Measurement of the Thermal Conductivity and Heat Capacity of Freestanding Shape Memory Thin Films Using the 3ω Method

An accurate measurement of the thermophysical properties of freestanding thin films is essential for modeling and predicting thermal performance of microsystems. This paper presents a method for simultaneous measurement of in-plane thermal conductivity and heat capacity of freestanding thin films based on the thermal response to a sinusoidal electric current. An analytical model for the temperature response of a freestanding thin film to a sinusoidal heating current passing through a metal heater patterned on top of the thin film is derived. Freestanding thin-film samples of silicon nitride and nickel titanium (NiTi), a shape memory alloy, are microfabricated and characterized. The thermal conductivity of thin-film NiTi, which increases linearly between 243K and 313K, is 40% lower than the bulk value at room temperature. The heat capacity of NiTi also increases linearly with temperature in the low temperature phase and is nearly constant above 280K. The measurement technique developed in this work is expected to contribute to an accurate thermal property measurement of thin-film materials. Thermophysical measurements on NiTi presented in this work are expected to aid in an accurate thermal modeling of microdevices based on the shape memory effect.