Deane, Steven C.;

Liquid crystal displays

A method of forming an active plate for a liquid crystal display using top gate TFTs is described. A black organic light shield layer (73) is used under the TFTs to shield the channel (91) of the TFTs from light passing through a substrate (71) from below. The active plate may be a high aperture plate having pixel electrodes (99) overlapping the row and column (79) conductors. The organic light shield layer may mask the gaps (102) between pixel electrodes.

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1. An active plate for a liquid crystal display, comprising:

a transparent substrate;

top gate thin-film transistors each having a source and a drain, a channel region connecting the source and drain and a top gate over the channel;

pixel electrodes connected to the top gate thin-film transistors; and

an organic light shield layer under the thin film transistors patterned to shield at least the channel regions of the top gate thin film transistors from light passing through the transparent substrate from below; and

a planarisation layer over the organic light shield layer and under the top-gate thin-film transistors.

2. An active plate according to claim 1 further comprising row and column electrodes connected to the top gate thin-film transistors, wherein the pixel electrodes partially overlap the row and column electrodes.

3. An active plate according to claim 2 further comprising a top planarisation layer arranged over the top gate thin film transistors, wherein the top planarisation layer defines a plurality of vias over the thin film transistors and the pixel electrodes are provided on the top planarisation layer connected to the thin film transistors through the vias.

4. An active plate according to claim 1 wherein the organic light shield layer is patterned to be present under gaps between adjacent pixel electrodes to shield the gaps between the pixel electrodes from light passing through the transparent substrate from below.

5. An active matrix liquid crystal display comprising:

an active plate according to claim 1;

a passive plate; and

a layer of liquid crystal sandwiched between the active and the passive plate for modulation by the pixel electrodes.

6. A method of making an active plate for a liquid crystal display, comprising:

depositing and patterning an organic light shield layer on a transparent insulating substrate;

depositing a source, drain and channel layer above the patterned organic light shield layer;

depositing an insulating layer at least over the source, drain and channel layer to act as a gate insulator layer;

depositing and patterning a gate layer over the insulating layer, to form a plurality of thin film transistors each having a source, a drain, a channel and a gate; and

forming a pixel electrode layer connected to one of the source and drain;

wherein the organic light shield layer is patterned to shield at least the channel from light passing through the transparent substrate from below.

7. A method according to claim 6 further comprising the step of depositing a planarisation layer on the organic light shield layer.

8. A method according to claim 6 further comprising the step of forming row and column conductors connected to the top-gate thin-film transistors wherein the pixel electrodes are formed to partially overlap the row and column electrodes.

9. A method according to claim 8 further comprising depositing a top planarisation layer over the top gate thin film transistors, defining a plurality of vias over the top gate thin film transistors and depositing pixel electrodes on the top organic planarisation layer connected to the thin film transistors through the vias.

10. A method according to claim 6 including patterning the organic light shield layer to be present under the gaps between adjacent pixel electrodes to shield the gaps between the pixel electrodes from light passing through the transparent substrate from below.

11. A method of forming an active matrix liquid crystal display comprising

forming an active plate using a method according to claim 6;

providing a passive plate; and

sandwiching a layer of liquid crystal between the active and the passive plates.