John Marciniec

HgCdTe MWIR back-illuminated electron-initiated avalanche photodiode arrays

This paper reports performance data for back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiode (e-APD) 4×4 arrays with large-area unit cells (250×250 μm2). The arrays were fabricated from p-type HgCdTe films grown by LPE on CdZnTe substrates. The arrays were bump-mounted to fanout boards and were characterized in the back-illuminated mode. Gain increases exponentially with reverse bias voltage, and gain versus bias curves are quite uniform from element to element. The maximum gain measured is 648 at -11.7 V for a cutoff wavelength of 4.06 μm at 160 K. For the same reverse bias voltage, the gain at 160 K for elements with two different cutoff wavelengths (3.54 and 4.06 μm at 160 K) increases exponentially with increasing cutoff wavelength, in agreement with Becks empirical model for gain versus voltage in HgCdTe e-APDs. Spot scan data show that both the V=0 response and the gain at V=-5.0 V are quite uniform spatially over the large junction area. To the best of our knowledge, these are the first spot scan data for avalanche gain ever reported for HgCdTe e-APDs. Capacitance versus voltage data are consistent with an ideal abrupt junction having a donor concentration equal to the indium counterdoping concentration in the as-grown LPE film. Calculations predict that bandwidths of 500 MHz should be readily achievable in this vertical collection geometry, and that bandwidths as high as 3 GHz may be possible with careful placement of the junction relative to the compositionally interdiffused region between the HgCdTe LPE film and the CdZnTe substrate.

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.

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.

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.

HgCdTe LWIR p-on-n photodiodes formed by arsenic diffusion from the vapor phase

We report current-voltage data for back-illuminated mesa photodiode test structures fabricated by arsenic-diffusion into n-type LPE HgCdTe films. Arsenic diffusion was carried out in a sealed quartz ampoule containing a source of both Hg and As. The arsenic-diffused p-on-n photodiodes were characterized at 70 K and 80 K. The cutoff wavelength was about 11 μm at 80 K. The data for 400 μm diameter photodiodes fabricated by the arsenic diffusion process are very similar to those from a conventional two-layer LPE P-on-n process for material with approximately the same cutoff wavelength. We outline process and doping level changes that should improve detector performance.

SWIR HgCdTe 256x256 focal plane array technology at BAE Systems

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.

Matrix Arrays for the 21st Century

Improved ultrasound image quality requires the use of matrix (n x m) arrays with a thousand or more elements. As element numbers increase and their dimensions grow smaller, limitations to present fabrication technologies arise. Cost, ergonomics, produceability and reliability are critical issues. Signal-to-noise loss due to the capacitance of interconnecting coax cables becomes a fundamental problem. Connecting an integrated circuit directly to the array elements alleviates all these problems.