Ramp-edge junctions with interface-modified barriers fabricated on YBCO thick films

Abstract

We fabricated ramp-edge junctions with an interface-modified barrier on YBa 2 Cu 3 O (YBCO) liquid phase epitaxy (LPE) thick films. The LPE thick films were used as ground-planes. For the insulating layer between the ground plane and base electrode, a SrTiO 3 (STO)/(LaAlO 3 ) 0 3 -(SrAl 0 5 Ta 0 5 O 3 ) 0 7 (LSAT)/STO multilayer with the dielectric constant of approximately 32 was employed. We fabricated ramp-edge junctions with La-doped YBa 2 Cu 3 O (La-YBCO) and La-doped YbBa 2 Cu 3 O (La-YbBCO) as base and counter electrodes, respectively. The fabricated junctions exhibited resistively and capacitively shunted junction (RCSJ)-like characteristics and typical c n products of 2.6 and 1.1 mV at 4.2 and 40 K, respectively. The 1 -spread in c as small as 8.1% was obtained for 100-junction series-arrays. The use of ground plane reduced the sheet inductance of electrodes to a value of 0.76-0.94 pH/square at 4.2 K.

Fabrication and Logic Operation of Oxide SFQ-Circuit-Components

“…The sheet inductance of the base electrode was 1.5 pH, and that of the counter electrode was 0.8-1.2 pH. The circuit fabrication procedures have been described in detail elsewhere [7]- [10].…”

Improvement in Reproducibility of Multilayer and Junction Process for HTS SFQ Circuits

“…To effectively oxygenate the La-YBCO ground plane, holes for oxygen supply were formed in the insulating layer at intervals of 200 distance. The fabricated samples were post-annealed in 1-atm oxygen atmosphere at 550 for 8 h, and cooled from 550 to 250 at a cooling rate of 10 [9].…”

“…There have been several reports on the fabrication of interface-modified ramp-edge junctions on thin film ground planes [7], [8]. We previously fabricated ramp-edge junctions on ground planes made of (YBCO) liquid phase epitaxy (LPE) films with high crystallinity comparable to single crystals and atomically flat surfaces [9]. Although the junctions exhibited a high product of 1.1 mV at 40 K and a small spread of 8.1% for a 100-junction array, it is difficult to partially remove the ground plane for high-speed input or output lines because the LPE films are very thick (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) ).…”

Fabrication of 123‐type high‐ T c superconducting thin films on BaZrO 3 ‐buffered MgO substrates

“…They have the advantages of low power consumption and high-speed operation at around 40 K, being much higher than the operation temperature of Nb circuits, that is 4.2 K. To realize HTS-SFQ devices, fabrication process of JJs integrated on a superconducting ground plane must be established. A few groups reported successful fabrication of JJs on the ground plane [2][3][4]. Excellent flatness and pure orientation are required for the lowest layer as a foundation of multilayer structures.…”

“…Katsuno et al [3] used a NdBa 2 Cu 3 O y thin film which usually has a flat surface because of the existence of a solid-solution of Nd 1+x Ba 2-x Cu 3 O y [5]. A polished LPE (liquid-phase-epitaxy)-YBa 2 Cu 3 O y thick film was also used as the ground plane [4]. However, it was difficult to fully load oxygen to the film located at the lowest of multilayer structures by relatively short-time annealing, being different from the case of YBa 2 Cu 3 O y thin films.…”