Ultra-fast Silicon Detectors Hartmut F.-W. Sadrozinski SCIPP – UC Santa Cruz Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Low-Gain Avalanche Detectors (LGAD) Timing Resolution Radiation Effects Development of 4-D Detectors

Effect of Timing at the HL-LHC UFSD introduces a 4th dimension in the partcicle coordinates allowing the disentangling of complicated events. to to+Dt x y Timing z Longitudinal view z y Transverse view x Timing layer Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Hartmut F.-W. Sadrozinski, Abraham Seiden, Nicolò Cartiglia, “4-Dimensional Tracking with Ultra-Fast Silicon Detectors“, arxiv 1704.08666

Low-Gain Avalanche Detectors (LGAD) Principle: Add to n-on-p Silicon sensor an extra thin p-layer below th junction which increases the E-field so that charge multiplication with moderate gain of 10-50 occurs without breakdown. High Doping Concentration: High Field Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Manufacturers of LGAD (30 µm – 300 µm): CNM Barcelona (RD50, ATLAS-HGTD) HPK Hamamatsu FBK Trento (INFN) very similar behavior with exception of breakdown voltage and special design features . 50µm 50µm 35µm

LGAD Thickness Effects UFSD Simulation WF2 Nicolo Cartiglia developed a full sensor simulation to optimize the sensor design F. Cenna et al, “Weightfield2: a Fast Simulator for Silicon …..”, NIMA796 (2015) 149-153 Available at http://personalpages.to.infn.it/~cartigli/weightfield2 LGAD Pulses It includes many “bells & whistles” required for the detailed description of the signals, i.e. charge generation, drift and collection, electronics shaping LGAD Thickness Effects Rise time dV/dt Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 50μm G=10 Landau fluctuations Radiation Effects Pulse Distortions

Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Timing with Silicon Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 𝜎 𝑡 2 = 𝜎 𝑇𝑖𝑚𝑒𝑊𝑎𝑙𝑘 2 + 𝜎 𝐿𝑎𝑛𝑑𝑎𝑢𝑁𝑜𝑖𝑠𝑒 2 + 𝜎 𝐷𝑖𝑠𝑡𝑜𝑟𝑡𝑖𝑜𝑛 2 + 𝜎 𝐽𝑖𝑡𝑡𝑒𝑟 2 + 𝜎 𝑇𝐷𝐶 2 𝜎 𝑇𝑖𝑚𝑒𝑊𝑎𝑙𝑘 = [ 𝑉 𝑡ℎ 𝑆/ 𝑡 𝑟𝑖𝑠𝑒 ] 𝑅𝑀𝑆 ∝ 𝑁 𝑑𝑉 𝑑𝑡 𝑅𝑀𝑆 , 𝜎 𝐽𝑖𝑡𝑡𝑒𝑟 = 𝑁 𝑑𝑉/𝑑𝑡 ≈ 𝑡 𝑟𝑖𝑠𝑒 𝑆/𝑁 Maximize slope dV/dt (i.e. large and fast signals) Signal ~ gain, expect jitter ~ 1/G Minimize noise N Time walk is corrected by using constant-fraction discriminator CFD

LGAD Capacitance & Current Amplifier (BBA) Noise vs. C for different BW: Data WF2 Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Keep area small! LGAD area 1x1 mm2 -> 3x3 mm2 Capacitance (50 μm): 2 pF -> 20 pF

LGAD Test in Particle beams and 90Sr β-Telescope To understand MIP signals from LGAD pre-rad and post-rad several low-noise single-channel, 2-channel and 4-channel broad band current amps (BBA) were developed by UC Santa Cruz, Kansas Univ., CERN, FNAL. (In addition commercial BBA amplifiers employing “bias-T” connection were used, but with somewhat reduced performance.) They were used in beam tests at CERN and FNAL and in 90Sr β-telescope. UC Santa Cruz boards: (Ned Spencer, Max Wilder, Zach Galloway) Input impedance: 23 , BW >1 GHz Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Now ASICs: expect improved noise performance Roberta Arcidiacono et al, “TOFFEE”, 11 am Nicolo Cartiglia, Angelo Rivetti et al (INFN Torino) , Tue Poster session Christophe De LaTaille et al , ALTIROC (Omega), Tue am Session. (being tested in HGTD beam test at CERN)

Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Dynamic Testing β-source : explore LGAD performance without position information in house and in time process parameters, geometrical variations, operating bias & temperature, ….. Strong temperature dependence of gain Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Investigate resolution vs. temperature: only gain matters! Investigate resolution vs. thickness ……but only for the same thickness: observe Landau fluctuations at large gain.

“Beam test results of a 16 ps UFSD timing system” N. Cartiglia et al., “Beam test results of a 16 ps timing system based on ultra-fast silicon detectors”, NIM. A850, (2017), 83–88. 3 identical 45 μm thick 1.3x1.3 mm2 LGAD produced by CNM To extract the time stamp of the LGAD employ constant-fraction discrimination (CFD) to correct for time walk (CFD ≈ 20%). Important: this can be reliably implemented in an ASIC. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Timing resolution vs. # of UFSD averaged Good matching of three LGAD Time resolution of single UFSD: ~ 25 ps (240V) Time resolution of average of 3 UFSD: 20 ps (200V) & 16 ps (240V) Timing resolution agrees with expectation σ(N) = σ(1)/N0.5 240V

HGTD beam tests at CERN SPS Results from testbeam in August 2016 at CERN SPS H6 beam line with 120 GeV pions DUTs in the middle of a beam telescope with 3 μm position resolution Simultaneous data taking of beam telescope and oscilloscope, combination done offline Gain uniformity in arrays of CNM run 9088 Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 W7 HG22 W8 HG11

UFSD Characterizations in Beam Tests FNAL Beam Test, A. Apresyan et al. Position scan of the time resolution in a 2x2 array of 3x3 mm2 pads, showing the improvement with lowered temperature. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Occupancy scan of two 2x2 array of 3x3 mm2 pads showing different width of the inter-pad gap: CNM (red) : 70µm HPK (blue) : 100 µm

Radiation Hardness of LGAD ATLAS HGTD will require radiation tolerance of LGAD up tp 5e15 neq/cm2 (CMS 1e15?) The small thickness of the LGAD will mitigate the usual radiation effects in Si Increase in leakage current (+ cooling to -30 oC): Increase of depletion voltage due to acceptor creation Decrease of collected charge due to trapping Modification of electric field due to trapped charge (“Double-junction”) A LGAD specific effect is the gain decrease due to acceptor removal in the gain layer. Technology Mitigation: Replacing Boron with Gallium as acceptor,. use Carbon enriched Silicon wafers: first encouraging results, new FBK structure under irradiation as we speak. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Z. Galloway et al, arXiv:1707.04961 Data from C-V scans Simulation from WF2

Radiation Hardness of LGAD In parallel to the technology improvements, explore radiation performance of existing technology ( i.e. Boron multiplication layer) through operational mitigation, i.e. raised bias Small thickness permits high voltage biasing -> part of gain in the bulk, smaller rise time. Radiation campaigns with CNM, HPK and FBK LGAD by RD50, ATLAS and CMS Here report on 1mm HPK 50D (i.e. 50µm), data taken at -20 oC, and -30 oC. Neutron fluence steps: 0, 1e14, 3e14, 6e14, 1e15, 2e15, 3e15 (HGTD), 6e15 n/cm2 Decrease of gain but also Decrease of rise time Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Z. Galloway et al, arXiv:1707.04961

Gain and Resolution after neutron irradiation Radiation campaigns with CNM, HPK and FBK LGAD by RD50, ATLAS and CMS Loss of gain due to acceptor removal can be recovered by increase in bias voltage. This works up to a fluence of about 1e15 n/cm2 there it becomes limited by breakdown. Note that for 6e15 operation at -30 oC allows to reach much higher gain than at -20 oC. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Time resolution in a scan of the CFD threshold showing very different behavior beyond a fluence of about 1e15 n/cm2 Z. Galloway et al, arXiv:1707.04961

Post-rad Rise time -20C, neutron Irradiation High gain (low fluence): drift time limits rise time at low gain pre-rad Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 High fluence, low gain: fast rise time from bulk multiplication! Rise time decreases at high fluences (small gain), and again at very high gain due to fast charge collection. Reality check: for fluence 6e15 n/cm2: 𝝈 𝑱𝒊𝒕𝒕𝒆𝒓 ≈ 𝐭 𝐫𝐢𝐬𝐞 𝑺 𝑵 =270ps/5 Z. Galloway et al, arXiv:1707.04961

Efficiency for HPK LGADs 6e15 n/cm2 , -30 oC Data are from the beta source scans of neutron irradiated HPK-I 50D LGAD. Pmax = max pulse height in event Tmax = time of Pmax The increase in gain with increased bias is visible 700 V Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Max Pulse height: Pmax 750 V

Efficiency for HPK LGADs 6e15 n/cm2 , -30 oC Bias = 750 V, Gain = 7 Bias = 700 V, Gain= 4 Raw Pmax spectrum + noise Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Noise subtracted Pmax spectrum: Bias = 700 V and 750 above noise

Efficiency, Noise Occupancy, Resolution HPK 50D 6e15 n/cm-2, -30 oC Noise sigma typically N = 1.6 mV , Noise occupancy = c* exp[-0.5*(Vth/ N)2], c≈1 Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Need Gain > 7 for good resolution Satisfied for all lower fluences

UFSD Time resolution vs. Fluence Operating voltage increases from about 300 V pre-rad to about 600 V - 700 V above 3e14 n/cm2 The bias allows for about 10% head room where the performance does not change much. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 The time resolution achieved: 20 ps (pre-rad), 35 ps (after 1e15 n/cm2), 50 ps (after 6e15 n/cm2).

Pulse shapes for irradiated LGAD: -20C, neutron Irradiation WF2 Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Data

UFSD Timing Resolution Smaller C Low noise Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Thin sensors The time resolution achieved with 50 µm LGAD with 1x1 mm2 pads is 20 ps (pre-rad), 35 ps (after 1e15 n/cm2), 50 ps (after 6e15 n/cm2): -> success! Their position resolution is 300 µm: -> needs work

Next Step: from Pads to Pixels High bias voltage capability of the LGAD require design details which have no gain. They are being shrunk but can’t be eliminated and limit the fill factor of pixelated LGAD Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 -> For pixels need to avoid segmenting the gain layer Separation of position (pixel) and time (pad) measurement: Double-sided LGAD (“iLGAD”) Un-segmented gain layer results in single-sided AC-LGAD

Separating the Collection and the Gain LGAD Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 n-LGAD iLGAD After Irradiation ?

Inverted LGAD “iLGAD”: 2-sided Readout p-on-p Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 M. Carulla et al. Produced by CNM: First try with laser on 300 μm iLGAD is “lessons learned”, i.e. can be explained by WF2 - which tells us to go thin!

WF2: MIP Pulse in 300 & 50 µm iLGAD p-on-p 300 µm p-on-p 50 µm n-on-p 50 µm 5 ns 500 ps Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Thin p-on-p and n-on-p LGAD seem both to be viable, the holes are a only bit more delayed than in n-on-p. Thick p-type LGAD rely on late hole collection: p-on-p not viable.

Less complex: Single-sided AC LGAD Tested: Single-sided pad LGAD Un-segmented LGAD (AC-coupled, resistive n++ implant sheet, pixelated metal contact) Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 First laser test on-going Could change the silicon sensor paradigm.

Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Conclusions Ultra-fast Silicon detectors are being realized in form of thin Low-gain Avalanche Detectors. The time resolution achieved with 50 µm LGAD pre-rad is 20 ps for 1x1 mm2 pads (3pF) , 35 ps for 3x3 mm2 pads (20pF). The radiation hardness is being improved with process engineering. The present design gives 35 ps for 1e15 n/cm2, 50 ps for 6e15 n/cm2. 2nd generation UFSD are thin double-sided iLGAD, thin single-sided AC-LGAD with much simplified layout. Improvements in performance are expected from ASICs , both existing (ALTIROC0) and in the planning stage. ….and read Helmuth’s 1982 IEEE paper! Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017

Contributors V. Fadeyev, P. Freeman, Z. Galloway, C. Gee, V. Gkougkousis, B. Gruey, H. Grabas, C. Labitan, Z. Liang, R. Losakul, Z. Luce, F. Martinez-Mckinney, H. F.-W. Sadrozinski, A. Seiden, E. Spencer, M. Wilder, N. Woods, A. Zatserklyaniy, Yuzhan Zhao SCIPP, Univ. of California Santa Cruz, CA 95064, USA R. Arcidiacono, B. Baldassarri, N. Cartiglia, F. Cenna, M. Ferrero, A. Staiano, V. Sola Univ. of Torino and INFN, Torino, Italy G. Pellegrini, S. Hidalgo, M. Baselga, M. Carulla, P. Fernandez-Martinez, D. Flores, A. Merlos, D. Quirion Centro Nacional de Microelectrónica (CNM-CSIC), Barcelona, Spain V. Cindro, G.Kramberger, I. Mandić, M. Mikuž, M. Zavrtanik Jožef Stefan Inst. and Dept. of Physics, University of Ljubljana, Ljubljana, Slovenia K. Yamamoto, S. Kamada, A. Ghassemi, K. Yamamura Hamamatsu Photonics (HPK), Hamamatsu, Japan beam test crews HGTD (CERN): Lucia Masetti & US LGAD R&D (FNAL):: Artur Apresyan Students in bold Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 This work was supported by the United States Department of Energy, grant DE-FG02-04ER41286. Part of this work has been financed by the European Union’s Horizon 2020 Research and Innovation funding program, under Grant Agreement no. 654168 (AIDA-2020) and Grant Agreement no. 669529 (ERC UFSD669529), and by the Italian Ministero degli Affari Esteri and INFN Gruppo V. This work was partially performed within the CERN RD50 collaboration.

Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Back-up Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017

Anything New in “Fast Timing with Silicon Detectors”? Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017

Fast Timing with Silicon Detectors: ‘82 -> ‘16 Helmuth Spieler (1982): Heavy Ions UFSD (2016): MIPS Signal Heavy Ion ( >>> 10 MeV) MIP (13keV) (+ Gain) Sensors Thin sensors 50μm Over-depletion of sensors Large over-voltage: saturated drift velocity Capacitance (C =100pF) degrades slew-rate dV/dt Small-area sensors C < 20pF Cooling to reduce “Plasma effect” Cooling reduces leakage current, decreases jitter: increases gain, faster drift Electronics Charge Sensitive Amp Current Amp Constant Fraction Discriminator. CFD=50% is best at largest dV/dt CFD = 20-30% eliminates time walk, reduces Landau jitter Electronics degrades τRise 2GHz SiGe, ASIC preserves τRise Large noise compromises jitter Low-noise amplifiers, ASICs (130nm) Minimize inductance Minimize wire bond length Analysis “Residual jitter δt “ WF2: Landau Noise and field distortions: 𝜎 𝐿𝑎𝑛𝑑𝑎𝑢𝑁𝑜𝑖𝑠𝑒 2 + 𝜎 𝐷𝑖𝑠𝑡𝑜𝑟𝑡𝑖𝑜𝑛 2 Resolution 8ps 25 ps Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017 Facit: Gain, modern electronics and WF2 makes H. Spieler’s HI sensors work for MIP’s

What is missing?: Landau Fluctuations Beam Tests show that we can correct for time walk. So assuming we can beat the time jitter with lower noise and higher gain, Landau fluctuations become the time resolution floor which we can’t go below. They depend on the sensors thickness, independent of the gain. Both thin sensors, and low noise (for low threshold) are required for good timing resolution. Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017

Neutron irradiated LGAD: Doping Profile Loss of gain due to acceptor removal can be recovered by increase in bias voltage. This works up to a fluence of about 1e15 n/cm2 . Hartmut F.-W. Sadrozinski, UFSD, TWEPP, Sep 13 2017