JP3305255B2 - Driving method of liquid crystal element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal device, and more particularly to a method for driving a liquid crystal device exhibiting a chiral smectic phase.

[0002]

2. Description of the Related Art Bistable liquid crystal devices are known as Clark and Lagerwal.
1) has been proposed in JP-A-56-107216 and U.S. Pat. No. 4,362,924. As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is generally used, and the first optical liquid crystal responds to an electric field applied in these states. It has one of a stable state and a second optically stable state, and has a property of maintaining the state when no voltage is applied, that is, has bistable properties, and has a quick response to a change in electric field. It is expected to be widely used in fields such as high-speed and storage type display devices.

In the case of a matrix display device in which stripe electrode groups are provided inside a pair of substrates used in the ferroelectric liquid crystal element, and the stripe electrodes are wired so as to be orthogonal to each other, for example, Japanese Patent Application Laid-Open Publication No. 59-193
Nos. 426, 59-193427 and 60-
The driving methods disclosed in JP-A-156046 and JP-A-60-156047 can be applied.

[0004]

One of the characteristics of the above-described device using a liquid crystal exhibiting ferroelectricity is that it takes one of a first optically stable state and a second optically stable state as the temperature rises. The required electric field becomes smaller. For this reason, a device has been devised to maintain a good display by changing the drive waveform according to the temperature.

[0005] However, in the conventional method, a problem may occur when driven at a high temperature. That is, if the pulse width is shortened at a high temperature, driving is performed at a high voltage. As a result, the response time of the liquid crystal is increased and the amplitude of the waveform is increased, so that the power consumption of the device is increased. . In addition, driving by a high voltage easily generates heat, causing temperature unevenness in the display region of the element. on the other hand,
If a high temperature is dealt with by lowering the driving voltage, the driving margin is reduced.

An object of the present invention is to solve the above-mentioned problems and to provide a method of driving a liquid crystal element which has low power consumption, a large driving margin and good image quality regardless of temperature.

[0007]

A first aspect of the present invention is a method for driving a liquid crystal element having at least one pixel by sandwiching a liquid crystal exhibiting a chiral smectic phase between a pair of substrates. The signal waveform applied to the pixel comprises a write pulse for bringing the liquid crystal into the second state in accordance with the input information after an erase pulse for bringing the liquid crystal of the pixel into the first state, and the write pulse comprises a high voltage. A low voltage period before and after the period, wherein the high voltage period is the total time of the low voltage period
It is characterized by having the above time width .

A second aspect of the present invention is a method for driving a liquid crystal element having at least one pixel by sandwiching a liquid crystal exhibiting a chiral smectic phase between a pair of substrates. The signal waveform applied to the pixel at the time of high temperature is changed so that the signal waveform applied to the selected pixel after the erasing pulse that brings the liquid crystal of the pixel into the first state changes according to the input information. A writing pulse for setting the second state is provided, and the writing pulse has a low voltage period before and after the high voltage period.

[0009]

[0010]

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have studied the voltage value and pulse width of a write pulse at a high temperature (55.degree. C.). As shown in FIG. 8, it was found that the higher the voltage value, the wider the drive margin. Was.

The data shown in FIG. 8 corresponds to the driving waveform shown in FIG.
In the matrix drive using₁~ V_FiveIs | V₁|
= | V_Two|, | V_Three| = | V_Four|, | V₁| = | V_Three｜ ×
2.5, | V_Five| = | V_ThreeWhile maintaining the relationship of | × 1.1
｜ V_Two| + | V_Three| (Drive voltage) to change
ΔT that can display two states of a mectic liquid crystal well_min,
ΔT_max) Was obtained. ΔT And 1H are
It is as follows.

[0013]

[Table 1]

Here, the Y-axis “M” in the graphs of FIGS.
2 ”will be described.

Good display can be performed when the driving voltage is fixed (especially, two states of the chiral smectic liquid crystal can be displayed well in matrix driving).
Assuming that the pulse width is T _max and the minimum pulse width is T _min , an index M2 indicating the drive margin is defined by the following equation.

M2 = (T _max −T _min ) / (T _max + T _min )

At this time, the value obtained by multiplying M2 by 100 is "What percentage of fluctuation of the pulse width deviates from the driving margin?"
It shows. It can also be used as an indication of "to what extent variation in the threshold distribution is allowed in the panel (element) plane". From the viewpoint of yield, a panel having a larger value of M2 can perform better display.

However, with respect to the voltage value and the pulse width of the writing pulse at a high temperature, if the voltage value is high, the power consumption increases as described above, causing temperature unevenness.

Therefore, the waveform of the write pulse was examined while keeping the scanning signal and the information signal simple. The results are shown in FIGS. FIG. 9 shows the write pulse waveforms (pulse waveforms applied to the pixels) under consideration for each pulse P.
The driving margin of ₁ to P ₄ shown in FIG. 10. As it is apparent from these figures, a partially high voltage only the center portion, in the case of using the pulse P ₃ of the waveform having a low voltage portion on both sides was found that the driving margin is wide. The pulse used P ₃ of Waveforms for only high voltage minimum required for the liquid crystal is applied, can heat generation to secure a wide driving margin with minimal increase in power consumption is suppressed It became.

In the present invention, the setting of the high voltage period in the address pulse is adjusted on the basis of the response characteristics of the liquid crystal material used and the temperature characteristics of the driving margin in relation to the low voltage period. It is preferable that the voltage value on the high side of the low voltage period provided before and after is twice or more and 5 times or less, and the time width of the high voltage period is equal to the time width of the low voltage period (the sum of the widths before and after the high voltage period). Equivalent or more (preferably, 0.5 ΔT to 0.8 Δ of write pulse period ΔT)
It is desirable to set to T).

The low voltage period may be the same or different before and after the high voltage period, and if different, at least the higher voltage side is made smaller than the voltage value in the high voltage period.

FIG. 1 is a block diagram showing an example of a display device incorporating a liquid crystal element to which the driving method of the present invention is applied. In the figure, reference numeral 107 denotes a graphic controller. Data transmitted from the graphic controller is input to a scanning signal control circuit 104 and an information signal control circuit 106 through a drive control circuit 105, and are converted into address data and display data, respectively. According to the address data, the scanning signal applying circuit 10
2 generates a scanning selection signal waveform and a scanning non-selection signal waveform, for example, a display unit 10 composed of 1280 × 1024 pixels.
1 is applied to one scanning electrode. The information signal applying circuit 103 generates an information signal waveform according to the display data, and
01 is applied to the information electrode. The drive control circuit 105 sends waveform data to the scan signal application circuit 102 and the information signal application circuit 103 via the scan signal control circuit 104 and the information signal control circuit 106.

FIG. 2 is a diagram schematically showing the electrode structure of the display unit 101, wherein 201 is a scanning electrode, 202 is an information electrode,
Reference numeral 203 denotes a pixel which is formed by an intersection between the scanning electrode 201 and the information electrode 202 and is a display unit.

FIG. 3 is a partial sectional view of the display unit 101. In the figure, reference numeral 301 denotes an analyzer, and 309, a polarizer. These polarizers are arranged in a crossed Nicols state so that the display unit 101 performs dark display when in the U2 state. 3
02 and 308 are glass substrates, 303 and 307 are insulating films,
304 and 306 are alignment films, 305 is ferroelectric liquid crystal, 31
0 is a sealing material.

It should be noted that one pixel of the present display device is further divided into three, and color filters of different colors, for example, R, G, and B are arranged in each of them, so that the display device can be used as a multicolor color display device.

FIG. 11 is a block diagram showing another example of a display device incorporating a liquid crystal element to which the driving method of the present invention is applied. In the present display device, signals are basically transmitted along the same route as the display device shown in FIG.
Of the temperature detection circuit 10 via the temperature detection element 108
9, the drive control circuit 105 sends waveform data to the scan signal application circuit 102 and the information signal application circuit 103 through the scan signal control circuit 104 and the information signal control circuit 106 based on the temperature data. Specifically, at least two or more non-overlapping temperature regions are set for the temperature of the display unit, and when the temperature in the higher temperature region is detected,
At least as a write pulse waveform applied to the liquid crystal shown in the P ₃ in FIG. 9 will have a low voltage portion and on both sides of a high voltage only the central portion, the scanning signal application circuit 102, the data in the information signal application circuit 103 And drive is performed by the waveform. The high-temperature side and low-temperature side regions may be set to at least two regions. For example, it is preferable to set the boundary of the regions in a range of 40 to 50 ° C.

Further, the driving method and the liquid crystal device according to the present invention can be applied to an optical shutter.

[0028]

【Example】

Example 1 A matrix electrode shown in FIG. 2 was constructed using a ferroelectric liquid crystal having the physical properties shown in Table 2 below.
A liquid crystal element (cell) having a cross-sectional structure shown in FIG.
The display device shown in FIG. The display unit in the display device shown in FIG. 1 is composed of 1280 × 1024 pixels with a diagonal size of 15 inches.

The cell structure shown in FIG. 3 (corresponding to the display unit 101) was manufactured by the following procedure.

First, a pair of glass substrates on which an ITO (indium oxide: tin) film having a thickness of 70 nm is formed by sputtering as the transparent electrodes 201 and 202 and a tantalum oxide film having a thickness of 120 nm is formed on one of the insulating films 307. 30
8 and 302 are prepared, and a polyamic acid LP-64, which is a precursor of polyimide, is formed on the ITO film of one substrate 308.
NMP (N-methylpyrrolidone) manufactured by Toray Industries, Inc .: n
-BC (n-butyl cellosolve) mixed solution was spin-coated. The coating solution was prepared by mixing LP-64 in a mixed solvent of NMP: n-BC = 2: 1 at 1% by weight, and spinning was performed at 45 rpm for 20 seconds.

After drying the substrate in an oven at 80 ° C. for 5 minutes, the substrate was baked for 1 hour in an oven at 200 ° C. to imidize the substrate. The obtained polyimide film was about 10 nm thick, and this film was rubbed to form an alignment film 306. Rubbing was performed using a nylon cloth wrapped around a roller having a diameter of 10 cm.
Rubbing was performed twice (one way) in the same direction at a pressure of 0.4 mm for pushing the cloth against the surface of the alignment film at a feed rate of 10 mm / sec.

Thereafter, an average particle size of 2.0 μm
An IPA (isopropyl alcohol) solution in which 0.008% by weight of silica beads (not shown) of
Spin coating is performed under the condition of rotation / second for 10 seconds, distribution density 3
Bead spacers were sprayed at about 00 pieces / mm ² .

On the other substrate 302, a silane coupling agent (O
DS-E) in 45% by weight ethyl alcohol
Spin coating was performed under the condition of rotation / second for 20 seconds to perform vertical alignment treatment (film 304). Thereafter, a thermosetting sealing material 310 was applied to the peripheral portion of the substrate by printing. Note that the substrate is not provided with the insulating film 303.

The two substrates obtained as described above were adhered to each other and heat-cured in an oven at 150 ° C. for 90 minutes to form a cell.

[0035]

[Table 2]

The above physical properties are measured by the following measuring methods.

(Measurement of Spontaneous Polarization Ps)
Miyasato et al., "Direct Measurement Method of Spontaneous Polarization of Ferroelectric Liquid Crystal by Triangular Wave" (Journal of the Japan Society of Applied Physics 22, 10 (66)
1) 1983, "Direct Method wit
h Triangle Waves for me
asuring Spontaneous Polar
Ization in Ferroelectric L
liquid Crystal ", as describ
ed by K. Miyasato et al. [J
ap. J. appl. Phys. 22. No. 10, L
661 (1983)]).

(Measurement of tilt angle Θ) ± 30 to ± 50 V,
While applying an AC (alternating current) of 1 to 100 Hz between the upper and lower substrates of the liquid crystal element via electrodes, the liquid crystal element disposed therebetween is rotated in parallel with the polarizing plate under orthogonal crossed Nicols, and at the same time, the photomultiplier ( The first extinction position (the position where the transmittance becomes lowest) and the second extinction position are obtained while detecting the optical response with Hamamatsu Photonics Co., Ltd. Then, 1/2 of the angle from the first extinction position to the second extinction position at this time.
Is the tilt angle Θ.

[0039] The driving waveform W ₁ used in this embodiment is shown in FIG. In the figure, (A) is a scanning selection signal having a pulse width Δ
It is composed of a write pulse of T, an erase pulse having a pulse width of 2.5ΔT disposed before the write pulse, and an auxiliary pulse having a pulse width (Ｔ) ΔT disposed after the write pulse. Note that the write pulse is (1/1 /
2) Before and after the high voltage period of ΔT, (1/1)
4) It has a low voltage period of ΔT (a pause period in the present embodiment). (B) is a scanning non-selection signal, which is always 0 V, and C is an information signal for bright display, which is composed of a write pulse having a pulse width ΔT and auxiliary pulses having a pulse width (１ ／) ΔT arranged before and after the write pulse. Is done. (D) is an information signal for dark display, in which the polarity of the bright information signal (C) is inverted. Note that the write pulse period of the scan selection signal and the write pulse period ΔT of the information signal are synchronized. In the figure, 1H indicates one horizontal scanning period, and ΔT indicates a selection period.

FIG. 5 shows a composite waveform applied to each pixel at this time. In the figure, a waveform (A) is a composite waveform for bright display, and a waveform (B) is a composite waveform for dark display.

In this embodiment, V ₁ = 7.2 in FIG.
V, V ₂ = 14.3 V, V ₃ = 2.8 V, V ₄ = −
2.8 V, V ₅ = 3.2 V, ΔT = 16 μs, 1H = 3
It was set to 2 μs. Therefore, (1/2) ΔT (high voltage period) at the center of the write pulse in FIG.
The (１ ／) ΔT (low voltage period) before and after is 2.8V.

FIG. 6 shows another drive waveform W ₂ of this embodiment. In FIG. 6, V ₁ = 7.2 V, V ₂ = 14.3.
V, V ₃ = 2.8 V, V ₄ = −2.8 V, V ₅ = 7.2
V, ΔT = 16 μs, and 1H = 32 μs.

[0043] Moreover, it was performed driven by using the driving waveform W ₃ shown in FIG. 7 which has been conventionally used in the display device of FIG. 1 as a comparison. In the figure, (A) is a scanning selection signal, which is a write pulse having a pulse width ΔT, an erase pulse having a pulse width of 2.5ΔT disposed immediately before the write pulse, and a pulse width (1) disposed immediately after the write pulse. / 2) An auxiliary pulse of ΔT. (B) is a scanning non-selection signal which is always 0 V, and (C) is an information signal for bright display and has a pulse width Δ
It is composed of a write pulse of T and auxiliary pulses of a pulse width (1/2) ΔT arranged before and after the write pulse.
(D) is an information signal for dark display, in which the polarity of the bright information signal (C) is inverted.

[0044] In this Example was carried out under different conditions of driving waveforms of the W _3. That is, in the condition (1), V ₁ = 1
_{4.3V, V 2 = -14.3V, V} 3 = 5.7V, V 4
= −5.7 V, V ₅ = 6.4 V, ΔT = 8 μs, 1H =
16 μs, under condition (2), V ₁ = 7.1 V, V ₂ = −
_{7.1V, V 3 = 2.8V, V} 4 = -2.8V, V 5 =
3.1 V, ΔT = 16 μs, and 1H = 32 μs.

The display device shown in FIG.
Driven by the driving waveform of ₁ to _W-3, they were evaluated for driving margin and calorific value. Regarding the drive margin, the drive voltage (| V ₂ | + | V ₃ |) under each of the above drive conditions is fixed,
The measurement was performed while changing the pulse width (1H). When the value of M2 was 0.1 or more, it was determined to be "wide", and when it was less than 0.1, it was determined to be "narrow". With respect to the heat generation amount, a value obtained by dividing “(１ ／) × panel capacity (C) × (square of the voltage value) by the pulse width ΔT using the voltage value and ΔT under each of the driving conditions described above, and obtaining the waveform obtained by normalizing the value of the value in the case of W ₁ other waveforms as 1, the conditions, it is determined that there is heat generation of 3 or more. as a result, good in the display unit entirely for W _1, W ₂ I was able to perform Do display, cause the temperature unevenness on the display unit the entire surface in the condition (1) for W _3,
Further, under the condition (2), the contrast of the entire display section was lowered, and good display could not be performed in any case. The following table shows a comparison of these display qualities.

[0046]

[Table 3]

Example 2 The display device shown in FIG. 11 was driven. As the liquid crystal of the display unit 101, a liquid crystal exhibiting the same ferroelectricity as that of the first embodiment is used.
It is designed to take values up to 4.3V. Display 1
01 is 1280 × 1024 pixels and 15 inches diagonally.

In this embodiment, W ₁ of Embodiment _{1 is changed} to V ₁ = 7.2 V, V ₂ = 14.3 V, and 55 ° C.
_{V 3 = 2.8V, V 4 =} -2.8V, V 5 = 3.2V,
ΔT = 16 μs, 1H = 32 μs, and drive
Since the driving voltage cannot be increased at 0 ° C., driving was performed with the same voltage value and pulse width ΔT = 36 μs and 1H = 72 μs.

[0049] Also, the same display device, V ₁ and W ₃ of Example 1 under the condition of _{55 ℃ = 14.3V, V 2 =} -14.3
V, V ₃ = 5.7 V, V ₄ = −5.7 V, V ₅ = 6.4
V, ΔT = 8 μs, 1H = 16 μs, and V ₁ = 14.3 V, V ₂ = 14.3 V, V ₃ at 30 ° C.
= 5.6 V, V ₄ = −5.6 V, V ₅ = 6.4 V, ΔT
= 24 μs and 1H = 48 μs, and each was driven.

Under the above-described driving waveforms and conditions, the driving margin and the amount of generated heat were measured in the same manner as in Example 1. In addition, the value of 1H, which is a reference for obtaining a drive margin, was evaluated as speed, and 1H = 50 μs, which is the minimum required for high-speed driving, was set as “slow”, and a larger value was set as “slow”.

The drive by the W ₁ has been able to perform good display throughout the display unit at any temperature, for W _3, but good display was obtained in 30 ° C., in 55 ° C. Temperature unevenness occurred on the entire display unit, and good display was not obtained. W ₁ and to compare the characteristics of the W ₃ is as follows.

[0052]

[Table 4]

In this embodiment, the drive waveform is selected according to the temperature of the display section.
° C. Set, the setting conditions of the 30 ° C. of W ₃ being less than 45 ° C., of W ₁ at 45 ° C. or more setting conditions of the 55 ° C.,
By selecting and driving each of them, good display is ensured and high-speed display is possible.

[0054]

As described above, by using the driving method of the present invention, a wide driving margin and a good display can be obtained without increasing the power consumption regardless of the environmental temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram of a display device according to the present invention.

FIG. 2 is a schematic diagram showing an electrode structure of a display unit of the display device shown in FIG.

FIG. 3 is a sectional view of a display unit of the display device shown in FIG.

FIG. 4 is a diagram showing a driving waveform used in the first embodiment of the present invention.

5 is a diagram showing a composite waveform of the drive waveform shown in FIG.

FIG. 6 is a diagram showing another driving waveform used in the first embodiment of the present invention.

FIG. 7 is a diagram showing a driving waveform of a conventional ferroelectric liquid crystal element.

FIG. 8 is a diagram showing a relationship between a driving voltage and a driving margin in a ferroelectric liquid crystal element.

FIG. 9 is an explanatory diagram of a relationship between a write pulse waveform and a drive margin in a ferroelectric liquid crystal element.

FIG. 10 is an explanatory diagram of a relationship between a write pulse waveform and a driving margin in a ferroelectric liquid crystal element.

FIG. 11 is a block diagram of another display device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Display part 102 Scan signal application circuit 103 Information signal application circuit 104 Scan signal control circuit 105 Drive control circuit 106 Information signal control circuit 107 Graphic controller 108 Temperature detection element 109 Temperature detection circuit 201 Scan electrode 202 Information electrode 203 Pixel 301 Analyzer 302, 308 Glass substrate 303,307 Insulating film 304,306 Alignment film 305 Ferroelectric liquid crystal 309 Polarizer 310 Sealing material

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinjiro Okada 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-5-297347 (JP, A) JP-A-6 -75540 (JP, A) JP-A-64-28623 (JP, A)

Claims (3)

(57) [Claims] 1. A method for driving a liquid crystal element having a liquid crystal exhibiting a chiral smectic phase sandwiched between a pair of substrates and having at least one pixel, wherein a signal waveform applied to a pixel at the time of selection is set to Yes after the erase pulse to the liquid crystal in a first state, a write pulse to the liquid crystal to the second state in accordance with input information,該書inclusive pulses, the low voltage period before and after sandwiching the high voltage period And the high voltage period is
A method for driving a liquid crystal element, wherein the method has a time width equal to or longer than a total time of a voltage period . 2. A method for driving a liquid crystal element having at least one pixel sandwiching a liquid crystal exhibiting a chiral smectic phase between a pair of substrates, wherein a signal waveform applied to a pixel at the time of selection according to a temperature of the liquid crystal element. And the signal waveform applied to the selected pixel at the time of high temperature changes the liquid crystal of the pixel to the second state according to the input information after the erase pulse for setting the liquid crystal of the pixel to the first state. A method for driving a liquid crystal element, comprising: a pulse; and the writing pulse has a low voltage period before and after a high voltage period. 3. A method for driving a liquid crystal device according to claim 2, wherein the high voltage period has a total time over the duration of the low voltage period.