Ziping Cao

Fabrication of Low-Residual-Stress AlN Thin Films and Their Application to Microgenerators for Vibration Energy Harvesting

For obtaining low residual stress, AlN thin films were prepared on Si substrates with diverse bottom electrode materials of Pt/Ti, Au/Cr, Al, and Ti by the electron cyclotron resonance (ECR) deposition technology. Among them, AlN thin films deposited on the substrate with the Al bottom electrode demonstrated not only low residual stress but also high enough c-axis orientation, and thus they were utilized to fabricate microgenerators by the micromachining process for converting environmental vibration energy into electric energy. The AlN microgenerator had a resonant frequency of 1042.6 Hz and the output power was 1.42 µW at the vibration frequency and 1g acceleration.

High output power AlN vibration-driven energy harvesters

This paper presents miniature AlN harvesters for harvesting low-frequency and two-dimensional vibration energy. A high fracture toughness and high yield strength stainless steel substrate was used to enhance output power and reduce resonate frequency of vibration energy harvesters. The thickness of 1.89 μm AlN films were deposited on 50 μm thick stainless steel (SUS) substrates for fabricating the harvesters. The Al/AlN/SUS multi-layer sheet was made into long and thin plate-like cantilevers with heavy proof masses attached at their free ends. The devices can collect vibration energy efficiently not only under perpendicular direction to the plate surface of cantilevers but also under the parallel direction. When vibration acceleration was 1.0 g, output power was 28.114 μW for perpendicular vibration and 51.735 μW for parallel vibration. When the acceleration of parallel vibration was 1.6 g, output power was 89.339 μW.

Processing and characteristics of piezoelectric microcantilevers without substrate

Based on a 4 μιη thick PZT films with (100) orientation, piezoelectric microcantilevers without a substrate support (free-stand) were fabricated with a typical micromachining process. These microcantilevers have low natural frequency which is suitable for the application on vibration energy harvesting. Simultaneously, their large linear displacement induced by voltage indicates they are also good microactuators, and the calculated piezoelectric coefficient d31 is one of third of that of bulky PZT ceramics.