MEMS and Sensors

Engineers Discover How to Make Sensors in Half the Time

02 November 2015

Bioengineers at the University of California, San Diego, have developed a method that reduces the time taken to make high-tech, flexible medical sensors by 50%.

The recent discovery brings the mass production of sensors for monitoring vital signs and brain activity closer to reality since the process makes it possible to manufacture the sensors similar to the way newspapers are printed off the press.

“A clinical need is what drove us to change our fabrication process,” says Todd Coleman, a bioengineering professor at the Jacobs School of Engineering at UC San Diego.

Coleman’s team at UC San Diego has been working in medical settings for four years. So far, they have developed sensors that are being used to monitor premature babies, pregnant women, patients in Intensive Care Units and those suffering from sleep disorders.

The sensors’ original fabrication process involved 10 steps, which included removing the sensors from the silicon wafer they are built on. During the process, the sensors remained fragile and susceptible to rips and tears.After looking into it, they found that nurses would benefit from a peel-and-stick form of sensor (like a Band Aid), so they used that as a starting point.

Sample of the sensor created. Image Credit: UC San Diego/Jacobs School of EngineeringSample of the sensor created. Image Credit: UC San Diego/Jacobs School of EngineeringHowever, what if you could use the adhesive properties of a Band Aid-like medium to help peel off the sensors from the silicon wafer easily and quickly? Wouldn’t that make the process much simpler—and faster? That was the question that DaeKang, a Jacobs School Ph.D. student in Coleman’s research group, set out to answer. The result of his efforts is a process that comprises only six steps—three of them in the clean room. The steps that took 10 to 20 minutes before now take just 35 seconds.

Kang created a coating about 20 to 50 micrometers thick, made of a silicon-like material called an elastomer, to easily remove the sensors, made of gold and chromium, from the silicon wafer. This was tricky work. The coating had to be sticky enough to allow researchers to build the sensors in the first place, but loose enough to allow them to peel off the wafer.

“It’s a Goldilocks problem,” Coleman says.

The new process they came up with does not require any chemical solvents so sensors can be peeled off with any kind of adhesive such as scotch tape or a lint roller.

Coleman’s team also showed that the sensors could be fabricated on a curved, flexible film typically used to manufacture flexible printed circuits and the outside layer of spacesuits. They were able to easily peel off the sensors from the curved film without compromising their functioning.

The key to making peel-off sensors was building the sensors upside down so that their functioning part would be exposed after they were removed from the wafer.

Now, not only did the researchers prove that the new method was quicker, but they also proved functionality by placing a sensor on a subject’s forehead and hooking it up to an electroencephalography machine. The sensors were able to detect a special brain signal present only when the subject’s eyes were closed—a classic electroencephalogram testing procedure.

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