BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a liquid crystal element and apparatus exhibiting
spontaneous polarization and, more particularly, to a liquid crystal element and apparatus
using a ferroelectric liquid crystal (FLC).
Related Background Art
[0002] A ferroelectric liquid crystal (FLC) as a liquid crystal exhibiting the spontaneous
polarization has received a great deal of attention in favor of advantages such as
high-speed response and good memory characteristics and has been actively developed
to obtain a light bulb and the like. Targets utilizing the above advantages are an
optical shutter array, a high-definition display unit by simple matrix driving, a
light bulb for high-density recording combined with a photoconductive body. In addition,
the ferroelectric liquid crystal is expected to display a motion picture by active
matrix driving using thin film transistors (TFTs). These characteristics are disclosed
in U.S.P. No. 4,840,462, the Proceeding of the SID, Vol. 30/2, 1989 "Ferroelectric
Liquid Crystal Video Display", and the like.
[0003] In driving of the FLC, the following problems are posed generally or found to be
caused as a result of experiments conducted by the present inventors.
[0004] One of the problems is a decrease in response speed of the liquid crystal when a
direct current (DC) component is continuously applied to the FLC for a long period
of time due to the following reason. Localization of internal ions in the liquid crystal
is assumed to be induced to form an electric field.
[0005] To solve this problem, the present applicant made a proposal (Japanese Patent Application
No. 2-69547) for canceling a DC component by an auxiliary pulse. In addition, since
an FLC has spontaneous polarization, an electric field is formed by internal ions
localized in correspondence with this spontaneous polarization, and a desired gradation
image becomes unstable. It is found that hysteresis occurs in optical response to
an external voltage value (applied voltage value).
[0006] The phenomenon occurring upon application of a reset pulse and a write pulse continuously
to the FLC at a drive frequency of about a television rate (60 Hz) will be described
with reference to Figs. 20 to 22.
[0007] In consideration of the problems found in the above experiments, in order to stably
obtain a gradation image (gradation display) at a television rate in the FLC optical
response, the present inventors have made further extensive studies in detail.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a liquid crystal apparatus suitable
for gradation display.
[0009] It is another object of the present invention to provide a liquid crystal apparatus
for realizing improved gradation display by using both an active matrix drive scheme
using TFTs and a liquid crystal exhibiting spontaneous polarization, such as a ferroelectric
liquid crystal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010]
Figs. 1(a) to 1(e) are waveform charts of drive signals used in the present invention;
Fig. 2A is a sectional view of a cell used in the present invention;
Fig. 2B is an equivalent circuit diagram of the cell;
Figs. 3 to 5C are diagrams showing polarization states in the cell of the present
invention;
Figs. 6A to 6C are waveform charts of drive signals used in the present invention;
Fig. 7 is an equivalent circuit diagram showing a polarization state in the cell used
in the present invention;
Fig. 8 is a waveform chart showing drive signals used in the cell of the present invention;
Fig. 9 is an equivalent circuit diagram showing a polarization state in the cell used
in the present invention;
Figs. 10 and 11 are views showing changes in response time upon continuous application
of a DC component of about 0.3 V as Vsx at a 44-Hz period;
Figs. 12 and 13 are waveform charts showing drive signals used in the present invention;
Fig. 14 is a perspective view of the FLC;
Fig. 15 is a block diagram of an apparatus according to the present invention;
Fig. 16(a) to 16(d) are waveform charts of drive signals used in the present invention;
Fig. 17 is a plan view of a panel;
Figs. 18A and 18B and Figs. 19A and 19B are views showing polarization states of the
cell of the present invention;
Fig. 20 is a graph for explaining a V-T curve and hysteresis instability obtained
upon continuous voltage application at a 60-Hz period;
Fig. 21 is a graph for explaining instability exhibited upon continuous voltage application
at a 44-Hz period;
Fig. 22 is a graph for explaining a change in response deterioration over time upon
continuous application of a 0.9 Va DC component at the 44-Hz period; and
Fig. 23 is a sectional view of a cell of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] A liquid crystal panel used in the present invention is a liquid crystal panel of
an active matrix drive scheme, as shown in Fig. 17. The liquid crystal panel comprises
switching elements (TFTs obtained by using thin film semiconductors such as amorphous
silicon and polysilicon) arranged along a plurality of rows (scanning lines) and a
plurality of columns (data lines), first wiring lines (gate lines) commonly connecting
the first terminals (gates) of the switching elements in units of rows, second wiring
lines (source lines) connecting the second terminals (sources) of the switching elements
in units of columns, a plurality of pixel electrodes (transparent electrodes) connected
in units of third terminals (drains) of the switching elements, counter electrodes
(transparent electrodes) arranged to oppose the pixel electrodes, and a liquid crystal
(chiral smectic C, H, I, G, F liquid crystal exhibiting ferroelectric properties)
exhibiting spontaneous polarization and arranged between the plurality of pixel electrodes
and the counter electrodes.
[0012] The distance between each pixel electrode and the corresponding counter electrode
is set to be a minimum distance (about 5 µm or less) capable of sufficiently suppressing
formation of a helical structure of the chiral smectic liquid crystal. However, the
formation of the helical structure need not be suppressed in the present invention.
[0013] Thermal control may be performed during driving of the liquid crystal to maintain
the liquid crystal within a desired temperature range.
[0014] As shown in Figs. 1(a) to 1(e), after a reset voltage signal V
R and a recording voltage signal V
W which are applied to a pixel for a predetermined period of time required to cause
an optical change of the pixel, an auxiliary voltage signal V
SX having a magnitude corresponding to that of the recording voltage signal V
W is applied, thereby controlling an internal electric field to be described below.
[0015] In order to describe the auxiliary voltage signal in more detail, the internal electric
field generated by ionic localization caused by the DC component spontaneous polarization
will be described below.
[0016] Figs. 2A and 2B show a pseudo equivalent circuit model of an FLC element. Fig. 3
shows an ionic localization diagram obtained when an external DC component is applied
for a long period of time. When a positive external DC component is applied, it is
assumed that ionic localization indicated by ⊕ and ⊖ occurs inside the liquid crystal
layer. At this time, if the upward direction

of spontaneous polarization (P
s) of the liquid crystal indicates that the liquid crystal corresponds to a black state,
an electric field is generated so that the liquid crystal molecules tend to be displayed
in black by this ionic localization.
[0017] Figs. 4A and 4B show ionic localization by spontaneous polarization (PS) itself.
When the direction of the spontaneous polarization (P
s) is kept in the "black"

state, the ionic localization in Fig. 4A is obtained. However, when the direction
of the spontaneous polarization (P
s) is kept in the "white"

state, the ionic localization in Fig. 4B is obtained. As a result, the ions generate
an electric field. When a new external voltage V
W equal to the previous voltage is applied, depending on whether the liquid crystal
state has been kept in the "black" or "white" state for a long period of time, the
degree of ease in change of the ionic localization to the "white state" varies, thus
causing the hysteresis in the optical response. In addition, instability occurs when
the same display state is repeatedly refreshed.
[0018] The function of the present invention will be described in more detail with reference
to the waveforms of the drive signals in Figs. 1(a) to 1(e).
[0019] Although the number of ions induced by spontaneous polarization is difficult to control,
the DC component can be controlled by an external voltage applied to the liquid crystal.
According to the present invention, the auxiliary voltage V
s serves as a DC component, and the ionic localization is kept "constant" regardless
of the state of the spontaneous polarization P
s. The term "constant" indicates a total amount of ionic localization. The "constant"
value may be a predetermined value or zero. However, the "constant" value need not
always be zero.
[0020] A method of adjusting the ionic localization to be "constant" will be described with
reference to Figs. 5A to 5C. For a example, a total amount of ionic localization is
apparently maintained to be an amount with which the "black" state as shown in Fig.
4A is kept set.
[0021] The ionic localization sate of the "black" state shown in Fig. 5A is taken as an
initial state. In this case, a drive signal having a waveform shown in Fig. 1(a) is
applied to the liquid crystal in advance. In order to display the "black" state from
this state, a drive signal having a waveform shown in Fig. 6A is applied to obtain
the "black" state. At this time, the superposition amount of the DC component by the
auxiliary voltage V
SX may be zero. In order to display a gradation state, as shown in Fig. 5B, the ionic
localization state to be obtained by this display is as shown in Fig. 18A. In order
to keep the total ionic localization amount constant in the "black" display state,
an auxiliary voltage +V
SX1 shown in Fig. 6A is applied to add the ionic localization of Fig. 18B. In order to
obtain a "white" state, as shown in Fig. 6C, an auxiliary voltage +V
SX2 (Fig. 6C) is applied to maintain the state of Fig. 19A (i.e., the ionic localization
state formed by this display) to the total amount obtained in the case of the "black"
display.
[0022] The numerical control of the auxiliary voltages V
SX1 and V
SX2 is appropriately performed in accordance with the magnitude of the instantaneous
polarization P
S and the ambient temperature. It is advantageous if the magnitude of the spontaneous
polarization P
S is set not so large (i.e., 10 nC/cm
2 or less, and preferably 5 nC/cm
2 or less) in the liquid crystal used in the present invention since then an excessive
increase in the amplitude of the auxiliary voltage signal V
SX can be suppressed. The numerical value for the amplitude of the signal V
SX1 preferably falls within the following range:

(where Δa is the gradation at the end of application of the voltage V
W and satisfies condition 0 < Δa < 1, and Ci is the capacitance of the insulating layer)
[0023] The criterion for this numeric value will be described below with reference to Fig.
7. Fig. 7 shows a measurement of a divided voltage applied to a liquid crystal layer
when a terminal voltage of a liquid crystal pixel is set at 0 V immediately after
a gradation recording voltage V
W is applied. At this time, the liquid crystal molecules are partially returned to
the "black" direction and are set in the gradation state. If the ratio of the "white"
state is defined as Δa, the divided voltage of the liquid crystal layer is given as
follows:

Since a voltage which causes movement of ions in this gradation state is given by
the above relation, if an external reverse voltage V
SX of the voltage which causes this movement of ions is applied and the divided voltage
of the liquid crystal
VSX by the voltage V
SX is set to equal to

, movement of ions is assumed not to occur. Therefore, the following equation is established:

and the solution can be obtained as follows:

[0024] For example, if P
S and Ci are 5 nC/cm
2 and 20 nF/cm
2, respectively, the voltage V
SX = about 0.5 V can be obtained even in the full "white" state.
[0025] When the voltage V
SX is applied within the range of 0 V to 0.5 V with the waveform shown in Fig. 8 in
accordance with the gradation state, the initial ionic localization state can be maintained
constant.
[0026] When the voltage V
SX corresponding to the gradation state of each frame is kept applied as a DC component
until the next frame in image display repetition, ionic localization can be kept constant.
Therefore, instability which may be caused by ionic localization can be eliminated.
[0027] Second, since the DC component also serves as a "white" retention voltage of the
liquid crystal, high-speed response of the liquid crystal can be obtained and can
cope with the motion picture.
[0028] Figs. 10 and 11 show an optical response test improved by the above driving method.
[0029] As described above, in order to stabilize the ionic localization state caused by
a display state, the peak value

of the auxiliary voltage is preferably stabilized. According to this driving method,
the maximum value of the voltage V
SX is preferably set as follows:

The present invention proposes the optical element on the basis of the findings that
the above condition must be essentially satisfied to balance the ions.
[0030] As a condition of a liquid crystal element structure shown in Fig. 23, the effective
magnitude of the spontaneous polarization P
S of the liquid crystal used and the composite capacitance Ci of the alignment layers
as important components constituting the element or an insulating layer portion including
an additional insulating layer in the element must satisfy the above permanent relationship,
thereby performing substantially stable gradation driving.
[0031] From the qualitative viewpoint, the composite capacitance Ci is preferably set to
be large, and the spontaneous polarization value P
S of the liquid crystal used is preferably set to be small.
[0032] In an experiment conducted by the present inventors, insulating layers formed to
prevent electrical short-circuiting of the upper and lower electrodes of each cell
are formed such that an oxide mixture (Ti-SiO
x) of Ti (titanium) and Si (silicon) is coated on the electrodes and baked to obtain
thin films each having a thickness of about 1,000 Å. A 200 Å thick polyimide alignment
layer is formed on this insulating film and baked. The resultant structure is rubbed
to maximize the composite capacitance Ci. In this case, the capacitance Ci can be
about several 10 nF/cm
2. In order to further increase the capacitance Ci, the physical film thickness must
be decreased, and a layer having a high dielectric constant is selected.
[0033] The magnitude of the spontaneous polarization P
S of the liquid crystal is a maximum of 10 nC/cm
2 when it is evaluated by a polarization reverse current. This magnitude is preferably
5 nC/cm
2 or less. As a result, the value 2P
S/Ci is set to be about 0.5 V or less. In order to increase the value Vth, the viscosity
of the liquid crystal is adjusted. However, it is generally disadvantageous to increase
the drive voltage.
[0034] In this case, the voltage Vth is defined as a DC application voltage limit with which
an optical change is substantially not detected during a period of gradation display
in driving the element.
[0035] A driving method of the element will be described below.
[0036] The above driving method cannot control each gradation level in formation of an image
by a simple matrix. However, in principle, this driving method can be applied to an
arrangement for driving pixels independently of each other as in driving of a single-bit
optical shutter or a 7-segment display, or as in active matrix driving of TFTs (Thin
Film Transistors).
[0037] Actual drive waveforms in TFT active matrix driving will be described in detail below.
[0038] Fig. 12 is a timing chart showing drive waveforms when the present invention is applied
to active matrix driving.
[0039] A reset signal V
R for setting a pixel in the "black" state is applied, and a time voltage for sufficiently
setting the pixel in the "black" state by utilizing the open characteristics of the
TFT is also applied (Vr in Fig. 12). A recording voltage V
W is applied, and this gradation level voltage V
W is kept applied for a predetermined period of time in accordance with similar open
characteristics. A ground signal V
E is then applied to the pixel. During application of a ground voltage V
e, the gradation transmittance is changed but can be stabilized by the following auxiliary
signal.
[0040] The auxiliary voltage signal V
SX is then applied to the pixel. This signal can be selected from V
SX1 and V
SX2 in accordance with a desired gradation display state. As indicated by the voltages
V
SX1 and V
SX2 in the display frame serving as one vertical scanning period in the gradation transmitting
state, the auxiliary voltage signal is applied as a voltage value containing an appropriate
DC voltage. Note that when a sufficiently high voltage is applied as the reset voltage,
the voltages V
SX1 and V
SX2 may be applied as values added with voltages for effecting the DC components corresponding
to the gradation levels after the voltage difference between the voltages Vr and V
W is compensated to be zero during the frame period.
[0041] The target DC component value of this auxiliary voltage signal V
SX is selected in accordance with the magnitude of the spontaneous polarization Ps of
the liquid crystal used. The target magnitude of the DC component value is given as

in accordance with the ratio Δa of the "white" state when the maximum transmittance
is defined as "1". For example, if Ps to 5 nC/cm
2, and the capacitance of the insulating layers constituting the liquid crystal cell
is about 20 nF/cm
2, the voltage V
W for recording the full "White" state is set to be about 0.5 V. In the gradation display
state, a DC component of about 0.5 V or less is superposed on the auxiliary voltage
signal.
[0042] The recording voltage V
W or the recording voltage signal V
W is a signal for determining the optical state of each pixel and represents a voltage
signal (gradation voltage signal) corresponding to display brightness of the pixel.
The auxiliary voltage V
SX or the auxiliary voltage signal V
SX is assumed to be a voltage for substantially stabilizing the gradation display state.
This voltage signal is stabilized well at a DC voltage equal to or less than the optical
threshold value Vth. In this case, the optical threshold value Vth is defined as a
value with which an optical change is substantially not detected even if the threshold
value Vth is kept applied throughout one frame.
[0043] The absolute value of the auxiliary voltage signal V
SX is preferably set to be about 1/50 to 1/5 that of the gradation voltage signal.
[0044] Referring to Fig. 12, the application interval of the ground voltage V
e between the voltages V
W and V
SX is given to stabilize a reaction component as response of the liquid crystal molecules
after the gradation voltage signal V
W is applied. However, even if this application interval is not provided in this element,
the driving effect is not impaired in this embodiment. In this case, the V
SX value must be appropriately regulated in accordance with a drive waveform.
[0045] If a change in state of the liquid crystal is assumed to occur by the application
interval of the reset voltage signal Vr, the application intervals of the voltage
signals V
W and V
E can be set equal to that of the reset voltage Vr.
[0046] In order to effectively practice the above driving method, a recording period of
each line is divided into at least four intervals (if the V
E application interval is not provided, only three intervals are required; and the
following description exemplifies a case wherein the V
E application interval is provided). Referring to Fig. 12, the lower timing chart represents
a case wherein the recording period A of the nth line is divided into four intervals.
That is, the recording period A is divided into a division interval
a for enabling a gate corresponding to a subsequent line a few lines after the current
line to reset the pixels of the subsequent line, a division interval
b for enabling a gate of the nth line to perform recording of the nth line itself,
a division interval
c for enabling a gate corresponding to a previous line a few lines before the current
line to apply the ground voltage to the recorded pixels of the previous line, and
a division interval
d for enabling a gate corresponding to another previous line a few lines before the
above previous line to apply an auxiliary voltage signal to the recorded pixels of
this other previous line. Note that the division intervals
a,
b,
c, and
d in the recording period A of the nth line may have any one of the following orders:
abcd, abdc, acdb, acbd, bacd, badc, bcad, bcda, bdac, bdca, cabd,....
[0047] Fig. 12 shows optical states 101 to 104 of a liquid crystal pixel of the nth line.
These states are enlarged in Fig. 13.
[0048] Fig. 14 is a view showing an FLC sandwiched between an upper electrode substrate
11 having a TFT active matrix and a lower substrate with its entire surface serving
as an electrode.
[0049] In principle, when the direction of the spontaneous polarization P
S is upward 201, the major axis of each FLC molecule is given as a direction indicated
by a solid line 1; and when the direction of the spontaneous polarization P
S is downward 202, the major axis of each FLC molecule is given as a direction indicated
by a dotted line 2. When the reset voltage Vr shown in Fig. 20 is applied to keep
the upper electrode in a negative state, the spontaneous polarization is ideally directed
in the upward direction 201 during this interval. When one of polarizing plates 301
and 302 arranged as a crossed polarizer is aligned with the major-axis direction indicated
by the solid line 1, the pixel is set in the "black" state. Therefore, full "black"
states 101 and 103 in Fig. 12 can be obtained.
[0050] When the gradation voltage signal as the recording voltage signal V
W has a magnitude larger than the reverse threshold value Vth of the liquid crystal,
a "white" domain is formed. However, if V
W is less than Vth, a reset "black" state is maintained. When the ground voltage signal
V
E is enabled to apply the ground voltage V
e, some molecules which are not latched to the "white" state tend to react, but the
state is transited to the gradation display state (103 in Fig. 12) corresponding to
the gradation voltage V
W. Thereafter, when the auxiliary voltage signal V
SX corresponding to the voltage V
W is applied, the gradation state is maintained, and variations in ionic localization
described above can be prevented. As a result, since the variations in ionic polarization
are eliminated in each frame, no undesirable change in transmittance occurs. Therefore,
a stable image display operation can be performed.
[0051] In a so-called high-vision compatible television display, when about 1,000 scanning
lines are interlaced-scanned at 30 or 60 Hz, each frame is driven for about 33 msec.
For this reason, a recording period assigned to each line is about 33 µsec per frame.
The recording period of 33 µsec for applying a recording voltage every nth line according
to the present invention is divided into four intervals (i.e., each interval is about
8 µsec or less). For example, these four intervals consist of an interval for applying
the VR pulse for resetting a line pixel applied with the recording voltage (V
W) six lines after the current line (= S
3), a recording pulse interval for applying the voltage V
W to the pixel of the nth line, a ground signal interval for applying the ground voltage
V
E to a line pixel having been applied with the voltage V
W six lines before the current line (= S
2), and an interval for applying the auxiliary voltage signal V
SX to a line pixel having been applied with the V
W 12 lines before the current line (= S
1). A total time for applying the respective voltages becomes about 198 µsec (= about
33 µsec x 6). A satisfactory image display could be obtained by the material used
by the present inventor at maximum V
R and V
W voltages of about 7 V. In addition, the DC component was superposed on the auxiliary
voltage V
SX by a voltage equal to or less than the threshold value Vth corresponding to the gradation
level to stabilize the gradation display state.
[0052] The driving method shown in Fig. 12 will be described in more detail with reference
to Fig. 13.
[0053] The pulse peak value of the auxiliary voltage signal V
SX can be determined as follows.
[0054] Assume that the peak value V
R of the reset voltage Vr in the ideal voltage waveform during the reset signal interval
a is -V
0, and that the peak value V
W of the recording voltage V
W during the recording signal interval
b is +V
0. If the times for applying these voltages are equal to each other, a peak value V
S0 of the auxiliary voltage signal V
SX during the auxiliary voltage signal interval
d is set at 0.5 V if Ps to 5 nC/cm
2 and Ci to 20 nF/cm
2, in accordance with calculation

(interval 401).
[0055] On the other hand, when gradation levels are assigned to the recording signal as
indicated by intervals 402, 403, and 404, peak values V
S1, V
S2, and V
S3 are defined as follows if the reset voltage is sufficiently high, the number of scanning
lines is 1,000, and a 24-line period is provided as the frame interval (blanking period)
as follows. If the reset interval, the recording interval, and the ground interval
are defined as S
2, S
3, and (S
4 - S
3), respectively, and if condition S
2 = S
3 = (S
4 - S
3) = S is established, the following equations can be approximated:



[0056] When the DC components by the voltages Vr and V
W are set to zero, and a voltage value corresponding to

is added to each zero DC component value, so that the peak values of the auxiliary
voltage signals are defined with respect to gradation values (based on transmittances
at the end of ground voltage application period) Δa
1, Δa
2, and Δa
3 as follows:




[0057] If the intervals S
2, S
3, and (S
4 - S
3) are different from each other, the voltage V
s1' can be rewritten as follows:

[0058] For example, assume that the spontaneous polarization P
S of the FLC used equals 5 nm/cm
2, the capacitance Ci is 20 nF/cm
2, the voltage V
W is -7 V, and a 60% transmittance is obtained at V
1 of 5.5 V. If the S
2 = S
3 = (S
4 - S
3) = 6, then the following equation is obtained:

and therefore,

[0059] The auxiliary voltage signal V
SX may be calculated in accordance with the analog recording signal voltage V
W on the spot, or may be automatically output from a prestored table T (V
W and V
SX) if the recording signal V
W is a digital signal.
[0060] The driving method of the present invention can be easily realized by arranging a
frame memory or a line memory of at least S
4 lines in principle.
[0061] That is, since a delay time of S
4 = 12 lines is present between generation of the recording signal and generation of
the auxiliary signal, information of S
4 = 12 lines must be stored for generation of recording signals for other lines during
this period.
[0062] Fig. 15 shows a simple block diagram of a driver circuit. All signal tuning operations
are performed in response to a clock (shown in Fig. 15). Gate signal output timings
of the lines, reset signals for the source electrodes, and recording and auxiliary
signal output timings are controlled by this clock.
[0063] It is readily understood that a good effect can be obtained by a combination of a
liquid crystal having spontaneous polarization and an active matrix element in order
to apply the auxiliary voltage.
[0064] In the above description, the ionic localization state is stabilized when the FCL
state is the full "black" state. However, this localization may be stabilized when
the FCL state is a full "white" state.
[0065] In this case, ionic localization in the initial "white" state is caused to occur
to start the operation. According to this method, a waveform in Fig. 16(d) is continuously
applied. The DC component source for maintaining the ionic localization in the "black"
state is

and this component is applied as the auxiliary signal. If the "white" domain ratio
is given as Δa, in order to maintain the ionic localization amount in the "white"
state with respect to the remaining black domain ratio (1 - Δa), an auxiliary voltage
having the following DC component superposing amount is applied (Figs. 16(a) to 16(d)):

That is, when the present invention is applied to the active matrix driving, the
auxiliary voltage signals are given as follows, as shown in Fig. 21:




In this case, the correspondence between the recording voltage values V
1, V
2, and V
3 (Fig. 13) and the gradation values Δa
1, Δa
2, and Δa
3 is different from the case wherein the ionic localization is stabilized in the "black"
state. A lower voltage is selected as the voltage V
W to obtain good gradation display as in the above embodiment.
[0066] When the stabilized gradation display is achieved, the DC component value

is always smaller than Vth.
[0067] According to the optical modulation element, as has been described above, there is
provided a good liquid crystal display. A high-precision direct viewing flat display
or a projection display can be arranged. As a matter of course, by arranging a color
filter on each pixel, or by using a plurality of liquid crystal elements of the driving
method of the present invention so as to perform color light projection, a transmission
or reflection type high-definition flat color television or projection color television
can be arranged.
[0068] The present invention is not limited to the driving techniques in the above embodiment.
The present invention is widely applicable as optical elements consisting of liquid
crystals having spontaneous polarization to perform stable gradation display.
[0069] Disclosed is a liquid crystal apparatus including a liquid crystal panel having a
pair of electrodes and a liquid crystal exhibiting spontaneous polarization and arranged
between the pair of electrodes, first means for applying a gradation voltage signal
corresponding to gradation information to the pair of electrodes, and second means
for applying, a DC component serving as a reverse bias of an internal electric field
generated upon application of the gradation voltage signal, to the liquid crystal
during one vertical scanning period. Disclosed is a liquid crystal element comprising
a liquid crystal exhibiting spontaneous polarization, a pair of electrode substrates
for sandwiching said liquid crystal therebetween, characterized in that insulating
layers are formed between said electrode substrates and said liquid crystal, wherein
a spontaneous polarization P
S value of said liquid crystal, an interelectrode composite capacitance Ci of said
insulation layers, and a voltage threshold value Vth of optical response of said liquid
crystal in said liquid crystal element satisfy the following condition:
