Atmospheric remote-sensing have been one of the primary drivers toward longer wavelength infrared sensors beyond
the 8 to 12 um atmospheric window typically used for terrestrial imaging systems. This paper presents the recent
performance improvement attained with very long wavelength infrared (VLWIR) focal plane arrays, by the stringent
control of the small bandgap HgCdTe material quality. Array operability is further enhanced by design using a 2:1
super-pixel detector format scheme with programmable bad element de-select and our new detector input offset
optimization circuitry within each unit cell. Focal plane arrays with peak quantum efficiencies in excess of 80 percent,
and cutoff wavelengths out to 15 μm have NEI operabilities around 95 percent for mid 1014 ph/s-cm2 fluxes operating
near 50 K. Average NEI of 3.5 x 1010 ph/s-cm2 was demonstrated for a 14 μm cutoff wavelength focal plane array,
consisting of over 55,000 elements, operating with an effective sample time of 87.5 ms.
This paper reports new performance data for SWIR HgCdTe 256x256 hybrid Focal Plane Arrays with cutoff wavelengths of 2.6-2.7 μm, operating at temperatures of 190 K to 220 K. The unit cell size is 30x30 μm2. Back-illuminated SWIR HgCdTe P-on-n photodiode arrays were fabricated from two-layer LPE films grown on CdZnTe substrates. Response uniformity is excellent, with σ/μ=3-4%, and response operabilities are better than 99.9%. At a temperature of 190 K and a background photon flux of 6.8x1011 ph/cm2-s, the median NEI is 1.1x109 ph/cm2-s, which is 1.4 times the BLIP NEI. NEI operabilities are better than 98.8%. Quantum efficiencies for large-area test diodes are 69% to 78%, close to the 79% upper limit imposed by reflection from the non-antireflection-coated CdZnTe substrate.
Readout integrated circuits (ROICs) for focal plane arrays (FPAs) have become increasingly complex to meet the needs of modern infrared systems. BAE Systems has pioneered a number of advanced signal processing architectures for FPA ROICs. Demonstrated signal processing capabilities of BAE Systems FPAs include analog-to-digital conversion, offset subtraction, individual pixel automatic gain compensation, transient noise suppression, on-FPA defect deselection, reconfigurable pixels, spatial neural network processing and subframe noise averaging. BAE Systems FPA advanced signal processing is not just for demonstrations, but is used in many of their deliverable FPAs, improving real system performance.
M. Reine, A. Hairston, P. Lamarre, K. Wong, S. Tobin, A. Sood, C. Cooke, M. Pophristic, S. Guo, B. Perez, R. Singh, C. Eddy, U. Chowdhury, M. Wong, R. Dupuis, T. Li, S. DenBaars
This paper reports the development of aluminum-gallium nitride (AlGaN or AlxGa1-xN) photodiode technology for high-operability 256×256 hybrid Focal Plane Arrays (FPAs) for solar-blind ultraviolet (UV) detection in the 260-280 nm spectral region. These hybrid UV FPAs consist of a 256×256 back-illuminated AlGaN p-i-n photodiode array, operating at zero bias voltage, bump-mounted to a matching 256×256 silicon CMOS readout integrated circuit (ROIC) chip. The unit cell size is 30×30 μm2. The photodiode arrays were fabricated from multilayer AlGaN films grown by MOCVD on 2" dia. UV-transparent sapphire substrates. Improvements in AlGaN material growth and device design enabled high quantum efficiency and extremely low leakage current to be achieved in high-operability 256×256 p-i-n photodiode arrays with cuton and cutoff wavelengths of 260 and 280 nm, placing the response in the solar-blind wavelength region (less than about 280 nm) where solar radiation is heavily absorbed by the ozone layer. External quantum efficiencies (at V=0, 270 nm, no antireflection coating) as high as 58% were measured in back-illuminated devices. A number of 256×256 FPAs, with the AlGaN arrays fabricated from films grown at three different facilities, achieved response operabilities as high as 99.8%, response nonuniformities (σ/μ) as low as 2.5%, and zero-bias resistance median values as high as 1×1016 ohm, corresponding to R0A products of 7×1010 ohm-cm2. Noise Equivalent Irradiance (NEI) data were measured on these FPAs. Median NEI values at 1 Hz are 250-500 photons/pixel-s, with best-element values as low as 90 photons/pixel-s at 1 Hz.
M. Reine, A. Hairston, P. Lamarre, K. Wong, S. Tobin, A. Sood, C. Cooke, M. Pophristic, S. Guo, B. Peres, R. Singh, C. Eddy, U. Chowdhury, M. Wong, R. Dupuis, T. Li, S. DenBaars
This paper reports the development of aluminum-gallium nitride (AlGaN or AlxGa1-xN) photodiode technology for high-operability 256×256 hybrid Focal Plane Arrays (FPAs) for solar-blind ultraviolet (UV) detection in the 260-280 nm spectral region. These hybrid UV FPAs consist of a 256×256 back-illuminated AlGaN p-i-n photodiode array, operating at zero bias voltage, bump-mounted to a matching 256×256 silicon CMOS readout integrated circuit (ROIC) chip. The unit cell size is 30×30 μm2. The photodiode arrays were fabricated from multilayer AlGaN films grown by MOCVD on 2" dia. UV-transparent sapphire substrates. Improvements in AlGaN material growth and device design enabled high quantum efficiency and extremely low leakage current to be achieved in high-operability 256×256 p-i-n photodiode arrays with cuton and cutoff wavelengths of 260 and 280 nm, placing the response in the solar-blind wavelength region (less than about 280 nm) where solar radiation is heavily absorbed by the ozone layer.
External quantum efficiencies (at V=0, 270 nm, no antireflection coating) as high as 58% were measured in backilluminated devices. A number of 256×256 FPAs, with the AlGaN arrays fabricated from films grown at three different facilities, achieved response operabilities as high as 99.8%, response nonuniformities (σ/μ) as low as 2.5%, and zero-bias resistance median values as high as 1×1016 ohm, corresponding to R0A products of 7×1010 ohm-cm2. Noise Equivalent Irradiance (NEI) data were measured on these FPAs. Median NEI values at 1 Hz are 250-500 photons/pixel-s, with best-element values as low as 90 photons/pixel-s at 1 Hz.
SWIR HgCdTe photodiode test chips and 256x256 Focal Plane arrays with a 2.1 micron cutoff wavelength have been fabricated and tested.
The base material was n-type HgCdTe. P-type junctions were created by ion implantation. Test chip arrays with 60-micron pixels exhibited an average RoA of 509 ohm-cm2 and internal quantum efficiency (QE) of 98% at 295 K; RoA and QE were uniform. Average RoA increased to 2.22x104 at 250 K and internal QE remained high at 93%. The mini-array of 30-micron pixels had lower RoA values, 152 and 6.24x103 ohm-cm2 at 295 and 250 K, but 100% internal quantum efficiency at both temperatures. There was no bias dependence of quantum efficiency, demonstrating that our junction formation process does not give rise to valence band barriers.
FPA test data have demonstrated NEI operability greater than 98% at 220 K and greater than 97% at 250 K along with QE operability in excess of 99.9% at 220 K and in excess of 99.8% at 250 K.
Accurate high resolution temperature sounding through our atmosphere is paramount to improving our weather forecasting, monitoring, and analysis capability. From the vantagepoint of earth Orbit, remote temperature sounding is becoming a reality and its accuracy is bolstered by recent advances in infrared hyper-spectral sensor capability. One promising approach takes advantage of a two-dimensional, imaging Fourier transform spectrometer to obtain a data cube with the field of view along one plane and multiple IR spectra (one for every FPA pixel) along the orthogonal axis. The spatial resolution is limited only by the pixel pitch in the imaging focal plane and the optics used to collect the data. The maximum optical path difference in the Michelson FTS defines the spectral resolution and dictates the number of path-length interferogram samples (FPA frames required per cube. This paper discusses the unique challenges placed on the focal plane by the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) approach and how advanced focal plane technology is applied to satisfy these challenges. Two focal planes are required to provide spectral coverage from 4.4 to 6.1um and 8.85-14.6um. Currently, the GIFT’s LWIR focal plane is the longest wavelength two-dimensional PV HgCdTe array of this size (128 square on 60 um centers) planned for space deployment. The paper presents performance data of Liquid Phase Epitaxy (LPE) fabricated HgCdTe detectors and design details of the advanced readout integrated circuit necessary to meet the demanding requirements of the imaging sensor for the GIFTS instrument.
While laparoscopes are used for numerous minimally invasive procedures, minimally invasive liver resection and ablation occur infrequently. the paucity of cases is due to limited field of view and difficulty in determination of tumor location and margins under video guidance. By merging minimally invasive surgery with interactive, image-guided surgery, we hope to make laparoscopic liver procedures feasible. In previous work, we described methods for tracking an endoscope accurately in patient space and registration between endoscopic image space and physical space using the direct linear transformation (DLT). We have now developed a PC-based software system to display up to four 512 Χ 512 images indicating current surgical position using an active optical tracking system. We have used this system in several open liver cases and believe that a surface-based registration technique can be used to register physical space to tomographic space after liver mobilization. For preliminary phantom liver studies, our registration error is approximately 2.0mm. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based/DLT registration methods, in combination with the video display and tracked endoscope, will hopefully make laparoscopic liver cryoablation and resection procedures feasible.
We report results for 64 X 64 simultaneous MW/LW dual-band HgCdTe Focal Plane Arrays (FPAs). The MW and LW average cutoff wavelengths at 78 K are in the 4.27 - 4.35 micrometer and 10.1 - 10.5 micrometer ranges respectively. The unit cell size is 75 X 75 micrometer2. These staring dual-band FPAs exhibit high average quantum efficiencies (MW: 79%; LW:67%), high median detectivities (MW: 4.8 X 1011 cm- (root)Hz/W; LW: 7.1 X 1010 cm-(root)Hz/W), low median NE(Delta) Ts (MW: 20 mK; LW: 7.5 mK for TSCENE equals 295 K and f/2.9), large dynamic ranges (MW: 77 dB; LW: 75 dB), and 87% stare efficiencies for both the MW and LW spectral bands. The dual-band HgCdTe detector array is fabricated from a four- layer P-n-N-P film grown in situ by MOVPE. The dual-band silicon CMOS input circuit utilizes a unique floating-direct- injection approach to achieve separate and simultaneous integration of both bands within each unit cell. There are two Compact Signal Averager circuits in each unit cell, to average subframes within every frame for each spectral band, allowing full stare efficiency in both spectral bands, as well as variable band-independent transimpedance gains. These data confirm that all key features of our P-n-N-P dual-band HgCdTe detector and our dual-band input circuit function as designed.
Cryogenic signal processing and A/D conversion for the IR imaging and high energy physics experiment applications place severe demands on the silicon process involved, particularly in ionizing radiation environments. This paper describes a process specifically optimized for operation in the 40 K - 77 K temperature range in a total dose environment. Trade-offs of hardness, supply voltage and hot electron vulnerability are discussed and preliminary device- level results are shown.
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