Self-excited piezoelectric PZT microcantilevers for dynamic SFM—with inherent sensing and actuating capabilities

Abstract

Currently three crucial components are necessary for the dynamic SFM, they are the microcantilever, oscillator, and cantilever deflection sensor. We demonstrate a piezoelectric microcantilever made of PZT thin films for SFM. This PZT microcantilever can perform the same functions which have to be done by the three crucial components. It is able to excite itself when an ac voltage is applied to it, and actuate itself in z-directional displacement by a superimposed dc voltage, while force sensing is executed concurrently. Since the motional admittance can be derived from the piezoelectric current output when the PZT microcantilever is vibrated at resonance frequency, the motional admittance will vary as the change of vibrational amplitude. Thus the topography of the sample can be recorded as the trace of the difference between output signals of motional admittance. The piezoelectric coefficient d 31 of the PZT layer is about −58 pC/N. The dimensions of piezoelectric microcantilevers used are 125×50×3.8 μm. The actuating ability is estimated as 75 nm/V. The vertical resolution of the self-excited PZT microcantilever can be derived as 1.2 Å at the bandwidth of 125 Hz. Very clear images of a 1.0 μm pitch Au coated SiO 2 grating and an evaporated gold film on a smooth glass plate are obtained by an SFM using this self-excited force sensing PZT microcantilever. The invention of this smart PZT microcantilever endows the possibility of constructing a stand-alone micro SFM system and a multiprobe SFM system.