Reflective liquid crystal display device having an array of display pixels

• US 6,441,873 B2
• Filed: 09/27/1999
• Issued: 08/27/2002
• Est. Priority Date: 10/02/1998
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Young, Nigel D.
• Primary Examiner(s): TON, MINH TOAN T
• Application Number:
  US09/406,647
• Publication Number:
  US 20010013913A1
• Time in Patent Office: 1,065 Days
• Field of Search: 349/42, 349/43, 257/59, 257/72
• US Class Current: 349/43
• CPC Class Codes: G02F 1/133345 Insulating layers G02F1/1335, G02F1/1337, G02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/136227 Through-hole connection of the pixel electrode to the active element through an insulation layer
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence

Abstract

In a reflective liquid crystal display device comprising on a substrate an array of reflective pixel electrodes which are each connected to the output of a respective switching device, e.g. a TFT, carried on the substrate and which are provided on an insulating layer that extends over the switching device, each pixel electrode is connected to the output of its associated switching device through a plurality of tapered contact openings in the insulating layer which form depressions in the pixel electrode surface for enhancing the pixel'"'"'s light reflection characteristics. The number, shape, size and relative disposition of such openings can be varied to tailor these characteristics. Preferably, a conductive layer extends from the switching device output beneath the area of the pixel electrode for contacting the electrode at each opening and may have a rough surface resulting in asperities at the pixel electrode surface which further enhance its reflection properties.

Claims

1. A reflective liquid crystal display device comprising first and second substrates between which liquid crystal material is disposed and electrodes provided on the substrates defining an array of display pixels, the first substrate having an array of optically reflective pixel electrodes each of which is connected to an output of a respective switching device carried on the first substrate and is provided on a single surface of an insulating layer extending over the first substrate and covering the switching devices, characterized in that the respective pixel electrode is connected to the output of the switching device via a plurality of mutually separate contact openings in the insulating layer at spaced locations over an area of the respective pixel electrode and the contact openings having sloping sidewalls over which the respective pixel electrode extends and all portions of the respective pixel electrode extending over the sidewalls separated from each other only by portions of the insulating layer.

2. A reflective liquid crystal display device according to claim 1, characterised in that the contact openings are arranged regularly over a substantial part of the pixel electrode area.

3. A reflective liquid crystal display device according to claim 2, characterised in that the contact openings of each pixel are of substantially identical size and shape.

4. A reflective liquid crystal display device according to claim 2, characterized in that the respective pixel electrode contacts, via the plurality of contact openings, an electrically conductive layer which electrically conductive layer extends beneath the insulating layer over the area occupied by the plurality of contact openings and is connected to the switching device output.

5. A reflective liquid crystal display device according to claim 2, characterised in that the contact openings are arranged in rows and columns.

6. A reflective liquid crystal display device according to claim 5, characterised in that the contact openings of each pixel are of substantially identical size and shape.

7. A reflective liquid crystal display device according to claim 1, characterized in that the respective pixel electrode contacts, via the plurality of contact openings, an electrically conductive layer which electrically conductive layer extends beneath the insulating layer over the area occupied by the plurality of contact openings and is connected to the switching device output.

8. A reflective liquid crystal display device according to claim 7, characterised in that the electrically conductive layer has a rough surface so as to form surface asperities in the pixel electrodes via the insulating layer extending thereover.

9. A reflective liquid crystal display device according to claim 8, characterised in that the switching device comprises a thin film transistor and in that the electrically conductive layer comprises an integrally formed extension of a drain electrode of the thin film transistor.

10. A reflective liquid crystal display device according to claim 7, characterised in that the switching device comprises a thin film transistor and in that the electrically conductive layer comprises an integrally formed extension of a drain electrode of the thin film transistor.