On-device extraction of thermal thin-film properties in calorimetric flow sensors

Roman Beigelbeck; Almir Talic; Samir Cerimovic; Franz Kohl; Franz Keplinger

doi:10.1117/12.887059

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5 May 2011 On-device extraction of thermal thin-film properties in calorimetric flow sensors

Roman Beigelbeck, Almir Talic, Samir Cerimovic, Franz Kohl, Franz Keplinger

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Proceedings Volume 8066, Smart Sensors, Actuators, and MEMS V; 80660B (2011) https://doi.org/10.1117/12.887059
Event: SPIE Microtechnologies, 2011, Prague, Czech Republic

Abstract

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.

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Roman Beigelbeck, Almir Talic, Samir Cerimovic, Franz Kohl, and Franz Keplinger "On-device extraction of thermal thin-film properties in calorimetric flow sensors", Proc. SPIE 8066, Smart Sensors, Actuators, and MEMS V, 80660B (5 May 2011); https://doi.org/10.1117/12.887059

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