JPS6111787A - Liquid crystal matrix display unit - 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 Application of the Invention] The present invention relates to a display device using liquid crystal, and particularly to a liquid crystal display device that can realize high-definition, large-area display with a simple structure.

[Background of the invention]

Conventionally, one of the methods for driving liquid crystals is an active matrix driving method.

In this driving method, an FBT (field effect transistor) is connected to each liquid crystal pixel, and a voltage is applied to the liquid crystal through this FET to display an image. Regarding this driving method, 1
3ernard J, Lechner et al.

Liquid Crystal matrix ])i
sprays, proceedings of the
IEBE, ■ol, 59. No, 11. no
vember 1971, JP-A-55-9517, JP-A-55-28649, etc.

A major feature of this driving method is that even if the number of electrodes (scanning lines) increases, the effective voltage applied to the liquid crystal does not decrease, so sufficient brightness and contrast ratio can be obtained.

FIG. 21 is a configuration diagram of a conventional liquid crystal active matrix drive circuit. Further, FIG. 22 shows an example of a cross-sectional view of an element using a single crystal silicon substrate.

The source line 1, gate line 2, FET 3, and storage capacitor 4 shown in FIG. 21 are formed on a single crystal silicon substrate 19 shown in FIG. 22.

Further, one terminal of the liquid crystal pixel 5 is connected to the drain terminal of the FET 3. The other terminal becomes the common electrode 17.

The FET 3 shown in FIG. 22 is composed of diffusion layers 9 and 12, a field interconnection film IO, and a gate electrode 11. Further, the storage capacitor 4 is composed of a diffusion layer 6 and a polysilicon layer 6. Note that the aluminum electrode 13 becomes one terminal of the liquid crystal pixel 5.

The transparent substrate 18 forms a transparent common electrode 17 and a liquid crystal alignment film 16 . The liquid crystal 15 is aligned by a liquid crystal alignment film 16 and a liquid crystal alignment film 14 formed on the single crystal silicon substrate side.

Note that, as the liquid crystal 15, a guest-host liquid crystal obtained by adding a dichroic dye to a DSM liquid crystal or a nematic liquid crystal is preferably used.

Next, the operation of the drive circuit shown in FIG. 21 will be explained using FIG. 23. To the source line 1, a voltage vllll whose polarity is inverted with reference to the voltage Vc7 is applied every - field.

On the other hand, a gate pulse Vol is applied to the gate line 2. As a result, when the voltage Vc is constantly applied to the common electrode 17, the voltage applied to the liquid crystal pixel 5 becomes vLc.

At this time, the gate pulse oI of vLc becomes H",
When FET3 conducts, it becomes 1, but the gate pulse V
When al becomes °L'' and FET 3 becomes non-conducting, it attenuates. At this time, the attenuation time constant is determined by the capacitance C of liquid crystal pixel 5.
It is determined by Lc and the resistance Rt, c and the capacitance Cgtg of the storage capacitor, and the off resistance Reff of the FET3.

Now, if 1%ott >> Rtc, the decay time constant τ of the voltage vLc applied to the liquid crystal pixel 5 is Rt,c (Cstg
+Ct,c).

On the other hand, it is well known that the brightness of liquid crystals is not limited to nematic liquid crystals, but also cholesteric liquid crystals and phase transition liquid crystals, and depends on the effective value of the applied voltage. From this, it can be seen that the brightness of the liquid crystal largely depends on the applied voltage VLC decay time constant τ.

Conventional nematic liquid crystals have an optical response time of 50 to 10
Because of the slow speed of 0 m5, especially when a video signal is input, the response of the displayed image cannot follow the video signal, and sufficient display characteristics cannot be obtained.

In addition, in the active matrix, the change over time of the capacitance CLC of the liquid crystal pixel is zero, whereas the resistance Rt
, c have problems such as large changes over time or large fluctuations during device assembly, and the capacitance may not be able to hold the applied voltage sufficiently, resulting in a problem that good display cannot be obtained. be.

Thus, improving high-speed response and memory performance has become a major issue.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a new type of liquid crystal display device that improves high-speed response and memory performance and provides excellent display performance.

[Summary of the invention]

The first feature of the present invention is that a switch is connected to a ferroelectric smectic liquid crystal display element, a predetermined voltage is selectively applied at regular intervals, and the relaxation phenomenon of the smectic liquid crystal display element is utilized to create a storage The purpose is to realize an active matrix method without adding a capacitor.

The second feature is that the liquid crystal display device uses an active matrix method and is driven with the same polarity of applied voltage during the same selection time.

The third feature resides in a liquid crystal display device that uses an active matrix method and drives the applied voltage with both positive and negative polarities at the same selection time.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be explained in order.

FIG. 1 is an overall configuration diagram of a liquid crystal matrix display device according to the present invention. This device consists of a liquid crystal display element 100, drive circuits 20a and 20b, and a control circuit 101. Among these, the liquid crystal display element 100 is a display element) 100a.
It is an array of multiple .

Next, the configuration and operation of each part will be explained in detail.

FIG. 2 shows a basic configuration diagram of the display 100H. The display element 100a includes a liquid crystal display element 22 and a switch element 2 that selectively applies a voltage to the liquid crystal display element.
Consists of 1.

-! Further, the switch element 21 is controlled by a drive circuit 20a, and its output Va is applied to one terminal of the liquid crystal display element 22. Furthermore, the output vb of the drive circuit 20b is
It is applied to the other terminal of the liquid crystal display element.

The switch element 21 may be a mechanical switch, but an electronic switch as shown in FIG. 3 is more convenient. Figure 3 (
In a), P-MO8 or N-MOS) run raster 23at is used, and in FIG. 3(b),
An electronic switch composed of an N-MOS) transistor 23b, a P-MOS) transistor 23C, and an inverting gate 24 is used as a switching element. This switch element is
For example, a bipolar element may be used.

Next, the structure and operation of the liquid crystal display element shown in FIG. 2 will be explained.

FIG. 4, FIG. 5, and FIG. 6 show cross sections of the liquid crystal display element used in the present invention.

FIG. 4 shows a transparent substrate 28 on which a transparent electrode 29a and a liquid crystal alignment film 30a are formed, and a transparent electrode 29 similar to this transparent substrate.
b and a transparent substrate 32 on which a liquid crystal alignment film 30b is formed are opposed, and a ferroelectric liquid crystal exhibiting a chiral smectic C phase or a chiral smectic H phase is sealed between them.

Further, a polarizer 27a is provided above the transparent substrate 28, and a polarizer 27b and a reflector 3 are provided below the transparent substrate 32.
2 will be provided. At this time, the illumination of the liquid crystal display element is lamp 2.
Do it in 6.

The liquid crystal alignment films aoa, a, and ob are made of a material that has both insulating properties and properties that regulate the arrangement of liquid crystal molecules, such as a polyimide polymer film, a polyamide polymer film, PVA, etc., with an appropriate thickness. It is something.

Further, the polarizers 27a and 27b do not need to be installed in close contact with the substrate, but may be installed separately from the substrate, or the polarizers themselves may be used as the substrate.

Further, the ferroelectric liquid crystal used in the present invention includes, for example, a mixture of equimolar amounts, or, or, or.

In order to align the liquid crystal molecules of the ferroelectric liquid crystal, the purpose can be achieved by rubbing the liquid crystal alignment film in a certain direction.

As a result, smectic liquid crystals have a layered structure, which is a well-known fact, but the examples of the present invention show that in smectic liquid crystals, the long axis direction of the liquid crystal molecules changes from layer to layer, and it appears as if the layers are separated. The molecular arrangement is like a spiral with the arm axes running in the vertical direction, and this spiral structure is thought to exhibit ferroelectricity.

By the way, it is known that materials exhibiting ferroelectricity exhibit responsiveness to a direct current electric field as a ferroelectric substance, and that the direction of spontaneous polarization is reversed and rearranged according to the direction of the electric field.

On the other hand, in the case of smectic liquid crystals that exhibit ferroelectricity, they form a helical structure in the absence of an electric field, but when an electric field is applied, the arm axes melt, and the long axis direction of the liquid crystal molecules is perpendicular to the direction of the electric field. and is rearranged at an angle corresponding to an angle unique to the material (an inclination angle formed between the radial arm axis and the long axis of the molecule, hereinafter referred to as θ) with respect to the radial arm axis before being excited. For smectic liquid crystals, the angle is θ-20' to 30°, but preferably π/4.

FIG. 5 shows an embodiment in which the liquid crystal display element is of a transmissive type. Furthermore, in FIG. 6, a guest-host liquid crystal 31a'i in which a dichroic dye is added to a smectic liquid crystal is used, and the display method is a transmission type.

Although not shown, a reflective type can also be realized as a modification of FIG. 6.

FIG. 7 schematically shows the behavior of liquid crystal molecules within a liquid crystal display element. In the electric field E=O, the liquid crystal molecules 34 are
Takes a spiral structure.

Further, depending on the direction of the electric field, the liquid crystal molecules 34 are rearranged in the ±θ direction from the arm axis 33 when E>EC. Ec at this time is the electric field required to rearrange the liquid crystal molecules 34t (
critical value).

FIG. 8 shows that in the liquid crystal display element of FIGS. 4 and 5,
This figure shows how to set the polarization axes of the polarizers 27a and 27b.

That is, when E>Ec, the two polarizers 27a, 2
7b (polarization axis 35, 36C7) (polarization axis 36 in the figure) is aligned with the director 37 of the liquid crystal molecules. Furthermore, the polarization axis 35 is perpendicular to the polarization axis 36.

FIG. 9 shows the polarizer 27 in the liquid crystal display element of FIG.
This figure shows how to set the polarization axis in b.

In this case, the director 37 of the dye molecule 38 (which almost coincides with the director of the liquid crystal molecule) is made to coincide with the polarization axis 39 of the polarizer. At this time, the amount of transmitted light is at its minimum.

The electro-optical characteristics of a liquid crystal display element will be explained using the example shown in FIG.

FIG. 10 shows an example of measurement of electro-optical characteristics, and FIG. 11 shows the measurement results. In the transmission and transmission intensity characteristics of the liquid crystal display element shown in FIG. 11 with respect to applied voltage, characteristics I and ■ are observed, but this is due to differences in the formation conditions of the smectic liquid crystal material and the liquid crystal alignment film. In either case, ±I
Transmitted light I in OV.

is almost saturated.

Further, FIG. 12 shows the change in the transmitted light intensity factor 0 when the polarity of the applied voltage VD is suddenly changed.

As can be seen from FIG. 12, the optical response time of smectic liquid crystal is faster than that of nematic liquid crystal, cholesteric-nematic phase transition liquid crystal, etc., and is 1 to several ms or less.

Furthermore, the transmitted light intensity Io of the smectic liquid crystal depends on the peak value of the applied voltage VD. This is different from the dependence of the transmitted light intensity of the liquid crystal on the effective value of the applied voltage.

Further, FIG. 13 shows a memorandum of the liquid crystal display element according to the present invention.
This is an example of measuring Je property.

In FIG. 13(a), one end of a switch 42 is connected to a liquid crystal display element 44, a DC power source 43 is connected to the other end, and a shunt resistor 41 is completely connected to the switch 42. In FIG.

Here, the switch 42 is turned on for a certain period of time, and a voltage is applied to the liquid crystal display element 44. Next, switch 42
turn off.

Figure 13 Φ) shows the changes in the applied voltage and the amount of transmitted light. When a pulse voltage is applied to the liquid crystal element, the amount of transmitted light increases, and even after the switch is opened, the amount of transmitted light does not decrease rapidly.A relaxation phenomenon can be seen in the change in the amount of transmitted light after the switch is opened. For example, when the open resistance of the switch is set to Roff'elO'Ω or more, the time constant τ of this relaxation phenomenon becomes 1 second or more, which can be used as a memory property.

It is believed that this relaxation phenomenon is due to the elasticity and viscosity of the smectic liquid crystal. For example, liquid crystal element Ct,
It is possible that the voltage across the liquid crystal element is held by the charge stored in c, but the time constant of the holding voltage C
The LO-RLC is about 1 to 10 m5, and the holding voltage decreases even with a sufficiently small time constant compared to the relaxation phenomenon targeted here.

Therefore, it is considered that this is a relaxation phenomenon in which the molecular orientation within the liquid crystal element returns to its original state due to the elasticity and viscosity peculiar to liquid crystal.

Next, a first embodiment of the method for driving a liquid crystal display element according to the present invention is shown in FIG.

FIG. 14(a) shows a combination of an FET 45 and a liquid crystal display element 46. ), (C), (in Fig. 14), (C), (
d) shows a time chart of the voltages applied to each part at that time. Note that the FET 45 is a general term for a P-MOS (P-MOS, N-MOS) transistor made of single crystal silicon, a thin film transistor made of polysilicon, amorphous silicon, Te, etc.

``Also, when the potential of the a terminal of the liquid crystal display element is higher than the potential of the b terminal, the display is turned on, and vice versa, the display is turned off.

If, Φ) in FIG. 14, a constant voltage of 18 is applied to the b terminal of the liquid crystal display element. Here, in order to turn on the display, the drain voltage V D k V is synchronized with the gate voltage Vo.
Make it s + V a. Furthermore, to turn off the display, the drain voltage VD is set to V[l V-.

As a result, a voltage of ±va is applied to the liquid crystal display element when selected, and the display is turned on or off. Also,
During the non-selection period, as explained in FIG. 13, the display is kept on or off. At this time, the selection period T
o≦τ0, and the relaxation time is set to be less than or equal to τ0.

FIG. 17(C) shows the drain voltage V within the selection period.

eVs Vb and Vs 10V- or vg +Vb
and Vs V-. At this time, Vst is applied to the b terminal of the liquid crystal display element.

FIG. 14(d) shows that the drain voltage Vn is changed to v within the selection period.
8 and V+s+Va or ①8 and Vs V-. At the time of power, the b terminal of the liquid crystal display element 46 has Vs +V.
b or Vg Vb' is applied.

The driving method in FIGS. 14(C) and 14(d) is to turn on the display, or
The polarity of the voltage on the liquid crystal display element 46 is reversed before applying the voltage to turn off the display. As a result, the liquid crystal display element always has stable brightness.

FIG. 15 shows a fifth embodiment of a method for driving a liquid crystal display element.

At each intersection of the drain line 50 and the gate line 51, an FET is connected.
52 and a liquid crystal display element 53 (hereinafter referred to as a liquid crystal pixel).

Furthermore, an output signal from the vertical shift register 49 (hereinafter referred to as a vertical scanning signal) is applied to the gate line 51 . Furthermore, an output signal from the horizontal scanning circuit 48 (hereinafter referred to as a horizontal scanning signal) is applied to the drain signal line 50.

Further, the vertical and horizontal scanning circuits operate with signals from the control circuit 47.

FIG. 16 shows a cross-sectional view of an embodiment for realizing the circuit shown in FIG. 17.

In FIG. 16, a transparent substrate 56 on which transparent electrodes 57 and a liquid crystal alignment film 58affi are formed, FETs 52, etc. are formed and nine single crystal silicon substrates 150t are placed facing each other, and a guest-host liquid crystal 59 is sealed between the side substrates.

The FET 52 is made up of diffusion layers 60a, 60b, 7 (lowered oxide film 61 and gate electrode 62).Furthermore, the liquid crystal pixel electrode 64 and the single crystal silicon substrate 150 are insulated by an insulating film 63.・Host LCD 59 and F
The ET 52 and the liquid crystal pixel electrode 64 are insulated by a liquid crystal alignment film 58b.

FIG. 17 shows another embodiment for realizing the circuit shown in FIG. 15.

The figure shows a transparent substrate 57 formed with a transparent electrode 58 and a liquid crystal alignment film 59a't, and a transparent substrate 66 made of glass, sapphire, etc., facing each other, and a smectic liquid crystal 60 or a guest prepared by adding a dichroic dye to the liquid crystal between the side substrates.・Encloses a host liquid crystal.

Further, on the transparent substrate 66, an FET 52tl- is formed.

The FET 52 includes a conductor layer 62 such as polysilicon or amorphous silicon, insulators 61 and 64, and a drain electrode 6.
2. Consists of a gate electrode 63, a source electrode 65, and a gate oxide film 69.

Furthermore, the FET 52, the transparent pixel electrode 68, and the smectic liquid crystal 60 are insulated by a liquid crystal alignment film 59b.

Note that the polarizer shown in FIGS. 16 and 17 is 55°, 56°, etc.
57 is installed as shown in FIGS. 8 and 9. Furthermore, in Figure 17, when using a guest-host liquid crystal,
One polarizer is enough.

Next, the operation of the circuit shown in FIG. 15 will be explained by taking as an example the case where the liquid crystal pixel at the upper left end is turned on or off. Note that when the potential of the opposing terminal 54 is lower than the other end, the display is on, and when it is higher, the display is off.

FIG. 18 shows a first example of operation.

When the vertical scanning signals L1 to L are H, each FET is conductive,
It becomes non-conductive at L. Therefore, in order to turn on the display of the liquid crystal pixel 53, when the vertical scanning signal Ll is H, the horizontal scanning signal C
1t V c + V a, and in other periods U, V
c V-.

Furthermore, the horizontal scanning signal 02~cm is set to Vc V-,
The drive voltage V LC of the opposing terminal 54 is assumed to be Vc.

Also, to turn off the display, set all C1 to cm to Vc
Let it be V-.

FIG. 19 shows a second embodiment.

When the display is turned on, when the vertical scanning signal L1 is H, the horizontal scanning signal is set to Vc V- and Vc+V-, and in other periods, it is set to Vc +V and Vc V-. Furthermore, other horizontal scanning signals 02 to cm are Vc +va and ■
. -va. At this time, the driving voltage V of the opposing terminal 54
Let Lc be Vc.

Also, to turn off the display, use C+ -C-t" all Vc
+V- and ■. -va.

FIG. 20 shows a third embodiment.

When turning on the display, when the vertical scanning signal L+ is H,
Let the horizontal scanning signal C1 be Vc V- and Vc+V. Furthermore, when the display is off, it is set to Vc-V-.

Further, the other horizontal scanning signals 02 to C are always Vc-V.
−. Furthermore, the driving voltage V L C of the opposing terminal 54
are Va+Vi and Vc.゛In the first to third embodiments, it is necessary to ensure that the scanning period To≦τ0, but the off-resistance Rouf, I of the FET 52
When the value is O' (Ω) or more, the attenuation time constant is equal to or greater than τowls, so a video image can be displayed even when a thin film semiconductor transistor such as polysilicon or amorphous silicon is used.

In this way, in an active matrix type liquid crystal display, a sufficient holding operation can be realized without adding a storage capacitor in parallel with the liquid crystal element.

〔Effect of the invention〕

According to the present invention, an active matrix type switch matrix board can be formed without adding a storage capacitor, so that the active matrix board of this board can be
The area can be practically reduced, and the manufacturing process of this board can be shortened.

Furthermore, since the display state is maintained by a relaxation phenomenon caused by the elasticity and viscosity of the liquid crystal, a liquid crystal material with relatively low resistance can be used, and the quality of the liquid crystal material can be easily controlled.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a display device of the present invention, and FIG. FIG. 3 is a diagram showing a specific example of a display device, and FIGS. 4 and 5. Fig. 6 is a specific example of a liquid crystal display element, Fig. 7 is a schematic diagram of liquid crystal molecules used in the present invention, Figs. 8 and 9 are polarizer installation methods, and Figs. 10 to 13 are in accordance with the present invention. 14 is a diagram showing the first driving method of the liquid crystal display element, FIG. 15 is a diagram showing the second driving method of the liquid crystal display element, and FIGS. 16 and 17 are diagrams showing the liquid crystal display element. Examples of cross-sectional views of elements, FIGS. 18, 19, and 20 are time charts showing the operation of the circuit shown in FIG. 15. FIG. 21 is a configuration of a conventional liquid crystal active matrix drive circuit, FIG. 22 is a sectional view of a conventional liquid crystal display element, and FIG. 23 is a diagram of voltage waveforms at various parts in FIG. 21. 20a, 20b...Drive circuit, 100...Liquid crystal display element 1 Figure III 204 Condolence? Quick vow flash (α) (su) New year's drawing fan q mouth En Ec E=OE>E. 8 Kasumi (α) (J) (E>Ec)
and E=Ec) name 9 figure 3'1 foil 10 mouth r, l figure 11 -15-to -505ro, 15 impression 0 city', /h '71) (V) spear 1? Kasumi (σ) YiQ 5
10th cycle 130 (α) ott (b) SWITCH IMPO IL4-KASUMI (α) (DE9 F+511 160 Shoenguchi 18th Suspension 19 KasumiqLCYcm 20th figure, L z S V, Knee V, L
. Moth Figure 21/q Leopard 22 [D a %.

Claims (1)

[Claims] 1. Two substrates each having an electrode formed thereon are placed facing each other, and a voltage is selectively applied to a liquid crystal display element which exhibits an optical memory phenomenon between the substrates and which sandwiches a liquid crystal, and to the liquid crystal display element. 1. A liquid crystal matrix display device comprising means for applying . 2. A liquid crystal matrix display device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting a chiral smectic C phase or a chiral smectic H phase. 3. two substrates arranged opposite to each other, at least one of which is transparent, and transparent electrodes provided on each of the opposing surfaces of the substrates;
A transparent liquid crystal alignment film having an insulating property on the transparent electrode and arranging adjacent liquid crystal molecules in a preferential direction parallel or almost parallel to the substrate surface, and a ferroelectric between the liquid crystal alignment film. a liquid crystal display element sealed with a liquid crystal, and displays an image by applying a predetermined voltage to the transparent electrode, each of which has a switch for selectively applying the predetermined voltage to the liquid crystal display element at a constant period. A liquid crystal matrix display device, characterized in that the liquid crystal matrix display device is connected to the liquid crystal display element. 4. The liquid crystal matrix display device according to claim 3, wherein the period of applying the predetermined voltage is equal to or less than an optical decay time constant. 5. The liquid crystal matrix display device according to claim 3, wherein the voltage applied to the liquid crystal display element has a uniform polarity within the same selection time. 6. The liquid crystal matrix display device according to claim 3, wherein the voltage applied to the liquid crystal display element has both positive and negative polarities at the same selection time. 7. A first transparent substrate and a second transparent substrate are opposed to each other, a first transparent electrode is formed on the opposing surface of the first transparent substrate, and an insulating and adjacent electrode is formed on the first transparent electrode. A transparent liquid crystal alignment film is formed in which liquid crystal molecules are arranged in a preferential direction parallel or substantially parallel to the surface of the first transparent substrate, and a second transparent substrate is formed on the opposite surface of the second transparent substrate. An electrode and a switch for applying a voltage to the second transparent electrode are provided, and the second transparent electrode and the switch have an insulating property, and
A liquid crystal matrix display comprising a transparent liquid crystal alignment film that aligns adjacent liquid crystal molecules in a preferential direction parallel or substantially parallel to the second transparent substrate surface, and ferroelectric liquid crystal sealed between the liquid crystal alignment films. 1. A liquid crystal matrix display device, further comprising means for selectively applying a predetermined voltage between the first and second transparent electrodes at regular intervals. 8. A liquid crystal matrix display device according to claim 7, characterized in that the period of applying the predetermined voltage is equal to or less than the optical decay time. 9. The liquid crystal matrix according to claim 7, wherein the voltage applied between the first and second transparent electrodes has the same polarity or has both positive and negative polarities at the same selection time. Display device.