The use of ions in semiconductor devices dates back to the first field-effect transistor in 1947, where an electrolyte was used to couple a metal gate to the semiconductor surface. While semiconductor devices still utilize ions to control electronic properties through doping, ionic conductivity is seldom leveraged in modern electronics. However, recent advances in bioelectronics, neuromorphic computing, and energy conversion have been driven by the ability to transport both ionic and electronic carriers. These mixed conductor devices utilize reversible and controllable ion intercalation which dynamically modifies the state of electronic charge throughout the bulk of the semiconductor. Despite their widespread use, the rational design of mixed conductor electronics is limited by the poor understanding of mixed conduction itself.
In my talk, I will present my research focusing on understanding mixed conduction in conjugated polymers for use in electronic devices. First, I will introduce an optical technique to monitor ion motion in conjugated polymers during electrochemical doping. The optical results inform a model for mixed conduction which captures the critical carrier dynamics across multiple length and timescales. Next, I will show how the fundamental insights derived from the optical characterization informs the improved design of conjugated polymers for ion-gated transistors. The findings show that the switching speed of mixed conducting devices is not inherently limited by the ionic transport properties of the active material. Instead, at low doping densities, the electronic transport properties limit the device operation speed. Last, I will show how an ion-gated transistor can be leveraged to amplify the signal of highly selective biosensors, allowing for an output signal which is independent of the electrode area. The device concept is used to demonstrate miniaturized biosensors which enable both implantable and spatially resolved biosensing.
Bio: Scott Keene received his B.S. in Materials Science and Engineering from the University of Washington in 2015. In 2020, he received his Ph.D. in Materials Science and Engineering from Stanford University where he worked in Prof. Alberto Salleo’s group as a Stanford Graduate Fellow. During his doctoral training, Scott developed wearable biosensors for detection of analytes in sweat as well as organic neuromorphic devices for artificial neural network accelerators and neural interfacing. He is currently a Marie Skłodowska Curie Actions Postdoctoral Fellow at the University of Cambridge working in the Department of Electrical Engineering and the Department of Physics under the Supervision of Prof. George Malliaras and Prof. Akshay Rao. His current research focuses on understanding the underlying physics of electrochemical doping in organic mixed ionic-electronic conductors.