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Proceedings Paper

Phase-sensitive techniques applied to a micromachined vacuum sensor
Author(s): Glenn H. Chapman; N. Sawadsky; P. P. S. Juneja
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Paper Abstract

Phase sensitive AC measurement techniques are particularly applicable to micromachined sensors detecting temperature changes at a sensor caused by a microheater. The small mass produces rapid thermal response to AC signals which are easily detectable with lock-in amplifiers. Phase sensitive measurements were applied to a CMOS compatible micromachined pressure sensor consisting a polysilicon sense line, 760 microns long, on an oxide microbridge separated by 6 microns on each horizontal side from similar polysilicon heaters, all over a micromachined cavity. Sinusoidal heater signals at 32 Hz induced temperature caused sense line resistance changes at 64 Hz. The lock-in detected this as a first harmonic sense resistor voltage from a DC constant sense current. By observing the first harmonic the lock-in rejects all AC coupling of noise by capacitance or inductance, by measuring only those signals at the 64 Hz frequency and with a fixed phase relationship to the heater driver signals. This sensor produces large signals near atmospheric pressure, declining to 7 (mu) V below 0.1 mTorr. Phase measurements between 760 and 100 Torr where the air's thermal conductivity changes little, combined with amplitude changes at low pressure generate a pressure measurement accurate at 5 percent from 760 Torr to 10 mTorr, sensing of induced temperature changes of 0.001 degree C.

Paper Details

Date Published: 17 September 1996
PDF: 12 pages
Proc. SPIE 2882, Micromachined Devices and Components II, (17 September 1996); doi: 10.1117/12.250713
Show Author Affiliations
Glenn H. Chapman, Simon Fraser Univ. (Canada)
N. Sawadsky, Simon Fraser Univ. (Canada)
P. P. S. Juneja, Simon Fraser Univ. (Canada)

Published in SPIE Proceedings Vol. 2882:
Micromachined Devices and Components II
Kevin H. Chau; Ray M. Roop, Editor(s)

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