Wearable sensor developers may soon be thanking University of California Berkeley (UC Berkeley) engineers. A team from the University’s Berkeley Sensor and Actuator Center developed a relatively faster and cheaper way to produce sensor prototypes than the common process used today. Currently, sensor designers fabricate prototype chips and sensors using photolithography, an expensive and time-consuming process that involves multiple steps using light in a clean room to create patterns on semiconductor wafers. Compared to photolithography, the new methodology developed at Berkeley is simpler, cheaper, and much faster.
Lead project researcher Renxiao Xu, now with Apple and formerly a mechanical engineering doctoral student at Berkeley, and Liwei Lin, professor of mechanical engineering and the co-director of the Berkeley Sensor and Actuator Center, published a study in ACS Nano that describes the slicing technique.
Wearable sensors need to be flexible and stretchable for a variety of topical and implant applications. They need to be comfortable for the wearer and able to withstand the rigors of the wearer’s daily life without tearing or straining the sensors’ circuitry. The team at Berkeley employed an island-bridge structure for low-strain flexibility. The bridges are flat wires that connect the electronic and sensor components. The team arranged the flat wire bridges in spiral and zigzag shapes to achieve flexibility and connected them to the more rigid components. The technique that makes the process possible is to mount the bridges and islands on a two-layer sheet the consists of an adhesive top layer of polyethylene and a bottom layer of Mylar. The researchers then made two types of cuts with a $200 vinyl cutter. Cutting through just the top layer provides places for flat wire interconnects. The second type of cut carves through both layers to create holding spots for the electronic components and sensors.
Xu, Lin, and their team of engineers created several types of wearable sensors using the island-bridge process. According to the Berkeley report, creating wearable prototype chips with their methodology saves 90% of the time and nearly 75% of the cost of photolithography. The Berkeley group foresees a time when their prototyping technology is used widely in labs developing wearable sensors and studying new diseases.
