LGAD R&D Status & Future
Koji Nakamura
Sayuka Kita, Tomoka Imamura,
Ikumi Goya, Kazuhiko Hara
24th June, 2022

TCHoU member meeting1Tracking detector with timing resolution• Collider experiment gets high energy and high intensity.
– Solving pileup issue is required for tracking, Timing resolution helps!
→Future Tracking detector should have timing information for all hits!

• Tentative Requirement– 30ps timing resolution– ~o(10)um spatial resolution (Pixel type).
– (hadron collider) ~o(1016)neq/cm2 radiation tolerance
Particle identification

4D tracking！
Detector Hit

Tracking

β=1

β = 0.95

150ps difference at R=1m
Solve pileup hits in an event
24th June, 2022

Mass spectrum for new particle

β measurement to obtain mass

K+ π+ separation

e.g. Mass measurementfor Long lived chargeno

TCHoU member meeting2

LGAD detector and spatial resolution (AC-LGAD)•• Low gain Avalanche Diode (LGAD)– General n+-in-p type sensor with p+ gain layer undern+ implant to make higher Electric Field→ Good timing resolution.
– 30ps timing resolution achieved already in 2015.
– R&D topics

Limitation of LGAD :– Need JTE and p-stop structure to have individual gain
layer →Low fill factor (20% for 80um strip)•

AC-LGAD :– Uniform gain layer with AC-Coupled electrode. 100% fill
factor. Signal shared on neighboring electrodes.
Al

DC-LGAD• Finer electrode separation for spatial resolution• Radiation tolerance

n++

n+

n+

p++

p++

--

+
- e ne+- eee-ehh
hhe hh nee--e- h- e- h- he++p hhhhhe hh p++
e-

ee-

JTE

Signal drivers : Gain Holes

e-

-

n+

n+

p++

p++

h

n++

Low fill factor

h

h

n+

e-eeh--h-h-ehe- ee- - - -hhh
pe++e-ehhhehhehhe- hee- h h

SiO2

p+

Al

AC-LGADDC elecn++Poly-Sin++n++

AC elec-eee- - +e- ee-e-- - - eehn-hhhhhe hh
e ehh ehhhh ph++h
e-

n++

p+

eee-

Electric field

SiO2

h

h

h

100% fill factor expected
But need to check Cross-talkp+

For finer electrode LGAD, Gain Uniformity is extremely important and no other way possible.
24th June, 2022

TCHoU member meeting3

AC-LGAD detector• Read out principle of AC-LGAD

Ccp

Ccp

Gain Voltage (Vgain) is quitesensitive to the p+ doping conc.

n+

Rimp

Rimp
signal readoutcrosstalk/sharing

Rimp
Cbulk

• Charge split : Impedance ratio
Assuming ZCbulk>>ZCcp…

𝑄=

𝑍𝑅𝑖𝑚𝑝

𝑄0

𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝
– Amount of produced charge:Q0– Readout Charge :Q
24th June, 2022

p++

Rimp

p+ doping concentration

Ccp

I-V characteristics
Lower p+ doping

Parameter space for doping concentration
Radiation tolerance
Low Vgain

DC
LGAD
Larger Signal & Smaller cross talkn+ doping concentration
TCHoU member meeting

4HPK LGAD development• JFY2015-JFY2018 DC-LGAD– We contributed only first prototype. HGTD took over.

JFY2019 Samples• JFY2019, JFY2020 AC-LGAD production Run I

JFY 2020 Samples• Electrode type– Pad type: 500um sq. 4pad/sensor– Strip type : 80um pitch– Pixel type : 50um sq. 14x14 electrode
Strip type
Pad type

Al width
45 40 35 30um

Poly-si electrode

500um

500um

24th June, 2022

Pixel typeAl size : 42,38,34,30um

p+ doping concentration– Vary n+ and p+ dope (A-E, 1-3)
– Vary thickness of SiO2 (capacitance : Cb=1.5xCa)➔Evaluated JFY2021
Parameter space for doping concentration
C-3

Low Vgain

B-3

A-3

B-2

A-2

B-1

DC
LGAD
A-1

C-2b
C-2
D-a/b

E-b

C-1

Larger Signal & Smaller cross talkx 1/10x 1/2 x 1/2

n+ doping concentration

TCHoU member meeting5Signal size and crosstalk• 80um pitch Strip type : Signal size and Crosstalk

MPV of Pulse height

JFY2019 JFY2020
sample sample

E-b

D-b
C2

D-a

C2-b
Larger n+ resistivity→larger signal

Normalized to C type5th September, 2022

Distance of signal reduce to 1/e– n+ resistivity dependence of signal size and crosstalk.
– Large n+ resistivity →Large signal & Smaller crosstalk
80um pitch Strip

JFY2019 JFY2020
sample sample

C2
C2-b

MPV 34mV

D-aD-b

Larger n+ resistivity→smaller cross talk

Normalized to C type
Monolith 2022 workshop

E-b

Successfully developed
Good S/N 80um pitch
strip detector!
6Signal size and crosstalk
Submitted to NIM A in July 2022 https://arxiv.org/abs/2207.07355• 80um pitch
Strip type : Signal size and Crosstalk

MPV of Pulse height

JFY2019 JFY2020
sample sample

E-b

D-b
C2

D-a

C2-b
Larger n+ resistivity→larger signal

Normalized to C type5th September, 2022

Distance of signal reduce to 1/e– n+ resistivity dependence of signal size and crosstalk.
– Large n+ resistivity →Large signal & Smaller crosstalk
80um pitch Strip

JFY2019 JFY2020
sample sample

C2
C2-b

MPV 34mV

D-aD-b

Larger n+ resistivity→smaller cross talk

Normalized to C type
Monolith 2022 workshop

E-b

Successfully developed
Good S/N 80um pitch
strip detector!
7

AC-LGAD run II (2021 sample) : in April 2022
CutlineUsed thinner di-electric layer (Oxide layer)→ Electrode capacitance increased by factor of 5 !!
Pixel sensor➢ Various of pitch
200um

Strip sensor
150um

100um

50um

➢ Strip sensor which has different electrodelength (to study inter electrode cap.)

Pattern diagram

Rimp [𝛀/□]➢ 5 times larger Ccp compared with E-b (2020) type : E-600
1600

E120

E240

E600

400

C120

C240

C600
Ccp [pF/mm2]

24th June, 2022

16 strips x 2

AC-LGAD run II-b 17th November 2022
Received new wafers with the same design :reduced active thickness 50um→30/20um
Expecting better timing resolution (no results today)

TCHoU member meeting8• Compared signal size of 6 types Ccp/Rimp.
– 150um pixel sensors– Two n+ resistivity types and 3 Ccp types• Compared signal size of 3 pixel size

Rimp [𝛀/□]Results for AC-LGAD pixel detector
1600

E120

E240

E600

400

C120

C240

C600

Signal MPV [V]– 100/150/200um pitches are compared.
Signal size comparison by Ccp/Rimp
150um pixel

Pulse height comparison by pixel pitches

Ccp [pF/mm2]
100 um pitch pixel

Noise

Signal MPV: 122.4±5.5mV
SignalSuccessfully developed
Good S/N 100um pitch
pixel detector!

Ccp [pF/mm2]
24th June, 2022

TCHoU member meeting9Inter electrode capacitance effect ??
Comparison of pulse height distribution between strip and pixel …

𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝

Strip

Pixel

Area of electrode9880x45 um2

100x100 um2

Ccp size of electrode

large

small

Signal size
(expected from Ccp)

large

small

Signal height(actual result)

39.26±0.08mV
small

122.4±5.5mV
large

Strip

Pixel

𝑄=

𝑍𝑅𝑖𝑚𝑝

Inter electrode capacitance

Cint

n

To check Cint effect…
Compared signal size & cross talk
For various length of strip electrodes
Pattern diagram
32 variation
strip lengthsp++24th June, 2022

TCHoU member meeting

𝑄010Strip type electrode : inter strip capacitanceTo evaluate the effect of signal attenuation and inter strip capacitance :short strip

long strip

E-600 type of strip sensor with cutline

Effect of interstrip capacitance

Crosstalk size
both neighbors/leading

Signal size [V]

16 strips

long strip

short strip

cutlineSignal reduction is consistent
to increase of crosstalk

reduced by 60%

Longer strip detector
should have worse S/N ratio
Strip length [mm]Strip length [mm]5th September, 2022

Monolith 2022 workshop

Usual a few cm strip
might not possible….
11

Results & publication
Sayuka Kita et. al. VERTEX 2022 conference @ Tateyama Japan© Koji Hara

© Koji Hara

Writing Proceedings for these results and will submit to JPS proceeding

24th June, 2022

TCHoU member meeting12What’s next? : 3 key development
Timing resolution of pixel and strip detector
Improvement

measurement

Radiation tolerance

Large size prototype
Gain Uniformity

Improvement

EIC prototype

MCP-PMT

HGTD prototype
Infra Red Laser

Fermilab testbeam
24th June, 2022

TCHoU member meeting

New Application to
Collider detector
13What’s next? : 3 key development
Timing resolution of pixel and strip detector
Improvement

Non-Uniform charge deposition
𝐼𝑖𝑛𝑑 = ෍ 𝒒𝒊 𝑣Ԧ𝑑𝑟𝑖𝑓𝑡,𝑖 ∙ 𝐸𝑤,𝑖50um

𝑖Introduces landau fluctuation of induced charge

testbeam
20um
Thinner active thickness
will help to reduce the effect30um and 20um active thick sensor have been received this month.
→ Results will come soon
24th June, 2022

TCHoU member meeting

IR Laser14

What’s next? : 3 key developmenttestbeam
Previously…

Timing resolution of pixel and strip detector
Improvement
New prototype wafer
to reduce Landau noise

measurement

2 layer coincidence→ 𝜎𝑡 = 𝜎∆𝑡 / 2

IR Laser

Takes very long time to take data for small electrode

RI laser (pico second)
5ps timing jitter

MCP-PMT

Photek PMT 240~8ps timing resolution

Infra Red Laser

20um

σ=44.7±2.1 ps

8um slit
RI laser (1.8um)
24th June, 2022

TCHoU member meeting15

What’s next? : 3 key development
Radiation torerance for the current sensor is not optimal.
➔ Survive only upto <1e15neq/cm2

ΔVgain=93.57±0.03V / 1e14neq/cm2
1e14neq/cm2
Non-irrad(-20oC)o(-20 C conv.)

Radiation tolerance

Large size prototype
Gain Uniformity

Improvement

EIC prototype

5e14neq/cm2(-20oC)HGTD prototype
Non-irrad (20oC)
Accepter removal for p+ gain layer
Interstitial Boron

Substitutional Boron
24th June, 2022

1. Carbon annealing•
2. Compensation method• Add Boron + Phosphorus
3. In-active Boron?
• 10 times Bi at the beginning to clean up Oi
TCHoU member meeting

Effective dope
Phosphorus for n+
Phosphorus dope
Boron dope

depth

16

What’s next? : 3 key development
JFY 2022 sample

Implemented 20mm x 20mm pixel sensor (compatible to ATLAS ITk chip)
KEK R&D : smaller electrodes, EIC prototype : all 500um pitch strip and pad
KEK R&D wafer

EIC prototype wafer

Large size prototype
Gain Uniformity
EIC prototype

HGTD prototype

New Application to
Collider detector
Could be a candidate of ATLAS HGTD replacement?
24th June, 2022

TCHoU member meeting17What’s next? : 3 key development
JFY 2022 sample

Implemented 20mm x 20mm pixel sensor (compatible to ATLAS ITk chip)
Large size prototype
Certainly…
need
fast
and
multi-channel
readout
ASIC
KEK R&D : smaller electrodes, EIC prototype : all 500um pitch strip and pad
Gain Uniformity
Fulvio Martinelli et. al. Si-Ge Bi-CMOS ASICKEK R&D wafer
EICUniversity
prototype of
wafer
collaboration with
GenevaEIC prototype

ASIC

HGTD prototype
100um pitch pixel
10x10 channels (100um pitch)with 3 analog + 1 discri. output

New Application to
Collider detector
Could be a candidate of ATLAS HGTD replacement?
24th June, 2022

TCHoU member meeting18

What’s next? : 3 key development
Timing resolution of pixel and strip detector
Improvement
New prototype wafer
to reduce Landau noise

measurement

Radiation tolerance

Large size prototype
Gain Uniformity

Improvement

EIC prototype

Effective dope
Phosphorus for n+
Phosphorus dope
Boron dope

MCP-PMT8ps timing
resolution

HGTD prototype

Infra Red Laser

20um

depth

5ps timing jitter
1.8um focus size

Fermilab testbeam : Feb-March 2023 @ FTBF
24th June, 2022

3cm length
500um pitch strip

TCHoU member meeting

2cm x 2cm
100um pitch pixel

New Application to
Collider detector
19

backup24th June, 2022

TCHoU member meeting20Challenge : Pixel detector• Prototype of 50um x 50um pitch pixel sensor– Wirebonded only 4x4 array at the center.
– First observation of AC-LGAD pixel sensor signal• Smaller signal and larger cross talk observed• S/N ratio is not enough and need improvement.
Pulse height distribution

Signal observed!

Eb type50x50um Pixel signal
Observed singal
But not so good S/N ratio

Clearly need improvement
Coupling capacitor Ccp (Effective area?)pad 500um
strip 45um pixel 50um
9880um500um
50um
MPV : 100mV

38mV

<15mV

Need high Ccp sensors → JFY2021 sample to be tested
24th June, 2022

TCHoU member meeting21

What should be understood and what’s next?
• Understand Strip detector

Strip pitch 80um
Strip width 45um

– Why so small signal?
– How much effect of interstrip capacitance?

9880umInter strip C• Significantly smaller signal compared with pad type detector.

– How much signal attenuation in the strip?
• This might affect to the signal size un-uniformity and delay of signal readout.

• Certainly we want to develop pixel type detector.
– First 50um x 50um pixel sensor does not have enough signal size.
– What is the minimum pixel size we can see good S/N signal?
– What is the effective area for electrode capacitance ?
24th June, 2022

TCHoU member meeting22Preliminary results : Strip type electrodeTo evaluate the effect of signal attenuation and inter strip capacitance :short strip

E-600 type of strip sensor with cutline
Pulse height [V]short strip

long strip

long strip

16 strips
Effect of interstrip capacitanceDue to different Vgain

cutline• Signal reduced by 60% in ~10mm– Because of inter strip capacitance?
– Because of signal attenuation?

• We will test smaller gap sample. (the same pitch)

Strip length [um]24th June, 2022

– Current gap 40um → 20um
– Smaller gap have larger inter strip capacitance andsmaller attenuation

TCHoU member meeting23

Preliminary results : Pixel type electrode
What is the minimum pixel size we can see good S/N signal?
E-600 type of pixel sensor
4x4 pixels are wirebonded.

Pulse height distribution
100um pitch

4 electrodes in the middle
observed different pulse height
MPV for ch6 and the other50um pitchch6

MPV : 48.3±2.2 mVGood SN separation !!!

ch11(similar in ch7
and 10)Electrode short in ch6 ?
7 11
6 10

AnalysisOnly center 2x2
channels was used.
(To avoid crosstalk effect)

24th June, 2022

under investigation …

First Pixelated AC-LGAD in the World! (100um x 100um)
We need to understand the 50um x 50um pixel
TCHoU member meeting24Preliminary results : Pixel type electrode
What is the effective area for electrode capacitance ?
E-600 type of pixel sensor

Tested various size of pixel sensor to see the saturation of signal size(all suppried 190V)

saturation region

Signal size [V]proportional region
50um

Effectivearea

100um Apparent

n+

area

Effective area > electrode size

150um

200um

n+

n+

Effective area < electrode size

• Signal seems like saturated at ~150um
Pixel pitch [um]– It makes sense small signal of 50um x 50um sample– Will test smaller n+ resistivity sample• Expected larger effective area.

24th June, 2022

TCHoU member meeting25

Snap shot from on-going ELPH testbeam• ELPH testbeam (6/17-24)– 800MeV electron beam

• Took huge set of data
– Pad/Strip/Pixel sensors– Combined run with 100um pixel and 80um strip
sensor→First LGAD tracker!!

24th June, 2022

LGAD and Telescope

Telescope [50 um pitch]

TCHoU member meetingx0

LGAD Pixel [100um]

LGAD Strip [80 um pitch]

Correlation of x position of two planes
x1

LGAD Strip and LGAD pixel

LGAD Strip [80 um pitch]
26

Conclusion
ACLGAD with 80um pitch strip sensor
Good S/N ratio : 99.98% at 1e-4 noise rate

Small signal due to :inter strip capacitance?
attenuation in strip?
→Strip specific issue

ACLGAD with 100um x 100um pixel sensor
Larger signal than strip sensor!!

Much better solution !

LGAD detector with 50um x 50um
Challenging but need to find a way
24th June, 2022

LGAD detector with Radiation tolerance
Currently up to 1.0x1015neq/cm2

TCHoU member meeting27

backup24th June, 2022

TCHoU member meeting28

Next generation of Collider experiment• Need “Higher Luminosity” and/or “Higher Energy”

Inner Tracking system– High Luminosity LHC (HL-LHC)• 20 times more data (~3000-4000fb-1) at 14TeV• Plan : Start at 2029

– High Energy LHC (HE-LHC)• Use Super Conducting Magnet with Higher Magnetic field(16T)• 28TeV collider in the same tunnel as LHC.

Very high density tracks

140 pileup @ HL-LHC
1500 pileup @ FCC-hh– Future Circular Collider (FCC-hh)– International Linear Collider (ILC)• 250GeV e+ e- collider in Japan

Only way to solve this so far…

finer pixel pitch• Use Super Conducting Magnet with Higher Magnetic field(16T)• 100TeV collider with 100km tunnel at CERN.

Current detector(ATLAS IBL)

250um

50um

New detector(Pixel @HL-LHC)
φ

50um
50um

Z
24th June, 2022

TCHoU member meeting29

Physics impact of timing detector
Higgsino production by using disappearing track
β measurement in FCC detector

ILC K/π separation

LSP: higgsinoΔm(~χ±,~χ0)~300MeV
τ ~χ± ~0.04ns (cτ~12mm)
Used timing information
only for pileup removal
50ps timing
information• See more information in timing
detector workshop in 2018:https://indico.cern.ch/event/747424/timetable/#20181208

24th June, 2022

TCHoU member meeting30

Spatial resolution measurement at ELPH TB• In principle, no dead area and small crosstalk– At least 23um(80um/ 12) resolution by binary readout• ELPH testbeam at Tohoku Univ. (8-9 July 2021)– 800MeV electron beam
– Trigger rate 200-400Hz– Strip E-b type 170V @ 20oCe-

5 layer of Telescope
2 upstr. + 3 downstr.
(25um x 500um pixel)
Scintillator + MPPC trigger
Region of interest (ROI)
24th June, 2022

Residual distributionof hit position and reconstructed position by tracking.
Ch9 Ch13
Ch10 Ch14
Ch11 Ch15
Average of spatial
resolution for all channel
Ch12 Sum
56.2 ± 1.4 um
Spatial resolutionof LGAD det.
20.3 ± 3.2um

TCHoU member meeting

Track pointing resolution
Fitted at sholder

52.4 ± 2.9 um

31

Timing resolution for AC-LGAD detector
Timing reference Detector

Fermilab Test Beam Facility (FTBF)
120GeV proton beam
Strip Detector based Telescope : ~15um pointing resolution

PHOTEK MCP photomultipliers (PMT140)
450ps FWHM with 5e3 Gain
~5ps timing resolution(SPEC: Multi-photon jitter below 10 ps)
Position dependent Timing resolution

ch1

ch2

ch0

ch3

• 25-35 ps timing resolution uniformly!
24th June, 2022

TCHoU member meeting32