新型LGAD検出器が切り拓く次世代飛跡検出器
Koji Nakamrua, Sayuka Kita^A^, Tatsuki Ueda^A^, Ikumi Goya^A^,
Kazuhiko Hara^A^
KEK, U.Tsukuba^A^
29nd Mar, 2021

TCHoU symposium1

背景
単一粒子に対して30psの時間分解能は光の速度で1cmの距離に相当する分解能！
位置分解能の改良

電極の透明化
他分野への応用

High Energy Collider

TOF PET

time: t1
511keV γ-ray
cancer

検出効率が低い
単純ではなさそう
Pixel size

Hit information

w/ timing info.

511keV γ-ray
time : t0

可視光や赤外線に感度があるとイメージング等に応用可能か？
高速光イメージング
バイオサイエンス

29nd Mar, 2021

TCHoU symposium2

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.
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

29nd Mar, 2021

TCHoU symposium

3What we need for Hadron Collider?
• High Luminosity LHC detector • Expected radiation level for 4000fb-1– Non Ionizing Energy Loss (NIEL):ITK upgrade detector• 3rd layer: 2.8x1015 neq /cm2 1st layer : 2.6x1016neq/cm2– Total Ionizing Dose (TID) :Strip• 3rd layer : 1.6MGy 1st layer : 19.8MGy
Could replace detector
at the middle of runs.

Pixel
η=4.0

• Strip : ~75.5um pitch• Pixel : 50um x 50um pitch

Survive upto 1e16neq/cm2?

Is this granularity possible?

If we have LGAD sensor with this granularity and radiation tolerance, all tracker can be replaced by LGAD!
29nd Mar, 2021

TCHoU symposium4高い位置分解能と時間分解能を併せ持つには• First prototype with 80um pitch strip (DC-LGAD)→Only 20% of active area has gain
• Common gain layer with AC-coupled readout (AC-LGAD) → Uniform gain expected!
DC-LGAD
n++

Aln+

n+

p++

p++

--+
- e ne+- eee-ehh
hhe hh nee--e- h- e- h- he++p hhhhhe hh p++
e-eee--SiO2

n+n+

p++

p++

hn++

Low fill factorhhp+

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– Cross talk expected in the n+ implant → Increase resistivity of n+ implantParameter space for doping concentrationp+

29nd Mar, 2021

Lower Operation Voltage
Radiation tolerance

DCLGAD
Smaller cross talkn+ doping concentration
TCHoU symposium5LGAD検出器の課題と応用• コライダー用の飛跡検出器

Pad型検出器– 電極の細分化

ch1• 80umピッチのストリップ型• 50x50umピッチのピクセル型• 信号の大きさとクロストークを抑えることが課題– 放射線耐性 →高エネルギー実験用• 5e15 1MeV中性子/cm2程度の放射線照射で時間分解能が30ps->50psほどに悪化する。

• 他分野への応用

Pulse height

Positive overshootfor highest signal only

Typical Event :Particle through ch2
Detected cross talk in ch0,1,3

ストリップタイプの波高分布
MPV– MIP粒子に対して30psの時間分解能の検出器の高エネルギー実験以外の応用？
– 可視光に対しても応答のある検出器に改良
29nd Mar, 2021

ch0ch3ch2

TCHoU symposium

21mV

信号の大きさが小さい…
6細密電極 ： 信号の大きさの理解と改善• Crosstalk and Readout charge
Assuming Zcbulk>>ZCcp…𝑍

𝑄=

𝑅𝑖𝑚𝑝

𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝

Equivalent Circuit

Ccp Q Ccp

𝑄0– Generated charge Q0– Readout charge Q

Rimp

Rimp

Q0 QxtalkRimp

n+p++

Pad type

Strip type
500um

45um

9880umSignalMPV = 62 mVx3

MPV = 21mV

JPS : 12aT3-7 Sayuka Kita (Tsukuba)
29nd Mar, 2021

Rimp

Cbulk
500um

To have larger signal
Larger Ccp
Larger Rimp

Ccp

TCHoU symposium

7Parameter space for doping concentration
C-3

B-3

JFY2019 Samples
New Samples (26th Mar)

A-3

Coupling capacitanceRadiation tolerance

Nominal x 1

Nominal x 1.5

Ax10

C-2

C-2-b

Ax20

D-aD-b

C-2bC-2

B-2

D-a/b

DCLGAD

Smaller cross talk
Larger signal

E-b

C-1

A-2

B-1

n+resistivity

p+ doping concentration

New samples (4 types of sensors)

Ax40

E-b

A-1

Thinner SiO2Ccp
n+x 1/2
29nd Mar, 2021

x 1/2

x 1/10n+ doping concentration
TCHoU symposium

Rimp

Rimpp

++

Cbulk
8

細密電極 ： 信号の大きさの理解と改善• Crosstalk and Readout charge

Ccp Q Ccp

Assuming Zcbulk>>ZCcp…𝑍

𝑄=

Equivalent Circuit

𝑅𝑖𝑚𝑝

𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝

𝑄0Rimp• New strip prototype with :MPVSample in JFY2020
MPV：38mV

21mV

Strip

improvement

Q0 QxtalkRimp

n+p++

Rimp

Cbulk

– 4x higher n+ resistivity– 1.5x larger coupling capacitanceSample in JFY2019

Rimp

Ccp

1. Set a threshold with 99% efficiency,
noise rate is less than 1e-3.
2. Cross talk distance is 87.4um ~ 1 strip.

Strip
Signal size & position resolution isgood enough for tracking detector.

29nd Mar, 2021

TCHoU symposium

9細密電極 ： 信号の大きさの理解と改善• 信号とクロストークの大きさのn+インプラント抵抗
値依存性を確認– n+インプラント抵抗が大→信号が大、クロストークが小E-b
D-b
C2C2-b29nd Mar, 2021

D-a

TCHoU symposium

10New challenge ! Pixel detector• 50um x 50um pitchのピクセルセンサーを制作– ワイヤーボンドして4x4ピクセルだけ読み出し– AC-LGAD pixelセンサーの信号を初めて観測• 大きなクロストーク(or ワイヤーボンドのショート？)• ただし、信号の大きさが小さく、S/Nが不十分

明らかに改善が必要
波高分布

S/Nが悪い29nd Mar, 2021

TCHoU symposium11

IV performance after irradiation• Irradiated sensors at CYRIC (Tohoku university) with 70MeV Proton.
• Operation/Gain voltage get higher by irradiation (almost linearly)– Current sensor does not work after 1x1015neq/cm2 fluence or more.
Max. operation VNon-irrad

Signal Size

1 x 1014 neq/cm2

5 x 1014 neq/cm2

Fluence

Signal MPV

Non-irrad35±2 mV

1x1014neq/cm2 39±1 mV
5x1014neq/cm2 30±2 mV
60V
400V

5x1014neq/cm2 may haveslight decrease of signal(But keep at least ~75%)

JPS 12aT3-8 Tatsuki Ueda (Tsukuba)
29nd Mar, 2021

TCHoU symposium

12放射線耐性の改善• P+ドープ量が高いほど放射線耐性に優れている– P+ドープ量が小さいほどGain Voltageが高い。
– 陽子線照射によってP+層のアクセプタリムーバルで見かけのドープ量が小さくなりGain Voltageが上がる。
– 耐圧を超えたときに寿命を迎える• P+ドープ量が高すぎると(特にn+濃度が低い場合)

深さ方向の広がりを小さくする
n+p++– 放射線損傷前のセンサーでGain Voltageが低すぎる(全空乏化電圧近くでbreak)
放射線損傷前改善のアイデア➢ P+ドープの深さ方向の広がりを小さくする➢ P+ドープのプロファイルを変えて解決できないか➢ 例えば二層構造
シミュレーションで検証予定
Electric field

29nd Mar, 2021

TCHoU symposiumn+p++

放射線損傷後

n+p++

n+p++

p++

p++

Electric field

浅いp+層がAccepter removal
で消える
13

Poly電極AC-LGAD• AC電極をAlではなくPoly-si(300um)にすると可ストリップ型
視光の約50%が透過(TBC)• 可視光の検出が可能

通常のAC-LGAD– 異分野への応用の幅がひろがる• パッド検出器とストリップ検出器でPoly-si電極のセンサーを製造済み• 最初のサンプルを測定 (とりあえずベータ線)
通常のAl電極 AC-LGAD

Poly-Si電極 AC-LGAD

Poly-si 電極 AC-LGAD
Poly-si

29nd Mar, 2021

TCHoU symposium

14

Poly-si電極AC-LGAD ベータ線試験• ストリップセンサー(80umピッチ)の信号とクロストークを評価– Al電極と比較するためベータ線で信号を観測• 信号の大きさはAl 電極と比較して同程度• クロストークはAl電極と比較して小さく見える。(次ページ)
Poly-Si電極

Al電極

信号の分離が悪い

29nd Mar, 2021

TCHoU symposium

15

Poly-si電極AC-LGAD ベータ線試験– Crosstalk and Readout charge
𝑄=𝑍𝑅𝑖𝑚𝑝

𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝 + 𝑍𝑅𝑠𝑡𝑟𝑖𝑝

𝑄0– 𝑍𝑅𝑠𝑡𝑟𝑖𝑝 はワイヤーボンドパッドからの距離に比例 (182Ω/um)

Wirebond近くのイベントか？

ワイヤーボンド
パッドに近い信号大
クロストーク小Threshold 0.03V

Threshold 0.08V

ワイヤーボンド
パッドから遠い信号小
クロストーク大ポリシリの抵抗値を下げる必要がある。
29nd Mar, 2021

TCHoU symposium16

p+ doping concentration

まとめParameter space for doping concentration
C-3

B-3

A-3

Radiation tolerance
C-2bC-2

B-2

New Samples (26th Mar)
• 電極の細密化– E-b typeがベスト– S/Nの良いストリップ検出器が完成– ピクセル検出器は改善が必要• 放射線耐性

D-a/b

DCLGAD

Smaller cross talk
Larger signal

E-b

A-2

JFY2019 Samples

C-1

B-1

A-1

– B-3がベスト。(ただしクロストーク大)– p+ドープ量が多いほどよい。(照射後もVopがさほど高くならない)– C-2タイプでは5e14くらいまで。
– DやEタイプはさらに耐性が弱いか…

• ポリシリ電極 (他分野応用)
x 1/2
29nd Mar, 2021

x 1/2x 1/10

n+ doping concentration
TCHoU symposium– PAD型はAl電極と同様に動作– Strip型は抵抗値を下げる必要がある
17backup

29nd Mar, 2021

TCHoU symposium

18Motivation
Higgs discovery and measurement by LHC experiment
New era!

• “Vacuum”– “Vacuum” is nothing? Filled by Higgs boson?
– How Higgs boson/field condensed to the “Vacuum”?
– Need to determine/observe the shape of Higgs Potential.
→Observe/measure “Higgs self coupling”.
interference
HH

HtH
H

• “Dark Matter/Energy”– We only know 4%. What’s the others?
– Beyond the Standard Model?
29nd Mar, 2021

TCHoU symposium

19

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 2027

– 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

Z29nd Mar, 2021

TCHoU symposium

20Future Semi-conductor Tracking Detectors• Further finer pitch pixel detector → Limited by front end Electronics (min : 50x50um2)– In addition to spatial resolution, Timing resolution helps!
→New generation of 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

Mass spectrum for new particle

Tracking

β=1

β = 0.95

150ps difference at R=1m
Solve pileup hits in an event
29nd Mar, 2021

K+ π+ separation
TCHoU symposium

β measurement to obtain mass
e.g. Mass measurementfor Long lived chargeno
21

First AC-LGAD by HPK
Pad type sensor (4x 500umx500um) Pixel type sensor (14x14 50umx50um)
Bias ring

Bias ring
Pixel pitch

DC ring

50µm

500µm

DC ring

50µm

20µm

40µm

Wire bondpad

GNDed DC ring via Poly-si→ To remove charge in n+

42µm

Poly-si 30µm
resistor

Poly-si
resistor

Strip type sensor (16x 80um pitch)

Strip pitch

45µm

80µm

n+ and p+ doping concentration

Poly-si
resistorN+ doping concentration / resistivity

p+ doping

Bias ringDC ring

Varied Al size (AC coupling capacitance)
Pixel : 42/38/34/30 um width/length
Strip : 45/40/35/30 um widthC(Ax10 resistivity)
3 (high)P+ dopingconcentration

B(Ax3.3 resistivity)

A (~DC-LGAD)

B-3

A-3
A-2

2 (mid)C-2

B-2

1 (low)

C-1

B-1

40µm

n+ doping
29nd Mar, 2021

TCHoU symposium

22Measurement setup and signal observation• Lab setup– Designed high speed amplifier board.
– Signal recorded by CAEN DT5742 digitizer– 90Sr β lay source– Triggered by Scintillator (MPPC readout)

KEK 16 ch Discrete Amp.

Pad Sensor

ch1ch2ch0 ch3BOX
LVHV90Sr

CollimatorSensor
Amp. boardScinti.

digitizerTrigger
CAEN DT5742
Desktop Digitizer
5GS/s 10bit
12bit ADC 2V full range

Scintillator /29nd Mar, 2021

TCHoU symposium

Sample with higher n+ resistivity (C-2)
ch1ch0ch3ch2
Pulse height

Positive overshootfor highest signal only

Typical Event :Particle through ch2
Detected cross talk in ch0,1,3First time : AC-LGAD signal
observed with small crosstalk23

Radiation Effect in LGAD sensor•The same as general n+-in-p sensor

AlAC-LGADDC elec

– Bulk damage (NIEL) : Lattice defect.
– Surface damage(TID) : Positive charge @ SiO2-Sin++

SiO2

Poly-Sin++n++

AC elec-eee- - +e- ee-e-- - - eehn-hhhhhe hhe ehh ehhhh ph++he-n++ee-• In addition to this ”Accepter Removal”

e-hhhp+– p+ (Boron) accepter change to doner levelp+ doping profile measured by bulk capacitance

What happened if p+ dope reduced by accepter removal?

Reduce p+ doping concentration
Current condition

non-irrad
non-irrad
non-irrad

Higher Gain (operation) Voltage

Improvement
After radiation damage1.5e15neq/cm2

Lower p+ doping
Operation Voltage > Max voltage(~700V)End of life

29nd Mar, 2021

TCHoU symposium

24Summary and plan
HPK Fabrication
JPY2019

JPY2020

Nov. : First AC-LGAD design

Oct. : New parameters

improve

New parameterization
Reception

JPY2022

Former TCAD simulation

29nd Mar, 2021

Readout
Amplifire

Measurement of Pad and Strip sensor
Understanding Signal and crosstalkfeatureSamples
Time resolution
Radiation tolerance CYRIC irrad.

improve

Large scale ACLGAD (20mm x 20mm)

Pixel sensor & rad hardness
CYRIC irrad.

Testbeam

Testbeam

Sensor ProductionJPY2023

US Collaborators
BNL AC-LGAD
SampleComparison

Rec. in Mar

Rec. in Mar
JPY2021

KEK/Tsukuba measurement

Solder Bump bonding(SnAg bump bonding developedby ATLAS experiment)
TCHoU symposium

Feb. : Testbeam

Si-Ge
BipolarASIC
Si-Ge
BipolarASIC

25

Photo29nd Mar, 2021

TCHoU symposium

26

Leakage current vs Bias voltage

High p+ doping

High p+ doping
High p+ doping

C-2 type :– Lower operational voltage– Smaller crosstalk
29nd Mar, 2021

Variation of p+ and n+ doping concentration
N+ doping concentration / resistivity

p+ dopingBreak down (gain) voltage get lower• Higher P+ dope
• Lower N+ dope
→ Radiation trelanceC(Ax10 resistivity)
3 (high)P+ dopingconcentration

B(Ax3.3 resistivity)

A (~DC-LGAD)

B-3

A-3
A-2

2 (mid)C-2

B-2

1 (low)

C-1

B-1

n+ doping
TCHoU symposium

27How to reduce “Accepter Removal” effect?
• Study by FBK LGAD sensors.

1. Lower diffusion of Boron doping profile
2. Adding carbon (or Gallium) to p+ layer
Not simple changes… (HPK)

29nd Mar, 2021

TCHoU symposium

28Radiation Tolerance• Radiation Tolerance

将来ハドロンコライダー(FCC-hh)

Timing resolution

Current : 0.6-2 x 1015neq/cm2
Goal : 1x1016neq/cm22x1015neq/cm26x1014neq/cm230ps

Idea for improvement?
Thinner active thickness and optimized p+ doping

Fluence
29nd Mar, 2021

TCHoU symposium

29Radiation environment• Expected radiation level for 4000fb-1– Non Ionizing Energy Loss (NIEL):• 3rd layer: 2.8x1015 neq /cm2 1st layer : 2.6x1016neq/cm2– Total Ionizing Dose (TID) :• 3rd layer : 1.6MGy 1st layer : 19.8MGy29nd Mar, 2021

TCHoU symposium

Could replace detector
at the middle of runs.

30

Accepter removal

29nd Mar, 2021

TCHoU symposium

3129nd Mar, 2021

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32

Test beam in Feb 2021 @ Fermilab
Fermilab Test Beam Facility (FTBF)
120GeV proton beam
Strip Detector based Telescope : ~15um pointing resolution

Beam Telescope

Beam Telescope

Cooling Box

Amp board
29nd Mar, 2021

Readout by Ocilloscope
LeCroyWR8208HD scope
12bit, 10GSa/s, 2GHz
8 channel

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

TCHoU symposium

33Time resolution measurement @ testbeam• Used PHOTEK : MCP PMT140 as a timing reference detector– Including 5ps PMT140 time resolution (<1% effect)
Very fresh results : Obtained 30-40ps time resolution for a couple of types of sensors

C-2 : 180V
σ = 37ps

29nd Mar, 2021

B-2 : 230V
σ = 33ps

TCHoU symposium

34

Efficiency and signal sharing @ testbeam

Beam position X• Efficiency measurement for the top left pad.

– Close to 100% efficiency @ 90mV threshold– ~40mV crosstalk observed. (consistent to lab meas.)
Need more study for the reason of flat crosstalk. (inter elec. Cap?)
29nd Mar, 2021

TCHoU symposium

Beam position X

Mean amplitude [mV]Beam position X

Efficiency, 20mV threshold
Beam position Y

Efficiency, 45mV threshold
Beam position Y

Beam position Y

Efficiency, 90mV threshold35