Matrix array display devices with light sensing elements and associated storage capacitors

• US 20010055008A1
• Filed: 05/22/2001
• Published: 12/27/2001
• Est. Priority Date: 06/20/2000
• Status: Active Grant

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Young, Nigel D., Shannon, John M.
• Granted Patent: US 6,738,031 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/78633 with a light shield
• CPC Class Codes: H10K 59/1216 the pixel elements being capacitors
• CPC Class Codes: H10K 59/13 comprising photosensors that control luminance

Abstract

A matrix array display device has an array of pixels (10) on a substrate (50) which each have a display element (20), for example an electroluminescent display element, and associated control circuit including a storage capacitor (36) and a light sensing element (40) connected thereto for regulating charge stored on the capacitor and responsive, for example, to light emitted from the display element so as to regulate operation of the display element. The light sensing elements (40) comprise thin film semiconductor devices each having a strip of semiconductor material (52) with laterally-spaced, doped, contact regions (53, 54) and the associated storage capacitor (36) is formed by a conductive layer (58) extending substantially transversely of the strip over one contact region with intervening dielectric material. A predetermined relationship between the storage capacitor and photosensitive device characteristics is then ensured even though dimensional variations in component layers may occur due to manufacturing tolerances. Preferably, the photosensitive device comprises a gated device whose gate extends over the semiconductor strip region intermediate the contact regions. The gate dielectric and storage capacitor dielectric may comprise parts of a common layer (56). Alternatively, the conductive layer may be provided at the side of the strip opposite the gate and used also as a shield for ambient light.

Claims

1. A matrix display device comprising on a substrate an array of addressable pixels each having a display element and a display element control circuit for controlling the operation of the display element, wherein the display element control circuit includes a charge storage capacitor and an associated thin film photosensitive semiconductor device coupled to the storage capacitor for regulating charge stored on the storage capacitor in accordance with light falling on the photosensitive device, wherein the photosensitive device comprises a strip of semiconductor material having doped contact regions laterally spaced on the substrate and an intervening region, and wherein the storage capacitor comprises a conductive layer extending substantially transversely of the semiconductor strip over one contact region thereof with a layer of dielectric material being disposed is between the conductive layer and that contact region.

2. A matrix display device according to

claim 1

, characterised in that the photosensitive device comprises a gated photosensitive device having a gate extending over the intervening region of the semiconductor strip and separated therefrom by dielectric material.

3. A matrix display device according to

claim 2

, characterised in that the gate dielectric of the photosensitive device and the dielectric material of the storage capacitor comprise portions of a common layer.

4. A matrix display device according to

claim 2

or

claim 3

, characterised in that the gated photosensitive device comprises a TFT structure having similarly doped contact regions and an intrinsic semiconductor region extending between the contact regions.

5. A matrix display device according to

claim 2

or

claim 3

, characterised in that the gated photosensitive device comprises a lateral gated pin device having oppositely doped contact regions and an intrinsic semiconductor region extending between the contact regions.

6. A matrix display device according to any one of

claims 2

to

5

, characterised in that the conductive layer of the storage capacitor is provided at the side of the semiconductor strip of the photosensitive device opposite to the gate of the photosensitive device and covers at least a part of the semiconductor strip so as to shield that part from light at that side.

7. A matrix display device according to any one of

claims 2

to

6

, characterised in that the gate of the photosensitive device is arranged to be biased such that current flow in the intervening region is due to generated photocurrent.

8. A matrix display device according to anyone of the preceding claims, characterised in that the strip of semiconductor material and the conductive layer at its part overlying the one contact region each have substantially parallel sides and extend generally at right angles to one another.

9. A matrix display device according to any one of the preceding claims, characterised in that the display element comprises a current-driven light emitting element and in that the photosensitive device is arranged to be responsive to light emitted by the display element.

10. A matrix display device according to

claim 9

, characterised in that the display element control circuit includes a drive TFT for controlling current through the display element in a drive period based on a drive signal applied to the pixel and stored as a charge on the storage capacitor, which capacitor is coupled to the gate of the drive TFT, and in that the photosensitive device is operable to regulate the charge on the storage capacitor and thereby the operation of the drive TFT.

11. A matrix device according to

claim 9

or

claim 10

, characterized in that comprises an electroluminescent display element.