PORTLAND, Ore. OmniVision Technologies, Inc. will show its second-generation CMOS imaging chip to OEMs during next week's Mobile World Congress (Barcelona, Spain Feb. 15-18, 2010).
OmniVision (Santa Clara, Calif.) uses a novel backside illumination technique in which photodetectors are fabricated at the bottom of the chip stack situated on a transparent window. After fabricating metal interconnection layers, the chip is then flipped so that its photodetectors are on top (under the window). Front-side illumination, on the other hand, requires that the light go through those multiple layers of metal before reaching the photodetectors, thereby dimming it (see photo).
OmniVision claims to be the first company to move from front- to back-side illumination. Bruce Weyer, vice president of marketing at OmniVision said that "as pixel dimensions were reduced, it was becoming increasingly difficult to force light through all the metal interconnection layers. But by flipping the imager over and illuminating it from the backside, we completely avoid the metal layers."
Back-side illumination was invented for special purpose imagers used in telescopes and other expensive instruments, but OmniViison has repurposed the technology for consumer electronics. Sony is the only other commercial vendor to announce back-side illumination for a captive digital cameras. lOnmiVision remains the only supplier of back-side illumination technology for camera phones, PCS, digital cameras and other consumer electronic devices.
OmniVision's second-generation imager was made using 65-nm design rules (from 110-nanometers) using Taiwan Semiconductor Manufacturing Co. Ltd.'s 300-mm copper process. The total area per pixel, just over 1 micron, permits OmniVision to squeeze many more chips onto a wafer, while simultaneously increasing low-light sensitivity and reducing dark current and full-well capacity.
The company also said its OmniBSI-2 uses a more compact pixel layout technique, has better isolation and reduced crosstalk among pixels.
The CMOS imager can be used for both still and video camera applications, and is available in various aspect ratios and sizes up to 14 megapixels.