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|High Temperature SOI CMOS Ultra Low Power Circuits for MEMS Co-Integrated Interfaces|
|Keywords: co-integration, ring oscillator, MEMS|
|Silicon-on-Insulator (SOI) technology allows efficient co-integration of MEMS with CMOS and offers tremendous advantages for high temperature / low power performances. CMOS ring oscillators can be readily used as sensor interfaces. In fact, a variation of the current flowing through the MOSFETs or a variation of the capacitance at the output node of the inverter, results in a change in the inverter delay and thus a change of the oscillator frequency. The RO configuration gives a direct digital signal, avoiding external analog circuitry and thus is less sensitive to noise compared to conventional analog interfaces requiring complicated circuits. We use this principle to measure the capacitance variations of out of plane (3D) movable cantilevers for temperature or flow monitoring , as well as stress variations in a 1µm-thick tri-layered oxide-nitride-oxide membrane for static or dynamic pressure sensing based on MOSFET piezoresistive effect . These designs were implemented in a 2µm fully depleted SOI CMOS technology  and were tested up to 300°C. The first encouraging results underline the opportunity for designing highly sensitive fully digital pressure/stress or capacitive sensors for high temperature and ultra low power applications.  N. André, B. Rue, C. Renaux, D. Flandre and J.-P. Raskin,“3-D capacitive MEMS sensors co-integrated with SOI CMOS circuits”, Int. IEEE SOI conf, 2007.  B. Olbrechts, B. Rue, J. Suski, D. Flandre, J.-P. Raskin, “Characterization of FD SOI devices and VCO's on thin dielectric membranes under pressure”, Solid-State Electronics,vol. 51, pp. 1229–1237, 2007.  D. Flandre, in: R. Kirshmann (Ed.), High Temperature Electronics, IEEE press, 1998, p.303.|
University Catholique de Louvain-la-Neuve