Solid state image sensor

• US 4,862,237 A
• Filed: 10/04/1988
• Issued: 08/29/1989
• Est. Priority Date: 01/10/1983
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Morozumi, Shinji
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/253,917
• Time in Patent Office: 329 Days
• Field of Search: 357/23.7, 357/30 I, 357/30 K, 357/41, 357/42
• US Class Current: 257/72
• CPC Class Codes: H01L 27/14665 Imagers using a photoconductor layer
• CPC Class Codes: H01L 27/14672 Blooming suppression

Abstract

A solid state image sensor including a plurality of sensing cells, each formed of a switching transistor and a thin film sensing device, arranged in a line or a matrix. The switching transistor is a thin film transistor (TFT) of polycrystalline silicon and the thin film sensing device utilizes a layer of amorphous silicon formed on a lower electrode which is electrically connected to the drain of the switching.

Claims

1. A solid state image sensor having a plurality of photo-sensitive sensing cells arranged in a line or matrix, comprising:

an insulating substrate having a plurality of photo-sensitive sensing cells arranged on the insulating substrate;

each sensing cell including a photo-sensitive member and a switching transistor electrically coupled thereto;

each photo-sensitive member formed of a lower electrode region on the insulating substrate, a thin film of photo-sensitive amorphous silicon semiconductor on the lower electrode region and an upper electrode region on the photo-sensitive film, said photo-sensitive silicon film having high photo-current and having high impedance in the dark;

each switching transistor associated with a photo-sensitive member being a thin film transistor formed by disposing a thin film of a poly-crystalline semi-conductor material forming an island of semiconductor material on the insulating substrate, said semiconductor material being selected to have high channel mobility and a low light absorption coefficient and being doped with an impurity forming a source and drain of the switching resistor and having an intrinsic channel region in the polycrystalline film having a thickness of less than 300 Å

;

one of the electrode of the photo-sensitive member being electrically coupled to one of the source and drain of the associated thin film switching transistor; and

a video signal line coupled to one of each transistor and photo-sensitive member.

2. The solid state image sensor of claim 1, wherein the thin film of photo-sensitive material is amorphous silicon.

3. The solid state image sensor of claim 1, wherein the thin film of semiconductor material of each switching transistor is polycrystalline silicon.

4. The solid state image sensor of claim 1, wherein the thin film of photo-sensitive material is amorphous silicon and the thin film semiconductor material of each switching transistor is polycrystalline silicon

5. The solid state image sensor of claim 1, wherein the thin film photo-sensitive material is selected from the group consisting of Zn-Se, Cd-Te, Se-As-Te and Si.

6. The solid state image sensor of claim 1, wherein the insulating substrate is formed of glass.

7. The solid state image sensor of claim 1, wherein the drain region of the switching transistor is enlarged, an insulating layer is disposed over the enlarged drain region and the thin film of photo-sensitive material is disposed over the insulator, said photo-sensitive film and drain region functioning as a capacitor.

8. The solid state image sensor of claim 1, further including peripheral circuit means for scanning the gate of each switching transistors for selecting the sensing cells, said peripheral circuit means is a C-MOS circuit formed on the substrate by depositing a thin film semiconductor material on said substrate.

9. The solid state image sensor of claim 1, wherein the video signal line is coupled to each transistor.

10. The solid state image sensor of claim 1, wherein the video signal line is coupled to each photo-sensitive member.

11. The solid state image sensor of claim 1, wherein the photo-sensitive member includes a transistor having a source electrode, drain electrode and gate electrode, the gate electrode being electrically coupled to one of the source and drain electrodes forming the upper electrode region and the lower electrode region.

12. The solid state image sensor of claim 11, wherein the source-drain path of the transistor forming the photo-sensitive member is coupled in series with the source-drain path of the switching transistor.

13. The solid state image sensor of claim 11, wherein the switching transistor is turned on by a signal applied to its gate electrode causing a bias voltage to be applied to the photo-sensitive member placing the photo-sensitive member in a charged state.

14. The solid state image sensor of claim 13, wherein light contacting the charged photo-sensitive member causes the photo-sensitive member to discharge from its charged state when the switching transistor is turned off.

15. The solid state image sensor of claim 13, wherein the photo-sensitive member is recharged when the switching transistor is turned on after the photo-sensitive member has been exposed to light, the recharging current going to the video line and being detected as a video signal.

16. A solid state image sensor having a plurality of photo-sensitive sensing cells arranged in a line or matrix, comprising:

a substrate having a plurality of photo-sensitive sensing cells arranged on the substrate;

each sensing cell including a photo-sensitive member and a switching transistor electrically coupled thereto;

each photo-sensitive member formed of a lower electrode on the substrate, a thin film of a photo-sensitive amorphous semiconductor material on the lower electrode and an upper electrode on the photo-sensitive film, said photo-sensitive material having high photo-current and having high impedance in the dark;

each switching transistor associated with a photo-sensitive member being a thin film transistor formed by disposing a thin film of a polycrystalline semiconductor material on the substrate, said semiconductor material being selected to have high channel mobility and a low light absorption coefficient;

one of the electrodes of the photo-sensitive member being electrically coupled to one of the source and drain of the associated thin film switching transistor; and

a video signal line coupled to one of each transistor and photo-sensitive member, wherein the drain region of the switching transistor is enlarged, a first insulating layer is disposed over the enlarged drain region, a conductive layer is disposed over the first insulating layer, a second insulating layer is disposed on the conductive layer, and a thin film of photo-sensitive material is disposed on the second insulating layer, said conductive layer and drain region functioning as a capacitor.

17. A solid state image sensor having a plurality of photo-sensitive sensing cells arranged in a line or matrix, comprising:

a substrate having a plurality of photo-sensitive sensing cells arranged on the substrate;

each sensing cell including a photo-sensitive member and a switching transistor electrically coupled thereto;

each photo-sensitive member is a transistor formed with a first photo-sensitive semiconductor thin film formed and patterned on the substrate into first source, first drain and first channel regions, a gate insulating layer disposed on the first thin film, a first gate electrode formed on top of the gate insulating layer so as to overlie the first channel region, the first channel region being the photo-sensitive element and the parasitic capacitance between the first gate electrode and one of the first drain and first source being used to store the photo-excited charges; and

each switching transistor is formed on the substrate with said first photo-sensitive semi-conductor thin film formed and patterned into second source, drain and channel regions, one of the first source and drain regions being coupled to one of the second source and drain regions, said gate insulating layer formed to overlie at least the second channel region of the first semiconductor thin film, a second gate electrode on top of the gate insulating film so as to overlie the second channel region, and a light protection layer being formed above the second gate electrode so as to overlie the second channel region so that the switching transistor is insensitive to incident light.

18. The solid state image sensor of claim 17, and including a video signal line coupled to one of each switching transistor and photo-sensitive member.