Abstract
In this paper, we present a study of various ZnO/SiO2-stacked thin film structures for flexible micro-energy harvesting devices. Two groups of micro-energy harvesting devices, SiO2/ZnO/SiO2 micro-energy generators (SZS-MGs) and ZnO/SiO2/ZnO micro-energy generators (ZSZ-MGs), were fabricated by stacking both SiO2 and ZnO thin films, and the resulting devices were characterized. With a particular interest in the fabrication of flexible devices, all the ZnO and SiO2 thin films were deposited on indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrates using a radio frequency (RF) magnetron sputtering technique. The effects of the thickness and/or position of the SiO2 films on the device performance were investigated by observing the variations of output voltage in comparison with that of a control sample. As a result, compared to the ZnO single-layer device, all the ZSZ-MGs showed much better output voltages, while all the SZS-MG showed only slightly better output voltages. Among the ZSZ-MGs, the highest output voltages were obtained from the ZSZ-MGs where the SiO2 thin films were deposited using a deposition power of 150 W. Overall, the device performance seems to depend significantly on the position as well as the thickness of the SiO2 thin films in the ZnO/SiO2-stacked multilayer structures, in addition to the processing conditions.
Highlights
With the recent rapid development of more advanced wireless sensors for the Internet of Things (IoT) and wearable electronic devices, the demand for devices that can harvest various forms of ambient energy, such as mechanical vibration [1], acoustic waves [2], human biomechanical movement [3], water waves [4], environmental wind [5], solar radiance [6], and even waste heat [7] has become increasingly urgent
Zinc oxide (ZnO) is a piezoelectric material frequently used for the fabrication of energy harvesting devices due to its large piezoelectric constant and superior film quality [8]
At all stages of the experiments, the ZnO layer for SiO2/ZnO/SiO2 micro-energy generators (SZS-MGs) was deposited for one hour while for ZnO/SiO2/ZnO micro-energy generators (ZSZ-MGs), both the upper and lower ZnO layers were deposited respectively for
Summary
With the recent rapid development of more advanced wireless sensors for the Internet of Things (IoT) and wearable electronic devices, the demand for devices that can harvest various forms of ambient energy, such as mechanical vibration [1], acoustic waves [2], human biomechanical movement [3], water waves [4], environmental wind [5], solar radiance [6], and even waste heat [7] has become increasingly urgent. Zinc oxide (ZnO) is a piezoelectric material frequently used for the fabrication of energy harvesting devices due to its large piezoelectric constant and superior film quality [8]. It is environmentally friendly and biocompatible because it contains no toxic elements such as lead. Lead-free ZnO-based piezoelectric materials are available for wearable piezoelectric devices. The lead-free materials are advantageous in transducers for the underwater and medical imaging applications mainly due to their relatively low density as well as lower acoustical impedance [9,10]
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