Inexpensive printed sensors, transistors, and memory devices that aren't as speedy or as high-capacity as silicon devices could enable the widespread use of sensors in places that aren't cost-effective today. Disposable devices could monitor and store information about the temperature of drugs, the safety of food during shipping, or air quality.
Memory reel: These reels of plastic are printed with 20-bit memory devices.
Researchers at the Palo Alto Research Center (PARC), which is owned by Xerox, have been developing a suite of materials for making printed electronics, including sensors and transistors. This week at the Printed Electronics USA conference in Santa Clara, California, PARC announced details about two partnerships to develop products based on its research prototypes. PARC will work with Norwegian company Thin Film Electronics to make higher-capacity printed memory devices that incorporate the research center's printed transistors. And PARC is working with Soligie of Savage, Minnesota, to develop products based on its printed temperature sensors.
Much of the excitement around printed electronics has centered on the potential to replace silicon electronics in complex devices such as display screens so that they can roll up. For these types of applications, researchers are working to match silicon's performance in materials that are just as fast and efficient, but flexible and inexpensive.
These more sophisticated printed electronics may be a few years from commercialization. "We want to go to market in simpler applications to prove that printed electronics can work today," says Davor Sutija, CEO of Thin Film. The company's 20-bit printed memory devices will be in toys early next year.
Products integrating these postage-stamp-sized memory devices will include playing cards paired with online games. Kids will use the cards to transfer their playing history between a PC and a handheld device. For a toy or a game that requires only a small amount of memory, using silicon-based memory like flash is impossibly expensive. "When you're only storing a small amount of data in lots of places, the cost threshold is right for printed electronics that cost a few cents," Sutija says.
Thin Film's memory devices are made on long reels of plastic using roll-to-roll printing, the same basic process used to churn out newspapers. They sandwich a layer of electrically sensitive polymer between top and bottom layers of wire-like electrodes that are perpendicular to one another. Where the electrodes cross, it creates a charge-storage device called a capacitor. When a small voltage is applied to the capacitor, the orientation of the polymer in the capacitor changes; this change in orientation makes the "1" and the "0."
The current devices have a large footprint relative to their storage capacity. By increasing the storage density in collaboration with PARC, Thin Film hopes to make a printed memory product that can be integrated with radio-frequency identification (RFID) tags for use in disposable packaging to store information about an individual item's history. Today, this requires silicon chips, which are too expensive to implement widely. However, cheaper devices could hold information about the history of, for example, individual bags of spinach, rather than about pallets that hold many boxes of bagged spinach. And more cell phones are expected to begin integrating near-field communications devices that will enable them to act as a contactless credit card and read ubiquitous RFID tags on things like bags of spinach.
To improve the storage density of the printed memory devices, Thin Film will integrate PARC's printed transistors. This will reduce the total number of electrical contact pads needed to read and write to the device. Sutija says the collaboration with PARC will lead to a 128-bit memory product that costs less than 10 cents.
Printed-electronics company Soligie is working with PARC to commercialize printed temperature sensors, or "thermistors," devices commonly found in air conditioners, ovens, and containers used to ship drugs. They're based on materials whose electrical resistance varies with temperature. To manufacture them usually requires baking ceramic materials at high temperatures to make a rigid wire-like structure. PARC has developed printable materials to make flexible thermistors that should be less expensive to make, says PARC's senior director of business development, John Knight.
The thermistors PARC will commercialize with Soligie will still need to be connected to a silicon chip to read out the temperature; down the line, the researchers expect to integrate them with all-printed circuits. The company will begin sending prototypes to customers early next year.
By Katherine Bourzac
From Technology Review