white or black. In the case of the typical combination shown in Fig. 24, the pulse immediately before the position is black. 25, 26 and 27 are curves showing observation results of ferroelectric liquid crystal materials CS-1022, CS-1016, and CS1017, respectively.

Regarding the white level (light transmission rate), the state where the white level is lowered as shown in FIG. 28 following the black level is a hysteresis phenomenon that contributes to two possible causes, for example. One of the causes is that with many white display times, the number of ions caused by the opposite electric field due to the black play just before the white display lowers the pulse voltage of the current white display. Another reason is that the spontaneous polarization of ferroelectric liquid crystal materials CS-1022 is 35 nCcm ^-2 while the spontaneous polarization of ferroelectric liquid crystal materials CS-1016 and CS-1017 is 9 nCcm ^-2 . Thus, taking into account the fact that the opposite electric field is dependent on spontaneous polarization, the memory level is thought to change due to the opposite electric field caused by spontaneous polarization.

The inventors of the present invention have demonstrated that the effectiveness of the first cause, that is, the black display immediately before the white display, can drop the pulse voltage of the white display. The effectiveness of the first cause was demonstrated by changing the pulse voltage of the white display and observing hysteresis. For ferroelectric liquid crystal material CS-1017, the ratio of 35 white display to 1 black display and the ratio of 34 white display to 2 black display each exhibit maximum hysteresis. FIG. 29 shows curves each showing the dependence of hysteresis on pulse voltage for ferroelectric liquid crystal material CS-1017 at a ratio of 34 white displays to 2 black displays.

29, the hysteresis phenomenon can be eliminated by applying at least 1.7 V / μm by applying a pulse voltage of 5 V / μm or more. However, it should be understood that the optical transmission rate is lower than in the prior art even if the memory level is stable.

Example 4

It was investigated whether the use of ions in the liquid crystal panel could neutralize the counter electric field caused by spontaneous polarization. Time is a large parameter of ion transport. Thus, the hysteresis phenomenon has been observed by varying the time during which the opposite charge is present, that is, the memory time. 30 to 32 show curves representing the dependence of hysteresis on memory time for ferroelectric liquid crystal materials CS-1022, CS-1016 and CS-1017, respectively, at a ratio of 34 white displays to 2 black displays.

These curves show at least 200 μs for the ferroelectric liquid crystal material CS-1022 whose hysteresis phenomenon is shown in FIG. 30, at least 100 μs for the ferroelectric liquid crystal material CS-1016 shown in FIG. 31, and the ferroelectric liquid crystal material CS- shown in FIG. 32. In case of 1017 it is shown to disappear for at least 500 μm of memory time. As mentioned above, memory time means the time during which the opposite charge is generated.

Since the compounds constituting the ferroelectric liquid crystal material are entirely different from each other, the type and number of ions contained therein are completely different from each other. Nevertheless, it has been found that these individual ferroelectric liquid crystal materials tend to equally equilibrate after a fixed length of time.

Of particular note is the fact that the ions and the counter electric field are in equilibrium at a point in time that saturates for a longer time than at a point in time rather than at a point in time. This trend indicates that it can provide a margin for the process of conversion of the liquid crystal to the product.

As mentioned above, the length of memory time is measured by the problem of false contour and the transfer rate. In such a case, the length of the memory time can be finally determined from the result provided by the embodiment. However, if this length cannot alternatively be laid within the time determined from the device side, this length is optimized by changing the liquid crystal material.

Example 5

In order to obtain information on the required precision of the voltage applied to the common electrode, a liquid crystal cell similar to Example 1 was used, and the DC offset was superimposed on the common electrode. The light transmission was then monitored to calculate the amount of contrast. 33 is a diagram showing the amount of contrast of the ferroelectric liquid crystal CS-1022 obtained at a DC offset overlapping with the common electrode. According to these results, the contrast is not affected for DC offsets below ± 2.5V (1.6V / μm).

For a pulse width of 50 μs, the threshold was set at 5 V / μm. Even when an offset of 1.6 V / μm overlaps, sufficient switching is performed, which can be considered that the overlap is neutralized by charge accumulation of ions. The DC offset is applied continuously during the application of the pulse voltage, which allows ions to accumulate easily.

The results show that the application of the DC asymmetric drive waveform and the optimal duration of the pulse signal display the ferroelectric liquid crystal as if there is no burning phenomenon and hysteresis phenomenon. In other words, very high quality images can be obtained. In addition, the accuracy of the voltage level applied to the electrode is almost unnecessary, which makes it possible to design various devices.

Example 6

By using the liquid crystal panel provided by Example 1, the dependence of the electro-optical properties on the through-speed was measured.

As the drive waveform, a monopole waveform as shown in Fig. 17 was used as the base. In this case, however, the through-speed of the pulse allows us to consider not changing the field strength region of the pulse. Fig. 34 is a diagram showing a waveform having the shape of an applied pulse corruption. The interruption time shown in the figure is converted to the shape of the third order function or the trapezoidal shape.

FIG. 35 is a graph showing a relationship between the interruption time of a corrupted waveform having a shape of a third order function and the threshold (or pulse height) revealed by the memory, and FIG. 36 is a liquid crystal display device ( A graph showing the relationship between the interruption time and the threshold value of a trapezoidal shaped waveform for a liquid crystal panel).

As shown in Fig. 35, in the case of a pulse of the corrupted waveform having the shape of the third order function, the threshold value revealed by the memory does not change even when the interruption time occupies the entire pulse width.

In the case of a pulse of a broken waveform having a trapezoidal shape, the threshold exposed by the memory does not change the interruption time to 15 μs as shown in FIG. On the other hand, for a interruption time of 15 μs or more, the strength of the applied electric field must be increased. However, it does not affect the switching driving force.

In other words, the through-speed only affects switching. The reason is that in the case of a pulse of a broken waveform having the shape of the third order function, only the rise time of the pulse is very short, which leads to the idea that it is not affected.

Therefore, any pulse has nothing to do with the original switching, regardless of the shape of the pulse, even if the threshold does not change.

Embodiments of the present invention described so far may be further modified based on the technical concepts provided by the present invention.

For example, the driving waveform can be changed into various shapes within the scope of achieving the object of the present invention. As the driving method, an active matrix method for a pattern having a matrix shape or a segment method for driving only a previously measured pattern can be adopted. In particular, a composite composed of a matrix electrode and an auxiliary capacitive element can be used to generate a drive waveform similar to that waveform, which will be finally applied to the liquid crystal.

Further, in the above driving method, the ratio of the pulse application time to the memory time (ie, the neutralization time) of the driving waveform in order to neutralize the accumulated charge of the ions by the electric field of the applied pulse and the counter electric field caused by spontaneous polarization. This can be changed. It should be appreciated that spontaneous polarization may vary with values ranging from 0.1 nC / cm ² to 100 nC / cm ² depending on the type of liquid crystal. Moreover, in the above driving method, no pulse is applied during the memory time. However, in the case of an electrical signal that does not select one state, it is not worthwhile that a pulse can be applied during memory time. In addition, in the above embodiments, one of two states is selected: a light reflection state and a light non-reflective state or a light transmission state and a light non-transmission state. It should be appreciated that one of two other states may be selected: an optical polarization state and an optical non-polarization state or an optical rotation state and an optical non-rotation state or substantially an ON state and an OFF state.

In addition, the elements constituting the pixel are not limited to those described above. As the memory element, a memory cell such as a static RAM can be used. As the control gate device, any may be selected from a variety of devices generally known.

As a ferroelectric liquid crystal which can actually be used in the present invention, it is preferable to use a liquid crystal obtained by synthesizing a liquid crystal made of a chiral compound and an achiral compound or two types of compounds. As an alternative, a plurality of types of liquid crystals may also be used.

As the chiral compound, materials such as generally known pyrimidine groups, biphenyl groups and phenylbenzoic acid groups can be used. It should be appreciated that these ferroelectric liquid crystals may exhibit chiral nematic phase or smectic phase in some cases due to temperature changes. As the achiral compound, generally known biphenyl groups, terphenyl groups, tricyclic cyclohexyl groups, cyclohexyl groups, biphenylcyclohexane groups, cyclohexylethane groups, ester groups, pyrimidine groups, pyridazine groups, ethane groups and Materials such as dioxane groups can be used. In addition, generally known antiferroelectric liquid crystals may be used in place of the ferroelectric liquid crystals.

As far as the elements constituting the liquid crystal are concerned, a transparent glass substrate can be used as the substrate, and materials such as ITO (indium tin oxide) or aluminum can be used as the electrode layer. As far as the liquid crystal aligning layer is concerned, a SiO lozenge deposited film or a polyimide film having completed the friction process can be used.

As the transparent electrode, a generally known transparent electrode made of a material other than ITO such as tin oxide or indium oxide can be used. If the reflective type is desired, a material having a large light reflectance such as aluminum or silver can be used as the reflective film. As far as the other elements constituting the liquid crystal, such as a special substrate, a spacer, and a sealing material, generally known conventional materials can be used.

The materials may be used for devices other than spatial light modulators such as light shutters, light switches and light blinds. When further combined with other materials such as electro-optical devices, these materials may be used, among other things, for liquid crystal prisms, liquid crystal lenses, light path change switches, display devices, phase diffraction gratings, A / D converters and optical logic circuits. have.

As described above, the first substrate having the first electrode and the second substrate having the second electrode are provided to face each other, sandwich a predetermined gap between the first electrode and the second electrode, and make a ferroelectric liquid crystal or By positioning the antiferroelectric liquid crystal in the gap, the liquid crystal element drives the liquid crystal element, which allows the liquid crystal element to substantially select one of two states, namely, an ON state and an OFF state, in accordance with an electrical signal applied between the first electrode and the second electrode. The driving method provided by the present invention to

A first period of application of an electrical signal to select one of the two states and an electricity to select neither of the two states without the application of the electrical signal or by the memory characteristics of the ferroelectric liquid crystal or the antiferroelectric liquid crystal A second period for maintaining the selected state by applying the signal is provided in the unit pixel selection period;

A pulse signal having a polarity with respect to a reference level is used essentially as an electrical signal for selecting one of two states;

It is characterized in that a pulse signal having a negative polarity with respect to a reference level is used essentially as an electrical signal for selecting another state.

Accordingly, the counter electric field caused by spontaneous polarization of the ferroelectric liquid crystal or antiferroelectric liquid crystal is replaced by the counter electric field generated by the accumulated charge of ions in the liquid crystal induced by spontaneous polarization during each unit pixel selection period (each bit plane). By bringing it into equilibrium with, i.e., by neutralizing the charge by adopting the driving method provided by the present invention, a driving method without the need for DC neutralization can be implemented. As a result, the driving method becomes very simple, which makes it possible to design various devices such as a liquid crystal spatial light modulator and a liquid crystal spatial light modulator. It may also have the effect of no longer having to pursue the strict accuracy of the voltage applied to the common electrode.

According to the spatial light modulator provided by the present invention and its driving method, a memory unit is provided according to a control gate device for electrically storing one of two states, and a state setting unit is provided for the spatial light of the spatial light modulator. It is used to set the state stored in the memory unit at the surface electrode of the modulation unit. As a result, one block of pixels or all the pixels can be operated simultaneously. Further, by discharging the charge accumulated in the state setting unit to the discharge line by the memory unit, the drive waveform used in the driving method provided by the present invention can be easily generated.

Claims (20)

A first substrate having a first electrode and a second substrate having a second electrode are provided to face each other, sandwich a predetermined gap between the first electrode and the second electrode, and ferroelectric liquid crystal or antiferroelectric liquid crystal. By placing it within the gap, the liquid crystal element substantially selects one of two states, i.e., ON state and OFF state, according to an electrical signal applied between the first electrode and the second electrode, Neither of the states is selected without a first period of application of the electrical signal and the application of the electrical signal to select one of the two states or by the memory characteristics of the ferroelectric liquid crystal or the antiferroelectric liquid crystal A second period of maintaining the selected state by applying an electrical signal for not being provided in the unit pixel selection period; A pulse signal having a polarity with respect to a reference level is used essentially as the electrical signal for selecting one of the two states; A method of driving a liquid crystal element in which a pulse signal having a negative polarity with respect to a reference level is essentially used as the electric signal for selecting another state. The liquid crystal element driving method according to claim 1, wherein the pulse signal having the polarity and the pulse signal having the negative polarity are each embodied substantially by a single pulse signal. The method of claim 1, wherein the accumulated charge of ions in the liquid crystal cell is neutralized by spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. The method of claim 1, The length of the first period is set to a value of at least 1 μs; The ratio of the length of the first period to the length of the second period (the length of the first period / the length of the second period) is the number of ions in the liquid crystal cell and the spontaneous of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. A method of driving a liquid crystal element which is set to a value of 1 or less by using polarization as a parameter for preventing the burning phenomenon from occurring in a state selected from the above two states. The liquid crystal element driving method according to claim 1, wherein the burning phenomenon is prevented from occurring when a voltage of the pulse signal for selecting one of the two states is selected among the two states. The method of driving a liquid crystal element according to claim 1, which is applied to a liquid crystal spatial light modulation display device or a liquid crystal spatial light modulator. According to an electrical signal applied to the surface electrode of the spatial light modulation unit of the spatial light modulation element, one of two states, namely, an ON state and an OFF state, can be substantially selected, wherein one of the states And a state setting unit for setting each state stored in the memory unit at the surface electrode of the spatial light modulation unit, and for each pixel. 8. The spatial light modulator of claim 7, wherein the charge accumulated in the state setting unit is discharged through the memory unit. 9. The apparatus according to claim 8, wherein the two states, i.e., ON state and OFF, are in accordance with an electrical signal applied between the first electrode provided on the first substrate of the spatial light modulator and the second electrode provided on the second substrate of the apparatus. One of the states can be substantially selected, provided that the first substrate and the second substrate are opposed to each other, sandwiching a predetermined gap between the first electrode and the second electrode, and ferroelectric liquid crystal or antiferroelectric Place a liquid crystal element in the gap, Neither of the states is selected without a first period of application of the electrical signal and the application of the electrical signal to select one of the two states or by the memory characteristics of the ferroelectric liquid crystal or the antiferroelectric liquid crystal A second period of maintaining the selected state by applying an electrical signal for not being provided in the unit pixel selection period; A pulse signal having a polarity with respect to a reference level is used essentially as the electrical signal for selecting one of the two states; A spatial light modulation device in which a pulse signal having a negative polarity with respect to a reference level is used essentially as the electrical signal for selecting another state. 10. The spatial light modulator of claim 9, wherein the pulse signal having polarity and the pulse signal having negative polarity are each embodied substantially by a single pulse signal. 10. The spatial light modulator of claim 9, wherein the accumulated charge of ions in the liquid crystal cell is neutralized by spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. The method of claim 9, The length of the first period is set to a value of at least 1 μs; The ratio of the length of the first period to the length of the second period (the length of the first period / the length of the second period) is the number of ions in the liquid crystal cell and the spontaneous of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. The spatial light modulator is set to a value of 1 or less by using polarization as a parameter for preventing the burning phenomenon from occurring in a state selected from the above two states. 10. The spatial light modulator of claim 9, wherein a burning phenomenon is prevented from occurring in a state in which a voltage of the pulse signal for selecting one of the two states is selected from the two states. According to an electrical signal applied to the surface electrode of the spatial light modulator of the spatial light modulator, one of two states, namely, an ON state and an OFF state can be substantially selected, and the memory unit and the state setting unit are each pixel. Provided for, The memory unit is used for electrically storing one of the states; And the state setting unit is used to set the state stored in the memory unit at the surface electrode of the spatial light modulation unit. 15. The method of driving a spatial light modulator according to claim 14, wherein electric charges accumulated in said state setting unit are discharged through said memory unit. The method of claim 15, wherein the first substrate with the first electrode and the second substrate with the second electrode are provided to face each other, sandwiching a predetermined gap between the first electrode and the second electrode, By placing a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal in the gap, the liquid crystal spatial light modulator can change one of two states, namely, an ON state and an OFF state, according to an electrical signal applied between the first electrode and the second electrode. Select it, Neither of the states is selected without a first period of application of the electrical signal and the application of the electrical signal to select one of the two states or by the memory characteristics of the ferroelectric liquid crystal or the antiferroelectric liquid crystal A second period of maintaining the selected state by applying an electrical signal for not being provided in the unit pixel selection period; A pulse signal having a polarity with respect to a reference level is used essentially as the electrical signal for selecting one of the two states; A method of driving a spatial light modulator, wherein a pulse signal having a negative polarity with respect to a reference level is essentially used as the electric signal for selecting a different state. 17. The method of driving a spatial light modulator of claim 16, wherein the pulse signal having polarity and the pulse signal having negative polarity are each embodied substantially by a single pulse signal. The method of driving a spatial light modulator according to claim 16, wherein the accumulated charge of ions in the liquid crystal cell is neutralized by spontaneous polarization of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. The method of claim 16, The length of the first period is set to a value of at least 1 μs; The ratio of the length of the first period to the length of the second period (the length of the first period / the length of the second period) is the number of ions in the liquid crystal cell and the spontaneous of the ferroelectric liquid crystal or the antiferroelectric liquid crystal. A method of driving a spatial light modulator, wherein polarization is set to a value of 1 or less by using as a parameter for preventing the burning phenomenon from occurring in a state selected from the above two states. 17. The method of driving a spatial light modulator of claim 16, wherein a burning phenomenon is prevented from occurring when a voltage of the pulse signal for selecting one of the two states is selected among the two states.