Ultra-thin film piezoelectric AlN cantilevers for flexible MEMS sensors

The fabrication and characterization of piezoelectric, ultra-thin (~300 nm) aluminum nitride (AlN) cantilevers are reported. The novel flexible, ultra-thin film AlN provides excellent compatibility for flexible sensors. Tri-layer cantilevers were fabricated with the AlN layer being sandwiched between two metal electrode layers. Low deposition temperature (300 °C) was maintained to deposit the AlN by the DC reactive magnetron sputtering for superior CMOS and flexible substrate compatibility. The characterization of AlN cantilevers was performed using dynamic signal analyzer to measure the output voltage due to piezoelectricity. The output voltage for different cantilevers measured experimentally range from 3.69×10^-5 V to 4.48×10^-4 V and the experimental Johnson noise floor range from 7.23×10^-12 V²/Hz to 6.9×10^-8 V²/Hz. The corresponding power spectral densities range from 5.70×10^-9 V²/Hz to 2.14×10^-6 V²/Hz. The ultra-thin AlN cantilever structure forms the basis for future flexible force/pressure sensors, accelerometers, and energy harvesters.