Behavioral Modeling and Simulation of MEMS Electrostatic and Thermomechanical Effects 

Gilbert Wong Advisors: Gary Fedder Tamal Mukherjee 


Project: The Nodal Design of Actuators and Sensors (NODAS) library previously developed at Carnegie Mellon University was extended and updated . NODAS is a library of atomic element lumped parameter behavioral models written in VerilogA, an analog hardware description language (AHDL). It is used for the simulation of MEMS devices in a SPICElike circuit simulator. Physics modeling, accuracy verification, and application examples are presented. The modeling of 2D beams and 2D electrostatic gaps for MEMS devices is presented in this thesis, however, the physics can be extended to 3D. The NODAS beam model was updated and new physical effects were added. The inconsistent use of a user parameter which caused the length of the beam to be miscalculated was corrected. A new variable was created to address this problem and verification of the NODAS beam model compared with analytic equations. When compared to analytic equations for a fixedfixed beam under a uniform distributed load and a fixedguided beam with axial compressive stress under a uniform distributed load, the NODAS beam model was shown to be accurate to within 6.1x106 percent and 15x103 percent respectively when using multiple NODAS beam segments. The moment generated by the differences between the thermal coefficients of expansion in a multilayer CMOSMEMS beam was implemented. A multilayer CMOSMEMS beam under an applied temperature was simulated in NODAS and ANSYS. The NODAS simulation reported inplane tip deflections to within 2% of the ANSYS simulation for different metal layer combin ations and offsets. A thermal conduction model was added to account for the effects of electrothermal heating. The electromechanical gap model was updated and an electriconly gap model was created. A electrostatically actuated fixedfixed beam simulation using electromechanical gap models was shown to produce beam deflections to within 2.2% of an ANSYS simulation when 128 NODAS beam/gap segments were used. The electriconly gap model was created to reduce the simulation time of large models such as an RF MEMS varactor. A thermal actuator, a varactor, and a mixer application example are given to demonstrate composability and hierarchical design. Finally, future areas of research are discussed.


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