Piezoresistance in polycrystalline silicon and its application to pressure sensors
Piezoresistance in polycrystalline silicon and its application to pressure sensors
A full investigation into the piezoresistive effect in polycrystalline silicon is described. A theoretical and experimental approach is applied and a new theoretical model developed. Transport across the grain boundary is based on the thermionic emission/diffusion theory. The change in conductivity, in bulk material, is due to a shift in the relevant band edges (minima for n-type and sub-bands for p-type) relative to each other and the subsequent transfer of carriers. This principle is applied to barrier conductivity where, the shift in band edges changes the contribution to thermionic emission and diffusion mechanisms for each minima or sub-bands. The result is a change in barrier conductivity. Barrier piezoresistive coefficients are calculated for both n and p-type material and these values are used in a new model incorporating all physical and electrical properties of polysilicon films. These include grain size, trap density, segregation and texture of the films. Temperature coefficients of resistance and gauge factor are modelled and calculated. Comparison between theory and experiment shows reasonable agreement for both longitudinal and transverse strain measurements. The difference in magnitude between longitudinal and transverse gauge factors depends on texture and is found to be explained by the anisotropy of piezo-resistance in silicon. The experimental work concentrates on the effects of three processing stages on the properties of the resultant films. These are the polysilicon deposition temperature (for an LPCVD system), ion implantation (dose and dopant type) and furnace anneal temperature. The experimental results have attained a peak gauge factor of ∼ 43 for boron doped material compared to ∼ -24 for phosphorus doped material. Theoretical estimates of gauge factor and temperature coefficients are used to predict sensor characteristics and an optimum process, within the confines of available processes, is suggested. (D71902/87)
University of Southampton
1986
French, Patrick James
(1986)
Piezoresistance in polycrystalline silicon and its application to pressure sensors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A full investigation into the piezoresistive effect in polycrystalline silicon is described. A theoretical and experimental approach is applied and a new theoretical model developed. Transport across the grain boundary is based on the thermionic emission/diffusion theory. The change in conductivity, in bulk material, is due to a shift in the relevant band edges (minima for n-type and sub-bands for p-type) relative to each other and the subsequent transfer of carriers. This principle is applied to barrier conductivity where, the shift in band edges changes the contribution to thermionic emission and diffusion mechanisms for each minima or sub-bands. The result is a change in barrier conductivity. Barrier piezoresistive coefficients are calculated for both n and p-type material and these values are used in a new model incorporating all physical and electrical properties of polysilicon films. These include grain size, trap density, segregation and texture of the films. Temperature coefficients of resistance and gauge factor are modelled and calculated. Comparison between theory and experiment shows reasonable agreement for both longitudinal and transverse strain measurements. The difference in magnitude between longitudinal and transverse gauge factors depends on texture and is found to be explained by the anisotropy of piezo-resistance in silicon. The experimental work concentrates on the effects of three processing stages on the properties of the resultant films. These are the polysilicon deposition temperature (for an LPCVD system), ion implantation (dose and dopant type) and furnace anneal temperature. The experimental results have attained a peak gauge factor of ∼ 43 for boron doped material compared to ∼ -24 for phosphorus doped material. Theoretical estimates of gauge factor and temperature coefficients are used to predict sensor characteristics and an optimum process, within the confines of available processes, is suggested. (D71902/87)
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Published date: 1986
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Local EPrints ID: 460777
URI: http://eprints.soton.ac.uk/id/eprint/460777
PURE UUID: 5175d129-8273-4149-929b-f5cf5399c767
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Date deposited: 04 Jul 2022 18:29
Last modified: 04 Jul 2022 18:29
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Author:
Patrick James French
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