JP2000292776A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal device permitting a high response stable image display maintaining high contrast. SOLUTION: A coincidence driving voltage for making a retardation value of a liquid crystal layer almost coincide with that of a phase difference film capable of displaying a relative dark state by compensating retardation of the liquid crystal layer is recorded in a recording means 11 corresponding to an ambient temperature. And, a driving voltage control means 2 sets a coincidence driving voltage corresponding to the ambient temperature based on the temperature information from a temperature detecting means 10 for detecting the ambient temperature of the liquid crystal elements, and also controls driving voltage applying means 4, 8 for applying the driving voltage to the liquid crystal elements, so as to apply this set coincidence driving voltage to the liquid crystal elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device,
More specifically, the present invention relates to a device having a liquid crystal element in which a nematic liquid crystal sandwiched between two substrates is bend-aligned.

[0002]

2. Description of the Related Art Conventionally, as a nematic liquid crystal alignment system, there is a TN (Twisted Nematic) alignment system in which the rubbing directions of the upper and lower substrates of a liquid crystal cell are rotated by 90 degrees to align the liquid crystal. In a liquid crystal element using a liquid crystal (hereinafter, referred to as a TN alignment element), twist alignment and homeotropic alignment are used for white display or black display.

In such a TN alignment element, as shown in FIG. 4, since the fluctuation in the amount of light for the darkest level display is extremely small above the threshold voltage, the driving is easily controlled by applying a bias voltage to the driving voltage. be able to. In addition, it is possible to relatively easily perform drive control corresponding to a temperature change by detecting a temperature or monitoring a transmitted light amount of a non-display pixel and applying a constant bias voltage to the drive voltage in consideration of a variation in a threshold value. Can be.

[0004] However, such a TN alignment element is not suitable for a moving image of 30 Hz or more, especially since the response speed of the halftone is as slow as 50 msec or more. Also,
The STN (Super Twisted Nematic) alignment element has a slower response speed, so that moving image display is impossible.

On the other hand, an alignment method (spray alignment) in which a nematic liquid crystal is sandwiched between two upper and lower electrode substrates that have been rubbed in the same direction has been known for a long time. A method in which the response speed is improved by applying a voltage to the splay alignment to change the alignment to the bend alignment is described in 198.
Published by Boss in three years.

In 1992, Uchida et al. Published a study in which viewing angle characteristics were improved by performing phase compensation on such a bend alignment type nematic liquid crystal element.
In addition, this bend alignment type nematic liquid crystal element (hereinafter, referred to as “nematic liquid crystal element”)
The OCB alignment element) enables high-speed response by suppressing the backflow phenomenon in the response of the liquid crystal. For example, it is possible to follow a 60 Hz moving image by driving a TFT.

In general, the OCB alignment element has a stable splay alignment as shown in FIG. 5 when no electric field is applied.
When a high voltage of 4 to 6 V or more is applied, the alignment changes to a bend alignment of a liquid crystal molecule arrangement as shown in FIG.

When the drive voltage is lowered after confirming that the entire surface of the cell is uniformly bent, the liquid crystal molecules in the vicinity of the alignment film interface rotate in the direction aligned with the substrate, and the entire OCB alignment element becomes Retardation increases. When the voltage reaches a certain voltage, the bend alignment becomes unstable, and returns to the splay alignment again via the misalignment plane.

In general, the voltage required to return to the splay alignment is lower than the voltage required to increase the voltage to change to the bend alignment. The former is called a bend holding voltage, and the latter is called a bend initialization voltage.

On the other hand, when the driving voltage is increased before the bend holding voltage, liquid crystal molecules near the interface of the alignment film rise, and the retardation of the entire OCB alignment element decreases as shown in FIG.

That is, the OCB alignment element has a range in which the transmittance monotonously decreases between a constant voltage equal to or higher than the bend holding voltage and a voltage higher than the constant voltage. I try to get the amount of light. In this case, by performing phase compensation in accordance with the high voltage side, the normally dark mode is displayed when the darkest is displayed on the high voltage side, and the normally black mode is displayed when the phase compensation is performed on the low voltage side. Display mode is possible.

It is appropriate to set the amount of change in retardation to about 250 nm in consideration of only the balance between coloring due to wavelength dispersion in the visible region and the amount of transmitted light, but in order to reduce coloring from an oblique direction, Smaller values are also possible.

[0013]

However, such a conventional OCB alignment element has several problems when put into practical use as a liquid crystal element. One of the problems is that the splay orientation is more stable than the bend orientation. If the driving voltage becomes lower than the bend holding voltage for some reason, the splay orientation returns to the splay orientation, and driving becomes impossible.
Therefore, at least during driving, continuous application of a voltage equal to or higher than a predetermined holding voltage is required.

Since the holding voltage fluctuates by about 0.2 V to 0.5 V in the range of 10 ° C. to 50 ° C., the value of the minimum driving voltage fluctuates according to the temperature change.

Another problem is that when the phase is compensated by a uniaxial or biaxial phase compensator, the retardation of the liquid crystal coincides with the retardation of the film to be phase compensated in both the normally black mode and the normally white mode. Since the amount of transmitted light has a minimum value as shown in FIG. 8, when a physical property value such as the refractive index anisotropy fluctuates due to a temperature change or the like, if the driving voltage corresponding to the fluctuation is excessive or insufficient, the transmission of a remarkably black level is caused. The amount of light increases and the contrast ratio fluctuates significantly.

That is, in the case of the OCB alignment element, the display quality with high contrast cannot be obtained unless the change in the amount of transmitted light (gamma characteristic) from low voltage to high voltage is optimized according to the change in environmental temperature.

If the contrast ratio is 10: 1 or more, characters and the like can be visually recognized, but in the case of an image having a large number of gradation levels such as a natural image, it is desirable that the contrast ratio be 30: 1 or more.
Here, in general, when the transmitted light amount is controlled by a change in retardation of the liquid crystal layer, the transmitted light amount I is given by: I = sin ² (πΔnd / λ) · sin ² (2α) · I
₀ (where d is the cell thickness, Δn is the birefringence of the liquid crystal, λ is the wavelength, and α is the angle between the optical axis of the liquid crystal and the polarizer). If the driving voltage is controlled so as to fall within the range of ± 32 nm or less, a contrast ratio of 30: 1 or more can be achieved.

However, since this drive voltage control changes the voltage-transmitted light quantity characteristic, it is impossible to appropriately control environmental temperature changes by a simple method such as bias voltage application.

Accordingly, the present invention has been made in view of such circumstances, and has as its object to provide a liquid crystal device capable of stably displaying a high-speed image while maintaining high contrast. It is.

[0020]

SUMMARY OF THE INVENTION The present invention is directed to a liquid crystal device having a liquid crystal element in which a nematic liquid crystal sandwiched between two substrates is oriented in a bend orientation, wherein a temperature detecting means for detecting an environmental temperature of the liquid crystal element is provided. A driving voltage application unit for applying a driving voltage to the liquid crystal element, a retardation film capable of displaying a relatively dark state by compensating for the retardation of the liquid crystal layer, and a retardation value of the retardation film. Recording means for recording a matching drive voltage for substantially matching the retardation value of the liquid crystal layer in accordance with the environmental temperature of the liquid crystal element; and a matching means recorded on the recording means based on temperature information from the temperature detecting means. A drive voltage control unit that sets a matched drive voltage according to the environmental temperature from the drive voltage and controls the drive voltage application unit to apply the set matched drive voltage. It is characterized in that it comprises a means.

Further, in the present invention, the matching drive voltage is controlled such that the retardation value of the liquid crystal layer is within a range of ± 32 nm with respect to the retardation value of the retardation film, and the light amount of the brightest level and the darkest level is controlled. The ratio is set so as to be 30: 1 or more.

Also, as in the present invention, a matching drive voltage that substantially matches the retardation value of the liquid crystal layer to the retardation value of the retardation film capable of displaying the relative dark state by compensating the retardation of the liquid crystal layer. Is recorded in the recording means corresponding to the environmental temperature. The drive voltage control means sets a matching drive voltage corresponding to the environmental temperature based on the temperature information from the temperature detection means for detecting the environmental temperature of the liquid crystal element, and applies a drive voltage to apply the drive voltage to the liquid crystal element. The means is controlled to apply the set matching drive voltage to the liquid crystal element.

[0023]

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

FIG. 1 is a block diagram showing the configuration of a liquid crystal device having a liquid crystal element according to the present invention.

In FIG. 1, reference numeral 1 denotes a graphic controller which is a data generating unit. Image information transmitted from the graphic controller 1 in synchronization with an information transfer clock is input to a display controller 2 and then a scanning signal control circuit. 3 and the information signal control circuit 4 are converted into a scan driver control signal and display data, respectively.

The scanning driver control signal is applied to the scanning driver group 7 of the active matrix panel 6 constituting the liquid crystal display unit, and the display data is applied to the information driver group 8 of the active matrix panel 6. ing. Reference numeral 9 denotes a drive voltage generation circuit that generates a drive voltage applied to the scan driver group 7 and the information driver group 8.

In the same figure, reference numeral 10 denotes a temperature sensor as temperature detecting means for detecting the environmental temperature of the active matrix panel 6, and reference numeral 11 denotes a temperature compensation memory as recording means provided in the display controller 2. In the memory 11, an optimum driving voltage (matching driving voltage) to be described later corresponding to the display level of 8 bits for each color of RGB in the driving guarantee voltage range equal to or higher than the holding voltage is recorded in advance for each 1 ° C.

Reference numeral 12 denotes a temperature compensating circuit for compensating the light quantity data signals of the respective colors of RGB in the image information from the graphic controller 1 by driving voltage data corresponding to the temperature data recorded in the temperature compensating memory 11.

The display controller 2 serving as drive voltage control means reads drive voltage data corresponding to the environmental temperature of the active matrix panel 6 from the temperature compensation memory 11 based on the temperature data from the temperature sensor 10, In the temperature compensation circuit 12 according to the voltage data, the RG
The light amount data signal of each color B is compensated for the optimum drive voltage data, and the drive voltage is applied to each pixel by controlling the information signal control circuit 4 and the information driver group 7 which constitute the drive voltage applying means.

On the other hand, the OCB alignment element constituting the active matrix panel 6 displays 1240 × 1024 dots in 256 gradations and has a structure as shown in FIG.

In the figure, 61 is an OCB alignment element, 21 is a glass substrate, 22 is a transparent conductive film (ITO),
23 is an insulating film, 24 and 25 are alignment films, 26 is a liquid crystal layer, 2
Reference numeral 7 denotes a TFT, a drain electrode 28 and a gate electrode 29.
Etc. In the present embodiment, the liquid crystal is KN5027XX (manufactured by Chisso), and the alignment films 24 and 25 are A
Using LO656 (manufactured by JSR), pretilt angle is 60
°, the bend initialization voltage is 6 V, and the bend holding voltage is 1.9.
V.

FIG. 3 shows the structure of the active matrix panel 6. In FIG.
Is a polarizing plate. These two polarizing plates 62 and 63 are arranged orthogonally, and the OCB alignment element 61 has a rubbing direction with respect to the two polarizing plates 62 and 63 so that the contrast ratio is maximized. Are arranged in a 45 ° direction.

Further, 64 has a retardation of 110 nm.
A first phase compensator composed of a retardation film of
Some of them compensate for retardation of light passing through the OCB alignment element. Reference numeral 65 denotes a second phase compensator composed of a retardation film having a negative retardation, which corrects the retardation difference in the optical path direction in the liquid crystal layer and improves the viewing angle characteristics.

Here, considering the refractive index ellipsoid of the light that has passed through the liquid crystal layer and the retardation film having the positive retardation (first phase compensator 64), the refractive index in the optical path direction is Nz,
Assuming that the refractive index in the direction orthogonal to the optical path is Nx (the refractive index in the direction orthogonal to Nx is Ny and Nx = Ny), the refractive index ellipsoid of the negative retardation film (second phase compensator 65) is The refractive index Nz 'in the direction of the optical path is Nx, and the refractive index Nx' in the direction perpendicular to the optical path is Nz (the refractive index in the direction orthogonal to Nx 'is Ny' and Nx '= Ny').
Set so that

The optimum drive voltage data compensated by the temperature compensation circuit 12 is set so that the retardation value of the liquid crystal layer 26 substantially matches the retardation value of the retardation films 64 and 65 as described above. It is. In the present embodiment, the retardation value of the liquid crystal layer 26 is controlled within a range of ± 32 nm with respect to the retardation values of the retardation films 64 and 65, and the light amount ratio between the brightest level and the darkest level is 30: It is set to be 1 or more.

Table 1 below shows the optimum driving conditions of the OCB alignment element 61 set at 10 ° C., 30 ° C., and 50 ° C. as set forth above.
The drive voltage at which the amount of transmitted light was minimum was 5.3 V, and the drive voltage at which the amount of transmitted light was maximum and was equal to or higher than the holding voltage was 1.9 V.

[0037]

[Table 1] Then, according to the optimum driving conditions, the OCB alignment element 61
, A good display quality with a front contrast ratio of 100 or more was obtained over all temperatures. When driven using the TFT 27 (see FIG. 2) described above as an active element, the response speed of the OCB alignment element 61 is 30 ° C. and 0.76 at τon (when a high voltage is applied).
In the case of ms and τoff (when a low voltage is applied), the time is 4.9 ms, and high-speed response image display is possible.

As described above, by setting the optimum driving conditions corresponding to the environmental temperature based on the temperature information from the temperature sensor 10, the bend alignment holding voltage accompanying the environmental change such as the ambient temperature change and the minimum amount of transmitted light can be obtained. Variations in values can be accurately corrected. In addition, by driving the OCB alignment element 61 under the set optimum driving conditions, it is possible to maintain a high-speed response for moving images and a stable image display quality with a stable contrast.

As described above, in the environmental temperature range of 10 ° C. to 40 ° C., it was confirmed that the relationship between the drive voltage and the transmittance was almost proportional to the temperature.
A driving voltage-transmitted light intensity characteristic at 0 ° C., a maximum driving voltage value and a minimum driving voltage value in a driving assurance voltage range are input in advance, and the minimum / maximum voltage according to the actual temperature is changed to 30 ° C. The driving voltage corresponding to the gradation level in the range of 10 ° C. to 40 ° C. may be obtained by the following approximate calculation formula based on the data.

Vn (T) = {Vmax. (T) -Vmi
n. (T)｝ × ｛Vn (30) -Vmin. (30)｝
/ ｛Vmax. (30) -Vmin. (30)｝ + Vm
in. (T) (However, when Vn (T) = T ° C., the voltage value of n gradations, Vn
(30) = n gradation voltage value at 30 ° C., Vmin.
(T) = minimum voltage value at T ° C., Vmax. (T) = T
° C, the maximum voltage value, Vmin. (30) = minimum voltage value at 30 ° C., Vmax. (30) = Maximum voltage value at 30 ° C.) Then, by using such an approximate expression, 30 ° C.
The gradation voltage data for all temperatures except for the temperature compensation memory 11
In the temperature compensation memory 11 can be reduced.

[0041]

As described above, according to the present invention, the retardation of the retardation film capable of displaying the relative dark state by compensating for the retardation of the liquid crystal layer in accordance with the environmental temperature is increased. By setting a matching drive voltage that substantially matches the retardation values of the above, it is possible to stably perform high-speed response image display while maintaining high contrast.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a liquid crystal device including a liquid crystal element according to the present invention.

FIG. 2 is a cross-sectional view of a main part of the liquid crystal element.

FIG. 3 illustrates a configuration of an active matrix panel including the liquid crystal element.

FIG. 4 is a diagram showing an optical response of a conventional TN alignment element.

FIG. 5 is a diagram illustrating splay alignment of a conventional OCB alignment element.

FIG. 6 is a diagram illustrating bend alignment of the OCB alignment element.

FIG. 7 is a diagram showing applied voltage-retardation characteristics of the OCB alignment element.

FIG. 8 is a view showing an applied voltage-transmittance characteristic of the OCB alignment element.

[Explanation of symbols]

 2 display controller 4 information signal control circuit 6 active matrix panel 8 information driver group 10 temperature sensor 11 temperature compensation memory 12 temperature compensation circuit 26 liquid crystal layer 27 TFT 61 OCB alignment element 64 first phase compensator 65 second phase compensator

Continued on the front page (72) Inventor Shinjiro Okada 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H088 GA02 HA06 HA16 JA04 MA02 MA20 2H093 NA16 NC21 NC28 NC49 NC57 NC63 ND02 ND04 NE06 NF04

Claims (2)

[Claims] 1. A liquid crystal device comprising a liquid crystal element in which a nematic liquid crystal sandwiched between two substrates is bend-aligned, a temperature detecting means for detecting an environmental temperature of the liquid crystal element, and a driving voltage applied to the liquid crystal element. A drive voltage applying means for applying, a retardation film capable of displaying a relative dark state by compensating for the retardation of the liquid crystal layer, and a retardation value of the liquid crystal layer substantially matching a retardation value of the retardation film. Recording means for recording the matched drive voltage to be made corresponding to the environmental temperature of the liquid crystal element; and, from the matched drive voltage recorded in the recording means based on the temperature information from the temperature detecting means, according to the environmental temperature. Drive voltage control means for setting the matched drive voltage, and controlling the drive voltage applying means to apply the set matched drive voltage. A liquid crystal device comprising: 2. The matching drive voltage, wherein the retardation value of the liquid crystal layer is controlled within a range of ± 32 nm with respect to the retardation value of the retardation film, and the light quantity ratio between the brightest level and the darkest level is 30. 2. The liquid crystal device according to claim 1, wherein the liquid crystal device is set to a value such that: 1 or more.