Effects of various loading on the performance of MEMS cantilever beam for in-field tuning of sensors and actuators for high temperature and harsh environment applications

摘要

MEMS devices require active mechanism for tuning in field operation because post fabrication, design parameters may change due to residual stress, fabrication imperfections, temperature etc. Application of axial compressive (C) or tensile forces (T) allows one to implement this tuning. Effects of C and T forces, stress gradient (SG) and transverse loading is analyzed for futuristic materials like Gallium Nitride (GaN) and Silicon Carbide (SiC) for use in high temperatures and harsh environments. The effects of above forces on pull in voltage (V-PI), bandwidth (BW) and resonance frequency (RF) are analyzed. Results for Aluminum cantilever beam show, that V-PI decreases by ~ 1.2 times at low beam lengths of 200 mu m and about 5 times at higher length of 800 mu m when T force is changed to C under loading. Similar trends are holding for GaN and SiC except that V-PI scales up in proportion to material's Young's modulus E. An analytical relations of V-PI versus E and Poisson's ratio'nu' are predicted. Effect of SG is also studied and it is found that although SG affects V-PI within 10% range, application of axial C or T forces further change it within 20% range. Comparison of analytical results for V-PI with Coventorware software shows a better agreement for low loading of 10% compared to full loading of 100%. Also, Log-Log plot of V-PI versus L can be used to estimate the contribution of charge re-distribution and fringing field. Furthermore, BW decreases by 16 Hz when C is applied and increases by 66 Hz when T is applied for Aluminum cantilever with 400 mu m length and 50 mu m width. Similarly, RF decreases by 165 Hz in C and increases by 623 Hz for T loading. The predictions of our model agree well with experimental and FEM results (within 4.54% and 6.46% respectively).