Thermal conductivity in nanoscale polysilicon structures with applications in sensors

[Display omitted] •Thermal conductivity of nanowires is an order of magnitude less than bulk value.•Increased grain size (15 nm–25 nm) results in a 50% increase in thermal conductivity.•Phonon grain boundary scattering is the dominant factor in thin film polysilicon. Thermal conductivity of polysilicon nanowires and thin films has been experimentally studied. Thermal conductivity has been measured with a microstructure fabricated alongside the polysilicon nanowires and thin films and a robust fabrication process has been developed. Results suggest that the in-plane and out-of-plane thermal conductivity are limited by phonon grain boundary and film boundary scattering respectively. The nanowires are fabricated by patterning a thin layer of low-pressure chemical vapor deposited polysilicon using e-beam lithography, consequently circumventing the prevalent process of pick-and-place process, in which metallic contacts are deposited to insure significant heat flow to the nanowire. By avoiding the need for metallic contacts a significant source of error in the calculation of the thermal conductivity is eliminated. Thermal conductivity of nanowires with a cross section of ˜60 nm × 100 nm and thin film with a cross-section of 3μm × 108 nm were measured to be both ˜3.5 W/m.K, suggeting that the thermal conductiviy is dominated by the out-of-plane phonon scattering in both cases. This is an almost 8× reduction from the thermal conductivity of bulk polysilicon at ˜30 W/m.K. The effect of grain size and doping concentration on the thermal conductivity of ˜100 nm polysilicon films is also experimentally studied.