A GUIDE TO CRYOGENIC APPLICATIONS OF SIPMS • Relatively young field • One running experiment (GERDA, LAr veto shield) • One experiment under commissioning (MEG II) • Few experiments in the preparation phase (DUNE, DarkSide, nEXO,…) • Liquid Noble Gases experiment, new requirements and emphasis (very large area detectors, radiopurity, VUV sensitivity, low noise electronics and massive ganging, infrared sensitivity?? ..) • Not much to standardize, yet, but rather share experience and guide the developments
MENU • Review of the existing/planned experiments (Fabrice Retiere) • Physics of SiPMs at cryogenic temperatures (Gianmaria Collazuol) • Review of the readout electronics approaches (Wataru Ootani) • Testing setups at cryogenic temperatures (Andrii Nagai) • Reliability issues for large scale applications (Vishnu Zutshi) • Interesting new contributions
PHYSICS OF SIPMS AT CRYOGENIC TEMPERATURES AND IMPLICATIONS FOR THEIR PERFORMANCE AND CHARACTERISTICS G.Collazuol, Department of Physics and AstronomyUnversita` di Padova and INFN A.Para, Fermilab ICASiPM 2018, Schwetzingen
SUMMARY • Cryogenic experiments (LXe/LAR) use SiPMs in the regime where the fundamental physics of silicon changes considerably (source of the figures: Gutierrez, Dean, Claeys “Low Temperature Electronics: Physics, Devices, Circuits and Applications”) • (Some) SiPMs characteristics may vary significantly from room temperature to the operating conditions • Cold/warm temperature variation may depend on the specific device design (room for the device optimization)
FREE CARRIERS IN DOPED SILICON LXe LAr Room temperature Donors/acceptors fully ionized by thermal excitations . Silicon is a semiconductor. Free carriers produced by a temperature- dependent combination of • Thermal excitations • ‘field-assisted’ excitations • tunneling Donors/acceptors levels filled up. Insulator.
SILICON PROPERTIES AT LOW T: HIGHER CARRIER MOBILITY • Carrier mobility è avalanche development, time development • Temperature variation depends on doping profiles and electric fields è effect onSiPM performance may depend on the details of the SiPM design 6
SILICON PROPERTIES AT LOW T: IONIZATION COEFFICIENTS • Impact ionization coefficient è avalanche development, time development, breakdown voltage • Electron/hole variation è Wavelength dependence of PDE • Temperature variation depends on doping profiles and electric fields è effect onSiPM performance may depend on the detais of the SiPM design 7
AVALANCHE BREAKDOWN: TEMPERATURE VARIATION Avalanche breakdown V is expected to show a non linear dependence on T (depending of the junction type and doping concentration) Breakdown V decreasing with T due to increasing mobility NOTE: in freeze-out regime Zener (tunnel) breakdown could be relevant. → negative Temperature coefficient (increasing with decreasing T) Crowell and Sze More recent model by Crowell and Okuto after Shockley, Wolff, Baraff, Sze and Ridley. 8
SILICON ABSORPTION LENGTH AT LOW TEMPERATURES • Variation of the wavelength-dependence of PDE with temperature 9 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
IN ADDITION: QUENCHING RESISTOR Adopting metal quenching resistor Improved temperature stability 10 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
PULSE SHAPE: DEPENDENCE ON TEMPERATURE The two current components behave differently with Temperature → fast component is independent of T because C tot couples to external R load → slow component is dependent on T because C d,q couple to R q (T) H.Otono, et al. PD07 HPK MPPC high pass filter / shaping → recover fast signals HPK MPPC Akiba et al Optics Express 17 (2009) 16885 11 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
REVERSE BIAS I-V CURVES → DARK CURRENT AND V BD Dark current decreases rapidly with T Reverse I-V characteristics at fixed T at rate ~ x2 / 10K Breakdown Voltage vs T FBK devices Breakdown voltage decreases at low T due to larger carriers mobility → larger ionization rate (electric E field fixed) G.C. et al NIM A628 (2011) 389 12
V BD VS T → TEMPERAURE COEFFICIENT ( D V STABILITY) Breakdown Voltage Vbr measured by fitting single ~80 mV/K p.e. charge vs bias voltage Temperature coefficient (pulsed mode) (above 240K) D v br /V br / D T ~0.25 %/K the line is for Improved FBK device eye guide dV br /dT (V/K) stability at low T G.C. et al NIM A628 (2011) 389 D v br /V br / D T ~0.20 %/K HPK device (400 pixels) T (K) J.Csathy et al NIM A 654 (2011) 225 13
PULSE SHAPE VS T Alberto Gola – IEEE NSS-MIC 2015 A.Para - G.Collazuol - Cryogenic behaviour of 14 Silicon PMs
sources of DCR contribution to DCR DARK CURRENT VS T from diffusion of minority carriers negligible below 350K Noise mainly comes from the high E Field region (no 1) Generation/Recombination SRH whole depletion region) noise (enhanced by trap assisted tunneling) FBK devices I re ve rse ~ T 1.5 exp − E a ct K B T Conventional constant D V SRH positive T coefficient trap assisted tunneling x1000 2) Band-to-band Tunneling noise (strong dependence on the Electric field profile) x10 negative T coefficient x10 x1000 E field engineering is Tunneling noise dominating for T<200K crucial for min. DCR (sharp high E field region → higher noise) (esp. at low T) 15 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
DARK COUNT RATE VS TEMPERATURE (CONSTANT D V) Measurement of counting rate of ≥ 1p.e. D V = 1.5V at fixed D V=1.5V d (→ constant gain) e c n a h n e d l e i f H R DCR~ T 1.5 exp − E a ct S K B T Activation energy E act ~0.36eV Tunneling ??? onset of carriers freeze-out (carrier losses at very low T due to ionized impurities acting as shallow traps) Under investigation 16
OPTIMIZE SIPM FOR CRYOGENIC OPERATION: FBK Alberto Gola – IEEE NSS-MIC 2015 17
AFTER-PULSES VS T (CONSTANT DV) Measurement by waveform analysis: - trigger on single carrier pulses (with no preceding pulses D V = 1.5V within D t=5 µ s), count subsequent pulses within D t=5 µ s (find the after-pulsing rate r AP ) FBK devices - Subtract dark count contribution - extract after-pulsing probability P AP corrected for after-pulsing cascade r AP P AP = 1+ r AP After-pulses envelope • Few % at room T • ~constant down to ~120K AP “trains” G.C. et al NIM A628 (2011) 389 T decreasing: increase of characteristic time constants of traps ( t traps ) compensated by increasing cell recovery time (R q ) • several % below 100K The growth of micro-cell recharge time T<100K: additional trapping centers activated help reducing the after-pulsing at low T possibly related to onset of carriers freeze-out 18 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
QUICK GUIDE: DARK RATE, AFTERPULSES, CROSS TALK After-Pulsing swift Dark Noise Rate increase below 100K dumped at low T P AP ~ independent of T above 100K !!! SRH vs Tunneling different slope d DR/ dD V (cfr PDE vs D V) (slight reduction expected due to lower PDE for large l at low T) Gain and Cross-Talk are independent of T 19 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
SPECTRAL SENSITIVITY PDE vs l ( D V constant) PDE D V vs ( l constant) PDE Simulation Data G.C. et al NIM A628 (2011) 389 l =400nm T=50,150,...,300K saturation starts earlier at low T D V (V) PDE spectrum at low T peaks at shorter l Data D V = 2V T=300K T=250K T=150K Simulation T=50K l ( µ m) 20
TIMING AT LOW TEMPERATURE • Timing resolution improves with decreasing T • Lower jitter at low T due to higher mobility: a) avalanche process is faster b) reduced fluctuations NOTE: • Ultimate timing resolution not likely to be a major factor for LXe/LAr experiments single photon FBK timing resolution devices G.C. (2011, unpublished) 21 A.PARA - G.COLLAZUOL - CRYOGENIC BEHAVIOUR OF SILICON PMS
SUMMARY • Area of intensive research. Large body of results (very selected examples shown for the illustration) confirming the ‘standard model’ of SiPMs (no physics beyond the standard model, yet) • Useful guide for the developments of specialized SIPMs (large area/low noise, VUV,..) • Useful guide for development of testing and characterization techniques and strategies. For example: different physics processes dominate at different temperatures hence some of the characteristics measured at cryogenic temperatures may not be well correlated with the same characteristics measured at room temperatures è need for dedicated cryogenic testing setups.
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