Defect-Engineered Electroforming-Free Analog HfO_x Memristor and Its Application to the Neural Network

Abstract

The thin-film growth conditions in a plasma-enhanced atomic layer deposition for the (3.0–4.5) nm thick HfO2 film were optimized to use the film as the resistive switching element in a neuromorphic circuit. The film was intended to be used as a feasible synapse with analog-type conductance-tuning capability. The 4.5 nm thick HfO2 films on both conventional TiN and a new RuO2 bottom electrode required the electroforming process for them to operate as a feasible resistive switching memory, which was the primary source of the undesirable characteristics as the synapse. Therefore, electroforming-free performance was necessary, which could be accomplished by thinning the HfO2 film down to 3.0 nm. However, the device with only the RuO2 bottom electrode offered the desired functionality without involving too high leakage or shorting problems, which are due to the recovery of the stoichiometric composition of the HfO2 near the RuO2 layer. In conjunction with the Ta top electrode, which provided the necessary oxygen vacancies to the HfO2 layer, and the high functionality of the RuO2 as the scavenger of excessive incorporated oxygen vacancies, which appeared to be inevitable during the repeated switching operation, the Ta/3.0 nm HfO2/RuO2 provided a highly useful synaptic device component in the neuromorphic hardware system.

Composite Memristors by Nanoscale Modification of Hf/Ta Anodic Oxides

“…Oxides of valve metals have shown remarkable performances as memristive elements. 15 − 18 Studies on Hf- and Ta-based memristors reported excellent electrical and memory properties, such as multilevel switching, high endurance, and data retention. 16 , 17 The deposition of oxide layers is commonly done by atomic layer deposition 19 , 20 or sputtering.…”

Artificial Neural Networks Based on Memristive Devices: From Device to System

“…[ 115 ] Kim et al realized the electroforming‐free device of Pt/Ta/HfO 2 /RuO 2 /Pt by thinning the HfO 2 film down to 3.0 nm, which increased the repeatability and uniformity of the switching performance. [ 116 ] Choi et al demonstrated a single‐crystalline SiGe epitaxial device with minimal cycle‐to‐cycle/device‐to‐device variations. [ 117 ] They utilized defect‐selective etching before electroforming to widen the dislocations providing preferential diffusion paths.…”

Halide perovskite for low‐power consumption neuromorphic devices

“…These training processes keep repeating until the degree of error is scarcely noticed between the input images and the result in the last layer. Once training is completed, the neural network can work on its own 12 …”