Linearization and tunability improvement of MEMS capacitors using flexible electrodes and nonlinear structural stiffness

This paper proposes solutions for high nonlinearity and structural instability in electrostatically actuated MEMS capacitors. The proposed designs use the flexibility of the moving electrode and nonlinear structural stiffness to control the characteristic capacitance- voltage (C-V) response. The moving plate displacements are selectively constrained by mechanical stoppers to prevent sudden jumps in the capacitance and to eliminate the pull-in. A symmetric double-humped electrode shape is utilized which results in a fairly constant sensitivity in the C-V curve and therefore a linearized response. An analytical and a finite-element coupled-field model are developed to study the behavior of the proposed capacitors and to optimize their design for maximum linearity. The experimental results verify that the designs introduced in this paper improve the linearity of the C-V response and increase the maximum tunability by three times compared to conventional MEMS parallel-plate capacitors. At the same time, they also eliminate the pull-in hysteresis of the response.