Alternative architecture for highly performing AlN vibrational energy harvester

This work reports on the development of new AlN-based vibrational energy harvester architecture, consisting of a standard wide beam with a proof mass shaped into the Si substrate and exploiting a matrix of deep circular holes realized on the hinge backside. This approach was effective in the increase of the mechanical strain of the holed backside (HB) structure device, when compared with the standard beam, resulting in an increase of the generated voltage/power as well as in a fine tuning and reduction of the device fundamental resonance frequency. Representative devices with a (9×7.2 mm²) area, based on HB structure and standard structure, have been fabricated by microfabrication technologies and analysed by laser Doppler vibrometry and electromechanical measurements. Experimental results demonstrate a generated open circuit voltage (V_oc) increase of 160%, at very low acceleration, with respect to the generated voltage of a standard beam together with a decrease of 5% of the fundamental resonance frequency. The maximum output power generated by HB structure device under optimal resistive load resulted in an improvement of 220% compared with that obtained for the standard beam, at 0.2g of acceleration. These results have been validated by Finite Element Method (FEM) analysis where the holes' matrix has been taken into account and the frequency response as well as the generated voltage have been investigated.