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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.
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.
cryostat
Temperature sensor
substrate
The change of the resistance
(NTD Ge, Superconducting TES)
The excess quasiparticle
(Superconducting tunnel junction)
Why Low Temperature Detector(LTD)?
High resolution!
Low threshold!
energy resolution 2.37 eV
(Sep. 2004)
55Mn K-line
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% 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
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 constant
2.0 mJ/mol/K2 0.695 mJ/mol/K2
The components of the Detector
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)
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 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
Fabrication of TES sensor
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
Fabrication of TES sensor
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
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 magn
etic 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
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