RESONANT DIAPHRAGM PRESSURE MEASUREMENT SYSTEM WITH ZnO ON S1 EXCITATION*

The prmclple of measurmg pressure by means of a resonant diaphragm has been studled An oscillator conslstmg of an integrated amphfler with a plezoelectrlcally driven diaphragm m its feedback loop has been bullt The oscillator frequency 1s accurately proportional to the square of the pressure m the range 60 to 130 Torr The frequency range 1s 1324 to 1336 Hz (this range being limited by a spurious mode which could be suppressed by better processing) for a 25 mm diameter diaphragm made of a slhcon wafer and with PZT ceramics as driver and receptor We have made an mtegrated version (1 X 1 mm2) of a square resonant diaphragm pressure gauge by selective etchmg of (1 0 0) planes with ethylenedlamme The plezoelectrlc drlvmg maternal was sputtered zmc oxide A driver was deposited midway between the bending point and the point of greatest curvature A receptor was located at a symmetrlcal posltlon to give an optimum transfer condltlon The integrated current amplifier had a low impedance differential mput stage, two gam cells and a high Impedance output stage These electrical conditions ensured maximum elastic freedom of the diaphragm A dlgltal clrcult m 12L technology has been designed and made with eight-bit parallel read out of the frequency This clrcult may be directly connected to a mlcroprocessor The whole system contams the sensor chip, the analog amphfler chip and the digital chip, all m compatible technology