An electrostatically actuated double-clamped beam test structure has been designed and fabricated for the quantitative determination of adhesion forces between two contacting polycrystalline silicon (polysilicon) surfaces. The experimental measurements of the beam profile at varied bias and simulations based on finite element methods are combined to evaluate more accurately the adhesion forces experienced between polysilicon surfaces. In particular, the electrostatic force at pull-off is obtained by measuring the pull-off voltage and the beam profile through optical interferometric methods. The adhesion force is then determined from the mechanical restoring force obtained by finite element methods simulations and the calculated electrostatic force. The results show a weak scaling of the adhesion force with the apparent contact area, defined via microfabricated dimples.

This paper reports on accurate analysis of adhesion force between polysilicon–polysilicon surfaces in micro-/nanoelectromechanical systems (M/NEMS). The measurement is carried out using double-clamped beams. Electrostatic actuation and structural restoring force are exploited to respectively initiate and terminate the contact between the two surfaces under investigation. The adhesion force is obtained by balancing the electrostatic and mechanical forces acting on the beam just before the separation of the two surfaces. Different finite element models are developed to simulate the coupled-field multiphysics problem. The effects of fringing field in the electrostatic domain and geometric nonlinearity and residual stress in the structural domain are taken into consideration. Moreover, the beam stiffness is directly obtained for the case of combined loading (electrostatic and adhesion). Therefore, the overall electrostatic and structural forces used to extract the actual adhesion force from measured data are determined with high accuracy leading to accurate values for the adhesion force. The finite element simulations presented in this paper are not limited to adhesion force measurement and can be used to design or characterize electrostatically actuated devices such as MEM tunable capacitors and micromirrors, RF switches and M/NEM relays.