Two-dimensional halide perovskite memristor arrays: linearly programmable for neuromorphic computing
The von Neumann architecture imposes fundamental limits on artificial neural networks, manifesting as the storage wall and power wall. Memristors, which encode data via conductance changes, offer a pathway to artificial synapses for neuromorphic computing. Three-dimensional halide perovskites (HPs) enable artificial synapses through mixed electronic-ionic conductivity, but suffer from poor stability and uncontrolled ion transport in polycrystalline films. Two-dimensional HPs provide phase versatility, microstructural anisotropy, and moisture resistance, yet asymmetric and nonlinear conductance changes arise from inconsistent growth orientation, degrading neuromorphic computing efficiency and accuracy. Dion-Jacobson (DJ) 2D HP memristors have now achieved highly linear and symmetric conductance changes by optimizing growth orientation. DJ-phase films were synthesized using butane-1,4-diammonium (BDA2+) as the divalent organic cation, with thiocyanate (SCN) pseudo-halide anion introduced into BDAMAn−1PbnI3n+1 (n = 2–5). SCN additives yielded vertically aligned [PbI6]4− octahedral inorganic layers, with n = 3 showing superior crystallinity. Optimized SCN concentration produced columnar grains with minimal grain boundaries, densely packed and vertically aligned. Moisture stability tests showed DJ HP films with SCN additives remained stable for up to 7 months in ambient air, versus 28 days for randomly oriented films. Crossbar array devices exhibited highly symmetric analogue switching, spike-width-dependent plasticity (SWDP), spike-voltage-dependent plasticity (SVDP), and nearly perfectly linear and symmetric potentiation and depression (P&D), attributed to homogeneous migration of charged interfacial ions. Biologically plausible synaptic plasticities—paired-pulse facilitation (PPF), paired-pulse depression (PPD), and spike-timing-dependent plasticity (STDP)—were demonstrated. First-principle density functional theory calculations revealed the resistive switching mechanism, highlighting the absence of van der Waals gaps between inorganic perovskite layers.