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Small size mesa structures on Bi2Sr2CaCu2O8+δ single crystals
PHYSICA ELSEVIER
Physica C 341-348 (2000) 1567-1568 www.elsevier.nl/locate/physc
Small Size Mesa Structures on Bi2Sr2CaCu2Os+~ Single Crystals S. Heim a, A. Irie b, S. Schromm a, M. MSi31ea, S. Rother a, R. Kleiner a'e , and P. M/iller a aphysikalisches Institut III, Universitgt Erlangen-Niirnberg D-91058 Erlangen, Germany bDepartment of Electrical and Electronic Engineering, Utsunomiya University Utsunomiya 321, Japan ephysikalisches Institut, Lehrstuhl f/ir Experimentalphysik II, Universit/it T/ibingen Auf der Morgenstelle 14, D-72076 T/ibingen, Germany We patterned small size mesa structures on top of single crystals of the high temperature superconductor Bi2Sr2CaCu2Os+a using a combination of photolithography and electron beam lithography. The mesas consisted typically of 4-12 intrinsic Josephson junctions formed between adjacent CuO2 double layers. The smallest lateral mesa size was 1 pro. We discuss the electrical properties of these stacks including current-voltage characteristics and critical current vs. external magnetic fields applied parallel to the layers.
1. I n t r o d u c t i o n For intrinsic Josephson junctions (IJ J) formed between adjacent CuO2 double layers in the high temperature superconductor Bi2Sr2CaCu2Os+6(BSCCO) [1] the Josephson penetration length Aj is well below 0.5 #m [2]. To avoid the formation of Josephson vortices and to reach the limit of short IJJ the fabrication of structures with lateral dimensions below 1 #m is necessary. Furthermore, to avoid heating, the stacks should contain only few junctions [3]. These requirements can be fullfilled with present day fabrication technologies. In this paper we report on results obtained for mesas with lateral dimensions down to 1 #m consisting of 4-12 IJJ.
10-Tftcm 2. Subsequently, quadratic mesa structures with lateral dimensions down to 1/~m were patterned using electron beam lithography and Argon-ion milling. For electrical insulation of the lead contacting the top of the mesa a 250 nm thick SiO layer was evaporated followed by a 300400 nm thick gold or silver layer. The leads and contact pads were patterned by photolithography and Argon-ion milling. Current-voltage (IV) characteristics were measured in a two-point configuration. Low pass filters were used for all leads to minimize external noise. External magnetic fields were applied by a 5T split coil. The field orientation relative to the CuO2 layers could be adjusted to an accuracy of 0.01% 3. R e s u l t s
2. S a m p l e s a n d m e a s u r e m e n t
Mesas were patterned on top of BSCCO single crystals using a combination of conventional electron beam lithography and photolithography [4]. To obtain a sufficiently small contact resistance the crystals were cleaved immediately before mounting them into the vacuum chamber and the crystal surface was covered with silver. The contact resistance was typically 10 -50921-4534/00/$ - see front matter © 2000 Elsevier Science B.~ PII S0921-4534(00)01340-X
Fig.1 shows a typical I-V characteristic of a mesa with a junction area of 1 x 1 #m 2. The mesa consisted of four IJJ. The critical current density was about 2 kAcm -2 yielding a Josephson penetration length of about 0.28 #m and ratio of junction width to Josephson length of about 3.5. The characteristic voltage, defined as the voltage jump at the critical current, was 25-30 mV. On larger current scale (Fig.2) a clear gap structure All rights reserved.
1568
S. Heim et al./Physica C 341-348 (2000) 1567-1568
A'
1,0
1.0
/
#-S1-1149
0.5
~
x×
%. 0.5
xx
-~ 0.0
0.0
•
-0.5
-1.0 ,
-1.0
-0.2
-0.1
i
,
0.0
J
,
0.2
0.1
-2
II"~
-;
T=4'2K
;
4 B/Bo 2
v (v)
Figure 1. Current-voltage characteristic of 1 x 1 /~m2 large 4 junction mesa. T--4.3 K.
1.5
e -
1.0
#SH149
0.5
T=4.3K
.
rent and for both polarities of magnetic field. The Fraunhofer pattern (solid line) is clearly approached, although the oscillations are somewhat washed out by thermal fluctuations. Similar behavior was found for all l # m wide mesas showing that small sized IJJ stacks can be fabricated with homogeneous critical current density.
~
OI0 -0.5
-1.o -1.5
Figure 3. Dependence of the normalized critical currents of 1 x 1 ]~m2 large 12 junction mesa on external magnetic field applied parallel to the layers. (B0=1.38 T)
i -01,5
0.10
0,5
v (v)
Figure 2. Current-voltage characteristic of same mesa as shown in Fig. 1 on large bias scale.
4. Conclusion
We fabricated mesas on top of BSCCO single crystals with lateral dimensions down to 1 ~m containing 4-12 IJJ. Measurements confirm Josephson tunneling as well as the homogeneity of the mesas obtained from our fabrication process. REFERENCES
appears confirming that interlayer transport occurs via tunneling. The gap value A per junction is about 25 mV yielding a ratio 2 A / ( k ~ T c ) of 6.8. When the width of the mesas approaches Ai the critical currents of all junctions in the stack should approach a Fraunhofer pattern with zeros at multiples of 13o = ' ~ o / A [5]. The area A is given by the product of the junction width perpendicular to the external field and the junction thickness of 1.5 nm. For the l # m wide junctions, Bo--1.38T. Fig.3 shows results for a 1 #m 2, 12 junction mesa for both polarities of bias cur-
1. R. Kleiner et al. Phys. Rev. Lett. 68 (15), 2394 (1992). 2. R. Kleiner et al. Rev. B 50, 3942 (1994). 3. M. Suzuki et al. Phys. Rev. B 82, 5361 (1999). 4. A. Yurgens et al. Physica C 235-240, 3269 (1994). 5. Y . I . Latyshev et al. Phys. Rev. Lett. 77 (5), 932 (1996).
Physica C 341-348 (2000) 1567-1568 www.elsevier.nl/locate/physc
Small Size Mesa Structures on Bi2Sr2CaCu2Os+~ Single Crystals S. Heim a, A. Irie b, S. Schromm a, M. MSi31ea, S. Rother a, R. Kleiner a'e , and P. M/iller a aphysikalisches Institut III, Universitgt Erlangen-Niirnberg D-91058 Erlangen, Germany bDepartment of Electrical and Electronic Engineering, Utsunomiya University Utsunomiya 321, Japan ephysikalisches Institut, Lehrstuhl f/ir Experimentalphysik II, Universit/it T/ibingen Auf der Morgenstelle 14, D-72076 T/ibingen, Germany We patterned small size mesa structures on top of single crystals of the high temperature superconductor Bi2Sr2CaCu2Os+a using a combination of photolithography and electron beam lithography. The mesas consisted typically of 4-12 intrinsic Josephson junctions formed between adjacent CuO2 double layers. The smallest lateral mesa size was 1 pro. We discuss the electrical properties of these stacks including current-voltage characteristics and critical current vs. external magnetic fields applied parallel to the layers.
1. I n t r o d u c t i o n For intrinsic Josephson junctions (IJ J) formed between adjacent CuO2 double layers in the high temperature superconductor Bi2Sr2CaCu2Os+6(BSCCO) [1] the Josephson penetration length Aj is well below 0.5 #m [2]. To avoid the formation of Josephson vortices and to reach the limit of short IJJ the fabrication of structures with lateral dimensions below 1 #m is necessary. Furthermore, to avoid heating, the stacks should contain only few junctions [3]. These requirements can be fullfilled with present day fabrication technologies. In this paper we report on results obtained for mesas with lateral dimensions down to 1 #m consisting of 4-12 IJJ.
10-Tftcm 2. Subsequently, quadratic mesa structures with lateral dimensions down to 1/~m were patterned using electron beam lithography and Argon-ion milling. For electrical insulation of the lead contacting the top of the mesa a 250 nm thick SiO layer was evaporated followed by a 300400 nm thick gold or silver layer. The leads and contact pads were patterned by photolithography and Argon-ion milling. Current-voltage (IV) characteristics were measured in a two-point configuration. Low pass filters were used for all leads to minimize external noise. External magnetic fields were applied by a 5T split coil. The field orientation relative to the CuO2 layers could be adjusted to an accuracy of 0.01% 3. R e s u l t s
2. S a m p l e s a n d m e a s u r e m e n t
Mesas were patterned on top of BSCCO single crystals using a combination of conventional electron beam lithography and photolithography [4]. To obtain a sufficiently small contact resistance the crystals were cleaved immediately before mounting them into the vacuum chamber and the crystal surface was covered with silver. The contact resistance was typically 10 -50921-4534/00/$ - see front matter © 2000 Elsevier Science B.~ PII S0921-4534(00)01340-X
Fig.1 shows a typical I-V characteristic of a mesa with a junction area of 1 x 1 #m 2. The mesa consisted of four IJJ. The critical current density was about 2 kAcm -2 yielding a Josephson penetration length of about 0.28 #m and ratio of junction width to Josephson length of about 3.5. The characteristic voltage, defined as the voltage jump at the critical current, was 25-30 mV. On larger current scale (Fig.2) a clear gap structure All rights reserved.
1568
S. Heim et al./Physica C 341-348 (2000) 1567-1568
A'
1,0
1.0
/
#-S1-1149
0.5
~
x×
%. 0.5
xx
-~ 0.0
0.0
•
-0.5
-1.0 ,
-1.0
-0.2
-0.1
i
,
0.0
J
,
0.2
0.1
-2
II"~
-;
T=4'2K
;
4 B/Bo 2
v (v)
Figure 1. Current-voltage characteristic of 1 x 1 /~m2 large 4 junction mesa. T--4.3 K.
1.5
e -
1.0
#SH149
0.5
T=4.3K
.
rent and for both polarities of magnetic field. The Fraunhofer pattern (solid line) is clearly approached, although the oscillations are somewhat washed out by thermal fluctuations. Similar behavior was found for all l # m wide mesas showing that small sized IJJ stacks can be fabricated with homogeneous critical current density.
~
OI0 -0.5
-1.o -1.5
Figure 3. Dependence of the normalized critical currents of 1 x 1 ]~m2 large 12 junction mesa on external magnetic field applied parallel to the layers. (B0=1.38 T)
i -01,5
0.10
0,5
v (v)
Figure 2. Current-voltage characteristic of same mesa as shown in Fig. 1 on large bias scale.
4. Conclusion
We fabricated mesas on top of BSCCO single crystals with lateral dimensions down to 1 ~m containing 4-12 IJJ. Measurements confirm Josephson tunneling as well as the homogeneity of the mesas obtained from our fabrication process. REFERENCES
appears confirming that interlayer transport occurs via tunneling. The gap value A per junction is about 25 mV yielding a ratio 2 A / ( k ~ T c ) of 6.8. When the width of the mesas approaches Ai the critical currents of all junctions in the stack should approach a Fraunhofer pattern with zeros at multiples of 13o = ' ~ o / A [5]. The area A is given by the product of the junction width perpendicular to the external field and the junction thickness of 1.5 nm. For the l # m wide junctions, Bo--1.38T. Fig.3 shows results for a 1 #m 2, 12 junction mesa for both polarities of bias cur-
1. R. Kleiner et al. Phys. Rev. Lett. 68 (15), 2394 (1992). 2. R. Kleiner et al. Rev. B 50, 3942 (1994). 3. M. Suzuki et al. Phys. Rev. B 82, 5361 (1999). 4. A. Yurgens et al. Physica C 235-240, 3269 (1994). 5. Y . I . Latyshev et al. Phys. Rev. Lett. 77 (5), 932 (1996).