HfOx-based resistive random-access memory (RRAM) devices are being widely considered as both non-volatile memories for digital computation and synaptic memory for neuromorphic computing applications. The resistive switching mechanism in these...
Hafnium oxide non-volatile memories have shown promise as an artificial synapse in neuromorphic computing architectures. However, there is still a need to fundamentally understand how to reliably control the analog resistance change induced by oxygen ions that partially rupture or re-form the conductive filament. In this work, the impact of measurement conditions (pulse amplitude and pulse width) and titanium dopants on the analog resistance change of atomic layer deposited hafnium oxide memristor synapses are studied. A lower pulse amplitude improves the linearity of resistance change as a function of the number of pulses but results in a smaller memory window. The addition of titanium dopants does not substantively change the analog resistance modulation of hafnium oxide. Density functional theory calculations show that titanium strongly impacts oxygen ion motion in the Hf xTi yO z matrix but does not impact significantly in the HfTi metallic filament. This study demonstrates that the analog characteristic of Hf xTi yO z artificial synapses is largely independent of the titanium doped bulk oxide since the resistance change is primarily controlled by the HfTi metallic conducting filament.
Understanding the resistance switching behavior of oxide-based
memristive devices is critical for evaluating their usefulness in
nonvolatile memory and/or in artificial neural networks. Oxide memristors
often employ bi- or multilayered metal oxide thin films for improved
performance compared to devices with a single-metal-oxide active layer.
However, a clear understanding of the mechanisms that lead to improved
performance for specific combinations of oxide thin films is still
missing. Herein, we fabricated two types of bilayered heterostructure
devices, with HfO
x
/AlO
y
and AlO
y
/HfO
x
bilayer films sandwiched between Au electrodes. Electrical
responses of these bilayer devices reveal a digital set and an analog
reset transition process. Single-layer HfO
x
and AlO
y
devices are also examined as
control samples to validate the switching mechanism. The role of bilayered
heterostructures is investigated using both the experimental and simulated
results. Our results suggest that synergistic switching performance
can be achieved with a proper combination of these materials, optimized
structures, and proper test conditions. These results open the avenue
for designing more efficient double- or multilayered memristive devices
for an analog response.
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