Very low resistance Al/Cu joints for use at cryogenic temperatures

Sébastien Triqueneaux (1) , James Butterworth (2) , Johannes Goupy (3) , Clément Ribas (4) , David Schmoranzer (5) , Eddy Collin (4) , Andrew D Fefferman (4)

1 NEEL - Cryo - Cryogénie
2 ALAT - Air Liquide Advanced Technologies [Sassenage]
3 NEEL - HELFA - Hélium : du fondamental aux applications
4 NEEL - UBT - Ultra-basses températures
5 UK - Univerzita Karlova [Praha, Česká republika] = Charles University [Prague, Czech Republic]

We present two different techniques for achieving low resistance ($<$20 n$\rm \Omega$) contacts between copper and aluminium at cryogenic temperatures. The best method is based on gold plating of the surfaces in an e-beam evaporator immediately after Ar plasma etching in the same apparatus, yielding resistances as low as 3 n$\rm \Omega$ that are stable over time. The second approach involves inserting indium in the Al/Cu joint. For both methods, we believe key elements are surface polishing, total removal of the aluminum oxide surface layer, and temporary application of large (typ. 11 kN) compression forces. We believe the values for gold plated contacts are the lowest ever reported for a Cu/Al joint of a few $\rm cm^{2}$. This technology could simplify the construction of thermal links for advanced cryogenics applications, in particular that of extremely low resistance heat switches for nuclear demagnetization refrigerators.

Domaines: Instrumentations et Détecteurs [physics.ins-det]

Sébastien Triqueneaux, James Butterworth, Johannes Goupy, Clément Ribas, David Schmoranzer, et al.. Very low resistance Al/Cu joints for use at cryogenic temperatures. Journal of Low Temperature Physics, 2021, 203 (3-4), pp.345-361. ⟨10.1007/s10909-021-02575-x⟩. ⟨hal-02931574⟩