JP3518873B2 - Driving method of phase change type liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method for causing a phase change type liquid crystal display device to perform a predetermined display operation. More specifically, the present invention provides a nematic-cholesteric phase transition type which has a memory effect that enables a bright and stable large-screen display to be obtained, enables writing and erasing of display contents, and is easy to miniaturize the device. In the liquid crystal display device using the liquid crystal display element, one measure for enabling not only monochrome display but also gradation display is described.

[0002]

2. Description of the Related Art Generally, TN (Twisted Nema)
tic) liquid crystal and STN (Super Twisted N)
A liquid crystal display (display) device using a liquid crystal of a normal type typified by an ematic liquid crystal has features that it is thin, lightweight, passive, and requires little power consumption. Because they almost satisfy the performance required for portable display devices, they have been attracting attention in various fields. In particular, recently, the performance and cost of liquid crystal display devices have been dramatically improved, and they have been widely used for OA equipment, wristwatches, and the like.

On the other hand, as a large screen display device, an overhead projector using a liquid crystal display element (hereinafter, referred to as an overhead projector).
Projection type liquid crystal display devices such as OHP) have been receiving attention, and some of them have begun to be put to practical use. In particular,
An N-C phase transition type liquid crystal display device having a liquid crystal display element using a nematic-cholesteric phase transition type (hereinafter abbreviated as N-C phase transition type) liquid crystal utilizes a memory property to perform bistable driving. It can be performed. Therefore, the above N
-C type phase transition type liquid crystal display device has a large capacity and a high definition,
In addition, it has the feature that a bright flicker-free screen can be obtained.It can be used as a projection-type display device in presentation terminals, conferences, education, etc., where many people are simultaneously viewing the same screen and discussing. This is expected (see, for example, JP-A-61-60782 and JP-A-61-198270). Here, N-
The operation of the N-C phase transition type liquid crystal display element, which is a main part of the C phase transition type liquid crystal display device, will be described with reference to the drawings.

FIG. 14 is a diagram showing light transmittance characteristics of a conventional NC phase transition type liquid crystal display device. Here, the vertical axis represents the light transmittance, and the horizontal axis represents the driving voltage. As can be seen from FIG. 14, the NC phase transition type liquid crystal display element is characterized by drawing a hysteresis curve, unlike the case of the TN liquid crystal and the STN liquid crystal. For example, when the driving voltage is low, light is hardly transmitted (F state), which is called focal-conic, and when the voltage is increased, light is similarly hardly transmitted F ′. Then, when the voltage is further increased, the light transmittance rapidly rises above a certain threshold value, and eventually reaches a state called transparent homeotropic (H state) having a constant transmittance (also referred to as an H state). . Conversely, when the voltage is lowered from the H state, as shown in the figure, a transparent state of H 'having a different path from that at the time of voltage rise is passed, and the state returns to the F state in which light is hardly transmitted.

Namely, since draw well-known hysteresis curve, eg, H the voltage V _d as a holding voltage '
By performing bright and dark binary driving with (bright) and F '(dark), stable storage type liquid crystal display, that is, black and white display is possible. In other words, large-capacity black-and-white display using a memory property by bistable (bistable) is possible.

FIG. 15 is a cross-sectional view for explaining the operation of the conventional NC phase transition type liquid crystal display element, and FIG.
The state (C: cholesteric phase) and (b) in the figure schematically show the H state (N: nematic phase).

In FIG. 1, reference numerals 10-1 and 10-2 denote a pair of transparent substrates (a first transparent substrate and a second transparent substrate), for example, a glass substrate, and 11-1 denotes a plurality of rows commonly used as scanning electrodes. First electrode, for example, ITO (In ₂ O ₃ —SnO)
₂ ) Transparent striped electrode made of a film or the like, 11-2
Is a plurality of rows of second electrodes commonly used as signal electrodes, for example, transparent striped electrodes also made of an ITO film or the like, and 12-1 and 12-2 are a pair of alignment films (a first alignment film and a second alignment film). An alignment film), 2 is an N-C phase transition type liquid crystal injected and sealed in a space between the two substrates, and 1 is a liquid crystal display element for causing such a liquid crystal to perform a predetermined operation.

That is, in the F state where the driving voltage is low, the molecules of the liquid crystal 2 have a helical structure, and when the helical pitch and the wavelength of visible light are almost the same (for example, 0.8 μm), the light is good. As a result, the light is not sufficiently transmitted through the liquid crystal 2 to be in a dark state ((a) in the figure).

On the other hand, when the driving voltage is increased, the helical pitch of the liquid crystal molecules is gradually increased. When the driving voltage is higher than a certain threshold voltage, the helical diverges, that is, the helical pitch becomes infinite, and as shown in FIG. The molecules stand perpendicular to the substrate surface and undergo a phase transition to the H state, and the light passes through the liquid crystal 2 without being scattered to be in a bright state ((b) in the figure). As a result, as shown in FIG. 14, bi-stable driving of light and dark binary values is performed.

By combining such a liquid crystal display device with an optical system and projecting an image formed on the liquid crystal display device on a screen in an enlarged manner, a projection type liquid crystal display device can be constructed.

Here, the means for fabricating the above type of liquid crystal display element will be described more specifically with reference to FIG. 15. First, an ITO is formed on a pair of transparent substrates 10-1 and 10-2.
A transparent striped electrode made of a transparent conductive film such as an (In ₂ O ₃ —SnO ₂ ) film is formed. One of the first
The electrode 10-1 is called a scanning electrode, and the other second electrode 10-2 is called a signal electrode. Furthermore, these electrodes 10-1, 1
0-2, an alignment film 12 for aligning the liquid crystal in a specific direction.
After forming -1 and 12-2, respectively, a spacer of about 10 μm is interposed between the pair of transparent substrates, and an N-C phase transition type liquid crystal 2 is injected into a space defined by the spacer and sealed. Then, N having the above-mentioned hysteresis characteristics can be obtained.
The liquid crystal display element 1 of the -C phase transition type is manufactured. A projection type liquid crystal display device such as an OHP is configured by projecting an image formed on the liquid crystal display element 1 on a screen in an enlarged manner.

In this case, unlike the TN liquid crystal display device and the STN liquid crystal display device, a polarizing plate is not required, so that the screen becomes bright, a good contrast is obtained, and the characteristics are deteriorated by a temperature rise due to light absorption of the polarizing plate. Will not be. Furthermore, in this case, light that does not enter the condenser lens, such as OHP, does not reach the screen because light scattering is used instead of the progress of the light phase.
It also has the advantage that the contrast is further improved.

[0013]

However, the above conventional N
In the display device having the liquid crystal display element of the -C phase transition type, as described above, the bi-stable driving of the light and dark binary values is performed by using the hysteresis characteristic. For this reason, unlike the TN liquid crystal display device and the STN liquid crystal display device, the relationship between the applied voltage and the light transmission characteristic does not correspond one-to-one, so that the intermediate state between the F state and the H state, that is, the intermediate brightness. Is difficult to display with good reproducibility. Therefore, there is a problem that it is difficult to perform a higher-performance gray scale display required by users in recent years, and there is a need for development of a phase change liquid crystal display device capable of performing this gray scale display. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and in a nematic-cholesteric phase transition type liquid crystal display device, not only black-and-white display by light-dark binary bistable driving but also intermediate brightness is displayed. It is an object of the present invention to provide a function of performing a phase change type liquid crystal display device that enables grayscale display.

[0015]

According to the present invention, the first
As a specific method, a first transparent substrate 10-1 provided with a plurality of rows of first electrodes 11-1 and a plurality of rows of second electrodes 11-2 orthogonal to the first electrodes 11-1 are provided. In a space formed by facing the second transparent substrate 10-2, a nematic phase having a spiral pitch of infinite length or a cholesteric phase having a constant spiral pitch is provided. Liquid crystal display element 1 in which liquid crystal 2 capable of phase transition is injected and sealed, and the first and second electrodes 11-1 and 11-2.
In the phase transition type liquid crystal display device having a driving means for the nematic phase or cholesteric phase by selectively applying a voltage to a predetermined portion of the liquid crystal 2 between the first conductive
Between each of the poles 11-1 and each of the second electrodes 11-2
Pixels in a liquid crystal display element formed in
Holding voltage to keep the phase or cholesteric phase stable
The phase change to a low voltage or a voltage higher than V _d is
Voltage that does not occur selectively for a predetermined time
Applied to said varying the voltage of the drive means by setting the holding voltage after the dark state of the intermediate state to display a brightness corresponding phase transition type which is characterized in that a gray-scale display A method for driving a liquid crystal display device is provided.

[0016]

More preferably, the operation of changing the voltage of the driving means and returning the voltage to the holding voltage _Vd is repeated a plurality of times.

As a second concrete method, a plurality of rows of the first
A first transparent substrate 10-1 on which the pole 11-1 is disposed,
A plurality of rows of second electrodes 11-2 orthogonal to the electrodes 11-1 are arranged.
The second transparent substrate 10-2 provided is formed so as to face each other.
Nematic with spiral pitch of infinite length in space
Cholester having a constant length of phase or spiral pitch
Liquid crystal 2 capable of phase transition with the liquid phase was injected and sealed.
A liquid crystal display element 1 of a phase transition type, and the first and second electrodes
By selectively applying a voltage between 11-1 and 11-2, the liquid crystal 2
To a nematic or cholesteric phase
Transition type liquid crystal display device having driving means for driving
Here, each of the first electrode 11-1 and the second electrode 1
The pixels in the liquid crystal display element formed between each of 1-2, the nematic phase or cholesteric phase by applying a holding voltage V _d to be held stably, further lower than the holding voltage V _d By selectively applying a voltage or a high voltage that does not cause the phase transition to a part of the pixel, it corresponds to an intermediate state between the light and dark states.
The characteristic feature is that gradation is displayed by displaying
Transition type liquid crystal display device driving method Ru are provided.

More preferably, in the above two specific methods, one of the first electrode 11-1 and the second electrode 11-2 is used to initialize all the pixels in the liquid crystal display element. It is configured to be a scan electrode that supplies a voltage. Then, at least one of the first and second electrodes is configured to be a signal electrode for selectively supplying a voltage for performing a gray scale display to the pixel.

Further, in the second specific method,
Preferably, a plurality of rows of auxiliary electrodes are respectively arranged between the signal electrodes and the signal electrodes adjacent to each of the signal electrodes, and a voltage for performing a gradation display is selectively applied to these auxiliary electrodes. Is being applied.

Further, it is preferable that both of the above two specific examples are applied to a projection type such as OHP.

[0022]

In the driving method of the present invention, the length of the helical pitch of the NC phase transition type liquid crystal is appropriately controlled by the driving voltage supplied from driving means such as a driver, and the light in the liquid crystal display element is controlled. The degree of scattering of the light is finely changed.

More specifically, even if the length of the helical pitch is changed for a short time so that the liquid crystal changes from one of the stable states to an intermediate state, if the liquid crystal is returned to the original state promptly, the phase transition will occur. Paying attention to the point that no hue occurs, the pitch of the spiral is temporally controlled to achieve a desired brightness corresponding to an intermediate state.

In still another specific method, if the electric field in one pixel is changed from a stable state, the length of the helical pitch of the liquid crystal partially changes according to the electric field change. Is used to appropriately adjust the degree of the partial change in the length of the spiral pitch so as to display the brightness corresponding to the intermediate state. That is, here, gradation display is realized by locally controlling the length of the helical pitch and changing the average length of the helical pitch in one pixel. In this case, even by changing the electric field in a portion of the pixel using the auxiliary electrode and the like, a liquid crystal of a large portion in the pixel holding voltage V _d is applied H state (nematic phase) or F state (cholesteric Since the phase is in the stable state, the intermediate brightness in the pixel does not change.

Incidentally, Japanese Patent Application Laid-Open No. 58-5791 discloses that
Although an example in which a driving voltage other than the holding voltage is applied to one pixel is disclosed, in this case, the holding voltage and another driving voltage are not simultaneously applied to one pixel. Therefore, in the above disclosed example, gray scale display cannot be performed by simultaneously applying the two types of voltages to the liquid crystal in one pixel using the signal electrode and the auxiliary electrode as in the present invention.

Thus, according to the present invention, in the NC phase transition type liquid crystal display device, the length of the helical pitch of the phase transition type liquid crystal in the selected pixel in the liquid crystal display element is temporally or appropriately controlled by an appropriate driving voltage. Since the liquid crystal can be locally controlled so that the light transmittance of the liquid crystal has an intermediate value between the nematic phase and the cholesteric phase, the desired brightness corresponding to the intermediate state is displayed and the level is displayed. Tone display can be realized.

[0027]

1 to 3 are views for explaining a first embodiment of the present invention. More specifically, FIG.
FIG. 2 is a cross-sectional view for explaining a gray scale display operation according to the method of the embodiment, FIG. 2 is a time chart showing a drive voltage waveform for executing the gray scale display operation of FIG. 1, and FIG. It is a hysteresis curve for explaining by a rate.
Here, in order to simplify the description, the liquid crystal 2, the first and second electrodes 11-1, 11-2, and the first and second transparent substrates 10 of the liquid crystal display element 1 in the phase change type liquid crystal display device are described. -1 and 10-2 only are displayed, and
One pixel portion is shown in an enlarged manner. The same components as those described above are denoted by the same reference numerals.

In FIG. 1, the upper plurality of first electrodes 11-1 are preferably used as scanning electrodes for supplying a voltage for initializing all the pixels in the liquid crystal display element 1. . On the other hand, it is preferable that the second electrodes 11-2 in the lower plurality of rows be used as signal electrodes for selectively supplying a voltage for performing grayscale display to the pixels.

Here, before explaining the method of the first embodiment, a procedure for manufacturing a liquid crystal display element applied to the present invention will be described. As shown in FIG. 1, for example, a stripe-shaped scanning electrode (first electrode 11-1) made of an ITO film is formed on a first transparent substrate 10-1 made of a glass substrate, and a vertical alignment property is formed thereon. Is coated with a first alignment film 12-1 made of a polymer having the following formula. On the other, second transparent substrate 10-2 also made of a glass substrate, a signal electrode (second
The electrode 11-2) is formed, and a second alignment film 12-2 made of the same material as the first alignment film 12-1 is coated thereon.

Further, the first and second alignment films 1 of both substrates
2-1 and 12-2 face each other so that the upper scanning electrode and the lower signal electrode are orthogonal to each other so as to form a matrix arrangement,
Here, a spacer (not shown) is interposed therebetween and a space of about 10 μm is opened, and the layers are stacked and sealed while leaving a liquid crystal injection port.

Thereafter, a liquid crystal 2, for example, a mixed nematic liquid crystal of 40% by weight of cyanobiphenyl, 10% by weight of cyanoterphenyl, 30% by weight of cyclohexane benzoate, and 10% by weight of tolan derivative liquid crystal is supplied from the liquid crystal injection port as a cholesteric liquid crystal. N mixed with 30% by weight of cyclohexane benzoate containing a chiral part
After injecting the -C phase transition type liquid crystal, the liquid crystal injection port is sealed to constitute the liquid crystal display element 1.

In the first embodiment, when a desired image is formed on such a liquid crystal display element 1, as shown in FIG. 1A (see also FIGS. 2 and 3A). , First, the entire liquid crystal into a nematic phase by a high driving voltage of about 2 times the holding voltage V _d to the liquid crystal display device the entire region is applied. That is, a homeotropic state (H state) in which light is transmitted almost completely (bright state). Since the phase transition type liquid crystal generally has a positive dielectric anisotropy, the major axis of the molecule is directed to the electric field direction. In this case, in order to prevent the liquid crystal from being electrolyzed by continuously applying the DC voltage for a long time and the characteristics of the liquid crystal from deteriorating, 4 msec
It is preferable to apply an alternating voltage whose polarity changes with a period of about. The driving voltage at this time has a peak value (zero)
-To-peak value).

Next, once the zero prior to V _d a driving voltage from 2V _d, as shown in the FIG. 1 (B) (see (B) also FIGS. 2 and 3), the liquid crystal molecules husk Become a cholesteric phase that turns. This helix is arranged continuously in a certain domain (indicated by-in the liquid crystal 2 in FIG. 1), and the refractive index is almost constant, but in the next domain, the refractive index is slightly twisted and the refractive index is different. As described above, each domain is slightly twisted to form a spiral staircase, and returns to the original state at a constant pitch (for example, 0.8 μm). Such a state of the liquid crystal molecules is called a focal conic state (F state), and the incident light on the liquid crystal 2 is strongly scattered at the boundary of the domain, and the light transmittance becomes close to zero (dark). Status).

Furthermore, by setting the driving voltage slightly higher than the holding voltage V _d, as shown in the FIG. 1 (C) (see (C) also in FIG. 2 and FIG. 3), the pitch of the spiral spreading domain Becomes longer, the degree of scattering of liquid crystal molecules becomes weaker, and the liquid crystal molecules become slightly brighter than in a dark state. In this case, the brightness of each pixel can be set to an arbitrary value corresponding to an intermediate state between the dark state and the bright state according to the set voltage level. When a voltage for displaying such intermediate brightness is continuously applied for a long time, (C) on the hysteresis curve in FIG. 3 gradually moves in the positive direction of the drive voltage due to the cumulative response effect, and finally becomes bright. It will be in a state. To avoid this, a short time (for example, 10
msec) only (to return once stable point V _d after applying a voltage corresponding to C) ((D in FIGS. 1, 2 and 3) in FIG. 3 reference).

[0035] If you want performs gradation display Following Thereafter, a short time only by changing again drive voltage after holding the driving voltage to the holding voltage V _d, further, the operation constant cycle (e.g., 20 msec ). If the operation is repeated at such a cycle (several tens of msec), human eyes do not feel flicker. Here, if the magnitude of the voltage to be temporarily applied is appropriately changed, the intermediate brightness can be continuously changed, so that fine gradation display can be performed. In the above, the method for increasing the brightness of the pixel in the dark state to realize the gray scale display has been exemplified. On the contrary, the brightness may be reduced in the bright state to perform the gray scale display. It is possible.

FIGS. 4 to 7 are views for explaining a second embodiment of the present invention. More specifically, FIG. 4 is a cross-sectional view for explaining a gray scale display operation by the method of the second embodiment, FIG. 5 is a cross-sectional view showing an intermediate state of the liquid crystal in FIG. 4, and FIG. 4 is a hysteresis curve for explaining the state of light transmission by light transmittance, and FIG. 7 is a diagram showing the relationship between signal voltage and light transmittance in FIG.

In FIG. 4, (A), (B) and (C) show the orientation of the liquid crystal in the dark state, intermediate state and bright state, respectively. Also in this case, one pixel portion is shown in an enlarged manner. Here, an auxiliary electrode 13 is provided between a signal electrode and a signal electrode adjacent to each of these signal electrodes, and these auxiliary electrodes 13 are provided.
, A voltage for performing a gradation display is selectively applied.
The configuration of the liquid crystal display device provided with the auxiliary electrode 13 will be described later in detail with reference to FIGS. In the figure, reference numeral 20 denotes a scan driver as a driving means, which is connected between an upper scan electrode (first electrode 11-1), a lower signal electrode (second electrode 11-2) and an auxiliary electrode 13. Have been. A data driver 30 is also connected as a driving means and is connected between the auxiliary electrode 13 and the ground. Further, in this case, all the signal electrodes are connected to the ground.

In FIG. 4A, a focal conic F is applied to the scanning electrode as the driving voltage (V ₂₀ ).
Since (F ') the holding voltage V _d to maintain the state is applied by the scan driver 20, the light is scattered by molecules of the liquid crystal 2 a dark state (corresponding to (A) in FIG. 6).

On the other hand, in FIG. 4B, the driving voltage (V ₂₀ ) is applied to the scanning electrode as a focal conic F
(F ') while applying a holding voltage V _d to maintain the state,
The signal voltage V between the signal electrode and the auxiliary electrode adjacent to each other
_s is selectively applied. The signal voltage V _s is based on the grayscale data signal input from the outside, a predetermined voltage so that a predetermined brightness is obtained (corresponding to (B) of FIG. 6). Thus, when the signal voltage between the signal adjacent electrodes and interpolation electrode V _s is applied, the vicinity of the electrodes, i.e., an electric field is applied to the molecules of the liquid crystal 2 pixels around the length of the partial Nira旋pitch Changes. Equivalently, it means that the holding voltage _Vd is applied to the entire pixel, and at the same time, the additional voltage is applied between the upper and lower electrodes provided in a part of the pixel. In this case, it is not necessary to precisely control the magnitude of the change in the helical pitch, and it is sufficient to control the change in the depth of the liquid crystal layer in which the helical pitch is extended. Furthermore, even continue over a long period of time the signal voltage V _s to the auxiliary electrode, the majority in the pixel because helical pitch is stable in a state of focal conic, a change in intermediate brightness state in the pixel Never. That is, here, the length of the helical pitch is locally controlled to change the average length of the helical pitch in one pixel to perform gradation display.

FIG. 5 is an enlarged view of the state shown in FIG. 5, between the signal electrode and the auxiliary electrode adjacent the phase, the signal voltage V _s having a polarity opposite to the holding voltage V _d
Is applied, a potential difference is generated between the signal electrode and the auxiliary electrode 13, and the major axes of the liquid crystal molecules are arranged along the direction of the electric field generated by the potential difference. In the portion where the electric field is generated in the lateral direction as described above, the molecules of the liquid crystal are continuously arranged, so that light is not strongly scattered as in other portions. As a result, the light transmittance in one pixel is better than that in the dark state, and an intermediate brightness state is realized.

[0041] Since FIG. 4 (C) is the holding voltage V _d to maintain the homeotropic H (H ') state to the scan electrode is applied by the scan driver 20, the light is scattered by the molecules of the liquid crystal 2 It becomes a bright state without any problem (corresponding to FIG. 6C).

[0042] As a result, by changing the signal voltage V _s as shown in the gradation display operation characteristics of FIG. 7, approximately linearly the light transmittance of the liquid crystal display device 1, and is possible to change stable By using this, it is possible to realize a phase change type liquid crystal display device capable of gradation display.

FIG. 8 is a time chart showing driving voltage waveforms for executing a gradation display operation according to the method of the second embodiment of the present invention. First, as shown in FIG. 8A, the scan driver 20 applies the holding voltage V _d to the scan electrode.
Initialization for writing is performed by applying a drive voltage (V ₂₀ ) that is about twice as large as the above.

Next, when writing in the dark state, the holding voltage _Vd is applied to the scanning electrodes at the timing shown in FIG. 8B, while in writing in the bright state, the same voltage is applied. The holding voltage _Vd is applied to the scanning electrodes at the timing shown in FIG. To be more specific, by setting the holding voltage V _d from immediately after initialization to reverse the polarity of the drive voltage by the drive voltage 2V _d (in the zero driving voltage once), the liquid crystal is the focal The dark state is written through the conic F state (FIG. 8B). On the other hand, by setting the holding voltage V _d without inverting the polarity of the driving voltage immediately after performing initialization at the driving voltage 2V _d, liquid crystal also becomes homeotropic H 'state from the homeotropic H state Then, the same writing in the bright state as in the initialization is performed (FIG. 8C).

When each write state is maintained, as shown in FIG. _8D , the drive voltage is held at the hold voltage Vd for a required time as it is. In the meantime, when writing a halftone (intermediate brightness), as shown in FIG. 8E, the data driver 30 applies a required voltage between adjacent signal electrodes and auxiliary electrodes constituting a required pixel. applying brightness signals voltage V _s to be obtained by a required time. 1
One of the liquid crystal state in the pixel, since it is governed mainly by the signal electrodes, also continuously applied for a long time signal voltage V _s to the auxiliary electrode, unlike the first embodiment described above, the cumulative response effect The liquid crystal does not undergo phase transition. However,
In this case, the extra electrode for applying a signal voltage V _s is required.

If the above-described driving process is controlled and performed based on an external signal, it is possible to perform gradation display of an arbitrary character, graphic or image.

In each of the first and second embodiments, the area gradation display for displaying the intermediate brightness in only one of the X and Y orthogonal directions has been described as an example. If a scanning electrode is also used as a signal electrode, it is possible to perform dot gradation display for each pixel.

FIGS. 9 and 10 are diagrams showing in detail an example of an electrode configuration for executing a gradation display operation according to the second embodiment of the present invention. FIG. 9 is a plan view thereof, and FIG. FIG.

For example, on a first transparent substrate 10-1 made of a glass substrate, scanning electrodes are formed as a plurality of stripe-shaped first electrodes 11-1 made of an ITO film, and a vertical orientation is formed thereon. First alignment film 12 made of a polymer having
Coating 1 The scan driver 20 is connected to the scan electrodes.

On the other, the second transparent substrate 10-2, also made of a glass substrate, is formed of a comb-shaped electrode having a plurality of electrode fingers crossed from both sides and connected to the data driver 30, respectively. Signal electrode (the second row of
An electrode) and an auxiliary electrode 13 are formed, and a second alignment film 12-2 made of the same material as the first alignment film 12-1 is coated thereon.

Further, the first and second alignment films 1 of both substrates
2-1 and 12-2 are opposed to each other so that the upper scanning electrode and the lower signal electrode and auxiliary electrode 13 are orthogonally arranged in a matrix arrangement, and a space of about 10 μm is sandwiched by a spacer (not shown). Open and laminate and seal leaving the liquid crystal injection port.

Thereafter, an N-C phase transition type liquid crystal was injected from the liquid crystal injection port, and then the liquid crystal injection port was sealed to complete the liquid crystal display element 1.

Here, the signal electrode is usually 1 / mm.
It is arranged in one (pitch → about 10 μm). Therefore, it is technically easy to insert the comb electrodes between the signal electrodes. In the second embodiment, when the pixel density of the phase change type liquid crystal display element is high (about 9 million pixels per panel), the distance between the upper and lower electrodes (the thickness of the liquid crystal layer) and the distance between the adjacent electrodes (on the same substrate). The scattering state of the liquid crystal is changed by controlling the electric field strength between adjacent electrodes by utilizing the fact that the distance between
Fine gradation display is performed.

FIG. 11 is a circuit diagram for realizing the method according to the second embodiment of the present invention.

In FIG. 11, reference numeral 40 denotes a host computer, which controls a series of operations for executing the gradation display of the liquid crystal display element 1. Reference numeral 50 denotes a data storage device, which includes a CD, an optical disk, and the like for storing required image data for the gradation display. Reference numeral 60 denotes an interface unit such as an RS-232C, which sends the image data to an image signal processor 70 for converting image data from the data storage device 50 into an image signal at high speed. 80 is a drive controller,
The image signal output from the data driver 70 is sent to two sets of scan drivers 20 and two sets of data drivers 30.

Here, a procedure for processing image data for gradation display to display a desired image having an intermediate brightness on the phase change type liquid crystal display element 1 will be briefly described.

The image data stored in the data storage device (CD, optical disk, etc.) 50 is sent to an image signal processor (comprising MPU, ROM, RAM) 70 under the control of the host computer 40 via the interface unit 60. Can be The data converted into the image signal is supplied to a drive controller (Drive Controller).
80 distributes the electrodes to the X and Y electrodes in a time-division manner. According to the drive control signal, a signal necessary for driving the liquid crystal is time-divisionally output from a drive circuit directly connected to the liquid crystal display element 1, and the liquid crystal is line-sequentially scanned. Once the liquid crystal is scanned line-sequentially, the image is maintained by the memory effect of the liquid crystal itself. In this case, by appropriately changing the image data by the host computer 40, a gradation display having an intermediate brightness is quickly performed on the image on the liquid crystal display element 1.

FIG. 12 is a perspective view showing an example in which the present invention is applied to a projection type liquid crystal display device. Here, an OHP type display device is representatively shown as a projection type display device.

In the figure, reference numeral 1 denotes a phase transition type liquid crystal display element, 3 denotes an optical system for enlarging and projecting an image displayed on the liquid crystal display element 1, for example, an overhead projector, 4 denotes a screen, and 5 denotes a drive control system. And the scan driver 20
And a control system including a data driver 30 for processing signals from a personal computer or a TV.

In the configuration shown in FIG.
Light that does not enter the condenser lens does not reach the screen 4.
For this reason, if any light is scattered to the surroundings at the liquid crystal display element 1 part, the scattered light will no longer reach the screen 4, and the screen contrast will be better than that of a display device other than the projection type. Therefore, it is practically preferable to use a phase change type liquid crystal display device utilizing scattering of light due to a helical pitch as a projection type.

FIG. 13 is a diagram showing the relationship between the signal voltage and the brightness of the projected image on the screen in the application example of FIG. Here, the brightness of the projected image on the vertical axis, and displays the actual data taking the magnitude of the signal voltage V _s on the horizontal axis. In the figure, is the transparent H state (homeotropic state)
Shows the data in the case of (1), and shows the data in the case of the F state (focal conic state) in which light is scattered.

In the H state, that is, when a sufficiently high driving voltage is applied between the scanning electrode and the signal electrode, when a signal voltage is applied between the adjacent signal electrode and the auxiliary electrode, a gradation with a high transmittance as a background is obtained. It can be seen that the display is performed.

On the other hand, in the F state, that is, in a state in which a voltage causing a weak scattering mode is applied between the scanning electrode and the signal electrode, a low transmittance is obtained when a voltage is applied between the adjacent signal electrode and auxiliary electrode. The gradation display as the background is performed.

That is, by controlling the signal voltage V _s , a projection type gradation display device with good contrast that can change the brightness of the projected image in a wide range and stably and continuously is realized. Was done.

It should be noted that the first and second embodiments are merely specific examples, and the materials and electrode configurations used may be other materials or combinations thereof unless they violate the gist of the present invention. Of course, it can be selectively used.

[0066]

As described above, according to the present invention, in a liquid crystal display element which is a main component of a nematic-cholesteric phase transition type liquid crystal display device, the magnitude of a driving voltage applied to a selected pixel is controlled by time. The transmittance of light passing through the pixel can be almost linearly and stably changed by appropriately or appropriately controlling the length of the helical pitch of the phase change liquid crystal in the liquid crystal display element by changing the position or the location. Therefore, the intermediate brightness corresponding to the light transmittance can be displayed almost continuously, and a fine gradation display can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a gray scale display operation by a method according to a first embodiment of the present invention.

FIG. 2 is a time chart showing a drive voltage waveform for executing the gray scale display operation of FIG. 1;

FIG. 3 is a hysteresis curve for explaining the state of FIG. 1 based on light transmittance.

FIG. 4 is a cross-sectional view for explaining a gray scale display operation by a method according to a second embodiment of the present invention.

FIG. 5 is an enlarged sectional view showing an intermediate state of the liquid crystal in FIG.

FIG. 6 is a hysteresis curve for explaining the state of FIG. 4 based on light transmittance.

FIG. 7 is a diagram showing a relationship between a signal voltage and a light transmittance in FIG. 4;

FIG. 8 is a time chart showing a drive voltage waveform and a signal voltage waveform for executing a gray scale display operation according to the method of the second embodiment of the present invention.

FIG. 9 is a plan view showing in detail an example of an electrode configuration for executing a gray scale display operation according to the method of the second embodiment of the present invention.

FIG. 10 is a sectional view taken along line AA of FIG. 9;

FIG. 11 is a circuit diagram for controlling a helical pitch of a liquid crystal by a method according to a second embodiment of the present invention.

FIG. 12 is a perspective view showing an example in which the present invention is applied to a projection type liquid crystal display device.

13 is a diagram illustrating a relationship between a signal voltage and the brightness of a projected image on a screen in the application example of FIG. 12;

FIG. 14 is a diagram showing light transmittance characteristics of a conventional NC phase transition type liquid crystal display device.

FIG. 15 is a cross-sectional view for explaining an operation of a conventional NC phase transition type liquid crystal display device.

[Explanation of symbols]

1: Liquid crystal display element 2 ... Liquid crystal 3. Optical system 4: Screen 10-1, 10-2: First and second transparent substrates 11-1, 11-2... A plurality of rows of first and second electrodes 12-1, 12-2: First and second alignment films 13 ... Auxiliary electrode 20 ... Scan driver 30 Data driver

   ────────────────────────────────────────────────── ─── Continuation of front page       (56) References JP-A-2-73225 (JP, A)                 JP-A-55-46789 (JP, A)                 JP-A-61-63895 (JP, A)                 JP-A-58-5579 (JP, A)

Claims (4)

(57) [Claims] A first transparent substrate provided with a plurality of rows of first electrodes and a first alignment film;
1), a second transparent substrate which is disposed the second electrode (11-2) and the second alignment film a plurality of rows orthogonal to the first electrode (11-1) (12-2) (10-2) And a liquid crystal capable of phase transition between a nematic phase having a helical pitch of infinite length and a cholesteric phase having a constant helical pitch in a space formed opposite to each other. A voltage is applied to the phase change type liquid crystal display element (1) in which (2) is injected and sealed, and the first electrode (11-1) and the second electrode (11-2). in the phase transition type liquid crystal display device having a drive means for a predetermined portion to a nematic phase or cholesteric phase, and displays each state of brightness on the liquid crystal display device (1) of the liquid crystal (2), the first electrode (11-1) and the second electrode (11-
2) any one of the electrodes is adjacent to each of the electrodes;
Select the voltage for gradation display between the electrodes
A plurality of rows of auxiliary electrodes (13) to be applied are respectively provided, and each of the first electrodes (11-1) and the second electrodes (11-1) are provided.
-2) a holding voltage (V _d ) for stably holding the nematic phase or the cholesteric phase is applied to the pixels in the liquid crystal display element (1) formed between each of the pixels, and further,
A voltage that is lower or higher than the holding voltage (V _d ) and before the phase transition becomes dominant is the first voltage.
Either the pole (11-1) or the second electrode (11-2)
One of the electrodes and the auxiliary electrode adjacent to the electrode
(13) a phase transition type wherein a gradation corresponding to an intermediate state between the light and dark states is displayed by selectively applying a voltage between the light and dark states to perform the gradation display. Liquid crystal display device driving method. 2. The first electrode (11-1) and the first electrode (11-1).
One of the two electrodes (11-2) is provided with the gradation.
A signal electrode used to perform display, and
The first electrode (11-1) and the second electrode (11-
2) The other one electrode is provided in the liquid crystal display element (1).
Scan used to initialize all pixels
The driving method according to claim 1, wherein the driving method is an electrode . 3. The signal electrode and the auxiliary electrode (1).
3) alternately disposes two types of electrode fingers extending from both sides
The driving method of claim 2, wherein that consists of comb-shaped electrodes formed by. 4. Formed on said liquid crystal display element (1)
An optical system (3) for enlarging and projecting an image on a screen (4)
In the phase transition type liquid crystal display device of the projection type having the liquid
Change the transmittance of light passing through the crystal display element (1),
By adjusting the amount of light reaching the optical system (3)
Corresponding to the intermediate state with respect to the screen (4)
The driving method according to claim 1, wherein brightness is displayed .