Simultaneous Electrothermal Test Method for Pyroelectric Microsensors

Abstract

Pyroelectric film materials, including polyvinylidene fluoride (PVDF) and its copolymers (e.g., P(VDF/trifluoroethylene)), are attractive candidates for low-cost infrared detection and imaging applications due to their compatibility with complementary metal-oxide semiconductor processing and inexpensive packaging requirements compared to semiconductor-based detectors. The pyroelectric coefficient (p) describes the material’s electric response to a change in sensor temperature and is the main contributor to the sensitivity and detectivity of the system. However, this value can vary greatly with film fabrication and poling processes, and its measurement is often highly coupled to the material’s thermal diffusivity. This paper describes a new approach to film characterization that combines the popular “3-omega” technique for thermal characterization with a modified version of the laser intensity modulation method for determining the film’s pyroelectric coefficient. The new method is capable of simultaneously measuring film conductivity, diffusivity, and pyroelectric coefficient. It could increase the accuracy of the pyroelectric measurements by providing in situ thermal data to the electrical model instead of relying on published values or thermal measurements of a different sample. We also present a fabrication process that can be used to pole and measure a variety of pyroelectric materials and a mathematical framework to study the thermal phenomena of the setup. The thermal model is used to highlight the methodology’s sensitivity to uncertainties in the geometric and material property values of the layers surrounding the pyroelectric film.