JPH02181724A - Liquid crystal element and driving method thereof - Google Patents

Abstract

PURPOSE:To make display with a high contrast without providing light shielding layers by applying a prescribed voltage to electrodes forming picture elements, thereby switching the stable state of the spacing part between the two adjacent picture elements. CONSTITUTION:A ferroelectric liquid crystal matrix panel is provided with the signal electrodes 3 and the scanning electrodes 4 on upper and lower substrates 1, 2 and is specified in the pitch of the picture elements to 90mum and the space between the picture elements to 5mum. Bipolar pulses of Vr=25 volts and Tr=1 millisecond are impressed over the entire surface in the period of a part 20 and the entire part of the panel including the space parts of the picture elements become black, when the voltage of the driving waveform shown in the figure is impressed to this panel. The state of the picture elements switches to exactly the opposite state when the polarity of the electrodes is reversed. The space parts thus exhibit bistability. The display of the high contrast ratio is, therefore, executed even if the light shielding layers are not provided between the electrodes.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a liquid crystal element having a ferroelectric liquid crystal as a liquid crystal layer, particularly a liquid crystal element having a fine pattern with a small pixel pitch and a small space between pixels, and its driving. The present invention relates to a method, an optical logic element using the liquid crystal element, a photomask, and a display device.

2. Description of the Related Art A conventional ferroelectric liquid crystal element includes, for example, a liquid crystal display panel having a structure as shown in FIG. A color filter and a light-shielding layer are formed on one glass substrate, and a smoothing layer is formed thereon, a transparent electrode is formed, and an alignment film is further applied. A transparent electrode and an alignment film are attached on the other glass substrate. These pair of substrates are opposed to each other at a certain distance between 1.5 μm and 5 μm using a spacer, and ferroelectric liquid crystal is injected between them and oriented (for example, Murakami, Ishikawa et al., “High-speed multicolor ferroelectric The thinned ferroelectric liquid crystal becomes stable in several states as shown in Figure 8. Figure 8 (aL ( In b), the directions of the liquid crystal molecules are almost aligned, and the spontaneous polarization is directed above and below the normal line of the substrate.

FIG. 8(C) shows a state in which the liquid crystal molecules are twisted in the normal direction of the substrate, and a state in which the twisting direction is reversed also exists.

Although it may differ from FIG. 8 depending on the type of alignment film, the angle of inclination of the liquid crystal molecules on the substrate, and the way the liquid crystal layer is bent, this schematic diagram basically represents the stable state of the liquid crystal molecules. FIGS. 9(a), (b), and (C) are plan views of the liquid crystals shown in FIGS. 8(a), (b), and (C), respectively, viewed from the upper substrate. When a liquid crystal cell is sandwiched between .72 and .72, Figure 9(a).

Brightness and darkness can be added using the --like state shown in (b). When the liquid crystal molecules have a twisted structure as shown in FIG. 9(C), the display becomes gray. A thin ferroelectric liquid crystal panel has such a stable state, and the transition between these states occurs very quickly and rapidly depending on the applied voltage, and the characteristics of the applied voltage and amount of transmitted light are sharp and dark. Indicates value characteristics. Therefore, a high-capacity, high-contrast display can be obtained using only electrodes in a simple matrix configuration without providing a nonlinear element such as an fjlWA transistor.

By the way, in Figure 7, a smoothing layer is formed on the color filter and the light-shielding layer, but this is because the unevenness on the color filter and the stepped portion at the boundary between the color filter and the light-shielding layer adversely affect the alignment of the liquid crystal. Because ferroelectric liquid crystals have a layered structure, they are more easily affected by such steps than nematic liquid crystals.
It has a 9I structure. Even in the case of a single-color panel without a color filter, especially when the pixel pattern becomes fine and the aperture ratio becomes small, the contrast will be very low unless the gaps between the pixels are darkened, creating a so-called black matrix state. Therefore, a light shielding layer is usually provided as shown in FIG. As a method other than the light-shielding layer, the polarity of the alignment film is made different between the upper and lower substrates to increase the stability of one of the states in which the directions of spontaneous polarization are aligned.
A method has been proposed in which the pixel gaps are darkened in the initial orientation (for example, Japanese Patent Application Laid-Open No. 63-225224).

In a matrix panel, adjacent electrodes are insulated, and there are electrodes on the substrate in the gap between the electrodes, but it is not normally thought that the liquid crystal in the gap responds to an electric field. In the case of ferroelectric liquid crystals, the alignment domains tend to spread two-dimensionally, but it is reported that the spread due to the movement of domain walls is at most about 1 μm (for example, Clark, Ragabar: Japan Display).
86, Proceedings fi 456 pages [C1ark, Lagerw
all: JAPAN DISPLAY'86゜PROC
EDINGS, P456]).

Problems to be Solved by the Invention When the pattern is very fine, forming a light-shielding layer to create a black matrix state is difficult to align with the electrode pattern, leading to increased costs (and
If the polarity of the alignment film is different between the upper and lower substrates, the stability of the dark state and bright state will become asymmetrical, so the unstable state will have negative effects such as brightness disturbance due to crosstalk voltage during matrix drive. . Furthermore, it is technically difficult to change the type of alignment film only in the gaps between pixels.

Furthermore, if the pixel pitch approaches the limit of electrode microfabrication accuracy, the aperture ratio will become significantly smaller, so creating a black matrix state will cause the problem of extremely low light transmittance. .

! ! Means for Solving the Problems In order to solve the above problems, the liquid crystal element of the present invention has a ferroelectric liquid crystal sandwiched between substrates having electrodes on opposing surfaces and forming matrix-like picture elements, and two adjacent By applying a predetermined pulse voltage to the electrodes forming the two picture elements to switch the stable state of the gap between the two picture elements? yiIt is possible to easily create a black matrix state without using a complicated configuration. Also, depending on the cell configuration, the gap between bright pixels can be in a bright state or an intermediate brightness state, and the gap between dark pixels can be in a dark state, so the aperture ratio of the electrode can be extremely high. Even if it becomes smaller,
Transmittance can be increased.

Effect It was discovered that in very fine patterns, the liquid crystal in the gap between the picture elements also responds to the electric field and assumes a stable state similar to that on the picture element.The dark value voltage of the liquid crystal in the gap between the picture elements is Although it is higher than the above, if a pulse with sufficient voltage and pulse width is applied, the stable state can be switched.0 The response speed of ferroelectric liquid crystal is roughly proportional to the product of voltage and pulse width, but for simplicity, the pulse width is When fixed, the stable state of the liquid crystal on the picture element changes from bright to dark.
24. Threshold voltage for switching from dark to bright. -■, 4° When the stable state of the gap changes from bright to dark and from dark to bright, the voltage applied to the two picture elements forming the gap is VB2. If ■*b, ■□〉■, 4 Vo>V,.

There is a relationship between A pulse with a voltage of -v, d or less is applied to the picture element when the picture element is on and when it is off during the 0 selection period in which the scanning electrode is selected after the picture element and the picture element gap are brought into a dark state. Each voltage is vOn +■. ff, there is a relationship of V oa≧V, b>Voff, but V, >>V.

Then, during the selection period, only the top of the picture element switches, creating a black matrix state. The width of the gap between pixels becomes narrower,
V□+VIk becomes smaller, V @a ≧V @>>
When V 61 f, a gap is formed in the selection period 2
When two picture elements are both on, the gap is also on.

EXAMPLE Hereinafter, a liquid crystal element and a driving method thereof according to an example of the present invention will be explained with reference to the drawings.

FIG. 1 is a plan view showing the state of pixels after a matrix driving waveform as shown in FIG. 3 is applied to the pixels in a ferroelectric liquid crystal matrix panel with a pixel pitch of 90 μm and an inter-pixel space of 5 μm. . FIG. 2 is a sectional view of the panel shown in FIG. 1, in which a striped transparent electrode is formed on glass, and an alignment film is formed thereon. The liquid crystal material uses ester-based ferroelectric liquid crystal, and the thickness of the liquid crystal layer is 2.0 am.
SiO was deposited from a direction tilted 82 degrees from the normal line of the substrate to form an alignment film. The drive waveform in Figure 3 has a reset period of 200
After darkening the entire panel in some areas, scanning is performed using the voltage averaging method. In the part 20 of Fig. 3, ¥r-2
A bipolar pulse of 5 volts and Tr-1 millisecond was applied to the entire panel, and the panel, which was twisted in its initial orientation, became completely black, including the gaps between pixels. When the voltage was 25 volts and the pulse width was less than 1 millisecond and the pulse width was 500 μsec or more, only the vertical picture element gaps became black, and when the pulse width was less than 500 μsec, there was no response at all. In the part of FIG. 11, a bipolar pulse of V, -25 volts is applied for Ts-200# seconds during the selection period, and only the inside of the picture element becomes a bright state, and in the part 12, the voltage is Ts-200μ during the selection period. sec, V-tt" A bipolar pulse of 15 volts was applied but remained in the dark state. If the polarity of the voltage was reversed from that in Figure 3, the state of the pixel in Figure 1 would be exactly the opposite. In a panel with a pixel pitch of 30 um and a pixel gap of 3 μm, the voltage and pulse width at which the stable state of the gap changes are smaller, and Vr-25 bolt,
A Tr-300 μsec bipolar pulse resulted in a dark state. In this panel, the ON picture element in FIG. 11 is in the bright state,
The liquid crystal in the gap between the on pixels takes a twisted state,
The brightness was at a medium level. In a panel with a pixel pitch of 6 μm and a pixel gap of 2 μm, the dark value voltage at the pixel gap becomes even smaller, and becomes a dark state at V r = 25 volts and Tr = 250 μs, and at this time, the threshold of the pixel Also 25 volts 2
The time increased slightly to 25 μsec, and the difference with the gap became very small. This panel was tested at Ts=250 μsec, ■. When driven with a pulse of 7-25 volts, which is slightly longer than the dark value, the gap between the on-pixel elements becomes a bright state, the gap between the off-pixel elements becomes a dark state, and the gap between the on-pixel and off-pixel elements becomes a dark state. The part became twisted.

As a result, the aperture ratio of the picture element formed by the transparent electrode is 1
Although it was 44% at 6 prff/36 μm, the brightness of displayed characters and figures was equivalent to that when the aperture ratio was 100%.

FIG. 4 shows an electric field strength distribution diagram calculated using the finite element method, which shows what kind of electric field is applied to the liquid crystal layer, especially the gap between the picture elements, when a voltage is applied to the entire surface of the panel. The upper electrode is O volts, the lower electrode is 20 volts, the thickness of the liquid crystal layer is 2 μm, 1
! The thickness of the electrode is 200 nm, the dielectric constants of the liquid crystal and glass are 7 and 6.7, respectively, and the gap between the electrodes is 4 μm.

It can be seen that even in the picture element gap, an electric field with an intensity of 70% above the picture element is applied near the upper electrode and 40% to 50% near the lower glass. Similar calculations revealed that the electric field in the gap becomes stronger as the pixel gap becomes narrower, and becomes weaker as it becomes wider. Therefore, if the electrode gap is narrowed, an electric field sufficient for the liquid crystal to respond will be applied to the gap, and it can be seen from Figure 4 that the liquid crystal molecules respond to this electric field. .

In a cell with an electrode gap of up to about 30 μm, a black matrix state could be achieved by increasing the pulse voltage or pulse width. However, in a cell with a gap of 5 μm or more, if the liquid crystal layer is made of a ferroelectric liquid crystal material with a low volume resistivity and many ionic impurities, even if the pulse width is lengthened, the gap will not be completely closed. I can't keep it in the dark, so
If I made it too long, it would become twisted. This is considered to be because the ionic impurities are moved by the applied voltage, and a voltage opposite to the applied voltage is generated due to the ion distribution. Therefore, by shortening the pulse width of the bipolar pulse and repeating it multiple times as shown in Figures 5 (a) and (b), ion movement is prevented, and the gap moves even with short pulses due to the effect of repetition. That's what I found out. In the driving waveform diagrams shown in Figures 3 and 5 (a), O)), scanning was performed after the entire panel was in a dark state, but if almost the same electric field is applied to adjacent electrodes, the gap between the picture elements will be Since it is easy to respond, bipolar pulses can be applied not only to the entire panel (but also to pixels on multiple consecutive scanning electrodes in sequence, or only to a part of the panel. Since the gap becomes more responsive when even short pulses are repeatedly applied, it is better to reset the gap after every one or several scans. In the waveform diagram of the example, the horizontal axis is time and the vertical axis is voltage.
) to (C) are scanning voltage waveforms, FIG. 6(d).

(e) is the signal voltage waveform, and Fig. 6 (f) to (h) are the signal voltage waveforms.
- represents the voltage applied to the picture element formed by X3 and Yl.

Looking at the reset period in FIGS. 6(a) to (C), when another scanning line is selected in the scanning voltage, the pulse width is reversed from the applied voltage during the selection period. When a voltage with a longer period of time is applied, pulses of the same polarity are continuously applied to picture element P1, regardless of whether the signal voltage at that time is an on signal or an off signal.
~P3, it was possible to cause the picture element gap to respond to the electric field. With this driving method, it is possible to apply a reset pulse with a long pulse width while performing continuous scanning, and
The scanning time is 2N times (N is the number of scanning lines) the response speed of the liquid crystal on the picture element (pulse width between selections) Ts, which is equivalent to the voltage averaging method for nematic liquid crystals, and the scanning time can be extremely shortened. . In addition, since this reset pulse does not include a DC component, it will not cause deterioration of the liquid crystal.In other words, the signal voltage is set in the first and second half of one selection period: on signal Vs and O, off signal (14/ a) Rate Vs and (2/a)*Vs
(a is the bias ratio), but the reset scanning signal takes Vs and 00 potential for several selection periods, so the product of the voltage applied to the picture element and the pulse width within one selection period is the scanning When the voltage is Vs, the on signal is (S5-Vs)*Ts+(Vs-0)ds-Vs11T
For s off signal, ('js-(1-2/a)*Vs) *1s+fVs
- (2/a) main VSl is equal to main Ts - Vsds, and when the scanning voltage is O volts, (0 - Vs) rate Ts + (0 - 0) ds - - Vs umbrella Ts for off signal (0 - Vs) -<1-2/a)*Vs) Umbrella Ts+ (0-(2
/a)*νsl 1sTs=-Vs*Ts, and the product of voltage and pulse width is equal to positive and negative for both on and off signals, so no DC component remains, and the pixel and pixel gap are independent of the signal voltage. section can be reset.

Using this method, the reset pulse can be applied at any time during scanning, with any pulse width, and any number of times, so for example, the drive waveform shown in Figure 6 can be applied even on panels with many ionic impurities. It was possible to switch the stable state of the elementary gap between continuous scanning within a short scanning time.

As described above, even when the liquid crystal element of the present invention has a very fine pattern and cannot obtain a sufficient aperture ratio, it has a simple structure without a light-shielding layer, has high contrast, and has high transmittance (or reflectance in the case of a reflective type). ) can realize a light valve with high performance.

By using the liquid crystal element of the present invention, it becomes possible to realize a large-capacity parallel optical logic operator by stacking liquid crystal elements.

Furthermore, when the pixel gap is small, adjacent picture elements in a bright state or a dark state are displayed as being connected, so the liquid crystal element of the present invention can be used as a photomask for use in the production of semiconductor integrated circuits, etc. If you use , you don't have to create a fixed pattern by etching a light-shielding layer such as chrome, which is the case with conventional methods.
Any pattern can be formed using a single liquid crystal element simply by sending data to the liquid crystal drive circuit.

Furthermore, a display device with unprecedented high precision and large capacity can be realized using the liquid crystal element of the present invention. In particular, in the case of a pattern with a pixel pitch of several tens of μm or less, by enlarging and projecting it onto a screen, a large, high-definition, large-capacity, high-contrast, and bright display device can be constructed.

Effects of the Invention The liquid crystal element of the present invention applies a predetermined voltage waveform to cause the ferroelectric liquid crystal molecules in the gaps between pixels of a fine pixel pattern to respond to an electric field and switch their stable state. Display with a high contrast ratio can be achieved with a simple configuration in which no light shielding layer is provided between the electrodes.

[Brief explanation of the drawing]

Figures 1 and 2 are a plan view and a cross-sectional view of a liquid crystal element according to an embodiment of the present invention, Figure 3 is a waveform diagram of a driving method for a liquid crystal element of the present invention, and Figure 4 is an electric field strength determined by calculation. Distribution diagrams, Figures 5 and 6 are driving waveform diagrams of the present invention, Figure 7 is a configuration diagram of a conventional ferroelectric liquid crystal panel, and Figures 8 and 9 are diagrams of the stable state of ferroelectric liquid crystal. It is a schematic diagram. l...upper board, 2...lower board, 3...
...Signal electrode, 4...Scanning electrode, 11...
...off picture element, 12...on picture element. Name of agent: Patent attorney Shigetaka Awano (1 person) b> (C) (α) (bn(C)

Claims (22)

[Claims] (1) A ferroelectric liquid crystal is sandwiched between substrates that have electrodes on opposing surfaces and form matrix-like picture elements, and a gap between two adjacent picture elements is provided with a predetermined gap between the electrodes forming the two picture elements. A liquid crystal element characterized in that the stable state of the gap is switched by applying a pulse voltage of. (2) When two adjacent picture elements are both in a dark state, the gap between the pixels is in a dark state, and when the two picture elements are in a bright state, the gap is in a bright or intermediate brightness state. The liquid crystal element according to claim 1, characterized in that the liquid crystal element is stabilized. (3) The liquid crystal element according to claim 1 or 2, wherein the same alignment film is used on the upper and lower substrates. (4) The gap is stabilized in a dark state by a predetermined pulse voltage, and the predetermined pulse voltage has a pulse width longer than the shortest pulse width that can bring the picture element into a dark stable state at the same voltage as the pulse voltage. The liquid crystal element according to claim (1). (5) The liquid crystal element according to claim 4, wherein the stable state of the gap does not change due to the voltage applied to the picture element forming the gap during the selection period of the scanning electrode. (6) The liquid crystal element according to claim (4), wherein a predetermined pulse voltage is applied every predetermined number of scans. (7) The liquid crystal element according to claim (6), wherein a predetermined pulse voltage is applied immediately before scanning. (8) A predetermined pulse voltage is an AC pulse whose pulse width is greater than or equal to the pulse width of the shortest pulse voltage that can stabilize a picture element in a dark state.
The liquid crystal device according to any one of claims 3, 4, 5, 6, and 7, wherein the liquid crystal device is repeated a plurality of times with a pause period of 0 times in between. (9) When a scan electrode other than the scan electrode connected to two picture elements is selected, the pulse width of the pulse train applied to the scan electrode during the selection period is twice or more. Claims (1) to (1), characterized in that by applying a pulse train in which the order of the voltage values is reversed from that of the pulse train, a pulse voltage sufficient to bring the gap portion into a stable state is applied to the two picture elements. 8) The liquid crystal element according to any one of 8). (10) The liquid crystal element according to any one of claims (1) to (4), wherein the width of the gap is 30 μm or less. (11) The liquid crystal element according to any one of claims (1), (2), and (3), wherein the width of the gap is 5 μm or less. (12) The liquid crystal element according to claim (2), wherein the width of the gap is 30% or more of the width of the picture element. (13) In a method for driving a liquid crystal device in which a ferroelectric liquid crystal is sandwiched between substrates that have electrodes on opposing surfaces and form a matrix of picture elements, the gap between the picture elements is darkened before selecting the scanning electrode. A method for driving a liquid crystal element, characterized in that a predetermined pulse voltage having a voltage and pulse width sufficient to stabilize the state is applied to the picture element. (14) The method for driving a liquid crystal element according to claim (13), wherein scanning is performed after applying a predetermined pulse voltage to the entire surface of the panel. (15) The method for driving a liquid crystal element according to claim 13, characterized in that after applying a predetermined pulse voltage to a portion where the display is switched, the portion is scanned to write the display. (16) Claim characterized in that after applying a predetermined pulse voltage to picture elements on a plurality of consecutive scanning lines, the scanning lines are sequentially selected, and then the same voltage is applied to the following scanning lines. (13) The method for driving a liquid crystal element described in (13). (17) A predetermined pulse voltage is an AC pulse having a pulse width greater than or equal to the pulse width of the shortest pulse voltage that can stabilize a picture element in a dark state, from twice to one times the pulse width of the AC pulse.
17. The method for driving a liquid crystal element according to claim 13, wherein the method is repeated a plurality of times with a pause period of 00 times in between. (18) When a scan electrode other than the scan electrode connected to two picture elements forming a gap is selected, the pulse train applied to the scan electrode during the selection period is twice or more By applying a pulse train in which the permutation of voltage values is reversed from the pulse train with a pulse width of 18. The method for driving a liquid crystal element according to claim 13, wherein the voltage is applied. (19) An optical logic device using the liquid crystal device according to claim (2). (20) A photomask for exposure equipment using the liquid crystal element according to claim (2). (21) A display device using the liquid crystal element according to claim (5). (22) The display device according to claim (21), wherein the display device is configured to enlarge and project the display of the liquid crystal element onto a screen.