Thermal Conductivity Measurements on Polycrystalline Silicon Microbridges Using the $3ω$ Technique

The thermal performance of microelectromechanical systems devices is governed by the structure and composition of the constituent materials as well as the geometrical design. With the continued reduction in the characteristic sizes of these devices, experimental determination of the thermal properties becomes more difficult. In this study, the thermal conductivity of polycrystalline silicon (polysilicon) microbridges are measured with the transient $3ω$ technique and compared with measurements on the same structures using a steady state Joule heating technique. The microbridges with lengths from $200μm$ to $500μm$ were designed and fabricated using the Sandia National Laboratories SUMMiT V™ surface micromachining process. The advantages and disadvantages of the two experimental methods are examined for suspended microbridge geometries. The differences between the two measurements, which arise from the geometry of the test structures and electrical contacts, are explained by bond pad heating and thermal resistance effects.