Flexible Piezoelectric Generators and Pulse Sensors Using Single-Crystalline III-N Thin Films



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Single-crystalline group III-nitride (III-N) thin films obtained by epitaxy have been widely used in electronic and optoelectronic devices, such as transistors, light-emitting diodes (LEDs) and photodiodes, as great progress has been made to achieve high crystal quality. III-N thin films are strong candidates to make piezoelectric devices due to their high piezoelectric coefficient which is readily available without electric poling since the atoms are already well aligned in the as-grown single-crystalline thin film. Compared with conventional piezoelectric materials such as lead zirconate titanate (PZT), zinc oxide (ZnO) and polyvinylidene fluoride (PVDF), III-N thin films have the advantages of good biocompatibility without containing toxic elements, high durability being chemically stable, and simple processing without extra electric poling. Unfortunately, applications in piezoelectric devices such as generators and sensors, which usually require flexibility, are still underdeveloped due to the brittleness of III-N thin films and device rigidity since they are usually grown on rigid substrates. In this research, flexible piezoelectric generators (F-PEGs) and flexible piezoelectric pulse sensors (F-PPSs) were developed with single-crystalline III-N thin films, which is composed of an AlN buffer layer, AlxGa1-xN interlayers and a top GaN layer, by transferring the as-grown thin film from the Si (111) substrate to a foreign flexible substrate. Large area and defect-free flexible single-crystalline III-N thin films were obtained by this layer-transfer method. The III-N thin-film F-PEG can generate an open-circuit voltage of 50 V, a short-circuit current of 15 µA, and a maximum power of 167 µW with a corresponding optimum load resistance of 5 MΩ. The III-N thin-film F-PEG is able to directly power commercial electronics and charge commercial capacitors and batteries. The III-N thin-film F-PPS is sensitive enough to detect and convert the subtle deflection caused by the arterial pulse into an electrical signal and detect the pulse waveform with detailed characteristic peaks from most arterial pulse sites. Both the F-PEG and the F-PPS showed high durability and stable outputs after being subjected to long-term tests. Piezoelectric devices made from single-crystalline III-N thin films have great potential applications in future flexible wearable electronics, such as the energy harvesters and self-powered pulse sensors.



Flexible, Piezoelectric, Generators, Sensors, III-N, Thin films


Portions of this document appear in: Liu, Dong, Yahong Jin, Yang Lv, Guifang Ju, Chuanlong Wang, Li Chen, Weiwei Luo, and Yihua Hu. "A single‐phase full‐color emitting phosphor Na3Sc2 (PO4) 3: Eu2+/Tb3+/Mn2+ with near‐zero thermal quenching and high quantum yield for near‐UV converted warm w‐LEDs." Journal of the American Ceramic Society 101, no. 12 (2018): 5627-5639. And in: Chen, Jie, Seung Kyu Oh, Noor Nabulsi, Heidi Johnson, Weijie Wang, and Jae-Hyun Ryou. "Biocompatible and sustainable power supply for self-powered wearable and implantable electronics using III-nitride thin-film-based flexible piezoelectric generator." Nano Energy 57 (2019): 670-679.