Thermal Phenomena in LTCC Sensor Structures

LTCC sensors can be used in harsh environments, but caution is needed if the measured medium or environment changes dynamically. In most cases, replacement of the medium in direct contact with the sensing structure can critically affect the sensor's response. In the case of diaphragm-type pressure sensors, problems can also arise with a non-homogeneous medium (gases with droplets of liquid or liquids with bubbles). We investigated a situation where droplets of different liquids appear on the diaphragm of a common, thick-film, piezoresistive, pressure-sensor configuration. Experiments with volatile liquids indicate that the sensor's time response depends on the dynamic changes in the temperature distribution. Furthermore, we built a simplified finite-element (FE) model in which the heat-transfer coefficient of the evaporating liquid film is defined by a time-dependent function. The simulations showed the same trends as the experimental measurements, which confirmed the assumed manifestation of the thermal phenomena. The presented work opens up new possibilities for the application of LTCC sensors. (C) 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).