JPS628130A - Driving method for liquid crystal electrooptic device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal electro-optical device, and more particularly to a method for driving a liquid crystal electro-optical device using ferroelectric liquid crystal.

[Summary of the invention]

The present invention is a method for driving a liquid crystal electro-optical device in which a high-frequency AC voltage pulse is applied as a scanning voltage when not selected, and its amplitude is determined by the difference in stability between the UP state and the DOWN state and the switching from the UP state to the DOWN state. Depending on the difference in threshold characteristics between the case and the case of switching from LIOWN-like deafness to 17F state, asymmetry with Ov as the center,
Furthermore, regarding the frequency and amplitude of the high-frequency AC voltage pulse, the composite waveform of the low-frequency signal range pressure pulse applied when not selected is always AC, and the permanent dipole of the ferroelectric liquid crystal responds to each voltage pulse. By setting the value to such a value that it is possible, even if the stability of the UP state or LIOWN state, that is, the bistability is low, the low bistability is assisted by the high frequency AC voltage pulse applied when not selected.
The present invention is intended to enable multiplex driving that provides sufficient contrast even with liquid crystal layer thicknesses of 2 μm or more, which has been difficult in the past.

[Conventional technology]

Fourth Display Re5e is a conventional method for driving a liquid crystal electro-optical device 4 using ferroelectric liquid crystal.
archConference, Proceedi
ng P, 217, patent application No. 58-179890.
Patent application 1982- (59,6,1 Yazaki application), Patent application 1982-
(59, April, 27 Sato application) etc.

[Problems and objects to be solved by the invention] As shown in FIG. 1, the molecules 11 of the ferroelectric liquid crystal are located on the cone 12 in the figure. In the absence of an electric field, if the liquid crystal layer thickness d is sufficiently thin, the liquid crystal molecules are aligned parallel to the substrate 14 due to the anchoring effect. At this time, the permanent dipole 15 is perpendicular to the substrate 14, and the second
As shown in Figure (a), the orientation is the +y direction (UP state) or the -y direction (lJOWN state), and either orientation is highly stable. This bistability is used as a memory effect in ferroelectric liquid crystals. However, if d is not sufficiently thin, this bistability deteriorates, and the orientation distribution of liquid crystal molecules becomes large as shown in FIG. 2 (1)). However, vector 21 in Fig. 2 is a projection of vector 11 indicating the liquid crystal molecular axis onto the conical base.] The shaded area in Fig. 2(b) shows the distribution range of vectors 2 +, , j. . Currently Shuang'an 1. In order to improve the quality, it is necessary to reduce d to about 5 μm, although it varies depending on the liquid crystal material, and a very important issue is how to increase bistability with a thick liquid crystal layer. .

Fourth LIisplay Re5earch
1IAIIh presented at the conference
The method uses a liquid crystal material in which the dielectric anisotropy ΔtH becomes negative after dielectric dispersion occurs due to the orientation of permanent dipoles of ferroelectric liquid crystals, as shown in Figure S, and a bias voltage is applied when not selected. By applying a high-frequency alternating voltage as a dielectric anisotropy effect, the low bistability is compensated for. In other words, when the bistability is low, the alignment of liquid crystal molecules in the absence of an electric field will be less parallel to the substrate surface (X-15 plane), but due to the high frequency AC voltage applied in the y direction and the dielectric anisotropy. Due to this interaction, the liquid crystal molecules are held parallel to the substrate surface, increasing bistability. However, in order to utilize the effect of dielectric anisotropy, it is necessary to apply a high frequency that is higher than the dispersion frequency that the permanent dipole cannot follow, and in addition, a high voltage must be applied to hold the liquid crystal molecules parallel to the substrate surface. Is required. Therefore, when driving a liquid crystal electro-optical device with a large total pixel area using this method, there are problems such as heat generation in the liquid crystal layer due to the application of high-frequency AC voltage and distortion of the high-frequency voltage waveform due to large capacitance. In order to do this, the applied voltage and frequency must be lowered.

The effect of applying high-frequency AC voltage is the Fredericks transition
This is the same phenomenon as □, and its threshold voltage Vν is expressed by the following equation.

vy-v'VΔgm・w K: Elastic constant So,
In order to reduce vFtl-, /ΔC may be reduced, but it is difficult to significantly change the values of both K and ΔtH. Alternatively, in order to lower the dispersion frequency, the response speed of the liquid crystal may be slowed down. However, one of the characteristics of ferroelectric liquid crystals is -ma/(P-11:)(τ
: response speed, M: viscosity, P: spontaneous polarization, E: applied electric field]
According to the formula, it responds to an applied electric field very quickly, but this %- must be sacrificed in order to lower the dispersion frequency, that is, the frequency of the alternating voltage. For example, the commonly known IJOBAMBO
In the case of , the response speed is d == 1μ, applied voltage 10V
It is about (QO/Jliee), and the frequency must be raised to several IQKHz or more.Dispersion frequency and response speed are considered to be approximately inversely proportional to each other, and it is not very desirable to slow down the response speed to the order of m5ae. do not have.

In addition, since this method utilizes the induced solder anisotropy, Δei
+(O) ferroelectric liquid crystal must be used.

As a ferroelectric liquid crystal with ΔCII<0, for example, W"OBAMB with 7γ groups etc. added in the direction transverse to the molecular axis.
It is known as OO, and its structure is as follows.

n-OBAMBOC Furthermore, n-On-0EA having no 7γ group has the following structure, and its dielectric anisotropy is positive.

(n=OBAM130) Since the dipoles of C= and C=O point in directions that sterically cancel each other out, the permanent dipole of n-OBn-0BA is n
-It is smaller than that of On-0BA. Therefore, in order not to reduce the permanent dipole of the liquid crystal material that serves as the pace, Δ
ε■ must be made negative, and material development becomes an issue.

Next, in the following driving method shown in Japanese Patent Application No. 58-179890, is it possible to perform static driving by supplementing the low bistability?Multiplex driving is not possible. If the drive method shown in the Japanese Patent Application No. 1983 (Yazaki) and the Patent Application No. 1983 (Sato) does not have sufficient bistability, multiplex driving is not possible: T3 is not possible, and d is made sufficiently thin. Bistability must be increased.

The present invention is intended to solve these problems, and its purpose is to compensate for the low bistability by using a high-frequency alternating current voltage with a lower voltage and lower frequency in mass-produced thicknesses, and to increase the The object of the present invention is to provide a multiplex driving method that can also be applied to liquid crystal electro-optical IIE devices.

[Means for resolving the gap @]

A method for driving a liquid crystal electro-optical device according to the present invention includes a) a method for driving a liquid crystal electro-optical device in which a ferroelectric liquid crystal is sandwiched between a pair of opposing transparent electrodes; Liquid crystal 1! by a composite voltage pulse of the low frequency selection voltage pulse and the low frequency signal voltage pulse applied to each of the liquid crystals 1! Select the ON state and OFF state of the air optics device, and press C.
) When not selected, scan I! Apply a high frequency AC concealed pressure pulse to the pole, and d) If at least one of the ON state and OFF' state is unstable, detect the difference in stability between them and switch from the ON state to the oyy state. and when switching from the 011FF state to the ONN state.e) The frequency and amplitude of the high-frequency AC voltage pulse are the same as those of the ferroelectric liquid crystal with respect to the low-frequency signal voltage pulse and the combined voltage pulse applied when not selected. It is characterized in that the value is such that the permanent dipole can respond, and f) the composite waveform of the high frequency AC voltage pulse and the low frequency signal voltage pulse is always AC.

〔Example〕

Hereinafter, a detailed explanation will be given based on examples.

Figure 4 shows the effect of high frequency AC bias.

@Figure 4 (a) is the applied voltage waveform, and Figure 4 ('b)
is the optical response of the ferroelectric liquid crystal to that voltage waveform.

Here, the response is shown when a liquid crystal element with low bistability is used, and the solid line is the response when AC bias is applied when not selected, and the broken line is the response when AC bias is not applied. When no AC bias is applied, the voltage pulse +v
1, the brightness is selected, or if the bistability is poor, the brightness changes as shown by the dashed line and becomes . A similar optical response is obtained when the voltage pulses -v,'t-inna are applied during the next selection. Next, when an AC bias is applied during non-selection, the optical response during selection is the same as when no AC bias is applied, and the brightness becomes 3 or 14 at the end of the selection period. However, by appropriately setting the frequency and amplitude V, , -V4 of the AC bias applied during non-selection, the brightness during non-selection can be made to oscillate at or near , as shown by the solid line. I can do it.

The stability of the UP state and the IJOWN state are equal to each other, and the U
When switching from P state to IJOWN state and IJO
If the threshold characteristics when transitioning from the WN state to the UP state are also the same, then V and X V4 may be used. Also, for example, if the stability is lower in the UP state than in the IJOWN state, the threshold voltage of UP→LIOWN is lower than that of the IJOWN state.
The threshold voltage of WN→σP is also considered to be low, and V,
) V, it is possible to obtain an optical response as shown by the solid line in FIG. 4(b).

The effect of AC bias will be further explained using the movement of liquid crystal molecules. In Figure 5, the coordinate system is taken as in Figure 1,
Define the azimuth angle φ as shown in the figure, and when φ=O, LIOWN
state, its brightness is crow, and the brightness when φ=φ4 is h. In addition, here, the stability of the IJOWN state is lower than that of the UP state, and in Fig. 4(a), V,
(Consider the case where a voltage waveform of V4 is applied. First, the voltage pulse -V switches to the LIOWN state, and even if φ-0 is applied, the orientation direction of the liquid crystal molecules deviates from the X-axis direction because the stability of the LIOWN state is low. Then, when the selection time is over, the voltage becomes φ−φ4 (brightness).After that, as shown in FA4 diagram (a), one voltage pulse with a short width and peak value +V is applied. ,φya±(φ.

+Δφ+). Next, apply a voltage pulse with a peak value of −■ to 1
If the application of
It is not possible to maintain the brightness by applying an AC bias of . However, depending on the difference in threshold characteristics between the two, the amplitude (+Vs * 7
4) If t- is set and the value of Δφ+ (Δφ-) is made as small as possible, the alignment direction of the liquid crystal molecules will be φ4 to φ4+Δφ or -φ by applying an AC bias.
It vibrates between 4 and -φ4-Δφya, and about 1. The brightness can be maintained.

FIG. 6 shows a cross-sectional view of the liquid crystal electro-optical device. A striped transparent plate 12 is formed on opposing surfaces of two glass substrates 11.
The two glass substrates 11 are stacked so that the striped transparent electrodes provided on the upper and lower substrate surfaces are orthogonal to each other to form a matrix. 15 is an alignment control film which has been subjected to a rubbing treatment. 14 is a polarizer whose polarization directions are almost perpendicular to each other, and 15 is a liquid crystal! -16
This is a spacer for determining the thickness of.

As a first example, nine drive waveforms shown in Section 7 were used. Figures 7(a) and 7(b) show the scanning voltage waveform V.
t and the signal voltage waveform Vd, and FIG. 7(C) shows Vt and Vd.
The composite waveform of d, VI+O FIG. 7(d) is the optical response of the liquid crystal to vr and a. The saturation voltage at the pulse width t1 when switching from the UP state to the 13OWN state is -
The threshold voltage and saturation voltage at Vs' and the pulse llt when switching from the DOWN state to the DI' state are +Vth and +V8, respectively. The same applies to the following examples. RpOBAMBC is used as the liquid crystal material, and the thickness of the liquid crystal layer is 55μ9k, t, x200.
/jlle, duty ratio 1/256. -)-V,
-+7 V #-Vt=-16V, +V, x+1sv,
-7, x-257° +v, +sv, -v, -5V,
The frequency of the AC bias was set as ft1m6KEr. If AC bias was not applied, the bistability was very low and multiplex driving was not possible, but by applying AC bias, the bistability was increased and a contrast ratio of 1:1.3 was obtained. I was able to do that.

In the second example, the driving waveform in the first example is used, and the thickness of the liquid crystal layer is set to 4.0 μs, t, = 150
μ(6), duty ratio 1/256, +V, =+5
V.

-7,=-15V,+v,=+14V,-7,=-
16V.

It was set as f'ba8KRZ. In this example, since the steepness of the threshold characteristic is very poor, +V, #+5V, -V6=
-SV as v1+v, -av, V, -V, = -2
I made it to be V. As a result, a contrast ratio of 1:14 was obtained.

As a third example, the interlocking waveform shown in FIG. 8 was used. The thickness of liquid crystal 1- is 1.5μs, t1=150μ
(8), duty ratio 1/256-f-1, wet +6v,
-V, ff1-10V, +V, -+5V, -V, =i-
5V, and in this example, '[TF state and IJOWN
Since the stability of the states was almost equal to each other, the amplitude of the AC bias was set to ±2°V and ft+#10KHz.

In this example, since the liquid crystal layer is thin, AC bias is not applied.
Although a contrast of approximately 1=6 was obtained without using the liquid, the contrast was increased to 1:6 by applying a current bias.
I was able to raise it to 121.

As a fourth example, the drive waveform in the second example is used, and the liquid crystal layer thickness is 1r, the shoulder is 2.0μ, the tl-100μ formula, the duty ratio is 1/128, +v, -+5v.
, -v.

-15v, +v, = +2v, -v6M-2v, +v,
= +15V, -V, = -17V, fb = 12KHz, 7ho In this example, a contrast ratio of 1:14 was obtained.

In the fifth embodiment, the drive waveform in the second embodiment is used, and the liquid crystal layer thickness is set to 1.5μ, t, x 1Q.
Qμ formula, duty ratio 1/256, +V, =6
V, -V, =-12V, +Va=+1v, -v
6=-1v, +vs--)-27V, -V4=-50
7, fb=-50KHz. In this example, 1:16
A contrast ratio of Figures 9 and 10 show logic circuit diagrams for generating the drive waveforms shown in Figures 7 and 8, respectively.

Both h and h' are signals for selecting ON and OFF'F of the liquid crystal. The signal waveforms at each point 1 to m in FIGS. 9 and 10 are shown in FIGS. 11 and 12.

Figure 15 is a transistor i driver circuit diagram for generating an AC bias drive waveform, and C2tl+f*
Input the signal waveform at each point in the dH4q and 1o diagrams to g and dH4q and 1o.

In the above embodiment, BpOBAMEC is used as the liquid crystal material, but any other ferroelectric liquid crystal can be used, and the fIi width and frequency of the alternating current can be set according to the characteristics of the liquid crystal material used. [Effects of the Invention] As described above, depending on the difference in stability between the UP state and LIOWN state and the difference in threshold characteristics between UP-41) OWN and IJOWN-+UP, an asymmetric AC bias is generated around the amplitude dlOV. By applying this as a scanning voltage when not selected, in order to ensure that the low stability is assisted by AC bias, it is possible to perform multiplex driving even in the case of I-thickness of the ridge crystal, which is impossible to perform multiplex driving with conventional driving methods. Driving becomes possible. Furthermore, both the voltage and frequency applied to the fc firing current can be lowered compared to the method using dielectric anisotropy, and there is no need to develop a new liquid crystal material with a negative dielectric anisotropy force of 3. Therefore, it is possible to provide a liquid crystal electro-optical device with a large area and a liquid crystal layer thickness that is easy to use for IL-skin at a low cost. The driving method of the present invention can be applied not only to large-area liquid crystal electro-optical devices, but also to liquid crystal shutters for printer heads, static driving methods that can prevent deterioration of liquid crystals due to the application of DC voltage, and the like.

[Brief explanation of the drawing]

Figure 1 is a coordinate system diagram of a ferroelectric liquid crystal, and Figure 2 (a). (b) is a diagram of the orientation distribution of liquid crystal molecules when there is no electric field, and Figure 5 is a strong! l! Dielectric dispersion diagram of conductive crystal, Figure 4 is the effect diagram of AC bias, Figure WJ5 is the orientation distribution diagram of liquid crystal molecules due to application of AC bias, Figure 6 is a cross-sectional diagram of the liquid crystal electro-optical device, Figure 7
Figure 1. FIG. 8 is a waveform diagram showing the AC bias drive waveform used in the second embodiment and the optical response of the liquid crystal. 4th.
A waveform diagram showing the AC bias drive waveform used in the fifth embodiment and the optical response of the liquid crystal, FIG. 9 is a logic circuit diagram for generating the drive waveform shown in FIG. 7, and FIG. 10 is a waveform diagram showing the optical response of the liquid crystal. 11 is a timing chart of the logic circuit in FIG. 9, FIG. 12 is a timing chart of the logic circuit in FIG. 10, and FIG.
The figure is a transistor driver circuit diagram for generating an AC bias drive waveform. 11...Liquid crystal molecules 12...Cone 15...Permanent dipole 14...Substrate 21...Projection of liquid crystal molecules onto the circular base 61...Glass substrate 62...Transparent electrode 65. ...Alignment control film 64...Polarizing plate 65...Spacer 66...Liquid crystal layer 91...NANLI gate 92...ANIJNOR gate...NOR gate 94...OI'l gate 95... ... Inverter 96 ... High output buffer 101 ... Transistor 102 ... Transistor 105 ... Resistor 104 ... Diode 105 ... Capacitor 106 ... Liquid crystal electro-optical device
x Tomb Crystal Bungo ^ Self-survey shoulder 1 弗圀 12 fig. rithing device ＾Ｏ 1 Figure 6 blowing J Reno 慴 入 g solicitation trap fit し fig 7 female L circumference ass, drive 5 - Ttn for fig. −−−−−−−−−−−−−
------5--1■1f'L---1--■shi-"
Plate tn, --------tn old-tm general---part "-
-m skin----IAILri bias j1. L1 time shift t chart UΔ 11th e knowledge U friend m--------1--------=-+ ++
24th stitch 1j low road - 9 Ikoshikuzama 1 Tom convex Figure 12

Claims (4)

[Claims] (1) a) A method for driving a liquid crystal electro-optical device in which a ferroelectric liquid crystal is sandwiched between a pair of opposing transparent electrodes, b) a low frequency selection voltage pulse applied to a scanning electrode and a signal electrode, respectively, at the time of selection; The ON state and OF of the liquid crystal electro-optical device are determined by the composite voltage pulse of the low frequency signal voltage pulse.
A method for driving a liquid crystal electro-optical device, comprising: selecting the F state; and c) applying a high-frequency AC voltage pulse to a scanning electrode when the F state is not selected. (2) If the stability of at least one of the ON state and the OFF state is low, the difference in stability between the ON state and the OFF state, and when switching from the ON state to the OFF state,
The amplitude of the high-frequency AC voltage pulse is adjusted to OV according to the difference in threshold characteristics when switching from the FF state to the ON state.
2. The method of driving a liquid crystal electro-optical device according to claim 1, wherein the driving method is asymmetrical about the center. (3) The frequency and amplitude of the high-frequency AC voltage pulse are such that the permanent dipole of the ferroelectric liquid crystal can respond to the voltage pulse combined with the low-frequency signal voltage pulse applied when not selected. 2. The method for driving a liquid crystal electro-optical device according to claim 1, wherein the driving method is a value. (4) The method for driving a liquid crystal electro-optical device according to claim 1, wherein the combined waveform of the high-frequency AC voltage pulse and the low-frequency signal voltage pulse is always AC.