A load cell with adjustable stiffness and zero offset tuning dedicated to electrical micro- and nanoprobing

The tasks of electrical micro- and nanoprobing require precision that goes beyond human perception and therefore, depend on sensors providing real-time feedback. Efforts towards automation in micro- and nanoprobing and emerging areas such as branched nanowire networks, has resulted in a growing number of applications where electrical probing without simultaneous force control is insufficient. This article presents the design of a novel mesoscale flexure-based load cell dedicated to micro- and nanoprobing. By integrating systems for stiffness adjustment and a zero offset tuning, the force-displacement characteristic of the device can be adapted to suit a wide range of applications, from the measurement of large forces up to 60 mN to a resolution as high as 10.1 nN, and even negative stiffness (bistable) behavior. By controlling the tuning during measurements, a virtual dynamic range of 6.38 ⋅ 106 is achievable, which is one order of magnitude greater than existing commercial products. We validated the results experimentally on a titanium alloy prototype fabricated by electrical discharge machining (EDM). Experimental and finite element results were also used to validate the analytical model of the load-cell. Additionally, the device allows for probe tip replacement, which is a significant advantage compared to existing MEMS load cells, and comprises a gravity compensation system to accommodate a wide range of commercially available probe tips.