Transcript Stand der SQUID Entwicklung

QUANTENELEKTRONIK
SQUID Gradiometer Arrays for Ultra-Low
Temperature Magnetic Micro-Calorimeter
V. Zakosarenko, R. Stolz, S. Anders, L. Fritzsch, and
H.-G. Meyer
Institute for Physical High Technology, Albert-Einstein-Str. 10,
D-07745 Jena, Germany
A. Fleischmann and C. Enns
Kirchhoff Institute of Physics, Ruprecht Karls University of Heidelberg,
Im Neuenheimer Feld 227, D-69120 Heidelberg, Germany.
The work is supported by the German BMBF under the
contract No. 13N8225.
Contents
QUANTENELEKTRONIK
• Principles of magnetic calorimeter
• Experiments in KIP Uni Heidelberg
• SQUID technology at IPHT Jena
• Layout of SQUID gradiometers as sensors
• Integrated field coil
• 8-pixel SQUID array with integrated field coil
• Conclusions
2
Principles of Magnetic Calorimeter
QUANTENELEKTRONIK
Eg => DT => DM
Sensor: Au:Er
Au:Yb
Bi2Te3:Er
PbTe:Er
3
Integrated SQUID Gradiometer
QUANTENELEKTRONIK
Optimal sensor parameters and
demands to SQUID?
4
Magnetization M [A/m]
Au:Er 300
300 ppm
ppm
Au:Er
Inverse Temperature T1 [K 1]
Specific heat C [104 J mol1K1]
Magnetization and Heat Capacity
QUANTENELEKTRONIK
Au:Er 300 ppm
Temperature T [mK]
Optimal magnetic field 5 mT
Challenge for SQUID !
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Magnetic Susceptibility of Au:Er
QUANTENELEKTRONIK
Au:Er 600ppm
Optimal working
temperature 50 mK
spin glass
Paramagnetic range
and spin-spin interaction
6
Double-SQUID Concept
Detector
SQUID
IB2
QUANTENELEKTRONIK
IB1, U
Noise can be very low
F
Detector SQUID read out by a
current-sensor SQUID
Amplifier
SQUID
IFB
Low noise
Large Slewrate
Small power dissipation on detector SQUID chip (Voltage bias)
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Experiments at KIP (University of Heidelber)
QUANTENELEKTRONIK
Two-pixel detector :
Detector SQUID: Ketchen, IBM
Two Au:Er 300 ppm sensors  50 m,
h = 25 m
Magnetic field:
3 mT
Two gold absorbers: 160 x 160 x 5 m3
Double SQUID scheme
SQUID amplifier – standard current sensor
Model CCblue from Supracon (Jena)
current noise ~2pA/ Hz1/2
Directly coupled SQUID electronics from
Supracon
voltage noise: 0.3nV/ Hz1/2
very low temperature dependence
ADR: VeriCold Technologies, Munich
base temperature:
21 mK,
holdtime below 30 mK:
2 days
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Results of the Experiment
QUANTENELEKTRONIK
raw data
Total heat capacity of 2.5 pJ/K .
Performance of both sensors are
almost identical.
Energy resolution: 3.4 eV @ 6 keV
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Baseline Noise
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Resolution is ‚constant‘
over the whole energy range,
Small temperature drifts,
Small position dependence.
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Thermalization
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Sensor bonded with vacuum grease to Si
Heat capacity 1.2 x 10-12 J/K
Sensor: 1000x larger, spot-welded to
copper block
Heat capacity 10-9 J/K
60 ms
Magnetic calorimeters can be made very fast.
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SQUID-Technologie am IPHT Jena
QUANTENELEKTRONIK
SQUID current sensor SC8B, fabricated in the
standard-Nb/Al2O3/Nb technology at IPHT Jena.
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Gradiometer MC1 - Layout
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Integrated field coil
a) in the washer 50mT/A
b) in the center 38mT/A
The magnetic field at both
washers is equal  drift
compensation.
SQUID inductance ~60 pH
Critical current
12µA
Voltage swing
50µV
Feedback coil coupling
27.5A/F0
White noise level (4.2K)
1.3F0/Hz1/2
Superconducting short with thermal switch
for operation with Persistant Current.
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Gradiometer MC3 – Coil
QUANTENELEKTRONIK
Problem
Critical current of
the coil in all
layouts does not
exceed 20mA:
Field~1...1,5 mT
Steps – reason for low Jc (?)
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Conclusions for the layout
QUANTENELEKTRONIK
 Josephson junctions operates in the desirable magnetic
fields.
 SQUIDs show
good parameters.
 Superconducting shorts with thermal switches operate
well.
 Critical current of the field coils is to low. => needs of
further dewelopment of the technology and/or layout.
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New Detector-SQUID layout
QUANTENELEKTRONIK
Field coil in the first wiring.
Coil with more turns.
Current leads in the upper
wiring is much wider.
SQUID as a serial
gradiometer.
Washer size optimized to
dimensions of Au/Er pill.
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Adapted Technology
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• Special etching technique to
get flat edges in the first
wiring.
• Larger film thickness of the
second wiring.
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Thermalization
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Gold strips for better
thermalization of the
sensor
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Eight-Pixels Array
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4 SQUIDS (8 pixels in
200 × 200 µm grid),
Bond pads for
thermal contact,
Field coil common for
two SQUIDs : 92mT/A,
Magnetic field up to 6mT,
Optimized persistent current
switch: 4mW in liquid He,
SQUID remains
superconducting!
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Conclusions
QUANTENELEKTRONIK
•
Gradiometer SQUIDs for magnetic micro-calorimeters are developed
and fabricated.
•
Josephson junctions are able to operate in the desirable magnetic
fields.
•
SQUID parameters correspond to the design values.
•
The integrated field coils were developed and tested.
•
Superconducting shorts with thermal switch operate well, the
desired persistent current could be frozen in the coil.
•
Eight-pixel SQUID arrays are designed and fabricated.
•
SQUIDs and SQUID arrays can be used for real measurements.
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