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SCIPPSCIPP
Hartmut Sadrozinski, 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
SCIPPSCIPP
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.
“4D”
SCIPPSCIPP 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
SCIPPSCIPP
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.
Time of Flight for Particle Identification in Space.
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.
SCIPPSCIPP
5
Range straggling limit for 200 MeV p
Future: 4-D Ultra-Fast Si Detectors ?
Hartmut F.-W. Sadrozinski: UFSD, Tredi 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
SCIPPSCIPP
6
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:
Hartmut F.-W. Sadrozinski, UFSD, Tredi 2013
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
Hartmut F.-W. Sadrozinski: UFSD, Tredi 2013 7
SCIPPSCIPP
8
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 SNRD
SNR
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
Hartmut F.-W. Sadrozinski: UFSD, Tredi 2013
SCIPPSCIPPUFSD Pixel / Strips 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
SCIPPSCIPP
)/exp(* ,,, EbE hehehe
E
bE
NN
he
hehe
,
,,
0
exp*
)*exp(*)(
Impact IonizationA. Macchiolo,16th RD50 Workshop Barcelona, Spain, May 2010
Charge multiplication in path length ℓ :
At the breakdown field in Si of 270kV/cm:ae ≈ 1 pair/umah ≈ 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
SCIPPSCIPPNon-uniform E-Field across a pixel/strip
Non-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 !
Gregor Kramberger, 19th RD50 Workshop, CERN, Nov 2011 A. Macchiolo, 16th RD50 Workshop Barcelona, Spain, May 2010
SCIPPSCIPP Epi, short drift on planar diode g = 6.5
Using red laser and a’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.
Charge multiplication in 3D sensors: M. Koehler et al.
Need uniform field: 3D or diode-like
SCIPPSCIPPWhat 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?
SCIPPSCIPP Firenze ps Laser Data: 50 um p-on-n 6kW-cm
Laser 1.2 ps pulse width & 10 ns period: pulse distortions 740 nm wavelength for red light, penetrate ~6 um.
Oscilloscope: 500 MHz bandwidth 2 BNC into 50 Ohm, 500 Ohm in scope
Charge collection of electrons moving away from laser spot Terminal velocity ~ 100um/ns, i.e. expected collection time ~500ps for high fields
SCIPPSCIPPBase line shift due to AC coupling?
SCIPPSCIPP
Pulse is convolution of electronic shaping and charge collection, Fit pulses to extract shaping time trise & 10%-90% RTFWHM is considered best measure of the convolution
FWHM becomes constant at about 150 V biasRise times RT and trise are ~ independent of bias: Bandwidth of system
Timing Properties of ps Laser signal
SCIPPSCIPP
Above 120V bias, the field > 25kV/cm, i.e. large enough to saturate the drift velocity, i.e. constant collection time.
Below 120V bias, the unsaturated drift velocity increases the charge collection time, causing the pulses to widen.
Collection of ps Laser signal
SCIPPSCIPPStudy 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)
Cu
rren
t (A
)
Diode 2
Diode 3
Challenge for manufacturers: For charge multiplication,
need breakdown voltage >1000V!!
SCIPPSCIPP NIST Range
0.00E+00
5.00E+00
1.00E+01
1.50E+01
2.00E+01
2.50E+01
3.00E+01
3.50E+01
4.00E+01
4.50E+01
5.00E+01
0 200 400 600 800 1000 1200
Alpha Energy [MeV]
Ran
ge
[g/c
m^
2]
SILICON
AIR (dry,
SILICON
0.00E+00
1.00E-03
2.00E-03
3.00E-03
4.00E-03
5.00E-03
6.00E-03
7.00E-03
8.00E-03
9.00E-03
1.00E-02
0 2 4 6 8 10
Alpha Energy [MeV]
Ran
ge
[cm
]
SILICON
Thorium 230: 4.7 MeV
SCIPPSCIPP
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
SCIPPSCIPP Bias dependence of pulse(mean values vs bias voltage)
SCIPPSCIPPExpected Performance from 50um epi Diode
SCIPPSCIPP
Thin Sensor Simulations Preliminary Results
Colin Parker
UCSC / UNITN
1/18/13
SCIPPSCIPPFinite Element Mesh
SCIPPSCIPPElectric FieldWidth = 2um Depth = 2um
SCIPPSCIPPElectric FieldWidth = 20um Depth = 2um
SCIPPSCIPPElectric FieldWidth = 10um Depth = 5um
SCIPPSCIPP
2um deep * width (um) Vbd
2 190
10 250
20 340
39 >500
5um deep * width (um) Vbd
2 350
10 450
20 >500
39 >500
Breakdown Voltage vs. Implant Dimension
SCIPPSCIPP Doping Profiles & Biasing Assume doping distributions with maximum 2 doping
distributions, uniform in depth,“pad fields”
Explore two basic conditions: Emax = 270 kV/cm, adjust bias -> maximum gain Common Bias for pairs of distributions: all 100 W-cm vs. 100 W-cm
with p+ implants of 5, 10, 20 W-cm (4um deep in 20 um, 2 um 5 um) Thickness 20, 5 um Resistivity 10, 50, 100, 1000 Ohm-cm
p+ substr.
p- epi
+ n
SCIPPSCIPP Emax = 270 kV/cm, (Bias adjusted), 5 mm
Electric Field 5um, Emax = 270 kV/cm
0
50
100
150
200
250
300
0 1 2 3 4 5Depth [um]
Fie
ld [
kV
/cm
]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
[3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 100W-cm]
Multiplication Factor 5um, Emax = 270 kV/cm
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1 2 3 4 5Depth [um]
Mu
ltip
lica
tio
n F
ac
tor
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
SCIPPSCIPPEmax = 270 kV/cm, (Bias adjusted), 5 mm
Charge vs. Depth 5um, Emax = 270 kV/cm
10
100
1000
10000
0 1 2 3 4 5Depth [um]
Ch
arg
e [
e]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
[3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 100WW-cm]
Charge vs. time 5um, Emax = 270 kV/cm
1.E+01
1.E+02
1.E+03
0 10 20 30 40 50Time [ps]
Ch
arg
e p
er
2 p
s [
e]
5 Ohm-cm
10 Ohm-cm
15 Ohm-cm
10 Ohm-cm only
50 kOhm-cm only
100 Ohm-cm only
1 kOhm-cm only
Shower development in Space Shower development in Time
SCIPPSCIPPEmax = 270 kV/cm, (Bias adjusted), 5 mm
Gain 5um, Emax = 270 kV/cm
0
2
4
6
8
10
12
14
16
18
20
1 10 100 1000Resistivity
ga
in
P+ Implant, 100 Ohm-cm
No P-implant
[3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 100W-cm]
Gain vs. Resistivity
Collected Charge 5um, Emax = 270 kV/cm
1.E+02
1.E+03
1.E+04
1 10 100 1000Resistivity
Co
llec
ted
Ch
arg
e [
e]
P+ Implant, 100 Ohm-cm
No P-implant
Collected Charge vs. Resistivity
SCIPPSCIPPEmax = 270 kV/cm, (Bias adjusted), 20 mm
Electric Field 20 um, Emax = 270 kV/cm
0
50
100
150
200
250
300
0 5 10 15 20Depth [um]
E F
ield
[k
V/c
m]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only50 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 10, 50, 100, 1000 W-cm]
Multiplication 20 um, Emax = 270 kV/cm
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 5 10 15 20Depth [um]
Mu
ltip
lica
tio
n F
ac
tor
alp
ha
[1
/um
]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only50 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
SCIPPSCIPPEmax = 270 kV/cm, (Bias adjusted), 20 mm
Charge vs. Depth 20 um, Emax = 270 kV/cm
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
0 5 10 15 20
Depth [um]
Co
llec
ted
Ch
arg
e [
e]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only50 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 10, 50, 100, 1000 W-cm]
Shower development in Space Shower development in TimeCharge vs. Time 20 um, Emax = 270 kV/cm
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
0 50 100 150 200
Time [ps]
Co
llec
ted
Ch
arg
e in
2 p
s [
e/2
ps
]
5 Ohm-cm10 Ohm-cm15 Ohm-cm10 Ohm-cm only50 Ohm-cm only100 Ohm-cm only1 kOhm-cm only
SCIPPSCIPP Emax = 270 kV/cm, (Bias adjusted), 20 mm
Gain 20um, Emax = 270 kV/cm
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1 10 100 1000Resistivity
ga
in
P+ Implant, 100 Ohm-cm
No P-implant
[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 10, 50, 100, 1000 W-cm]
Gain vs. Resistivity Collected Charge vs. Resistivity
Collected Charge 20 um, Emax = 270 kV/cm
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1 10 100 1000Resistivity
Co
llec
ted
ch
arg
e in
20
20
0 p
s
P+ Implant, 100 Ohm-cm
No P-implant
SCIPPSCIPPCommon Bias of 100 W-cm Bulk and Implant, 5 mm
Electric Field 5um, Bias = 103 V
0
50
100
150
200
250
300
0 1 2 3 4 5
Depth [um]
Fie
ld [k
V/c
m]
5 Ohm-cm g = 2.4
100 Ohm-cm only g = 1.8
Electric Field 5um, Bias = 119 V
0
50
100
150
200
250
300
0 1 2 3 4 5
Depth [um]
Fie
ld [k
V/c
m]
10 Ohm-cm g = 4.3
100 Ohm-cm only g = 3.7
[3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 100W-cm]
Electric Field 5um, Bias = 124 V
0
50
100
150
200
250
300
0 1 2 3 4 5
Depth [um]
Fie
ld [k
V/c
m]
15 Ohm-cm g = 5.7
100 Ohm-cm only g = 5.2
SCIPPSCIPPCommon Bias of 100 W-cm Bulk and Implant, 5 mm
Gain 5um, Emax(Implant) = 270 kV/cm
0
2
4
6
8
10
1 10 100
Resistivity
ga
in
P+5 Ohm-cm, 100 Ohm-cm, 103 VP+10 Ohm-cm, 100 Ohm-cm 119VP+15 Ohm-cm, 100 Ohm-cm 124 V
[3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 100W-cm]
Collected Charge 5um, Emax(Implant) = 270 kV/cm
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 10 100
Resistivity
Co
llect
ed
Ch
arg
e [e
]
P+5 Ohm-cm, 100 Ohm-cm, 103 VP+10 Ohm-cm, 100 Ohm-cm 119VP+15 Ohm-cm, 100 Ohm-cm 124 V
SCIPPSCIPPCommon Bias of 100 W-cm Bulk and Implant, 20 mm
Electric Field 20 um, Bias = 212 V
0
50
100
150
200
250
300
0 5 10 15 20Depth [um]
E F
ield
[k
V/c
m]
5 Ohm-cm g = 2.3
100 Ohm-cm only g = 1.0
Electric Field 20 um, Bias =364 V
0
50
100
150
200
250
300
0 5 10 15 20Depth [um]
E F
ield
[k
V/c
m]
10 Ohm-cm g = 7.1
100 Ohm-cm only g = 3.4
[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 100W-cm]
Electric Field 20 um, Bias = 415 V
0
50
100
150
200
250
300
0 5 10 15 20Depth [um]
E F
ield
[k
V/c
m]
15 Ohm-cm g = 27.6
100 Ohm-cm only g = 17.6
SCIPPSCIPPCommon Bias of 100 W-cm Bulk and Implant, 20 mm[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 100W-
cm]
SCIPPSCIPP Collected Charge in 5 & 20 um[16um 100 W-cm + 4um of p+ implants (5, 10, 15 W-cm)] vs. [20um 100W-
cm][3um 100 W-cm + 2um of p+ implants (5, 10, 15 W-cm)] vs. [5um 10, 100, 1000W-cm]