US 5,576,763 AGranted

Single-polysilicon CMOS active pixel

AssigneeLucent Technologies Inc.

InventorsBryan D. Ackland, Alexander G. Dickinson, El-Sayed I. Eid, David A. Inglis

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Abstract

The single-polysilicon active pixel comprises a photo site located on a substrate for generating and storing charge carriers, the charge carriers being generated from photonic energy incident upon the photo site and semiconductor substrate, a photo gate, a transfer transistor and output and reset electronics. The gate of the transfer transistor and the photo gate are defined in a single layer of polysilicon disposed on the semiconductor substrate. The source of transfer transistor is a doped region of substrate, referred to as a coupling diffusion, which provides the electrical coupling between the photo gate and the transfer transistor. The coupling diffusion allows for the transfer of a signal stored in a photo site under the photo gate to the output electronics for processing. The single-polysilicon active pixel may be operated by biasing the transfer transistor to the low operating voltage of the pixel, for example, 0 volts. By virtue of the structure of the single-polysilicon active pixel, this mode of operation results in the same timing as if the transfer transistor were clocked, but neither a clock nor the associated driving circuitry are required. However, there is little no tendency for image lag as occurs in double polysilicon active pixels when they are operated in a manner which avoids clocking the transfer gate.

A single polysilicon CMOS active pixel for converting an optical signal to an electronic signal by applying a first collection voltage and a second transfer voltage, comprising:

a semiconductor substrate wherein charge carriers are generated from incident photonic energy;
a photo gate and a transfer transistor gate defined in a single layer of polysilicon disposed on the semiconductor substrate, the photo gate having a first and a second state wherein in the first state the first collection voltage is applied to the photo gate that causes the charge carriers to be stored in a first region within the semiconductor substrate beneath the photo gate, the stored charge carriers defining a signal, and in the second state the second transfer voltage is applied which results in movement of the charge carriers from the first region;
a transfer transistor comprising the transfer transistor gate, a first diffusion region and a second diffusion region, wherein the first diffusion region is located between the photo gate and the transfer transistor gate and functions as a source of the transfer transistor, and wherein the second diffusion region functions as a drain of the transfer transistor, the second diffusion region having a first potential and a second potential, wherein the second potential is a predetermined fixed value based on the first collection voltage and the first potential is a function of the second potential and the signal;
output electronics, electrically connected to the second diffusion region, which receives the signal from the second diffusion region and conducts the signal to processing electronics;
and
reset electronics to reset the second diffusion region to the second potential;
wherein in the first state of the transfer transistor, the transfer transistor is inactive so that the signal remains in the first region and in the second state the transfer transistor is active so that the signal flows from the first region to the first diffusion and to the output electronics.

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Facts

Application

08/344,785Filed 22 Nov 1994

Granted

19 Nov 1996

Term ends

Not estimatedThe source records don’t support an estimate.

Classification6 codes

H10F 39/803
Constructional details of image sensors: pixels having integrated switching, control, storage or amplification elements
H04N 25/76
SSIS architectures; Circuits associated therewith: addressed sensors, e.g. MOS or CMOS sensors
H10F 30/282
The devices being characterised by field-effect operation, e.g. junction field-effect phototransistors: insulated-gate field-effect transistors…
H10F 39/18
Image sensors: complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors

Abstract

Claims16