Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/Al–AlOx/Nb Josephson junctions
Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/Al–AlOx/Nb Josephson junctions
复制标题
高质量 Nb/Al-AlOx/Nb 约瑟夫森结免阳极氧化制造工艺的可靠性和均匀性表征
DOI：
10.1088/0953-2048/26/6/065012
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发表时间：
2013
影响因子：
3.6
通讯作者：
C. Enss
中科院分区：
文献类型：
--
作者：
S. Kempf;A. Ferring;A. Fleischmann;L. Gastaldo;C. Enss
我们开发了一种可靠且可重复的高质量Nb/Al-AlOx/Nb约瑟夫森结制造工艺，该工艺完全避免了阳极氧化技术，该技术通常用于限定结区域，以使基极以及对电极的侧壁电绝缘，并保护隧道势垒。因此，该工艺非常适合于制造基于电浮置结的器件，例如非滞后rf-SQUID。在4.2K下已经制备出各种尺寸的约瑟夫森结并进行了表征。我们发现，我们的结有一个高品质，这是证实了测量的间隙电压Vg和Ic Rn产品高达2.9和1.8 mV和晶圆上的电阻比Rsg/Rn的平均值在大多数情况下超过30。这里，Rsg和Rn表示约瑟夫森结的子带隙和正常状态电阻。虽然整个晶片上约瑟夫森结特性的均匀性很高，但我们观察到整个晶片上的临界电流密度和差距电压的一些系统性变化。这些变化是最有可能归因于在Nb膜以及Nb基电极的表面粗糙度的残余应力。
We have developed a reliable and reproducible fabrication process for high-quality Nb/Al–AlOx/Nb Josephson junctions that completely avoids anodization techniques, that are typically used to define the junction area, to electrically insulate the base electrode as well as the sidewalls of the counter-electrode and to protect the tunnel barrier. Hence, this process is well suited for the fabrication of electrically floating junction-based devices such as non-hysteretic rf-SQUIDs. Josephson junctions of various sizes have been produced and characterized at 4.2 K. We found that our junctions have a high quality, which is confirmed by measured gap voltages Vg and Ic Rn products up to 2.9 and 1.8 mV and on-wafer average values of the resistance ratio Rsg/Rn above 30 in most cases. Here, Rsg and Rn denote the subgap and the normal state resistance of a Josephson junction. Although the uniformity of the properties of the Josephson junctions across a wafer is high, we observe some systematic variations of the critical current density and the gap voltage over an entire wafer. These variations are most likely to be attributed to residual stress in the Nb films as well as the surface roughness of the Nb base electrode.