LGAD R&D
Koji Nakamura
Sayuka Kita, Ikumi Goya,Tomoka Imamura, 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

Trackingβ=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Low gain Avalanche Diode (LGAD)• Low gain Avalanche Diode (LGAD)– General n+-in-p type sensor with p+ gain layer under n+ implant
to make higher Electric Field → Good timing resolution.
– 30ps timing resolution achieved already in 2015.
beam– Next development• Finer electrode separation for spatial resolution• Radiation tolerance

Measure time difference

Signal drivers : Gain Holesn+ - eee--h--e- eeee--h--eh-hh-hehh++
pe-hhhhehhee- h hehp+Electric field

24th June, 2022

TCHoU member meeting3

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

Al

n++

n+

n+

p++

p++

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

e--SiO2

n+n+

p++

p++

hn++

Low fill factor

hhp+

AlAC-LGAD
DC elecn++

SiO2

Poly-Sin++n++

AC elec-eee- - +e- ee-e-- - - eehn-hhhhhe hhe ehh ehhhh ph++he-n++eee-hhh100% fill factor expected
But need to check Cross-talkp+ doping concentration– Uniform gain layer with AC-Coupled electrode. 100% fill factor. Signal shared on neighboring electrodes.
Parameter space for doping concentration
Radiation tolerance
Low Vgain

p+24th June, 2022

DCLGAD
Smaller cross talkn+ doping concentration
TCHoU member meeting4

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

Ccp

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

n+RimpRimp
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 concentrationRadiation tolerance
Low Vgain

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

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

JFY2019 Samples• JFY2019, JFY2020 AC-LGAD production

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 electrode500um500um

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

DCLGAD
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 meeting

6Signal size and crosstalk• Strip type : Signal size and Crosstalk

MPV of Pulse heightE-b
D-bC2D-a

Larger n+ resistivity→larger signal
JFY2019 JFY2020
sample sampleC2-b

Distance of signal reduce to 1/e– n+ resistivity dependence of signal size and crosstalk.
– Large n+ resistivity →Large signal & Smaller crosstalk
JFY2019
sample JFY2020
sampleLarger n+ resistivity→smaller cross talk

Normalized to C type

Normalized to A type24th June, 2022

TCHoU member meeting7

Mile stone : 80um Strip detector
Pulse height distribution
MPV 24mV

Noise rate 10-4 Efficiency 99.98%

Successfully developed
Good S/N strip detector!
Spatial resolution were tested at testbeam :20.3 ± 3.2um
assuming binary readout (@ELPH)
24th June, 2022

TCHoU member meeting8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 meeting9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 meeting

10New sample (2021 sample) : received in April 2022
Used thinner di-electric layer (Oxide layer)→ Basic electrode capacitance increased by factor of 5 !!
Pixel sensor

Cutline

Strip sensor➢ 5 times larger Ccp compared with E-b (2020)
type : E-600➢ Strip sensor which hasdifferent electrode length➢ Various of pitch
200um

150um

100um

50um
Pattern diagram
16 strips x 2

24th June, 2022

TCHoU member meeting11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 meeting12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 ch7and 10)

Electrode short in ch6 ?
7 11
6 10Analysis
Only center 2x2channels 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 meeting13

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 Apparentn+

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 meeting

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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 stripsensor→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]
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ConclusionACLGAD 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 meeting16

backup24th June, 2022

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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)
φ50um
50um

Z
24th June, 2022

TCHoU member meeting18

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 timinginformation• See more information in timingdetector workshop in 2018:https://indico.cern.ch/event/747424/timetable/#20181208

24th June, 2022

TCHoU member meeting

19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, 2022Residual 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

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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 meeting21