Displays controlled by MIM switches of small capacitance

• US 4,413,883 A
• Filed: 12/03/1980
• Issued: 11/08/1983
• Est. Priority Date: 05/31/1979
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Baraff, David R., Streater, Richard W., Serinken, Nur M., Westwood, William D., MacLaurin, Blair K., Miner, Carla J., Boynton, Robert J.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Lewis, David
• Application Number:
  US06/212,271
• Time in Patent Office: 1,070 Days
• Field of Search: 350/332, 350/333, 350/334, 350/339, 350/356, 350/357
• US Class Current: 349/51
• CPC Class Codes: G02F 1/1365 in which the switching element is a two-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G09G 3/367 with a nonlinear element in series with the liquid crystal cell, e.g. a diode, or M.I.M. element
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A matrix multiplexed field effect display has switch devices at matrix crosspoints to provide a turn-on threshold for the field effect material. The switch devices are thin film metal-insulator-metal (MIM) switches. The display is operated at low current so that the MIM switches, which may be deposited on glass, do not degrade rapidly in use.

Claims

1. A matrix multiplexed display comprising a pair of plates, at least one of the plates being transparent, the plates having sealed therebetween a layer of liquid characterized by electric field dependent optical transmissivity, a first plurality of electrodes on an inside surface of one plate and a second plurality of electrodes on an inside surface of the other plate, the display having a plurality of picture elements, each element defined by a pair of opposed electrodes on the inside surfaces of respective plates, means for applying a voltage between the opposed electrodes of each element, each picture element being series connected to a respective switch comprising a thin insulating film flanked by thin film conducting layers, the insulating film characterized by a gross change in resistivity at a predetermined voltage thereacross, the switches formed on the inside surface of at least one of the plates, each switch having a capacitance substantially less than the capacitance of its series connected picture element.

2. A matrix multiplexed display as claimed in claim 1 in which each switch is substantially smaller in area than the picture element controlled thereby.

3. A matrix multiplexed display as claimed in claim 2 in which each switch is laterally offset from the picture element controlled thereby.

4. A matrix multiplexed display as claimed in claim 2 in which each picture element and its series connected switch are superimposed, one picture element electrode having a part extending therefrom to provide a relatively small contact area with the switch insulating film.

5. A matrix multiplexed display as claimed in claim 1 in which on the inside of at least one of the plates, a thin film capacitor is formed in parallel with each picture element.

6. A matrix multiplexed display as claimed in claim 1 the picture elements and the switches being arranged in rows and columns, first lead means electrically connecting the thin film conducting layer at one side of each switch to an electrode of its series connected picture element, second lead means electrically connecting the thin film conducting layer at the other side of the switches in rows, and third lead means electrically connecting the electrodes on the other plate in columns.

7. A matrix multiplexed display as claimed in claim 1 in which the thin film conducting layer at said one side of each switch is formed as a single homogeneous substantially transparent layer with an electrode of its series connected picture element.

8. A matrix multiplexed display as claimed in claim 1 in which the insulating film of each switch is one of a group consisting of tantalum pentoxide, silicon dioxide, silicon oxynitride, silicon monoxide and zinc oxide.

9. A matrix multiplexed display as claimed in claim 1 in which the thin film conducting layer of at least one side of each switch is one of a group consisting of tantalum, aluminum, chromium, gold, indium tin oxide, and NiCr+Au.

10. A matrix multiplexed display as claimed in claim 1 in which each switch is a tantalum-tantalum pentoxide-gold device.

11. A matrix multiplexed display as claimed in claim 1 in which each switch is an aluminum-aluminum oxide-gold device.

12. A matrix multiplexed display as claimed in claim 1 in which the liquid is a liquid crystal.

13. A matrix multiplexed display as claimed in claim 12 in which the liquid crystal is a twisted nematic liquid crystal and the plates confining the liquid crystal are crossed polarizing plates.

14. A matrix multiplexed display as claimed in claim 12 in which the liquid crystal is in combination with a pleochroic dye.

15. A matrix multiplexed display as claimed in claim 1 in which said liquid is an electophoretic display medium.

16. A matrix multiplexed display as claimed in claim 1 in which said gross change in resistivity of said insulating layer results from a tunnelling mechanism.

17. A matrix multiplexed display as claimed in claim 1 in which said gross change in resistivity of the insulating layer results from a trap depth modulation mechanism.

18. A matrix multiplexed display as claimed in claim 1 in which the gross change is resistivity of said insulating layer results from the combination of a tunnelling mechanism and a trap depth modulation mechanism.

19. A matrix multiplexed display as claimed in claim 1 in which the picture elements and switches are arranged in rows and columns, the metal layer at one side of each switch being in the form of first and second distinct regions, first lead means for electrically connecting each of said first regions to a series connected picture element, second lead means for electrically connecting said second regions together in rows, and third lead means electrically connecting the electrodes on the other plate in columns.

24. A matrix multiplexed display as claimed in claim 1 in which at least one of the thin film conducting layers is a thin film metal layer.

20. In a method of fabricating a display, the steps of:

depositing onto a transparent plate a row-column array of thin film metal regions, each region constituting a first terminal of a switch;

anodizing said metal regions thereby forming a dielectric layer on said metal regions;

forming a thin film conducting region over said anodized regions, the conducting regions forming a second terminal of respective switches;

forming a corresponding array of transparent electrodes on the plate;

forming a plurality of thin film leads parallel to the rows;

forming thin film interconnects between one terminal of each switch and the electrode adjacent thereto;

forming thin film interconnects between the other terminal of each switch and the row leads whereby to interconnect the switches in rows;

forming a corresponding array of transparent electrodes on a second transparent plate;

forming a plurality of thin film leads parallel to the columns on the second plate;

forming thin film interconnects between the electrodes and the column leads to interconnect the electrodes on said second plate in columns; and

sealing between the plates a liquid having electic field related optical characteristics.

22. A method as claimed in claim 20 or 21 in which at least some of the conducting regions electrically connected to the second terminal of each switch are deposited simultaneously as a single homogeneous layer.

23. A method as claimed in claim 20 in which at least some of the conducting regions electrically connected to the first terminal of each switch are deposited simultaneously as a single homogenous layer.

21. In a method of fabricating a display the steps of:

depositing onto one transparent plate a row-column array of thin film metal regions, each region constituting first terminals of a pair of switches;

anodizing said metal region;

forming spaced conducting regions on each anodized region, the conducting regions forming second terminals of the pair of switches;

forming a corresponding array of transparent electrodes on the plate;

forming a plurality of thin film leads parallel to the rows;

forming thin film interconnects between the second terminal of one switch of each pair and the electrode adjacent thereto;

forming thin film interconnects between the second terminal of the other switch of each pair a lead adjacent thereto whereby to interconnect the switches in rows;

forming a corresponding array of transparent electrodes on a second transparent plate;

forming a plurality of thin film leads parallel to the column;

forming thin film interconnects between the electrodes and the column leads to interconnect the electrodes in columns on the second plate; and

sealing between the plates a liquid having electric field related optical characteristics.