Journal of Physics and Chemistry of Solids 69 (2008) 702–707 Silicon single-charge transfer devices Yukinori Ono a,Ã , Akira Fujiwara a , Katsuhiko Nishiguchi a , Yasuo Takahashi b , Hiroshi Inokawa a a NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan b Graduate School of Information Science and Technology, Hokkaido University, Sapporo, Hokkaido 060-0814, Japan Abstract The single-electron device (SED) enables the control of electron motion on the level of an elementary charge. Single-charge transfer devices are special SEDs that enable single-electron transfer synchronized with the gate clock. They have the potential for extremely low transfer error rates and are expected to be building blocks for future information processing and electrical metrology. We have been pursuing the fabrication of Si-based SEDs using CMOS technology with the help of electron-beam lithography and have recently demonstrated the single-charge transfer devices. The devices are composed of one Si quantum dot sandwitched between two tiny MOS gates and can operate at much higher temperatures than those of former metal-based and compound-semiconductor-based devices. This opens up the possibility of the practical use of clocked single-charge transfer. r 2007 Elsevier Ltd. All rights reserved. Keywords: A.Semiconductors; A. Nanostructures; D. Transport properties 1. Introduction—development of single-charge transfer devices In this article, we discuss single-charge transfer with a gate clock, which means the transfer of just a single charge during one cycle of an ac gate voltage. The single-electron transistor (SET) [1–3], the most fundamental single- electron device (SED), unfortunately does not have this ability. This is because the time interval of each transfer in the SET is uncontrollable due to the stochastic nature of the electron tunneling. In order to transfer single electrons synchronized with the gate clock, we need more sophisti- cated devices. Sometimes called single-charge transfer devices, they include single-electron pumps and single- electron turnstiles. In these devices, an electron is conveyed from the source to drain in one cycle of the gate clock. Thus, the generated current is equal to ef, where e is the elementary charge and f the clock frequency. Owing to the clocked transfer, single-charge transfer devices are expected to be key components for future information processing and electrical metrology based on fundamental physical constants. The research on the single-charge transfer device started with Al–AlO x multiple junctions and then expanded to semiconductors of GaAs and Si. The first single-charge transfer device was reported in 1990 by Geerligs et al. and is now known as the single-electron turnstile. The turnstile has three sequentially connected dots and the central dot has a gate. Its operation has been demonstrated using Al–AlO x junctions at temperatures below 50 mK [4]. The current characteristics exhibit a step-like structure as a function of the drain voltage, and the level of each plateau is equal to multiples of ef. Although this turnstile achieved a fairly good transfer accuracy of the order of 10 3 , few experimental studies followed. This is because another charge transfer device, the single-electron pump, which provides a higher transfer accuracy, was invented soon after. The single-electron pump, which was first demonstrated by Pothier et al.[5] in 1991, has so far been the most intensively studied single-charge transfer device. As the name indicates, this device can convey single electrons from the source to drain even when the drain is grounded or negatively biased. The pump is composed of (at least) two ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.07.102 Ã Corresponding author. Tel.: +81 46 240 2641; fax: +81 46 240 4317. E-mail address: ono@aecl.ntt.co.jp (Y. Ono).