Double oxidation scheme for tunnel junction fabrication

Abstract

The authors report a method to achieve Al–AlOx–Al tunnel junctions with high specific resistance in a controlled manner using a double oxidation technique. The technique is based on the standard method for oxidation repeated on an additional Al layer. The tunnel junctions were characterized with standard methods, such as comparison of room temperature resistance with liquid helium resistance and the authors found them to be of comparable quality to junctions fabricated with standard single oxidation. Fitting with the Simmons model suggests that both the barrier width and barrier height are consistent with those obtained in a single oxidation step. The junction specific capacitance was determined at low temperature to be 68fF∕μm2. These junctions, employed in low temperature measurements and applications, demonstrate expected and stable conductance characteristics. The double oxidation method is straightforward to implement in a basic setup for tunnel junction fabrication.

Reduced resistance drift in tunnel junctions using confined tunnel barriers

“…11 Typically, during the initial fabrication of AlO x , the aluminum closest to the surface is oxygen-rich compared to deeper in the aluminum. 8,35 Once the oxidation is complete, the oxygen concentration profile relaxes with time and temperature from this asymmetric AlO x towards a more uniform Al 2 O 3 -like stoichiometry throughout the barrier. 35 Annealing the barriers accelerates this relaxation process, helping the material to reach a lower energy configuration.…”

“…8,35 Once the oxidation is complete, the oxygen concentration profile relaxes with time and temperature from this asymmetric AlO x towards a more uniform Al 2 O 3 -like stoichiometry throughout the barrier. 35 Annealing the barriers accelerates this relaxation process, helping the material to reach a lower energy configuration. 10 Alternatively, improving the oxygen concentration profile created during the initial oxidation can also reduce the resistance drift, since the system is initially closer to a relaxed state.…”

“…As another approach, some groups have formed the barrier by sequential partial depositions and oxidations to improve the uniformity of the tunnel barriers and reduce the resistance drift. 35 …”

Character and fabrication of Al/Al2O3/Al tunnel junctions for qubit application

“…To discover the best conditions for junction barrier formation, we have adjusted the exposure conditions by changing either the oxygen pressure or the oxidizing time to obtain different barrier thicknesses. Since the tunnel junction resistance R J is inversely proportional to the area of the junction, then the junction specific resistance R c (the product of the tunnel junction resistance R N and the junction area) is used as a characteristic figure [24].…”

Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions

“…2,6 Just like for any other electronic components, it is desirable to fabricate tunnel junction devices whose characteristics are reproducible, stable and exhibit minimal aging effects. Unfortunately, many fabrication protocols do not automatically guarantee this, but special measures such as vacuum annealing, 7 agressive cleaning 8 and multistep oxidation 9 have been shown to improve the stability of Al-AlO x -Al tunnel junctions.…”