Uncooled amorphous silicon microbolometers have been established as a field-worthy technology for a broad range of
applications where performance and form factor are paramount, such as soldier-borne systems. Recent developments in
both bolometer materials and pixel design at L-3 in the 17μm pixel node have further advanced the state-of-the-art.
Increasing the a-Si material temperature coefficient of resistance (TCR) has the impact of improving NETD sensitivity
without increasing thermal time constant (TTC), leading to an improvement in the NETD×TTC product. By tuning the
amorphous silicon thin-film microstructure using hydrogen dilution during deposition, films with high TCR have been
developed. The electrical properties of these films have been shown to be stable even after thermal cycling to
temperatures greater than 300<sup>o</sup>C enabling wafer-level vacuum packaging currently performed at L-3 to reduce the size
and weight of the vacuum packaged unit. Through appropriate selection of conditions during deposition, amorphous
silicon of ~3.4% TCR has been integrated into the L-3 microbolometer manufacturing flow. By combining pixel design
enhancements with improvements to amorphous silicon thin-film technology, L-3's amorphous silicon microbolometer
technology will continue to provide the performance required to meet the needs to tomorrow's war-fighter.
Recent developments in low-noise, high temperature coefficient of resistance (TCR) amorphous silicon and amorphous
silicon germanium material have led to the development of uncooled focal plane arrays, with TCR in the range 3.2%/K
to 3.9%/K, which has been leveraged in the small pixel FPA development at L-3 EOS. In the 17μm pixel technology
node at present, 1024x768, 640×480, and 320x240 FPAs have thus far been developed. All three formats employ waferlevel
vacuum packaging, with the 1024x768 representing the largest format uncooled FPA wafer-level packaged to date.
FPA results from all three formats will be discussed and images will be presented.
Continued reduction of α-Si bolometer pixel size has led to increases in array size as well as improvements in
temporal response for a given level of sensitivity. Programs funded by DARPA and NVESD are developing
advanced 320×240, 640×480 and 1024×768 α-Si bolometer arrays with 17μm pixels, on-chip A/D conversion,
significant improvements in dynamic range, significant reductions in thermal time constant and other specialized
functions. The push to 17μm is motivated not only by system size and weight, but also by improvements in
performance resulting from increased resolution. Smaller pixels permit fabrication of larger arrays without
subverting the field-size constraints of ordinary photolithographic processes. Reducing pixel size also reduces the
effects of stress mismatches. This permits reduction of device thickness, thereby reducing thermal time constant.
Improvements in bolometer material properties have served to improve responsivity while lowering 1/f noise.
Because these arrays substantially reduce sensor size, they are becoming the preferred format for most applications,
particularly for weapon sights and for head-mounted and UAV applications. The larger array sizes are of interest for
pilotage and surveillance.
This paper presents recent developments in next generation microbolometer Focal Plane Array (FPA) technology at L-3 Communications Infrared Products (L-3 CIP). Infrared detector technology at L-3 CIP is based on hydrogenated amorphous silicon (a-Si:H) and amorphous silicon germanium(a-SiGe:H). Large format high performance, fast, and compact IR FPAs are enabled by a
low thermal mass pixel design; favorable material properties; an advanced ROIC design; and wafer level packaging. Currently at L-3 CIP, 17 micron pixel FPA array technology including 320x240,
640 x 480 and 1024 x768 arrays is under development. Applications of these FPAs range from low power microsensors to high resolution near-megapixel imager systems.