Piezoelectrically driven silicon beam force sensor, Sens. Actuators A 25–27

A resonant silicon beam force sensor with piezoelectric excitation and detection is being developed. The realization is based on IC and thin-film technology with ZnO as the piezoelectrical layer. The theory, realiza-tion and measurements of a bent-frame sen-sors are described. A frequency shift of about 3.3 times the unloaded resonance frequency f0 (fO N 6 kHz) is measured with an external load force up to 0.4 N. The absohite sensitiv-ity of the force sensor is 64 kHz/N and the full-scale sensitivity is 29 kHz/N. Using a simple model for the load-force transduction from external to sensor force, the measure-ments are in good agreement with the theory. electrical excitation and detection of the vi-bration of the sensor beam using the piezoelectrical effect of a ZnO layer [ 1, 31. The bottom electrode is a highly boron doped (p++-)silicon layer and the top one is an aluminium layer. In order to improve the efficiency of the electromechanical transduction of the ZnO at low frequencies, a p + +-ZnO structure is used. This structure will have a better efficiency than the pi + SiO,-ZnO (MOS) structure presented in ref. 4 because of the complete depletion of the ZnO layer [5] and the ab-sence of a voltage drop across the oxide layer in the MOS structure