Stretchable Diode Cuts Robot Skin Sensor Crosstalk to 0.3%

Crosstalk between pressure sensors in electronic skin dropped from 63.1% to 0.314% when engineers paired the sensors with a new intrinsically stretchable diode. Even stretched by 30%, the unwanted signal share fell to 0.697% from 40.0%, letting each sensor measure pressure independently and accurately.

Researchers at the Ulsan National Institute of Science and Technology (UNIST) announced the work on the 11th. Professor Shim Kyo-seung of the Department of Chemistry led the team, and the findings appeared online in Science Advances on Oct. 21.

Why does crosstalk matter for robot skin?

A robot handling small objects precisely needs electronic skin that senses where and how hard it's being touched. That means densely arrayed pressure sensors. But press one sensor and current bleeds into its neighbors, mixing the signals. The fix is a diode — a component that passes current in only one direction. Conventional organic electrochemical diodes, however, use rigid substrates and electrodes plus a liquid electrolyte, so they break when the skin stretches.

Shim's group replaced every layer with soft polymer-based materials. Silver nanowires and gold nanoparticles form the electrodes, embedded in a polydimethylsiloxane (PDMS) stretchable substrate. On top sits a composite of P3HT polymer semiconductor nanofibers and PDMS, sealed with an ion gel — a solid electrolyte made from an ionic liquid mixed into a polymer.

How does it rectify?

The device's one-way behavior comes from geometry, not exotic chemistry. The two electrodes contact the semiconductor layer over different areas. Apply positive voltage to the smaller electrode and a large voltage difference arises between semiconductor and ion gel, pushing anions into the semiconductor so current flows. Reverse the polarity and the voltage difference shrinks, blocking current.

Keeping that asymmetric structure intact under strain took a new process the team calls ultrathin ion gel transfer printing. An ion gel film averaging 62.7 micrometers thick — roughly the width of a human hair — forms on a silicone rubber stamp and is pressed onto the semiconductor. The thin film exploits surface adhesion differences between materials, so it stays uniformly attached without delaminating through repeated stretching.

What did the tests show?

The numbers are what practitioners will want to check:

• Forward current reached 22,300 times reverse current within a ±1 V range — a rectification ratio of about 23,000 at low voltage.
• Rectification held when the device was stretched 30% and survived 1,000 stretch-release cycles.
• The team built half-wave and full-wave rectifier circuits, plus OR and AND logic gates, from the diode and soft resistive elements. All operated normally while stretched.

"By replacing both the rigid substrate and the liquid electrolyte of conventional devices with soft materials, we secured high rectification performance at low voltage," Shim said. "We applied it directly to stretchable logic circuits and to suppressing sensor signal crosstalk, demonstrating the potential for integrating intrinsically stretchable electronic systems, so we expect it to be widely used in developing electronic skin and wearable devices."

Kim Se-hyun, a combined master's-doctoral researcher in UNIST's Department of Chemistry, served as first author. The Ministry of Science and ICT and the National Research Foundation of Korea funded the study through programs for outstanding early-career researchers and for core technology development in next-generation convergence free-form displays.

For anyone building soft robots or wearables, the practical takeaway is simple: you can now route and rectify signals on a substrate that stretches by a third, without liquid electrolytes or rigid parts failing at the joints.