Characterization of micromachined piezoelectric PZT force sensors for dynamic scanning force microscopy

The key component for the piezoelectric scanning force microscopy (SFM) is the piezoelectric force-sensing microcantilever. In this article, the resonance frequency and quality factor of Pb(Ti,Zr)O₃ (PZT) microcantilevers; effective Young's modulus and piezoelectric Pb(Ti,Zr)O₃ property of PZT layer of piezoelectric microcantilevers are discussed. The PZT microcantilevers after poling have quality factors such as 204 to 248 in air, and 608 to 1094 in vacuum. The calculated spring constants are in the range of 1.0-30.0 N/m for cantilevers with 0.64-1.7-μm-thick PZT layer and 125-300 μm length. The force sensitivity and resolution of the PZT microcantilever are studied when it is oscillated by an external oscillator and applied to the cyclic contact SFM. Then the real transverse piezoelectric coefficient d₃₁ of piezoelectric PZT thin films is derived from the measured sensitivity and effective Young's modulus. The derived effective Young's moduli of PZT layers slightly increases from 53.5 to 58 GPa as the thickness of the PZT layer increases. The d₃₁ is around -35 pC/N which is about 8 times larger than the value of ZnO, and half the value of bulk PZT ceramics. The sensitivity of 0.98 fC/nm can be obtained by PZT force sensors. The longitudinal resolution obtained is 1.5 Å at a bandwidth of 125 Hz. Cantilevers with proper characteristics for different applications can be predicted, designed, and fabricated via the adjustment of the thickness ratio of each layer and the total thickness of the cantilever. Very clear images of an evaporated Au film on a smooth glass plate are obtained by an SFM with a PZT force sensor.