Stress controlled CMUT fabrication based on a CMOS compatible sacrificial release process

We report a stress control method for Capacitive Micromachined Ultrasonic Transducers (CMUTs) fabricated with sacrificial release process. By annealing a TiAl plate the stress can be shifted from compressive to tensile and its behavior is visualized over temperature and time. Furthermore, a linear dependency of annealing temperature and stress is shown, allowing uncomplicated stress adjustment. Remaining deflection can be explained by both atmospheric pressure and temperature influence of the final process steps. Mechanical long term stability is proven with stress measurements over several months.