4D Sensors: Unifying the Space and Time Domain with Ultra-Fast Silicon Detectors

SCIPPSCIPP

Hartmut Sadrozinski, with

Scott Ely, Vitaliy Fadeyev, Zachary Galloway, Jeffrey Ngo, Colin Parker, Brett Petersen, Abe Seiden

SCIPP, Univ. of California Santa Cruz

Nicolo Cartiglia, Amadeo Staiano INFN Torino

Mara Bruzzi, Riccardo Mori, Monica Scaringella, Anna VinattieriUniversita de Firenze

4D Sensors: Unifying the Space and Time Domain

with Ultra-Fast Silicon Detectors

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“4D”

Ultra-Fast Silicon Detectors (UFSD) incorporate the time-domain into the excellent position resolution of semiconductor sensors

they provide in the same detector and readout chain• ultra-fast timing resolution [10’s of ps]• precision location information [10’s of mm]

2 questions need to be addressed for UFSD:• can they work: signal, capacitance, collection time vs. thickness • will they work: required gain and E-field, fast readout

We hope that we will answer the questions within an RD50 Common Project (Giulio Pellegrini)

A crucial element for UFSD is the charge multiplication in silicon sensors investigated by RD50, which permits the use of very thin detectors without

loss of signal-to-noise.

Hartmut F.-W. Sadrozinski: UFSD SCIPP 2013 2

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Motivation for UFSD

Up to now, semiconductor sensors have supplied precision data only for the 3 space dimensions (diodes, strips, pixels, even “3D”), while the time dimension has had limited accuracy (e.g. to match the beam structure in the accelerator).

We believe that being able to resolve the time dimension with ps accuracy would open up completely new applications not limited to HEP

Proposal: Combined-function pixel detector will collect electrons from thin n-on-p pixel sensors read out with short shaping time electronics

Charge multiplication with moderate gain g ~10 increases the collected signal

Need very fast pixel readout


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Benefits of Ultra-Fast Silicon Detectors

- Tracking: Identifying with high precision the temporal signature of different events allows for their association and it reduces random coincidences. Traditional tracking is often overwhelmed by combinatorial backgrounds, which can be dramatically reduced by adding a 4th dimension (time) per point.- Time of Flight (ToF): ToF is already used in many commercial applications such as ToF-enhanced PET and Mass Spectroscopy ToF, however with precision one order of magnitude higher than the goal of UFSD (~500 ps vs. ~50 ps). ToF is also used in particle physics as a tool for particle identification. ToF can also be used in 3D and Robotic Vision: the ability to accurately measure the travel time of light pulses reflected by an object at unknown distance is of paramount importance to reconstruct 3D images, fundamental in imaging and robotic vision. UFSD will offer a spatial precision of a few mm at low illumination power, allowing for battery operated, portable systems.- Particle counting: UFSD performance would allow developing new tools in single particle counting applications with unprecedented rate capabilities. For example, in the treatment of cancer using hadron beams, such a tool would measure the delivered dose to patients by directly counting the number of hadrons.Material science experiments using soft x-rays will benefit from the combination of high rate and precision location that UFSD offers.

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Remote Sensing in HEPTime of flight determines position:

with σt=10 ps, σx= 3 mm, i.e. locate a proton within 3 mm in 20 cm long IPtx c

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TOF for Particle Identification in Space

The Alpha Magnetic Spectrometer (AMS) detector, operating in the International Space Station since 2011, performs precision measurements of cosmic ray composition and flux. The momentum of the particles is measured with high-resolution silicon sensors inside a magnetic field of about 1 m length.

A time resolution of 10 picoseconds, the “Holy Grail” of Cosmic Ray Physics: the distinction between anti-carbon ions and anti-protons can be achieved up to a momentum of 200 GeV/c.


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Range straggling limit for 200 MeV p

Future: 4-D Ultra-Fast Si Detectors ?

Hartmut F.-W. Sadrozinski: UFSD SCIPP 2013

Protons of 200 MeV have a range of ~ 30 cm in plastic scintillator. The straggling limits the WEPL resolution.

Replace calorimeter/range counter by TOF:Light-weight, combine tracking with WEPL determination

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A. Del Guerra, RESMDD12

Positron Emission Tomography PETStudy accumulation of radioactive tracers in specific organs. The tracer has radioactive positron decay, and the positron annihilates within a short Distance with emission of 511 keV γ pair, which are observed in coincidence.

Resolution of detector (pitch)Positron rangeA-collinearityParallax (depth)

T: true event S: Compton ScatterR: Random Coincidence

Resolution and S/N Effects:


Perfect Picture:

SCIPPSCIPPReduce Accidentals & Improve Image: TOF-PET

t1

t2

Localization uncertainty:Dd = c x Dt /2

When Dt = 200 ps ➔ Dd = 3 cm

PET

TOF-PET

@ VCIK. Yamamoto 2012 IEEE NSS-MIC


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1. For a given acquisition time and dose to the patient, TOF can provide better image quality and improved lesion detection.

OR2. with TOF the scan time and dose can be

reduced while keeping the same image quality ( better clinical workflow and added comfort for the patient).

2/tx c

TOFNonx

TOF SNRDSNR

TOF – PET SNR Improvement

M. Conti, Eur. J. Nucl. Med. MoI Imaging (2011) 38:1147-1157

The improved source localization due to timing

leads to an improvement in signal-to-noise

and an increase in Noise Equivalent Count NEC x

DGainNEC


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Can it work? UFSD Collected Charge

Signal = thickness*EPM (EPM = 73 e-/mmCollection time = thickness/vsat (vsat = 80 mm/ns)

For thickness > 5 um, Capacitance to the backplane Cb << Cint

For thickness = 2 um, Cb ~ ½ of Cint, and we might need bipolar (SiGe)?

Realistic gain & cap

Good time resolution

Thickness BackPlane Capacitance Signal Coll. Time[um] Pixels [fF] Strips [pF] [# of e-] [ps] for 2000 e for 12000 e0.1 2500 500 8.3 1.3 241 14461 250 50 83 12.5 24 1452 125 25 166 25.0 12 725 50 10 415 62.5 4.8 2910 25 5 830 125.0 2.4 1420 13 3 1660 250.0 1.2 7.2

100 3 1 8300 1250.0 0.2 1.4300 1 0 24900 3750.0 0.1 0.5

Gain required

Per 1 cm

WRONG


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Energy loss measurement for charged particles in very thin silicon layers

S. Meroli, D. Passeri and L. Servoli

11 JINST 6 P06013

Details of Collected Charge in Thin Sensors


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Correct UFSD Collected Charge

Gain needed for a sensor thickness of 10 µm

Pixel about 4

1 cm long strips about 20

(much less than APD’s or SiPM)

Realistic gain & cap

Good time resolution

Thickness BackPlane Capacitance Signal Coll. Time[um] Pixels [fF] Strips [pF] [# of e-] [ps] for 2000 e for 12000 e

2 125 25 80 25.0 25 1495 50 10 235 62.5 8.5 5110 25 5 523 125.0 3.8 2320 13 3 1149 250.0 1.7 10.4

100 3 1 6954 1250.0 0.29 1.7300 1 0 23334 3750.0 0.09 0.5

Gain required

Per 1 cm


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Impact Ionization

)/exp(* ,,, EbE hehehe

Eb

E

NN

hehehe

,,,

0

exp*

)*exp(*)(

A. Macchiolo,16th RD50 Workshop Barcelona, Spain, May 2010

Charge multiplication in path length ℓ :

At the breakdown field in Si of 270kV/cm:e ≈ 1 pair/um

h ≈ 0.1 pair/um

→ In the linear mode (gain ~10), consider electrons only

Raise maximum and minimum E-field

as close to breakdown field as possible


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Non-uniform E-Field across a pixel/stripNon-uniform Field across the implant results in charge collection difference

Example of electric field: Ф = 1.6·1015 n/cm2, U = 900 V

Even if non-uniformity of field across the implant is only 30%, a large fraction of the center of the implant does not exhibit charge multiplication before sensor breakdown !

Gregor Kramberger, 19th RD50 Workshop, CERN, Nov 2011 A. Macchiolo, 16th RD50 Workshop Barcelona, Spain, May 2010


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Charge Multiplication C.M.

M. Köhler, et al., Nucl. Physics B – Proceed. Supplements 215, 1, (2011), 247-249

G. Casse et al, NIM A 624, 2, (2010) 401–404

I. Mandic et al., Nucl. Instr. and Meth. A 612, (2010 ) 474-477.

Expectationfrom trapping extrapolation

RD50 investigated C.M. and found it in irradiated sensors only.C.M. exists if signal is in excess of pre-rad value

orin excess of trapping measurements

Advantage of thin sensors because of high E-field But indication of excess noise.


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Epi, short drift on planar diode g = 6.5

Using red laser and ’s probes E-field and gainclose to the junction, where it counts. Diode gives uniform field.

J. Lange et al., Nucl.Instrum.Meth A622, 49-58, 2010.

Need uniform field: 3D or diode-like


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What about fast readout:

CERN fixed-target experiment (NA62) needs very fast pixel sensors: Gigatracker (GTK)

Prototype CFD system (INFN Torino) has ~ 100 ps resolution, predicted to be 30 ps in next iteration.

Optimized for 200mm sensors and hole collection (?), could it be re-designed for electron collection from 2 – 10mm sensors?


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Firenze ps Laser Data: 50 um p-on-n 6kW-cm

Laser: 1.2 ps pulse width & 10 ns period,red 740 nm, penetrates ~6 um. Oscilloscope: 500 MHz bandwidth Charge collection of electrons moving away from laser spot

Terminal velocity ~ 100um/ns, i.e. expected collection time ~500ps for high fields


FWHM becomes constant at about 150 V biasRise times RT and trise are ~ independent of bias: Bandwidth of system

Above 120V bias, the field > 25kV/cm, i.e. large enough to saturate the drift velocity, i.e. constant collection time.

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Study of ’s from Thorium 230 50 um thick P-type epi diodes

IV Measurements for diode 2 & 3 during C-V

Epi Diode IV Curve: Diode 2 & 3

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0 50 100 150 200 250 300 350

Bias (V)

Cur

rent

(A)

Diode 2Diode 3 Challenge for manufacturers:

For charge multiplication, need breakdown voltage >1000V!!


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Do NOT expect: Charge multiplication

Pulses from Th 230 alpha’s

Expect collection time of ~ 500ps for over-depleted bias (drift velocity is saturated)large rise time dispersion for low bias voltage

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Doping Profiles & Biasing

Assume doping distributions with maximum 2 doping distributions, uniform in depth,“pads fields”

p+ substr.

p- epi

+ n


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Hartmut F.-W. Sadrozinski: UFSD SCIPP 2013 32G. Kramberger, Preliminary!

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Rapid rise of signal up to 100V during the depletion of the sensor.“plateau” beyond this : gain almost constant beyond ~50V ?

Explanation of rapid rise and level

Toy Simulation


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Why/How does C.M. work stably?

Planar vs. 3D: “smart money” is on planar, although 3D has a uniform 1/r field around electrodeit seems to be harder to get the proper implant profile for the high field section.

Breakdown associated with charge multiplication in high fields:Our experience with drift chambers tells us that you need a “quenching” mechanism That’s why the “magic gas” worked, a mixture of 4 gases:It added to the high gain of Ar the quenching of CO2, isobutane, and methylal or DME.

The fact that we observe gain in low-resistivity (low-R) silicon at RT and low currents as well as in irradiated sensors with large numbers of defects and high currents seems to indicate that the quenching comes from the large numbers of defects which provide trapping of excessive charges.

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4D UFSD Score Card March 2013

Gain in irradiated sensors (pads + strips) √ 2009

Gain in un-irradiated pads √ 2013

Gain in un-irradiated strips/pixels Fall 2013 ?

Fast Readout ASIC Proto type (60 ps) 2012

Fast Readout ASIC (50 ps) 2014

Pixel System (Sensor, ASIC, DAQ) 2016

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Quo Vadis with 4D UFSD?

Fast developments:

First Presentation June 2, 2012 in Bari for RD50November 2012: Common Project within RD50 accepted

Research project funded by DoE within the SCIPP Instrumentation Section

2 EU Research proposals submitted including Torino (Frontend ASIC), Vienna (DAQ)

March 2013: Gain of ~10 seen in un-irradiated diodesMarch 2013: submission of dedicated strip sensors for gain studies

(CNM)Spring 2013: Spanish grad student Marta to come to SCIPP

SCIPP’s role:

Application of SiGe in front-end (work with Torino)Simulations (Marta & Colin & ..)Pulse shape studies (need fast scope and increasingly faster pre-

amps!)Strip readout vs. pixel readout

Documents

4D Sensors: Unifying the Space and Time Domain with Ultra-Fast Silicon Detectors