Abstract
Thin films of ZnO:Ga2O3 (ZGO) were deposited by radio frequency (RF) sputtering at voltages of 0.5, 0.9 and 1.1 kV. The films were studied with respect to their suitability in flexible piezoelectric nanogenerators. The analysis of the spectroscopic and microscopic results showed that piezoelectric features were revealed for the films grown at all sputtering voltages, but the most favorable morphology in terms of low roughness was achieved at 1.1 kV. The effect of the sputtering voltage on the films crystallinity and lattice strain was studied. It was found that the increasing sputtering voltage promoted the films crystallization. Additionally, the presence of oxygen vacancies in the piezoelectric films was negligible as it is not a major factor affecting their performance. The electrical measurements of the Ag/ZnO:Ga2O3/Ag harvester on a flexible substrate in the low-frequency range showed a piezoelectric voltage of 414 mV, a current of 10.4 µA and an electric power output of 1.4 µW at a mass load of 100 g. These results were achieved by a simple architecture of a single piezoelectric layer with a relatively small size of 3 cm2 and small piezoelectric film thickness (600 nm) containing lead-free material. It was proven that the sputtered ZGO films are suitable for energy harvesting elements and their performance could be tuned by the sputtering voltage. Another possible application of the proposed device, excluding low-frequency vibrational harvesting, could be a pressure sensor or strain gauge, due to the good linearity of the electrical parameter dependences on the strain.
Highlights
In recent years, piezoelectric energy harvesting devices have put the focus on the study of piezoelectric lead-free oxides as environmentally friendly materials [1,2,3]
The results showed that the gallium-doped zinc oxide films exhibited good piezoelectric properties and that these properties can be tailored by the sputtering voltage
It should be noted that some typical absorption features for the ZnO lattice, reported as fundamental for ZnO:Ga2 O3, appeared in all ZGO films regardless of the sputtering voltage
Summary
Piezoelectric energy harvesting devices have put the focus on the study of piezoelectric lead-free oxides as environmentally friendly materials [1,2,3]. ZnO films, with their good piezoelectric properties and their possibility of being produced by conventional deposition technologies, have become preferable lead-free materials for piezoelectric micro- and nanoelectromechanical (MEMS and NEMS) sensors, actuators, and energy harvesting devices [4,5]. Among them ZnO:Ga2 O3 (ZGO) is preferable due to lack of diffusion or the migration of gallium, as compared to the aluminum or to the neighboring zones or interfaces. This is a desirable property for well-defined piezoelectric behavior, especially in thin film energy harvesting, where short circuits can occur due to the short path of the particles between the opposite electrodes [8]. Surface smoothness becomes one of the crucial conditions to guarantee the high performance of the piezoelectric energy harvesters
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
