EIIRIS

1 Introduction
Comparison of superconducting
tunnel junctions (STJs)

Scanning probe microscope (SPM)

Overview of the fabrication flow

SPM is a term for microscopes based on a scanning tunneling microscope (STM).

Rod development
2c-axis Bulk

XY drive circuit

Piezoelectric
devices

XYZ

New probe(This work)
Vacuum I
Tunnel current

Fine cuttermachine(0.5 0.5 10 mm3)

GapProbe development

Sample surface

Focus
unknown sample(metallic probes)

rectangular Rod(40 40 10 mm3)

Z-voltage
feedbackcircuit

Tunnel current
detection circuitPolishingmachine

3ProbeStage(Tip ~1 m)
Bias voltage

sharp Rod

Focused ion beam
(FIB)

(Tip ~100 m)

An STM equipped with an HTS probe is expected to realize SIS junctions
that are separated by a vacuum insulator.

2 Rod development(a) Bulk evaluation
RINT-2500 diffractometer(Rigaku Corporation, Japan)(b) Rod fabrication

c-axis YBCO(CSYL-404010, Can
Superconductors)

Crystalline evaluation by X-ray diffraction

caxis

SlicedFine cutter machine(HS-100, Heiwa Technica)

YBCO
Cu-K

Source voltage

40 kVcurrent

100 mA

Scan angle

10 ~ 70step

0.02speed

4/min

3 K cryostat

silver paint

Sliced Bulk

1000 cps

Thin Film

Cooling water(013)

ICDD 01-079-0469(103)(213)(001) (002) (003) (004) (005) (006) (007)0102010 mm

40 mm

20000 cps

Measuring conditions
SampleYBCO bulk(schematic)

Grinding stone(0.5mmt)caxis

X-ray source(c) Rod evaluation

30405060

YBCO bulk showed the similar diffraction peaks to a sputtered film.

ViseYBCO rod(0.5 0.5 10 mm3)

Machining conditions
Abrasive grains

DiamondFeed speed

10 mm/minFeed amount (X)

1.1 mmFeed amount (Y)

40 mm

Feed depth [mm]1.2 mmRotation speed

3,000 rpm

Measuring conditions
Material

YBCO

Sample size

10 0.5(rod)

0.5 mm3

10 10 0.5 mm3(sliced bulk)

High fabrication yield of >90%
without breaking the rod

Refrigerator

Gifford-McMahon

Temperature

300 ~ 3 K

Rod has the same Tc as sliced bulk.
1No damage to superconductivity

3 Probe development(a) Rod polishing(c) Probe evaluation(b) Probe fabrication

Analysis of influence of Ga-ion implantation

Focused Ga-ion beam system(NB5000, Hitachi High-Tech)
Top view

Energy dispersive X-ray spectroscopy in FE-SEM (EMAX ENERGY EX-250, Horiba)
Au-coated YBCO probe

Side view
20 m

Polishing machine(SBT900, MeiwafosisCo., Ltd.)

BeforepolishingAfterpolishing

600 m
Tip radius ofcurvature

20 m

300 m
Machining conditions

Tip thickness
Goal

Measured

Tip thickness [ m]

100

68.9

Tip radius [ m]

100

62.7

One end of the rod was polished to a pyramid
shape with <70- m radius of curvature.

Acceleration voltage

40 kV

Aperture diameter

550 m

Beam current

56 nAdensity

Fullwidth

1 pixelIrradiation time

20 minRadius ofcurvature~ 1.0 mScanning probe microscope(SPM-M Kit, Mad City Labs Inc.)

Sample stage

Counting rate

~3 kcpsAcceleration voltage 30 kV
20 m

Sharp YBCO probe was processed by FIB.

4 Installation to SPM (AFM mode)
Comparison of AFM images (at 300 K)

Experimental setup

Measuring conditions

YBCO probe witha quartz tuningfork

Measurement time

100~120 sec

Working distance

15Magnification

0.1 mm10k

Ga-ion penetration depth < 1 m
The chemical composition
was conserved within the rod.

5 Summary
We proposed, fabricated, and evaluated a YBCO probe for realizing SIS junctions.

Rod development
A c-axis oriented bulk was cut into a rectangular rod using a fine cutter machine.
Tc of the rod was ~90 K, which was almost the same as that of the original bulk,indicating no critical damage to superconductivity owing to the cutting.

Probe development
One end of the rod was ground to a pyramid shape of ~70 m radius, and thenthe apex was further sharpened to ~1 m using a focused Ga ion beam.
The penetration depth of Ga ions from the YBCO surface was <1 m at 40 kV,
suggesting that the chemical composition was conserved inside the rod.

Patterned Si substate

Installation to SPM (AFM mode)
A YBCO probe was installed in an AFM system, where the probe temperature
was set at 300 K at the time. Depending on the tip radius, a clear AFM image wasobtained by gluing the probe to a quartz-tuning fork.

Specifications
Probe mount

Tuning fork

Range ofmotion

200 m (XY)
30 m (Z)Resolution

0.4 nm (XY)
0.06 nm (Z)Future works
250 m/div

Depending on the tip radius, a clear AFM image was obtained by gluing
the probe to the tuning fork.

Optimization of FIB process
Sharper probe tip, reduced Ga-ion damage
Construction of 77 K-cooled AFM
AFM image in liquid nitrogen
Construction of STM
YBCO-based SIS nano-junctions