Impact of the Casimir force on movable-dielectric RF MEMS varactors

An analysis of factors affecting the tuning range of movable-dielectric RF MEMS varactors, in particular, lateral and vertical spring stiffness and plate-slab gap asymmetry, is conducted. The analysis is based upon simple analytical models for spring and electrostatic forces, and on Lifshitz's formula for molecular interaction forces. It is found that, due to the large sensitivity of Casimir forces to asymmetry, these are very likely to play a greater role than spring vertical stiffness, in limiting the varactor tuning range.