Thermal conductivity of micromachined low-stress silicon-nitride beams from 77 to 325 K

We present thermal conductivity measurements of micromachined 500 nm thick silicon-nitride (Si-N) beams suspended between two Si-N islands, in the temperature range from 77 to 325 K. The measured thermal conductivity, k, of Si-N at high temperatures is in good agreement with previously measured values for Si-N grown by low-pressure chemical vapor deposition, but behaves much differently as temperature is lowered, showing a dependence more similar to polycrystalline materials. Preliminary structural characterization by x-ray diffraction suggests that the material is likely nano- or polycrystalline. The micromachined suspended platform structure is designed to allow highly accurate measurements of the thermal conductivity of deposited metallic, semiconducting, or insulating thin films. As a demonstration, we present measurements of a 200 nm thick sputtered molybdenum film. In the entire temperature range the measured thermal conductivity matches the prediction of the Wiedemann-Franz thermal conductivity determined from measured electrical conductivity.