Likely Implementations of Printed Electronics Will Require Mobile Power
Printed devices have been around for a long time. A few transistors here, optoelectronic and photovoltaic elements there, maybe an RFID tag or a ring oscillator. But commercial products are built around complete systems, not individual devices. As Ana Claudia Arias of UC Berkeley pointed out at the Materials Research Society Spring Meeting in April, complete systems incorporate several different elements. For example, a device to track a soldier’s exposure to concussions might need a pressure sensor or accelerometer, but would probably also include an amplifier, a detector, a clock or other time stamp capability, and memory. Additional circuit elements would be needed to facilitate data retrieval, whether through wireless transmission or some other means. All of those functions need power.
Current generation small electronics depend on coin batteries, but even those are often too big and too expensive for printed electronics applications. Consider the thickness that a battery would add to a smartcard, or the cost that a battery would add to a disposable sensor or smart bandage.
So where does the power come from?
Photovoltaics offer one possible answer. At this week’s Extreme Electronics session on printed and flexible electronics, to be held Thursday at the Extreme Electronics TechXPOT in South Hall, Vishal Shrotriya, technology director of Solarmer Energy, will review recent developments in cell architectures and manufacturing processes for organic photovoltaics (OPV). His presentation discusses work on improved efficiency and device lifetime: though OPV can now achieve conversion efficiencies in the neighborhood of 9%, they still fall short of the benchmarks set by inorganic PV. Shrotriya’s talk also outlines the development of roll-to-roll production processes, which are essential both for low-cost production of OPV and for integration of photovoltaics with other printed circuit elements.
In the same session, NanoMarkets principal analyst Lawrence Gasman will discuss his firm’s recent analysis of the printed battery and printed photovoltaic sectors, as well as other printed and flexible electronics markets.
Although Arias views printed batteries as an enabling technology for printed electronics systems, it is not yet clear where the best market opportunities lie, given the current state of both printed electronics and printed battery technology. While applications like flexible, printed displays are often discussed, real world applications are so far much more prosaic. For example, Power Paper has designed a cosmetic patch that uses printed batteries to drive moisturizers and other active ingredients into the skin. The same technology could also be used for medical patches, and it is easy to imagine the gradual incorporation of more sophisticated electronics, turning a simple drug delivery patch into a smart bandage that monitors and assists wound healing.
Printed electronics are also being considered for use in sensor nets, such as a vibration or stress-sensitive net that wraps around an airplane wing, or an array of wireless proximity sensors used to monitor traffic through an area. Proximity and other environmental sensors are a particularly interesting case. The individual sensors can build their own network, with each sensor reporting its data to its neighbors until a bridge is formed to a central data storage and transmission point. This approach allows many sensors to fail — whether through device failures or destructive environments — without compromising the network as a whole.
The underlying premise of such a sensor network is that the individual devices are simple and inexpensive enough for the user to distribute hundreds or thousands of them. This requirement makes roll-to-roll printed electronics a natural fit. Some sensors might use printed batteries, but others might turn to energy harvesting devices: a piezoelectric sensor that flexes under stress might also generate the power it needs to broadcast or store its data.
The printed and flexible electronics worlds merge in more closely coupled networks, such as stress-monitoring nets or an array of sensors built into clothing for hazardous environments. In these examples, the sensors are connected to each other and to a central controller by wires, but the network of wires needs to be flexible enough to conform to a surface. Another speaker in the Extreme Electronics session, Stan Farnsworth, VP of marketing at NovaCentrix, will discuss printing of copper oxide on paper using conventional screen printing methods and the subsequent reduction of the lines to copper thin film.
– Katherine Derbyshire