Multi-axis AlN-on-Silicon vibration energy harvester with integrated frequency-upconverting transducers

This paper presents fully-integrated multi-axis piezoelectric-on-silicon kinetic energy harvesters (KEHs) that demonstrate enhanced power output via mechanical frequency upconversion. Mechanical energy is converted to electrical energy by out-of-plane and in-plane devices that are micromachined on the same substrate. The out-of-plane device demonstrates nearly 100× frequency upconversion of 134 Hz input vibrations, while the in-plane harvester demonstrates more than 3000× frequency upconversion of 2 Hz input vibrations. The batch-fabrication process is compatible with AlN-on-Si devices such as RF resonators and sensors. The total volume of an individual harvester is 5 mm³ (in-plane) and 1 mm³ (out-of-plane), implying that stacked arrays of such devices can easily increase power density.