Design and characterization of miniature piezoelectric generators with low resonant frequency

In this study, both materials selection and device configuration design were considered for developing miniature piezoelectric generators with low resonant frequency. Instead of single crystal Si, stainless steel (SUS) was chosen as the substrate of AlN thin films owing to its higher fracture toughness, which made it possible that millimeter-scale generators had resonant frequency of less than 100 Hz. The device configuration including the aspect ratio (the length of the cantilever to the width of the cantilever) and the thickness ratio (the substrate layer to the AlN film layer) were analyzed for optimizing transverse electromechanical coupling coefficient of generators. Using AlN thin films deposited on stainless steel, millimeter-scale generators were fabricated and their vibration energy harvesting performance was characterized. Output power and resonant frequency of the devices are, respectively, 5.130 μW and 69.8 Hz when they were vibrated at 1 g acceleration and connected with 0.7 MΩ electric loading.