GERDA Phase I: Status GERDA FE Phase II meeting Milano Bicocca 16 april 2010 Carla Cattadori, Alberto Pullia, Stefano Riboldi, Alessio D’Andragora, Francesca Zocca, M. Barnabe-Heider, K. Gusev, D. Budjas C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Outline GERDA Phase I specs GERDA Phase I Detectors & Detector Assembly The developed CSA based on semi-integrated architecture (further integration see S. Riboldi talk) Exp. Results for CSA based on CMOS ASIC PZ0 CMOS ASIC PZ1 Commercial CMOS OPAMP Radiopurity issues Conclusion Outlook and next steps C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

GERDA Phase I FE electronic: Speca as in year 2005 (1st meeting at Milano Celoria Physic Department, and subsequent refinements) Charge Sensitive Amplifier Sensitivity: ~ 150 mV / MeV Range Dynamic: > 5-6 MeV (now 8-9 MeV) Working @ Criogenic T Large Open loop gain (~ 105) to guarantee stability (but cryogenics helps) Noise: <1 keV in Ge (< 150 e- r.m.s) @ 1 MeV, t = 8 -10 ms, at T= 77°K Rise time: < 30 ns to allow PSD of ionization events in Ge detectors Compact / integrated as possible Drive 50 W load through 6 m (later 10 m and then 20 m) long cables Power dissipation: < 50 mW /ch (as low as possible) Output stage: Better differential (later single ended) PCB requirements 3ch modularity to serve 1 string Radiopurity: as low as possible later set limit < 500 mBq 232Th and 2.5 mBq 238U for distance Interconnection with input detector and output/LV cables by pins Cryogenic (stable vs deformations for thermal cycles etc.) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

GERDA Phase I detectors & detector assembly 8 enrGe + 6 natGe p-type coaxial Ge detector mass:1-3 kg Cdet = 30-50 pF Deployed in strings Mounted in low-mass Cu holders Cable from Detector to CSA Input & HV : Cu unshielded strip insulated in Teflon pipe HV contact: on Li surface by pressure Readout contact: in borehole spring-loaded C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Phase I detectors above:Non-enriched prototype detector assembly (p-type, 1.6 kg). Same performance as in a vacuum cryostat. IGEX and HDM crystals after dismounting from cryostat (prior to reprocessing at manufacturer) Drawing of phase I detector array: All Phase-I detectors reprocessed and mounted in a low-mass holder. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 The chosen strategy First rule to reduce significantly background is to minimize mass of each component close to crystals  integrated front end. As a trade-off of noise, radioactivity and other specs a semi-integrated architecture was chosen and pursued: external JFET first stage followed by an ASIC second stage amplifier. First stage FET: Philips BF862 as: Noise good Bandwidth good Can work at VGS =0 FET can be replaced @ cryo -T C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

BF862 characterization at room and cryo-T: gm drops ~ 2-3 at cryo-T Parallel white noise contribution substantially decreases at 77K as expected. The decreased temperature only partially compensates the effect of decreased transconductance the overall series white noise is higher at 77 K than at room temperature. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

CSA based on PZ0 (Pullia Zocca 0) ASIC CMOS circuit designed by A. Pullia in 2005 Produced by AMS foundry in 0.8 mm 5V CZX CMOS technology Single ended circuit External feedback components Tested circuit structure: external BF862 JFET + 0.8m 5V CMOS single-ended preamplifier +3V -3V VCC Closed loop gain A = gm x RD x G C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Test chip TEST struct PREAMP 1 PREAMP 2 MOSFETs PREAMP 1 pMOS + ext RF + ext bias Vmax = 550mV (50 Ohm) resistors PREAMP 2 pMOS + ext RF + int bias Vmax = 550mV (50 Ohm) MOSFETs PREAMP 3 TEST struct PREAMP 4 MOSFETs PREAMP 3 pMOS + reset pMOS + shaper MOSFETs PREAMP 4 pMOS + ext RF + ext bias Vmax = 2V (1 kOhm) HIGH VOLTAGE comp’s 3.3 mm CSP+OS simple CC=1.4pF CSP+OS simple CC=0.2pF CSP+OS simple CC=0.6pF CSP+OS simple CC=0pF CSP+OS simple CC=1pF CSP + OS simple CSP with new rail-to-rail output stage. Various comp cap’s CSP+OS cplx CC=0pF CSP+OS cplx CC=2pF CSP+OS cplx CC=0.4pF CSP+OS cplx CC=1.4pF CSP+OS cplx CC=1pF CSP + OS cplx CSP with new rail-to-rail output stage. Various comp cap’s OPAMP OPAMP OPAMP OPAMP C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 3.3 mm

Working temperature from -196°C to 55°C (from 77 K to 328 K) Negative output voltage swing on 150 W impedance ~ 2.5 V (against a negative power supply of -2.7V) Energy sensitivity (CF = 0.2 pF) ~ 290 mV/MeV at preamp output ~ 217 mV/MeV after 150W termination Input dynamic range ~ 8.6 MeV Rise time ~ 16 ns with ~ 10m terminated coaxial cable Fall time ~ 250 ms ( RF = 1.2 GW ) Open-loop gain ~ 3.5 *105 Loop gain ~ 600 Resolution at T= 77 K (  = 6s ) 2.2 keV @ 1.332 MeV ( 60Co ) 1.6 keV @ 932 keV pulser line Power required at T=77K 23.4 mW (VFET = +4V ID = 3mA VCC= +3.6V VEE = -2.8V) Comparison between noise measured at room temperature (T=300°K) and in LN (T=77°K) Acquired output signal driving a 50  coaxial cable of ~ 10 m : rise time of ~ 15 ns C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Working temperature (from 77 K to 328 K) from -196°C to 55°C Negative output voltage swing on 150 W impedance ~ 2.5 V (against a negative power supply of -2.7V) Energy sensitivity (CF = 0.2 pF) ~ 217 mV/MeV after 150W termination ~ 290 mV/MeV at preamp output Input dynamic range ~ 8.6 MeV Rise time ~ 16 ns with ~ 10m terminated coaxial cable Fall time ~ 250 ms ( RF = 1.2 GW ) Open-loop gain ~ 3.5 *105 Loop gain ~ 600 Resolution at T= 77 K (  = 6s ) 1.6 keV @ 932 keV pulser line 2.2 keV @ 1.332 MeV ( 60Co ) Power required at T=77K (VFET = +4V ID = 3mA 23.4 mW VCC= +3.6V VEE = -2.8V)

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Spectroscopic performances of prototype PZ0 with prototype detectors @ Cryotemp T With encapsulated SUB detector: R = 2.06 keV (best); 2.2 keV (typical) in LN (both CSA & Detector) With prototype naked detector in LAr in Gerda Underground Detector Lab: 2.6 keV @ 60Co Best resolution obtained with (encapsulated) prototype crystal and cold PZ0 CSA 1ch CSA based on PZ0 ASIC (in ceramic carrier) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 The 3ch CSA based on PZ0 C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Experimental Setup 1 Test Input Cable 7 LVPS Cables (connected to the Power Supply Unit, through a “filters box”) 3 Output Cables (50 W terminated) JFET Power Supply = 3.7 v LV Power Supply = ±3.1 V; - 2.0 V Power Consumption ~ 40 mW 3 ch Dynamic Range ~ 8 MeV on high imp. 11 cables used All cables 10/20 meters long Ch1 and Ch3 : 33 pF cap. Ch2 : Prototype HPGe detector Acquired data with both MCA and Flash ADCs (Caen) Ch1 Ch2 Ch3 GND GND HPGe LN C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 CSA, Cu EM shield ~ 40 cm from 1st detector (+15 cm 2nd, +15 cm 3rd) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

RIN FADC removed Working Temperature 89 K Rise Time SM 50 + RG 174 Ch-1 (CDET=33 pF, on board ) 74 ns 40 ns Ch-2 (CDET=33 pF, short leg ~1 cm) 72 ns 41 ns Ch_3 (DETECTOR) 73 ns Fall Time 250 ms (RF = 1 GW, CF = 0.3 pF) Resolution 1.2 keV @ 1 MeV pulser line Ch-3 (DETECTOR) 2.7 keV @ 1.332 MeV (60Co) 2.3 keV @ 1 MeV pulser line Power Required (T=77K) ~ 40 mW (VFET = +3.7 V, ID = 3 mA; VCC= +3.1 V; VEE = -2 V) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 PZ0 solved issues Removed ceramic carrier and ASIC bonded on board Defined technology for chip gluing Sealing of Cu cup to protect the ASIC and its bonding wires En res and x-talk among ASIC on same chip OK for high impedence load PZ0 open issues Large number of physical components needed on PCB Some mortality of CSA due to not fully optimized technology of ASIC gluing on PCB and Cu cup sealing Some x-talk among channels (~1 %) going through LV ASIC VCC & VEE PS in relation to the 10 m long resistive Habia SM50 cables (10 W for 10 m), and to PSRR of PZ0 circuit C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K) Chip area ~5 mm2 Chip includes 3 versions of TRIPLE PZ1 and one TRIPLE PZ0 (as spare) PZ1 prototype mounting (single channel, ceramic carrier, only for testing purpose) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Response of PZ1 at room T, Cdet=33pF, 12.5m cables and 50 ohm terminations. Transition time = 88ns. Response of PZ1 at 77K, Cdet=33pF, 12.5m cables and 50 ohm terminations. Transition time = 21ns.

PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K) Two PS needed for 3 ch array: 1 OK when removed VCC, -VEE 2 VC, -VE Power supply of output buffer (VC, -VE) separated from first stage (VCC, -VEE) Bulk connection separated from power supply of output buffer Output buffer optimized C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

PZ1 chip (PZ0 modified to drive 50W terminated cables at 77K) First tests* @ 300K and 77K of a single PZ1 very promising No need of RC stabilizing network Able to drive 50 W cable at 300K and 77K Noise ok (same as PZ0: ~1.1 keV @ 6us shaping time with Cdet=33pF) Dynamic range ok (8MeV with CF=0.2pF, still to be tested with 0.3pF) Triple channel / cross-talk still to be measured Still to be tested with Ge detector C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 *tests performed in March 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 PCBs A high degree of radiopurity is required for the CSA,  long R&D on physical components & PCBs materials to make a radiopure CSA. PCB material: Cuflon© (PTFE embedded in two Cu foils) for PCBs Selected a company: PCB production process & electrogalvanic Ni/Au deposition (for ASIC bonding) qualified for radiopourity. The ASIC is bonded directly on board and sealed by a radiopure Cu cup, providing both the EM shield and the protection of the bonding wires. SMD Resistors and capacitors are of 0402 and 0603 size to reduce mass, and protection diodes have been added at the FET input (Philips BF862). All the components (FET, C, R, Rf (high values), solder paste) screened and selected for radiopurity Qualified the contacting pins. C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Radioisotopes concentration in FE circuits FE circuits: available at LNGS 3 x 3 ch PZ0 circuits (tested). Result of individual radioactivity measurement (reference value for B = 10-3 c/keV kg y): Th < 500 mBq/PCB U < 3 mBq/PCB 8 x 3-ch circuit in production U-238/Ra-226 Th-232/Ra-228 Th-232/Th-228 K-40 [mBq/PCB] [mBq/PCB] [mBq/PCB] [mBq/PCB] 0.54 +/- 0.08 0.24 +/- 0.09 0.29 +/- 0.08 3.2 +/-0.8 Pb-210: < 5.3 Bq/PCB --------------------------------------------------------------------------------------------------------- Pins for PCB to Habia Cable connection U-238/Ra-226 Th-232/Ra-228 Th-232/Th-228 K-40 [mBq/PCB] [mBq/PCB] [mBq/PCB] [mBq/PCB] <0.076 < 0,120 0,060+/- 0.02 0.4 +/- 0.2 C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

CSA Based on Commercial CMOS OPAMP Architecture: external JFET + CMOS OPAMP and Rf,Cf Tested with encapsulated SUB detector along 3 weeks In test in these days at LNGS GDL with naked BEGe detector PCB manufactured in FR4 material (2 layers) Same size as PZ0 for compatibility purpose (65 mm x 40 mm) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Experimental Setup Test Input Cable 3 LVPS Cables (directly to the Power Supply Unit, no need for the “filters box” in between) 3 Output Cables (50 Ohm terminated) JFET Power Supply = 6 - 12 V LV Power Supply = ± 2.5 V Power Consumption < 140 mW Dynamic Range > 15 MeV 7 cables used All cables 10 meters long Ch1 and Ch3 : 33 pF cap. Ch2 : SUB HPGe detector Acquired data with both MCA and Flash ADCs (Caen) Ch1 Ch2 Ch3 GND GND HPGe LN C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Summary of CC2 measured characteristics Best energy resolution @ LNT : 0.7 kev FWHM (0 pF Cdet) 1.1 kev FWHM (33 pF Cdet) (with 1 Mev pulser signal, 12 us shaping time) Best energy resolution @ LNT : 1.96 kev FWHM for 22 Na (12 us shaping time, 5k counts acquisition) 15 MeV guaranteed energy dynamic range 50 W drive capability with 10 m long cables Power consumption < 140 mW (down to 100 mW for 10 Mev dynamic range) Rise time : less then 55 ns with 50 Ohm terminated, long cables and energy up to 15 Mev Cross-talk : < 0.1% Power Supply Rejection Ratio : should allow HPGe spectroscopy within the Gerda setup Expected reduction on CSA radio-activity < 150 mBq for both 232Th & 238U Operated (in Milano) with 7 cables (3 for power supplies, 3 for outputs, 1 for input test) Small size, no bonding wires, no PCB copper shield, no LVPS “filters box”, simple and robust C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

CC2- PCB Redesigned Reduced PCB Size (38 mm x 50 mm) Pin Connector Reduced PCB Size (38 mm x 50 mm) Mechanical Stability (4 distributed holes: M25) (no need for Teflon Layer in Copper Shield) Reduced Connector Pin Number (11 vs 14) Eliminated Feedback and Test Capacitors (implemented with PCB copper traces, after Alessio’s work) Various BOM configurations to trade-off between: Radiopurity and Channel Crosstalk CSA BOM (as tested in Milano) 3 JFET 3 Operational Amplifiers 11 Tantalum Capacitors (LV decoupling) 22 Resistors 3 Discharge Protection Devices (JFET) Less than 0.1% measured crosstalk Redesigned CC2 PCB First CC2 PCB (same size as PZ0) Minimum CSA BOM 3 JFET 3 Operational Amplifiers 3 Tantalum Capacitors (LV decoupling) 13 Resistors 3 Discharge Protection Devices (JFET) Crosstalk ? ? ? Detector Input Contacts C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 CC2-PCB Redesigned PCB capacitors Component layer Bottom layer Value of PCB copper traces capacitors (FR4 PCB) reproducible. (Cf=0.7 pF,Ct= 0.2pF) a 3 ch CC2 CSA will be coupled to a naked BEGe detector in the next days C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Conclusions 2 CSA available semi-integrated architecture: external JFET BF862 + CMOS ASIC PZ0-1 / Commercial OPAMP with adequate performances for GERDA specs (cryo-T). R&D to produce low radioactivity PCB and selected physical components to produce CSA with radionuclide concentrations << limit value for Phase I Background index (10-3 c/kg y keV); valid for both options. Implementation of printed Cu traces Capacitors instead of C physical components allow to produce a very low background CSA (expected <150 mBq for a 3 ch circuit) the CSA can be approached to detector string  possible to separate the Very FE (VFE= FET,Cf,Rf) to detectors to reduce Cu strip cable length i.e. reduce microphonism, pick-up etc. Very good solution for Phase II unsegmented detectors Can be a solution for Phase II segmented detctors, but PCB needs to be re-designed +……… C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 Outlook and next steps C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 EXTRA slides C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Radioactivity issues CC2 CSA expected to improve the radioactivity issues related to the FE electronics Radioactivity budget estimated on the base of already measured components is: < 150 mBq / PCB (for both Th & Ra) pins included as a result of: - 3 BF862 JFET (228Th= 15 ± 4 mBq / PCB, 226Ra= 14 ± 4 mBq / PCB) - 3 OpAmp (228Th < 11 mBq / PCB, 226Ra= 6.3 ± 1.2 mBq / PCB) - 0 NP0 Ceramic Capacitor (for test and feed-back) replaced by PCB Capacitors - 11 max. (down to 3 min.) Tantalum Capacitors for LVPS decoupling (228Th= 88 ± 22 mBq / PCB , 226Ra= <33 mBq / PCB, 40K=770 ± 330 mBq / PCB) - Cuflon for PCB (228Th <12 mBq / PCB , 226Ra <3 mBq / PCB, 40K =200 ± 62 mBq / PCB) - 22 max. (down to 13 min.) resistors (3 for feed-back; 19 for polarization and LVPS decoupling) Only upper limit available, but from integral radioactivity of PZ0 are not dominant - 7 (for signals) + 4 (for ground) PCB Pins for cable connection (228Th = 42 ±14 mBq / PCB , 226Ra= < 53 mBq / PCB, 40K= 280 ± 140 mBq / PCB) but research of better pins in progress C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

CSA Intrinsic Energy Resolution Room Temperature LN Temperature Circle : 6 V JFET Power Supply Triangle : 12 V JFET Power Supply Cdet = 33 pF C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010 CSA Rise Time Blue line: CSA + 10 m long output cables (50 Ohm terminated) Red line: CSA + 1 m long output cables (50 Ohm terminated) Pulser signal 5 ns rise time Rise time defined as time interval between 10% and 90% of CSA output signal C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Spectroscopy with CC2 CSA Analog Amplifier (10 us Shaping Time) MCA Reproducible Energy Resolution (σ = 0.03 kev over 20 short measurements) Irradiation with 22Na source. FWHM = 2.15 kev C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Spectroscopy with CC2 CSA Analog Amplifier (10 us Shaping Time) MCA Background long acquisition (over the night) FWHM = 2.75 kev (232 Th) FWHM = 2.28 kev (40 K) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Digital Spectroscopy with CC2 CSA CAEN FADC Off-line processing Digital FIR filtering with symmetric weighting function for baseline CSA output signals with 700 us decaying time (from 10% to 90%) Good agreement with single-pole exponentially decaying pulse model FWHM = 2.27 keV C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

Crosstalk between Channels Between Ch2 (detector) and Ch1 Same procedure as for PZ0: Ch1 and Ch2 through analog shaper (10us) Gain amplification for Ch2 = 200 Gain amplification for Ch1 = 1000 Experimental Result: ΔCh1 / ΔCh2 = (15 mV / 5 V) / 5 = 0.06 % Very similar results for cross-talk measurement between Ch2 and Ch3 Because cross-talk is low, it is also difficult to estimate because of the electronic noise As a conservative assumption : Cross-talk < 0.1% Inducing signal: Ch2 Inducted signal: Ch1 256 Scope Averages: Ch1 C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010

CSA Power Supply Rejection Ratio Important parameter to be evaluated (because of unavoidable LVPS variation across long and resistive cables) Low PSRR may cause: cross-talk between channels noise on output signals as a result of disturbances on LVPS In order to practically estimate the CSA PSRR: we measured the 22Na peak shift on the energy spectrum for ± 10% variation of each LVPS Less than 1/4000 shift of the centroid of the peak (5k counts) C. Cattadori GERDA Phase II FE electronic- MiB 16th april 2010