Dear Huang:
all MEMS simulation software that I am aware of is very expensive. The
company I interact with, Microcosm, sells a license for about $100,000.
They do, however, have academic discounts (I don't know exactly how big,
but certainly significant). They have a package that combines design
and simulation under one shell, which saves you a lot of trouble. They
can model mechanics, electrostatics and some electrodynamics, fluid
mechanics etc.
If interested, please let me know and I can get more detailed
information for you.
Good luck with your thesis project.
Alex