Biodegradable, Bifunctional Electro-acoustic Transducers Based on Cellular Polylactic Acid Ferroelectrets for Sustainable Flexible Electronics

Abstract

Nowadays, humans rely increasingly on smart electronics to address grand challenges and to improve life conditions in the era of digitalization and big data. However, electronics often have a limited lifespan, and they may bring electronic waste problems after their service. To mitigate this problem, environmentally sustainable methods of electronic device production and disposal are highly recommended, where advanced functional materials should be redesigned with improved sensing performance over the entire operational life while also being naturally degradable at the end. Herein, a biodegradable and flexible bifunctional electroacoustic transducer was fabricated with the utilization of cellular polylactic acid (PLA) ferroelectret films, possessing a small acoustic impedance of ∼0.02 MRayl which is quite close to that of air and a high figure of merit (FOM: d 33 •g 33 ) of ∼11 GPa −1 . Such devices have a prominent signal-to-noise ratio (SNR) of ∼23.5 dB @1 kHz and can work either as a microphone by direct piezoelectric effect or a loudspeaker by reverse piezoelectric effect in air medium. When used as a microphone, the flexible device exhibits a prominent receiving sensitivity up to 4.2 mV/Pa (∼−47.5 dB/ref. 1 V/Pa) at 1 kHz. When served as a loudspeaker, it is capable of yielding high sound pressure levels (SPLs) ranging from 60 to 103 dB (ref. 20 μPa) in a broad frequency range of 1−80 kHz with an active area of 3.14 cm 2 . Additionally, the electrical response curve of the device is very flat in a wide frequency range from 300 to 3000 Hz. With the high-performance acoustic-electric conversion capacity, the PLA ferroelectret-based flexible and filmlike electroacoustic transducer was used to realize accurate speech recognition and control, providing a strong impetus for its advanced and eco-friendly applications in the era of the internet of things (IoT) and artificial intelligence.