Ferroelectret nanogenerator (FENG) for mechanical energy harvesting and self-powered flexible electronics

Harvesting energy from our natural environment has been the focus of multiple research efforts in the past decades. Progress in this field has far-reaching implications for the growing environment problems resulting from greenhouse gas emission of fossil fuels. Furthermore, advances in portable energy scavenging devices will shed light on the development of self-powered and autonomous electronics; which will impact a broad range of applications in wireless sensors, biomedical implants, infrastructure monitoring, and portable/wearable electronics. This thesis research explores the designs, fabrications, simulations, characterizations and applications of flexible thin film nanogenerator based energy harvesting technologies. Materials and designs for flexible nanogenerator based on nanocrystalline aluminum nitride (AlN) thin film are reported. AlN nanoparticles were grown on aluminum layer by pulsed laser deposition (PLD) at room temperature. Piezoresponse force microscopy (PFM) indicates that their electromechanical energy conversion metrics are as high as highly c-axis oriented AlN or ZnO thin film. Polyimide thin film encapsulated the entire structure of flexible nanogenerator to further improve mechanical robustness, protecting the device from invasive chemicals and enhance its potential biocompaibility. Besides, this thesis research introduces polypropylene ferroelectret (PPFE) as the active material in an efficient, flexible, and biocompatible ferroelectret nanogenerator (FENG) device. PPFE is a type of charged polymers with empty voids and inorganic particles that create giant dipoles across the material's thickness. The mechanical-electrical energy conversion mechanism in PPFE films is verified by finite element method (FEM). Investigation of the developed device shows that the magnitudes of the generated voltage and current signals are doubled each time the device is folded, and an increase with magnitude or frequency of the mechanical input is observed. The developed FENGs is sufficient to light twenty commercial green and blue light-emitting diodes (LEDs), and realize a self-powered liquid-crystal display (LCD) that harvests energy from user's touch. A self-powered flexible/foldable keyboard is also demonstrated. Furthermore, this thesis reports the device's intrinsic properties which allow for the bi-directional conversion of energy between electrical and mechanical domains; thus extending its potential use in wearable electronics beyond the power generation realm. This electromechanical coupling, combined with their flexibility and thin film-like form, bestows dual-functional transducing capabilities to the device that are used in this research to demonstrate its use as a thin, wearable, and self-powered loudspeaker or microphone patch. To determine the device's performance and applicability, sound pressure level is characterized in both space and frequency domains for three different configurations. The confirmed device's high performance is further validated through its integration in three proposed systems: a music-playing flag, a sound recording film, and a flexible microphone for security applications.