Multifunctional BiFeO₃ Thin Film-Based Memristor Device as an Efficient Synapse: Potential for Beyond von Neumann Computing in Neuromorphic Systems

Abstract

We report the potential of low-cost sol–gel-synthesized phase pure BiFeO3 thin films as an active material with Cu as the top contact and fluorine-doped tin oxide (FTO) as the bottom contact, that is, Cu/BiFeO3/FTO-based devices for analogue resistive switching characteristics, suitable for beyond von Neumann computing. The Cu/BiFeO3/FTO device showed robust repeatability of bipolar resistive switching up to 3000 cycles. Moreover, retention measurements suggest that the device is stable for 17,000 s at 0.2 V, and endurance measurements suggest reliability for 5000 cycles at 1 and −1 V. Moreover, the Cu/BiFeO3/FTO device showed synaptic behavior, including short- and long-term plasticity and change in ionic conductance with time-dependent pulses suitable for neural network applications. The pulse paired facilitation (PPF) measurements demonstrated a reduction in the PPF value from 9 to 1% with the increasing pulse width from 10 to 400 ms. The strengthening in signal transmission is shown by increasing the synaptic weight from 20 to 22.5 approximately, with the increasing scan rate from 100 to 400 mV/s. The increase in the scan rate resulted in the synaptic weight saturation, and a change in ionic conductance is observed at 0.7 and 0.2 V with varying pulse widths ∼10, 20, and 50 ms, having a 10 ms pulse interval. The spike time-dependent plasticity measurement is carried out for the symmetric and asymmetric Hebbian rule with 4 s pulse width at 1.2 and −1.2 V pulse amplitude. The device also showed ∼96% recognition characteristics, as estimated from retention loss characteristics. Thus, the present work emphasizes the utility of BiFeO3-based analogue devices for memristive neuromorphic computing devices.

Artificial Synapse Emulated by Indium Tin Oxide/SiN/TaN Resistive Switching Device for Neuromorphic System

“…Thus, when emulating the human brain, a cohabitation of short-and longterm actions may be incorporated as an added strength [42,73]. PPF is a standard method to seek short-term memory behavior by applying two identical pulse trains with different pulse intervals [74]. Figure 7a shows the PPF index that is defined as ((I 2 − I 1 )/I 1 ) × 100, where I 1 is the current achieved by the first pulse train and I 2 is the current achieved by the next pulse train.…”

Implementation of Artificial Synapse Using IGZO-Based Resistive Switching Device

“…PPF is a function acquired by applying twin pulses to the device under different conditions. Due to the volatile behavior of the device, as the time interval increases, the current response of the second pulse will decrease, which can be interpreted as the forgetting process of the biological brain [56,57]. To acquire PPF behavior in the ITO/IGZO/TaN device, a twin pulse of 1.5 V, 5 µs was applied with intervals varying from 1 µs to 5 ms.…”

Low power highly flexible BiFeO3-based resistive random access memory (RRAM) with the coexistence of negative differential resistance (NDR)

“…BiFeO 3 is an interesting room temperature multiferroic material, exhibiting both ferroelectric and anti/ferromagnetic ordering simultaneously. 28,29 It also exhibits bipolar RS characteristics, relying on the distribution of intrinsic charge carriers with applied electric field, providing the RRAM behavior in the BFO. The uniform distribution of charge carriers in BFO together with oxide interfaces at electrodes may assist in translating the DS to AS in this system.…”