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Publication
Featured researches published by Walter Allegretto.
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems | 1991
Walter Allegretto; Arokia Nathan; H. Baltes
Two-dimensional numerical solutions to the system of partial differential equations governing galvanomagnetic carrier transport in magnetic-field-sensitive integrated bipolar transistors are presented. The equations are discretized using the finite box procedure with a variation in the standard Scharfetter-Gummel approach adopted for the current continuity equations. High-resolution computations of the potentials in the base region of realistic device structures and operating conditions show that the magnitude of the Hall voltage at the emitter-base junction is too small to cause any appreciable asymmetric minority carrier injection thus invalidating the widely invoked emitter injection modulation model. Measured data obtained using in situ Hall probes are in support of the conclusions derived from the numerical model. >
IEEE Transactions on Electron Devices | 1989
A. Nathan; K. Maenaka; Walter Allegretto; H. Baltes; T. Nakamura
Computations using a two-dimensional numerical model as well as experimental data obtained from Hall probe measurements indicate the presence of a weak Hall field along the emitter-base junction of magnetotransistors. This field is too minute to cause any appreciable emitter-injection modulation or asymmetric injection, an effect that has been widely invoked to describe the magnetic sensitivity of magnetotransistors (MT) fabricated in standard IC technologies. The results indicate that emitter-injection modulation as an MT operating principle can be ruled out in favor of carrier deflection (for linear MTs) and magnetoconcentration (for nonlinear MTs). >
IEEE Transactions on Electron Devices | 1987
A. Nathan; Walter Allegretto; H. Baltes; Y. Sugiyama
Carrier transport in Hall-type devices detecting magnetic domains is analyzed in terms of a two-dimensional numerical model, using a finite element scheme. The numerical model allows the calculation of magnetic sensitivity for general device geometries or structures, any homogeneous semiconductor material, and arbitrary domain shapes and sizes. We specifically consider three types of commonly used Hall detectors: the conventional Hall plate, the split-electrode Hall device, and the Hall cross. The magnetic sensitivity for these devices is computed for various domain configurations. In particular, the devices output response for moving domains is investigated and appropriate figures of merit are established with respect to spatial resolution. A comparison of the numerical solutions with previously reported experimental results supports the validity of our analysis.
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems | 1990
Arokia Nathan; H. Baltes; Walter Allegretto
With the increasing need for microsensors, development of simulation tools (based on adequate physical models to facilitate microsensor analysis and design) is a crucial task. The authors review the variety of physical approximations, model equations, and boundary conditions along with an outline of pertinent numerical procedures used in the numerical simulation of semiconductor microsensors. In particular, physical microsensors for thermal, optical, magnetic, and mechanical measurands are considered and selected simulation results are presented. >
Journal of Vacuum Science & Technology B | 2001
K. B. Brown; Yuan Ma; Walter Allegretto; R. P. W. Lawson; F. E. Vermeulen; A.M. Robinson
Enhanced hysteresis effects are seen in the resonant behavior of a magnetically actuated oscillating microcantilever at large deflections. These effects, which are produced by resonant mode coupling, take the form of abrupt changes in the amplitude of oscillation. These changes in amplitude and the actuating frequencies at which they occur depend on whether the actuating frequency is being increased or decreased. We have fabricated a microcantilever in which this phenomenon is strongly affected by the damping produced by the pressure of ambient gas. We have investigated this device for use as a pressure sensor in air from 10−3 to 102 Torr.
IEEE Transactions on Electron Devices | 1993
Arokia Nathan; Walter Allegretto
A geometric factor applicable to a wide range of device geometries of the van der Pauw dual configuration is presented. Such a configuration allows a direct retrieval of the Hall mobility in a single measurement of the magnetic-field-induced imbalance in output current. In view of scaling considerations, the geometric factor is characterized simply in terms of device aspect ratio (L/W) and relative electrode separation (d/W). The geometric factor, which is based on numerical computations, overcomes the limitations inherent in the existing form that has been analytically obtained for an infinitesimally small electrode separation. Hence, it is now possible to design practical device geometries which readily lend themselves to in situ measurement and characterization of the material or process in question, without being constrained by photolithography limitations. >
canadian conference on electrical and computer engineering | 1996
Bing Shen; A.M. Robinson; Walter Allegretto; Yuan Ma; Bing Yu; Ming Hu
A CMOS-compatible magnetically actuated micromachined cantilever device is described. The structure employs the concept of nested cantilevers to enhance the angular deflection produced by Lorentz forces acting at the ends of each cantilever. Devices fabricated by two CMOS processes were tested. Static and dynamic bi-directional deflection responses were measured; static deflections of more than 2.5/spl deg/ and dynamic resonance deflections of 65/spl deg/ were obtained, Resonant frequencies were observed from 4.5 kHz to 56 kHz. Numerical simulations were performed and agree well with experiment.
Canadian Journal of Physics | 1996
Bing Shen; Ming Hu; Bing Yu; A. M. Robinson; R. Lawson; Walter Allegretto
Canadian Journal of Physics | 1989
Walter Allegretto; Arokia Nathan; K. Chau; H.P. Baltes
Canadian Journal of Physics | 1991
Kris Chau; Walter Allegretto; Ljubiśa Ristic