Monolithic germanium SWIR imaging array

NoblePeak Vision is developing a new night vision technology based on visible to short-wave infrared (SWIR) imaging. Imaging in this band is important because of the "night glow", light emitted by the night sky between 1μm and 2μm wavelength. The night glow provides sufficient illumination to allow passive imaging even under moonless overcast conditions, but it cannot be detected with conventional imagers such as silicon CCDs or CMOS imagers, or with image intensifier tubes. NoblePeak's camera cores are based on novel, monolithic, visible-to-SWIR imaging arrays which incorporate germanium photodetectors. An innovative growth technique exploits dislocation trapping at the germanium/silicon interface to grow high-quality single- crystal germanium islands on a silicon substrate. NoblePeak has implemented a modified CMOS process at a high volume silicon foundry. Photodiodes formed in the germanium islands are integrated with the silicon transistors in the substrate and metal layers of the CMOS process. Imaging arrays at a 10μm pitch have been designed and fabricated, with the silicon photodiodes of a conventional CMOS imager replaced by germanium photodiodes. Dielectric isolation between the detectors eliminates electronic blooming. Over five hundred imagers of a planned PAL/NTSC/VGA format product will fit on a single 200 mm silicon wafer, allowing high volume production. Broad-band response from 400 nm to 1650 nm has been measured. Quantum efficiency (QE) greater than 40% is seen from 450 nm to 1450 nm with a peak QE of 75%, even without an anti-reflective coating. A noise floor of 10 nW/cm
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has been measured in early imagers, with continuing improvements in progress. Imaging die have been packaged with a Peltier cooler and built into a camera evaluation kit. Features incorporated include 30 fps video capture, 12 bit readout, and exposure times from 150μs to 30 ms. Imaging arrays at 128×128 have been demonstrated in the camera kit. A 744×576 imager has been designed and is in fabrication.