JPH03157622A - Liquid crystal device and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a liquid crystal device improved in time constant by arranging transparent conductors on the surfaces of substrates, coating these conductors and substrate surfaces with polyimide alignment layers and further, exposing these alignment layers to a glow discharge of an inert gas. CONSTITUTION: This liquid crystal device 10 is constituted by arranging a liquid crystal material 11 between two sheets of transparent insulating substrates 12 and 13. The transparent electrode 14 is arranged on the surface on the liquid crystal material 11 side of the substrate 13 and the surface on the liquid crystal material side of the substrate 12 is provided with the transparent electrodes 15. The surface of the transparent electrode 14 is provided with the polyimide alignment layer 16 which apply a required molecular arrangement and good inclination angle. Similarly, the polyimide alignment layer 17 is formed to cover the transparent electrode 15. When the surfaces 18, 19 of the alignment layers 16, 17 are exposed to the glow discharge of the inert gas such as Ar or N2 , etc., by a glow discharge method prior to assembling the device 10, the value of the RC time constant of the device increases drastically and the stability of the resistance and the stability of the resistance to the time when the device is exposed to a high temp. are improved. The substrates are rubbed after the polyimide is subjected to the glow discharge, by which the molecules of the liquid crystal material are aligned to the treated polyimide layers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to liquid crystal devices (including liquid crystal cells), and particularly to a liquid crystal device with an improved time constant and a manufacturing method thereof.

[Background of the invention]

A display device using twisted nematic liquid crystal includes a liquid crystal material disposed between two insulating substrates, at least one of which is transparent. Electrical control electrodes are arranged on the surface of the substrate facing the liquid crystal material. In one type of liquid crystal device, both the substrates and their associated electrodes are transparent, allowing light to pass through the entire structure when the elongated molecules of the liquid crystal material assume one orientation; When it is in another orientation, it does not allow light to pass through. In another type of liquid crystal device, only one substrate and its associated electrodes are transparent. In this device, when the liquid crystal material is in one state, light passes through the substrate and is reflected by the liquid crystal material, and when the liquid crystal material is in another state, light passes through the liquid crystal material and is reflected by the other substrate. be done. In both of the two types of devices mentioned above,
An image is formed by applying a voltage bias to the control electrodes of selected devices to alter the light transmission capabilities of the energized devices.

In both types of liquid crystal devices, the molecules of the liquid crystal material are elongated and must be properly aligned with respect to the surface of the substrate to ensure uniform operation and high contrast of the displayed information. Aligning the molecules is done by coating the surface of the electrode with an alignment material and rubbing the alignment material in the direction required to obtain alignment of the liquid crystal molecules.

In active matrix liquid crystal displays, a switching device, such as a thin film transistor (TPT) or solid state diode, is provided for each liquid crystal element in the display. The liquid crystal molecular alignment layer of an active matrix liquid crystal device must control three properties in order to obtain optimum operation and optimum contrast: the tilt angle between the principal axis of the molecule and the substrate; ,
Molecular alignment (parallel alignment of liquid crystal molecules) and high RC time constant. The tilt angle should be between 10 and 5 degrees to give adequate response time and good visibility of the device. Good molecular alignment of the liquid crystal molecules is necessary to provide uniformity of operation and high contrast between energized and deenergized states. Since a high RC time constant is required, the resistance of the liquid crystal material must be high enough to allow the liquid crystal device to store charge long enough to display the desired image. Must be.

In direct-drive liquid crystal devices, for example liquid crystal devices that do not employ solid-state switching devices, the alignment layer only needs to control the tilt angle and the alignment of liquid crystal molecules; in this case, the liquid crystal device is charged during the information display period. Since there is no need to store , the time constant or resistance of the liquid crystal material is not an issue.

Polyimide is often used as an alignment layer for direct drive displays. Polyimide provides good molecular alignment and also provides desirable tilt angles in the range of 1.5° to 3°. However, the electrical properties of devices using polyimide are insufficient for active matrix liquid crystal display devices. The resistance of liquid crystal deteriorates at 90°C. The time constant of the device with polyimide alignment layer is initially 30-100 seconds, but when exposed to high temperature the time constant decreases to 10-30p.
A time constant of this length, which drops to seconds, is insufficient for active matrix liquid crystal displays.

For the above reasons, it can be used with active matrix liquid crystal devices, has an acceptable tilt angle, good liquid crystal molecular alignment, and an RC time constant that is stable over long periods of time and even when exposed to high temperatures. A liquid crystal device with the following is desired. This invention attempts to satisfy the above requirements.

[Summary of the invention]

A method of manufacturing a liquid crystal device according to the present invention includes the step of disposing a transparent conductor on the surface of a substrate. The conductor and substrate surface are coated with a polyimide alignment layer. This alignment layer is exposed to a glow discharge of an inert gas.

[Explanation of Examples]

The illustrated liquid crystal device IO includes a liquid crystal material 11 disposed between two transparent insulating substrates 12 and 13. A transparent electrode 14 is arranged on the surface of the substrate 13 on the liquid crystal material 11 side. For example, TP required for active matrix display devices.
Solid state switching devices such as T (Thin Film Transistor) or MIM (Metal-Insulator-Metal Diode) are not shown, but the space required for solid state switching devices is generally limited by eliminating a small portion of the corner of electrode 14. and the space is provided with a solid state switching device using solid state manufacturing techniques known in the art.

A transparent electrode 15 is provided on the surface of the substrate 12 on the liquid crystal material side. A polyimide alignment layer 16 is provided on the transparent electrode 14 to provide the required molecular alignment and good tilt angle. Similarly, a polyimide alignment layer 17 is provided over the transparent electrode 15 on the substrate 12, which also provides the required molecular alignment and good tilt angle.

Prior to assembly of the device IO, surfaces 18 and 19 of polyimide alignment layers 16 and 17 are exposed to a glow discharge of an inert gas, such as argon or nitrogen, using conventional glow discharge techniques. If you do it like this.

The value of the RC time constant of the device is significantly increased, and the stability of the resistance when exposed to high temperatures and the stability of the resistance over time is also improved. After exposing the polyimide to the glow discharge described above, the substrate is rubbed in the conventional manner to bring the molecules of the liquid crystal material into alignment with the treated polyimide layer.

A polyimide coated liquid crystal device substrate was placed in a glow discharge device on a plate approximately 1 inch away from the electrodes. The glow discharge apparatus was evacuated to 10-5 Torr and argon was introduced into the apparatus at a pressure of 75 microns and 50 cm for 37 minutes. A power of 100 W at 13.56 MHz was supplied to the electrode for 1 minute.

A liquid crystal device substrate coated with polyimide was treated as in Example 1, except that nitrogen was used instead of argon.

Devices made according to Examples 1 and 2 above and a control device using untreated polyimide were assembled and time constants were measured for each device immediately after fabrication and after 30 minutes of exposure to a temperature of 110°C. . The measurement results are summarized in the table below.

1st period Kasumi” [Example 1 734 msec 615 msec Example 2
564 msec 426 msec comparison 5
0 msec 20 msec

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view of a recommended embodiment of this invention! 2.1
3... Substrate, 14.15... Conductor (electrode), 16
．． 17...Polyimide alignment layer.

Claims (2)

[Claims] (1) placing a transparent conductor on the surface of the substrate;
A method of manufacturing a liquid crystal device comprising the steps of: coating the conductor and substrate surface with a polyimide alignment layer; and further exposing the alignment layer to a glow discharge of an inert gas. (2) A liquid crystal material disposed between a pair of substrates, an electrode arranged on the surface of the substrate adjacent to the liquid crystal material, and a polyimide alignment layer provided covering the electrode and the surface of the substrate. 1. A liquid crystal device comprising: a polyimide alignment layer exposed to glow discharge of an inert gas.