Flexible Sensors Begin Ramping

Technology opens up new possibilities for the Internet of Everything.

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Sensors are at the heart of the Internet of Things. Flexible sensors promise to extend the Internet of Everything to the battlefield, the gymnasium, the hospital, and many other places.

Flexible sensors represent the forefront of a sea of change in electronics, marking the transition from rigid semiconductors made with silicon and other hard materials to flexible circuits on polymers, often printed on plastic substrates.

While wearable electronics seem to be a natural fit for flexible sensors, the first generation of wearables typically employs solid-state circuitry, silicon-based microchips made with the standard complementary metal-oxide-semiconductor (CMOS) process.

“Currently, most of the wearable devices are still based on conventional sensors that are rigid. However, in the future it will represent an important opportunity for flexible electronics. For instance, the strap of a smartwatch could be used to integrate flexible components,” says Guillaume Chansin, an analyst and consultant with IDTechEx Research.

IDTechEx forecasts the market for products fabricated on flexible substrates to grow from $6.4 billion last year to $14.9 billion in 2025. “Currently on the market, the most common flexible sensors are based on a set of electrodes. For example, there are capacitive touch sensors that can be layered on any surface or biopotential sensors that measure your heartbeat in a smart garment,” Chansin notes.

The market for flexible sensors is expected to span a number of verticals. “The next generation of flexible sensors will have far more complexity and will be able to turn many surfaces into sensing areas,” Chansin says. “When you look at a glucose test strip used by diabetics, it is basically a flexible electrochemical sensor made with printed electrodes. This is the application dominating at the moment as it is so critical for the health of so many people.”

Yole Développement points out that may not be the best example. “Glucose sensors are the biggest market using printing technology, but flexibility is not necessarily what is required here.” Flexible weight sensors for cars are another leading application, according to Yole.

Wearables don’t currently dominate the market for flexible sensors, Yole says, pointing instead to force sensors for medical applications and for test and measurement technology.

Are flexible sensors being paired with other types of sensors? “Not yet, but there is a trend toward hybrid systems that integrate chips on flexible devices,” says Chansin.

Mapping the future
In the United States, development of flexible sensors is coalescing around NextFlex, the Flexible Hybrid Electronics Manufacturing Institute. The FlexTech Alliance, an industry organization based in San Jose, Calif., last summer received a $75 million grant from the Department of Defense to establish and manage a Manufacturing Innovation Institute (MII) for flexible/hybrid electronics.

Another $96 million in costs will be shared by companies, universities, laboratories and not-for-profit enterprises, and state and regional organizations. The NextFlex consortium announced in February the signing of 30 partnership agreements with academic, industrial, and non-profit organizations. Boeing, Brewer Science, E Ink, Eastman Chemical, Jabil Circuit, Molex, ON Semiconductor, and Raytheon are among the founding corporate members of NextFlex.

The path to establishing NextFlex, which has its own hub office in San Jose, began just over a year ago with a request for proposals by the federal government’s MII program, according to Michael Ciesinski, president of the FlexTech Group. The proposal was completed last June, followed by a site visit in July, he notes. The Air Force Research Laboratory awarded the contract to the FlexTech Alliance in August.

FlexTech has since become a “Strategic Association Partner” with SEMI, the industry group representing worldwide suppliers of semiconductor equipment and materials, and it has its offices in SEMI’s headquarters.

“We’ve formed lots of communities,” Ciesinski says of FlexTech. Now that the alliance (once known as the U.S. Display Consortium) is closely allied with SEMI, “we’re doing even more programming.”

FlexTech has drawn together parties involved in flexible electronics from around the country. “There are rich technology veins throughout the United States,” Ciesinski observes. It is also working with Thinfilm Electronics of Norway, which maintains a Product Development Center in Sweden and has its NFC Innovation Center in San Jose, near the SEMI/FlexTech office building.

Heidi Hoffman, senior director of the FlexTech Group, said the organization is working on a materials registry database for flexible sensors and other flexible/printed electronics. FlexTech is also collaborating with SEMI and IPC on developing industry standards for flexible/hybrid electronics manufacturing and design.

Why flexible sensors and electronics matter

So why is all of this work so important? Flexible electronics “opens up the electronics application space,” Ciesinski says. But he notes that with chips going into PCs and organic light-emitting diodes taking over in thinner displays, flexible devices are not looking to displace any of that.

Flexible sensors can serve as life-monitoring, lifesaving devices. “They can be put on aircraft wings, helicopter blades,” according to Ciesinski. They also can be applied to bridges and roads for structural health monitoring, with sensors being embedded into critical infrastructure. “This is game-changing technology” to promote safety, for emergency responders and the military.

Hoffman says flexible goes “beyond boxes or wires. It’s a completely different manufacturing paradigm for the industrial IoT.”

Ciesinski notes manufacturers of flexible/hybrid electronics “make rolls of the stuff; they cut off a piece.” Such roll-to-roll manufacturing offers “great economies of scale in making electronics by the roll, instead of a wafer or a platter.” Flexible sensors mark the “evolution of the silicon industry,” he adds. Manufacturers can use “ribbons of silicon, almost flexible,” in developing flexible electronics.

R&D
ISORG of Grenoble, France, is a startup specializing in organic photodetectors (OPDs). The CEA spinoff makes large-area photodetectors and image sensors on plastic at its pilot production line. The company’s photodetectors could be used, among other things, for “smart” shelves in stores and keeping track of inventory, according to IDTechEx, which predicts the market for printed photodetectors could grow from about $10 million in 2017 to more than $160 million in 2023. ISORG also is targeting industrial IoT applications for its OPD technology.

The number of applications is growing rapidly. “There is some exciting work being done on skin patches that have sensing functionalities, such as sweat analysis,” IDTechEx’s Chansin says. Yole notes the development of “thinning silicon substrates to take benefit of CMOS processes instead of using polymer substrates.”

A University of Illinois at Urbana-Champaign research team reported on development of a flexible “epidermal electronics” device that can monitor blood flow when applied to the skin. The blood-flow monitor can track flows in 1 or 2 millimeters below the skin surface, even while the person is moving around. The monitor was developed in conjunction with the National Institutes of Health and with other researchers in China and the United States.

The University of Tokyo is working on a flexible and transparent pressure sensor, as well, that could be applied to the fingers of health-care practitioners for breast-cancer screening. The device is made with organic transistors, electronic switches incorporating carbon- and oxygen-based organic materials, and a pressure-sensitive nanofiber structure. The researchers added carbon nanotubes and graphene to an elastic polymer to create the nanofibers, measuring 300 to 700 nanometers in diameter.

“Flexible electronics have great potential for implantable and wearable devices,” says Sungwon Lee, a team leader at the University of Tokyo’s Graduate School of Engineering. “I realized that many groups are developing flexible sensors that can measure pressure but none of them are suitable for measuring real objects since they are sensitive to distortion.”

UC Berkeley researchers have come up with a flexible sensor system that measures metabolites and electrolytes in sweat, calibrates the data based on skin temperature, and transmits the results in real time to a smartphone application. The sensor can alert users to dehydration, fatigue, and abnormally high body temperatures, the Cal engineers report. The prototype device combines five sensors on a flexible circuit board. The sensor array is adjacent to a wireless printed circuit board with off-the-shelf silicon-based components. NIH was also involved in this project.

“Human sweat contains physiologically rich information, thus making it an attractive body fluid for non-invasive wearable sensors,” Berkeley Professor Ali Javey says.

All told, flexible sensors promise to usher in a new era of electronics for health, safety, and well-being. The market is just beginning to grasp the applications and implications.

Related Events
The SEMICON West conference in mid-July will feature a two-day Flexible Hybrid Electronics Forum. The first day, on July 12 in San Francisco, will focus on “Flex Hybrid Electronics Processing and Packaging,” with the second day on July 13 targeting “Next Generation Flexible Health Monitoring Devices,” a program put together by the Nano-Bio Manufacturing Consortium and NextFlex. The latter includes the development of a “smart Band-Aid,” a flexible device that could be applied to the skin for 36 hours to monitor the vital signs of chronically ill patients and premature babies, according to Ciesinski. The plan is to bring the cost of such intelligent bandages down to about $2.
Events on the horizon this month include the Flexible Sensors 2016 Workshop and Exhibition, scheduled for April 26 in Santa Clara, Calif., and IDTechEx’s Printed Electronics Europe conference and exhibition, set for April 27 and 28 in Berlin, Germany.

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