02-09-2017, 10:40 AM
A pressure sensor is manufactured and tested which combines two measuring principles into an integrated unit with optical and electronic parts. The sensor element for both integrated parts is a raised silicon diaphragm which is deflected under differential pressure. The optical part of the sensor is based on Fabry-Perot interferometry; the electronic part of the sensor is based on the piezoresistive effect on the silicon. In the application of Fabry-Perot interferometry, the sensor element uses an optical cavity, where the interference of multiple reflections changes with the movement of the diaphragm caused by the pressure. In the application of the piezoresistive effect, a change in the electrical resistivity of a sensor material is induced by mechanical stress in the diaphragm and detected by a Wheatstone bridge circuit. The advantages of introducing the embossed diaphragm in the manufacture of sensors and their benefits for integration are discussed. The existence of an almost ideal Fabry-Perot interferometer on the optical part of the sensor is experimentally demonstrated. The noise characteristics of the Fabry-Perot part of the sensor are presented. The independently produced electronic output serves to establish the quiescence point (Q point) of the output of the optical part of the sensor.