JPH04337711A - Reflective phase shift type liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the reflective phase shift type liquid crystal display element and its application device which makes, specially a bright paper white display and can be carried while holding its written image as to the reflective phase shift type liquid crystal element and its application. CONSTITUTION:Phase shift type liquid crystal 3 which shifts between a nematic phase and a cholesteric phase by voltage application is injected and charged between a transparent substrate 2 where a transparent driving electrode 20 and an orienting film 21 are laminated and a transparent substrate 1 where a reflection driving electrode 4 formed of two layers, i.e., a thin Cr film 4a and a thick Al film 4b and an orienting film 11 are laminated to constitute the reflective phase shift type liquid crystal display element and its application device so that a display image formed with reflected light is observed from the side of the transparent substrate 2 provided with the transparent driving electrode 20.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective phase change type liquid crystal display device and its applications. More specifically, the present invention relates to the structure and application of a novel reflective phase change type liquid crystal display element that provides a bright paper white display and is portable while retaining the written image.

0002

[Background Art] In recent years, with the advancement of office automation equipment, there has been a demand for smaller and lighter display devices, and liquid crystal display devices have become particularly popular in portable devices such as notebook computers. There is.

[0003] Normally, STN (S
An upper twisted nematic (upper twisted nematic) type liquid crystal display element is used, but in order to obtain a bright screen, a light source is placed on the back and is incorporated into the main body as a transmissive display device.

However, since the STN type liquid crystal display element has two polarizing plates arranged before and after the liquid crystal display cell, the display screen inevitably becomes dark. Moreover, the viewing angle dependence is generally as large as ±30° with respect to the normal to the display surface, and the background color is likely to be colored due to the birefringence effect. Furthermore, since there is no accumulation effect of written images, so-called refresh driving is required for driving, and image waveform voltage must be constantly applied to maintain the display screen. Therefore, when the need to provide the transmitted light source is added, a considerable amount of power is consumed, and long-term battery operation is difficult.

A nematic-cholesteric (NC) phase change type liquid crystal display element has already been proposed by the present inventors as a new liquid crystal display element that overcomes the problems of the STN type liquid crystal display element. Kaisho 61-6078
2, 61-198270, etc.).

FIG. 5 is a diagram showing the characteristics of an N-C phase change type liquid crystal display element, with the vertical axis representing the light transmittance and the horizontal axis representing the driving voltage. That is, normal TN (Twisted N
ematic) type liquid crystal and STN (Super T
Unlike the twisted nematic type liquid crystal, it is characterized by drawing a hysteresis curve. For example, when the drive voltage is low, F (Focal conic
) When the voltage is increased, the state passes through the state F' where it is difficult for light to pass through, and when the voltage is further increased, the light transmittance rapidly decreases above a certain threshold. and eventually reaches a transparent H (Homeotropic) state with a constant transmittance. On the contrary, when the voltage is lowered from the H state, the path is different from that when the voltage is increased, and as shown in the figure, the transparent state called H' is passed through, and the state returns to the F state where light is difficult to pass through.

That is, since the well-known hysteresis curve is drawn, for example, a stable storage type liquid crystal can be created by performing binary driving of brightness and darkness at H' (bright) and F' (dark) with the voltage Vd as the holding voltage. It is possible to display it.

FIG. 6 is a diagram explaining the operation of a transmissive phase change type liquid crystal display element, in which (a) shows the F state (C: cholesteric phase), and (b) shows the H state (N: nematic phase). phase)
This is a schematic diagram.

In the figure, 1 and 2 are transparent substrates, for example, glass substrates, and 10 and 20 are transparent drive electrodes, that is, signal electrodes and scanning electrodes, for example, made of ITO (In2O3-
Transparent striped electrodes made of SnO2) film, etc.
11 and 21 are alignment films, and 3 is a nematic-cholesteric phase transition type liquid crystal that is injected and sealed in the space between both substrates.

That is, in the case of a transmission type structure in which light passes through the liquid crystal cell, molecules 3 of the liquid crystal 3 in the F state where the driving voltage is low.
'It has a helical structure, and when the helical pitch and the wavelength of visible light are approximately the same, light is well scattered, and as a result, the light does not pass through the liquid crystal cell sufficiently, resulting in a dark state. (stomach)〕
.

On the other hand, as the applied voltage is increased, the helical pitch of the liquid crystal molecules gradually increases, and when the voltage exceeds a certain threshold voltage, the helical pitch diverges, that is, the helical pitch becomes infinite, as shown in the figure. The liquid crystal molecules 3'' stand perpendicular to the substrate surface and undergo a phase transition to the H state, and light passes through the liquid crystal cell without being scattered and enters the bright state.As a result, as shown in FIG. A bistable drive of values is performed.

[0012] This liquid crystal display element is combined with an optical system,
A projection type liquid crystal display device is constructed by enlarging and projecting an image formed on a liquid crystal display element onto a screen. Transmissive phase change type liquid crystal display elements using nematic-cholesteric phase change type liquid crystals can perform bistable driving by utilizing memory properties, so they have large capacity, high definition, and are bright and flicker-free. The major feature of this device is that it can provide a large screen, and it has attracted attention as a large-screen projection type liquid crystal display device, and is beginning to be put into practical use in fields such as conferences and education.

[0013]

[Problems to be Solved by the Invention] However, the conventional nematic-cholesteric phase change type liquid crystal display device described above is intended for large-screen display of a transmission type and projection type, and has the problem that it is not suitable for small-sized devices. Therefore, there is a need to develop portable and portable liquid crystal display devices with higher functionality.

[0014]

[Means for Solving the Problems] The above-mentioned problems are solved by a transparent substrate 2 on which a transparent drive electrode 20 and an alignment film 21 are laminated, and a reflective drive electrode 4 made of a two-layer film of a thin Cr film 4a and a thick Al film 4b. and a transparent substrate 1 on which an alignment film 11 is laminated, and a phase change type liquid crystal 3 that causes a phase transition between a nematic phase and a cholesteric phase by applying a voltage is injected and sealed, and the transparent substrate 1 is provided with the transparent drive electrode 20. This problem can be solved by a reflective phase change type liquid crystal display element configured so that a display image using reflected light can be observed from two sides.

Then, an I for a drive control circuit is provided on a part of the transparent substrates 1 and 2 of the reflective phase change type liquid crystal display element 50.
The portable liquid crystal display is equipped with a C chip 5 and is housed in a portable case 103 together with a battery 101 for driving the IC chip 5 and a connector 102 for connecting to the main body, and is covered with a cover 104 that protects the display surface 30 when carried. By configuring an information processing apparatus including a display device storage section 200 to which the portable liquid crystal display device 100 can be attached and detached, a new field of application can be opened.

[0016]

[Operation] According to the present invention, the nematic-cholesteric phase transition type liquid crystal display element is constructed so that it can be observed with reflected light, so that the display surface 30 can be viewed directly.
A small, lightweight liquid crystal display device with high display quality, including high definition, wide viewing angle, and paper white display, can be obtained.

Moreover, it has a bistable drive memory operation function and can retain a written image for a long time with extremely low power consumption, so it is a portable liquid crystal display with a memory function that can be attached to and detached from the main body. A display device can be realized.

[0018]

[Embodiment] FIG. 1 is a diagram showing the basic configuration of an embodiment of the present invention.
The part in (a) of the figure schematically shows the white display area, and the part in the figure (b) schematically shows the black display area.

In the figure, 1 and 2 are transparent substrates, for example,
A transparent drive electrode 20 is formed on a glass substrate 20 with a thickness of 1.1 mm, and is made of, for example, ITO (In
2O3-SnO2) striped electrode consisting of a film
Reference numeral 1 denotes an alignment film, for example, an alignment film spin-coated with polyimide resin to impart vertical alignment.

Reference numeral 4 denotes a reflective driving electrode, which is formed on the transparent substrate 1 by forming a thin Cr film 4a with a thickness of about 20 nm and a thin Cr film 4a with a thickness of 300 nm.
It is composed of a two-layer film formed by continuous sputtering of an Al film 4b with a thickness of approximately nm.

Then, an alignment film 11 similar to the alignment film 21 described above is formed thereon. Both of the above substrates are placed with the alignment film surface inside, the transparent drive electrode 20 and the reflective drive electrode 4 are crossed,
The periphery of the substrate is sealed with a sealing layer with a spacer (not shown) in between so that a narrow space is formed between the pixels, and the number of pixels is 64.
An empty cell with 0×400 dots and a display screen size of 10 inches diagonally was formed.

Next, a phase change liquid crystal 3 that undergoes a phase transition between a nematic phase and a cholesteric phase by applying a voltage to the narrow space formed in the empty cell, such as an ester liquid crystal, a biphenyl liquid crystal, an ethane liquid crystal, and a tranquil liquid crystal, is added. When chiral nematic liquid crystal is added to a nematic liquid crystal mixture consisting of system liquid crystals, the helical pitch is 1.0 μm at room temperature.
A nematic-cholesteric phase transition type liquid crystal was injected and sealed to form a liquid crystal display element.

When a voltage is applied to the above liquid crystal display element from a drive circuit (not shown), for example, in the F state where the drive voltage between both drive electrodes is low, the liquid crystal molecules 3' of the phase change type liquid crystal 3 change.
It has a helical structure, and the light incident from the top is scattered by the liquid crystal molecules 3', and the light scattered downward is reflected by a reflection drive composed of a two-layer film of a thin Cr film 4a and a thick Al film 4b. Since the light is randomly reflected by the electrode 4, an extremely bright white display can be obtained [FIG. 4(A)].

On the other hand, when the applied voltage is increased and the helical pitch becomes infinite, the liquid crystal molecules 3'' stand perpendicular to the substrate surface and undergo a phase transition to the H state as shown in the figure. Therefore, light incident from the top surface of the liquid crystal The light passes through the molecules 3' without being scattered, and is directly reflected by the reflective drive electrode 4, which is composed of a two-layer film consisting of a thin Cr film 4a and a thick Al film 4b, resulting in a black display [FIG. 2(B)].

In this case, if the reflective drive electrode 4 is composed of only an Al film, the surface becomes a perfect mirror surface, and the viewer's face and illumination are reflected on the display surface during black display, making it difficult to see. Further, it is necessary to configure the reflective drive electrode 4 so that the display is as white as possible in the scattering state and as black as possible in the transmitting state, that is, a display with a high white/black contrast ratio can be obtained.

For this purpose, it has been found that selection of the film thickness ratio between the Cr film 4a and the Al film 4b is important. for example,
As the thickness of the Cr film 4a increases relative to the thickness of the Al film 4b, the background color in the scattering state changes from white to gray; Cr film 4a on the other side
When the film thickness is increased relative to the film thickness of , the background color in the transparent state shifts from black to silver.

That is, the film thickness ratio of Cr film/Al film is 1/
The thickness of the thin Cr film 4a is preferably about 10 nm, but the thickness of the thin Cr film 4a is preferably within a range not too thin, for example, within a range of 10 nm or less.

FIG. 2 is a diagram showing an example of a drive voltage waveform. To drive the liquid crystal display element, first, as shown in the same figure (a), initialization for writing is performed by applying a voltage approximately twice the holding voltage Vd between both drive electrodes from the drive control circuit. . Next, when writing in the white (OFF) state, a holding voltage Vd is applied between the drive electrodes at the timing shown in FIG. A holding voltage Vd is applied between the drive electrodes at the timing shown in c). In order to maintain each write state, it is sufficient to hold it at the holding voltage Vd for the required time.

FIG. 3 is a diagram showing an embodiment of the liquid crystal display element of the present invention, in which FIG. 3(a) is a perspective view and FIG. 3(b) is a sectional view taken along line A-A. In the figure, 50 is the reflective phase change type liquid crystal display element according to the present invention, and 30 is its display surface. 12 is a sealing layer that seals the peripheral edges of both substrates.

Reference numeral 5 denotes an IC chip which supplies, for example, a drive voltage and a control signal for causing the drive electrodes to perform a display operation. This example has a so-called chip-on-glass (COG) configuration in which chip-type driving IC elements are directly mounted on the wiring patterns of the overhanging portions of transparent substrates 1 and 2, and is extremely lightweight. It is suitable for use as a portable liquid crystal display device as it can be made thinner.

[0031] Parts equivalent to those explained in the above-mentioned drawings are given the same reference numerals, and explanations of the same parts are omitted. FIG. 4 is a diagram showing an application example of the present invention, in which (a) is a perspective view of the external appearance of a portable liquid crystal display device, and (b) is an example of the external appearance of the main body.

For example, the reflective phase change type liquid crystal display element 50 is housed in the portable housing 103, and the IC chip 5 is placed inside the portable housing 103.
A battery 101 for driving the main body 200, for example, two AA batteries is mounted therein, and a connector 102 for connecting to the circuit of the main body 200, for example, a personal computer, for example,
Implement a jack connector. Furthermore, a cover 10 is provided to protect the display surface 30 when transporting the mobile device, if necessary.
4 is removably provided to constitute a portable liquid crystal display device 100 shown in FIG.

On the other hand, as shown in FIG.
0 is provided with a display device housing section 201 into which the portable liquid crystal display device 100 is mounted, and the connector 10 is installed therein.
2, a connector 202, for example a plug connector, is installed.

With this configuration, the main body 20
0. For example, you don't need to carry around a desktop computer, just the portable liquid crystal display device 100 that stores important display images, and then move it to a suitable main body 2 when you're on the go.
It can be installed in the display device housing section 201 of No. 00 to easily perform display operations.

The portable liquid crystal display device 100 has, for example, a size of 220×140 mm or less, a thickness of 5 mm or less,
It weighs less than 450g, making it extremely portable and portable.Moreover, black characters were displayed on a bright paver white background, and a high contrast ratio of 9:1 was obtained. Furthermore, the viewing angle dependence is as large as ±45° with respect to the normal to the display surface, and the storage time of accumulated images can be continuously maintained for 50 hours or more. In addition, it is powered by dry batteries of the same capacity as the conventional reflective type S.
The power consumption was 1/10 or less compared to the case of a TN type liquid crystal display device.

Note that the portable liquid crystal display device 1 of the above embodiment
In 00, only one display screen was accumulated based on the characteristics of the liquid crystal cell itself, but it goes without saying that a plurality of display screens may be accumulated by incorporating an image memory if necessary.

[0037] The above embodiments are merely examples, and it is of course possible to select and use other materials and structures, or combinations thereof, as long as it does not go against the spirit of the present invention. be.

[0038]

As explained above, according to the present invention, the nematic-cholesteric phase change type liquid crystal display element is configured so that it can be observed with reflected light, so that the display surface 30 can be viewed directly, and the size is small.・It is lightweight, provides high definition, wide viewing angle, and paper white display, and has a bistable drive memory operation function, and can retain written images for long periods of time with extremely low power consumption. A portable storage type liquid crystal display device that can be attached to and detached from the main body has been realized, which greatly contributes to improving the functions and performance of liquid crystal display devices.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing an example of a drive voltage waveform.

FIG. 3 is a diagram showing an example of a liquid crystal display element of the present invention.

FIG. 4 is a diagram showing an application example according to the present invention.

FIG. 5 is a diagram showing the characteristics of an N-C phase transition type liquid crystal display element.

FIG. 6 is a diagram illustrating the operation of a transmission type phase change type liquid crystal display element.

[Explanation of symbols]

1 and 2 are transparent substrates, 3 is a phase change liquid crystal, 3', 3'' are liquid crystal molecules, 4 is a reflective drive electrode, 4a is a Cr film, 4b is an Al film, 5 is an IC chip, 11 and 21 are alignment films. , 20 is a transparent drive electrode, 30 is a display surface, 50 is a reflective phase change type liquid crystal display element, 100 is a portable liquid crystal display device, 101 is a battery, 102 is a connector, 200 is a main body, 201 is a display device housing part,

Claims (3)

[Claims] [Claim 1] A transparent drive electrode (20) and an alignment film (21)
) layered transparent substrate (2) and a thin Cr film (4a
) and a thick Al film (4b), a reflective drive electrode (4) and an alignment film (11) are laminated on a transparent substrate (1).
a transparent substrate (2) on which a phase change type liquid crystal (3) that undergoes a phase transition between a nematic phase and a cholesteric phase is injected and sealed by applying a voltage between the substrate and the transparent drive electrode (20);
A reflective phase change type liquid crystal display element characterized by observing a displayed image using reflected light from the side. 2. An IC chip (5) for a drive control circuit is mounted on a part of the transparent substrates (1, 2) of the reflective phase change type liquid crystal display element (50) according to claim 1; (5
) is housed in a portable casing (103) together with a battery (101) that drives the battery (101) and a connector (102) for connecting to the main body, and the display surface (30) is covered with a cover (104) that protects the display surface (30) when carried. A portable liquid crystal display device. 3. The portable liquid crystal display device according to claim 2 (
100) is provided with a removable display device storage section (201).