Visible-band cameras using silicon imagers
provide excellent video under daylight
conditions, but become blind at night. The
night sky provides illumination from 1-2 μm
which cannot be detected with a silicon sensor.
Adding short-wave infrared detectors to a
CMOS imager would enable a camera which
can be used day or night.
A germanium-enhanced CMOS imager
(TriWave®) has been developed with
broadband sensitivity from 0.4 μm to 1.6 μm.
A 744 x 576 format imager with 10 μm pixel
pitch provides a large field of view without
incurring a size and weight penalty in the
optics. The small pixel size is achieved by
integrating a germanium photodetector into a
mainstream CMOS process. A sensitive
analog signal chain provides a noise floor of 5
electrons. The imagers are hermetically
packaged with a thermo-electric cooler in a
windowed metal package 5 cm3 in volume. A
compact (<650 cm3) camera core has been
designed around the imager. Camera
functions implemented include correlated
double sampling, dark frame subtraction and
non-uniformity corrections.
In field tests, videos recorded with different
filters in daylight show useful fog and haze
penetration over long distances. Under clear
moonless conditions, short-wave infrared
(SWIR) images recorded with TriWave make
visible individuals that cannot be seen in
videos recorded simultaneously using an
EMCCD. Band-filtered videos confirm that
the night-sky illumination is dominated by
wavelengths above 1200 nm.
NoblePeak Vision has developed monolithic visible to short-wave infrared (SWIR) imaging
arrays. An innovative growth technique is used to integrate germanium islands with the silicon
transistors and metal layers of a CMOS process. Imaging arrays of 128x128 pixels at a 10 μm
pitch were designed and fabricated, with the silicon photodiodes of a conventional CMOS
imager replaced by germanium photodiodes. Broadband response from 400 nm to 1650 nm has
been measured. Imaging die have been packaged with a Peltier cooler and built into a camera
evaluation kit.
A 256 X 256 CMOS photo-gate active pixel image sensor is presented. The image sensor uses four MOS transistors within each pixel to buffer the photo-signal, enhance sensitivity, and suppress noise. The pixel size is 20 micrometers X 20 micrometers and was implemented in a standard digital 0.9 micrometers single-polysilicon, double-metal, n-well CMOS process; leading to 25% fill-factor. Row and column decoders and counters are monolithically integrated as well as per column analog signal correlated double-sampling (CDS) processors, yielding a total chip size of approximately 4.5 mm X 5.0 mm. The image sensor features random accessibility and can be employed for electronic panning applications. It is powered from a single 5.0 V source. At 5.0 V power supply, the video signal saturation level is approximately 1,200 mV with rms read-out noise level of approximately 300 (mu) V, yielding a dynamic range of 72 dB (12 bits). The read-out sensitivity is approximately 6.75 (mu) V per electron, indicating a read-out node capacitance of approximately 24 fF which is consistent with the extracted value. The measured dark current (at room temperature) is approximately 160 mV/s, equivalent to 3.3 nA/cm2. The raw fixed pattern noise (exhibited as column-wise streaks) is approximately 20 mV (peak-to-peak) or approximately 1.67% of saturation level. At 15 frames per second, the power dissipation is approximately 75 mW.
Conference Committee Involvement (1)
Microelectronics: Design, Technology, and Packaging
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