Ultrathin (<10 nm) Electrochemical Random‐Access Memory that Overcomes the Tradeoff between Robust Weight Update and Speed in Neuromorphic Systems

Electrochemical random‐access memory (ECRAM) devices are a promising candidate for neuromorphic computing, as they mimic synaptic functions by modulating conductance through ion migration. However, the use of a thick electrolyte layer (>40 nm) in conventional ECRAMs leads to an unavoidable tradeoff between synaptic weight updates and operating speed. To address this problem, a Cu‐based ultrathin ECRAM (UT‐ECRAM) that uses a single 5 nm HfO x active layer and a ≈1.2 nm AlO x liner is designed. The highly efficient gate‐tunable fast Cu‐ion transport in the AlO x /HfO x UT‐ECRAM enables 1) near‐ideal linearity in weight updates (0.45) even achieved with a pulse width ( t w ) of 50 μs, 2) dynamic multilevel retention of 10 4 s, and 3) reliable cycling endurance of 10 4 cycles. A numerical analysis based on device scaling quantitatively reveals that a relatively high concentration of field‐driven Cu ions (≈10 20 cm −3 ) contributes to each synaptic weight update per gate voltage ( V G ) pulse in the UT‐ECRAM without becoming deactivated by traversing thicker layers. This improved gate sensitivity can ultimately overcome the linearity and the ratio/speed tradeoff relationships, paving the way for robust neuromorphic synaptic units.