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

2. 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

3. 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 E g (energy gap) = 1.2eV 70 % of W goes into the phonon. This phonon energy is detectable through the cryogenic detector.

4. 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)

5. Why Low Temperature Detector(LTD)? High resolution! Low threshold! energy resolution 2.37 eV (Sep. 2004) 55 Mn K  -line

6. 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

7. Our design of LTD Electro-Thermal Feedback Transition Edge Sensor(ETF-TES) cryostat absorber R s ~m  ~V ~k  Superconducting film ~  Squid

8. 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 Weight12.01 Density3.51 g/cm 3 Debye temperature2340 K Energy gap5.4 eV

9. 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

10. 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

11. The components of the Detector Superconducting film – Mo/Cu bilayer Using proximity effect, we can control the critical temperature of the bilayer superconductor. MoCu Atomic weight95.9463.546 Density10.2 g/cm 3 8.96 g/cm 3 TcTc 0.92 KX Heat capacity constant  2.0 mJ/mol/K 2 0.695 mJ/mol/K 2

12. 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)

13. The components of the Detector We expect the transition will be at around 0.1K. At 0.1K, C diamond + C bilayer = 3.06x10 7 eV/K If 1keV deposited, after thermalization, 3.2x 10 -5 K increased. Because of the athermal phonon, the temperature change in the Bilayer will be higher.

14. 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 Mo electrode Mo/Cu bilayer(1x0.1mm) Si wafer

15. Fabrication of TES sensor Mo/Cu (40/200) 1mm x 0.1 mm R(  ) T(K) The result of R-T test of Mo/Cu bilayer

16. Fabrication of TES sensor  ~ 10 Mo/Cu (40/200) 1mm x 0.1mm

17. 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.

18. 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.

19. 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

20. 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.