Fabrication of aluminum nitride barrier SIS mixer devices using nitrogen plasma diluted by noble gases

Nb/Al-AlNx/Nb SIS junctions have been fabricated by various RF plasma nitridation techniques. The reproducibility of the RNAproduct from batch to batch was improved by diluting the N2 plasma with He or Ar. For the He+N2 process, a power-law relation between the RNA product and the nitridation time was found to hold along 100-106Ω μm2, which implies that the thickness of the barrier grows logarithmically during the time it is exposed to the plasma. By applying a pulse-time-modulated RF power, we were able to slow down the nitridation significantly. Finally, we present the results of preliminary RF measurements. The Nb/Al-AlNx/Nb SIS mixers were tested at around 150GHz and 350GHz, and showed noise performances comparable to those of Nb/Al-AlOx/Nb SIS mixers