The vertical electrochemical transistor is based on a new kind of electronic polymer and a vertical, instead of planar, architecture. (Image:

A Northwestern University research team has developed a revolutionary transistor that is expected be ideal for lightweight, flexible, high-performance bioelectronics. The electrochemical transistor is compatible with blood and water and can amplify important signals.

Such a transistor could enable wearable devices for onsite signal processing — right at the biology-device interface. Potential applications include measuring heartbeat and levels of sodium and potassium in blood, as well as eye motion for studying sleep disorders.

“All modern electronics use transistors, which rapidly turn current on and off,” said co-corresponding author Tobin J. Marks. “Here we use chemistry to enhance the switching. Our electrochemical transistor takes performance to a totally new level. You have all the properties of a conventional transistor but far higher transconductance [a measure of the amplification it can deliver], ultra-stable cycling of the switching properties, a small footprint that can enable high density integration, and easy, low-cost fabrication.”

The vertical electrochemical transistor is based on a new kind of electronic polymer and a vertical — as opposed to planar — architecture, and it conducts both electricity and ions and is stable in air. The work was published in the journal Nature.

“This exciting new type of transistor allows us to speak the language of both biological systems, which often communicate via ionic signaling, and electronic systems, which communicate with electrons,” said Professor Jonathan Rivnay. “The ability of the transistors to work very efficiently as ‘mixed conductors’ makes them attractive for bioelectronic diagnostics and therapies.”

“With their vertical architecture, our electrochemical transistors can be stacked one on top of another,” said Professor Antonio Facchetti. “Thus, we can make very dense electrochemical complementary circuits, which is impossible for the conventional planar electrochemical transistors.”

Two types of transistors are necessary to make more reliable and powerful electronic circuits: p-type transistors that carry positive charges and n-type transistors that carry negative charges — complementary circuits. Past challenges researchers have faced in the past include that n-type transistors are difficult to build and are typically unstable.

This is the first work to demonstrate electrochemical transistors with similar and very high performance for both types of electrochemical transistors.

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