Development of Low Temperature Detector S.C. Kim (SNU, DMRC)

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) = 3.6eVEg(energy gap) = 1.2eV

70 % of W goes into the phonon. This phonon energy is detectable through the cryogenic detector.


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.

cryostat

Temperature sensor

substrate

The change of the resistance

(NTD Ge, Superconducting TES)

The excess quasiparticle

(Superconducting tunnel junction)


High resolution!

Low threshold!

energy resolution 2.37 eV

(Sep. 2004)

55Mn K-line


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

We can reject the charged background.

Calcium tungstate, Scintillation + phonon

99.7% discriminationFrom 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)

cryostat

absorber

Rs ~m

~V

~k

Superconducting film ~

Squid

R

Bias point

TTc

R

Bias point

TTc

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


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 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


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 constant

2.0 mJ/mol/K2 0.695 mJ/mol/K2


Diamond

(10mm x 10mm X 1mm)

Single crystal

Mo/Cu Superconducting bilayer

(1mm x 0.1mm x 0.25um)

Deposited on (100) direction

Of the absorber

Mo(40nm) Cu(200nm)


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 theBilayer 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 sputtering2. Patterned by the lift-off method3. In the same way, Mo electrode deposited

Mo electrode

Mo/Cu bilayer(1x0.1mm)

Si wafer


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.2 0.4 0.6 0.8 1 1.2

Mo/Cu (40/200)

1mm x 0.1 mm

R()

T(K)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.2 0.4 0.6 0.8 1 1.2

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


0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

~ 10

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1

Mo/Cu (40/200)

1mm x 0.1mm


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 magn

etic shielding room. Noise level is 1pA.


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

LHe monitoring gauge

Lock-in Amp for resistance measurement

Temperature monitoring above 4 K : Sidiode, carbon resistor

Power programmer – current controller for ADR

Power supply

ADR system

ACRB

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.

Development of Low Temperature Detector S.C. Kim (SNU, DMRC)

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