Pressure micro-sensor based on Radio-Frequency transducer

A new type of pressure micro-sensors is reported in this communication. It is based on the use of a Radio-Frequency transducer. The pressure to be measured is applied on a silicon membrane located in the close vicinity of a coplanar millimeter-wave resonator: when varying the applied pressure, the distance between the membrane and the planar resonator is modified and consequently, the resonant frequency of the cavity changes. From the measurement of the resonant frequency the applied pressure is derived. Coplanar technology has been chosen because, on the one hand, it confers a better sensitivity to the pressure cell compared to the microstrip technology and, on the other hand, it does not require backside technological processing. In the millimeter frequency range, HFSS simulation results predict a good sensitivity of the resonant frequency to the applied pressure. Very first prototypes of the original pressure micro-sensor based on Radio-Frequency transducer were micro-machined and the obtained measured performances are presented here. Experimental results confirm the expected sensitivity of this new type of pressure micro-sensors.

I. Introduction

Nowadays sensing devices are widely exploited in many domains and are used in everyday life to transform mechanical, chemical or thermal events into electrical signals. The last 50 years have seen a real technological progress in sensor activities going from the first micro-machined silicon devices (since the earliest days of microelectronics) to the wireless integrated micro-sensors (e.g., wireless capacitive devices hermetically sealed at wafer level) [1]. Today the emergence of competitive silicon RF circuits and RF microsystems allows the combination of sensors and RF circuits. The research work reported here is in the framework of the realization of an original smart sensor for pressure measurement. As communication systems are increasingly moving to millimeter-wave frequency range, the novel system proposed here has a working frequency around 30 GHz.