JPH063504B2 - Liquid crystal device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a liquid crystal device, and more particularly to a liquid crystal device using a ferroelectric liquid crystal.

[Prior art]

A display element of the type in which transmitted light rays are controlled by combining with a polarizing element by utilizing the anisotropy of refractive index of ferroelectric liquid crystal molecules has been proposed by Clark and Lagerwall (Japanese Patent Laid-Open No. 56-56,561). -107216, U.S. Patent No. 4367924, etc.). This ferroelectric liquid crystal generally has a chiral smectic C phase (S
mC ^* ) or H phase (SmH ^* ), and in this state, takes one of a first optical stable state and a second optical stable state in response to an applied electric field, and applies an electric field When it is not present, it has the property of maintaining that state, that is, has bistability, and has a quick response to changes in the electric field, and is expected to be widely used as a high-speed and memory type display element.

The above-mentioned ferroelectric liquid crystal device is disclosed in
Pixel information is written by the driving method disclosed in Japanese Patent No. 2141279. According to the above-mentioned publication, the scanning lines incorporated in the ferroelectric liquid crystal element are sequentially selected, and
A one-polarity voltage is applied to all or a predetermined number of pixels on the scanning line selected by the phase so that the optical state of the pixel becomes one optical state (for example, "light transmission state (white)"), Of the previous or a predetermined number of pixels on the scan line selected by the phase,
Line-sequential scanning writing is performed by applying a voltage of the other polarity to the selected pixel so that the optical state of the pixel becomes the other optical state (for example, "light blocking state (black)").

[Problems to be solved by the invention]

In general, a ferroelectric liquid crystal device is difficult to form a bistable state as disclosed by Clark et al., And has a strong tendency to form a monostable state. Therefore, when a still image is formed on a display panel using a ferroelectric liquid crystal element by the above-mentioned driving method and then the still image is displayed by releasing the voltage, the problem that the still image disappears was there.

Therefore, in order to solve the above-mentioned problems, a driving method in which line-sequential writing is performed by periodically repeating a predetermined period (for example, one field or one frame) in which a sequential scanning signal is sequentially applied to a scanning line ( The refresh driving method) can be applied. That is, when writing a still image on the ferroelectric liquid crystal panel, a stable still image can be displayed by sequentially and repeatedly applying information signals that generate the still image.

However, in such a refresh driving method, when the ferroelectric liquid crystal panel is multiplexed and driven with the above-mentioned first phase (line clear phase) and second phase (writing or holding phase), the line clear occurs at the first phase. In this case, the saturation voltage for inverting one of the optical states in the case of writing in the second phase by line clearing in the first phase is about 2 to 3 times the saturation voltage for maintaining the optical state. It became clear from various studies by the inventors. Therefore, in the normal line erasing / line writing driving method, due to the above-mentioned characteristics, the driving voltage is increased due to the increase in the entire driving voltage, and the liquid crystal material is deteriorated or the alignment film is deteriorated. It also caused a short circuit between the electrodes.

[Outline of Invention]

The present invention provides a novel method of driving an optical modulation element capable of identifying contrast according to the direction of an electric field such as an optical modulation element, particularly a ferroelectric liquid crystal element, which solves the above-mentioned problems of the conventional example, and a liquid crystal device thereof. To provide.

That is, according to the present invention, in a liquid crystal device in which a ferroelectric liquid crystal is arranged at an intersection of a scanning electrode group and a signal electrode group to form a pixel, a voltage applied to a scanning non-selected electrode is used as a reference for the scanning electrode. , Polarity voltage with pulse width larger than Δt
A scan selection signal having V _x and the other polarity voltage V _y with a pulse width of Δt is provided before and after, respectively, and an information signal synchronized with the scan selection signal is synchronized with the one polarity voltage V _x. Then, in synchronization with the voltage signal that gives the pixel group on the scan selection electrode a voltage V _R exceeding one threshold voltage of the ferroelectric liquid crystal and the other polarity voltage V _y , the selection on the scan selection electrode is performed. Voltage that exceeds the other threshold voltage of the ferroelectric liquid crystal
And a voltage signal giving V _B, and a DC voltage is applied to the information signal so that the voltage applied to the pixel on the scanning non-selection electrode has a DC component having a polarity opposite to that of the voltage V _R. It is characterized by the superimposed liquid crystal device.

[Detailed Description of Embodiments of the Invention]

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a waveform diagram of the driving method used in the present invention. or,
FIG. 2 is a schematic diagram showing a matrix electrode of a cell in which a ferroelectric liquid crystal is sealed.

The cell structure 10 shown in FIG. 2 is a cell structure in which a pair of substrates 1a and 1b made of glass plates are held at a predetermined interval by a spacer 4, and the periphery is adhered with an adhesive 6 to seal the pair of substrates. An electrode group consisting of a plurality of transparent electrodes 2a (for example, a scanning voltage applying electrode group in the matrix electrode structure) is formed in a strip pattern on the substrate 1a, and on the substrate 1b. An electrode group (for example, an information voltage applying electrode group in the matrix electrode structure) is formed of a plurality of transparent electrodes 2b intersecting the transparent electrodes 2a.

Of the drive waveforms shown in FIG. 1, S _S is the scan selection signal and S _NS
Represents a scanning non-selection signal, I _S represents an information selection signal, and _{IN S} represents an information non-selection signal.

When the minimum pulse width of the driving pulse is Δt, the scanning selection faith S _S is the voltage V _S1 having the pulse width 2Δt and the pulse width Δt.
Voltage − Alternating voltage of V _S2 (| V _S1 | = | -V _S2 |)
Is formed. The information selection signal I _S is the phase t of the voltage 0.
₁ and the phase t ₂ of the voltage −V _I and the phase t _{3 of} the voltage _VDC + V _{I on} which the DC offset voltage V _DC is superimposed, the information non-selection signal I
_NS includes a phase t ₁ of the voltage 0, and the phase t ₂ of the voltage V _DC + V _1, and the phase t ₃ of the voltage -V _1. These information signals have a voltage value of positive polarity (based on the voltage applied to the scanning non-selected electrodes) whose voltage average value is based on the DC offset voltage V _DC .

Therefore, the applied voltage (I _S −
As shown in (S S _S ) and (I _NS −S _S ), at the phases t ₁ and t ₂ , all or a predetermined pixel group on the scan selection electrode has one threshold voltage (for example, one) of the ferroelectric liquid crystal. , the average voltage value at the phase t ₁ and t ₂ of the voltage V _R is applied (voltage V _R the display state) over the "white" is different between I _S -S _S and I _NS -S _S However, in any case, the voltage is set to exceed one threshold voltage of the ferroelectric liquid crystal). Then, at phase t ₃ , the information selection signal
To the pixel to which I _S is applied, a voltage V _I + V _DC + V _S2 that exceeds the other threshold voltage of the ferroelectric liquid crystal (for example, a black display state) is applied, and the information non-selection signal _INS is applied. In the pixel,
A voltage V _S2 −V _I that does not exceed the threshold voltage of the ferroelectric liquid crystal is applied.

The voltage -V _I applied to the signal electrodes in phase t ₂ (voltage in the phase t ₂ of the information non-selection signal) (Information voltage in the phase t ₂ of the selection signal) and the voltage V _I + V _DC are each auxiliary signal Correspondingly, the application time of the same polarity voltage applied to the pixel on the scanning non-selection electrode is inverted by synthesizing with the voltage applied to the scanning non-selection electrode to invert the stable state of the ferroelectric liquid crystal selected at the time of scanning selection. Before the application time is reached, the voltage of the same polarity and the voltage of the opposite polarity can be applied to the pixels on the scan non-selection electrodes.

According to the present invention, the writing step at the phase t ₃ is followed by the step of erasing the pixels on the line at the phases t ₁ and t ₂ to white (or black) by superimposing the DC offset voltage V _DC on the information signal. It is possible to reliably write black (or white).

FIG. 3 shows another driving example of the present invention. In the driving example shown in FIG. 3, the step of erasing the pixels on the line corresponds to the period of the phases t ₁ , t ₂ and t ₃ , and the selective writing period corresponds to the phase t ₄ . At this time, of the drive pulses
The pulse width of the voltage V _X of the scan selection signal is set to 3Δt and the voltage V _y is set to the pulse width Δt, where the minimum pulse width is Δt. At this time, the scan selection signals V _S1 and V _S2 are
_S1 | <| -V _S2 |.

The DC offset voltage V _DC amount used in the present invention is 0.5 to 10.0%, preferably 1.0% with respect to the information signal voltage | ± V _I |.
A voltage of ~ 5.0% is recommended.

FIG. 4 shows a driving device of the ferroelectric liquid crystal panel 41 in which the matrix electrodes used in the present invention are arranged. In the panel 41 of FIG. 4, the scanning lines 42 and the data lines 43 intersect each other, and the ferroelectric liquid crystal is arranged between the scanning lines 42 and the data lines 43 at the intersections. . Also, in FIG.
44 is a scanning circuit, 45 is a scanning side driving circuit, 46 is a signal side driving voltage generating circuit, 47 is a line memory, 48 is a shift register, 49 is a scanning side driving voltage generating power supply, and 40 is a multi-processor unit (MPU). Is represented.

The scanning side drive voltage generating power supply 49 is provided with voltages V _S1 , V _S2 and 0. For example, the voltages V _S1 and V _S2 are used as the power supply of the scan selection signal and the voltage 0 is used as the power supply of the scan non-selection signal. be able to.

The scan selection signal described above is sequentially applied to the scan electrodes, and so-called refresh scan can be performed.

The liquid crystal cell used in the present invention has a 1 μm gap using, for example, “CS1014” (trade name) manufactured by Chisso Corporation, which is an ester-based mixed liquid crystal as a liquid crystal material. A rubbing-treated polyvinyl alcohol film was used as an orientation control film in the liquid crystal cell. The phase transition of this liquid crystal material was as follows.

−21 ℃ 54.4 ℃ 69.1 ℃ 80.5 ℃ Crystal → SmC ^* → SmA → Ch → I _so SmC ^* ; Chiral smectic C phase SmA; Smectic A phase Ch; Cholesteric phase I _SO ; Isotropic phase Also, drive shown in Fig. 1 The voltage used in the waveform is 27.0
V _S1 = 15 V, V _S2 = −1 at ΔC = 28 μsec
Although 5 V, V _I = 5 V, and V _I ^′ = 6 V were used, refresh driving was performed using these voltages, and a good still image was obtained with about half the driving voltage of the driving method in which the DC offset voltage V _DC was not applied. It was possible to rewrite and scroll.

The optical modulator used in the device of the present invention has at least two stable states, and in particular, has either a first optical stable state or a second optical stable state depending on an applied electric field. That is, a substance having a bistable state with respect to an electric field, particularly a liquid crystal having such a property is used.

As a liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable, and a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) liquid crystal is most preferable. Are suitable. About this ferroelectric liquid crystal, "Le Journal de Physiove let"
ter ") 36 (L-69), 1975" Ferroelectric Liquid Crystals "
stals ”);“ Applied Physics Letters ”
("Applied Physics Letters") Vol. 36 (No. 11), 1980 Submicron Second Bistable Electro-Optic Switching In Liquid Crystal ("Submicro Second Bistable Electrooptic S
witching in Liquid Crystals ”);“ Solid physics 16 (141)
1981 "Liquid crystal" and the like, and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of the ferroelectric liquid crystal compound used in the method of the present invention include desiloxybenzylidene-P'-amino-2-methylbutylcinnamate (DOBAMBC) and hexyloxybenzylidene-P'-amino-. 2-chloropurupircinnamate (HOBACPC) and 4-o- (2
-Methyl) -butyl resorcylidene-4'-octylaniline (MBRA8) and the like, U.S. Pat.
U.S. Patent No. 4614609 Publication U.S. Patent No. 4622165 Publication,
Ferroelectric liquid crystals described in US Pat. No. 4639089 and the like can be mentioned.

When an element is formed using these materials, the element is supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the temperature state in which the liquid crystal compound is in the SmC ^* phase or the SmH ^* phase. be able to.

Further, in the present invention, in addition to the above-mentioned SmC ^* and SmH ^* , it is also possible to use a ferroelectric liquid crystal which appears in a chiral smectic F phase, I phase, J phase, G phase or K phase.

FIG. 5 schematically shows an example of a ferroelectric liquid crystal cell. 51a and 51b are substrates (glass plates) coated with transparent electrodes such as In ₂ O ₃ , SnO ₂ and ITO (Indium-Thein-Oxide), between which the liquid crystal molecular layer 52 is perpendicular to the glass surface. The liquid crystal of the SmC ^* phase oriented like this is enclosed. A thick line 53 represents a liquid crystal molecule, and the liquid crystal molecule 53 has a dipole moment (P⊥) 54 in a direction orthogonal to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 51a and 51b, the helical structure of the liquid crystal molecules 53 is unraveled, and all the dipole moments (P⊥) 54 are oriented in the electric field direction. Can be changed. The liquid crystal molecule 53 has an elongated shape,
Liquid crystal optical modulation that exhibits refractive index anisotropy in the major axis direction and the minor axis direction, and therefore, for example, by placing polarizers arranged in a crossed Nicol position above and below the glass surface, the optical characteristics change depending on the polarity of voltage application It is easy to understand that the device is an element. Furthermore, when the liquid crystal cell is made sufficiently thin (for example, 1 μm), the helical structure of the liquid crystal molecules is unwound even when no electric field is applied as shown in FIG. 6, and its dipole moment Pa or Pb is It can be either up (64a) or down (64b). In a cell like this,
As shown in FIG. 6, electric fields Ea of different polarities and above a certain threshold value
Or, if Eb is applied for a certain period of time, the dipole moment becomes an electric field.
64a upward or 6 downward with respect to the electric field vector of Ea or Eb
4b, and the liquid crystal molecules are aligned in either the first stable state 63a or the second stable state 63b accordingly.

There are two advantages of using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. Explaining the second point with reference to FIG. 6, for example, when an electric field Ea is applied, the liquid crystal molecules are aligned in the first stable state 63a, but this state is stable even when the electric field is cut off. In addition, when a reverse electric field Eb is applied, the liquid crystal molecules are in the second stable state 63.
It is oriented to b and changes its molecular orientation, but it remains in this state even when the electric field is turned off. Further, unless the applied electric field Ea exceeds a certain threshold value, the respective alignment states are also maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, generally 0.5 μ to 20 μ, and particularly 1 μ to
5μ is suitable.

〔The invention's effect〕

As described above, according to the present invention, as described above,
It is possible to drive the ferroelectric liquid crystal panel with a small driving voltage and obtain a good image.

[Brief description of drawings]

FIG. 1 is a waveform diagram of drive waveforms used in the present invention. FIG. 2 is a plan view of the liquid crystal element used in the present invention. Third
The figure is a waveform diagram of another drive waveform used in the present invention. FIG. 4 is a block diagram of the liquid crystal device of the present invention. 5 and 6 are perspective views of the ferroelectric liquid crystal used in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Mizudome 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non-Co. Ltd. (56) References JP-A-61-286819 (JP, A) JP-A-62-9323 (JP, A)

Claims (6)

[Claims] 1. A liquid crystal device in which a ferroelectric liquid crystal is arranged at an intersection of a scanning electrode group and a signal electrode group to form a pixel,
To the scanning electrodes, one polarity voltage V _x with a pulse width larger than Δt and the other polarity voltage V _y with a pulse width Δt, based on the voltage applied to the scanning non-selection electrodes, respectively, before and after, An information signal synchronized with the scanning selection signal is applied to the pixel group on the scanning selection electrode to exceed one threshold voltage of the ferroelectric liquid crystal in synchronization with the one polarity voltage V _x. a voltage signal providing a voltage V _R and the other polarity voltage in synchronism with V _y, the selected pixel on the scan selection electrode, the voltage to provide a voltage V _B across the other threshold voltage of the ferroelectric liquid crystal And a DC voltage is superimposed on the information signal so that the voltage applied to the pixel on the scanning non-selection electrode has a DC component having a polarity opposite to that of the voltage V _R. And liquid crystal device. 2. The liquid crystal device according to claim 1, wherein the pulse width of the one-polarity voltage V _x is 2ΔT or more. 3. The information signal is applied to a pixel on a scanning non-selection electrode by applying a voltage of the same polarity voltage applied to the pixel for inverting the stable state of the ferroelectric liquid crystal selected during scanning selection. 2. The liquid crystal device according to claim 1, further comprising an auxiliary signal that gives a voltage having the same polarity and a voltage having a reverse polarity by synthesizing the voltage with the voltage applied to the scanning non-selection electrode before reaching the voltage. 4. The liquid crystal device according to claim 1, wherein a predetermined period for sequentially applying a scan selection signal to the scan electrodes is periodically repeated. 5. The liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. 6. The film thickness of the chiral smectic liquid crystal,
The liquid crystal device according to claim 1, wherein the liquid crystal device is set to be thin so that the helical structure inherent to the chiral smectic liquid crystal disappears when no electric field is applied.