Temperature-dependent thermal conductivity of undoped polycrystalline silicon layers

Polycrystalline silicon is used in microelectronic and microelectromechanic al devices for which thermal design is important. This work measures the in -plane thermal conductivities of free-standing undoped polycrystalline laye rs between 20 and 300 K. The layers have a thickness of 1 mum, and the meas urements are performed using steady-state Joule heating and electrical-resi stance thermometry in patterned aluminum microbridges. The layer thermal co nductivities: are found to depend strongly on the details of the deposition process through the grain size distribution, which is investigated using a tomic force microscopy and transmission electron microscopy. The room-tempe rature thermal conductivity of as-grown polycrystalline silicon is found to be 13.8 W (.) m(-1) (.) K-1 and that of amorphous recrystallized polycryst alline: silicon is 22 W (.) m(-1) K-1, which is almost an order of magnitud e less than that of single-crystal silicon. The maximum thermal conductivit ies of both samples occur at higher temperatures than in pure single-crysta lline silicon layers of the same thickness. The data are interpreted using the approximate solution to the Boltzmann transport equation in the relaxat ion time approximation together with Matthiessen's rule. These measurements contribute to the understanding of the relative importance of phonon scatt ering on grain and layer boundaries in polysilicon films and provide data r elevant for the design of micromachined structures.