Stand der SQUID Entwicklung
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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 T1 [K 1]
Specific heat C [104 J mol1K1]
Magnetization and Heat Capacity
QUANTENELEKTRONIK
Au:Er 300 ppm
Temperature T [mK]
Optimal magnetic field 5 mT
Challenge for SQUID !
5
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
8
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
9
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
QUANTENELEKTRONIK
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
QUANTENELEKTRONIK
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
27.5A/F0
White noise level (4.2K)
1.3F0/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.
16
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!
19
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.
20