Rapidly Testing Stretchable Sensors

UC Berkeley College of Engineering, CA

A supercapacitor array made using a new fabrication technique that is faster and less expensive than photolithography. (Image: Peisheng He/UC Berkeley)

Engineers at UC Berkeley have developed a new technique for making wearable sensors that enables medical researchers to prototype and test new designs much faster and at a far lower cost than existing methods.

The new technique replaces photolithography — a multistep process used to make computer chips in clean rooms — with a $200 vinyl cutter. The novel approach slashes the time to make small batches of sensors by nearly 90 percent while cutting costs by almost 75 percent, said Renxiao Xu, who developed the technique while pursuing his Ph.D. in mechanical engineering at Berkeley.

Wearable sensors are often used by researchers to gather medical data from patients over extended periods of time. They range from adhesive bandages on skin to stretchable implants on organs, and harness sophisticated sensors to monitor health or diagnose illnesses.

A stretchable “smart mesh” made from the two-mode cutting fabrication process. This device could be applied in skin-mounted sweat extraction and sensing. (Image: Peisheng He/UC Berkeley)

These devices consist of flat wires, called interconnects, as well as sensors, power sources and antennas to communicate data to smartphone apps or other receivers. To maintain full functionality, they must stretch, flex, and twist with the skin and organs they are mounted on — without generating strains that would compromise their circuitry.

To achieve low-strain flexibility, engineers use an “island-bridge” structure. The islands house rigid electronics and sensor components, such as commercial resistors, capacitors, and lab-synthesized components like carbon nanotubes. The bridges link the islands to one another. Their spiral and zigzag shapes stretch like springs to accommodate large deformations.

In the past, researchers have built these island-bridge systems using photolithography, a multistep process that uses light to create patterns on semiconductor wafers. Making wearable sensors this way requires a clean room and sophisticated equipment.

The new technique is simpler, faster and more economical, especially when making the one or two dozen samples that medical researchers typically need for testing.

A description of the technique was published in ACS Nano. Xu, who now works at Apple, and Liwei Lin, professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Center, were the lead researchers.

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