Zinc nitride thin films: basic properties and applications

Zinc nitride films can be deposited by radio frequency magnetron sputtering using a Zn target at substrate temperatures lower than 250 degrees C. This low deposition temperature makes the material compatible with flexible substrates. The as-grown layers present a black color, polycrystalline structures, large conductivities, and large visible light absorption. Different studies have reported about the severe oxidation of the layers in ambient conditions. Different compositional, structural and optical characterization techniques have shown that the films turn into ZnO polycrystalline layers, showing visible transparency and semi-insulating properties after total transformation. The oxidation rate is fairly constant as a function of time and depends on environmental parameters such as relative humidity or temperature. Taking advantage of those properties, potential applications of zinc nitride films in environmental sensing have been studied in the recent years. This work reviews the state-of-the-art of the zinc nitride technology and the development of several devices such as humidity indicators, thin film (photo) transistors and sweat monitoring sensors.