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Non-Uniform Gate-Dielectric Charge for CMOS Optical Imagers

IP.com Disclosure Number: IPCOM000193240D
Original Publication Date: 2010-Feb-15
Included in the Prior Art Database: 2010-Feb-15
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Abstract

A method of providing a non-uniform gate-dielectric charge for a CMOS optical imager is disclosed. The CMOS optical imager includes a photo-collector region and a transfer FET with a channel, a portion of which is composed of SiGe. The SiGe portion is positioned to assist in evacuation of charge away from the photo-collector region.

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Non-Uniform Gate-Dielectric Charge for CMOS Optical Imagers

Disclosed is a method of providing a non-uniform gate-dielectric charge for a CMOS optical imager.

Typically, in a CMOS optical imager, the pass gate is switched off after the charge is erased and prior to exposing the CMOS optical imager to a new image. However, in switching off the pass gate, some channel charge may leak back into the photo-collector region contaminating the erased state and raising the noise floor.

The method disclosed herein evacuates charges in a channel of a CMOS optical imager away from the photo-collector region. The CMOS optical imager includes a photo-collector region and a transfer FET. The transfer FET includes the channel, a portion of which is composed of SiGe. The SiGe is positioned in the channel to assist in evacuating charge in the channel away from the photo-collector region. The CMOS optical imager including the photo-collector region and the transfer FET is illustrated in the figure.

Figure

Further, the method uses a laterally non-uniform PFET channel composed of a SiGe portion to provide a built-in field when the transfer FET in the optical imager is switched off. The built-in field pushes the charges in the CMOS optical imager away from the

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photo-collector region.

Thus, the method provides a built-in field when a transfer FET in a CMOS optical imager is switched off. The built-in field pushes the...