ECRAM—Progress, Challenges and Opportunities

Electrochemical random access memory (ECRAM) is a three terminal device that operates by tuning electronic conductance in functional materials through solid-state electrochemical redox reactions. This mechanism can be considered as a gate-controlled bulk modulation of dopants and/or phases in the channel. Early work demonstrating that ECRAM can achieve nearly ideal analog synaptic characteristics has sparked tremendous interest in this approach. More recently, the realization that electrochemical ion insertion can be used to tune the electronic properties of many types of materials including transition metal oxides, layered 2D material, organic and coordination polymers, and that the changes in conductance can span orders of magnitude, from gradual increments needed for analog elements, to large, abrupt changes for dynamically reconfigurable adaptive architectures, has further attracted interest in ECRAM as the basis for analog synaptic elements for inference accelerators as well as for dynamical devices that can emulate a wide range of neuronal characteristics for implementation in analog spiking neural networks (SNNs). At its core, ECRAM shares many fundamental aspects with rechargeable batteries, where ion insertion materials are used extensively for their ability to reversibly store charge and energy. Computing applications, however, present drastically different requirements: systems will require many millions of devices, scaled down to tens of nanometers, all while achieving reliable electronic-state tuning at scaled-up rates and endurances, and with minimal energy dissipation and noise. In my presentation, I will discuss recent progress for several different types of ECRAM, including devices based on inorganic, polymer and coordination compounds, and with Li, protons, and oxygen vacancies as mobile ions. I will also discuss strategies for realizing tunability, reconfigurability and long term stability and state retention all in one device.