Piezoelectric free-standing thick-film structures for material characterization and energy harvesting applications

This paper reports the fabrication and characterization of a free-standing piezoelectric thick-film structure: single-layer films and multi-layer cantilevers, for the application of vibrational energy harvesting. Piezoelectric properties without constraint effect are properly characterized. The single-layer thick-films exhibit d31 values of approximately 100 pC/N, which is much larger than in other reports. This can provide a more reasonable and accurate way to measure real properties of piezoelectric thick-films, and thus offer more reliable data to modelling and design of thick-film structured piezoelectric devices. Flat, free-standing thick-film cantilevers free from residual stress are also fabricated. The requirements of ink composition and sintering procedure are defined. When tested under harmonic vibration conditions, the cantilevers show increases of 20-120 % in output power density under different vibration accelerations at their resonant frequencies compared to the reported energy harvesters based on similar materials and structures. This work demonstrates the potential for fabricating co-sintered piezoelectric multi-layer thick-film structures with higher potential flexibility and energy conversion efficiency.