Papers by Charles Westgate
IEEE Journal of Solid-State Circuits, 1987
A method to predict the small-signal linear gain and level of harmonic distortion in analog MOS c... more A method to predict the small-signal linear gain and level of harmonic distortion in analog MOS circuits is presented. This method, based on a generalized nonlinear transfer function approach, lends itself to implementation in the AC small-signal analysis routine of the circuit simulation program SPICE. A low-frequency nonlinear distortion model based on the CSIM simulator MOSFET model is applied to three simple MOSFET circuits. Results presented emphasize the need to consider small-signal quantities in the development of MOSFET models and in the determination of device parameters. The method can be easily extended to include capacitive effects and a prediction of intermodulation distortion.
Fluid Phase Equilibria, 1992
Comparison of the dielectric behavior of mixtures of methanol with carbon dioxide and ethane in t... more Comparison of the dielectric behavior of mixtures of methanol with carbon dioxide and ethane in the mixture-critical and liquid region. Fluid Phase Equilibria, 77: 241-259. Dielectric data are reported for the CO,-methanol system at 3.5, 50 and 65°C and the ethane-methanol system at 35,65 and 95°C at a number of composition and over a pressure range from the saturation pressure of the mixture to 300 bar. Experimental pressure-composition isotherms and molar volume data are also reported for the ethane-methanol system. The dielectric constant for both types of methanol mixtures can be increased by decreasing the temperature or by increasing the permanent dipole concentration of the mixture through increasing the mixture density or the methanol mole fraction. The dielectric constants for CO,-methanol mixtures are consistently greater than those for ethanemethanol mixtures over the entire pressure-temperature-composition space investigated in this study. The higher dielectric constants for CO,-methanol mixtures are conjectured to be a consequence of the quadrupole interactions between CO, and methanol and to the contribution from the CO,-methanol complex which is present in these mixtures.
Solar Energy, 2012
We report transmittance and conductivity measurements of aluminum-doped zinc oxide films grown by... more We report transmittance and conductivity measurements of aluminum-doped zinc oxide films grown by atomic layer deposition. The results show that the films have 80-90% transmittance in the visible region and good transmittance in the infrared. To our knowledge, this is the first time that the transmittance of aluminum-doped zinc oxide is reported to extend beyond 2500-5000 nm. Following annealing, an optimal sheet resistance of 25 X/h was obtained for a 575 nm thick film with a carrier density of 2.4 Â 10 20 cm À3 without compromising the transmittance in the visible regime.
Rev Sci Instr, 1975
The relationships of microwave Hall mobilities and microwave conductivities in a semiconductor, p... more The relationships of microwave Hall mobilities and microwave conductivities in a semiconductor, placed at the center of a dual mode TE sub-111 cavity, are expressed in terms of the loaded and unloaded voltage reflection coefficients, the sample and the cavity dimensions, the ratio of the output power to the input power of the cavity, and the magnetic field. Scattering matrix analysis and perturbation theory are used.
Journal of Physics and Chemistry of Solids
ABSTRACT
Review of Scientific Instruments, 1975
The relationships of microwave Hall mobilities and microwave conductivities in a semiconductor, p... more The relationships of microwave Hall mobilities and microwave conductivities in a semiconductor, placed at the center of a dual mode TE sub-111 cavity, are expressed in terms of the loaded and unloaded voltage reflection coefficients, the sample and the cavity dimensions, the ratio of the output power to the input power of the cavity, and the magnetic field. Scattering matrix analysis and perturbation theory are used.
Journal of Physics and Chemistry of Solids, 1970
... Rev. 90, 120(1953). 13. L WDWP.O.,Phys.Rev.94 1600(1954). 14. HERMAN F. andSKILLMAN S., Atomi... more ... Rev. 90, 120(1953). 13. L WDWP.O.,Phys.Rev.94 1600(1954). 14. HERMAN F. andSKILLMAN S., Atomic Structure Calculations. Prentice Hall, Englewood Cliffs. NJ (1963). 15. ... Rev. 129, 1029(1963). 29. BALSLEV I. and LAWAETZ P., Phys. Rev. Lett. 19,6(1965). 30. ...
J Phys D Appl Phys, 1974
A reply is given to a recent letter by Wintle in this journal.
2015 ASEE Annual Conference and Exposition Proceedings, 2015
Solid State Communications, 1969
ABSTRACT
Journal of Physics D: Applied Physics, 1974
Metal-insulator contact charging models are presented for insulators having (a) traps uniformly d... more Metal-insulator contact charging models are presented for insulators having (a) traps uniformly distributed in the energy gap and (b) discrete traps in the energy gap. It is shown that in the former case the relationship between the magnitude of the charge transferred ...
Journal of Physics D: Applied Physics, 1974
... 0 1974 LETTER TO THE EDITOR Comments on 'Contact charging of polymers' A Chowdry an... more ... 0 1974 LETTER TO THE EDITOR Comments on 'Contact charging of polymers' A Chowdry and CR Westgate The Johns Hopkins University, Baltimore, Maryland 21218, USA Received 8 July 1974 Abstract. A reply is given to a recent letter by Wintle in this journal. ...
The Journal of Chemical Physics, 1970
ABSTRACT
IEEE Transactions on Electron Devices, 1992
A small-signal ac transport description is formulated to characterize the high-frequency operatio... more A small-signal ac transport description is formulated to characterize the high-frequency operation of unipolar semiconductor heterostructures. The physical transport model combines diffusion-drift currents through compositionally graded regions with a thermionic-emission current imposed at an abrupt material interface. This sinusoidal steady-state analysis can be employed to determine the dynamic terminal admittance of devices at microwave frequencies and cryogenic temperatures. AI,Ga, _,As alloy ramp heterostructures have been fabricated by molecular beam epitaxy and tested over wide ranges of temperature, dc bias, and frequency. Experimentally measured microwave admittances are favorably compared with simulated results at room and liquid-nitrogen temperatures, and are used to verify the theoretical approach.
IEEE Transactions on Electron Devices, 2000
IEEE Transactions on Electron Devices, 2000
IEEE Transactions on Electron Devices, 1991
The electron transport properties of AlGaAs ramp diodes are investigated using a physical model w... more The electron transport properties of AlGaAs ramp diodes are investigated using a physical model which combines current transport through the heterostructure bulk with current across the abrupt heterointerface in a fully self-consistent numerical approach. Transport at the abrupt material discontinuity is described by thermionic and thermionic-field emission processes, whereas transport in regions of smoothly varying alloy composition is modeled by diffusion-drift mechanisms. Several devices whose bandgaps are graded over several thousand angstroms have been fabricated by MBE and tested at room and liquid-nitrogen temperatures. The experimentally observed rectification properties are compared with the simulated results over a wide range of dc bias. Through appropriate choice of alloy composition and doping profiles, majority carrier devices based on internal (bulk) barriers may be realized.
Magnetic Resonance in Medicine, 2001
Parallel, spatial-encoded MRI requires a large number of independent detectors that simultaneousl... more Parallel, spatial-encoded MRI requires a large number of independent detectors that simultaneously acquire signals. The loop structure and mutual coupling in conventional phased arrays limit the number of coils and therefore the potential reduction in minimum scan time achievable by parallel MRI tchniques. A new near-field MRI detector array, the planar strip array (PSA), is presented that eliminates the coupling problems and can be extended to a very large number of detectors and high MRI frequencies. Its basic structure is an array of parallel microstrips with a high permittivity substrate and overlay. The electromagnetic (EM) wavelength can be adjusted with the permittivity, and the strip lengths tuned to a preselected fraction of the wavelength of the MRI frequency. EM wave analysis and measurements on a prototype four-element PSA reveal that the coupling between the strips vanishes when the strip length is either an integer times a quarter wavelength for a standingwave PSA, or a half wavelength for a travelling-wave PSA, independent of the spacing between the strips. The analysis, as well as phantom and human MRI experiments performed by conventional and parallel-encoded MRI with the PSA at 1.5 T, show that the decoupled strips produce a relatively high-quality factor and signal-to-noise ratio, provided that the strips are properly terminated, tuned, and matched or coupled to the preamplifiers.
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Papers by Charles Westgate