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)
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.