Ultra-fast Silicon Detectors (UFSD)
Introduction and MotivationEffect of Timing at the HL-LHC
UFSD introduces a 4th dimension in the
particle coordinates allowing the disentangling of
complicated events.
Potential applications:
Thin sensors for tracking,
Ultra-Fast Silicon Detectors UFSD
Fast sensors for Time-of-Flight TOF
Radiation-resistant sensors,
Soft X-rays (good conversion %, improve S/N)
Low-Gain Avalanche DetectorsPrinciple:
Add to n-on-p Silicon sensor an extra thin
p-layer below the junction which increases
the E-field so that charge multiplication with
moderate gain of 10-50 occurs without
breakdown.
AcknowledgmentsThis work was partially performed within the CERN RD50 collaboration.
The work was supported by the United States Department of Energy, grant DE-FG02-04ER41286. Part of this work has been financed by the Spanish Ministry of Economy and Competitiveness through the Particle Physics National
Program (FPA2015-69260-C3-3-R and FPA2014-55295-C3-2-R), 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.
UFSD Simulation WF2
Timing with Silicon
> Maximize slope dV/dt (ie. large and fast
signals)
> Signal ~ gain, expect jitter 1/G
> Minimize noise N
> Time walk is corrected by using constant-
fraction discriminator (CFD)
Conclusions
Bench testing
* Corresponding author: Hartmut F.-W. Sadrozinski, UC Santa Cruz, [email protected]
Beam test results of a 16 ps UFS timing system
High Doping Concentration: High Field
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
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
LGAD Pulses
Radiation Effects
Pulse Distortions
The left is a screen-shot of one event, showing the
signals of 3LGADs biased at 200V and the SiPM at 28V.
Each horizontal division corresponds to 2ns, while each
vertical divisions is 100mV.
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.
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
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
Investigate resolution vs. temperature:
only gain matters!
Investigate resolution vs. thickness
……but only for the same thickness:
observe Landau fluctuations at large
gain.
Gain and resolution after neutron irradiationRadiation 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.
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
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.
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
Radiation Hardness of LGAD
Y.Zhao, 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
SCIPP, Univ. of California Santa Cruz, CA 95064, USA
N. Cartiglia, M. Ferrero, M. Mandurrino, A. Staiano, V. Sola (INFN Italy)
A. Arcidiacono (Universitàdel Piemonte Orientale, INFN 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
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.
Improvements in performance are expected from ASICs , both existing (ALTIROC0) and in the planning stage.
….and read Helmuth’s 1982 IEEE paper! (Helmuth Spieler, “Fast timing methods for semiconductor detectors”, IEEE Transactions on Nuclear Science,
Vol. NS-29, No. 3, June 1982 GSI/LBL.)
H.F.-W, Sadrozinski,
A. Seiden, N.Cartiglia
arXiv:1704.08666
Students in bold
Longitudinal view
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Transverse view
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Timing
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Timing layer