Bulk lifetime determination of etch-thinned InSb wafers fortwo-dimensional infrared focal plane array

The bulk lifetime of etch-thinned InSb wafers, with lithography on both sides, has been measured. A device was specially designed to directly measure the diffusion length of the etch-thinned layer. The diffusion length was found to be approximately 35 μm at 77 K, which yields a lifetime of approximately 250 ns. No degradation to the semiconductor due to the thinning process, the passivation on both sides, possible defects or mechanical stress in the thinned layer, or other fabrication processes was found. The reported measurements characterize the fabrication technology of the etch-thinned and processed InSb wafers, designed for backside-illuminated two-dimensional detector arrays for an infrared hybrid focal plane     

Experimental verification of a design methodology for torsion actuators based on a rapid pull-in solver

In this work, an experimental and theoretical study of the effect of various geometrical parameters on the electromechanical response and pull-in parameters of torsion actuators is presented. A lumped two-degrees-of-freedom (L2DOF) pull-in model that takes into account the bending/torsion coupling, previously proposed for cantilever suspended actuators, is tailored for the torsion actuators under study. This model is shown to better capture the measured pull-in parameters than previously proposed lumped single-degree-of-freedom (L1DOF) models. The measurements were conducted on torsion actuators with various shapes, fabricated on silicon-on-insulator (SOI) wafers using deep reactive ion etching (DRIE) and flip-chip bonding. Furthermore, a novel rapid solver, for extracting the pull-in parameters of the L2DOF model of the torsion actuators, is proposed. The proposed solver is based on a Newton-Raphson scheme and the recently presented DIPIE algorithm and is shown to be /spl sim/10 times faster than the prevalent voltage iterations based solvers. The rapid and more accurate pull-in extraction of the proposed approach renders it as a tool for extensive analysis and design optimization of torsion actuators.     

Optimal design and noise consideration of micromachined vibratingrate gyroscope with modulated integrative differential optical sensing

A novel design of a micromachined vibrating rate gyroscope is presented. The rate gyroscope consists of a suspended proof mass which is attached by indium bumps to a CMOS chip. The proof mass is excited to vibration by electrostatic force. The displacements due to rate are sensed optically, using CMOS-integrated photodiodes and analog electronics. System considerations, including the mechanical behaviour, optical sensing, electronics, and noise sources of the rate gyroscope, are discussed. An expression for the noise equivalent rate (NER) of the system is obtained in order to derive an optimal design approach for the rate gyroscope. Optimal design and simulations of a case study of a rate gyroscope are presented. The device shows the ability of sensing 1 deg/h even at moderate quality factors of the order of 5000 and low-excitation voltages of 2.25 V     

Tomographic reconstruction of incompressible flow

In many experiments facilitating tomography the reconstruction problem is under-determined, meaning there are many possible solutions consistent with the measurements. If the sampling rate is fast relative to the typical evolution time, the known physical dynamics of the system can be used as additional reconstruction constraints. Here we demonstrate that incorporating the requirement of incompressible flow can improve significantly the fidelity of the reconstructed sequence. The incompressibility of the reconstruction is assured by requiring the conservation of the density moments. It is demonstrated that the "incompressible" reconstruction can be significantly more accurate than the reconstruction using standard methods. A consequence of the density moments' conservation is the conservation of the density histogram throughout the reconstructed sequence.     

Spectroscopic evaluation of n-type CdZnTe gamma-ray spectrometers

This work focuses on the evaluation of the spectroscopic performance of n-type CdZnTe gamma-ray spectrometers, grown by a modified horizontal Bridgman Technique developed at IMARAD Imaging Systems Ltd. Two types of devices are studied: (i) detector arrays grown and produced by IMARAD and employing ohmic indium contacts and (ii) detectors and arrays fabricated at Technion in crystals provided by IMARAD, employing different types of contacts. Alpha particle spectroscopy as well as gamma-ray spectroscopy is used to evaluate and characterize the energy resolution of gamma-ray spectrometers fabricated on n-type CdZnTe grown by a modified horizontal Bridgman and doped with indium. The electron and hole mobility lifetime products of the n-type CdZnTe material grown by IMARAD are estimated by measuring the dependence of charge collection efficiency upon the bias voltage, using a calibrated multichannel analyzer. The measured results indicate that the average electron and hole mobility-lifetime products are, respectively, of the order of μ_nτ_n=(1–2)·10⁻³ cm²/V and μ_pτ_p=6·10⁻⁶ cm²/V. The measured energy resolution of 122 keV photons is −(5–6)% when the source is not collimated and is reduced to −4.5% when the source is collimated. These results are obtained with ohmic cathode as well as with a rectifying cathode. A statistical model for the calculation of the pulse height spectra as a function of photon energy, electron and hole mobility-lifetime products and applied electric field, which has been recently reported in Applied Physical Letters, is used to determine the role of incomplete charge collection in the spectral performance of the n-type CdZnTe spectrometers. The comparison between the measured and modeled results indicates that the dark noise, cross talk and non-uniformity are the main limiting factors of the spectral performance of the n-type spectrometers rather than incomplete charge collection. The good spectroscopic performance of the arrays under study is attributed to an adequate hole mobility lifetime for the geometry of the pixilated arrays. The study indicates that the n-type CdZnTe spectrometers are useful for a wide range of imaging applications.     

Nuclear Resonance Photon Scattering Studies of N2 Adsorbed on Grafoil and of NaNO2 Single Crystal

The nuclear resonance photon scattering (NRPS) from ¹⁵N₂ adsorbed on graphite was investigated. The resonantly scattered intensities from the 6324 keV level of ¹⁵N with the photon beam parallel and perpendicular to the adsorbing grafoil planes was measured at 140 K and coverages below 0.7 monolayers (ML), where the ¹⁵N₂ occur in the vapor phase. The data were used for deducing the out-of-plane tilt angle of adsorbed N₂ relative to the graphite surface and the results were compared with grand canonical Monte Carlo (GCMC) calculations. Using the same method, a single crystal of NaNO₂ was studied by measuring the scattering intensities with the nitrite planes aligned parallel and perpendicular to the photon beam. At 80 K, a huge anisotropy (R≈3.6) was observed, caused by the anisotropy in the zero-point motion of the internal modes of vibration of the NO₂ ion. The variation of the scattering intensity from a powdered isotopic ¹⁵NaNO₂ sample versus T in the range 12 K to 297 K was also measured and explained by accounting for the internal and external vibrational modes in NaNO₂.     

Photocurrent in CdTe NIP solar cells

A simple analytical model for the voltage dependence of the photocurrent in CdTe n–i–p solar cells is presented. The physical model is corroborated with a numerical solution of Poisson and the two continuity equations under illumination and shows excellent agreement with the numerical data. The new model is compared with previously reported models of Bube and Crandall. The new model illuminates the loss mechanism of carriers near the front interface of CdTe solar cells. It is shown that the photocurrent is high when the carrier velocity due to the electric field is higher than the product of the absorption coefficient and the diffusion coefficient, almost regardless of the interface recombination velocity value. At lower electric field values, the interface recombination velocity has a stronger effect on the photocurrent. Experimental conditions leading to a reduction of the electric field and a corresponding decrease in the collection efficiency in CdTe n–i–p solar cells are discussed.     

Study of contacts to CdZnTe radiation detectors

This study characterizes, for the first time, contacts to CdZnTe radiation detectors by measuring the dark noise spectra as a function of the applied bias. The noise currents are correlated with the dc dark current-voltage characteristics of CdZnTe x-ray and gamma-ray detectors. In order to identify and separate the role of the contacts in the overall performance, the measured noise phenomena is correlated with detector configuration and contact design as well as the growth method of the CdZnTe crystals, contact technology, and passivation. Several contact technologies (electroless gold, and a number of evaporated metallic contacts including gold, indium, zinc, titanium, aluminum, and platinum contacts) are compared. Contacts to CdZnTe crystals grown by high pressure Bridgman are compared with contacts to CdZnTe crystals grown by modified Bridgman. Contacts of resistive detectors as well as of Schottky detectors are reported. Large area symmetric contacts are compared with small area pixelized contacts. The role of the metallization used for contacts, the role of surface effects and passivation, and the role of contact design are discussed.     

Quantum efficiency and crosstalk of an improvedbackside-illuminated indium antimonide focal-plane array

The quantum efficiency and crosstalk of backside-illuminated indium antimonide photodiodes in hybrid focal plane arrays are calculated. An improved structure with crosswise ohmic contacts at the backside of the thinned InSb substrate is described. The simulations predict a significant reduction in the crosstalk while retaining high quantum efficiency