Modeling and Analysis of Fabrication Defects in MEMS based Comb Actuators

Pawar, Vishal and Pandey, Ashok Kumar (2019) Modeling and Analysis of Fabrication Defects in MEMS based Comb Actuators. Masters thesis, Indian institute of technology Hyderabad.

Text
Mtech_Thesis_TD1484_2019.pdf
Restricted to Repository staff only until 10 July 2021.
Download (2MB) | Request a copy

Abstract

Deep reactive-ion etching (DRIE) process is one of the most widely used manufacturing processes for micro-electro-mechanical-systems (MEMS) devices, but the main problem with this process is that it leads to undesirable fabrication defects such as slanting, undercut and scalloping. In this report, we first study the theoretical models involving these defects for a MEMS-based comb structure, according to which we can predict the nature of different performance criteria such as stiffness of the folded beam, stability, electrostatic force and displacement of the structure. Subsequently, we develop finite element method (FEM) based model to model coupled electrostatic and structural effects in COMSOL Multiphysics and validate it with the theoretical results for various parameters such as the angle of the slanted profile and amount of the undercut. In this work, we also develop an analytical model to capture the effect of scalloping on electrostatic forces generated across comb fingers and stiffness of folded beam in a MEMS-based comb actuator. Additional, we also modify the formula to include the parameters related to the size as well as the number of scallops. To develop the model, we assume the shape of a scallop as elliptical, which is characterized by major axis length (2a) and semi-minor axis length (b). To validate the model, we compare results with finite element results obtained using Coventerware for single as well as multi-scallops. Subsequently, we discuss the combined effect of scalloping and slanting on electrostatic forces in a comb drive structure. The model presented in the report may be useful at the design stage of various comb drive MEMS devices such as MEMS gyroscopes.

[error in script]

IITH Creators: