Title :
Low-loss epitaxial NbN/MgO/NbN trilayers for THz applications
Author :
Kawakami, Akira ; Wang, Zhen ; Miki, Shigehito
Author_Institution :
Commun. Res. Lab., Kansai Adv. Res. Center, Kobe, Japan
fDate :
3/1/2001 12:00:00 AM
Abstract :
To improve the performance of Josephson oscillators and SIS mixers over 700 GHz, we have developed a fabrication process to grow epitaxial NbN/MgO/NbN trilayers by reactive dc-sputtering. Trilayers were fabricated on a single-crystal MgO substrate at ambient temperature. NbN and MgO films were deposited by reactive dc-sputtering with an Nb and Mg target, respectively. The MgO inter-layer thickness was changed up to 480 nm, but, TC and 20-K resistivity of the NbN upper-layer showed no remarkable dependency and they were 15.7 K and about 60 μΩcm, respectively. To evaluate the RF performance of the epitaxial NbN films, we fabricated Josephson junctions with a microstrip resonator constructed from an epitaxial NbN/MgO/NbN trilayer. The I-V characteristics of the junction exhibited resonance steps up to 2.5 mV, which suggests that the epitaxial NbN films have low loss up to 1.2 THz
Keywords :
Josephson effect; electrical resistivity; magnesium compounds; microstrip resonators; niobium compounds; sputter deposition; submillimetre wave mixers; submillimetre wave oscillators; superconducting epitaxial layers; superconducting resonators; superconducting transition temperature; superconductor-insulator-superconductor mixers; type II superconductors; vapour phase epitaxial growth; 15.7 K; 2.5 mV; 20 K; 480 nm; 60 muohmcm; 700 GHz to 1.2 THz; I-V characteristics; Josephson oscillators; MgO inter-layer thickness; NbN-MgO-NbN; SIS mixers; TC; THz applications; ambient temperature; epitaxial NbN films; epitaxial NbN/MgO/NbN trilayers; fabrication process; low-loss epitaxial NbN/MgO/NbN trilayers; microstrip resonator; reactive dc-sputtering; resistivity; resonance steps; single-crystal MgO substrate; Conductivity; Fabrication; Josephson junctions; Microstrip resonators; Niobium; Oscillators; Radio frequency; Resonance; Substrates; Temperature;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
