> What are the factors influencing polysilicon piezoresistive
> coefficient
> ? Is there any relation with the poly thickness or doping
> concentration ?

One of the unpleasant things about polysilicon piezoresistors is that their
properties are dependent upon the processing history.

Large-grained polysilicon can have coefficients as high as 60-70% of single
crystal [1]. It seems as though the big factors for piezoresistive
coefficients are morphology (grain size, grain crystal orientation
distribution, grain shape), doping, and dopant type. Paddy French did some
great work in the 1980s on piezoresistance in poly [2-4].

Other references are David Burns' dissertation from the University of
Wisconsin[5], and my own dissertation from the University of New Mexico [6]
(which might be still available from the Sandia website)

[1] Gridchin and Lubinsky, Sensors and Actuators A, Vol 49, pp 67-72 (1995).
[2] French and Evans, Sensors and Actuators, Vol 8 pp. 219-225 (1985).
[3] French and Evans, Solid State Electronics, Vol 32, No 1, pp. 1-10
(1989).
[4] French and Evans, Journal of Physics E, Vol 19, pp. 1055-1058 (1986).
[5] David Burns, "Micromechanics of Integrated Sensors and the Planar
Processed Pressure Transducer", Ph.D. dissertation, University of
Wisconsin -Madison, (May 1988).
[6] W P Eaton, Ph.D. dissertation, University of New Mexico (May 1997)
http://mems.sandia.gov/search/micromachine/docs/eaton%5Fdissertation.pdf


Bill Eaton, Ph.D.
Materials & Analysis Manager
NP Photonics
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