Contents
Sommario iii
Abstract v
Contents vii
Introduction 1
1 Fast release of large dielectric membranes for MEMS applica-
tions 3
1.1 Release of large MEMS structures . . . . 3
1.2 A possible solution for fast release . . . . 5
1.3 A small scale validation of the proposed approach . . . . 8
1.4 Structure design . . . . 11
1.5 Experimental test . . . . 13
1.6 Etch evolution: a simple mathematical model . . . . 19
2 MEMS resonators for biosensing applications 25 2.1 An introduction to MEMS resonators . . . . 26
2.2 Magnetically actuated MEMS microbalances for biosensing ap- plications . . . . 28
2.3 Theory of operation . . . . 28
2.4 Device design: issues and solutions . . . . 32 vii
Contents
2.4.1 Enhancement of the output voltage level . . . . 33
2.4.2 Reduction of direct magnetic feedthrough . . . . 34
2.4.3 Enhancement of the sensitivity by thinning . . . . 34
2.5 Fabrication process: challenges and solutions . . . . 35
2.6 Electro-mechanical characterization . . . . 40
2.6.1 Analysis of the frequency response . . . . 40
2.6.2 Resonator response to a test mass density . . . . 43
2.6.3 Experimental validation of probe/target interaction . . 50
2.7 A single chip oscillator based on the MEMS microbalance . . . 53
2.7.1 Frequency measurement for mass sensing: circuit ap- proaches . . . . 53
2.7.2 Circuit design . . . . 54
2.7.3 Simulation results . . . . 57
2.7.4 Measurements . . . . 60
Conclusions 63
Bibliography 65
viii
