Piezo MEMS Technology Platform

The Fraunhofer ISiT has been working for more than 10 years on the deposition of thin films of the piezoelectric materials aluminum nitride (AlN) and lead zirconium titanate (PZT). Currently, sputtering processes with film thicknesses of up to 4 µm for AlN and up to 3 µm for PZT are available. The integration into MEMS structures is typically realised via unimorphs consisting of a piezoelectric layer embedded between two metal electrodes on top of a passive support layer made from mono- or polycrystalline silicon. PZT is mainly used for actuator applications, as its high piezoelectric coefficients enable particularly large deflections and high forces with only low drive voltages. The PZT actuators are integrated for their utilization in MEMS scanners and loudspeakers. For sensory applications, AlN is preferred due to its considerably better signal-to-noise ratio. At ISIT it is currently used in ultrasonic transducers, MEMS microphones and vibrational energy harvesters. In addition to these established materials scandium-doped AlN (AlScN) is being developed in cooperation with the Christian-Albrecht University of Kiel. Despite the higher piezoelectric coefficients compared to pure AlN, this material retains the advantageous properties (high dielectric strength, IC-compatible, low dielectric losses) of the AlN and is therefore suitable for both sensor and actuator MEMS components. In the long term, it is intended to completely replace the lead-containing PZT. Among other things, a highly sensitive magnetoelectric sensor and MEMS scanners based on AlScN films of higher piezoelectric performance are currently being developed.