JP2001514399A - Driving method of bistable cholesteric liquid crystal device - Google Patents

Abstract

(57) A liquid crystal device comprising a bistable twisted nematic liquid crystal cell having at least three different optical attenuation levels and having a first metastable state and a second metastable state, comprising: A metastable state having a first degree of twist and being metastable in the absence of a substantial applied electric field, wherein a second metastable state is different from the first degree of twist A liquid crystal device having a twist of and is metastable in the absence of a substantial applied electric field. The liquid crystal device includes an address generator for applying an electric field having a waveform to the cell, the waveform comprising a first portion for resetting the liquid crystal to a reset state having a first degree of twist; Including a second portion for allowing relaxation to a relaxed state having a second degree of twist, and any of at least three different waveforms for respectively selecting the at least three different optical attenuation levels Third part. At least one of the attenuation levels, a first part of the liquid crystal of the cell is in a first metastable state and a second part of the liquid crystal is in a second metastable state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a liquid crystal device.

BACKGROUND OF THE INVENTION The term “twist” as used herein is the angle in the plane of a liquid crystal cell, where the liquid crystal director rotates from one surface of the cell to another.

[0003] The bistable twisted nematic (BTN) effect is described in EP 0 018 180, US Pat. No. 4,239,345, and "New Bistable Liqui.
d Crystal Twist Cell ", D.C. W. Berreman et al.
J. Appl. Phys. 1981, Vol. 52 (4), pp. 3032. FIG. 1 of the accompanying drawings shows a simple example of operation in the BTN mode. Cholesteric (twisted nematic) materials having a pitch substantially twice the cell gap in cells having a parallel or anti-parallel orientation have an initial state with a 180 ° twist. In the anti-parallel orientation, the 180 ° twist state has the drawback of being sprayed. Thus, apart from the initial stable state, there may be two further metastable states with less twisting but less preferred twist angles, ie 0 ° and 360 °. These metastable states can be generated more quickly than the 180 ° state and are the two states used in the BTN mode. In thin cells between crossed or orthogonal polarizers, the 360 ° twist state appears as black, while the 0 ° twist state with the optical axis oriented at 45 ° to the polarizer direction becomes white. Appear.

A stable “twist-spray” state is indicated by a 1 in a liquid crystal cell having antiparallel alignment layers 2 and 3. The initial reset pulse 4 is applied between the electrodes (not shown). The liquid crystal 5 and the alignment layers 2 and 3 are arranged between the electrodes. Reset pulse 4 has a sufficient amplitude and duration to cause a transition to the homeotropic state, indicated at 6. In the homeotropic state, the liquid crystal molecules 5 in most of the liquid crystal layer (parts away from the immediate vicinity of the alignment layers 2 and 3) are directed perpendicular to the cell surface, for example as shown by the molecules 7.

[0005] One of two types of selective addressing pulses 8 are applied to the electrodes to select a desired state of the device. The selective addressing pulse causes the homeotropic state 6 to switch to a metastable black state. The metastable black state is indicated by 9 and the liquid crystal has a 360 ° twist. This is a maximally attenuated or black state, where the cells are placed between orthogonal polarizers. The other kind of addressing pulse 8 causes the liquid crystal to switch from the homeotropic state 6 to the metastable white state 10. In the metastable white state 10, there is a 0 ° twist and the cell is in a minimally attenuated or white state with orthogonal polarizers. The prior art provides a selective addressing pulse 8 by rapidly or gradually reducing the voltage from the initial reset pulse 4. However, other waveforms can also be used. For example, EP 0 569 0
29 discloses addressing a BTN liquid crystal device (LCD) with a variable voltage selection pulse following an initial reset pulse. JP-A-7-248
No. 485 discloses a technique for providing faster addressing by inserting a preset pulse between an initial reset pulse and an addressing pulse.

[0006] EP 0 579 247 discloses a technique for optimizing the position of polarizers and analyzers to provide optimal contrast in BTN LCDs.

[0007] "A Bistable Twisted Nematic (BTN) LCD
Driven by a Passive Matrix Address
ng ", T.M. Nanaka et al., Proceedings of Asia Di.
spray 1995, page 259, discloses passively addressed black and white BTN panels.

[0008] EP 0 613 116 discloses a technique for providing a short address time by optimizing the position in time after a reset pulse of a short select pulse. This is illustrated in FIG. 2 of the accompanying drawings. BTN LCD
The panel is configured as a rectangular array of picture elements (pixels) having a row electrode common to each row of pixels receiving the strobe waveform and a column electrode common to each column of pixels receiving the data signal. The normal strobe or row waveform is indicated by 11, the normal data or column waveform is indicated by 12, and the voltage applied to the liquid crystal layer is indicated by 13, and the resulting voltage magnitude or absolute The value is shown at 14. The optical transmission of the cell is shown at 15.

The liquid crystal is in a metastable black state 9 at the beginning of the addressing interval shown in FIG.
As shown in The reset pulse 4 changes the liquid crystal layer to the homeotropic state 6
And a selection pulse 16 follows. At the same time, a data waveform for selecting a desired state of the liquid crystal is applied to the row electrodes as shown at 17. This results in a voltage and an electric field of amplitude 18 across the liquid crystal such that the liquid crystal relaxes to the white metastable state 10.

[0010] During the subsequent addressing of the pixel of interest here, a further reset pulse 4 'resets the liquid crystal to the homeotropic state 6, and a further select pulse 16' applies the appropriate data waveform 17 '. Cooperates to generate a pulse amplitude 18 that results in the liquid crystal relaxing to the black metastable state 9.

A disadvantage of the known BTN LCD is that only the black and white states are addressed because it is in metastable mode. Various techniques may be used to accommodate the gray levels. For example, a mixture of black and white regions may be formed within each pixel by sub-pixellation. This sub-pixel conversion is performed so that the sub-pixel is equal to or smaller than the resolution of the eyes. However, such a configuration is not limited to relatively small, low quality display panels,
It requires more driver circuits and faster switching liquid crystal mixtures. In addition, higher construction accuracy is required.

Another known technique is to apply different voltages or voltage sequences to pixels to provide different amounts of black and white areas. For example, this can be achieved with non-uniform pixels such that different regions of the pixel have characteristics that would require different switching voltages. This technique is known as "multi-threshold modulation" and again requires sub-pixellation, meaning an additional manufacturing step, and requires higher build accuracy. Thus, all known types of BTN LCDs have disadvantages in terms of spatial or temporal multiplexing and the associated increased addressing speed, increased construction difficulties, or both. Without, it does not allow grayscale addressing to be achieved.

[0013] EP 0 234 624 discloses a super twisted nematic (STN) LCD capable of displaying gray scales by multi-domain technology. 4 shows the electro-optical (voltage / transmittance) characteristic hysteresis of this device. Different gray levels can be achieved by applying and maintaining different magnitudes of electric field across the liquid crystal cell.

According to a first aspect of the present invention, a bistable twisted nematic having at least three different optical attenuation levels and having a first metastable state and a second metastable state A liquid crystal device comprising a liquid crystal cell, wherein the first metastable state has a first degree of twist and is metastable in the absence of a substantial applied electric field, and the second metastable state comprises: A liquid crystal device having a second degree of twist different from the first degree of twist and being metastable in the absence of a substantial applied electric field, wherein the liquid crystal device applies an electric field having a waveform to the cell. An address generator for applying, the waveform comprising a first portion for resetting the liquid crystal to a reset state having a first degree of twist, and a liquid crystal for applying a second degree of twist. A second portion for allowing relaxation to a relaxed state and a third portion including any of at least three different waveforms for selecting at least three different optical attenuation levels, respectively. A first portion of the liquid crystal including at least one of at least three different optical attenuation levels.
A liquid crystal device, wherein the liquid crystal device is in a metastable state and the second portion of the liquid crystal is in a second metastable state.

According to another aspect of the invention, the second part of the waveform may include a space, ie have a sufficiently low magnitude to allow for relaxation.

According to another aspect of the invention, the relaxed state may be a second metastable state.

According to yet another aspect of the present invention, the at least three different optical attenuation levels may include a maximum attenuation level, a minimum attenuation level, and at least one intermediate attenuation level.

According to yet another aspect of the invention, the first and third parts may include at least one pulse, at least one pulse may include a unipolar pulse, and at least one pulse
One pulse may include a bipolar pulse, and each bipolar pulse may include first and second sub-pulses having substantially equal amplitudes and opposite polarities.

According to yet another aspect of the invention, the third part may include a first part and a second part, the first part may include first and second pulses, and the second pulse may include a first part and a second part. One pulse may be spaced, the amplitude of the first pulse may be less than or equal to the amplitude of the second pulse, the second part may include a plurality of pulses having sequentially decreasing amplitudes, The pulses can be continuous.

According to yet another aspect of the invention, the address generator may include a data signal generator and a strobe signal generator, wherein the cell is configured to receive a strobe signal from the strobe signal generator. A liquid crystal layer is disposed between the strobe electrode and a plurality of data electrodes for receiving a data signal from the data signal generator, the data electrode intersecting the strobe electrode to define a picture element. The data signal generator may be configured to supply a data signal having an amplitude equal to or less than the first and second metastable Freedericksz transition voltages to a data electrode. The above liquid crystal is
It may have an initial stable state and an amplitude of the data signal equal to or less than the initial stable state Freedericksz transition voltage. All of the data signals may include pulses of the same amplitude. All of the data signals may include symmetric bipolar pulses. All of the data signals may include unipolar pulses. All of the data signals may be at the same effective voltage. The data signal for selecting a different one of the optical attenuation levels may have different pulse widths.

According to yet another aspect of the present invention, the amplitude of the strobe signal may be greater than the smaller twisted Fredericks transition of the first and second metastable states. The amplitude of the strobe signal may be less than or equal to four times the less twisted Fredericks transition of the first and second metastable states.

According to yet another aspect of the invention, the liquid crystal of the cell may be arranged between first and second polarizers, wherein the first and second polarizers are substantially orthogonal. May be a linear polarizer having a polarization direction oriented as described above. The polarization directions may be directed between 80 ° and 100 ° with respect to each other.

According to yet another aspect of the present invention, the liquid crystal of the cell provides a first and second orientation for providing a substantially anti-parallel orientation oriented substantially at 45 ° to the polarization direction. It can be arranged between alignment layers. The anti-parallel orientation may be oriented between 40 ° and 50 ° with respect to the polarization direction. The first and second alignment layers may have first and second alignment directions oriented at angles included between 135 ° and 225 °. The included angle may be between 170 ° and 190 °. The included angle may be between 175 ° and 185 °. The included angle may be between 178 ° and 182 °.

According to still another aspect of the present invention, each of the first and second alignment layers includes one
It can be configured to provide a pretilt between {and 25}. The pretilt may be between 3 ° and 15 °. The pretilt may be between 5 ° and 10 °.

According to yet another aspect of the invention, the liquid crystal of the cell may have a thickness between 1 and 3 micrometers.

According to yet another aspect of the invention, Δn · d may be between 0.1 and 0.3 micrometers, where d is the thickness of the liquid crystal of the cell, and Δn = ne−no And ne and no are the abnormal and normal refractive indices of the liquid crystal in the second metastable state, respectively.

According to yet another aspect of the invention, the difference between the twists of the liquid crystal layer in the first and second metastable states may be substantially equal to 360 °. The liquid crystal layer is substantially at 0 ° and 3 ° in the first and second metastable states, respectively;
It may have a twist equal to 60 °. The liquid crystal layer twist in each of the first and second metastable states may differ from the initial stable state by substantially 180 °.

According to yet another aspect of the present invention, the ratio of the thickness of the liquid crystal to the bulk pitch of the cell may be between 0.2 and 1.2. The ratio can be between 0.5 and 0.95. The ratio can be between 0.6 and 0.9.

According to yet another aspect of the invention, the device may include a row and column matrix of picture elements, such that the address generator supplies each frame of image data as n consecutive subframes. Where n is an integer greater than or equal to 1 and each i
The sub-frame includes the (i + n · m) -th row, where i is an integer such that 0 <i ≦ n, and m is a non-negative integer.

Thus, it is possible to achieve the gradation addressing of a BTN LCD without the need for a special structure of the LCD and the use of faster switching liquid crystal materials. The disadvantages associated with sub-dividing pixels or using pixels with non-uniform geometry are avoided and other such as active matrix twisted nematic LCDs, super twisted nematic LCDs, ferroelectric and anti-ferroelectric LCDs It is possible to provide a relatively inexpensive display with good viewing angle and speed while avoiding the difficulties associated with different types of liquid crystals.

(Best Mode for Carrying Out the Invention) The present invention will be further described with reference to the accompanying drawings and embodiments.

Like numbers refer to like parts throughout the drawings.

FIG. 3 illustrates a passive matrix BTN LCD constituting an embodiment of the present invention. The device includes a waveform generator, shown as a data signal generator 20, and a strobe signal generator 21 for providing an addressing waveform to a rectangular panel of pixels. Data and strobe signal generators 20 and 21 have inputs connected to timing inputs 22 for receiving timing signals.
Data signal generator 20 has a data input 2 for receiving data to be displayed.
3

The data signal generator is connected to n column electrodes 24, while the strobe signal generator 21 is connected to m row electrodes 25. Each column electrode 24 is common to the pixels in that column, while each row electrode 25 is common to the pixels in that row. A pixel is defined at the intersection between the column and row electrodes, where the column electrode overlaps the row electrode, and is indicated, for example, at 26.

The data signal generator 20 outputs the data signals Vd1,. . . , Vdn are simultaneously supplied to n column electrodes 24 to refresh the pixels one row at a time. The strobe signal generator 21 outputs the strobe signals Vs1,. . . , Vs
m is supplied to the m row electrodes 25 one at a time in a repeating sequence and is configured to strobe new image data to pixels one row at a time.

FIG. 4 is a schematic cross-sectional view illustrating the structure of the BTN LCD of FIG. 3 in the form of a transmissive display, but a reflective display may also be provided. The device includes a polarizer 30 fixed on the outer surface of a transparent substrate 31 made of, for example, glass.
including. The substrate 31 includes a row electrode 25 made of a transparent conductor such as indium tin oxide (ITO), and the alignment layer 3 containing, for example, rubbed polyimide.
The polarizer 32 is fixed to the outer surface of another transparent substrate 33 made of, for example, glass. The substrate 33 has column electrodes 24 made of a transparent conductor such as ITO on its inner surface.
And an alignment layer 2 containing, for example, rubbed polyimide. To define a liquid crystal layer, the device is assembled such that opposing alignment layers 2 and 3 are spaced by spacers 34. The resulting gap is filled with cholesteric liquid crystal 5 to form a layer. This layer is sealed in any suitable way.

The polarization and orientation directions of the polarizers 30 and 32 and the orientation layers 2 and 3 are illustrated in FIG. In particular, the polarization directions of polarizers 30 and 32 are illustrated at 35 and 36, respectively, while the surface alignment directions of alignment layers 2 and 3 are illustrated at 37. The polarization directions 36 and 35 are substantially orthogonal, while the orientation direction 37 is anti-parallel and is oriented at substantially 45 ° to the polarization directions 35 and 36. The liquid crystal 5 has a substantially twisted and substantially untwisted metastable state. The twisted state is illustrated by the orientation of the liquid crystal molecules shown at 38 and has a substantially 360 ° twist in this state. The untwisted state is illustrated at 39, where all molecules are oriented in direction 37.
In the twisted metastable state, light 40 is polarized by polarizer 30 in direction 35, and its polarization is substantially unaffected by passing through liquid crystal 5. The pixels appear black or opaque because the orthogonal polarization 36 results in the absorption of light 40.

In the untwisted metastable state, indicated at 39, the birefringence of the liquid crystal 5 is such that the polarization of the light from the polarizer 30 is rotated by substantially 90 ° and oriented in the polarization direction 36. . Thus, the pixels appear white or transparent.

FIG. 6 shows a waveform diagram of the data and strobe signals supplied by data and strobe signal generators 20 and 21. The strobe or row waveform 11 includes a first part followed by a second part, followed by a third part including first and second parts. The first part includes a reset pulse 41. The second part includes a space or reset period. The first part of the third part includes what is referred to as a partial reset pulse 42. The second part of the third part includes what is referred to as the change support pulse 43.

The column or data waveform includes bipolar pulses having a constant amplitude but varying width to select the desired gray level of the pixel. Data pulses are bipolar and have no net DC component. The strobe pulse is monopolar, and its polarity changes periodically, for example, every frame, to preserve DC balance and
Avoid deterioration.

The resulting waveform appearing on the liquid crystal is shown at 13, and the amplitude or standard value of the waveform is shown at 14.

To refresh a row of pixels, a reset pulse 41 is provided by the strobe signal generator 21 to the appropriate row electrode 25 during the first part of the strobe waveform, ie, the waveform of the electric field across the row of pixels. While the other rows are refreshed. The standard value of the result, designated 44, is Frederix
icksz) Since it is above the transition voltage, the liquid crystal is reset to the homeotropic state 6 with zero twist. During the second part of the strobe signal or pixel field waveform, the pixels in the refreshed row receive only the data signal waveform. These have substantially smaller amplitudes and allow the liquid crystal to relax to a 360 ° twist. The state is considered to be a twisted or black metastable state 9, but may be or include a partially homeotropic state with a 360 ° twist.

In the third part of the strobe signal waveform, the pixel field waveform, a partial reset pulse 42 is applied to the row electrode 25 and, along with the data waveform,
A standard value 45 provides a voltage intended to select a relatively light gray.
In particular, the height and width of pulse 42 are selected to achieve what is currently considered a partial blanking or resetting. Thus, the degree of blanking or resetting varies in different regions of the pixel. This change can be caused by director fluctuations during cholesteric or heterogeneous flows during the Fredericks transition. In the region where the blanking caused by the pulse 42 is sufficient, an untwisted homeotropic or pre-white state is formed, while in the region where the partial reset pulse 42 has little effect, the liquid crystal will have a 360 ° twist representing the pre-black state. Is blanked to a state close to homeotropic. The relatively large pre-white and pre-black domains are determined by the data voltages applied simultaneously using the partial reset pulse.

A change support pulse 43 is then applied, and acts as a “kick white” pulse, as now considered, producing white in regions that are in a pre-white state. The region that is in the pre-black state is not affected by the pulse 43 and is relaxed to the black state. The changing preference pulse 43 is selected such that the simultaneously applied data voltage does not substantially affect which final state is selected.

Another addressing technique differs from the one described above in that pulses 42 and 43 are selected in such a way that the resulting transmission is substantially determined by the data voltage provided during pulse 43. different. Pulse 43 is believed to contribute to the Freedericksz transition initiated during pulse 42, and thus affects the ratio of pre-white and pre-black regions. As mentioned above, pulse 43 also
It is considered to assist the relaxation from the pre-white region to the white relaxation state.

It is believed that local differences in the degree of blanking are caused by thermal fluctuations in the cholesteric liquid crystal, or dynamic non-uniformities induced by voltage changes, or both. In particular, during the resetting and relaxation of the liquid crystal, all of the liquid crystal molecules cannot move in the same direction, so they temporarily get different directions at different positions. By changing the absolute value 45 of the waveform of the electric field applied to the liquid crystal, analog selection of gray levels can be achieved.
For example, the data waveform shown at 46 results in a waveform that selects or addresses a darker gray level than the standard value 47 is addressed by the standard value 45.

FIG. 7 illustrates the types of waveforms used in the above known addressing scheme, while FIG. 8 illustrates various types of waveforms that can be used in accordance with the present invention. FIG. 7 is disclosed in EP 0 018 180, in which the reset pulse 41 in (a) attenuates rapidly, as indicated at 50, and addresses black, or addresses white more slowly, as indicated at 51. An example of the type of waveform is shown below.

FIG. 7 illustrates in (b) and (c) two types of waveforms as disclosed in EP 0 569 029. Following the reset pulse 41,
Variable pulse 52 is continuous in (b) and is spaced from reset pulse 41 in (c).

FIG. 8A shows a reset pulse 41, followed by a space, followed by a partial reset pulse 42 and a change support pulse 43 in FIG. In (a), pulses 42 and 43 are spaced in time.

[0050] Variations of this waveform structure within the scope of the present invention are illustrated in FIGS. 8 (b)-(i).
In particular, pulses 42 and 43 may be spaced from one another in time or continuous in time, and each may include a combination of pulses. For example, as shown in (b) and (c), the partial reset pulse 42 may be split into two portions 42a and 42b. Portions 42a and 42b comprise (b)
May be continuous, as shown at, or spaced in time as shown at (c). The first portion 42a has a lower amplitude than the second portion 42b, and the second portion 42b is shaped such that only data provided during the first portion 42a affects the gray level selection. You.

The single changing support pulse 43 is combined with the pulses 42, 42 a and 42 b shown in (a), (b) and (c) to form (d), (e) and (f), respectively.
) May include successive pulses of decreasing amplitude. The partial reset pulse 42 and the change preference pulse 43 cannot be clearly distinguished in the waveform as shown, for example, in (d)-(i).

FIG. 9 illustrates a waveform diagram and light transmittance for a waveform of the type shown in FIG. 8C. Column waveform 12 (a) is the first of bipolar partial reset pulse 42.
In cooperation with portion 42a, substantially all pixels are switched to a transparent or white state as shown at 15 (a). The column or data waveform indicated by 12 (b) controls intermediate or gray level addressing as exemplified by the transparency curve 15 (b). The column or data waveform illustrated at 12 (c) causes the switching of substantially all pixels to black as illustrated at 15 (c).

The performance illustrated in FIG. 9 is achieved using a device of the type illustrated in FIGS. This device has a liquid crystal thickness of 2 micrometers and a chiral dopant R- such that the cholesteric pitch is 3 micrometers.
A liquid crystal comprising a nematic liquid crystal mixture ZLI-4792 doped with 1011 is used (both materials are available from Merck). Alignment layer 2
And 3 comprise an antiparallel polyimide having a pretilt of about 5 °. Row waveform 11
Includes a reset pulse 41 having a duration of 3 milliseconds and an amplitude of 37 volts. This is followed by an 11 millisecond zero volt space, followed by a bipolar pulse 42a having a duration of 0.25 milliseconds and an amplitude of 4.5 volts. In addition, 0.2
This is followed by a gap of 5 ms and a section 42b with a duration of 0.25 ms and an amplitude of 35 volts. This is followed by a gap of 0.5 ms and a pulse 43 with a duration of 0.25 ms and an amplitude of 9 volts. This is followed by a gap having 30 ms, after which the waveform repeats. The column waveform includes bipolar pulses having an amplitude of 2.5 volts and based on a pulse duration of 25 milliseconds.

FIG. 10 illustrates a data waveform for providing ten gray levels including black and white for a display of the type illustrated in FIGS. 3-5.
In this case, the polarization directions 35 and 36 are 4 ° and 86 °, and the orientation direction 37
Is 45 °. Alignment layers 2 and 3 include anti-parallel polyimide configured to provide about 7 ° pretilt. The polyimide is, for example, RN715 available from Merck. The liquid crystal layer has a thickness of 1.4 micrometers and comprises a nematic liquid crystal mixture ZLI-4792 doped with a chiral dopant R-1011 having a weight ratio of about 1.3%. Row waveform 11 includes a bipolar reset pulse 41 having a duration of 3 milliseconds and an amplitude of 30 volts, followed by a 4.2 millisecond gap. Monopolar pulse 42 has a duration of 88 ms and an amplitude of 17.1 volts, followed by a gap of 0.204 ms. This includes a bipolar pulse train 4 having a duration of 1 millisecond and an amplitude of 5.3 volts.
3 follows. Next, there is a 24.308 ms gap, after which the row waveform repeats. The polarity of pulse 41 changes by half during the duration of pulse 41, while pulse 42 changes polarity with each repetition. Pulse train 43 includes individual pulses having a width of 8 microseconds offset by 4 microseconds from the polarity change in column waveform 12.

The column waveform includes a bipolar pulse of 8 microseconds in length and 1.7 volts in amplitude.

The specific data pulse waveform required to achieve 10 gray levels from black to white (numbering the waveforms from 1 to 10) is synchronized with the partial reset pulse 42. Is shown.

FIG. 11 shows the results obtained using the above device having the waveforms illustrated in FIG. 9 in (a), (b) and (c). In particular, the transmittance 15 (c
) Is indicated by (c) in FIG. Transmittance curve 15 (
The white obtained by the column waveform 12 (a) as exemplified by a)
This is shown in FIG. Similarly, the gradation level indicated by the transmittance curve 15 (b) is indicated by (b) in FIG. Therefore, it is possible to maintain a good contrast ratio between black and white, and to provide a halftone level that can sufficiently distinguish black and white.

Industrial Applicability According to the present invention, to achieve the gradation level addressing of a BTN LCD without the need for a special configuration of the LCD and without the use of faster switching liquid crystal materials. Is possible. Avoids the disadvantages associated with pixel sub-division or pixels having non-uniform geometry, and reduces the difficulties associated with other types of liquid crystals such as active matrix twisted nematic LCDs, super twisted nematic LCDs, ferroelectric and anti-ferroelectric LCDs. While avoiding, it is possible to provide a relatively inexpensive display with good viewing angle and speed.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating the operation of a known type of BTN LCD.

FIG. 2 is a schematic view illustrating a waveform and a liquid crystal mode of a known type of BTN LCD.

FIG. 3 is a schematic diagram of a passively addressed BTN LCD constituting an embodiment of the present invention.

FIG. 4 is a cross-sectional view of the device of FIG.

FIG. 5 illustrates the orientation of various optical components in the device of FIG.

FIG. 6 illustrates the various waveforms used in the device of FIG. 3 and the resulting performance of the device.

FIG. 7 schematically illustrates a known type of addressing waveform.

FIG. 8 schematically illustrates various types of waveforms that may be used in the device of FIG.

FIG. 9 illustrates another set of various waveforms used in the device of FIG. 3 and the resulting optical performance of the device.

FIG. 10 illustrates a further set of various waveforms used in the device of FIG.

FIG. 11 shows a micrograph illustrating the performance of the device of FIG. 3 using the waveform illustrated in FIG.

──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA15 NA33 NA43 NA53 NA56 NB09 NB13 ND06 ND13 NE04 NE06 NF05 NH01 NH12 NH14 NH18 5C006 AA16 AC02 BA12 BA13 BB12 FA11 FA55 5C080 AA10 BB05 DD08 DD27 FF09 JJ02 JJ06 JJ05 JJ05 JJ05

Claims (46)

[Claims] 1. A liquid crystal device comprising a bistable twisted nematic liquid crystal cell having at least three different optical attenuation levels and having a first metastable state and a second metastable state. The metastable state has a first degree of twist and is metastable in the absence of a substantial applied electric field and corresponds to a first level of one of the at least three different optical attenuation levels And
The second metastable state has a second degree of twist different from the first degree of twist and is metastable in the absence of a substantial applied electric field and the at least three different optical states. A liquid crystal device corresponding to a second one of the attenuation levels, the liquid crystal device being an address generator for applying an electric field having a waveform to the cell, wherein the waveform comprises the liquid crystal. A first part for resetting the liquid crystal to a reset state having the first degree of twist, and a second part for allowing the liquid crystal to relax to a relaxed state having the second degree of twist. A third portion comprising any of at least three different waveforms for respectively selecting the at least three different optical attenuation levels. In at least one of the Kutomo three different optical attenuation levels, a first portion of the liquid crystal is in a metastable state of the first and second parts of the liquid crystal is second
Liquid crystal device in a metastable state. 2. The device of claim 1, wherein the second portion of the waveform includes a space. 3. The device of claim 1, wherein said relaxed state is said second metastable state. 4. The device of claim 1, wherein the at least three different optical attenuation levels include a maximum attenuation level, a minimum attenuation level, and at least one intermediate attenuation level. 5. The device of claim 1, wherein said first and third parts include at least one pulse. 6. The method according to claim 5, wherein said at least one pulse comprises a unipolar pulse.
A device as described in. 7. The method of claim 5, wherein the at least one pulse comprises a bipolar pulse.
A device as described in. 8. The device of claim 7, wherein each bipolar pulse includes first and second sub-pulses having substantially equal amplitudes and opposite polarities. 9. The device of claim 1, wherein said third part comprises a first part and a second part. 10. The method of claim 9, wherein the first portion includes first and second pulses.
A device as described in. 11. The device of claim 10, wherein said second pulse is spaced from said first pulse. 12. The device of claim 10, wherein the amplitude of the first pulse is less than or equal to the amplitude of the second pulse. 13. The device of claim 9, wherein the second portion includes a plurality of pulses having a decreasing amplitude. 14. The device of claim 13, wherein the pulses of the second portion are continuous. 15. The device of claim 1, wherein said address generator comprises a data signal generator and a strobe signal generator. 16. The cell according to claim 1, further comprising a plurality of strobe electrodes for receiving a strobe signal from the strobe signal generator and a plurality of data electrodes for receiving a data signal from the data signal generator. Including a liquid crystal layer disposed on the
The device of claim 15, wherein the data electrode intersects the strobe electrode to define a pixel. 17. The data signal generator, wherein the data signal generator is configured to supply a data signal having an amplitude equal to or less than the first and second metastable state Freedericksz transition voltages to the data electrode. A device as described in. 18. The device of claim 17, wherein the liquid crystal has an initial stable state and an amplitude of the data signal less than or equal to the initial stable state Freedericksz transition voltage. 19. The device of claim 16, wherein all of the data signals include pulses of the same amplitude. 20. All of the data signals include symmetric bipolar pulses;
The device according to claim 16. 21. The method of claim 1, wherein all of the data signals include unipolar pulses.
7. The device according to 6. 22. The device of claim 16, wherein all of the data signals are at the same effective voltage. 23. The device of claim 19, wherein the data signals for selecting a different one of the optical attenuation levels have different pulse widths. 24. The strobe signal according to claim 1, wherein the amplitude of the strobe signal is equal to or greater than the smaller twisted Fredericks transition of the first and second metastable states.
7. The device according to 6. 25. The device of claim 24, wherein the amplitude of the strobe signal is less than or equal to four times the less twisted Fredericks transition of the first and second metastable states. 26. The device of claim 1, wherein the liquid crystal of the cell is located between a first and a second polarizer. 27. The device of claim 26, wherein the first and second polarizers are linear polarizers having polarization directions oriented substantially orthogonal. 28. The device of claim 27, wherein the polarization directions are oriented between 80 ° and 100 ° with respect to each other. 29. The liquid crystal of the cell, wherein the liquid crystal is substantially 4
28. The device of claim 27, wherein the device is disposed between first and second alignment layers to provide a substantially anti-parallel orientation oriented at 5 [deg.]. 30. The anti-parallel orientation as set at 40 ° and 5 ° with respect to the polarization direction.
30. The device of claim 29, wherein the device is oriented between 0 °. 31. The first and second alignment layers having first and second alignment directions oriented at an angle comprised between 135 ° and 225 °.
10. The device according to 9. 32. The device of claim 31, wherein the included angle is included between 170 ° and 190 °. 33. The device of claim 32, wherein the included angles are included between 175 ° and 185 °. 34. The device of claim 33, wherein the included angles are included between 178 ° and 182 °. 35. The device of claim 29, wherein each of the first and second alignment layers is configured to provide a pretilt between 1 ° and 25 °. 36. The pre-tilt is between 3 ° and 15 °.
6. The device according to 5. 37. The pretilt is between 5 ° and 10 °.
7. The device according to 6. 38. The device of claim 1, wherein said liquid crystal of said cell has a thickness between 1 and 3 micrometers. 39. Δn · d is between 0.1 and 0.3 micrometers, where d is the thickness of the liquid crystal of the cell, Δn = ne−no, and
The device of claim 1, wherein and no are the extraordinary and normal refractive indices of the liquid crystal in the second metastable state, respectively. 40. The device of claim 1, wherein a difference between the twists of the liquid crystal layer in the first and second metastable states is substantially equal to 360 °. 41. The device of claim 40, wherein the liquid crystal layer has a twist substantially equal to 0 ° and 360 ° in the first and second metastable states, respectively. 42. The device of claim 40, wherein the twist of the liquid crystal layer in each of the first and second metastable states differs by substantially 180 ° from an initial stable state. 43. A ratio of a thickness of the liquid crystal to a bulk pitch of the cell is equal to 0.
The device of claim 1, wherein the device is between 2 and 1.2. 44. The method according to claim 43, wherein the ratio is between 0.5 and 0.95.
A device as described in. 45. The device of claim 44, wherein said ratio is between 0.6 and 0.9. 46. A row and column matrix of picture elements, wherein the address generator is configured to supply each frame of image data as n consecutive subframes, where n is an integer greater than or equal to 1; The device of claim 1, wherein each i-th subframe includes an (i + n · m) -th row, where i is an integer such that 0 <i ≦ n and m is a non-negative integer. .