SAN JOSE, Calif. — Flexible hybrid electronics face big hurdles, but the technology is making progress toward big opportunities, experts said at an annual NextFlex gathering here. Two battery startups showed promising work.  

A mix of printed and traditional chips and traces on plastic substrates are enabling devices that bend and stretch and can made cheaply and fast. But the processes for making such devices are still immature.  

At an annual open house here, members of the NextFlex initiative shared their concerns and showed advances. The group was formed in September 2015 with about $165 million in public and private financing. 

A milestone that researchers are striving for is creating the equivalent of a process development kit (PDK) to steer engineers through a maze of different manufacturing systems and processes currently in use. Richard Vaia, a senior technologist with the U.S. Air Force Research Lab, hopes NextFlex will deliver such a document in the next year or two. 

“Today you have to have a hardcore expert who tweaks things almost by hand, but with a PDK even undergrads can do designs,” Vaia said in an interview. 

Without it, engineers currently stumble over variations in interconnects, resistance levels and other dynamics from one design to the next, Vaia said, calling variability control the chief problem in the field today.  

“Materials and manufacturing techniques are colliding. It may be something in the inks, nozzle heads, post-processing anneals — there are so many different ways to print and deposit materials, each with its own constraints,” he said. 

Harry Partridge, a chief technologist at NASA Ames Research Center, wants to use flexible electronics to monitor astronauts. But currently, the lack of suitable designs for fluidics is a barrier to analyzing the contents of sweat and saliva. 

Another big challenge is powering the thin and light designs. “For a lot of apps it's limiting, although stretchable batteries have come a long way, and ARPA-E [a U.S. energy research agency] has moved toward solid batteries with flexible connections,” Partridge told EE Times. 

"You won’t have the performance of a coin cell or rechargeable, so there will be trade-offs,” said Vaia. “It’s hard to miniaturize batteries, the power subsystem with the battery and power conditioning is not shrinking at the same rate as the rest of the system, so we may need a separate flex design,” he added. 

Millibat's battery is conventional but tiny. (Images: EE Times)
Millibat's battery is conventional but tiny. (Images: EE Times)

Two battery startups exhibiting at the open house showed promising prototypes. 

Millibatt is producing 200 samples/week of a 1.5 milliampHour (mAh) lithium-ion battery that can power a Bluetooth sensor, and in six months it aims to have a 2.5 mAh version ready. The battery is not flexible, but it is tiny, measuring 7x7x0.8mm and delivers 10 milliamps peak. The startup is seeking $5 million in funding to buy gear to help it transition from a four-inch fab at UCLA to a commercial eight-inch fab where products could be made in volume. 

Imprint Energy is somewhat further along with a printed battery. It uses a high conductivity solid polymer electrolyte that can be packed into designs large enough for a 40 mAh battery delivering 50 millamps current.  It validated a smart label design for Semtech, vendor of the chips for the LoRa IoT network. The startup can print 10,000 batteries a week and is seeking a $12 million Series B to scale up volumes, improve 80% yields, and validate more customer designs. 

Imprint Energy showed batteries of various sizes on various substrates.
Imprint Energy showed batteries of various sizes on various substrates.

Flexible electronics stretches from high schools to Mars 

The two battery startups were among some 20 other exhibitors at the open house. They included a handful of other startups and major commercial companies as well as a large group of academics. 

Matternet, a startup making drones to deliver emergency drugs and blood supplies to hospitals, showed early work on a project with NextFlex and Boeing to make a printed radar component light enough for future models. GE displayed a flexible stress sensor for spinning shafts now in use in one high-end product. The industrial giant aims to redesign it using printed passives and lowering costs for use in a wide variety of other systems, especially in oil and gas mining. 

“Long term, the number of solutions [flexible electronics] can enable is exciting. We can attack a problem from a new direction and dramatically reduce size or power or put sensors where you couldn’t put them before,” said Stephen Frick, a former astronaut, now director of space hypersonic and advanced materials at Lockheed Martin. 

For example, after the Challenger space shuttle broke apart, “we put some accelerometers on the wing so if something came off and hit the wing you would feel a vibration and could look at the area. It was very crude, the batteries died after a couple days. If you had technology like this, you could retrofit sensors much more thoroughly around the vehicle to have better coverage and keep the crew safe,” Frick said in a panel discussion. 

Partridge of NASA called for new ways to measure an astronaut’s fluid flows to determine their effects on cognitive functions with prolonged time in microgravity. He also imagined a need for smart habitats, future space stations or lunar or Mars colonies that are self-repairing and report their safety factors thanks to flexible sensors.

Richard Vaia (Image: NextFlex)
Richard Vaia (Image: NextFlex)

“Nextflex...started out quite mundane with printing an antenna but that was a game changer, not needing to rip old electronics out, it was something real and has continued to progress piece by piece so you can make stuff adding functionality to existing platforms or designing new things like attritible systems that might last just five missions rather than 50 years,” said Vaia, speaking on the panel. 

Engineers need to be bold, he said noting calls from a recent Air Force 2030 study for “cutting down the tyrannies of distance and time...We can empower people far out in the field with things like field manufacturing, making parts or electronics needed on a battlefield without a logistics trail,” Vaia said. 

Today’s rapid pace of innovation “drives risk avoidance in senior leaders and even senior designers,” Vaia said. “They want to continue to deliver new stuff that works so by default they are forced into using what exists and not bringing in new technologies.  

“As funding constricts...the balance [of existing and new technologies] is getting out of whack. Ten years from now, will we have what we need to create the next thing beyond flexible hybrid electronics,” he asked. 

Malcolm Thompson, executive director of NextFlex gave one promising data point. To date the center’s FlexFactor program has schooled 3,000 secondary students on the future possibilities of electronics manufacturing.