Complementary Resistive Switching and Synaptic-Like Memory Behavior in an Epitaxial SrFeO_2.5 Thin Film through Oriented Oxygen-Vacancy Channels

Abstract

Oxygen-vacancy-ordered brownmillerite oxides offer a reversible topotactic phase transition by significantly varying the oxygen stoichiometry of the material without losing its lattice framework. This phase transition leads to substantial changes in the physical and chemical properties of brownmillerite oxides, including electrical and ion conductivity, magnetic state, and oxygen diffusivity. In this study, the variations in the resistive switching mode of the epitaxial brownmillerite SrFeO 2.5 thin film in the device were studied by systematically controlling the oxygen concentration, which could be varied by changing the compliance current during the first electroforming step. Depending on the compliance current, the SrFeO 2.5 devices exhibited either low-power bipolar resistive switching or complementary resistive switching behaviors. A physical model based on the internal redistribution of oxygen ions between the interfaces with the top and the bottom electrodes was developed to explain the complementary resistive switching behavior. This model was experimentally validated using impedance spectroscopy. Finally, the gradual conductance variation in the brownmillerite SrFeO 2.5 thin films was exploited to realize synaptic learning.

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

“…In search of new materials and structures for low-variability analog switching memristors, here, we propose a novel synapse, namely, topotactic phase transition RAM (TPT-RAM), using brownmillerite (BM) oxides [such as SrCoO 2.5 (SCO) ( 17 , 18 ) and SrFeO 2.5 ( 19 – 21 )] as the resistive switching oxide. We chose SCO as an exemplary material whose unique crystal structure formed by alternating stacks of oxygen octahedra and oxygen tetrahedra provides the favorable conditions to achieve uniform analog switching: (i) The highly ordered one-dimensional oxygen vacancy channels (OVCs) provide predefined freeway for the migration of oxygen ions to induce phase transition and resistive switching ( 22 ).…”

Solid-state electrochemical redox control of the optoelectronic properties for SrFeOx thin films

“…SrFeO x exhibits a clear phase transition from orthorhombic BM antiferromagnetic insulator (x = 2.5, Fe 3+ ) to cubic PV helimagnetic metal (x = 3, Fe 4+ ) 16,17 at different oxide ion (O 2− ) concentrations. [18][19][20] In 2017, Khare et al 21 realized the phase transformation of SrFeO x epitaxial films from SrFeO 2.5 to SrFeO 3 by post-annealing in O 2 atmosphere. In 2019, Saleem et al 22 demonstrated the electrochemical topotactic phase transition of SrFeO x epitaxial films using ionic liquid as the electrolyte.…”

Research on Pt/NiOx/WO3–x:Ti/W Multijunction Memristors with Synaptic Learning and Memory Functions

“…For instance, when the intersection of the high resistance state (HRS) is surrounded by the intersection of the low resistance state (LRS) in the cross array, the surrounding path is likely to form current leakage and thus cannot be operated or read correctly. The larger the array is, the more current leakage paths there are, which can cause more serious misreading problems. − In the previous reports, the most common solution involves connecting a transistor in series to each RRAM (1T1R). ,− Other solutions, such as a series selector (1S1R), ,, a series diode (1D1R), − and complementary memristors, , were designed so that every unit of the array had rectification characteristics to eliminate misoperation and misreading caused by cross-talk.…”

“…8−11 In the previous reports, the most common solution involves connecting a transistor in series to each RRAM (1T1R). 1,5−7 Other solutions, such as a series selector (1S1R), 9,11,12 a series diode (1D1R), 13−15 and complementary memristors, 8,16 were designed so that every unit of the array had rectification characteristics to eliminate misoperation and misreading caused by cross-talk.…”