June 3, 2008--CMOS image sensor manufacturer OmniVision (Sunnyvale, CA) launched a new CMOS architecture called OmniBSI that uses backside illumination (BSI) to offer improved image quality while extending its pixel roadmap down to 0.9 micron pixels, crucial to continued miniaturization of digital imaging technology. OmniVision developed OmniBSI architecture with the support of its long-time foundry and process technology partner, Taiwan Semiconductor Manufacturing Corporation (TSMC).
BSI methodology involves turning the image sensor upside down so that it collects light through what was previously the backside of the sensor, the silicon substrate. This approach differs from conventional front side illumination (FSI) image sensors, where the amount of light reaching the photosensitive area is limited, in part, by the multiple metal and dielectric layers required to enable the sensor to convert photons into electrons. The FSI approach can block or deflect light from reaching the pixel, ultimately reducing the fill factor and causing additional problems, such as crosstalk, between pixels. BSI reverses the arrangement of layers so that the metal and dielectric layers reside below the sensor array, providing the most direct path for light to travel into the pixel. This novel approach optimizes light absorption, enabling OmniVision to build a 1.4 micron BSI pixel that surpasses all the performance metrics of 1.4 micron, and even most 1.75 micron, FSI pixels.
"Moving FSI pixel architectures down to 1.4 micron and below, under current design rules, poses some real challenges because metal lines and transistors are driving the aperture of the pixel close to the wavelength of light, its physical limit," said Howard Rhodes, VP of process engineering at OmniVision. "To overcome this with traditional FSI pixel technology would require a migration to 65 nm copper process technologies, which would significantly increase the complexity and cost of manufacturing. Because it allows for more than three layers of metal, BSI achieves significant manufacturing benefits without moving to smaller process nodes. This means routing can be simplified and die sizes can be smaller than in FSI sensors, without the need to move to smaller process nodes with all their associated complexities and additional costs."
OmniVision is currently demonstrating an 8 megapixel, OmniBSI CameraChip sensor, and expects to start sampling first products before the end of June.
For more information, visit www.ovt.com.