Characterization of AlScN-based multilayer systems for piezoelectric micromachined ultrasound transducer (pMUT) fabrication

Scandium-alloyed aluminum nitride (AlScN) is a potential material for micro-electromechanical systems because of its unique advantages, such as strong piezoelectric effect and high thermal stability. However, issues related to its stability and interaction with other materials in multilayer systems require investigation. The formation of new phases at the interface between piezomaterial and electrode material can lead to the device failure. In this study, multilayer structures Si substrate/AlN/Ti-Mo/Al_0.8 Sc_0.2N/top electrode (TE) were studied after annealing at a wide range of temperatures and durations. Four different TE materials (i.e. Al, AlSi (1%), Mo/Al, and Mo) were examined to determine the most reliable electrode material for the structure. The phase stability, interfacial quality, and piezoelectric response of the multilayer systems after thermal annealing were investigated. The structure with Mo TE layer was stable after annealing at 800 °C for 300 h and at 1000 °C for 100 h. None of the structures formed any new phases at the interface between the electrode layer and AlScN. The transverse piezoelectric coefficient (e_31,f) was determined for Al_0.8Sc_0.2N before and after annealing. The absolute value of the e_31,f was-1.39 C/m² for as-deposited structure and-1.67 C/m2 for the same structure annealed for 300 h at 800 °C. [2020-0361].