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17 September 1996 Phase-sensitive techniques applied to a micromachined vacuum sensor
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Proceedings Volume 2882, Micromachined Devices and Components II; (1996)
Event: Micromachining and Microfabrication '96, 1996, Austin, TX, United States
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.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Glenn H. Chapman, N. Sawadsky, and P. P. S. Juneja "Phase-sensitive techniques applied to a micromachined vacuum sensor", Proc. SPIE 2882, Micromachined Devices and Components II, (17 September 1996);

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