Bi-Doped Single-Crystalline (001) Epitaxial TiO₂ Anatase Nanostructures for Resistive Random Access Memory Applications

Abstract

Resistive switching memory devices are an emerging class of nonvolatile memories and have shown that outstanding device performance originates from the migration of oxygen vacancies. Research efforts are made to enhance the resistive switching behavior of metal oxide nanostructures. This work reports resistive switching properties of bismuth doped singlecrystalline epitaxial anatase TiO 2 nanostructures fabricated on (001) oriented Nb:SrTiO 3 substrates. These nanostructures are fabricated with a Bi 4 Ti 3 O 12 precursor using a "phase separation and evaporation" approach. Resistive switching measurements, performed by conducting atomic force microscopy on the as-fabricated TiO 2 nanostructures, reveal a stable ON/OFF ratio (∼5 × 10 4 ) (irrespective of the spatial position of the tip) at a read voltage of −0.4 V. Energy dispersive X-ray spectroscopy mapping by scanning transmission electron microscopy confirms presence of trapped bismuth (Bi) near the interface for these as-grown nanostructures. Annealing the nanostructures under high vacuum (10 −7 Torr) and temperature (900 °C), i.e., conditions that promote Bi loss and evaporation, results in a marked drop in the ON/OFF ratio to ∼2 × 10 2 . As none of the other morphological or structural parameters change after annealing, it reveals the key role played by the trapped Bi. We propose that these residual Bi ions in the vicinity of the interface act as charge trapping/detrapping sites for carriers under the applied electric field, which enhances the resistance switching behavior. This work demonstrates that purposely introducing defects or dopants during oxide heteroepitaxy can be a very potent method to realize emergent electronic properties in metal oxide nanostructures for the next generation resistive switching application.

A Review on the Progress of Optoelectronic Devices Based on TiO2 Thin Films and Nanomaterials

“…The excellent durability and retention properties make this device structure a suitable candidate for capacitive memory applications. The resistive conversion properties of bismuth-doped anatase type TiO 2 nanostructures prepared on Nb:SrTiO 3 (Nb:STO) substrates were reported by Bogle et al [ 79 ]. Figure 12 a shows the synthesis process of TiO 2 nanostructures.…”

Multitasking Memristor for High Performance and Ultralow Power Artificial Synaptic Device Application

“…Inspired by neurotransmission of the brain, memristors (memory + resistor) with an inherent resist switching performance have been recognized as excellent candidates for mimicking both artificial synapses and neurons. − The excellent switching performance matrix, such as long retention (>10 years), stable endurance (>10 10 cycles), small switching energy (<10 pJ), , fast switching speed (<1 ns), , and nanoscale cells (<10 nm) pave the way for memristor to be the next-generation in-memory computing. Memristors are formed by an active layer with the top and bottom electrodes. − The conductance of the memristors can be varied by external stimuli, including external electrical field, , optical illumination, , tactile and auditory sensory systems; − therefore, the multiple analog resistance states can be obtained by historical stimuli. Till now, various materials have been applied for the active layer of the memristor including nitrides, oxides, chalcogenides, MXenes, and polymers .…”

“…Memristors provide excellent potential as fundamental neuronal and synaptic components for realizing energy-efficient and high-performance in-memory computing. However, several synaptic characteristics should be considered for superior computing capability, including dynamic range (ON/OFF ratio), nonlinearity in the weight update, multistorage capability, cycle-to-cycle variation, and device-to-device variation. − TiO 2 thin film-based memristors, including the single crystalline (001) epitaxial TiO 2 nanostructure as the active layer, have been intensively studied as a promising candidate for next-generation nonvolatile memristors . Recently, a tunable synaptic performance has been realized in a Ti/TiO 2 /Si memory device, demonstrating its potential for the in-memory computing applications …”

“…Memristors are formed by an active layer with the top and bottom electrodes. 21−25 The conductance of the memristors can be varied by external stimuli, including external electrical field, 23,24 optical illumination, 26,27 tactile and auditory sensory systems; 28−30 therefore, the multiple analog resistance states can be obtained by historical stimuli. Till now, various materials have been applied for the active layer of the memristor including nitrides, 31 oxides, 32 chalcogenides, 33 MXenes, 34 and polymers.…”

“…40−42 TiO 2 thin film-based memristors, including the single crystalline (001) epitaxial TiO 2 nanostructure as the active layer, have been intensively studied as a promising candidate for next-generation nonvolatile memristors. 24 Recently, a tunable synaptic performance has been realized in a Ti/TiO 2 /Si memory device, demonstrating its potential for the in-memory computing applications. 32 Here, we report a multitasking memristor with the heterostructure of Au/Ti/TiO 2 /Nb:STO.…”