In diaphragm-based micromachined calorimetric flow sensors, the convective heat transfer through the test fluid
competes with the spurious heat shunt induced by the thin-film diaphragm where the heater and the temperature
sensors are embedded. Therefore, accurate knowledge of the thermal transport properties (thermal conductivity
and diffusivity) and the emissivity of the diaphragm is mandatory for design, simulation, and optimization of
such devices. However, these parameters can differ considerably from those stated for bulk material and they
are typically dependent on the production process. Commonly used methods for their determination require the
fabrication of custom specimens. In order to overcome this serious drawback, we developed a novel technique
to extract the thermal thin-film properties directly from measurements carried out on calorimetric flow sensors.
Here, the heat transfer frequency response from the heater to the thermistors is measured and compared to a
theoretically obtained relationship arising from an extensive two-dimensional analytical model. This model covers
the heat generation by the heater, the heat conduction in the diaphragm, the radiation loss at the diaphragm's
surface, and the heat sink caused by the supporting silicon frame. In this contribution, we report in detail on the
measurement setup, the theoretical model for the associated parameter extraction, and the results obtained from
measurements on calorimetric flow sensors featuring dielectric thin-film diaphragms made of PECVD Si3N4.