Characterization and application of piezoelectric microcantilever sensors fabricated from substrate-free PMN-PT layers

Piezoelectric Microcantilever Sensor (PEMS) has attracted tremendous attention and numerous biological and chemical detections have been demonstrated. During detection, adsorption induced surface stress causes the PEMS flexural resonance frequency shift, however, the sensing mechanism due to stress effect is still unclear. The goal of this dissertation is to carry out fundamental study of sensing mechanism and then demonstrate chemical warfare agent detection. When a PEMS is subject to a DC bias field, the flexural resonance frequency shifted as a result of Young's modulus change in the PMN-PT layer which was confirmed by the measurement of width mode frequency and the relative dielectric constant measurement indicated that the Young's modulus change was a result of non-180° domain switching. Similarly, the flexural resonance frequency shift of a PEMS during humidity detection was also due to the Young's modulus change which was two-order-of-magnitude larger than could be accounted for by the mass loading alone. Furthermore, a negative DC field of -6 kV/cm enhanced the relative resonance frequency shift in humidity detection by more than 3 times of the detection without a DC bias. It was shown that during humidity detection, the frequency shift of the flexural mode, [delta]f, was inversely proportional to the square of the PEMS length, L2; relative resonance frequency shift, [delta]f/f, was inversely proportional to the PEMS thickness, t; and the mass detection sensitivity, [delta]f/[delta]m, was inversely proportional to wL3 where w is the width. The Young's modulus change and scaling were validated in another independent system - DMMP detection using SAM MUA/Cu2+ coated PEMS. In addition, the flexural frequency shift of the microporous silica powder coated PEMS followed mass loading model while the planar MPS coated PEMS showed two-order-of-magnitude enhancement indicating a continuous coating of adsorbent on PEMS is desired. Array PMN-PT/Cu PEMSs coated with planar MPS, SAM MUA/Cu2+, and no coating as control can be used to selectively detect DMMP at room temperature. Other gas species such as acetone and ammonia were examined as well using the same array. The resonance frequency shifts of the array PEMSs exhibited a unique pattern in response to DMMP and the detection can be achieved in less than 5 minutes.