Simulation of rarefied flows in MEMS devices by atomistic and multiscale methods

Advances made in MEMS technology introduces new physical phenomena that need to be studied and modeled for fabrication of integrated microelectronic systems. This thesis concentrates on the gas flow in MEMS devices. In the small dimensions encountered in microdevices, the gas flow cannot be analyzed using classical continuum models. Direct simulation Monte Carlo (DSMC) can be used to analyze the flow in these devices; however, the computational cost is large.; In this thesis, DSMC is used to analyze the gas flow in microfilters. Using an efficient parallel implementation of DSMC, the gas flow in microfilters is investigated in detail. The dependence of the flow properties on filter geometry, pressure difference, and the surface characteristics is investigated.; To reduce to computational cost associated with such analysis, multiscale coupling of DSMC with the continuum models for fluid flow is studied. The Schwarz alternating method is utilized for coupling, and the continuum equations are solved using the finite cloud method. The agreement of the coupled method with DSMC is shown and the dependence of the convergence of the DSMC/Stokes coupling on the overlap, DSMC noise, and the number of DSMC time steps is investigated. Significant computational time savings are demonstrated with the coupled method. The coupling of DSMC with compressible Navier-Stokes equations is also developed. It is shown that by using DSMC/Navier-Stokes coupling, the computational time savings can be increased. The agreement of the results of DSMC/Navier-Stokes coupling with DSMC is shown for pressure, velocity and temperature.