Research On Superconducting NbN, NbTi Films Preparation And Related Devices

Superconducting hot electron mixer (HEB) has a unique advantage in the attractive 0.1～6THz band because of its low local power requirements and unlimited operating frequency to superconducting energy gap. Therefore, it has a wide range of applications in astronomy, atmospheric ozone detection, and detection of THz imaging. The main work in this thesis is to study the fabrication of superconducting NbN, NbTi thin film, and the design and preparation of the phonon cooled HEB mixers based on the superconducting thin films.The fabrication and Properties of NbN, NbTi Thin FilmsUsing Magnetron sputtering technology, we fabricated 4-8nm ultra-thin superconducting NbN films on single crystal Si substrates with different sputtering pressure and different mixing ratio of gases. For the 4nm thick NbN films, the superconducting transition temperature(Tc0) was 7.1K, superconducting critical current density reached the order of 106 A/cm2.In addition to Sputtering of the NbN films, we also fabricated the superconducting NbTi thin films of different thickness using a target ratio is 53:47(purity of 99.9%). Through continuous improvement, we prepared 6.5nm thick NbTi thin films, and its Tc0 reached 6.8K. Jc reached 106 A/cm2.We found that NbTi superconducting films will decline rapidly because of the oxygen affinity. To solve this problem, a layer of AlN insulating film was prepared on the surface of NbTi films to cut off contact with the air. Then the NbTi superconducting properties of thin films did not change over time, but also the Tc0 of the thin film of 6.5nm thick, covered with 1nm AlN of NbTi films,reached 7.1K.HEB device performance testAccording to the superconducting properties of NbN thin films, we designed NbN HEB device, and by electron beam lithography, reactive ion etching (RIE), lithography and other processes, we prepared NbN HEB devices. In the key process-the preparation of micro-bridge, before the electrode preparation, we improved the quality of NbN by adding the ionic cleaning process and got a micro-bridge with a clear edged 0.4×4μm2 micro-bridge structure. This ensured the performance of NbN HEB device.After successfully prepared NbN HEB devices, we measured the IV curves under DC voltage source. Using the noise-temperature measurement system in the lab, we measured noise temperature of NbN HEB devices. NbN HEB is highly sensitive to external high-frequency signals. At 1.6THz, noise temperature can reach 1668K.