Allen W. Hairston

Simultaneous MW/LW dual-band MOVPE HgCdTe 64x64 FPAs

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.

AlGaN UV focal plane arrays

This paper presents characterization data, including UV imagery, for 256 x 256 AlGaN UV Focal Plane Arrays (FPAs). The UV-FPAs have 30 x 30 μm 2 unit cells, and use back-illuminated arrays of AlGaN p-i-n photodiodes operating at zero bias voltage. The photodiode arrays were fabricated from multilayer AlGaN films grown by MOCVD on sapphire substrates. Data are also presented for individual AlGaN photodiodes and variable-area diagnostic arrays.

A128 X128 (16K) Ultrasonic Transducer Hybrid Array

Ultrasonic imaging in the low MHz frequency range with large two dimensional arrays presents many challenges in design and fabrication. In this paper, a 128 × 128 (16,384 total) element receiver array, consisting of a 1−3 composite piezoelectric transducer array bonded directly to large custom integrated circuits is described. This Transducer Hybrid Array (THA) is intended for use in a real-time 3D imaging system or acoustical camera (Fig. 1) for medical and underwater applications.

AlGaN p-i-n Photodiode Arrays for Solar-Blind Applications

This paper presents UV imaging results for a 256×256 AlGaN Focal Plane Array that uses a back-illuminated AlGaN heterostructure p-i-n photodiode array, with 30×30 μm 2 unit cells, operating at zero bias voltage, with a narrow-band UV response between 310 and 325 nm. The 256×256 array was fabricated from a multilayer AlGaN film grown by MOCVD on a sapphire substrate. The UV response operability (>0.4×average) was 94.8%, and the UV response uniformity (σ/μ) was 16.8%. Data are also presented for back-illuminated AlGaN p-i-n photodiodes from other films with cutoff wavelengths ranging between 301 and 364 nm. Data for variable-area diagnostic arrays of p-i-n AlGaN photodiodes with a GaN absorber (cutoff=364 nm) show: (1) high external quantum efficiency (50% at V=0 and 62% at V=-9 V); (2) the dark current is proportional to junction area, not perimeter; (3) the forward and reverse currents are uniform (σ/μ=50% for forty 30×30 μm 2 diodes at V=−40 V); (4) the reverse-bias dark current data versus temperature and bias voltage can be fit very well by a hopping conduction model; and (5) capacitance versus voltage data are consistent with nearly full depletion of the unintentionally-doped 0.4 μm thick GaN absorber layer and imply a donor concentration of 3-4×10 16 cm −3 .

VLIWR HgCdTe staring focal plane array development

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.

Advanced readout integrated circuit signal processing

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.

Imaging with a 2D Transducer Hybrid Array

Imaging with fully populated 2D arrays using acoustical lenses in the low MHz frequency range offers the potential for high resolution, real-time, 3D volume imaging together with low power and low cost. A 2D composite piezoelectric receiver array bonded directly to a large custom integrated circuit was discussed1 at the 23rd International Symposium on Acoustical Imaging. This 128 × 128 (16,384 total) element Transducer Hybrid Array (THA) uses massively parallel, on-chip signal processing and is intended for medical and underwater imaging applications. The system under development, which is a direct analog of a video camera, will be discussed in this paper.

High-operability SWIR HgCdTe focal plane arrays

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.

Imaging sensor for the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS)

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.

Real-time 3D underwater acoustical camera

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.