Piezoelectric aluminum nitride thin films for CMOS compatible MEMS: Sputter deposition and doping

Amongst the piezoelectric thin films suited for microelectromechanical systems (MEMS), AlN has gained particular technological relevance due to its unique material properties (large bandgap, high dielectric strength, resistivity, thermal conductivity, elastic modulus, and acoustic velocity), sufficient piezoelectric coefficients, and compatibility with CMOS microfabrication processes. This critical review targets the CMOS-compatible low-temperature deposition of AlN by reactive magnetron sputtering and various possibilities for AlN doping with Sc and other transition metal ions. Deposition process parameters such as the substrate temperature, gas ratio, discharge power, deposition and base pressure, as well as the effects of the substrate/underlying layer roughness and post-deposition annealing, are discussed. This review aims at digesting the most relevant information for process development and quality control of doped and undoped CMOS-compatible piezoelectric AlN thin films.