• Progress in Superconductivity
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• v.2 no.2
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• pp.81-85
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• 2001

Uniformity of critical currents of YBa$_2$Cu$_3$O$_{7}$ step-edge Josephson junctions on SrTiO$_3$(100) substrates have been studied at various step-line angles. 15 identical junctions were made in series on each substrate that has a long straight step-edge line. Step-line angles studied were 0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$, and 45$^{\circ}$with respect to the crystal major axes of the substrate. Scattering of junction critical currents among the junctions on the same substrate increased with the step-line angle. Current-voltage curves showed standard resistively-shunted-junction (RSJ) characteristics in most of the 0$^{\circ}$junctions. However, the number of junctions showing RSJ behavior decreased with increasing step-line angle. Variations of detailed microstructure of the step-edge among junctions, which are coupled with the d-wave symmetry of YBa$_2$Cu$_3$O$_{7}$, are believed to be the main cause for the nonuniformity in the critical current.ent.

• Progress in Superconductivity
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• v.1 no.2
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• pp.146-150
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• 2000

Step edge Josephson junctions in c-axis oriented $YBa_2Cu_3O_7$ films were fabricated on $CeO_2$ buffered sapphire substrates. The step angle was controlled in the wide range of $20^{\circ}\sim75^{\circ}$ by the Ar ion milling technique. I-V curves of junction fabricated on the thickness ratio of $\sim$0.8 and the step angle of $35^{\circ}$ were exhibited RSJ-like behavior with $I_CR_N$ product of $\sim250{\mu}A$ and critical current density of $\sim2\times10^4A/cm^2$ at 77 K. Critical current of step edge junction was increased linearly with decreasing temperature but the normal resistance was almost constant. Total samples of step edge Josephson junction was satisfied a scaling behavior of $I_CR_N{\propto}(J_C)^{0.5}$.

• Progress in Superconductivity
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• v.2 no.2
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• pp.71-75
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• 2001

The effect of annealing step-edges of LaAlO$_3$ and MgO single crystal substrates on YBa$_2$Cu$_3$O$_{7}$ junction has been studied. The step-edge was fabricated by argon ion milling and was annealed at 105$0^{\circ}C$ in 1 attn oxygen pressure. We compared AFM image near step-edge of the substrates between before and after annealing process. And YBa$_2$Cu$_3$O$_{7}$ thin film was deposited on the step-edge by a standard pulsed laser deposition. The step-edge junctions were characterized by current-voltage curves at 77 K. The annealing of step-edges of MgO substrate improved the current-voltage characteristic of Josephson junction: double steps in the current-voltage characteristic disappeared. However the annealing for LaAlO$_3$ did not improve the junction property.rty.

• Progress in Superconductivity
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• v.1 no.1
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• pp.31-35
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• 1999

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-$T_c$ superconducting (HTS) $YBa_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed on the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height, t/h. The spread of step-edge junction parameters was measured from each 13 junctions with t/h=1/3, 1/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.99-102
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• 2000

We have studied the effects of d-wave symmetry on the critical current of YBa$_2$Cu$_3$O$_7$ step-edge Josephson junctions. The critical current along various misorientation angle was measured and analyzed with the concept of grain-boundary junctions with d-wave symmetry. Experimental results of c-oriented YBCO step-edge junctions with various in-plane misorientation angles were qualitatively in good agreement with the theory. The out-of-plane misorientation angle is usually formed between two grains with the c axes perpendicular to each other and is normally not controllable.

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.45-45
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• 2001

• Progress in Superconductivity
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• v.1 no.2
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• pp.95-98
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• 2000

We have studied critical currents of $YBa_2Cu_3O_7$ step-edge junctions with different step orientations with respect to the major axes of $SrTiO_3$ (100) substrates. The junctions were prepared by pulsed laser deposition and argon ion milling with photoresist mask. We investigated current-voltage characteristics and critical current of the junctions as a function of the angle. The junction critical current showed an angle dependent modulation with maxima near 0 or 90 degree and minima near 45 and 135 degrees. The experimental results were analyzed based on the microstructure of the junction along the step and the d-wave symmetry of $YBa_2Cu_3O_7$ superconductor.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.146-150
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• 2000

Two methods have been investigated to fabricate good quality step-edge Josephson junctions on STO, MgO, and LAO single crystal substrates. One is the annealing of substrates at 1050$^{\circ}$C in 1 atmospheric oxygen after Ar-ion milling. The other is the cleaning of step-edge by using Ar ion milling. The step-edge is characterized with atomic force microscope (AFM) images. And YBCO thin films are deposited by using pulsed laser. The I-V properties of step-edge junctions are characterized. The yield rate of step-edge junction is increased by new fabrication methods.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.147-151
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• 1999

YBCO step-edge Josephson junction were fabricated on sapphire substrates. The steps were formed on R-plane sapphire substrates by using Ar ion milling with PR masks. The step angle was controlled in the wide range from 25$^{\circ}$ to 50$^{\circ}$ by adjusting both the Ar ion incident angle and the photoresist mask rotation angle relative to the incident Ar ion beam. CeO$_2$ buffer layer and in-situ YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) thin films was deposited on the stepped R-plane sapphire substrates by pulsed laser deposition method. The YBCO film thickness was varied to obtain the ratio of film thickness to step height in the range from 0.5 to 1. The step edge junction exhibited RSJ-like behaviors with I$_cR_n$ product of 100 ${\sim}$ 300 ${\mu}$V, critical current density of 10$^3$ ${\sim}$ 10$^5$ A/ cm$^2$ at 77 K.

• Progress in Superconductivity
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• v.5 no.2
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• pp.94-97
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• 2004

Step-edge Josephson junctions (SEJ) have been fabricated on sapphire substrates with in situ deposited films of CeO$_2$ buffer layer and YBa$_2$Cu$_3$O$_{7}$ films on the low angle steps. Direct coupled SQUID magnetometers with the SEJ were formed on 1 cm X 1 cm R-plane sapphire substrates. Typical 5-${\mu}{\textrm}{m}$-wide Josephson junctions have R$_{N}$ of 3 Ω and I$_{c}$ of 50 $mutextrm{A}$ at 77 K. The direct coupled SQUID magnetometers were designed to have pickup coils of 50-${\mu}{\textrm}{m}$-wide 16 parallel loops on the 1 cm X 1 cm substrates with outer dimension of 8.8 mm X 8.8 mm. The SEJ SQUID magnetometers exhibit relatively low 1/f noise even with dc bias control, and could be stably controlled by flux-locked loops in the magnetically disturbed environment. Field noise of the do SQUID was measured to be 200∼300 fT/Hz$^{1}$2/in the white noise region and about 2 pT/Hz$^{1}$2/ at 1 Hz when measured with dc bias method.hod.d.