Recent progress in ultra-low noise, ultra-low background detectors V. Marian, M.O. Lampert, B. Pirard, P. Quirin CANBERRA France (Lingolsheim) Workshop on Ge detectors Tübingen, April 2013

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.2 Point Contact Ge Detectors Crystal Design and Choice Cold Preamplifier Materials Used Obtained Results Conclusion Outline

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.3 Point Contact Ge detectors CANBERRA France (Lingolsheim) developed a new Point Contact GeHP detector for low energy threshold applications The PCGe consists of a modified Electrode, coaxial Ge detector Energy threshold below 500eV Applications:  New innovative tool in astroparticle & neutrino physics by direct interaction measurement within the Germanium detector  Double-beta decay  Neutrino magnetic moment  WIMP searches

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.4 From Barbeau, Collar, Tench, JCAP 09 (2007) 009 Point Contact Ge detectors Standard coaxial vs PCGe

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.5 Noise in PCGe Detectors Intrinsic noise: Electronic noise (pulser injection): Material contamination noise Other noise sources:  Room temperature preamp  Microphonics  Li implantation Noise reduction techniques  FET selection and optimization  Detector capacitance reduction  Minimizing stray capacitance  Use of ultra low background materials

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.6 Crystal design and choice HPGe crystal  Selection of large crystals based on simulations  Current manufactured sizes: -D62 × L62 -D50 x L50  Stepwise investigation going on to optimize the crystal capacitance (and thus the overall detector noise performance)  It’s all about a question of tradeoff in the design:  Detector size (depletion capability vs price)  Point contact diameter (E-field strength vs PC capacitance)  Noise contribution (detector capacitance vs FET noise, etc.)  Record performance vs manufacturing capability  Process of the crystal with smallest « spot »  Current tradeoff: 2-3 mm in diameter

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.7 Resistive vs Pulsed  Charge sensitive preamplifiers can be used in resistive mode or pulsed mode For resistive preamplifiers:  Simple circuitry  The feedback is permanent through a resistance with significant noise contribution In pulsed mode:  Added complexity  The reset signal is initiated by a small bipolar transistor  In normal operation the bipolar transistor is showing a high impedance Cold Preamplifier Resistive input stage Pulsed input stage

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.8 FET selection  Extensive benchmarking of commercially available and internal Canberra Ultra Low Noise FETs  Characterization:  Room temperature noise versus frequency  FWHM vs Shaping time and detector capacitance  Intrinsic FET noise versus temperature  Working point optimization:  Optimal working temperature  Fine tweaking of bias point (Vd, Vsub, Ids … )  Influence of bias point on device temperature Cold Preamplifier

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.9 Cold Preamplifier  Best available low dielectric loss and low leakage substrate  Low electronic and low radioactive background materials ULB Cryostat  OFHC Copper cryostat  Carefully selected and tested low radioactive background materials Other improvements  Minimizing Stray capacitance  Diode holder  Cold PA support  Detector contact method  New improved room temperature preamplifier with better EMI immunity Materials Used

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.10 Obtained Results The interest of double electrode is to further decrease the noise level by pulse shape analysis in coincidence mode P-type 500g 50x50 (100cc) with two electrodes delivered recently

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.11 Obtained Results Evolution of the performances of Canberra PCGe Detectors Latest delivered Canberra P-type PCGe Detector  500g PCGe Germanium Detectors in ULB cryostat (OFHC copper)  High performances low energy threshold central contact  Best performances at low energies close to theoretical values  External AC coupled preamp for veto and spectrum cleaning  Record 95 eV resolution with test pulser on large 500g Crystal  Low energy threshold below 400 eV

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.12 Obtained Results Spectrum with test 1kcps; 3.6 keV

V. MARIAN Workshop on Ge detector, Tübingen - 10 June p.13 Conclusion Canberra Point Contact Ge Detectors  Continuous improvement process on all levels  Cold and warm preamplifier  Crystal structure and holder  Cryostat design and materials used  Well defined selection and benchmarking criteria for all components  Up to 1 kg PCGe with best resolution and low energy threshold  Proven high reproducibility and reliability process  Good yields for implantation, pasivation, thin film deposition Good mastering of manufacturing parameters of high quality ultra low noise and ultra low background PCGe Detectors