Liquid crystal display with transparent storage capacitors for holding electric charges

• US 5,724,107 A
• Filed: 09/26/1995
• Issued: 03/03/1998
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Shimada, Toshio, Nishikawa, Ryuji
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Malinowski, Walter J.
• Application Number:
  US08/534,109
• Time in Patent Office: 889 Days
• Field of Search: 359/59, 359/67, 349/38, 349/39, 349/137, 349/110, 349/111, 349/187
• US Class Current: 349/38
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode

Abstract

A storage capacitor is constituted by a storage capacitor electrode, made of a transparent and conductive film extending substantially all over a substrate, and pixel electrodes overlapping with the storage capacitor electrode via an interlevel insulation layer. The storage capacitor holds charges. The storage capacitor electrode is positioned such that it faces the entire surface of the pixel electrodes. Since the transparent and conductive storage capacitor electrode does not reduce the aperture ratio, the storage capacitor can have a large capacitance. A signal voltage applied to the storage capacitor electrode is determined so as not to activate the thin film transistors which are not selected. A light-shielding layer is present at a position between pixel electrodes on or under the storage capacitor electrode. The light-shielding layer shields the thin film transistors, gate lines and drain lines from incident light, thereby preventing reduction of contrast of displayed pictures. Further, an anti-reflection layer formed by heat treatment is placed on a boundary between the storage capacitor electrode and the light-shielding layer, and is effective in assuring visibility of the picture on the liquid crystal display.

Claims

1. A liquid crystal display comprising a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween, wherein:

the first substrate includes thereon;

a plurality of pixel electrodes arranged in a matrix array;

drain lines formed between columns of the pixel electrodes;

gate lines formed between rows of the pixel electrodes;

thin film transistors, each of said thin film transistors having a source electrode connected to a respective one of the pixel electrodes, a drain electrode connected to a respective one of said drain lines, and a gate electrode connected to a respective one of said gate lines;

a first light-shielding layer having a first aperture shielding light between the pixel electrodes;

a storage capacitor electrode opposed to the pixel electrodes with an interlevel insulation layer interposed therebetween, said storage capacitor electrode being a transparent conductive layer disposed substantially all over the first substrate including under each of said thin film transistors; and

storage capacitors holding charges, the storage capacitors formed in an area where the pixel electrodes are opposed to the storage capacitor electrode; and

the second substrate includes a common electrode extending substantially all over an area where the first and second substrates face each other.

2. The liquid crystal display of claim 1, wherein the second substrate includes a second light-shielding layer at a position corresponding to the first light-shielding layer, and the second light-shielding layer has a second aperture larger than the first aperture of the first light-shielding layer.

3. The liquid crystal display of claim 1, wherein said storage capacitor electrode extends substantially all over the first substrate except at a peripheral edge portion thereof.

4. The liquid crystal display of claim 1, wherein the first light-shielding layer is formed on the storage capacitor electrode.

5. The liquid crystal display of claim 4, wherein the storage capacitor electrode is made of an oxide alloy of indium and tin, the first light-shielding layer is made of chromium, and an anti-reflection layer made of chromium oxide is formed on a boundary between the first light-shielding layer and the storage capacitor electrode by heat treatment after formation of the storage capacitor electrode and the first light-shielding layer.

6. The liquid crystal display of claim 1, wherein the first light-shielding layer is formed under the storage capacitor electrode, the storage capacitor electrode is made of an oxide alloy of indium and tin, the first light-shielding layer is made of chromium, and an anti-reflection layer made of chromium oxide is formed on a boundary between the first light-shielding layer and the storage capacitor electrode by heat treatment after formation of the storage capacitor electrode and the first light-shielding layer.

7. The liquid crystal display of claim 1, wherein an interlevel insulation layer and a semiconductor layer are formed under the gate lines, said thin film transistors each have:

said source electrode formed by a part of said respective one of said pixel electrodes,

said drain electrode formed by a part of said respective one of said drain lines,

a channel layer formed by a part of the semiconductor layer positioned at an area where the source electrode and the drain electrode lie adjacent to each other,

a gate interlevel insulation layer formed by a part of the interlevel insulation layer extending over the channel layer, and

said gate electrode formed by a part of said respective one of said gate lines positioned on the gate interlevel insulation layer, and

the gate lines, the interlevel insulation layer and the semiconductor layer are identically patterned.

8. The liquid crystal display of claim 7, wherein the voltage of the storage capacitor signal applied to the storage capacitor electrode is determined such that when a respective one of said thin film transistors is not selected, a first potential difference between the drain electrode of said respective one of the thin film transistors and the storage capacitor electrode and a second potential difference between the source electrode of said respective one of the thin film transistors and the storage capacitor electrode are both smaller than a threshold voltage of the thin film transistors.

9. The liquid crystal display of claim 8, wherein a first voltage of the storage capacitor electrode signal is level-shifted from a second voltage of a common electrode signal applied to the common electrode.

10. The liquid crystal display of claim 7, wherein the storage capacitor electrode extends to a vicinity of an end of the first substrate, and is opposed to an input terminal electrode via the interlevel insulation layer, and a desired signal applied to the input terminal electrode controls a voltage of the storage capacitors.

11. A liquid crystal display comprising a first substrate and a second substrate facing each other with a liquid crystal layer interposed therebetween, wherein:

the first substrate includes thereon;

a plurality of pixel electrodes arranged in a matrix array;

drain lines formed between columns of the pixel electrodes;

gate lines formed between rows of the pixel electrodes;

thin film transistors, each of said thin film transistors having a source electrode connected to a respective one of the pixel electrodes, a drain electrode connected to a respective one of said drain lines, a semiconductor layer having first and second end regions connected to the source electrode and the drain electrode, respectively, an insulation layer formed on the semiconductor layer, and a gate electrode connected to a respective one of the gate lines and formed on the semiconductor layer with the insulation layer interposed therebetween, stacked in this order;

a first light-shielding layer shielding light between the pixel electrodes;

storage capacitor electrodes opposing the pixel electrodes with an interlevel insulation layer interposed therebetween, said storage capacitor electrodes being a transparent conductive layer applied practically all over the first substrate; and

storage capacitors holding charges, the storage capacitors being formed in an area where the pixel electrodes and the storage capacitor electrodes overlap with one another; and

the second substrate includes a common electrode extending substantially all over an area where the first and second substrates face each other.

12. A method for making a liquid crystal display having a first substrate and a second substrate sandwiching a liquid crystal layer, the method comprising:

forming a transparent conductive storage capacitor layer covering substantially an entire upper surface of said first substrate except for a first peripheral edge portion of said first substrate;

forming a first light-shielding layer on said transparent conductive storage capacitor layer, said first light-shielding layer patterned to have a first aperture;

forming an interlevel insulation layer on said transparent conductive storage capacitor layer and said first light-shielding layer;

forming a transparent conductive electrode layer on said interlevel insulation layer;

patterning said transparent conductive electrode layer to form a plurality of pixel electrodes, a plurality of source electrodes integral with said pixel electrodes, a plurality of drain lines between columns of said pixel electrodes, a plurality of drain electrodes integral with said drain lines, and an input terminal electrode on part of said first peripheral edge portion of said first substrate;

forming a semiconductor layer on said patterned transparent conductive electrode layer;

forming a gate insulating layer on said semiconductor layer;

forming a gate conductive layer on said gate insulating layer; and

patterning said semiconductor layer, said gate insulating layer and said gate conductive layer to form a plurality of gate lines between rows of said pixel electrodes and a plurality of gate electrodes integral with said gate lines.

13. The method of claim 12, wherein said semiconductor layer includes amorphous silicon, said transparent conductive electrode layer includes phosphorus, and said phosphorus diffuses into said semiconductor layer forming an n-conductivity type amorphous silicon layer at a boundary between said transparent conductive electrode layer and said semiconductor layer.

14. The method of claim 12, wherein said transparent conductive storage capacitor layer includes an oxide alloy of indium and tin, said first light-shielding layer includes chromium, and an anti-reflection layer including chromium oxide is formed at a boundary between said transparent conductive storage capacitor layer and said first light-shielding layer by a heat treatment following said forming of said patterned first light-shielding layer.

15. The method of claim 12 including:

forming a second light-shielding layer on said second substrate, said second light-shielding layer patterned to have a second aperture opposite to said first aperture, said second aperture larger than said first aperture; and

forming a transparent conductive common electrode layer on said second light-shielding layer and said second substrate, said transparent conductive common electrode layer covering said second light-shielding layer and all portions of a lower surface of said second substrate not covered by said second light-shielding layer, except for a second peripheral edge portion of said second substrate.

16. The method of claim 15 including:

forming a first orientation layer on said patterned gate conductive layer, gate insulation layer, semiconductor layer, said patterned transparent conductive electrode layer and said interlevel insulation layer; and

forming a second orientation layer on said transparent conductive common electrode layer.

17. The method of claim 16 including:

bonding said first substrate to said second substrate by a sealant with said first orientation layer facing said second orientation layer; and

filling a space between said first orientation layer and said second orientation layer with said liquid crystal layer.

18. A method for making a liquid crystal display having a first substrate and a second substrate sandwiching a liquid crystal layer, the method comprising:

forming a first light-shielding layer on said first substrate, said first light-shielding layer patterned to have a first aperture;

forming a transparent conductive storage capacitor layer entirely covering said first light-shielding layer and all portions of an upper surface of said first substrate not covered by said first light-shielding layer, except for a first peripheral edge portion of said first substrate;

forming an interlevel insulation layer on said transparent conductive storage capacitor layer;

forming a transparent conductive electrode layer on said interlevel insulation layer;

patterning said transparent conductive electrode layer to form a plurality of pixel electrodes, a plurality of source electrodes integral with said pixel electrodes, a plurality of drain lines between columns of said pixel electrodes, a plurality of drain electrodes integral with said drain lines, and an input terminal electrode on part of said first peripheral edge portion of said first substrate;

forming a semiconductor layer on said patterned transparent conductive electrode layer;

forming a gate insulating layer on said semiconductor layer;

forming a gate conductive layer on said gate insulating layer; and

patterning said semiconductor layer, said gate insulating layer and said gate conductive layer to form a plurality of gate lines between rows of said pixel electrodes and a plurality of gate electrodes integral with said gate lines.

19. The method of claim 18, wherein said semiconductor layer includes amorphous silicon, said transparent conductive electrode layer includes phosphorus, and said phosphorus diffuses into said semiconductor layer forming an n-conductivity type amorphous silicon layer at a boundary between said transparent conductive electrode layer and said semiconductor layer.

20. The method of claim 18, wherein said transparent conductive storage capacitor layer includes an oxide alloy of indium and tin, said first light-shielding layer includes chromium, and an anti-reflection layer including chromium oxide is formed at a boundary between said transparent conductive storage capacitor layer and said first light-shielding layer by a heat treatment following said forming of said transparent conductive storage capacitor layer.

21. The method of claim 18 including:

forming a second light-shielding layer on said second substrate, said second light-shielding layer patterned to have a second aperture opposite to said first aperture, said second aperture larger than said first aperture; and

forming a transparent conductive common electrode layer on said second light-shielding layer and said second substrate, said transparent conductive common electrode layer entirely covering said second light-shielding layer and all portions of a lower surface of said second substrate not covered by said second light-shielding layer, except for a second peripheral edge portion of said second substrate.

22. The method of claim 21 including:

forming a first orientation layer on said patterned gate conductive layer, gate insulation layer, semiconductor layer, said patterned transparent conductive electrode layer and said interlevel insulation layer; and

forming a second orientation layer on said transparent conductive common electrode layer.

23. The method of claim 22 including:

bonding said first substrate to said second substrate by a sealant with said first orientation layer facing said second orientation layer; and

filling a space between said first orientation layer and said second orientation layer with said liquid crystal layer.

24. A liquid crystal display having a first substrate and a second substrate sandwiching a liquid crystal layer, said liquid crystal display comprising:

a first light-shielding layer formed on said first substrate, said first light-shielding layer patterned to have a first aperture;

a transparent conductive storage capacitor layer formed entirely covering said first light-shielding layer and all portions of an upper surface of said first substrate not covered by said first light-shielding layer, except for a first peripheral edge portion of said first substrate;

an interlevel insulation layer formed on said transparent conductive storage capacitor layer;

a transparent conductive electrode layer formed on said interlevel insulation layer, said transparent conductive electrode layer patterned to form a plurality of pixel electrodes, a plurality of source electrodes integral with said pixel electrodes, a plurality of drain lines between columns of said pixel electrodes, a plurality of drain electrodes integral with said drain lines, and an input terminal electrode on part of said first peripheral edge portion of said first substrate;

a semiconductor layer formed on said patterned transparent conductive electrode layer;

a gate insulating layer formed on said semiconductor layer; and

a gate conductive layer formed on said gate insulating layer, wherein said semiconductor layer, said gate insulating layer and said gate conductive layer are patterned to form a plurality of gate lines between rows of said pixel electrodes and a plurality of gate electrodes integral with said gate lines.