Electrostatic arch micro-tweezers

This paper presents a novel electrostatic micro-tweezers to manipulate particles with diameters up to 14 μm. The tweezers consist of two grip-arms mounted to an electrostatically actuated initially curved micro-beam. It exploits bistable equilibria, resulting from a snap-through instability, to close the separation distance between the two arms allowing them to grasp a large range of objects. The tweezers offer further control beyond the snap-through point, via electrostatic actuation, to increase pressure on larger objects or grasp smaller objects. The tweezers are fabricated in a p-type Silicon on Insulator (SOI) wafer. Euler-Bernoulli beam theory is utilized to derive the governing equation of motion taking into account the arms' rotary inertia and the electrostatic fringing field. A reduced-order model (ROM) is developed utilizing two, three and five symmetric modes in a Galerkin expansion. A finite element model (FEM) is also developed to validate the ROM and to study the arm tips' separation as a function of actuation voltage. The five-mode ROM is found to be convergent and accurate except in the vicinity of the snap-through saddle-node bifurcation. Our analysis shows that the tweezers can manipulate micro-particles with diameters ranging from 5 to 12μm with an operating voltage range limited by the snap-back voltage 100.2 V and the pull-in voltage 153.2 V.