An array of 100 Al–Al₂O₃–Cu SIN tunnel junctions in direct-write trilayer technology

Abstract

We present superconductor-insulator-normal metal (SIN) tunnel junction thermometers made of arrays of 4-100 Al-Al 2 O 3-Cu SIN tunnel junctions fabricated in direct-write technology. The technology is based on in situ evaporation of the superconductive electrode followed by the oxidation and the normal counter-electrode as a first step and deposition of normal metal absorber as a second one. This approach allows one to realize any geometry of the tunnel junctions and of the absorber with no limitation related to the size of the junctions or the absorber, which is not possible using the shadow evaporation technique. Measurements performed at 300 mK showed the high quality of the fabricated tunnel junctions, low leakage currents, and that an R d /R n ratio of 500 has been achieved at that temperature. The junctions were characterized as temperature sensors, and voltage versus temperature dependence measurements showed a dV /dT of 0.5 mV K −1 for each single junction, which is typical for this kind of tunnel junction. A temperature resolution of ±5 µK has been achieved which is much better than the previously reported value of ±30 µK for this type of thermometer.

Ti–TiO2–Al normal metal–insulator–superconductor tunnel junctions fabricated in direct-write technology

“…Therefore, by increasing the number of junctions in the array, one can increase the temperature sensitivity of the whole array and compensate for the poor quality of some single junctions in the array, if the number of relatively poor junctions is negligible in comparison with the total number of junctions in the array. This is fully confirmed for an array of 100 Al-based tunnel junctions [11], where the dV /dI of 52 mV K −1 has been achieved for 100 junctions in series, which corresponds to 0.52 mV K −1 for each single junction, very close to the value of 0.5 mV K −1 for a standalone junction.…”

Finline-integrated cold electron bolometer

“…In this paper we present DC measurements and preliminary optical measurements of two cold electron bolometers with SIN tunnel junctions and normal metal absorbers, one fabricated using e-beam direct-write patterning of trilayer SIN junctions and the absorber, 3,4 and the other using an advanced shadow mask evaporation technique. 5 The CEBs are designed for operation at 70 − 110 GHz, and are deposited across unilateral finlines on a silicon substrate.…”