An Aluminum-Nitride PMUT with Pre-Concaved Membrane for Large Deformation and High Quality-Factor Performance

We proposed a new pre-concave membrane piezoelectric micro-machined ultrasonic transducer (PMUT), which is presented with highest quality factor as 600 in air coupling. Surface micromachining process is used for fabrication and AlN is chosen for piezoelectric material, which makes process compatible with Pre-CMOS fabrication. It has been proved that non-flat piezoelectric membrane has better coupling in others' previous work. In this design, we also use sealed cavities and molybdenum electrodes to further improve the device performance. 9 different radii of PMUT circular membranes are made for comparison, which exhibits extremely high quality factor of up to 600 in the air and large peak displacement of up to 52nm/V around 5.94MHz to 8.38MHz. The experimental and FEM simulation results are compared in the end. This design combines the advantages of pre-concaved membrane structure and surface micromachining technique, which can be used in high resonance frequency application such as medical ultrasonic filed.