On the design of GaAs (hhl) resonant cantilevers: Study of piezoelectric excitation, of piezoresistive sensing and of micromachined structure

This paper reports on GaAs micro-resonators with torsional vibration modes. An analytical model is used to design better GaAs resonant {hhl} cantilevers. In particular geometry of (4 4 1) and (1 1 4) resonators are optimized for specific alignments of the cantilever. The temperature response of the resonance frequency is also given. A piezoresistive four-terminal element is used to sense changes in frequency induced by a mechanical input. Sensitivity and non-linearity of the transverse output voltage are studied for the two selected orientations showing that the (4 4 1) orientation is preferable. The cantilever is fabricated by micromachining. Hence, the simulator TENSOSIM is used to predict etching shapes at the opening of the mechanical structure and after subsequent etchings. Here, again results call for the choice of a (4 4 1) beam. Finally, performances of the final (4 4 1) micro-resonator and of the piezoresistive sensor are evaluated with a special emphasis on errors caused by misalignments or by some uncertainty about the angle of cut. This study shows that GaAs resonators with piezoelectric excitation and piezoresistive detection open up new sensors applications.