United States Patent
US Patent 6498331: Method and apparatus for achieving uniform low…
US 6498331 · granted 2002-12-24
Abstract
An apparatus and method for achieving uniform low dark currents with CMOS photodiodes. A threshold voltage of a reset FET is set to an appropriate value such that the dark current from a photodiode is actively removed through the reset FET during signal integration. This reduces the dark current by over 3 orders of magnitude as compared to conventional active pixel sensors, without requiring pinned photodiodes.
| Patent Number | 6498331 |
|---|---|
| Title | Method and apparatus for achieving uniform low dark current with CMOS photodiodes |
| Filed | 1999-12-21 |
| Granted | 2002-12-24 |
| Inventor(s) | Kozlowski; Lester J., Mann; Richard A. |
| Assignee | Pictos Technologies, Inc. |
| Number of Claims | 23 |
Abstract
An apparatus and method for achieving uniform low dark currents with CMOS photodiodes. A threshold voltage of a reset FET is set to an appropriate value such that the dark current from a photodiode is actively removed through the reset FET during signal integration. This reduces the dark current by over 3 orders of magnitude as compared to conventional active pixel sensors, without requiring pinned photodiodes.
Claim 1
An apparatus for reducing dark current associated with a CMOS photodiode, the apparatus comprising; a reset transistor connected to the photodiode, the reset transistorhaving a threshold voltage set to a value that allows dark current to be removed during signal integration; and wherein the reset transistor is a MOSFET, and the threshold voltage is set according to the following equation; ##EQU7## where V.sub.x=nkT/e n is the ideality of a reset MOSFET, J.sub.dark is a dark current density for the photodetector, A.sub.det is a photodetector area., .mu. is a MOSFET mobility, W.sub.rst is a width of the reset MOSFET, L.sub.rst is a length of the reset MOSFET,and C.sub.ox is a MOSFET capacitance density.
Claims
23 totalAn apparatus for reducing dark current associated with a CMOS photodiode, the apparatus comprising; a reset transistor connected to the photodiode, the reset transistorhaving a threshold voltage set to a value that allows dark current to be removed during signal integration; and wherein the reset transistor is a MOSFET, and the threshold voltage is set according to the following equation; ##EQU7## where V.sub.x=nkT/e n is the ideality of a reset MOSFET, J.sub.dark is a dark current density for the photodetector, A.sub.det is a photodetector area., .mu. is a MOSFET mobility, W.sub.rst is a width of the reset MOSFET, L.sub.rst is a length of the reset MOSFET,and C.sub.ox is a MOSFET capacitance density.