Integration of silver nanowires into SU-8 hollow cantilevers for piezoresistive-based sensing

Abstract

We established a process for the microfabrication of SU-8 AFM cantilevers with an embedded microchannel and an integrated layer of silver nanowires as piezoresistive element. The self-sensing detection is based on the electrical resistance increase of the silver nanowire network associated with the strain applied upon deflection of the cantilever. We observed a sensitivity of 1.4 × 10−6 nm−1 at large strains of 4 % (gauge factor of 10) and a sensitivity of 0.1 × 10−6 nm−1 at small strains of 0.6 % (gauge factor of 1). We obtained a still higher sensitivity (gauge factor of 28) by coating the silver nanowires network with a thin (∼10 nm) aluminum oxide layer acting as an insulating barrier. As application, we studied the cantilever deformation as a function of the overpressure applied in the microchannel while the cantilever was kept in contact with a glass surface confirming their large deflection detection capabilities. The results were qualitatively rationalized in the percolation framework. The presented self-sensing micropipettes could be used for experiments that require remarkably important bending, such as localized single cell deposition by squeezing the micropipette against the substrate, as well as force-controlled electrochemical additive manufacturing at the sub-mm scale.