MINIMUM DETECTABLE FORCE GRADIENTS OF PIEZOELECTRIC MICROCANTILEVER

The purpose of this paper is to describe the relation between minimum detectable force gradients and level dimensions in noncontact scanning force microscopy (SFM) using the piezoelectric microcantilever. The piezoelectric microcantilever is preferred to the noncontact mode SFM because the lever can be Vibrated by applying a voltage to the piezoelectric layer. Since the SFM requires no external oscillator, a simple system for the frequency modulation (FM) detection method can be easily constructed. In the noncontact SFM, the minimum detectable force gradient should be as small as possible. Using the piezoelectric cantilever, thermally induced vibration and electrical noise of the piezoelectric layer determine the minimum detectable force gradient. We will describe the minimum detectable gradients determined by electrical noise far the slope and the FM detection methods, and investigate their dependence on the lever dimensions for the unimorph cantilever in comparison with the minimum detectable gradients due to the thermal noise. We will also discuss the critical dimensions at which the dominant noise source changes from electrical noise to thermal noise.