JPH04215617A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which performs a high- quality full color display by taking advantage of excellent characteristics of a surface stabilizing ferroelectric liquid crystal. CONSTITUTION:A surface stabilizing ferroelectric liquid crystal l for reversing spontaneous polarization by externally applying an electric field to a ferroelectric liquid crystal in which permanent dipole moments are the same and lined up in one direction, and spontaneous polarization exists with any electric field not applied externally, a pulse voltage applying means 2 for applying a pulse voltage of specified value to the surface stabilizing ferroelectric liquid crystal 1, and a frequency control means 3 for controlling the frequency of pulse voltage applied by the pulse voltage applying means 2 are provided, and the transmissivity is controlled by applying pulse voltages which differ in frequency to the above surface stabilizing ferroelectric liquid crystal 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid crystal display device.
Specifically, the present invention relates to a liquid crystal display device suitable for use in the field of flat panel displays, for example, for colorizing large-capacity displays compatible with full-color displays such as personal computers. In recent years, surface stabilized ferroelectric liquid crystals (SSFLCs) have become popular due to their fast response speed, wide viewing angle, and large capacity display.
bilized ferr-oelectric li
Liquid crystal display devices using QUID crystal are attracting attention.

Ferroelectric liquid crystal (FLC)
A ctric liquid crystal refers to a liquid crystal in which the smectic C phase exhibits ferroelectricity in the arrangement of liquid crystal molecules, that is, a liquid crystal in which the spontaneous polarization of the smectic C phase liquid crystal molecules is extremely large. , for example, TN (twisted nematic
), STN (super twisted nema)
tic), which use dielectric torque generated by an electric field to display information, they have a memory effect (memory characteristic) due to their own bistable state.

[0003] Surface-stabilized ferroelectric liquid crystal displays by utilizing the spontaneous polarization of this ferroelectric liquid crystal, and the transition to two stable states is several to several tens of microns compared to ordinary liquid crystal.
It is expected to be used as a flat panel display for office automation as it is fast at 200 ms and can provide high contrast. However, due to its basically bistable property, it is difficult to display gradation, and a full color display cannot be realized as it is.

[0004]Therefore, it is required to perform multi-gradation display while taking advantage of the excellent characteristics of surface-stabilized ferroelectric liquid crystals.

[0005]

[Prior Art] Conventional liquid crystal display devices of this type include:
(1) The average amount of transmitted light is controlled by changing the number of switching times of liquid crystal molecules per unit time to display gradation, and (2) the pixels are made finer so that more light per unit area is transmitted. There are devices that display gradations by controlling the amount of transmitted light by changing the area.

[0006] In other words, (1), which controls the amount of transmitted light by changing the number of times of switching, uses a relatively fast-responsive liquid crystal and changes the number of times of switching for each pixel depending on the gradation to be displayed. The gradation is determined by the ratio of the two states of black and white of the liquid crystal per predetermined unit time, and in (2), the amount of transmitted light is controlled by changing the area through which light passes, for example. , the number of pixels per unit area is increased according to the number of gradations, such as 4 pixels for displaying 4 gradations and 16 pixels for displaying 16 gradations, and the number of pixels per unit area is increased according to the number of gradations. The gradation is determined by the ratio of the two states of black and white of the liquid crystal.

[0007]

[Problem to be solved by the invention] However, (1)
The problem with liquid crystal display devices was that the number of times the liquid crystal was switched per unit time was changed depending on the gradation to be displayed, so a liquid crystal that had a high-speed response had to be used. was there. In other words, it is necessary to use a liquid crystal that can switch a predetermined number of times per unit time, so if you want to increase the number of gray levels, the liquid crystal must respond faster depending on the number of gray levels to be displayed. However, this has limitations from the viewpoint of materials. Furthermore, since the response speed of liquid crystals changes depending on the temperature, there are also constraints such as the need to limit the environmental temperature.

[0008] Furthermore, in the liquid crystal display device (2), the black and white area of the liquid crystal per unit area is changed according to the gray scale to be displayed, so in order to increase the number of gray scales, it is necessary to There was a problem that the number of pixels per unit area had to be increased. This means that the liquid crystal area per pixel becomes small, and there is a limit in terms of microfabrication technology for transparent conductive films. Furthermore, as the number of pixels increases, the display capacity of one screen increases, so if the number of pixels increases, the writing time for one screen also increases.

That is, it is not practical to realize a full color display using the above-described gradation control. Currently, the most effective colorization method is to use a black and white display as a shutter and place a color filter in series with each pixel, but the conditions for the liquid crystal used in the shutter are: 1. High display contrast.

2. Multiplex drive characteristics of 400 lines or more, or characteristics similar thereto. One method that satisfies these two conditions is to use a ferroelectric liquid crystal with surface stabilization. However, as mentioned above, due to its basically bistable property, it is difficult to display gradation, and a full-color display cannot be realized as it is.

[0011]

[Object] Therefore, it is an object of the present invention to provide a liquid crystal display device that makes full use of the excellent characteristics of surface-stabilized ferroelectric liquid crystals and performs high-quality full-color display.

0012

[Means for Solving the Problems] In order to achieve the above object, the liquid crystal display device according to the present invention has permanent dipole moments that are the same and aligned in one predetermined direction in a state where no electric field is applied from the outside, and spontaneous polarization. A surface-stabilized ferroelectric liquid crystal 1 whose spontaneous polarization is reversed by applying an external electric field to the existing ferroelectric liquid crystal, and a pulse voltage of a predetermined voltage value applied to the surface-stabilized ferroelectric liquid crystal 1. a pulse voltage applying means 2 for applying the voltage, and a frequency control means 3 for controlling the frequency of the pulse voltage applied by the pulse voltage applying means 2.
The transmittance is controlled by applying pulse voltages of different frequencies to the surface-stabilized ferroelectric liquid crystal 1.

[0013]

In the present invention, by applying pulse waves of different frequencies to the surface-stabilized ferroelectric liquid crystal, the transmittance of the liquid crystal is controlled and multi-gradation display is performed. In other words, ferroelectric liquid crystals have two stable states, and when a pulse voltage is applied from the outside and the state of the liquid crystal molecules becomes one of the stable states, two displays, for example white and black, are produced. Ru. In order to transition the state of liquid crystal molecules, the width of the pulse voltage applied to the liquid crystal must be longer than the response time of the liquid crystal molecules. Conversely, as shown in FIGS. 4 and 5, when the width of the pulse voltage is shorter than the response time of the liquid crystal molecules, the liquid crystal molecules are not sufficiently transitioned and take a state different from the two stable states.

[0014] Therefore, by changing the frequency of the pulse voltage applied to the liquid crystal, gray scales are displayed on the ferroelectric liquid crystal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. 1 to 3 are diagrams showing one embodiment of a liquid crystal display device according to the present invention, and FIG. 1 is a block diagram showing the overall configuration. First, the configuration will be explained.

The liquid crystal display device of this embodiment is roughly divided into a liquid crystal panel 1 made of surface-stabilized ferroelectric liquid crystal, an oscillator 2 as a pulse voltage applying means, and a frequency control means 3. The liquid crystal panel is shown in FIG. , 3, the liquid crystal panel 1
As shown in FIGS. 2 and 3, the substrate 8 includes a glass 4, a transparent electrode 5, an alignment film 6, and a liquid crystal layer 7.

The alignment film 6 is a rubbed PVA film, and the liquid crystal layer 7 uses phenylpyrimidine liquid crystal in order to obtain high contrast during multiplex operation. The liquid crystal display panel 1 of this example has an outer dimension of 25 m.
A transparent electrode 5 with a diameter of 15 mm is placed on a glass 4 of m x 25 mm.
A cell with a cell gap of 2 μm was created using a substrate 8 with a .

Ferroelectric liquid crystal has two stable states.
By applying a pulse voltage from the outside to bring the state of the liquid crystal molecules into one of the stable states, two types of display, for example, white and black, can be achieved. The width of the pulse voltage must be longer than the response time of the liquid crystal molecules. This means that if the width of the pulse voltage is shorter than the response time of the liquid crystal molecules, the liquid crystal molecules will not undergo sufficient transition and will take a state different from the two stable ones. Therefore, by changing the frequency of the pulse voltage applied as a means for displaying gray scales using ferroelectric liquid crystals, it was actually confirmed that gray scale display using ferroelectric liquid crystals could be achieved.

The liquid crystal display device of this embodiment, in which the transmittance is controlled by changing the frequency of the applied pulse voltage, is similar to the conventional liquid crystal display device in which the transmittance is controlled by changing the number of times of switching. However, with devices that control transmittance by changing the number of switching times, the average amount of transmitted light is controlled by the number of times that liquid crystal molecules completely respond to the applied pulse voltage within a unit time. Then, by applying a pulse voltage shorter than the response time of the liquid crystal molecules, we create a state in which the liquid crystal molecules do not respond sufficiently.
That is, the major difference is that the state of the liquid crystal molecules is changed by changing the frequency of the applied pulse voltage to control the amount of transmitted light.

Next, the operation will be explained. First, a pulse voltage of ±10 V with varying frequency is applied to the liquid crystal cell shown in FIGS. 2 and 3, and changes in the amount of light transmitted through the cell at that time are observed. FIG. 4 is a diagram showing the relationship between the frequency of the pulse voltage applied to the ferroelectric liquid crystal and the amount of transmitted light, and it can be seen that the amount of transmitted light through the cell can be controlled simply by changing the frequency of the pulse voltage applied. In other words, in a frequency band where the amount of transmitted light changes significantly, the pulse voltage width is shorter than the response time of the liquid crystal molecules, so by changing the state of the liquid crystal molecules other than the two stable states, As shown, the amount of light transmitted through the cell is controlled. Note that in FIG. 5, ■ to ■ indicate states corresponding to ■ to ■ shown in FIG.

[0021] Furthermore, the value of the amount of transmitted light at each frequency does not change even if the pulse frequency voltage continues to be applied for several minutes.
A stable and constant amount of transmitted light can be obtained. That is, by changing the frequency of the applied pulse voltage, the state of the liquid crystal molecules can be changed and the amount of transmitted light can be stably controlled. In this way, in this example, it is possible to relatively easily obtain a full-color display, which has been difficult to achieve with conventional gradation displays due to material problems and problems with microfabrication techniques such as transparent electrodes. Multi-gradation display can be performed using a surface-stabilized ferroelectric liquid crystal that has a fast response speed, a wide viewing angle, and is capable of large-capacity display.

[0022] Therefore, a stabilized ferroelectric liquid crystal that provides a liquid crystal display device with a large display capacity at low cost can be used to display gradations and provide high-quality full-color display. Although the above embodiment uses a phenylpyrimidine-based ferroelectric liquid crystal, it is not limited to this; for example, a cyanobiphenyl-based liquid crystal or an ester-based liquid crystal with good stability may be used. Any material may be used as long as it has the characteristics of a ferroelectric liquid crystal material.

[0023]

Effects of the Invention In the present invention, by applying pulse voltages of different frequencies to a surface-stabilized ferroelectric liquid crystal that has a fast response speed, a wide viewing angle, and is capable of displaying a large capacity,
The transmittance of the liquid crystal can be controlled and multi-gradation display can be performed. Therefore, a stabilized ferroelectric liquid crystal that provides a liquid crystal display device with a large display capacity at a low cost can be used to display gradations and provide high-quality full-color display.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a plan view and a side view of a liquid crystal panel according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of the liquid crystal panel of FIG. 2;

FIG. 4 is a diagram showing the relationship between the frequency of a pulse voltage applied to a ferroelectric liquid crystal and the amount of transmitted light.

FIG. 5 is a diagram showing the relationship between incident light and transmitted light in states 1 to 2 in FIG. 4;

[Explanation of symbols]

1 Liquid crystal panel (surface stabilized ferroelectric liquid crystal) 2
Oscillator (pulse voltage application means) 3 Frequency control means 4 Glass 5 Transparent electrode 6 Alignment film 7 Liquid crystal layer 8 Substrate

Claims (1)

[Claims] [Claim 1] In a state where no electric field is applied from the outside,
A surface-stabilized ferroelectric liquid crystal in which the spontaneous polarization is reversed by applying an external electric field to a ferroelectric liquid crystal in which the permanent dipole moment is the same and aligned in one predetermined direction, and the spontaneous polarization is present. , comprising a pulse voltage applying means for applying a pulse voltage of a predetermined voltage value to the surface-stabilized ferroelectric liquid crystal, and a frequency control means for controlling the frequency of the pulse voltage applied by the pulse voltage applying means, A liquid crystal display device characterized in that transmittance is controlled by applying pulse voltages of different frequencies to a surface-stabilized ferroelectric liquid crystal.