Characterization of sputtered ZnO thin film as sensor and actuator for diamond AFM probe

Abstract In order to develop a diamond atomic force microscopy (AFM) probe with a piezoelectric sensor and actuator, we fabricated piezoelectric zinc oxide (ZnO) thin film and measured its piezoelectric constant. First, we developed a simple measurement method for the piezoelectric constant of the thin film, d 31 . This was based on the free vibration theory of cantilever beams. The values of d 31 were determined by measuring an electric charge induced in the piezoelectric thin film on the vibrating cantilever beam and its displacement. Using this method, we evaluated d 31 for ZnO thin film sputtered at various substrate temperatures. The ZnO thin film deposited at temperatures of less than 350 °C was highly c -axis oriented and showed a high piezoelectric constant d 31 of −3.5 pC/N. Using this value, we calculated properties of the diamond cantilever AFM probes of various dimensions and of 5 μm in thickness with a ZnO sensor and actuator of 1 μm in thickness. The resolution of displacement and actuation force for a probe of 150 μm in length and 50 μm in width were estimated to be about 1.5 nm at a resolution of charge measurement of 1×10 −15  C and 7 μN at an applied voltage of 10 V, respectively.

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