A systematic review of magnetron sputtering of AlN thin films for extreme condition sensing

In this article, a systematic overview of the published works on magnetron sputtering of AlN thin films for harsh condition applications is presented. Harsh environments may be defined as the operating conditions exhibiting extreme shock loads, high temperature, high pressure/forces and corrosive media. Some of the harsh environments include petrochemical plants, automobile/engine, marine, aerospace, in-situ health monitoring, prosthetics, etc. In these applications, sensors are necessary to monitor and control process parameters such as pressure, temperature, fluid flow, chemical contents, PH and among others. As such, the sensor materials should be able to withstand the high and cyclic conditions within such operations. Aluminum nitride (AlN) is a ceramic material, which finds application in microelectromechanical systems (MEMS) such as acoustic sensors, energy harvesters, transducers and resonators. These applications are motivated by its (AlN) high piezoelectric effect, high surface acoustic wave velocity, excellent dielectric permittivity, high thermal stability, wide band gap, chemical inertness, and so forth. As such, AlN films have been deposited on various non-metallic substrates such as Si, sapphire and polymers and on metallic substrates such as Ti6Al4V, diamond, Al, Cr and 304L stainless steel for different sensing applications. It is deduced that studies involving characterization of RF magnetron sputtered AlN thin films in harsh conditions are still scarce. The review serves as a resource for researchers and industry for development of sensors and transducers for harsh condition applications.