JPH04133027A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To obtain the effective critical electric field and to improve a contrast by providing a carbon film on electrodes and further forming display unit picture element electrodes consisting of transparent conductive film on the carbon film. CONSTITUTION:The electrodes 3 are provided on the 1st substrate 2 consisting of polyethylene terephthalate. The carbon film 4 consisting of a non-single crystal material consisting of carbon atoms, hydrogen atoms and nitrogen atoms as essential texture forming elements is provided on the electrodes 3. Further, the picture element electrodes 5 are provided by using the transparent conductive film consisting of a material contg. at least one among indium oxide, zinc oxide and tin oxide on the carbon film 4. The greater part of the electric field is applied on the ferroelectric liquid crystal 1 when the large electric field is applied and on the element consisting of the electrodes 3, the carbon film 4 and the picture element electrodes 5 when the small electric field is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a liquid crystal device using a smectic liquid crystal, which is one of the representative examples of liquid crystal, particularly a ferroelectric liquid crystal (hereinafter referred to as FLC), and relates to a microcomputer, Liquid crystal devices that aim to make the display parts of word processors, television stations, etc. thinner,
Furthermore, the present invention relates to a liquid crystal device applied to memory devices such as disk memories, and audio equipment such as speakers.

"Prior Art" Conventionally, when manufacturing a liquid crystal device using liquid crystal, a method is known in which a pair of electrodes is provided inside a pair of substrates of the liquid crystal, and a symmetrical alignment film is provided on the electrodes.

However, in such a simple matrix structure or an active element structure in which a nonlinear element is connected in series to each pixel, the most important element is that the smectic liquid crystal described above has a sufficiently large Ec (critical electric field or threshold electric field). is important. This Ec is a phenomenon in which the liquid crystal maintains its initial state (for example, non-transmissive) below a predetermined electric field, reverses extremely sharply and assumes another state (for example, transmissive) when the electric field exceeds a predetermined electric field, and vice versa. This refers to a phenomenon that becomes more opaque. That is, the second Ec is Ec+
(critical electric field observed when a positive electric field is applied) and Ec- (an electric field that exists when a negative electric field is applied). It is extremely difficult to control whether Ec+ and Ec- are not necessarily the same in absolute value, or can be made approximately equal depending on the process conditions of the alignment treatment in contact with the liquid crystal.

However, such Ec+ and Ec- are extremely scarce in the liquid crystal itself, and in particular in a ferroelectric liquid crystal using a chiral smectic C phase, the value of the electric field strength and pulse width of the pulsed electric field applied to this liquid crystal is It depends a lot. Therefore, in matrix display, an excitation method known as the "rAC bias method" must be used, and when rewriting in the positive direction, a negative pulse is applied once, and then a positive pulse is applied with a predetermined electric field strength. Add time with precise control. Conversely, when rewriting in the negative direction is desired, a pulse of -transformation must be applied, and then a negative pulse must be applied under precise control of predetermined electric field strength and time.

``Problems to be solved by invention'' When trying to use such liquid crystals, especially ferroelectric liquid crystals,
The conventional technology is the rAc bias method as described above.
"Two-frequency drive" or the like must be used. The former rA
The "C bias method" applies an AC bias pulse during non-selection in addition to a write pulse with a large electric field.

When using this driving method, the liquid crystal material itself needs to have stable bistability and memory properties. If there are not enough of them, the AC bias pulse during non-selection will cause a decrease in contrast.

Furthermore, even liquid crystal materials with stable bistability and memory properties may or may not simultaneously satisfy other properties (response speed, temperature range, etc.).

Since "two-frequency drive" requires extremely complex peripheral circuits, there is a need for simpler peripheral circuits when used in display devices.

When such a ferroelectric liquid crystal is used, the present invention does not require that the liquid crystal itself has Ec, but considers the liquid crystal, the carbon film on the electrode, and the pixel electrode as an integrated entity, and the entire structure substantially The purpose was to obtain an effective Ec.

"Means for solving the problem" Electrodes and leads are provided on the first substrate, polyethylene terephthalate (PET), and a non-single crystal material containing carbon atoms, hydrogen atoms, and nitrogen atoms as the main structure-forming elements. Further, a display unit electrode (pixel) is provided on top of the carbon film using a transparent conductive film made of a material containing at least one of indium oxide, zinc oxide, and tin oxide. Elements with this structure have nonlinear resistance (impedance) and a large electric field (write pulse).
When a small electric field is applied, most of the electric field is applied to the liquid crystal material, and when a small electric field is applied, most of the electric field is applied to the device.

A longitudinal cross-sectional view is shown in FIG.

In Figure 1, a ferroelectric liquid crystal (FLCXI), a first substrate (2), electrodes and leads (3) on the first substrate DL
It has a C coating (4), a pixel electrode (5), an alignment film (6), a second substrate (7), and electrodes and leads (8) on the second substrate.

FIG. 2 shows the electrical characteristics of this nonlinear element.

Judging from this electrical characteristic, this device conducts by Poole-Fronkel emission, I=αVexp (β/V), (9) The coefficients α and β in equation (9) have temperature as a coefficient, and α is proportional to the element area and the thickness of the carbon film, and β represents nonlinearity.

When an element with such nonlinearity and a ferroelectric liquid crystal are electrically connected in series, and when the signal waveform shown in Figure 3(a) is applied, the electric field applied to the liquid crystal and the electric field applied to the element are ,
The waveform becomes as shown in FIG. 3(b). As a matter of course,
If there is no element, the electric field shown in FIG. 3(a) will be applied as is.

Examples of the present invention are shown below.

Example 1 After forming a 0.2 micron film of molybdenum on a polyethylene terephthalate (PET) film by sputtering, electrodes and leads were fabricated using photolithography.

Thereafter, a carbon film was formed by a plasma CVD method under the following conditions: [Gas flow rate] C2H420SCCM H2380SCCM NF310 SCCM [RF power] 0 W Electrode area 9 m2 [Discharge pressure 1 0.0075 Torr].

After that, by DC sputtering method, indium oxide
A tin oxide film was formed to a thickness of 0.1 micron, a pixel electrode was formed by the odolithography method, and then polyimide was applied and rubbed to obtain a first substrate.

A 0.1 micron indium oxide/tin oxide film was formed on a glass substrate by DC sputtering, and electrodes were formed by photolithography to obtain a second substrate.

Spread epoxy resin spheres with a diameter of 2.5 microns on the second substrate, screen print epoxy resin adhesive around them, overlap them with the first substrate, and apply pressure and heat to , formed a cell.

After that, a liquid crystal composition exhibiting ferroelectricity is injected into the cell,
Obtained a liquid crystal device.

"Effect" As shown in Figure 3, when a carbon film element is electrically connected in series with a liquid crystal, the AC
Since most of the bias pulse is applied to this device, the action of the liquid crystal molecules due to the AC bias pulse is suppressed. As a result, the contrast was improved. In implementing the present invention, it has been confirmed that the contrast ratio of a liquid crystal device that does not use a carbon film element was improved from 15 to 30. The effect is shown in FIG.

In addition, in a liquid crystal device that does not use a carbon film element, the optimum bias value for obtaining maximum contrast at a certain arbitrary temperature is one point, or in a liquid crystal device with a carbon film element,
It has a width of about 15V, and this is intended to simplify the drive circuit. FIG. 5 shows a graph of the optimal bias characteristics.

Furthermore, even when the environmental temperature changed, it was confirmed that the system operated with a constant bias as shown in FIG. 6, and it was confirmed that there was no need for the operator to make troublesome contrast adjustments.

From these results, depending on the impedance ratio between the liquid crystal and the carbon-coated element, it was possible to determine which of the applied electric fields or the above-mentioned one would receive more of the applied electric field, depending on the magnitude of the applied electric field. This is definitely the Ec that was needed.

In addition, one side of the board is made of polyethylene terephthalate (PE).
T), it was possible to reduce the sound peculiar to ferroelectric liquid crystals.

[Brief explanation of drawings]

Cross-sectional view of liquid crystal device Ferroelectric liquid crystal composition first board electrode carbon coating pixel electrode alignment film second board electrode Figure 2 Electrical characteristics of carbon film element Figure 3 Applied electric field (a) Applied electric field (b) Electric field applied to liquid crystal Figure 4 Characteristics of carbon film elements with and without carbon film elements figure Contrast with and without carbon film elements Voltage dependent characteristics of figure Contrast with and without carbon film elements temperature characteristics

Claims (1)

[Claims] 1. In a liquid crystal device in which liquid crystal is filled inside a pair of substrates, an electrode is provided on the inner surface of at least one of the substrates, and carbon atoms, hydrogen atoms, and nitrogen atoms are arranged on the electrode. A transparent conductive film comprising a carbon film made of a non-single-crystal material whose main structure-forming elements are atoms, and which is made of a material containing at least one of indium oxide, zinc oxide, and tin oxide on the carbon film. A liquid crystal device characterized in that a display unit pixel electrode is configured by: 2. In claim 1, at least one of the substrates is polyethylene terephthalate (PET). 3. In claim 1, the liquid crystal material is ferroelectric. 1. A method for driving a liquid crystal device, characterized in that it exhibits