Leonardo DRS is a leader in small pixel uncooled FPA technology with the development of 10μm pixel 640×512 and 10μm pixel 1280×1024 FPA formats. Leonardo DRS offers the Tenum®640 and Tenum®1280 uncooled commercial camera cores based on these FPA formats. The Tenum®640 operates in 60Hz and 9Hz framerate modes with f/1 equivalent NETD sensitivity of <60mK and nominal power dissipation of 1.2W. The Tenum®1280 operates in 30Hz and 9Hz framerate modes with f/1 equivalent NETD sensitivity of <60mK and nominal power dissipation of 2.3W. The Tenum®640 uses a wafer-level vacuum packaged 10µm 640×512 FPA. In this paper, the Leonardo DRS Tenum®640 and Tenum®1280 camera cores will be discussed along with relevant 10µm FPA technology and advances in wafer-level vacuum packaging. In addition, a summary of Leonardo DRS 10µm and 17µm FPA formats in production will be presented. Finally, a broadband IR version of the Tamarisk®640 will be discussed.
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 300oC 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.
A method is described for the direct measurement of the thermal time constant of microbolometer arrays: The emitted radiation from an array due to time varying Joule heating is monitored by a fast photodetector. Applying a bias voltage pulse to the array the thermal time constant is measured from the time dependence of the emission decay at the end of the pulse. In particular, we have used HgCdTe photodetector and digital signal acquisition and analysis to measure the thermal time constant of uncooled a-Si:H microbolometer 120 x 160 arrays with 50 micron pixels. Measured typical thermal time constant values for such arrays are in the range of 8ms to 10ms.
Amorphous silicon (a-Si) microbolometer technology is a silicon fab-compatible uncooled detector technology which offers a low cost, high volume approach for infrared sensor and imager applications. Raytheon has used this detector technology to develop a 160x120 a-Si based infrared camera. The systems goal was to develop an affordable infrared imaging product that provides acceptable performance for many commercial and military applications. To meet low power goals, a non-temperature controlled detector approach was required. This led to the challenge of developing a technique for operating over ambient temperature that includes correction techniques that account for offset and responsivity non-uniformities over ambient operating temperature. This paper describes the operating performance parameters of a typical a-Si 160 X 120 IR camera. This camera is currently entering production, and will be produced by the Raytheon Commercial Infrared business.
KEYWORDS: Amorphous silicon, Cameras, Infrared cameras, Digital signal processing, Packaging, Microbolometers, Staring arrays, Sensors, Signal processing, Temperature metrology
Low power and low cost are primary requirements for an imaging infrared camera serving law enforcement applications. These include handheld, vehicle and helmet mounted systems for search and surveillance applications. In this paper, a 120 X 160 amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 120 X 160 micro infrared camera has been demonstrated which exhibits a noise equivalent temperature difference sensitivity approximately 50 mK using f/1 optics and approximately 80 mK using f/1.2 optics. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements.
We have developed high dynamic range (105-106 g's) tunneling accelerometers1,2 that may be ideal for smart munitions applications by employing both surface and bulk micromachining processing techniques. The highly miniaturized surface-micromachined devices can be manufactured at very low cost and integrated on chip with the control electronics. Bulk-micromachined devices with Si as the cantilever material should have reduced long-term bias drift as well as better stability at higher temperatures. Fully integrated sensors may provide advantages in minimizing microphonics for high-g applications. Previously, we described initial test results using electrostatic forces generated by a self-test electrode located under a Au cantilever3. In this paper, we describe more recent testing of Ni and Au cantilever devices on a shaker table using a novel, low input voltage (5 V) servo controller on both printed wiring board and surface-mount control circuitry. In addition, we report our initial test results for devices packaged using a low-temperature wafer-level vacuum packaging technique for low-cost manufacturing.
Low power and low cost are primary requirements for an imaging infrared camera used in unattended ground sensor arrays. In this paper, a 120 X 160 amorphous silicon (a- Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 120 X 160 micron infrared camera (MIRC) has been demonstrated which exhibits an f/1 noise equivalent temperature difference sensitivity approximately 63 mK. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements. Chopperless camera operation at a 20 Hz frame rate with power consumption of 380 mW has also been demonstrated. The 120 X 160 MIRC operates under digital signal processor (DSP) control. To reduce cost, this DSP-controlled architecture employs commercial off-the-shelf DSP, A/D, memory and voltage regulator chips. The detector chip, employing an integrating amplifier per unit cell ROIC design, is the single custom chip used. The camera also employs low cost f/1 optics, as well as low cost wafer-level vacuum packaging. In this paper, a-Si microbolometer technology for the MIRC will be presented. Also, the key features and performance parameters of the MIRC are presented.
Low power and low cost are primary requirements for an imaging infrared camera used in unattended ground sensor arrays. In this paper, an amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 15 X 31 micro infrared camera (MIRC) has been demonstrated which exhibits an f/1 noise equivalent temperature difference sensitivity approximately 67 mK. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements. The chopperless camera is capable of operating from snapshot mode (1 Hz) to video frame rate (30 Hz). Power consumption of 0.4 W without display, and 0.75 W with display, respectively, has been demonstrated at 30 Hz operation. The 15 X 31 camera demonstrated exhibits a 35 mm camera form factor employing a low cost f/1 singlet optic and LED display, as well as low cost vacuum packaging. A larger 120 X 160 version of the MIRC is also in development and will be discussed. The 120 X 160 MIRC exhibits a substantially smaller form factor and incorporates all the low cost, low power features demonstrated in the 15 X 31 MIRC prototype. In this paper, a-Si microbolometer technology for the MIRC will be presented. Also, the key features and performance parameters of the MIRC are presented.
A new class of uncooled IR systems has been developed based on advances in both amorphous silicon detectors and signal/system processing techniques. Not only are these devices uncooled but they operate over a wide system ambient temperature range without the use of TEC's or choppers. The devices are DC biased and provide radiometric information from each pixel without the use of a calibrated source. The current imaging system are medium to low resolution. They were designed with a very disciplined 'concept-to-cost' technique in which cost, power, sizes, weight and performance were traded off in the stated order. The result has been a new generation of 'ambient temperature' thermal imaging system and radiometers.
An amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology, offering a low- cost, low-power solution to infrared surveillance for both civilian and military application is presented. A- Si exhibits a temperature dependent resistance with a 3000K temperature coefficient of resistance (TCR) of 2.7 percent/K. The uncooled a-Si microbolometer detector structure employs a low thermal mass a-Si membrane structure with high thermal isolation legs monolithically integrated on a CMOS readout integrated circuit (ROIC) chip. A refractive resonant cavity design results in approximately 90 percent infrared absorptance over the 8-13 um spectral band. A-Si also exhibits a UV/visible photoconductive response for multispectral applications. The ROIC involves an integrating amplifier per pixel and a column multiplexed output. A 15 x 31 micro infrared camera (MIRC) has been developed, which exhibits f/l noise equivalent temperature difference, thereby significantly reducing the power requirements. The 15 x 31 camera demonstrated exhibits a 35 mm camera form factor employing a low cost f/l singlet optic and LED display, as well as low cost vacuum packaging. A larger 120 x 160 version of the MIRC is also in development and will be discussed.
Recent developments in MOCVD growth of Hg1-xCdxTe photodiodes using the interdiffused multilayer process are reported. Iodine doping of HgCdTe is described using ethyl iodide. Using ethyl iodide, the iodine doping level can be controlled in the range of 7 X 1014 - 2 X 1018 cm-3 without any memory effect. Activation of the iodine as a singly ionized donor is near 100% at concentrations < 1 X 1017 cm-3. Ethyl iodide was not found to react with the other organometallic precursors and abrupt dopant profiles are obtained. The iodine doped HgCdTe films exhibit 80 K electron mobilities >= 1 X 105 cm2/V-s, auger limited lifetimes of approximately 1 microsecond(s) for concentrations of (1-3)X1015 cm-3, and x-values approximately 0.22. LWIR p-on-n heterojunctions have been grown in situ using iodine doping for the n-type absorber layer and arsenic doping for the p- type cap layer. Detailed characterization data for the photodiodes are reported.
A noncontact, noninvasive lifetime characterization technique for measuring the excess carrier lifetime in long wavelength infrared (LWIR) Hg1-xCdxTe (x approximately equals 0.20-0.225) using transient millimeter-wave (90 GHz) reflectance is presented. Excess carrier lifetime results for both p-type (vacancy-doped >= 1 X 1016 cm-3) and n-type (annealed <= 1x1015 cm-3 epilayer material are given. The lifetimes in vacancy-doped p-type HgCdTe are short, i.e., approximately 25 ns at 80 K, thereby requiring a short-pulsed laser source and high-bandwidth electronics in the lifetime test system. The lifetime test system employs either YAG (1.06 micrometers ) or CO2 (9-11 micrometers ) pulsed laser excitation. Lifetime results for both frontside and backside laser illumination of the epilayer HgCdTe are presented. The effect of surface recombination of lifetime and reflected millimeter-wave signal amplitude is discussed.
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