Key Takeaways & Executive Findings
- •• • SCN additive incorporation into BDAMAn−1PbnI3n+1 (n = 3) films yields vertically aligned [PbI6]4− octahedral layers and superior crystallinity, enabling columnar grains with minimal grain boundaries; this microstructure directly reduces ion migration heterogeneity, a prerequisite for linear conductance updates in crossbar arrays. • • Moisture stability of SCN-modified DJ HP films reaches 7 months in ambient air, compared to 28 days for randomly oriented films—a 7.5-fold improvement. This threshold is critical for commercial neuromorphic hardware, where device lifetime must exceed 5 years under uncontrolled humidity. • • Potentiation and depression (P&D) characteristics are nearly perfectly linear and symmetric, with homogeneous migration of charged interfacial ions. This linearity minimizes weight update errors in analog neural network training, directly impacting inference accuracy and training convergence rates. • • First-principle DFT calculations identify the absence of van der Waals gaps between inorganic perovskite layers as the key structural feature governing resistive switching. This mechanistic insight provides a design rule for eliminating nonlinear conductance artifacts in 2D HP memristors.
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Abstract
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.
1. Introduction
Artificial neural networks have achieved remarkable success in deep learning, yet their deployment on von Neumann architecture confronts the storage wall and power wall. Memristors, which store data through conductance changes, are pivotal for artificial synapses in neuromorphic hardware. Three-dimensional halide perovskites (HPs) offer mixed electronic-ionic conductivity and ion migration, but practical application is hindered by 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—arising from inconsistent growth orientation—limit neuromorphic computing efficiency and accuracy.
Dion-Jacobson (DJ) 2D HP memristors have now achieved highly linear and symmetric conductance changes by optimizing the growth orientation of 2D HP films. 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 produced vertically aligned [PbI6]4− octahedral inorganic layers, with n = 3 showing superior crystallinity. Optimized SCN concentration facilitated columnar grains with minimal grain boundaries, leading to densely packed, vertically aligned films. Moisture stability tests showed SCN-modified DJ HP films 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.
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Hudie Wei, Liang Chu (2025). Two-dimensional halide perovskite memristor arrays: linearly programmable for neuromorphic computing. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3257-y
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Frequently Asked Questions
What is the failure mechanism under prolonged electrical stress for DJ-phase 2D HP memristors, and how does the SCN additive mitigate it?
The primary failure mechanism is ion migration heterogeneity leading to nonlinear conductance changes. SCN additives promote vertically aligned [PbI6]4− octahedral layers and columnar grains with minimal grain boundaries, which homogenizes charged interfacial ion migration. This structural control yields nearly perfectly linear and symmetric potentiation and depression (P&D), reducing weight update errors. Without SCN, randomly oriented films decompose within 28 days, whereas SCN-modified films remain stable for 7 months in ambient air.
What are the scalability bottlenecks for integrating DJ-phase 2D HP memristors into large-scale crossbar arrays?
Scalability is constrained by the need for uniform growth orientation across large areas. The optimized SCN concentration enables columnar grains with minimal grain boundaries, but maintaining this microstructure over wafer-scale dimensions remains challenging. The n = 3 composition exhibited superior crystallinity, yet higher n values (up to 5) showed weakened diffraction peaks and increased 3D HP peaks, indicating phase purity degradation. Crossbar arrays require consistent device-to-device linearity; any deviation in grain orientation reintroduces asymmetric conductance changes.
How does the linearity of P&D in these memristors compare quantitatively to conventional resistive switching devices, and what is the impact on neural network training accuracy?
The P&D behaviors are described as almost perfectly linear and symmetric, attributed to homogeneous migration of charged interfacial ions. This contrasts with conventional 2D HP memristors that exhibit asymmetric and nonlinear conductance changes due to inconsistent growth orientation. In neuromorphic computing, nonlinear weight updates cause training divergence and reduced inference accuracy. The linearity achieved here minimizes update errors, enabling more precise analog weight adjustments during backpropagation.
What is the operational temperature range and humidity tolerance for the SCN-modified DJ HP memristors, and how do these compare to commercial non-volatile memory technologies?
The SCN-modified DJ HP films maintained stability for up to 7 months in ambient air, compared to 28 days for randomly oriented films. This represents a 7.5-fold improvement in moisture resistance. However, commercial non-volatile memory (e.g., flash) typically operates from -40°C to 85°C and withstands 85% relative humidity for 10 years. The perovskite memristors have not yet demonstrated equivalent temperature cycling or accelerated humidity testing, which remains a critical gap for industrial qualification.
What is the resistive switching mechanism in DJ-phase perovskites, and how does the absence of van der Waals gaps influence device performance?
First-principle density functional theory calculations revealed that the absence of van der Waals gaps between the inorganic perovskite layers is key to the resistive switching mechanism. In DJ-phase 2D HPs, the divalent organic cation (BDA2+) directly bridges adjacent inorganic layers, eliminating the weak van der Waals gaps present in Ruddlesden-Popper phases. This structural continuity facilitates homogeneous ion migration and charge transport, enabling symmetric and linear conductance changes. The lack of gaps also enhances mechanical robustness and moisture stability, as evidenced by the 7-month ambient stability.
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