Suspended tip overhanging from chip edge for atomic force microscopy with an optomechanical resonator

Raising the mechanical frequency of atomic force microscopy (AFM) probes to increase the measurement bandwidth has been a long-standing expectation in the field and a technically difficult challenge. Recent advances in cavity optomechanics and in-plane probe designs have yielded significant progress. In situations in which an AFM tip extends a few micrometers from a planar optomechanical resonator, we present an approach to make it overhang from the probe die with precise control of the edge-line position. This fabrication step, which exposes the tip apex to the sample surface, is a prerequisite for any AFM experiment with optomechanical probes. We utilize a combination of saw dicing and time-controlled isotropic plasma etching to undercut the 725-mu m-thick silicon substrate beneath the tip. The technique is easy to implement without any lithography steps. The overhang length of the tip is controlled to less than 5 mu m with very good smoothness of the edge, reproducibility, and yield.