Back Illuminated CMOS

From ITLWiki

The Imaging Technology Laboratory, with a grant from the National Science Foundation, has investigated CMOS image sensors for use in scientific applications. Unlike CCDs, CMOS imagers are "cameras-on-a-chip". Nearly all that is needed to run a CMOS device is already on the chip, whereas CCDs need more electronics to control them. For CMOS imagers to be used for scientific applications like astronomy, the sensors must be optimized for high quantum efficiency, low read noise, and improved fill-factor. ITL has successfully thinned several types of CMOS imagers.

A thinned CMOS imager processed in our Lab is seen in the center of the image (rectangular-shaped). The chip is mounted on a silicon substrate with gold traces visible (see below for detail). The "white dots" along side the device are the nickel diffusion barriers peeking out from under the chip. The outer gold traces are part of the ceramic package.

Prior to thinning, a CMOS device is flip-chip bonded to a support substrate. Small white dots can be seen which are 25-micron high indium pads measuring 100 microns x 100 microns). The silver-colored metal running down part of the gold traces is a nickel diffusion barrier. The trace ends in a gold wire bonding pad, found near the edge of the die.