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, hartmut@ucsc.edu

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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to+Dt

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Timing

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Timing layer