Study of Morphological Defects on Dual-Band HgCdTe on CdZnTe

HgCdTe dual-band epitaxial layers on lattice-matched CdZnTe substrates often have morphological defects. These defects, unlike normal void and microvoid defects, do not contain a polycrystalline core and, therefore, do not offer a good contrast for observation using optical and electron microscopes. This paper reports a way of identifying these defects by using a Nomarski optical microscopy image overlay on focused ion beam microscopy images for preparation of thin cross-sectional foils of these defects. Transmission electron microscopy was used to study the defect cross-sections to identify the origin and evolution of the morphological defects and their effect on the epitaxial layer. This paper reports cross-sectional analysis of four morphological defects of different shape and size.     

The design and implementation of a low-power clock-poweredmicroprocessor

We describe the design and implementation of a 16-bit clock-powered microprocessor that dissipates only 2.9 mW at 15.8 MHz based on laboratory measurements. Clock-powered logic (CPL) has been developed as a new approach for designing and building low-power VLSI systems that exploit the benefits of supply-voltage-scaled static CMOS and energy-recovery CMOS techniques. In CPL, the clock signals are a source of ac power for the other large on-chip capacitive loads. Clock amplitude and waveform shape combine to reduce power. By exploiting energy recovery and an energy-conserving clock driver, it is possible to build ultra-low-power CMOS processors with this approach. We compare the CPL approach with a conventional, fully dissipative approach for a processor with a similar ISA and VLSI architecture which was designed using the same set of VLSI CAD tools. The simulation results indicate that the CPL microprocessor would dissipate 40% less power than the conventional design     

Using perturbation theory to compute the morphological similarity of diffusion tensors

Computing the morphological similarity of diffusion tensors (DTs) at neighboring voxels within a DT image, or at corresponding locations across different DT images, is a fundamental and ubiquitous operation in the postprocessing of DT images. The morphological similarity of DTs typically has been computed using either the principal directions (PDs) of DTs (i.e., the direction along which water molecules diffuse preferentially) or their tensor elements. Although comparing PDs allows the similarity of one morphological feature of DTs to be visualized directly in eigenspace, this method takes into account only a single eigenvector, and it is therefore sensitive to the presence of noise in the images that can introduce error intothe estimation of that vector. Although comparing tensor elements, rather than PDs, is comparatively more robust to the effects of noise, the individual elements of a given tensor do not directly reflect the diffusion properties of water molecules. We propose a measure for computing the morphological similarity of DTs that uses both their eigenvalues and eigenvectors, and that also accounts for the noise levels present in DT images. Our measure presupposes that DTs in a homogeneous region within or across DT images are random perturbations of one another in the presence of noise. The similarity values that are computed using our method are smooth (in the sense that small changes in eigenvalues and eigenvectors cause only small changes in similarity), and they are symmetric when differences in eigenvalues and eigenvectors are also symmetric. In addition, our method does not presuppose that the corresponding eigenvectors across two DTs have been identified accurately, an assumption that is problematic in the presence of noise. Because we compute the similarity between DTs using their eigenspace components, our similarity measure relates directly to both the magnitude and the direction of the diffusion of water molecules. The favorable performance characteristics of our measure offer the prospect of substantially improving additional postprocessing operations that are commonly performed on DTI datasets, such as image segmentation, fiber tracking, noise filtering, and spatial normalization.     

The Pb−Pu (Lead-Plutonium) system

This work was supported by the Department of Energy through the Joint Program on Critical Compilations of Physical and Chemical Data, coordinated through the Office of Standard Reference Data, National Bureau of Standards. Literature searched through 1984. Dr. Peterson is the ASM/NBS Data Program Category Editor for binary actinide alloys.     

Developments in the fabrication and performance of high-quality HgCdTe detectors grown on 4-in. Si substrates

We are continuing to develop our growth and processing capabilities for HgCdTe grown on 4-in. Si substrates by molecular beam epitaxy (MBE). Both short-wave and mid-wave infrared (SWIR and MWIR) double-layer hetero-junctions (DLHJs) have been fabricated. In order to improve the producibility of the material, we have implemented an in-situ growth composition-control system. We have explored dry etching the HgCdTe/Si wafers and seen promising results. No induced damage was observed in these samples. Detector results show that the HgCdTe/Si devices are state-of-the-art, following the diffusion-limited trend line established by other HgCdTe technologies. Focal-plane array (FPA) testing has been performed in order to assess the material over large areas. The FPA configurations range from 128×128 to 1,024×1,024, with unit cells as small as 20 μm. The MWIR responsivity and NEDT values are comparable to those of existing InSb FPAs. Pixel operabilities well in excess of 99% have been measured. We have also explored the role of growth macrodefects on diode performance and related their impact to FPA operability. The SWIR HgCdTe/Si shows similar results to the MWIR material. Short-wave IR FPA, median dark-current values of less than 0.1 e⁻/sec have been achieved.     

5-GHz 32-bit integer execution core in 130-nm dual-V/sub T/ CMOS

A 32-bit integer execution core containing a Han-Carlson arithmetic-logic unit (ALU), an 8-entry /spl times/ 2 ALU instruction scheduler loop and a 32-entry /spl times/ 32-bit register file is described. In a 130 nm six-metal, dual-V/sub T/ CMOS technology, the 2.3 mm/sup 2/ prototype contains 160 K transistors. Measurements demonstrate capability for 5-GHz single-cycle integer execution at 25/spl deg/C. The single-ended, leakage-tolerant dynamic scheme used in the ALU and scheduler enables up to 9-wide ORs with 23% critical path speed improvement and 40% active leakage power reduction when compared to a conventional Kogge-Stone implementation. On-chip body-bias circuits provide additional performance improvement or leakage tolerance. Stack node preconditioning improves ALU performance by 10%. At 5 GHz, ALU power is 95 mW at 0.95 V and the register file consumes 172 mW at 1.37 V. The ALU performance is scalable to 6.5 GHz at 1.1 V and to 10 GHz at 1.7 V, 25/spl deg/C.     

Thin film transmission matrix approach to fourier transform infrared analysis of HgCdTe multilayer heterostructures

The ability to achieve high-yield focal plane arrays from Hg_1−xCd_xTe molecular beam epitaxy material depends strongly on postgrowth wafer analysis. Nondestructive analysis that can determine layer thicknesses as well as alloy compositions is critical in providing run-to-run consistency. In this paper, we incorporate the use of a thin film transmission matrix model to analyze Fourier transform infrared (FTIR) transmission spectra. Our model uses a genetic algorithm along with a multidimensional, nonlinear minimization Nelder-Mead algorithm to determine the composition and thickness of each layer in the measured epitaxial structure. Once a solution has been found, the software is able to predict detector performance such as quantum efficiency and spectral response. We have verified our model by comparing detector spectral data to our predicted spectral data derived from the room-temperature FTIR transmission data. Furthermore, the model can be used to generate design curves for detectors with varying absorber thicknesses and/or different operating temperatures. The consequence of this are reduced cycle times and reduced design variations.     

Modeling Energy Recovery Using Thermoelectric Conversion Integrated with an Organic Rankine Bottoming Cycle

Engine and industrial waste heat are sources of high-grade thermal energy that can potentially be utilized. This paper describes a model system that employs thermoelectric conversion as a topping cycle integrated with an organic Rankine bottoming cycle. The model has many parameters that define combined system quantities such as overall output power and conversion efficiency. The model can identify the optimal performance points for both the thermoelectric and organic Rankine bottoming cycle. Key analysis results are presented showing the impact of critical design parameters on power output and system performance.     

Large-Format HgCdTe Dual-Band Long-Wavelength Infrared Focal-Plane Arrays

Raytheon Vision Systems (RVS) continues to further its capability to deliver state-of-the-art high-performance, large-format, HgCdTe focal-plane arrays (FPAs) for dual-band long-wavelength infrared (L/LWIR) detection. Specific improvements have recently been implemented at RVS in molecular-beam epitaxy (MBE) growth and wafer fabrication and are reported in this paper. The aim of the improvements is to establish producible processes for 512 × 512 30-μm-unit-cell L/LWIR FPAs, which has resulted in: the growth of triple-layer heterojunction (TLHJ) HgCdTe back-to-back photodiode detector designs on 6 cm × 6 cm CdZnTe substrates with 300-K Fourier-transform infrared (FTIR) cutoff wavelength uniformity of ±0.1 μm across the entire wafer; demonstration of detector dark-current performance for the longer-wavelength detector band approaching that of single-color liquid-phase epitaxy (LPE) LWIR detectors; and uniform, high-operability, 512 × 512 30-μm-unit-cell FPA performance in both LWIR bands.