Thermal Properties of a Thin-Film Membrane Embedded in a Multiparameter Wind Sensor—On-Device Characterization Utilizing a Transient Measurement Approach

We present a novel transient measurement method to characterize effective values of the thermal conductivity, thermal diffusivity, and emissivity of a thin-film membrane implemented in a micromachined multiparameter wind sensor. Accurate values for these parameters are mandatory as they considerably influence the thermal heat shunt induced by the membrane, which is the main limiting factor for reliable sensor operation in gases with low thermal admittance and thus determines the ultimate device sensitivity. Compared with commonly used measurement techniques for these thermal thin-film parameters, our method does not require custom-built specimens, i.e., the results can directly be obtained from transient excess temperature measurements on the wind sensor device utilizing the embedded thin-film heater and thermistors. The presented method as such is universal and can easily be applied to other configurations of heating and temperature sensing elements placed on a circular thin-film membrane. In this contribution, we describe the theoretical background of this method, provide an efficient semianalytical model for the data evaluation including its validation by computer numerical simulations, and showcase sample measurements on multilayer Si
_x
N
_y
-SiO
₂
thin films.