Mixed Conduction in Polymeric Materials: Electrochemical devices for Biosensing and Neuromorphic Computing

Event Dates: 

Wednesday, December 12, 2018 - 9:00am

CTQM Seminar Type: 

  • Related Seminar Series

Speaker Name(s): 

Alberto Salleo

Speaker Affiliation(s): 

Stanford University

Abstract, Event Details: 

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. A particularly interesting class of materials in this application area takes advantage of mixed ionic and electronic conduction in certain semiconducting polymers. Indeed, the ability to transduce ionic fluxes into electrical currents is useful when interacting with living matter or bodily fluids. My presentation will first discuss the fundamental aspects of how mixed conduction works in polymeric materials and then focus on two families of devices made with such materials: electrochemical transistors and artificial synapses.
1- Biosensing using electrochemical transistors: The continuous monitoring of human health can greatly benefit from devices that can be worn comfortably or seamlessly integrated in household objects, constituting “health-centered” home automation aka "domotics". I will describe electrochemical transistors that detect ionic species either directly present in body fluids or resulting from a selective enzymatic reaction (e.g. ammonia from creatinine) at physiological levels. Additionally, I will show that non-charged molecules can be detected by making use of custom-processed polymer membranes that act as “synthetic enzymes”. Using these membranes in conjunction with electrochemical transistors we demonstrate that we are able to measure physiological levels of cortisol in real human sweat. Finally, I will show a more biomimetic approach where the sensing layer is a lipid membrane stabilized at a liquid-liquid interface, which we use to detect antimicrobial compounds. The same basic device that we use for sensing can also be used for computing.
2- Polymer-based artificial synapses: 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 (500 distinct, non-volatile conductance states within a ~1 V operating range. Furthermore, it achieves record classification accuracy when implemented in neural network simulations. Our organic neuromorphic device works by combining ionic (protonic) and electronic conduction and is essentially similar to a concentration battery. The main advantage of this device is that the barrier for state retention is decoupled from the barrier for changing states, allowing for the extremely low switching voltages while maintaining non-volatility. I will show that the device can rival commercial flash memory in terms of endurance and possibly switching time. When accessed with an appropriate switching device it exhibits excellent linearity, which is an important consideration for neural networks that learn with blind updates.