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In metal-based single-electron devices (SEDs), charge-offset drift has been observed, which is a time-dependent instability caused by charge noise. This instability is an issue in the application of new information processing devices, such as neural network devices, quantum computing devices (charge sensing), and reservoir computing devices. Therefore, the charge-offset drift in metal-based SEDs needs to be suppressed. However, the charge-offset stability of metal-based SEDs has not been investigated in depth, except in the case of Al and Al2O3 SEDs. In this work, Fe-based SEDs formed by single-layer Fe nanodot arrays embedded in MgF2 were studied with regard to their charge-offset stability. Using devices that produce simple current oscillations, the charge-offset drift (ΔQ0) of Fe-based SEDs was evaluated by focusing on peak shifts of the simple current oscillation over time, despite the use of a multi-dot system. This drift (ΔQ0 ≈ 0.3e) was shown to be much lower than in SEDs with Al-dots and Al2O3 tunnel junctions. Notably, the charge-offset drift in the metal-based SEDs was suppressed using the Fe–MgF2 system. The excellent stability of these devices was attributed to the material properties of the Fe–MgF2 system. Finally, as the Fe nanodot array contained numerous dots, the effect of satellite dots acting as traps on the charge-offset instability was discussed. The findings of this study will be important in future applications of metal-based SEDs in new information processing devices.

Multidot single-electron devices (SEDs) can enable new types of computing technologies, such as those that are reconfigurable and reservoir-computing. A self-assembled metal nanodot array film that is attached to multiple gates is a candidate for use in such SEDs for achieving high functionality. However, the single-electron properties of such a film have not yet been investigated in conjunction with optimally controlled multiple gates because of the structural complexity of incorporating many nanodots. In this study, Fe nanodot-array-based double-gate SEDs were fabricated by vacuum deposition, and their single-electron properties (modulated by the top- and bottom-gate voltages; VT and VB, respectively) were investigated. The phase of the Coulomb blockade oscillation systematically shifted with VT, indicating that the charge state of the single dot was controlled by both the gate voltages despite the metallic random multidot structure. This result demonstrates that the Coulomb blockade oscillation (originating from the dot in the multidot array) can be modulated by the two gates. The top and bottom gates affected the electronic state of the dot unevenly owing to the geometrical effect caused by the following: (1) vertically asymmetric dot shape and (2) variation of the dot size (including the surrounding dots). This is a characteristic feature of a nanodot array that uses self-assembled metal dots; for example, prepared by vacuum deposition. Such variations derived from a randomly distributed nanodot array will be useful in enhancing the functionality of multidot devices.

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