Piezoelectric resonant MEMS strain sensors and their temperature behavior

Abstract

For investigation of the temperature behavior of piezoelectric resonant MEMS train sensors, a double-clamped beam design is proposed and different design variations are realized in hardware as microbridges. For stimulation of the natural vibrational modes, the inverse transversal piezoelectric effect (d31-effect) of aluminium-nitride is used. The shift in resonance frequency of different modes is exploited to determine the applied strain. Due to the intrinsic film stress of aluminium-nitride, the manufactured double-clamped beam structures tend to buckle, which affects the behavior of the modes and also the strain gauge factor, an important performance indicator of strain sensitive devices. To modify the amount of stress in the sputtered aluminium-nitride, devices with adjusted sputter process parameters have been additionally fabricated and compared to those based on a conventional sputter process. The manufactured sensors were characterized with Laser-Doppler-Vibrometry in order to identify the vibrational modes and their resonance frequencies. Additionally, their electrical conductance spectrum was measured with an impedance analyzer. Finally, the temperature behavior of the piezoelectric MEMS resonators was characterized in a climate chamber.