Development of Low Temperature Detector

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					Development of Low Temperature Detector



               S.C. Kim
              (SNU, DMRC)
Contents


Why low temperature detector (LTD) ?

Our design of LTD

The principle of the detector

The components of the detector

The fabrication of the sensor

Plan
Why Low Temperature Detector(LTD)?



Most detectors measure the charged secondaries produced by
particle interaction in the detector. But the dominant effect
of the interaction is the phonon excitation.



For Si,
W(E needed for producing one electron-hole pair) = 3.6eV
Eg(energy gap) = 1.2eV
70 % of W goes into the phonon.
This phonon energy is detectable through the cryogenic
detector.
Why Low Temperature Detector(LTD)?


At sub-Kelvin Temperature,
the heat capacity of the lattice vibration and   the thermal
fluctuation are very small.


We can measure the lattice vibration induced by the particle
interaction at the sub-kelvin temperature.


           Temperature sensor

                                The change of the resistance
           substrate            (NTD Ge, Superconducting TES)
                                The excess quasiparticle
                                (Superconducting tunnel junction)
  cryostat
Why Low Temperature Detector(LTD)?


High resolution!

Low threshold!
                                      55Mn   K-line



                        (Sep. 2004)




                       energy resolution     2.37 eV
Why Low Temperature Detector(LTD)?

By hybrid detection,
ionization + phonon or scintillation + phonon,

We can reject the charged background.



                            Calcium tungstate, Scintillation + phonon
                            99.7% discrimination
                                                   From CRESST

           LTD is very useful tool to observe the phenomena
           which requires low energy threshold & high energy
           resolution.
                                -> Coherent neutrino scattering
                                    Dark matter search
                                    Double Beta Decay
Our design of LTD



Electro-Thermal Feedback Transition Edge Sensor(ETF-TES)
                                                          Rs ~m
                            Superconducting film ~


 R
                                         ~k
               Bias point                             absorber

                                         ~V
                                                                   Squid
                                                cryostat
          Tc         T
The components of the Detector


Absorber – Diamond

Diamond is distinguished by its high Debye temperature, so,
low heat capacity at the low temperature. Besides it can be
used as the ionization detector.

           Atomic Weight            12.01

              Density             3.51 g/cm3

         Debye temperature          2340 K

             Energy gap             5.4 eV
The components of the Detector


In the diamond-structure crystal, there’s the phonon focusing.




                                                        (100)




                                                          (111)




         The ballistic phonon imaging of Diamond
           D. C. Hurley et al J. Phys. C 17 (1984) 3157-3166
 The components of the Detector




The position dependence of detected energy in the diamond-
structure crystal - phonon focusing & quasidiffusion
H.Kraus et al. Superconducting tunnel junctions NIM A315(1992) 213-222
 The components of the Detector


Superconducting film – Mo/Cu bilayer

Using proximity effect, we can control the critical temperature
of the bilayer superconductor.


                               Mo               Cu

         Atomic weight        95.94           63.546

            Density         10.2 g/cm3       8.96 g/cm3

              Tc             0.92 K              X

         Heat capacity    2.0 mJ/mol/K2   0.695 mJ/mol/K2
           constant 
The components of the Detector


 Mo/Cu Superconducting bilayer
 (1mm x 0.1mm x 0.25um)
                                 Diamond
 Deposited on (100) direction
                                 (10mm x 10mm X 1mm)
 Of the absorber
                                 Single crystal




                   Cu(200nm)
   Mo(40nm)
The components of the Detector



We expect the transition will be at around 0.1K.

At 0.1K,

Cdiamond + Cbilayer = 3.06x107 eV/K

If 1keV deposited, after thermalization, 3.2x 10-5K increased.

Because of the athermal phonon, the temperature change in the
Bilayer will be higher.
Fabrication of TES sensor


The fabrication of Mo/Cu bilayer

For the test, we fabricated the bilayer on Si wafer.

1.   Sputtered by the ion beam sputtering
2.   Patterned by the lift-off method
3.   In the same way, Mo electrode deposited

              Si wafer
                                       Mo electrode




                              Mo/Cu bilayer(1x0.1mm)
       Fabrication of TES sensor

        The result of R-T test of Mo/Cu bilayer

       1.6
                                                           Mo/Cu (40/200)
       1.4
                                                           1mm x 0.1 mm
       1.2


        1

R()   0.8

                                                     1.6
       0.6
                                                     1.4
       0.4
                                                     1.2
       0.2
                                                      1
        0
             0   0.2   0.4     0.6   0.8   1   1.2
                                                     0.8


                             T(K)                    0.6


                                                     0.4


                                                     0.2


                                                      0
                                                           0   0.2   0.4   0.6   0.8   1   1.2
          Fabrication of TES sensor

 3



2.5
                                                 Mo/Cu (40/200)
 2                                               1mm x 0.1mm

1.5



 1                                    1.2



0.5                                     1


 0
      0      0.2   0.4   0.6   0.8   1 0.8



                                      0.6
                                                              ~ 10
                                      0.4



                                      0.2



                                        0
                                             0   0.2   0.4     0.6    0.8   1   1.2
The components of the Detector


SQUID system

SQUID controller
-> Product made by Magnicon, with 8MHz Bandwidth



SQUID current sensor
-> Made by PTB. DC SQUID type, second gradiometer, which
   doesn’t need magnetic shielding room. Noise level is 1pA.
The components of the Detector


Cryostat

Adiabatic Demagnetization Refrigerator(ADR)

It reaches 50mK.

The cooling process is the single shot. It can’t be operated
at the constant cooling power.
ADR system
    LHe monitoring gauge
                  Lock-in Amp for resistance measurement


                      ACRB

                                       ADR



Temperature monitoring above 4 K : Sidiode, carbon resistor

                        Power programmer – current
                        controller for ADR
                        Power supply
Plan


SQUID controller & SQUID based current sensor
Will be delivered on late February or March.

Full set-up except TES will be possible on March.

We must find more effective and efficient way to
fabricate robust TES.

				
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posted:9/14/2012
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