Modeling of thermal conductivity for a CMOS-compatible MEMS-ROIC contact by TiN nanotubes

Size reduction in microelectromechanical systems (MEMS) leads to more complex behavior of physical parameters affected by quantum mechanical effects. Besides specific electrical resistance, thermal conductivity is a characteristic parameter for designing application-specific MEMS. Nanotubes are able to realize an electrical contact between a sensor element and a CMOS substrate while providing sufficient thermal isolation. A model for the prediction of thermal conductivity of nanotubes, compounded of alloys and demonstrated for titanium nitride, is presented here. The influence of the crystal structure on the mean free path is considered to limit electron and phonon mobility in thin layer geometries. A 3-D-2-D transition in the density of states of electrons and phonons is taken into account because feature sizes today are below the boundary scattering regime. We show that the dominating thermal conductance mechanism varies between phonons and electrons as a function of film thickness in TiN.