Electrochemical Ionic Synapses with Mg²⁺ as the Working Ion

Dynamic doping by electrochemical ion intercalation is a promising mechanism for modulating electronic conductivity, allowing for energy-efficient, brain-inspired computing hardware. While proton-based devices have achieved success in terms of speed and efficiency, the volatility and environmental pervasiveness of hydrogen (H) might limit the robustness of devices during fabrication, as well as the long-term retention of devices after programming. This motivates the search for alternative working ions. In this work, a proof-of-concept is demonstrated for electrochemical ionic synapses (EIS) based on intercalation of Mg²⁺ ions. The reported device has a symmetric design, with Mg_xWO₃ used as both the gate and channel material. Increasing the Mg fraction, x, in WO₃ increases the electronic conductance in a continuum over a large range (80 nS − 2 mS). Ex situ characterization of the channel confirms that modulation of channel conductance is due to Mg²⁺ intercalation. Unlike H-EIS which rapidly loses programmed conductance states over a few seconds when exposed to air, Mg-EIS can be operated and has good retention in air, with no sign of degradation after 1 h. Mg²⁺ as a working ion with WO₃ as the channel is a promising material system for EIS with long-term retention and low energy consumption.