Korean-based researchers have been pushing the potential of zinc oxide (ZnO) nanomaterials as a platform for piezoelectric power generators for at least the last five years.
Once again researchers from Korea, this time out of the Korea Advanced Institute of Science and Technology (KAIST), have focused on the potential of ZnO nanomaterials to tap into their piezoelectric capability of converting mechanical energy into electrical energy to power micro devices.
In this latest research, published in Applied Physics Letters, the aim was to exploit the piezoelectric capabilities of ZnO-based nanostructures to serve as nanogenerators in wearable electronics.
“ZnO nanostructures are particularly suitable as nanogenerator functional elements, thanks to their numerous virtues including transparency, lead-free biocompatibility, nanostructural formability, chemical stability, and coupled piezoelectric and semiconductor properties,” said Giwan Yoon, a professor in the Department of Electrical Engineering at KAIST, in a press release.
Flexibility was the key feature the researchers were trying to exploit in the ZnO-based nanogenerators. To achieve this flexibility, the Korean researchers used piezoelectric ZnO nanorods or nanowire arrays sandwiched between two electrodes that were laid down upon flexible substrates.
“When flexible devices can be easily mechanically deformed by various external excitations, strained ZnO nanorods or nanowires tend to generate polarized charges, which, in turn, generate piezoelectronic fields,” Yoon said. “This allows charges to accumulate on electrodes and it generates an external current flow, which leads to electronic signals. Either we can use the electrical output signals directly or store them in energy storage devices.”
To ensure that charges can accumulate on the electrodes, research has focused on how to apply insulating materials so that a large enough potential barrier is created without adversely impacting the operation of the device.
What distinguishes this latest research is that they developed an entirely new insulating material made from zinc oxide and aluminum nitride (AlN).
“We discovered that inserting AlN insulating layers into ZnO-based harvesting devices led to a significant improvement of their performance – regardless of the layer thickness and/or layer position in the devices,” said Eunju Lee, a postdoctoral researcher in Yoon’s group, in a press release. “Also, the output voltage performance and polarity seem to depend on the relative position and thickness of the stacked ZnO and AlN layers, but this needs to be explored further.”
The researchers believe this work will serve as a platform from which they can further study and refine devices designs to reach the optimum device configurations and dimensions.
Yoon added: “This is particularly useful for self-powered electronic systems that require both ubiquity and sustainability – portable communication devices, healthcare monitoring devices, environmental monitoring devices and implantable medical devices.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.