Electric Field-Moderated Filament Control for Cryogenic RRAM Synapse

To implement in-cryostat neural processing in next-generation computing platforms, analog synaptic devices based on resistive random-access memories (RRAMs) should be operated at cryogenic temperatures (<123 K). We propose a cryogenic RRAM synapse based on an HfO_y/HfO_x stack. The RRAM exhibited gradual switching with a highly linear and symmetric update at room temperature. However, at 90 K, electric field (E-field)-driven ion migration was dominant during the set operation. This abruptly formed a conductive filament (CF), causing a nonlinear update. To control the CF evolution, we investigated the link between the reset operation and the following set dynamics via real-time transient current analysis. Two distinct reset modes were observed depending on the reset voltage step: (i) fully disconnected and (ii) partially ruptured CF. Particularly, when the CF remained connected in the high-resistance state, the local E-field across the RRAM stack was moderated. Therefore, cryo-RRAM at 90 K yielded a linearly updated current under identical 50 ns pulses and reliable multilevel retention.