1. 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.

2. Laboca
Sub-mm??? Und lambda =1.mm????
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

3. Bolometer Principles Infrared power Peiwt  dT  dR  dI
Thermistor = transition edge sensor (TES)

4. Electro Thermal Feedback
Transition edge sensor with voltage bias
The transition temperature Tc is slightly above the bath temperature T0 .
Due to the power dissipation
PBIAS = VBIAS2/RW = (TC-T0)/G
the thermistor warms up to TC .
The working point is stable:
T  R  PBIAS  T
Electro-Thermal Feedback (ETF)
Resistance
Working point Rw T0 Tc
Temperature

5. Signal Response L>>1 ; wt << 1 Current response
Sharpness of the transition
Effective time constant
Open loop gain
L>>1 ; wt << 1

6. TES Bilayer
Au-Pd (8 nm)
Proximity bilayer with TC~ 0.5K
Mo (60 nm)

7. 7-pixel Array
Si N membrane ~1µm thick with Ti absorber film on the back side
Si wafer
Au ring
Thermistor (TES)
7-pixel array chip mounted in the Cu holder plate (1,5 cm x 1,5 cm)
Nb wiring

8. SQUID current sensors SQUID current sensor chip µ-metal shield
SQUID holder with 4 mounted current sensors

9. 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)
1.5K pot of 4He cryostat

10. First Light
30m - radiotelescope of IRAM on Pico Veleta in Spain, Sierra Nevada.
Cryostat with TES bolometers in telescope cabin

11. First Results The whole system worked stable in the cabin.
But: bad weather (snow) 
Power calculated as IBIAS x RBIAS x Si
Response of the bolometers on the change of black body temperature (77K  300K)

12. Next Step Laboca should be ready in the middle of the year 2005!
LABOCA: Large Bolometer Camera: 300 pixel on 4 inch wafer
Laboca should be ready in the middle of the year 2005!

13. Multiplexing Two possibility: parallel readout b) multiplexing
 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 !)

14. Time Domain MUX TES bias Digital control bias switches Bias Sinch
RBIAS
Digital control bias switches
TES
RBIAS
Bias
Sinch
TES
RBIAS
Amplifier
SQUID
Active SQUID
RESET
FLL electronics,
Out
TES
RBIAS
0.3K
Feedback
1.5K
300K

15. Test of the MUX Electronics
Sampling frequency 5 kHz
Sampling frequency 100 kHz
6 separate SQUIDs, SQUID-array as amplifier,
the simplest FLL with two operational amplifiers

16. Integrated Bolometer
First samples are fabricated. Tests in the laboratory will be performed in the next weeks.

17. Conclusions
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.