Fabrication Of Nb/Al-AlO_x/Nb Superconducting Tunnel Junctions

In recent years, for both the national defense and civilian, researches of theory and applications on Terahertz(THz) object imaging, satellite radars, radio astronomy and other fields gradually have become popular. Terahertz detection technology based on superconducting tunnel junctions(STJs) caught much attention because of their relatively simple process and high sensitivity. And research on direct detectors based on Nb/Al-AlOx/Nb superconducting tunnel junctions is one of the hottest subjects. Those STJs based on Nb/Al-AlOx/Nb for direct detectors require high Josephson critical current densities, low leakage currents, strong noise immunities and a certain manufacturing yield. Thus, a mature, stable and repeatable fabrication process is the basis to achieve this objective. We draw attention to the follow parts in the thesis:i. We did research to find a stable and repeatable fabrication method. We had fabricated Nb/Al-AlO_x/Nb superconducting tunnel junctions on high resistance silicon substrate, by using a process including photolithography, DC magnetron sputtering, reactive ion etching (RIE) and plasma enhanced chemical vapor deposition method (PECVD).ii. We measured Nb/Al-AlO_x/Nb STJs’I-V curve at liquid helium environment, and recorded the size of the critical current, leakage current and other performance parameters. At 4.2K, we measured the I-V curve of the junction sample with the diameter of 8μm, shown the Josephson critical current density of 1.6kA/cm2, and the leakage current of 50μA.iii. We tried to fabricate some direct detectors depending on the experience of fabrication of Nb/Al-AlO_x/Nb STJs.