The automated data acquisition system developed in the Space Science Laboratory at Marshall Space Flight Center for measuring electrical properties of high temperature superconductors is described. The acquisition system, consisting of a computer and computer-controlled hardware, allows large numbers of voltage, current, temperature, and magnetic measurements to be performed on bulk and thin film samples. Typical results are shown characterizing transition temperature (T sub c), critical current density (J sub c), and magnetic properties of bulk high T(sub c) materials as a function of temperature

Peters, P. N.

Sisk, R. C.

English

NASA Technical Reports Server

NASA
Technical
Memorandum
NASA TM- 100380
CHARACTERIZATIONS OF ELECTRICAL PROPERTIES OF
HIGH T c SUPERCONDUCTING MATERIALS
Center Director's Discretionary Fund Final Report
By R. C. Sisk and P. N. Peters
Space Science Laboratory
Science and Engineering Directorate
September 1989
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N/%SA
National Aeronautics and
SDace Admintstratlon
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George C. Marshall Space Flight Center
MSFC- Form 3190 (Rev. May 1983)
https://ntrs.nasa.gov/search.jsp?R=19900003029 2020-03-20T00:44:17+00:00Z

TABLE OF CONTENTS
Page
I. Introduction ............................................ 1
If. Voltage Measurement Approach .............................. 1
Ill.Text Fixture ........................................... 2
IV. Data Acquisition ........................................ 2
V. Results ............................................... 4
VI. Conclusions ............................................ 4
VII. Reference ............................................. 4
PRECEDIr_G PAGE BLANK NOT FILMED
iii
Figure
LIST OF ILLUSTRATIONS
Title
1 Test fixture ............................................
2 Data acquisitionsystem ...................................
3 Schematic of the data acquisitionsystem .......................
4 Typical current-voltage trace ...............................
5 Typical resistance-temperature trace .........................
6 Typical magnetic measurement trace ..........................
Page
5
6
7
8
9
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iv
TECHNICAL MEMORANDUM
CHARACTERIZATIONS OF ELECTRICAL PROPERTIES OF
HIGH T_ SUPERCONDUCTING MATERIALS--
CENTER DIRECTOR'S DISCRETIONARY FUND FINAL REPORT
I. INTRODUCTION
The goal of this project is to develop a data acquisition
system that will automatically characterize transition
temperatures (Tc) and their widths, critical current
densities (Jc) , and magnetic properties of thin films and
bulk samples of high T_ materials as a function of
temperature. While hardware already exists for making
current-voltage (I-V) traces of niobium thin film
microbridges, much higher currents are carried by bulk high
T_ samples even when sliced into small cross sections. In
a_dition to requiring larger currents for driving the
superconducting sample normal, the existing hardware is not
easily adaptable for computer interfacing.
The new hardware consists of three current sources, each
selected to cover a specific range of current at a particular
resolution. The system also uses a nanovoltmeter to measure
the voltage across the sample and a multiplexed, ten-channel
multimeter for measuring either the sample voltage or the
platinum temperature sensor. During superconducting
transition, a multi-frequency inductance meter measures the
change in inductance of a small test coil wound around the
high T c sample. Each instrument's sequence of events is
smoothly controlled by a computer, eliminating human error and
fatigue involved in making a large number of repetitious
measurements.
II. VOLTAGE MEASUREMENT APPROACH
The high T c sample resistance is calculated from the
carefully measured voltage across a length of sample divided
by the current passing through the sample. Typical voltages
measured across a bulk high T_ sample may vary from zero
volts (superconducting state) to a few mllllvolts (normal
state) depending on the current passing _hrough the sample.
High T critical currents through a 2 mm cross sectional
area _ sample may vary from a few milliamperes to tens of
amperes depending on sample quality and measurement
temperature.
To measure vanishing small voltages down to background
levels of the system (±35 nV), a four-wire measurement
approach must be used in order to cancel thermally induced
voltages and eliminate lead resistance. With the sample
cooled to 77 K, a thermally induced error voltage of 26 _V is
produced on this system offsetting any small voltages
completely off scale. Thermal voltage error can be canceled
by measuring not one voltage but two voltages, provided they
are made before the thermal gradients change. The first
voltage (Vl) is measured across the sample while the current(I) flows in one direction. The second voltage (V2) is
measured across the sample while the same magnitud_ of current
flows in the opposite direction. The corrected voltage (Vc)
and corrected resistance(Rc) a_e given by:
Vc = (Vl-V2)/2 , R c = Vc/I.
III. TEST FIXTURE
High T_ materials typically have rough surfaces that
are difficuIt to wet with solder. These poor contact areas
may result in unacceptable levels of ohmic heating at higher
current values. One satisfactory sample connection and
mounting technique involves the ultrasonic soldering of indium
(99.99 percent pure) pads to the upper and lower surface of
each end of the sample. The high T_ sample is then mounted
into a indium-filled copper test fixture ralsed to a
temperature slightly above the melting point of indium. The
sample's ultrasonically bonded indium melts on contact with
the hot test fixture, forming good contacts between the sample
and current contacts. The test fixture consists of a
double-sided circuit board sandwiched between two copper
blocks soldered together with higher melting point solder.
The higher temperature solder remains solid and keeps the two
copper blocks bonded together while the sample can be mounted
in or removed from the molten indium. Each copper block has a
deep channel milled for holding a small reservoir of indium
and the sample. Current leads are attached to each side of
the test fixture by bolt-on lugs, and indium voltage lead pads
are ultrasonically attached to the sample about 1 mm apart.
Magnetic measurements are made by winding a small test coil
around each sample located between the two voltage pads. A
photograph of the test fixture complete with the high T
sample and four-point probe electrical connections is s_own in
Figure I.
IV. DATA ACQUISITION
Instrument control, data acquisition, and data reduction
by computer are essential for an acquisition system to operate
with minimum human interaction. The computer chosen for this
project is the Hewlett Packard Model 310 Low Cost Color
Workstation. Built into the workstation is a HP-IB (IEEE-488)
interface for communicating with the voltmeter, current
sources, inductance meter, multimeter, printer, plotter, and
disc drive. The system voltmeter is a Keithley instruments
model 181 nanovoltmeter. Two of the three current sources
used in the system are also Keithley instruments, models 220,
and 228. The multimeter, inductance meter, and other current
source are Hewlett Packard instruments models 3457A, 4275A,
and 6031A. A photograph and schematic of the complete data
acquisition system is shown in Figures 2 and 3, respectively.
The data acquisition software was written in-house and
allows three types of measurements to be performed. The first
type of measurement, the current-voltage (I-V) trace, varies
the current passing through the superconducting sample in
discrete known values. At each value of current the
temperature is measured and the voltage across the sample is
measured using the technique described earlier. The
information obtained at each point is displayed graphically on
the screen in real time. The voltage will remain essentially
zero, except for background noise, as long as the sample is
superconducting. As soon as the current exceeds a critical
value, known as the critical current (Ic) , voltage across
the sample begins to increase with increasing current. Some
time later the (I-V) trace is stopped and all current,
voltage, and temperature data are stored on disc for plotting
at a later time. A typical (I-V) trace is shown in Figure 4.
The sample is submerged in a bath of either liquid helium (4.2
K) or liquid nitrogen (77 K) during this measurement.
The second type of measurement, the
resistance-temperature (R-T) trace, passes a small constant
excitation current through the high T c sample while the
temperature is varied. A range of temperatures is obtained by
first dipping the sample into a liquid nitrogen bath and then
raising the sample slightly above the liquid level after the
sample has completely cooled. As the sample slowly warms,
voltage, magnetic, and temperature measurements are made every
few seconds and displayed in real time. The critical
temperature (Tc) is determined by these data. After the
trace is complete the information is stored for later use. A
typical (R-T) trace is shown in Figure 5.
The third type of measurement records the magnetic
behavior of the sample during the resistance-temperature
trace. A small coil of copper wire, about 15 turns, wound
around each sample gives about 1.5 _H inductance at room
temperature. As the sample cools through the transition
temperature, magnetic field is expelled and shielded by the
superconductor causing a change in measured inductance of the
coil. The quality of a high T c superconductor can be
inferred by looking at the transition width of the trace. The
$
sharper the transition the better the sample. In multiphase
superconducting compounds, this type of measurement can show
the transition temperature associated with each phase. A
typical trace of the magnetic measurement is shown in Figure
6.
V. RESULTS
The high temperature superconductivity data acquisi£ion
system performs extremely well. Noise for the system is very
low, fluctuating on average only ±35 nV for a superconducting
sample at 77 K. Over 250 measurement traces have been
performed on 70 different high T_ samples thus far.
Current-voltage data were obtained and publlshed In a paper on
the enhanced properties of silver oxide doped YBa2Cu30 x
compounds [i].
VI. CONCLUSIONS
Even though the system performs well, there are two areas
under improvement. Presently resistance-temperature
measurements are limited from room temperature down to 65 K.
Below this value the temperature sensors are not calibrated.
Currently the temperature rate of change and range during a
resistance-temperature measurement is controlled by raising
the sample out of a liquid nitrogen bath. The greater the
sample height above the liquid level the faster the warmup.
This scheme provides no control for holding long periods of
time at a fixed temperature. Both of these shortcomings will
be alleviated with the addition of a closed cycle helium
refrigerator system. This refrigerator system can control the
temperature from 300 K to I0 K and incorporates two calibrated
silicon diodes for measuring temperature over this complete
range.
.
VII. REFERENCE
P. N. Peters, R. C. Sisk, E. W. Urban, C. Y. Huang, and
M. K. Wu, Appl. Phys. Lett. , 5_22 , 2066 (1988).
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10
APPROVAL
CHARACTERIZATIONS OF ELECTRICAL PROPERTIES OF HIGH T c
SUPERCONDUCTING MATERIALS--
CENTER DIRECTOR'S DISCRETIONARY FUND FINAL REPORT
By R. S. Sisk and P. N. Peters
The information in thisreport has been reviewed for technical content. Review of
any information concerning Department of Defense or nuclear energy activitiesor pro-
grams has been made by the MSFC Security ClassificationOfficer. This report, in its
entirety,has been determined to be unclassified.
E. TANDBERG-HANSSEN
Director
Space Science Laboratory
11
"_'U.S. GOVERNMENT PRINTING OFFICE 1989--631-056/00179

TECHNICAl
1. REPORT NO. 2. GOVERNMENT ACCESSION NO.
NASA TM- 100380
4. TITLE AND SUBTITLE
Characterizations of ElectricalProperties of High T_ Supercon-
ducting Materials--Center Director'sDiscretionary 1_und Final
Report
7. AUThOR(S)
R. C. Sisk and P. N. Peters
9. PERFORMINGORGANIZAT'ONNAMEANDAODRESS
George C. Marshall Space Flight Center
Marshall Space Flight Center, AL 35812
Iz. SPONSO.INGAGENCYNAMEANO*ODRESS
National Aeronautics and Space Administration
Washington, DC 20546
REPORT STANDARD TITLE PAGE
3. RECIPIENT'S CATALOG NO.
S. REPORT DATE
September 1989
6. PERFORMING ORGANIZATION COOE
ES63
81 PERFORMING ORGANIZATION REPORt R
10. woRK UNIT NO.
111 CONTRACTOR GRANTNO.
_a TYPE Or REPORTa PERIODCOVERED
TechnicaIMemorandum
14. SPONSORINGAGENCYCODE
15. SUPPLEMENTARY NOTES
Prepared by Space Science Laboratory, Science and Engineering Directorate
16. ABSTRACT
This report describes the automated data acquisition system developed in the Space Science
Laboratory at Marshall Space Flight Center for measuring electrical properties of high tempera-
ture superconductors. The acquisition system, consisting of a computer and cmmputer-eontrolled
hardware, allows large numbers of voltage, current, temperature, and magnetic measurements to
be performed on bulk and thin film samples. Typical results are shown characterizing transition
temperature (Te) , eritieal current density (Ja), and magnetic properties of bulk high T a materials
as a funetion ot_temperature. -
17_ KEY WORDS
,
High Temperature Supereonduetivlty
High Te Eleetrleal Measurements
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Characterizations of electrical properties of highT(sub c) superconducting materials

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