Photosensor suited for image sensor

• US 4,823,178 A
• Filed: 09/26/1985
• Issued: 04/18/1989
• Est. Priority Date: 09/29/1984
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Suda, Yoshiyuki
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US06/780,598
• Time in Patent Office: 1,300 Days
• Field of Search: 357/30 K, 357/30 P, 357/30 I, 357/30 G, 357/2, 357/23.7, 357/4, 357/51, 357/31, 357/84
• US Class Current: 257/444
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 31/108 the potential barrier being of the Schottky type

Abstract

A photosensor for realizing an image sensor which can meet the requirements of high resolution, high operation speed and high signal-to-noise ratio is disclosed. The photosensor comprises a circuit substrate, a thin film transistor formed on the circuit substrate and an amorphous silicon photodiode formed on the substrate integral with the thin transistor between the drain and gate electrodes thereof. Also formed on the circuit substrate adjacent to the thin film transistor and photodiode are a charging switch element for coupling the photodiode to a DC power source to charge an inter-electrode capacitance of the photodiode, a charge storage capacitor charged by a channel current of the thin film transistor controlled by an inter-electrode capacitance voltage of the photodiode which varies in response to incident light after the inter-electrode capacitance has been charged, and a detecting switch element for coupling the capacitor to an output amplifier. The charging and detecting switch elements are each formed of a thin film transistor.

Claims

1. A photosensor comprising:

a circuit substrate;

a thin film transistor formed on said circuit substrate and having a gate electrode and drain and source electrodes forming a channel therebetween in response to a control voltage applied to said gate electrode, a channel current controlled by said control voltage flowing through said channel;

an amorphous silicon photodiode formed on said substrate integral with said thin film transistor between one of said drain and source electrodes and said gate electrode of said thin film transistor, said amorphous silicon photodiode having an inter-electrode capacitance;

charging means coupled to said photodiode for charging said inter-electrode capacitance of said photodiode; and

detecting means coupled to said thin film transistor for detecting the channel current of said thin film transistor which is controlled by a voltage across said inter-electrode capacitance of said photodiode, the voltage varying in response to incident light after said inter-electrode capacitance has been charged, said detecting means including a charge storage capacitor coupled to said thin film transistor and adapted to be charged by the channel current thereof;

an output amplifier for taking out an output signal of said photosensor; and

detecting switching element adapted to be turned on and off by an externally applied control signal to couple said charge storage capacitor to said output amplifier.

2. The photosensor according to claim 1, wherein said photodiode includes a cathode electrode;

an anode electrode formed of transparent electrical conductive film; and

hydrogenated amorphous silicon film sandwiched between said cathode and anode electrodes, said cathode and anode electrodes being electrically connected to said drain and gate electrodes of said thin film transistor, respectively.

3. The photosensor according to claim 1, wherein said photodiode includes a cathode electrode;

an anode electrode formed of transparent electrical conductive film; and

hydrogenated amorphous silicon film sandwiched between said cathode and anode electrodes, said cathode and anode electrodes being electrically connected to said gate and source electrodes of said thin film transistor, respectively.

4. The photosensor according to claim 1, wherein said charging means comprises a DC power supply;

and a charging switching element for coupling said DC power supply to said photodiode for charging said inter-electrode capacitance thereof, said charging switching element formed of a thin film transistor formed on said circuit substrate adjacent to said first-mentioned thin film transistor and photodiode, and adapted to be turned on and off by an externally supplied control signal.

5. The photosensor according to claim 1, wherein said detecting switch element is formed of a thin film transistor, and said charge storage capacitor and said detecting switching element are formed on said circuit substrate.

6. An image sensor comprising:

a circuit substrate; and

a plurality of photosensors formed in line on said circuit substrate;

each of said photosensors comprising;

a thin film transistor formed on said circuit substrate and having a gate electrode and drain and source electrodes forming a channel therebetween in response to a control voltage applied to said gate electrode, a channel current controlled by said control voltage flowing through said channel;

an amorphous silicon photodiode formed on said substrate integral with said thin film transistor between one of said drain and source electrodes and said gate electrode of said thin film transistor, said amorphous silicon photodiode having an inter-electrode capacitance;

charging means coupled to said photodiode for charging said inter-electrode capacitance of said photodiode; and

detecting means coupled to said thin film transistor for detecting the channel current flowing through said thin film transistor controlled by a voltage across said inter-electrode capacitance of said photodiode, the voltage varying in response to incident light after said inter-electrode capacitance has been charged;

said detecting means including a charge storage capacitor coupled to said thin film transistor and adapted to be charged by the channel current thereof;

an output amplifier for taking out an output signal of said photosensor; and

a detecting switching element adapted to be turned on and off by an externally applied control signal to couple said charge storage capacitor to said output amplifier.

7. A photosensor comprising:

a circuit substrate;

a thin film transistor formed on said circuit substrate and having a gate electrode and drain and source electrodes forming a channel therebetween in response to a control voltage applied to said gate electrode, a channel current controlled by said control voltage flowing through said channel;

an amorphous silicon photodiode formed on said substrate integral with said thin film transistor between one of said drain and source electrodes and said gate electrode of said thin film transistor, said amorphous silicon photodiode having an inter-electrode capacitance;

charging means coupled to said photodiode for charging said inter-electrode capacitance of said photodiode; and

detecting means coupled to said thin film transistor for detecting the channel current of said thin film transistor which is controlled by a voltage across said inter-electrode capacitance of said photodiode, the voltage varying in response to incident light after said inter-electrode capacitance has been charged;

said detecting means including a charge storage capacitor coupled to said thin film transistor and adapted to be charged by the channel current thereof;

an output amplifier for taking out an output signal of said photosensor; and

a detecting switching element adapted to be turned on and off by an externally applied control signal to couple said charge storage capacitor to said output amplifier.

8. A photosensor according to claim 7, wherein said charge storage capacitor is formed integrally with said thin film transistor between the other of said drain and source electrodes of said thin film transistor.