Liquid crystal display assembly having dielectric coated electrodes

• US 3,932,026 A
• Filed: 05/27/1975
• Issued: 01/13/1976
• Est. Priority Date: 11/03/1972
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Sprokel, Gerard J.
• Primary Examiner(s): Bauer, Edward S.
• Application Number:
  US05/580,635
• Time in Patent Office: 231 Days
• Field of Search: 350/160 LC
• US Class Current: 349/138
• CPC Class Codes: G02F 1/133345 Insulating layers G02F1/1335, G02F1/1337, G02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/1375 using dynamic scattering

Abstract

A display assembly in which a nematic liquid crystal is sandwiched between two supporting substrates. Each substrate has a layer of a conductive coating on the inside surface, at least one of which is overcoated with a dielectric film or layer to separate the conductive layer from the liquid crystal material. Embodiments include varied thicknesses of the dielectric in association with image and lead portions of the conductive coating.

Claims

1. A liquid crystal cell comprising:

A. first and second spaced electrodes;

B. a dielectric coating on the inner face of said first electrode;

C. a nematic liquid crystal material between said coating and the said second electrode, with said coating separating said liquid crystal material from said first electrode; and

D. means for applying a voltage of predetermined magnitude and frequency across said first and second electrodes to cause dynamic scattering of said liquid crystal material;

wherein

E. said dielectric coating is of at least two different thicknesses characterized with a corresponding number of breakdown voltages therefor; and

F. said voltage applying means controllably supplies a voltage with a frequency of zero and at magnitudes above selected ones of said breakdown voltages.

2. The liquid crystal cell of claim 1 wherein said second electrode is transparent.

3. The liquid crystal cell of claim 2 wherein said first electrode and said coating are transparent.

4. The liquid crystal cell of claim 1 including parallel first and second support plates with the inner face of said first plate having said first electrode coated thereon;

and the inner face of said second plate having said second electrode coated thereon.

5. The liquid crystal cell of claim 4 wherein said second electrode comprises a transparent conductive coating on said second plate, and said second plate is transparent.

6. The liquid crystal cell of claim 4 wherein said first electrode comprises a transparent conductive coating on said first plate;

and wherein said first plate and said dielectric coating are transparent.

7. The liquid crystal cell of claim 6 wherein said second electrode comprises a transparent conductive coating on said second plate, and said second plate is transparent.

8. A liquid crystal cell comprising:

A. first and second spaced electrodes;

B. a dielectric coating on the inner face of said first electrode;

C. a nematic liquid crystal material between said coating and the said second electrode, with said coating separating said liquid crystal material from said first electrode; and

D. means for applying a voltage of predetermined magnitude and frequency across said first and second electrodes to cause dynamic scattering of said liquid crystal material;

wherein

E. said dielectric coating is of at least two different thicknesses, each characterized with a corresponding capacitance forming, in combination with the resistance of said liquid crystal material, a corresponding number of different threshold frequencies for said cell, at least one of which is below the cut-off frequency of said liquid crystal material; and

F. said voltage applying means supplies an A.C. voltage operable at frequencies between the lowest of said threshold frequencies and said cutoff frequency.

9. The liquid crystal cell of claim 8 wherein said second electrode is transparent.

10. The liquid crystal cell of claim 9 wherein said first electrode and said coating are transparent.

11. The liquid crystal cell of claim 8 including a pair of parallel first and second support plates with the inner face of said first plate having said first electrode coated thereon;

and the inner face of said second plate having said second electrode coated thereon.

12. The liquid crystal cell of claim 11 wherein said second electrode comprises a transparent conductive coating of said second plate, and said second plate is transparent.

13. The liquid crystal cell of claim 11 wherein said second electrode comprises a transparent conductive coating on said first plate;

and wherein said first plate and said dielectric coating are transparent.

14. The liquid crystal cell of claim 13 wherein said second electrode comprises a transparent conductive coating on said second plate, and said second plate is transparent.

15. A liquid crystal cell comprising:

A. first and second spaced electrodes;

B. a dielectric coating on the inner face of said first electrode;

C. a nematic liquid crystal material between said coating and said second electrode, with said coating separating said material from said first electrode;

D. with said first electrode comprising an image portion connected to a lead portion,

E. said dielectric coating comprising

a. a thin first coating portion over said image portion and having a thickness characterized by a capacitance forming in conjunction with the resistance of said liquid crystal material, a first threshold frequency below the imaging frequency cut-off of said liquid crystal material, and

b. a relatively thicker second portion over said lead portion having a thickness characterized by a capacitance forming in conjunction with said resistance of said liquid crystal material, a second threshold frequency above said first threshold frequency, and

F. means for applying an alternating voltage

a. below the breakdown voltage of said coating,

b. across said first and second electrodes, operable at

c. frequencies between said first threshold frequency and the cut-off frequency of said liquid crystal material.

16. A liquid crystal display assembly comprising a layer of nematic liquid crystal material having one face disposed in contacting relationship adjacent a dielectric layer, and voltage means for applying a voltage of predetermined magnitude and frequency to cause dynamic scattering of said liquid crystal material, and including:

A. a first electrode having said dielectric layer coated thereon and comprising an image electrode portion and a lead electrode portion with said dielectric layer comprising

a. a first coating portion over said image portion and having a thickness characterized by a capacitance forming, in conjunction with the resistance of said liquid crystal material, a first threshold frequency below the imaging frequency cut-off of said liquid crystal material, and

b. a relatively thicker second coating portion over said lead portion and having a thickness characterized by a capacitance forming, in conjunction with said resistance of said liquid crystal material, a second threshold frequency above said first threshold frequency,

B. a second electrode disposed adjacent the opposite face of the said liquid crystal layer, with said voltage means applied across said first and second electrodes below the breakdown voltage of said first dielectric portion and at a frequency

C. between said first threshold frequency and the said cut-off frequency of said liquid crystal material.

17. A liquid crystal display assembly comprising:

A. first and second spaced electrodes with at least one of said electrodes comprising an image portion and a connected lead portion;

B. first and second dielectric coatings on the innerfaces of respective ones of said first and second electrodes with at least one of said dielectric coatings comprising

a. a thin first coating portion in register and coextension with said image portion and having a thickness characterized by a capacitance forming, in combination with the resistance of said liquid crystal material, a first threshold frequency below the imaging frequency cut-off of said liquid crystal material,

b. and a relatively thicker second coating portion in register and coextension with said lead portion, and having a thickness characterized by a capacitance forming, in conjunction with said resistance of said liquid crystal material, a second threshold frequency above said first threshold frequency;

C. a nematic liquid crystal material between said coatings with said coatings separating said liquid crystal material from their respective electrodes; and

D. means for applying an alternating voltage of predetermined amplitude and frequency

a. below the breakdown voltage of said coatings,

b. across said first and second electrodes

c. and with said frequency being in a range between said first threshold frequency and said cutoff frequency of said liquid crystal.

18. A device comprising:

A. spaced dielectric substrates at least one of which is transparent;

B. spaced electrodes between adjacent surfaces of said substrates for generating an electric potential therebetween;

C. a dielectric film overcoated on at least one of said electrodes;

D. a nematic liquid crystal material disposed between said electrodes;

E. means for applying an electric signal of predetermined magnitude and frequency to said electrode means to cause dynamic scattering in said liquid crystal material;

wherein

F. one of said electrodes comprises an image portion and a lead portion;

with

G. said dielectric film including at least

a. one film portion in register with said image portion and having a thickenss characterized by a capacitance forming, in conjunction with the resistance of said liquid crystal material, a first threshold frequency below the imaging frequency cut-off of said liquid crystal material, and

b. A second film portion in register with said lead means and having a thickness characterized by a capacitance forming, in conjunction with said resistance of said liquid crystal material, a second threshold frequency above said first threshold frequency and below said imaging frequency cut-off of said liquid crystal material; and

H. said signal is AC below the breakdown voltage of said thin dielectric film portion and operable at frequencies between said first threshold frequency and said cut-off frequency of said liquid crystal material.