A High Resolution Near-Infrared (NIR) Camera has been developed and tested. This NIR camera uses a HgCdTe detector array which allows for imaging at high operating temperatures. The camera's format is 640x512 pixels with an 18 μm pitch. We have obtained high broadband spectral response from 0.9 to 2.0 micron with near 100% optical fill factor. The camera is designed as a turnkey system that uses the industry standard Camera Link digital interface. The electronics are located remotely from the sensor head allowing it to be adapted to existing optical systems. This compact camera has been targeted for military, scientific and telecommunication applications. This paper will detail the measured camera performance.
The past 2 to 3 years has been a period of explosive growth in technology development for imaging sensors at Rockwell Scientific Co. (RSC). The state of the art has been advanced significantly, resulting in a number of unique advanced imaging sensor products. A few key examples are: 2048 x 2048 sensor chip assemblies (SCA) for ground and space-based applications, 4096 x 4096 mosaic close-butted mosaic FPA assemblies, a very high performance 10 x 1024 hybridized linear SCA for optical network monitoring and other applications, the revolutionary CMOS ProCam-HD imaging system-on-a-chip for high definition television (HDTV), and RSC's near-infrared emission microscope camera for VLSI defect detection/analysis. This paper provides selected updates of these products and thereby provides an overview of the ongoing highly fertile period of technology and product development at Rockwell Scientific. A view into future directions for advanced imaging sensors is also provided.
The HAWAII-2 is an IR 20482 focal plane array (FPA) that is being developed for next-generation IR astronomy. It will supplant our HAWAII 10242 as the largest high- performance imaging array available for IR astronomy. As with our prior IR sensor, the flip-chip hybrid will consist of a low-capacitance HgCdTe detector array mated to a low- noise CMOS silicon multiplexer via indium interconnects. In order to accommodate reasonable telescope optics and fabrication of the large sophisticated readout using world- class submicron CMOS, the FPA has 18 micrometers pixel pitch. We anticipate > 5 percent yield of defect-free multiplexers using 0.8 micrometers CMOS. The HgCdTe detector arrays will be fabricated on large wafers including sapphire and silicon. Though the first FPAs will have 2.5 micrometers cut-off, the readout will be able to support longer wavelengths. Also reported are the latest 1024 X 1024 FPA results with 2.5 micrometers HgCdTe detectors.
We have developed 1024 X 1024 HAWAII (HgCdTe Arrays for Wide-field Astronomical Infrared Imaging) focal plane arrays (FPAs) for use in astronomical applications. These devices have been delivered to various astronomy organizations around the world and have resulted in increased sensitivities and decreased observation times for deep space imaging. The detector material is PACE-I for SWIR and Molecular Beam Epitaxy (MBE) HgCdTe on CdZnTe for MWIR. The 1024 X 1024 multiplexer has a 18.5 micrometer unit cell pitch, source follower per detector (SFD) input, and it was fabricated at or internal commercial CMOS process line with excellent yield. Mean dark currents as low as 0.02 e-/s have been measured at 77 K for 2.5 micrometer devices (1024 X 1024 format, 18.5 micrometer pitch) and 0.39 e-/s for 5.3 micrometer devices at 50 K (256 X 256 format, 40 micrometer pitch). Quantum efficiencies are greater than 50% for both SWIR and MWIR detectors; with AR coatings, these are expected to be above 75%. Noise levels of 3 e- have been measured by multiple sampling techniques for the SWIR and 75 e- for the MWIR. All of these devices are simple to operate and are readily available. We are presently developing 2048 X 2048 FPAs with 18 micrometer unit cell pitch for both SWIR and MWIR applications.
We have developed two high performance 1024 multiplied by 1024 focal plane arrays for astronomy, spectroscopy, surveillance and conventional imaging. Each hybrid consists of a photovoltaic HgCdTe detector array, fabricated on Al2O3 substrate and having photoresponse cutoff wavelength optimized for each specific application, mated to a CMOS silicon readout via indium column interconnects. In addition to updating the performance of our 1024 multiplied by 1024 FPA for astronomy developed in 1994, we introduce a second 1024 multiplied by 1024 having capability for operation at TV-type frame rates. The latter device also has low read noise but at much higher bandwidth by virtue of its capacitive transimpedance amplifier input and pipelined readout architecture. Both devices have been shown capable of consistently achieving background-limited sensitivity at very low infrared backgrounds (less than or equal to 109 photons/cm2-sec) by their low read noise, low dark current including negligible MOSFET self-emission, and high quantum efficiency. FPA pixel operability as high as 99.94% with mean peak D* of 1014 cm-Hz1/2/W has been demonstrated. Proprietary hybridization and mounting techniques are being used to insure hybrid reliability after many thermal cycles. The hybrid methodology has been modeled using finite element modeling to understand the limiting mechanisms; very good agreement has been achieved with the measured reliability.
A comparison of photovoltaic HgCdTe/Al2O3, HgCdTe/CdZnTe, InGaAs/InP and photoconductive GaAs/AlGaAs quantum well infrared photodetector detector technologies has been conducted at Rockwell by exploiting the ability to selectively hybridize disparate mosaic detector arrays to an assortment of silicon multiplexers. Hybrid FPA characteristics are reported as functions of operating temperature from 32.5 K to room temperature and at photon backgrounds from approximately equals 106 to mid-1016 photons/cm2-sec. The staring arrays range in size from about sixteen thousand to over a million pixels. Background-limited detectivities significantly exceeding 1014 cm-(root)Hz/W were achieved.
Rockwell Science Center and the University of Hawaii have developed a short wavelength infrared (SWIR) 1024 X 1024 focal plane array (FPA). The continuing project is funded by the U.S. Air Force Phillips Laboratory in connection with their Advanced Electro Optical System (AEOS) 3.67 m telescope project on Haleakala, Maui. We have achieved our objective of developing a 1024 X 1024 FPA with a cut-off wavelength of 2.5 micrometers . The device is named the HgCdTe Astronomical Wide Area Infrared Imager (HAWAII). The first hybrids have been characterized, delivered and first light achieved two days ahead of schedule; performance highlights include successful elimination of the reset anomaly (whose presence limited the noise performance of prior astronomical 256 X 256 FPAs), total FPA dark current < 0.1 e-/sec at 77 K, pixel yield > 99%, quantum efficiency > 50%, BLIP-limited sensitivity at low-109 photons/cm2-sec background and operating temperatures to 120 K, and read noise < 10 e-.
The University of Hawaii and the Rockwell International Science Center are developing a large format SWIR detector array optimized for low background astronomical imaging and spectroscopic observations. This so called HgCdTe astronomical wide area IR imager (HAWAII) device will be based on the technology developed for the NICMOS project, but will incorporate several modifications of this design to improve the performance.
Cost-effective high-performance IR imaging cameras need affordable staring focal plane arrays (FPAs) that can operate effectively at temperatures compatible with inexpensive long-life coolers. We report on staring hybrid 128 x 128 and 256 x 256 Hg1-xCdxTe FPAs that have requisite yield, sensitivity, operability, and reliability at a medium-wavelength IR (MWIR) cutoff wavelength (λc ~4.6 μm at 180 K) and elevated operating temperatures. Mean 256 x 256 FPA noise-equivalent temperature differences (NEΔT) using broadband f/1.7 optics were 4.3, 7.7, and 55 mK at 120, 140, and 180 K, respectively. We extrapolate that camera NEΔT ≤ 0.02 K can be achieved at 190 K using optimized (λc of ~4.4 μm (180 K), a 3.4- to 4.2-μm bandpass filter, and f/1 optics. Because the CMOS multiplexers have a low-power dissipation and need little ancillary circuitry in the dewar, a viable thermoelectrically-cooled FPA technology is thus implied once the λc is optimized for MWIR imaging.
A high-performance 5-μm 640 X 480 HgCdTe/CdTe/Al2O3 infrared focal plane array (FPA) that offers full TV-compatible resolution with excellent sensitivity at temperatures below 120 K has been developed. Mean FPA D* at 95 K and background of 1014 photons/cm2 s is background-limited at ~1 x 1012 cm Hz1/2/W for the typical mean quantum efficiency of 60 to 70%. The key technology making this large, high-sensitivity device producible is the epitaxial growth of HgCdTe on a rugged CdTe-buffered sapphire substrate. Mean camera noise-equivalent temperature difference NEΔT of 13 mK has been achieved at ≤ 120 K operating temperature and 3.4- to 4.2-μm passband; this is about an order of magnitude better than similar currently available cameras, which use PtSi FPAs and require cooling to ≤ 77 K to maintain performance at low scene temperatures.
Exploiting hybrid focal plane array methodology and a flexible multiplexing readout, 128 X 128 FPAs were made and directly compared using several short wavelength infrared (SWIR) and long wavelength (LWIR) detector technologies. The detector types include two GaAs/AlGaAs quantum well infrared photodetectors (QWIP), 1.7 micrometers InGaAs/InP, and 2.5 micrometers PV HgCdTe. The tests were performed at operating temperatures ranging from 35 K for the LWIR devices to as high as 175 K for the SWIR FPAs. Highlights include the first FPA demonstrations (to the best of our knowledge) of BLIP-limited detectivity (D*) for both LWIR GaAs/AlGaAs QWIP and 1.7 micrometers PV InGaAs/Inp. The 9 micrometers QWIP peak detectivity is near the theoretical background limit at 1.2 X 1010 photons/cm2-s background and 35 K operating temperature. The mean D* of 4.5 X 1013 Jones at 8.3 micrometers peak wavelength is 75% of BLIP. A maximum peak D* of 5.7 X 1014 Jones was achieved with the PV InGaAs/InP device at 200 K. This is also believed to be the highest reported FPA-level D* for a staring mosaic array operated at TV-type frame rate and integration time.
A hybrid HgCdTe 640 X 480 infrared (IR) focal plane array (FPA) that meets the sensitivity, resolution, and field-of-view requirements of high-performance medium wavelength infrared (MWIR) imaging systems has been developed. The key technology making this large, high sensitivity device producible is the epitaxial growth of HgCdTe on a CdTe-buffered, sapphire substrate (referred to as PACE, for Producible Alternative to CdTe for Epitaxy; PACE-I refers to sapphire). The device offers TV resolution with excellent sensitivity at temperatures below 120 K. Mean NE(Delta) T as low as 13 mK has been achieved at operating temperatures < 130 K, which is about an order of magnitude better than has been achieved with PtSi 640 X 480 FPAs. In addition, the latter require cooling to <EQ 77 K. Mean PACE-I FPA D* at 78 K and background of 1014 photons/cm2-sec is BLIP-limited at 1 X 1012 cm-Hz1/2/W for the typical mean quantum efficiency of 60 - 70%. Imagery having excellent quality has been obtained using simple two-point nonuniformity compensation.
Staring 128 X 128 hybrid HgCdTe FPAs have been demonstrated with very good sensitivity and operability at temperatures compatible with thermoelectric cooling (> 160 K). The FPAs consist of HgCdTe/sapphire (PACE-I; producible alternative to CdTe for epitaxy) detector arrays hybridized to a CMOS readout having a gate modulation input circuit. FPAs with SWIR (2.5 micrometers at 78 K) and MWIR (4.56 micrometers at 180 K) cutoff wavelengths ((lambda) co) were made and evaluated. The SWIR arrays were ZnS passivated; the MWIR arrays were CdTe-passivated. Though the (lambda) co of the MWIR devices was not specifically optimized for terrestrial imaging at TE-cooled temperatures in the preferred 3.4 to 4.1 micrometers band, very good sensitivity was achieved, particularly relative to other technologies at temperatures >= 120 K. Mean laboratory noise equivalent temperature differences (NE(Delta) T) at 120 K, 170 K, and 180 K were 0.0048 K, 0.053 K, and 0.061 K respectively, for the MWIR device. While the NE(Delta) T was measured without a spectral filter, the sensitivity for 3.4 to 4.1 micrometers bandpass extrapolates to camera NE(Delta) T <EQ 0.05 K, if f/1.5 or faster optics are used. Near BLIP Detectivity (D*) of 1.62 X 1013 cm-Hz1/2/W and mean NE(Delta) T of 0.04 K were measured on the SWIR hybrid at 22.5 msec integration time and operating temperatures <EQ 162 K. Imagery of corresponding quality was subsequently generated. Since the CMOS multiplexer dissipates little power and needs a minimum of support circuitry, a viable thermoelectrically cooled FPA technology is implied.
A 10 x 132 CMOS/CCD readout has been developed for low background (photon incidence less than 10 exp 12 photons/sq cm s) IR applications requiring fine orthoscan pitch (25 microns), on-chip signal processing including time delay integration (TDI) and correlated double sampling, high sensitivity, and high speed at operating temperatures compatible with passive or thermoelectric coolers. When hybridized to SWIR (2.5 microns) detectors, TDI channel read noise of not greater than 10 e(-) was measured at 145 K operating temperature. This implies a minimum per pixel read noise of about 3 electrons, approaching the goal of about 1 e(-) read noise needed for stringent SWIR applications including NASA's MOI and NGST missions.
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