How fast can vanadium dioxide neuron-mimicking devices oscillate? Physical mechanisms limiting the frequency of vanadium dioxide oscillators

Stefania Carapezzi (Corresponding author), Andrew Plews, Gabriele Boschetto, Ahmed Nejim, Siegfried F. Karg, Aida Todri-Sanial (Corresponding author)

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The frequency of vanadium dioxide (VO2) oscillators is a fundamental figure of merit for the realization of neuromorphic circuits called oscillatory neural networks (ONNs) since the high frequency of oscillators ensures low-power consuming, real-time computing ONNs. In this study, we perform electrothermal 3D technology computer-aided design (TCAD) simulations of a VO2 relaxation oscillator. We find that there exists an upper limit to its operating frequency, where such a limit is not predicted from a purely circuital model of the VO2 oscillator. We investigate the intrinsic physical mechanisms that give rise to this upper limit. Our TCAD simulations show that it arises a dependence on the frequency of the points of the curve current versus voltage across the VO2 device corresponding to the insulator-to-metal transition (IMT) and metal-to-insulator transition (MIT) during oscillation, below some threshold values of $C_{\mathrm{ext}}$. This implies that the condition for the self-oscillatory regime may be satisfied by a given load-line in the low-frequency range but no longer at higher frequencies, with consequent suppression of oscillations. We note that this variation of the IMT/MIT points below some threshold values of $C_{\mathrm{ext}}$ is due to a combination of different factors: intermediate resistive states achievable by VO2 channel and the interplay between frequency and heat transfer rate. Although the upper limit on the frequency that we extract is linked to the specific VO2 device we simulate, our findings apply qualitatively to any VO2 oscillator. Overall, our study elucidates the link between electrical and thermal behavior in VO2 devices that sets a constraint on the upper values of the operating frequency of any VO2 oscillator.
Original languageEnglish
Article number34010
Number of pages17
JournalNeuromorphic Computing and Engineering
Issue number3
Publication statusPublished - Sept 2023

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S C and A T S conceived the idea. S C designed and performed the TCAD simulations. S C analyzed and validated the simulated data. S C, G B and A T S critically interpreted the data. A P and A N implemented the customized version of the PCM model used to simulate the VO material, and gave useful suggestions to implement TCAD simulations. S K supplied the experimental data used for the calibration of the TCAD model, and provided useful discussions to interpret them. All the authors discussed the results. S C drafted the manuscript and A T S critically revised it. The manuscript has been read and approved by all authors. A T S had the management, coordination responsibility and supervision for the planning and execution of the research activity leading to this publication. A T S acquired the financial support for the project leading to this publication. 2

FundersFunder number
European Union's Horizon 2020 - Research and Innovation Framework Programme871501


    • device simulation
    • frequency
    • neuromorphic circuits
    • oscillatory neural network
    • relaxation oscillator
    • vanadium dioxide


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