Graphene Temporary Tattoo Tracks Vital Signs

Super-thin graphene-based health monitor could have wide range of benefits

2 min read
Super-thin graphene-based health monitor is mechanically invisible
Photo: The University of Texas at Austin

A graphene health sensor that goes on the skin like a temporary tattoo takes measurements with the same precision as bulky medical equipment. The graphene tattoos, presented in December at the International Electron Devices Meeting in San Francisco, are the thinnest epidermal electronics ever made. They can measure electrical signals from the heart, muscles, and brain, as well as skin temperature and hydration.

Researchers at the University of Texas at Austin who are developing the sensors hope to develop them for consumer cosmetic use. They also hope the ultrathin sensors will provide a more comfortable replacement for existing medical equipment.

Today, if your doctor wants to monitor your heart rate over an extended period of time to help diagnose some cardiac irregularity, you’ll be sent home with a bulky EKG monitoring harness to wear for 24 hours. The Texas researchers hope to make a system that can take measurements of the same quality or better, but that’s unobtrusive. Deji Akinwande, an electrical engineer who specializes in 2D materials, is collaborating on the project with Nanshu Lu, who works on epidermal electronics.

Materials scientists have for years sung the praises of graphene’s electrical properties and mechanical toughness. What’s been underappreciated, says Akinwande, is that this single-atom-thick stuff is mechanically invisible. When it goes on the skin, it doesn’t just stay flat—it conforms to the microscale ridges and roughness of the epidermis. “You don’t feel it because it’s so compliant,” says Akinwande.

The Texas researchers start by growing single-layer graphene on a sheet of copper. The 2D carbon sheet is then coated with a stretchy support polymer, and the copper is etched off. Next, the polymer-graphene sheet is placed on temporary tattoo paper, the graphene is carved to make electrodes with stretchy spiral-shaped connections between them, and the excess graphene is removed. Now the sensor is ready to be applied by placing it on the skin and wetting the back of the paper.

In their proof-of-concept work, the researchers used the graphene tattoos to take five kinds of measurements, and compared the data with results from conventional sensors. The graphene electrodes can pick up changes in electrical resistance caused by electrical activity in the tissue underneath. When worn on the chest, the graphene sensor detected faint fluctuations that were not visible on an EKG taken by an adjacent, conventional electrode. The sensor readouts for electroencephalography (EEG) and electromyography (EMG, which can be used to register electrical signals from muscles and is being incorporated into next-generation prosthetic arms and legs) were also of good quality. And the sensors could measure skin temperature and hydration, something cosmetics companies are interested in, says Akinwande.

Graphene’s conformity to the skin might be what enables the high-quality measurements. Air gaps between the skin and the relatively large, rigid electrodes used in conventional medical devices degrade these instruments’ signal quality. Newer sensors that stick to the skin and stretch and wrinkle with it have fewer airgaps, but because they’re still a few micrometers thick, and use gold electrodes hundreds of nanometers thick, they can lose contact with the skin when it wrinkles. The graphene in the Texas researchers’ device is 0.3-nm thick. Most of the tattoo’s bulk comes from the 463-nm-thick polymer support.

The next step is to add an antenna to the design so that signals can be beamed off the device to a phone or computer, says Akinwande.

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper
Green

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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