Fabrication of Ramp-Edge Junctions With High I_CR_N Products by Using Cu-Poor Precursor

Abstract

We have fabricated ramp-edge Josephson junctions using a Cu-poor oxide layer as a precursor of the barrier. La 0 2 Y 0 9 Ba 1 9 Cu 3 O (La-YBCO) and La 0 2 Yb 0 9 Ba 1 9 Cu 3 O (La-YbBCO) were used for the base-electrode and the counter-electrode, respectively. A Cu-poor precursor was deposited on a pattered base-electrode at a substrate temperature ( s ) of approximately 660 C by a pulsed laser deposition (PLD) method employing deposition conditions different from those for the counter-electrode layer. The fabricated junctions on a La-YBCO ground plane showed resistively and capacitively shunted junction-type current-voltage characteristics. They exhibited the products of the critical current ( c ) and the junction resistance ( n ) higher than 3 mV and excess current ratio less than 30% at 4.2 K. The c n products were nearly 1.5 times larger than those for junctions with an interface-modified barrier in a temperature range of 4-50 K. The junctions had a barrier region with the thickness of approximately 1 nm and a Cu-poor transition region narrower than that for the latter type of junctions.

Recent Developments of High-Tc Electronic Devices with Multilayer Structures and Ramp-Edge Josephson Junctions

“…Formation of a clear barrier having sharp interfaces between electrodes was also expected. Enhancement in I c R n values was actually observed for JJs prepared in this method [33].…”

“…4 fortunately. To reduce such possibility, we have developed a new method for JJ preparation [33], namely Cupoor precursory method, as illustrated in Fig. 5.…”

Preparation of multilayer films for integrated high-Tc SQUIDs with ramp-edge Josephson junctions

“…L1ErBCO counter-electrode was prepared by pulsed laser deposition. To form an adequate barrier, the ''Cu-poor precursor method" which was recently developed by us [30] was applied. Gradiometer arrays having multilayered feedback coils and pickup loops were successfully fabricated in a chip and their proper operation at 77 K was confirmed.…”

“…The laser energy density on the target was 1.5 J/cm 2 for each beam. The Cu content of the layers was controlled by changing the deposition parameters [30]. The precursory layer was deposited at a target-substrate distance H t-s = 80 mm, an oxygen pressure P = 6 Pa, a laser frequency f = 5 Hz.…”

Improved reproducible fabrication process of HTS-SQUIDs with ramp-edge Josephson junctions and multilayer structures

“…L1ErBCO counter-electrode was prepared by pulsed laser deposition. To form a junction barrier, the ''Cu-poor precursor method" developed in our group [15] was applied.…”