Analog memristive synapse based on topotactic phase transition for high-performance neuromorphic computing and neural network pruning

Abstract

Inspired by the human brain, nonvolatile memories (NVMs)–based neuromorphic computing emerges as a promising paradigm to build power-efficient computing hardware for artificial intelligence. However, existing NVMs still suffer from physically imperfect device characteristics. In this work, a topotactic phase transition random-access memory (TPT-RAM) with a unique diffusive nonvolatile dual mode based on SrCoOx is demonstrated. The reversible phase transition of SrCoOx is well controlled by oxygen ion migrations along the highly ordered oxygen vacancy channels, enabling reproducible analog switching characteristics with reduced variability. Combining density functional theory and kinetic Monte Carlo simulations, the orientation-dependent switching mechanism of TPT-RAM is investigated synergistically. Furthermore, the dual-mode TPT-RAM is used to mimic the selective stabilization of developing synapses and implement neural network pruning, reducing ~84.2% of redundant synapses while improving the image classification accuracy to 99%. Our work points out a new direction to design bioplausible memristive synapses for neuromorphic computing.

Manipulating the Resistive Switching in Epitaxial SrCoO2.5 Thin-Film-Based Memristors by Strain Engineering

“…Simultaneously, oxygen vacancies migrate to the LSM bottom electrode and then form the paths for oxygen ions by the external voltage, enabling the formation of the multiple filaments within the BM-SCO film to connect the top and bottom electrodes eventually, leading to the LRS. 43 As shown in the DFT calculation, the formation energy and the migration barrier along [001] direction of oxygen vacancies are noticeable higher for the BM-SCO film under compressive strain than those for the unstrained sample. In addition, Jalili et al 56 reported that the compressive strain can also enhance the oxygen vacancy formation energy in the LSM layer, making the oxygen ions more difficult to pull out from the LSM layer under compressive strain.…”

“…In addition, both devices undergo a forming process at a negative voltage (see Figures S3 and S4 for details), consistent with those reported in some previous studies. 50,51 However, some other studies 41,43 reported a forming process with opposite polarity, i.e., positive forming. The possible origin for the different forming polarities is discussed in Figure S4.…”

“…The formation and rupture of P-SCO CFs in the BM-SCO matrix may rely on the electric-field-induced oxygen migration. − The effect of strain on the oxygen migration dynamics can thus explain the different RS characteristics of Au/BM-SCO/LSM/LAO and Au/BM-SCO/LSM/STO. To shed light on it, first-principles calculations were performed.…”

“…41−43 Recent studies further revealed that the RS mechanism in the BM-SCO epitaxial thin films lies in the oxygen-migration-induced formation and rupture of P-SCO conductive filaments (CFs) in the BM-SCO matrix. 43 Because the oxygen vacancy formation and migration dynamics are likely to be modulated by the epitaxial strain, it is interesting to use strain engineering to tune the RS characteristics of BM-SCO epitaxial thin films. Experimentally, we fabricate zero-strained and −2.74% compressively strained BM-SCO epitaxial thin films on SrTiO 3 (STO) and LaAlO 3 (LAO) substrates, respectively, with Au and La 0.7 Sr 0.3 MnO 3 (LSM) acting as the respective top and bottom electrodes.…”

“…The topotactic phase transformation between BM-SCO and P-SCO leads to a significant change in conductivities. Previous works have proved that SCO is a good candidate for RS memories and neuromorphic devices. − Recent studies further revealed that the RS mechanism in the BM-SCO epitaxial thin films lies in the oxygen-migration-induced formation and rupture of P-SCO conductive filaments (CFs) in the BM-SCO matrix . Because the oxygen vacancy formation and migration dynamics are likely to be modulated by the epitaxial strain, it is interesting to use strain engineering to tune the RS characteristics of BM-SCO epitaxial thin films.…”