Active matrix display device with Schottky contact switching elements

• US 5,301,048 A
• Filed: 10/28/1992
• Issued: 04/05/1994
• Est. Priority Date: 02/07/1990
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Huisman, Frederikus R. J.
• Primary Examiner(s): Mintel, William
• Assistant Examiner(s): TRAN, MINH LOAN
• Application Number:
  US07/967,921
• Time in Patent Office: 524 Days
• Field of Search: 357/4, 357/23.7, 357/15, 357/2, 357/13, 357/58, 350/333, 350/336, 350/334, 340/784, 359/54, 359/57, 359/58, 359/60, 359/87, 257/53, 257/54, 257/449
• US Class Current: 349/24
• 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

Abstract

By arranging a Schottky diode so that it is sensitive to grazing light only in the back-bias mode, a switching element is obtained which, when used in, for example an active matrix LCD display, has a current-voltage characteristic which is comparable to that of a zener diode and can be driven in a reset mode.

Claims

1. An active matrix display device comprising

(a) an electro-optical display between two supporting plates having facing surfaces,

(b) a system of pixels defined by picture electrodes arranged in rows and columns on one of said supporting plates,

(c) a system of row and column electrodes for presenting selection and data signals to said picture electrodes,

(d) switching means between each row or column electrode and a corresponding pixel for generating a current-voltage characteristic comparable to a zener diode, said switching means including a light sensitive semiconductor material providing an anti-parallel circuit of both a forward driving Schottky diode and a photodiode providing a back-bias photo-current driven by incident light.

2. An active matrix display device according to claim 1, wherein said switching means includes said light sensitive semiconductor material in electrical contact with said each row or column electrode, a passivating layer of insulating material covering at least parts of a top surface of said semiconductor material, and an opaque electrical conductor in contact with said top surface free of said passivating layer, said opaque electrical conductor also being in contact with a corresponding picture electrode for said pixel.

3. An active matrix display device according to claim 2, wherein said opaque electrical conductor contacting said semiconductor layer provides said Schottky diode.

4. An active matrix display device according to claim 3, wherein said Schottky diode is provided in an approximately central portion of said light sensitive semiconductor material, and wherein said passivating layer covers peripheral portions of said top surface.

5. An active matrix display device according to claim 3, wherein said passivating layer has a thickness much smaller than a total length of said passivating layer on said light sensitive semiconductor material, said opaque electrical conductor covering said total length.

6. An active matrix display device according to claim 2, wherein said opaque electrical conductor is one of tungsten, molybdenum, platinum, and nickel.

7. An active matrix display device according to claim 1, wherein said light sensitive semiconductor material is amorphous silicon.

8. An active matrix display device comprising

(a) an electro-optical display between two supporting plates having facing surfaces,

(b) a system of pixels defined by picture electrodes arranged in rows and columns on one of said supporting plates

(c) a system of row and column electrodes for presenting selection and data signals to said picture electrodes,

(d) switching means between each row or column electrode and a corresponding pixel for generating a current-voltage characteristic comparable to a zener diode, said switching means including a light sensitive semiconductor material providing an anti-parallel circuit of both a forward driving Schottky diode and a photodiode providing a back-bias photo-current driven by incident light,

wherein said switching means includes said light sensitive semiconductor material in electrical contact with each said row or column electrode, a passivating layer of insulating material covering at least parts of a top surface of said semiconductor material, and an opaque electrical conductor in contact with said top surface free of said passivating layer, said opaque electrical conductor also being in contact with a corresponding picture electrode for said pixel,

wherein said opaque electrical conductor contacting said semiconductor layer provides said Schottky diode,

wherein said passivating layer has a thickness much smaller than a total length of said passivating layer on said light sensitive semiconductor material, said opaque electrical conductor covering said total length, and

wherein said photocurrent is generated at said parts of said semiconductor material beneath said passivating layer.

9. An active matrix display device comprising

(a) an electro-optical display between two supporting plates having facing surfaces,

(b) a system of pixels defined by picture electrodes arranged in rows and columns on one of said supporting plates

(c) a system of row and column electrodes for presenting selection and data signals to said picture electrodes,

(d) switching means between each row or column electrode and a corresponding pixel for generating a current-voltage characteristic comparable to a zener diode, said switching means including a light sensitive semiconductor material providing an anti-parallel circuit of both a forward driving Schottky diode and a photodiode providing a back-bias photo-current driven by incident light,

wherein said switching means includes said light sensitive semiconductor material in electrical contact with each said row or column electrode, a passivating layer of insulating material covering at least parts of a top surface of said semiconductor material, and an opaque electrical conductor in contact with said top surface free of said passivating layer, said opaque electrical conductor also being in contact with a corresponding picture electrode for said pixel, and

wherein a thin region of said light sensitive semiconductor material in electrical contact with said row or column electrode is highly doped n-type.