Mixed Conduction in Polymeric Materials: Imparting Plasticity to Electrochemical Devices for Brain-Like Computing

 Alberto Salleo

Department of Materials Science and Engineering, Stanford University, Stanford CA 94305



Abstract Organic semiconductors have been traditionally developed for making low-cost and flexible transistors, solar cells and light-emitting diodes. In the last few years, emerging applications in health case and bioelectronics have been proposed. An interesting class of materials in this application area takes advantage of mixed ionic and electronic conduction in certain semiconducting polymers. In particular, mixed conductors can be used to emulate the compute-in-memory operation of the brain that is the key to its energy efficiency. This principle has been invoked as one of the keys to neuromorphic, or brain-like, computing. Indeed, the brain can perform massively parallel information processing while consuming only ~1- 100 fJ per synaptic event. I will describe a novel electrochemical neuromorphic device that switches at record-low energy (<0.1 fJ projected, <100 fJ measured), displays >500 distinct, non-volatile conductance states within a ~1 V operating range. The tunable resistance of the device behaves very linearly, allowing low write-noise and blind updates in a neural network when operated with the proper access device. Organic electrochemical synapses also display outstanding endurance achieving over 109 switching events with very little degradation. I will describe our recent efforts at scaling and materials selection, allowing us to reach 20 ns write pulses and operation at high temperature (up to 120°C) in an all-solid-state device. These properties are very promising in terms of the ability to integrate with Si electronics to demonstrate online learning and inference. The outstanding performance of these devices can be attributed to proton transport, which leads to high speed and low-energy switching. Finally, the organic synapses were interfaces with living matter and modulated by a neurotransmitter (dopamine) demonstrating promising operation as a bio-hybrid assembly.

Speaker Bio: Alberto Salleo is currently Professor of Materials Science and Department Chair at Stanford University. Alberto Salleo holds a Laurea degree in Chemistry from La Sapienza and graduated as a Fulbright Fellow with a PhD in Materials Science from UC Berkeley in 2001. From 2001 to 2005 Salleo was first post-doctoral research fellow and successively member of research staff at Xerox Palo Alto Research Center. In 2005 Salleo joined the Materials Science and Engineering Department at Stanford as an Assistant Professor. Salleo is a Principal Editor of MRS Communications since 2011.While at Stanford, Salleo won the NSF Career Award, the 3M Untenured Faculty Award, the SPIE Early Career Award, the Tau Beta Pi Excellence in Undergraduate Teaching Award, and the Gores Award for Excellence in Teaching, Stanford’s highest teaching award. He has been a Thomson Reuters Highly Cited Researcher since 2015, recognizing that he ranks in the top 1% cited researchers in his field.