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QUANTENELEKTRONIK
TES Bolometer Array with
SQUID readout for Apex
V. Zakosarenko, T. May, R. Stolz, H.-G. Meyer,
Institute for Physical High Technology, Jena
E. Kreysa, W. Esch,
Max Planck Institute for Radioastronomy, Bonn
The work is supported by the German BMBF under the contract No. 05 AA2PC1/3.
Laboca
Project purpose: Large Bolometer Camera (Laboca) with
300 pixel for sub-millimeter range
for Atacama Pathfinder Experiment (APEX) on
array of 12m-telescopes in Chili , Atacama
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Bolometer Principles
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Infrared power Peiwt  T  R  I
Thermistor = transition edge sensor (TES)
Electro Thermal Feedback
Transition edge sensor with voltage bias
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• The transition temperature Tc is
slightly above the bath temperature T0 .
Resistance
• Due to the power dissipation
PBIAS = VBIAS2/RW = (TC-T0)/G
the thermistor warms up to TC .
Working point
Rw
•The working point is stable:
T
R
 PBIAS
T
Electro-Thermal Feedback (ETF)
T0
Tc
Temperature
Signal Response
I
1
L
1
Si 



P
VBIAS ( L  1) (1  iw )
PBIAS  
L(w ) 
GT (1  iw 0 )
d (log R)

d (log T )
Open loop gain
Sharpness of the
transition
Si  
1
VBIAS
L>>1 ; w << 1
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Current response

0
L 1
Effective time
constant
TES Bilayer
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Au-Pd (8 nm)
Proximity bilayer with TC~ 0.5K
Mo (60 nm)
7-pixel Array
Si wafer
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Si N membrane ~1µm thick
with Ti absorber film on the
back side
Au ring
Thermistor (TES)
Nb wiring
7-pixel array chip mounted in
the Cu holder plate (1,5 cm x
1,5 cm)
SQUID current sensors
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SQUID current
sensor chip
µ-metal shield
SQUID holder with 4 mounted current sensors
Measuring System
SQUID holder
with 4 current
sensors. The
µ-metal shield
is not installed.
Superconducting
bolometer
chamber (Al) with
7-pixel horn array
3He
stage with sorption
pump (300mK)
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1.5K pot of 4He cryostat
First Light
30m - radiotelescope of IRAM on Pico
Veleta in Spain, Sierra Nevada.
Cryostat with TES bolometers in telescope cabin
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First Results
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The whole system worked stable in the cabin.
But: bad weather (snow)

120
Channel No.
1
2
3
RBIAS = 90 mOhm
110
100
P, pW
Bolometer Signal, µA
2,0
1,5
RBIAS = 90 mOhm
90
Channel No.
1
2
3
80
70
1,0
0,4
0,5
0,6
0,7
0,8
0,9
1,0
Bias Current, mA
1,1
1,2
1,3
60
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
1,2
1,3
IBIAS, mA
Power calculated as IBIAS x RBIAS x Si
Response of the bolometers on the change of black body temperature (77K  300K)
Next Step
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LABOCA: Large Bolometer Camera: 300 pixel on 4 inch wafer
Laboca should be ready in the middle of the year 2005!
Multiplexing
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Two possibility:
a) parallel readout
 300 current sensors each in separate packaging, ~1250 wires to
room temperature electronics, 300 FLL electronics.
 low risk (familiar way)
 mechanical complexity, thermal last, too expensive !
b) multiplexing
 300 SQUID integrated on the wafer with bolometers, ~30 SQUID
amplifier in separate packaging, ~200 wires to room temperature,
30 FLL electronics, and digital controller .
 less expensive
 new development (challenge !)
Time Domain MUX
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TES bias
Digital control
bias switches
TES
RBIAS
TES
RBIAS
Bias
TES
Active
SQUID
RBIAS
Sinch
Amplifier
SQUID
RESET
FLL electronics,
TES
RBIAS
0.3K
Feedback
1.5K
300K
Out
Test of the MUX Electronics
Sampling frequency 5 kHz
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Sampling frequency 100 kHz
6 separate SQUIDs, SQUID-array as amplifier,
the simplest FLL with two operational amplifiers
Integrated Bolometer
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First samples are fabricated. Tests in the laboratory will
be performed in the next weeks.
Conclusions
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• 7 pixel TES bolometer array with SQUID readout
shows stable operation in real environment in
telescope cabin.
•
7 pixel TES bolometer array with integrated
SQUID is ready for test.
• Time domain multiplexing operates. Optimization
of bandwidth and noise figure is in progress.
• Great challenge to perform the proposed
schedule.