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Creep deformation in RF-MEMS
Simulates creep deformation in fixed - fixed beam MEMS model
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Abstract
The MEMSCreep tool simulates the response of a radio frequency MEMS switch fabricated at Purdue’s Birck Nanotechnology Center for our Center on the Prediction of Reliability, Integrity and Survivability of Microsystems (PRISM).
RF-MEMS devices are capacitive switches in which a membrane is moved to change the capacitance between the RF signal and ground. The metallic membrane in the PRISM device is made of polycrystalline Nickel with a thickness between 1 to 5 mm. The center metal conductor carries the RF signal and the actuation voltage. When no voltage is applied the membrane remains undeflected and the air gap of about 3 mm leads to a low capacitance; for sufficiently high applied voltages the membrane deflects and becomes in contact with the dielectric leading to an increase in capacitance of several orders of magnitude.
The deflection of the metal membrane due to the electrostatic force can be modeled using Euler-Bernoulli’s beam theory. To calculate the deflection, w(x), we assume that the middle plate remains flat while the four legs deform as cantilever beams of length L, width W and thickness t with an applied force F distributed equally among the four legs. The electrostatic force between the electrode and the beam is modeled using a parallel plate capacitor model.
Creep deformation proceeds as the applied voltage is applied as a result of the stress field in the membrane. The plastic deformation resulting from creep is calculated using a Coble creep model.
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