The intrinsic stochasticity of the memristor can be used to generate true random numbers, essential for non-decryptable hardware-based security devices. Here, we propose a novel and advanced method to generate true random numbers utilizing the stochastic oscillation behavior of a NbOx mott memristor, exhibiting self-clocking, fast and variation tolerant characteristics. The random number generation rate of the device can be at least 40 kb s−1, which is the fastest record compared with previous volatile memristor-based TRNG devices. Also, its dimensionless operating principle provides high tolerance against both ambient temperature variation and device-to-device variation, enabling robust security hardware applicable in harsh environments.
Valence change-type resistance switching behaviors in
oxides can
be understood by well-established physical models describing the field-driven
oxygen vacancy distribution change. In those models, electroformed
residual oxygen vacancy filaments are crucial as they work as an electric
field concentrator and limit the oxygen vacancy movement along the
vertical direction. Therefore, their movement outward by diffusion
is negligible. However, this situation may not be applicable in the
electroforming-free system, where the field-driven movement is less
prominent, and the isotropic oxygen vacancy diffusion by concentration
gradient is more significant, which has not been given much consideration
in the conventional model. Here, we propose a modified physical model
that considers the change in the oxygen vacancies’ charged
state depending on their concentrations and the resulting change in
diffusivity during switching to interpret the electroforming-free
device behaviors. The model suggests formation of an hourglass-shaped
filament constituting a lower concentration of oxygen vacancies due
to the fluid oxygen diffusion in the thin oxide. Consequently, the
proposed model can explain the electroforming-free device behaviors,
including the retention failure mechanism, and suggest an optimized
filament configuration for improved retention characteristics. The
proposed model can plausibly explain both the electroformed and the
electroforming-free devices. Therefore, it can be a standard model
for valence change memristors.
A memristive stateful neural network allowing complete Boolean in-memory computing attracts high interest in future electronics. Various Boolean logic gates and functions demonstrated so far confirm their practical potential as an emerging computing device. However, spatio-temporal efficiency of the stateful logic is still too limited to replace conventional computing technologies. This study proposes a ternary-state memristor device (simply a ternary memristor) for application to ternary stateful logic. The ternary-state implementable memristor device is developed with bilayered tantalum oxide by precisely controlling the oxygen content in each oxide layer. The device can operate 157 ternary logic gates in one operational clock, which allows an experimental demonstration of a functionally complete three-valued Łukasiewicz logic system. An optimized logic cascading strategy with possible ternary gates is ≈20% more efficient than conventional binary stateful logic, suggesting it can be beneficial for higher performance in-memory computing.
NbO
x
-based Mott memristors exhibit
fast threshold switching behaviors, making them suitable for spike
generators in neuromorphic computing and stochastic clock generators
in security devices. In these applications, a high output spike amplitude
is necessary for threshold level control and accurate signal detection.
Here, we propose a materialwise solution to obtain the high amplitude
spikes by inserting Au nanodots into the NbO
x
device. The Au nanodots enable increasing the threshold voltage
by modulating the oxygen contents at the electrode-oxide interface,
providing a higher ON current compared to nanodot-free NbO
x
devices. Also, the reduction of the local switching
region volume decreases the thermal capacitance of the system, allowing
the maximum spike amplitude generation. Consequently, the Au nanodot
incorporation increases the spike amplitude of the NbO
x
device by 6 times, without any additional external
circuit elements. The results are systematically supported by both
a numerical model and a finite-element-method-based multiphysics model.
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