Introducing a Thermal-Based Method for Measuring Dynamic Thin Film Thickness in Real Time as a Tool for Sensing Applications

Abstract

In many sensing applications, ranging from processes monitoring to bioassays, interactions occur between a thin film and a liquid medium. For such applications, it is generally crucial to monitor physical changes in the film over time. Consequently, the demand for sensitive yet robust readout methods that can be used to do so is high. In this article, we present a new, thermal-based readout principle that can be applied to monitor physical changes in thin samples over time. This new transient thermal offset (TTO) method is derived from the widely used transient plane source (TPS) method but intentionally deviates from the condition to not apply thermal pulses that probe deeper than the boundaries of the thin sample. By doing so, it is possible to use the properties of the sample on top of the film as a reference with the novel data processing method. The sensing principle was first demonstrated via numerical simulations in COMSOL Multiphysics software. Then, for experimental validation, we performed TTO measurements to monitor the removal process of a thin film over time. The results show that the TTO method can be used reliably in practice for monitoring physical changes in thin films. Since also the properties of the surrounding material are measured, it is possible to distinguish between changes in the thin film and changes in the direct environment.