High performance atomic force microscope based on air-spaced piezoresistive cantilevers

This paper reports the study of the air-spaced piezoresistive cantilever for atomic force microscopy (AFM). The cantilever is composed of a bottom mechanical layer and a top piezoresistive layer separated by a gap. Analytical models for the mechanical properties of the air-spaced cantilever are established. To evaluate the performance of AFM, the minimum detectable force gradient is expressed as the product of force and displacement signal-to-noise ratios. For the air-spaced cantilever, this product is improved by orders of magnitude compared with the conventional piezoresistive cantilever of similar length and spring constant. This paper also discusses the advantage of the air-spaced cantilever from the energy point of view. The overall energy conversion efficiency of air-spaced cantilever reaches over 90% by allowing the majority of the mechanical energy to be used to strain the piezoresistors. A specific comparison of air-spaced cantilever and the conventional piezoresistive cantilever with the same spring constant of 1000N/m and same length is presented to illustrate the advantage of the new structure.