Abstract
A thickness variation of only one Ångström makes a significant difference in the current through a tunnel junction due to the exponential thickness dependence of the current. It is thus important to achieve a uniform thickness along the barrier to enhance, for example, the sensitivity and speed of single electron transistors based on the tunnel junctions. Here, we have observed that grooves at Al grain boundaries are associated with a local increase of tunnel barrier thickness. The uniformity of the barrier thickness along the tunnel junction thus increases with increasing Al grain size. We have studied the effect of oxidation time, partial oxygen pressure and also temperature during film growth on the grain size. The implications are that the uniformity improves with higher temperature during film growth.
Highlights
The rapid advances of quantum electronics has resulted in an increased need for improved circuit elements (Nakamura et al 1999; Oh et al 2006; Vion et al 2002; Mooij et al 1999; Kline et al 2009)
More attention has been paid to the undeniable influence of materials and fabrication techniques on the performance of devices, such as superconducting- and normal tunnel junctions (Lang et al 2004; Tan et al 2005; Martinis 2009; Roddatis et al 2011), which are used in a wide variety of devices such as superconducting quantum bits (Clarke and Wilhelm 2008), radiation detectors (Zmuidzinas and Richards 2004), SQUID magnetometers (Clarke 2011), electron pumps (Pothier et al 1992), and single-electron transistors (Averin and Likharev 1986)
The composition and structure of the thin aluminum oxide layer formed by thermal oxidation are found to be sensitive to the oxidation parameters such as oxygen pressure, oxidation time and substrate temperature (Snijders et al 2002; Cai et al 2011; Flodström et al 1976; El-mashri et al 2006)
Summary
The rapid advances of quantum electronics has resulted in an increased need for improved circuit elements (Nakamura et al 1999; Oh et al 2006; Vion et al 2002; Mooij et al 1999; Kline et al 2009). The possible effects of different parameters such as oxidation parameters, substrate material and temperature on the grain size of Al and tunnel barrier thickness have been studied.
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