Modelling and simulation of silicon-on-sapphire mosfets for analogue circuit design
Modelling and simulation of silicon-on-sapphire mosfets for analogue circuit design
This thesis reports on a study of analytical modelling of metal-oxide-semiconductor field effect transistors (MOSFETs) fabricated in silicon-on-sapphire technology. In the work, two models for these transistors are described which are suitable for implementation in a circuit simulation program. These models have been developed for the design of analogue integrated circuits, but can equally be applied to digital circuits. The first model is restricted to strong inversion operation and accounts for the kink effect in the drain current characteristics. A separate formulation is developed for the device capacitances which is reciprocal. The equivalent circuit includes the effect of parasitic substrate resistance. The second model is more comprehensive; both the channel current as well as the total charges and capacitances are derived from a physical analysis of the gate, channel and depletion charge densities. These are defined as functions of the surface potential which is computed from knowledge of the terminal voltages. Since the surface potential function is continuous from subthreshold to strong inversion, both the channel current and device capacitances are smooth and continuous throughout all regions of operation. Both models have been implemented in the SPICE circuit simulation program by rewriting sections of the Fortran source code and including new subroutines. Evaluation of the models against measured device characteristics shows a significant improvement in predicting the d.c. drain conductance characteristics compared with a bulk MOSFET model. Measured characteristics of the frequency dependent drain admittance are presented and explained with a developed small-signal model. Comparison of measured and simulated amplifier circuit characteristics also shows a considerable modelling improvement over bulk MOSFET models which are unable to predict the correct gain and d.c. operating point.
University of Southampton
1991
Howes, Rupert
(1991)
Modelling and simulation of silicon-on-sapphire mosfets for analogue circuit design.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis reports on a study of analytical modelling of metal-oxide-semiconductor field effect transistors (MOSFETs) fabricated in silicon-on-sapphire technology. In the work, two models for these transistors are described which are suitable for implementation in a circuit simulation program. These models have been developed for the design of analogue integrated circuits, but can equally be applied to digital circuits. The first model is restricted to strong inversion operation and accounts for the kink effect in the drain current characteristics. A separate formulation is developed for the device capacitances which is reciprocal. The equivalent circuit includes the effect of parasitic substrate resistance. The second model is more comprehensive; both the channel current as well as the total charges and capacitances are derived from a physical analysis of the gate, channel and depletion charge densities. These are defined as functions of the surface potential which is computed from knowledge of the terminal voltages. Since the surface potential function is continuous from subthreshold to strong inversion, both the channel current and device capacitances are smooth and continuous throughout all regions of operation. Both models have been implemented in the SPICE circuit simulation program by rewriting sections of the Fortran source code and including new subroutines. Evaluation of the models against measured device characteristics shows a significant improvement in predicting the d.c. drain conductance characteristics compared with a bulk MOSFET model. Measured characteristics of the frequency dependent drain admittance are presented and explained with a developed small-signal model. Comparison of measured and simulated amplifier circuit characteristics also shows a considerable modelling improvement over bulk MOSFET models which are unable to predict the correct gain and d.c. operating point.
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Published date: 1991
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Local EPrints ID: 460987
URI: http://eprints.soton.ac.uk/id/eprint/460987
PURE UUID: d3f628c6-0e08-4945-b53b-abc8568d9569
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Date deposited: 04 Jul 2022 18:33
Last modified: 04 Jul 2022 18:33
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Author:
Rupert Howes
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