Flexible energy harvesting: enabling new form factors in electronics

Dr Harry Zervos
Flexible energy harvesting: enabling new form factors in electronics
Market analysts IDTechEx have been following the market for flexible electronics technologies for over a decade now, and as more and more companies are moving from prototypes towards efforts to scale up manufacturing, it goes without saying that allied technologies will also experience a transformation in requirements, in order to develop hand-in-hand with the target markets they will serve. This is especially true for energy harvesting and storage technologies: flexible portable electronics, in order to retain their versatility would benefit from harvesters and batteries or supercapacitors on plastic substrates.
Find out more at our co-located shows - Energy Harvesting & Storage and Printed Electronics USA 2013 in Santa Clara on November 20-21 - www.IDTechEx.com/ehUSA.

Nanogenerators for body area networks at KAIST

But it's not just incremental optimization of consumer electronics that attract the attention of researchers, there are also concepts being developed that make new devices possible in fields such as artificial skins, biosensors, biomimetic technologies, etc. Some work of this type is taking place in the Korean Advanced Institute of Science and Technology (KAIST), where the Flexible and Nanobio Device lab (FAND) is developing highly efficient flexible nanogenerators using freely bendable piezoelectric ceramic thin film nano-materials and nanocomposite materials that can convert movements of the human body, such as heart beats and blood flow, into electricity.
Schematic of a thin Film nanogenerator being developed by the FAND group, KAIST
This nanogenerator technology is based on transferring ceramic thin film nano-materials on flexible substrates using soft lithography. The device can be used to turn on an LED display for instance, flexible variants of which are also being developed at KAIST. In addition, utilizing thin film nano-materials of barium titanate allows for both high efficiency and lead-free bio compatibility, which can be used in future medical applications.
Flexible storage is also being developed at KAIST, based on lithium ion battery technology. Issues with high temperature processing that could damage plastic substrates are tackled by the use of a transfer approach using mica substrate delamination that enables the highly crystalline lithium cobalt oxide cathode to be annealed at high temperatures (>700°C) and allow for optimized performance on polymer substrates.

Artificial skin and flexible sensors at Berkeley

On the other side of the world, Professor Ali Javey at UC Berkeley is also involved with researching enabling technologies for body area networks, such as artificial skin, flexible sensors, etc. He is the co-director of Berkeley Sensor and Actuator Center (BSAC), and the Bay Area PV Consortium (BAPVC).
The pictures below demonstrate macroscale integration of parallel nanowire arrays as the active-matrix backplane of a flexible pressure-sensor array.
(a) Schematic of the passive and active layers of nanowire e-skin. Optical photographs of a fully fabricated e-skin device 7x7 cm2 with a 19x18 pixel array under bending (b) and rolling (c) conditions
The integrated sensor array effectively functions as an artificial electronic skin capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5 V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5 mm) for over 2,000 bending cycles. This work, published in Nature Materials Letters, presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.
The topics of flexible sensors and energy harvesting will both be addressed at the upcoming IDTechEx Energy Harvesting & Storage conference in Santa Clara, California on November 20-21, with speakers from KAIST and UC Berkeley discussing their research work and developments.
For more information visit www.IDTechEx.com/EHUSA or contact Mrs Corinne Jennings at c.jennings@IDTechEx.com
Top image of an artist's illustration of an artificial e-skin with nanowire active matrix circuitry covering a hand source: UC Berkeley