Random telegraph signals in silicon single-electron devices for quantum technologies

Abstract

As a result of aggressive scaling in the size of silicon (Si) metal-oxide-semiconductor (MOS) field-effect-transistors (FETs), random telegraph signals (RTSs) has recently emerged as one of the reliability issues in Complementary-MOS (CMOS) technology. An RTS has been traditionally considered to be caused by a trapping and de-trapping of an electron at the Si-SiO₂ interface or a trap in the gate dielectric, which degrades the reliability of CMOS circuit. On the other hand, the presence of an RTS indicates an existence of a single isolated energy level originated from atomic-scale features in a Si device, which could be used for spin-qubit devices for quantum information processing and single-electron-pump (SEP) devices for quantum metrology. However, as far as traps in the oxide or at the interface are concerned, the variability (presence and absence) and characteristics (amplitudes and average lifetime of current states) of RTSs cannot be controlled, which hindered the possibility of exploiting the discrete energy level exhibiting itself as an RTS.
In this PhD project, I discovered that characteristics of RTSs originated from electrically defined quantum dot and a solitary dopant in the substrate at low temperature can be controlled. Firstly, Si nanowire FETs with a triple-gate structure were fabricated, which consistently exhibited RTSs at room temperature when two of the three gates electrically formed a QD in the channel. The amplitude of the RTS, translated into the shift in threshold voltage, matched with the value expected from the size of the QD. This result means that the variability and amplitude of RTSs were well controlled in these devices. Also, a p-type MOSFET fabricated using standard 65nm technology was characterised at 3.8K, and an RTS was observed only when reverse bias was applied to phosphorous implanted n-well region. Based on this observation, a solitary phosphorous dopant was considered to be responsible for the observed RTS. Furthermore, a transition in trapping and de-trapping mechanism from quantum mechanical to thermal activation was also observed, where the lifetime of RTSs increased as temperature increased. This suggests that the lifetime of RTSs in this system was also tunable. This work presents the diversity of physical mechanisms behind RTSs in single-electron devices, which could be further exploited for applications envisaging SEP or even spin-qubit devices.

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Identifiers

ORCID for Kouta Ibukuro: orcid.org/0000-0002-6546-8873

ORCID for Shinichi Saito: orcid.org/0000-0003-1539-1182

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