Oxygen Vacancy Transition in HfO_x‐Based Flexible, Robust, and Synaptic Bi‐Layer Memristor for Neuromorphic and Wearable Applications

Abstract

In this work, a reliable bilayer flexible memristor is demonstrated using TaOx/HfOx Bi‐layer (BL) to mimic synaptic characteristics by using oxygen concentration engineering in the oxide layers. Due to low Gibbs free energy of TaOx layer and stable properties of the single layer memristor, TaOx is inserted in the HfOx‐based memristor for making the BL flexible device. Such device exhibits stable gradual switching behavior with low set/reset voltages (1 V/−1 V) and multilevel cell characteristic making it favorable for synaptic application. The presence of oxide layers and change in oxygen vacancy concentration in two layers are examined by transmission electron microscopy and X‐ray photoelectron spectroscopy, respectively. Further, the device shows potentiation and depression epochs for more than 10 000 pulses and switching up to bending radius of 4 mm for 1000 bending cycles. The device mimics biological synaptic time‐dependent plasticity (STDP) operation when presynaptic and postsynaptic pulses are applied on top and bottom electrodes, respectively. The relationship between nonlinearity coefficient and control parameters in STDP is derived and established. It achieves more that 96% accuracy only after 20 iterations for neuromorphic application when a system of 2500 synapses incorporating 50 × 50 pixel image for recognition is deployed.

An Opto-Electronic HfO x -Based Transparent Memristive Synapse for Neuromorphic Computing System

“…These holes would dominate the migration rate of holes along the mentioned bending band depending upon the illumination intensity. Those photo-generated holes would cause the transformation of oxygen ions back to O 2 and desorb from the ITO surface [46], [47]. The detrapped and photoexcited electrons could move to the conduction band.…”

Progress of Materials and Devices for Neuromorphic Vision Sensors

“…Therefore, it is expected that ECM and VC ESs will provide advantages such as high pixel density, low power consumption, and a wide sensing dynamic range in OSCs for neuromorphic image processing. However, in the future, the serious problems arising from CF-based operating mechanisms must be addressed, including device-to-device non-uniformity, nonlinear and asymmetric conductance update characteristics, and performance differences during repeated cycle operations [ 47 ].…”

Flexible ZnO Nanosheet‐Based Artificial Synapses Prepared by Low‐Temperature Process for High Recognition Accuracy Neuromorphic Computing

“…The realization of memristive properties in ZnO hinges on the distribution of intrinsic defects or ions, mainly oxygen vacancies. [ 24 ] However, The uniform distribution of oxygen vacancies in ZnO thin films usually results in unstable synaptic plasticity, such as poor memory effect small variation in conductance and nonlinear and asymmetric weight change. [ 25–27 ] In contrast, oxygen vacancies are usually distributed on the surface of ZnO nanosheets (ZnO NS), which provide conducting pathways and assisting carrier transport.…”