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Self-Consistent Physics-Based Numerical Device/Harmonic-Balance Circuit Analysis of Heterostructure Barrier and Schottky Barrier Varactors Including Thermal Effects

Authors:
J. R. Jones, S. H. Jones, G. B. Tait
Abstract:
In order to effectively design millimeter and subrnillimeter wave frequency multipliers, both the electrical and thermal properties of the device and circuit must be analyzed in a fully selfconsistent manner. To facilitate a self-consistent analysis of Heterostructure Barrier Varactor (HBV) and Schottky Barrier Varactor (SBV) frequency multipliers, large-signal time- and temperature-dependent numerical device simulators, with excellent computational speed and convergence properties, have been developed for generic GaAs/InGaAs /A1GaAs HBV and conventional GaAs SBV structures having arbitrary doping profiles. The numerical device simulators are based on the first two moments of the Boltzmann transport equation coupled to Poisson's equation, and combine current transport through the device bulk with therrnionic and thermionic-field emission currents imposed at the Schottky interface or heterojunction interfaces. Given the importance of both the active device and its embedding circuit in the design of frequency multipliers, the numerical device simulators have been combined with a novel and efficient harmonic-balance circuit analysis technique to provide unified computer-aided design environments for entire HBV or SBV multiplier circuits. The steady-state thermal properties of frequency multipliers are analyzed based on the amount of power dissipated in the active region of the device and the thermal resistance to heat flow presented by the various elements that make up the circuit. From these quantities, the average temperature across the active region of the varactor can be estimated for use in the appropriate device simulator. The thermal model presented here uses simple geometrical expressions for the various thermal resistances of circuits utilizing both planar and whisker-contacted diode geometries assuming the ambient air is a perfect insulator. For planar diodes, the thermal resistance of the diode substrate is calculated using a three-dimensional finite-element heat flow analysis to account for the substrate's irregular heat flow geometry. Using the numerical device/harmonic-balance circuit simulators, an investigation is undertaken to determine the frequencies at which the widely used quasi-static equivalent circuit varactor models fail, and for what reasons these models fail. A comparison is made between published experimental results and a full analysis, including both electrical and thermal properties, of frequency multipliers utilizing the UVA 6P4 GaAs SBV and a single barrier GaAs/A10.7Ga0.3As HBV.
Categories:
Varactors
Year:
1995
Session:
9
Full-text:
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Page Number(s):
423-441