MEASURING THE THERMAL CONDUCTIVITY OF THIN FILMS: 3 OMEGA AND RELATED ELECTROTHERMAL METHODS

This review describes the major electrothermal methods for measuring the thermal conductivity of thin films in both cross-plane and in-plane directions. These methods use microfabricated metal lines for joule heating and resistance thermometry. The 3ω method for crossplane measurements is described thoroughly, along with a related DC method. For in-plane measurements, several methods are presented for suspended and supported films. Various practical matters are also discussed, including parasitic thermal resistances, background subtraction, and instrumentation issues. The review contains sufficient detail to be accessible to researchers new to the field of thin film thermal conductivity measurements, and also includes information relevant for 3ω measurements of bulk substrates. The review also contains new analytical results for the variable-linewidth 3ω method, the related heat spreader method, and the distinction between isothermal and constant flux heater approximations.