Seeing Photons Progress and Limits of Visible and Infrared Sensor Arrays (2010) / Chapter Skim
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3 Key Current Technologies and Evolutionary Developments
3 Key Current Technologies and Evolutionary Developments
Pages 60-90
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From page 60... ...
Clever design architectures, adding powerful on-focalplane processing features, lowering power dissipation, increasing detector operating temperature, and dramatically reducing costs are examples of seemingly evolutionary changes that could enable revolutionary capabilities. Innovation will likely not be driven exclusively by moving closer to the physical limits of detector performance.
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From page 61... ...
arrays; photon counting technologies and lower readout noise; curved focal surfaces; lower-power operation; radiation hardening; cost reduction; and improved cooler technology. KEY TECHNOLOGIES EXPECTED TO DRIVE ADVANCEMENTS IN EXISTING DETECTOR TECHNOLOGIES OVER THE NEXT 10-15 YEARS With respect to areas in which near-term technology advances are expected, this section examines each of the advances and addresses benefits, risks or drawbacks, impact on system performance, and implications for military applications of the expected advances.
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From page 62... ...
Visible 50-megapixel arrays are now available with digital outputs hav ing ROIC noise levels of less than 10 electrons and offering a sensitivity advantage over consumer products. In the IR, highly sensitive, multi-megapixel infrared focal plane arrays (FPAs)
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From page 63... ...
Even beyond the diffraction limit of the optical system, oversampling can lead to slightly enhanced resolution. Mosaic Tiling Technologies For a number of years, visible-band CCD imagers have been built in three-side buttable and four-side buttable formats, allowing tiling of large focal planes from
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From page 64... ...
2008. High-definition infrared focal plane arrays enhance and simplify space surveillance sensors.
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From page 65... ...
Commercial CMOS imagers and CMOS chips have been demonstrated with pixels sized in the 1 to 2 µm range, with some examples less than 1 µm. On the silicon CMOS imager side, much of the interest in pixel size reduction has been driven by the desire to deliver a large number of megapixels to a consumer while keeping the silicon area used by the chip as small as possible to minimize cost for consumer applications, such as cell phone cameras.
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From page 66... ...
2 Brian Leininger, Jonathan Edwards, John Antoniades, David Chester, Dan Haas, Eric Liu, Mark Stevens, Charlie Gershfield, Mike Braun, James D Targove, Steve Wein, Paul Brewer, Donald G
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From page 67... ...
Usually the desire is to achieve cost reductions for high-volume applications by having a single-chip solution, but monolithic integration can also have other substantial benefits, such as power and noise reduction and enabling new interconnection-rich processing architectures that would not be feasible using off-chip inputs and outputs. In the IR and high-performance visible imaging area, fully digital focal planes are just entering the market.
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From page 68... ...
PMC with ADV212 - JPEG 2000 Serial sensor Virtex 5 FPGA control ADV212 - JPEG 2000 EMCORE Multimedia Fiber Dual Core Pentium 3 Fibers - 6 FPA Video Streams Optic Converter Single Board Computer 160 GB 2.5" with 3 1Gbit/sec SATA HD EMCORE Ethernet 3 Fibers - 6 FPA Video Streams Multimedia Fiber Optic Converter ADV212 - JPEG 2000 PMC with Virtex 5 FPGA ADV212 - JPEG 2000 1 Gbit Ethernet 6U cPCI Single Board Computer FIGURE 3-1-2 ARGUS-IS airborne processing module. SOURCE: Leininger, Brian, Jonathan Edwards, John Antoniades, David Chester, Dan Haas, Eric Liu, Mark Stevens, Charlie Gershfield, Mike Braun, James D
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From page 69... ...
key current technologies evolutionary develoPments and FIGURE 3-1-3 Sample of ARGUS-IS imagery. Mounted under a YEH-60B helicopter at 17,500 feet over Quantico, Va., Argus-IS images an area more than 4 km wide and provides multiple 640 × 480-pixel real-time video windows.
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From page 70... ...
2005. Solution for the nonuniformity correction of infrared focal plane arrays.
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From page 71... ...
While high operating temperature work is generally focused on the MWIR and LWIR, even silicon visible sensors used in applications requiring long integration times must be cooled to reduce dark current, and improvements in
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From page 72... ...
2006. nBn detector, an infrared detector with reduced dark current and higher operating temperature.
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From page 73... ...
2008. Mid-IR focal plane array based on type-II InAs/GaSb strain layer superlattice detector with nBn design.
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From page 74... ...
While the MCT material system has been the dominant material used for dual-band MWIR and LWIR focal planes, work is going on with other materials and device types. QWIPs generally have lower quantum efficiency (QE)
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From page 75... ...
FINDING 3-4 Existing, mature mercury cadmium telluride, indium antimonide, indium gallium arsenide, silicon charge-coupled devices, silicon complementary metal oxide semiconductors, and avalanche photodiode focal plane technologies provide sensors with excellent performance and set a very high barrier to entry for any emerging technology. For some performance parameters, such
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From page 76... ...
However, there is still considerable opportunity to improve other parameters such as operating temperature, power dissipation, manufac turability, and cost. Improved SWIR Arrays Access to the SWIR band provides the tactical advantage of being able to see in a band that has more night illumination than the visible and near-IR bands and that sees signals from all current laser designators, pointers, and range find ers.
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From page 77... ...
The principal game changers in SWIR will be technologies that can significantly reduce the cost of FPA fabrication, currently a material or process yield issue, facilitate finer-pitch FPAs (less than 10 µm) , or exhibit dark current densities that best InGaAs at any cutoff wavelength or operating temperature.
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From page 78... ...
For example, Geiger-mode detector arrays that have been developed for UV, visible, and SWIR, and are already used in active imaging systems such as direct detection LADAR, will be further developed and applied to passive photon counting imaging applications in increas ingly large array sizes. Photon counters have a number of important applications, including some low-light imaging applications, hyperspectral sensors, high-speed imaging, 3-D LADAR, and dual-mode active-passive pixels.
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From page 79... ...
The utility of curved focal planes becomes evident when one realizes that the human retina is curved, because this dramatically simplifies the design and complexity of the lens. Lower Power Moore's law scaling of CMOS technology has led to steady reductions in the power consumed, especially for digital logic operations.
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From page 80... ...
. The proliferation of low-cost, visible sensors offers opportunities for DOD if it is quick to exploit this technology; however, such technologies are proliferated globally and are also accessible to current and potential adversaries.11 As discussed above, in the IR, alternatives to MCT such as InAs-GaSb SLS detectors may provide both a large decrease in cost and an increase in key per formance capabilities.
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From page 81... ...
Development of higher-coefficient-of-performance coolers: Visible and SWIR systems using thermoelectric coolers, as well as IR systems using refrig eration cycles, would benefit from more efficient coolers, because cooling power often dominates total sensor power consumption. This is particularly important for power-constrained systems, such as unattended ground sen sors, and systems that are used only intermittently but must continuously be in a ready-to-operate state.
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From page 82... ...
The two technologies cur rently available for addressing the cooling requirements of IR and visible detectors are closed-cycle refrigerators and thermoelectric coolers. Closed-cycle refrigerators can achieve the cryogenic temperatures required for cooled IR sensors, while ther moelectric coolers are generally the preferred approach to temperature control for uncooled visible and IR sensors.
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From page 83... ...
Often, the COP is given as a fraction of the ideal FIGURE 3-4 Cooling of IR sensors represents one of several commercial and research applications for cryocoolers. NOTE: FCL = freon coolant line; HTS = high-temperature superconductivity; LNG = liquid natural gas; LTS = low-temperature superconductivity; MRI = magnetic resonance imaging; SMES = superconducting magnetic energy storage; SQUID = superconducting quantum interference device; ZBO = zero boil-off.
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From page 84... ...
In general, recupera tive systems have advantages in terms of reduced noise and vibration, whereas regenerative systems tend to obtain higher efficiencies and greater reliability at the temperatures of interest for many IR detector applications. The relative perfor mances of the different technologies as a fraction of the limiting Carnot efficiency are shown in Figure 3-5.
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From page 85... ...
In a generator configuration, thermoelectric devices exploit the Seebeck effect -- the voltage created between two dissimilar conductors in the presence of a temperature difference. Thermoelectric coolers work by exploiting the Peltier effect, which refers to the creation of heat flux at the junction of two dissimilar conductors in the presence of current flow.
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From page 86... ...
Thermoelectric coolers are essentially solid-state heat pumps where the flow of thermal energy is determined by the polarity of the applied current. The coef ficient of performance for a thermoelectric cooler is a function of ZT as well as the overall temperature difference between the hot side and the cold side of the cooler.
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From page 87... ...
This section focuses on what is currently achievable with existing bulk commercial thermoelectric materials and what developments are likely to occur over the next 10-15 years.20 Current commercially available thermoelectric coolers are based on alloys of bismuth telluride and antimony telluride materials. These materials exhibit ZT values close to 1 unity, but in a device configuration achieve values closer to ZT = 0.7.
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From page 88... ...
at ∆T of ~30 K If the bulk materials available for commercial coolers were to achieve ZT values closer to 1.5, then the achievable COPs would be anticipated to approach 1.5 (1.5 W of cooling for 1 W of electrical input)
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From page 89... ...
In addition, the higher frequency of operation may induce additional unwanted vibrational noise and susceptibility to electromagnetic interference. FINDING 3-8 Low-cost uncooled infrared focal plane arrays are approaching the perfor 21 Lon Bell, Amerigon, Inc., personal communication with the committee on March 3, 2010.
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From page 90... ...
FINDING 3-9 For both cryocooler and TE cooler technologies, there are a number of com mercial market drivers, separate from sensor cooling applications, that will drive evolutionary improvements in SWaP. Over the next 10-15 years, it is reasonable to expect that these improvements will achieve overall reductions in SWaP on the order of 20-30 percent.
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