Development status and plan for precision
timing detector(LGAD)
Koji Nakamura (KEK)
TCHoU meeting

12/28/2023

1

Recent developments
Successfully developed AC-LGAD detector with both time and spatial resolution.
Good SN ratio samples with 80um pitch strip and 100um x100um pitch pixel detector
20um active thick sensor achieved 20ps timing resolution!

Recently detailed understanding of developed device are on-going
Gain measurement by the samples w/ and w/o gain layer. 堀越君
Signal sharing study for large pitch with small electrodes. 村山君
Quantitative understanding of Charge Collection Noise by simulation. 西野君

New prototype and future development
Study of Radiation hard gain layer. 今村さん

VERTEX2023 ORAL Presentation

Readout Electronics for hybrid pixel detector 中村

Monolithic AC-LGAD detector (funding requests)

TCHoU meeting

12/28/2023

2

Operating and Planning Collider Experiment
World highest energy collider !

2011～ Large Hadron Collider (LHC experiment)
13.6TeV Proton collider
Planning ExperimentInternational Linear Collider (ILC)
Focusing on Higgs measurement (e+e-)x10 Luminosity
Approved & constructing
2029～
High Luminosity Large Hadron Collider (HL-LHC)

Electron Ion Collider (EIC)

Nuclear experimentHigh Energy LHC
Twice Energy

14TeV Proton Collider

Future Circular Collider(FCC-ee/hh)

Muon Collider

7 times Energy
100TeV Proton Collider

TCHoU meeting

12/28/2023

3

Operating and Planning Collider Experiment
World highest energy collider !

2011～ Large Hadron Collider (LHC experiment)
13.6TeV Proton collider
Planning ExperimentInternational Linear Collider (ILC)
Focusing on Higgs measurement (e+e-)x10 Luminosity
Approved & constructing
2029～
High Luminosity Large Hadron Collider (HL-LHC)

Nuclear experiment2034?
HL-LHC++High Energy LHC
Twice Energy

14TeV Proton Collider

Future Circular Collider(FCC-ee/hh)

Muon Collider

7 times Energy

Timing detector is necessary for all of these colliders
TCHoU meeting

Electron Ion Collider (EIC)

100TeV Proton Collider
12/28/2023

4

Impact for tracker with time resolution• Collider experiment gets high energy and high intensity.

→Future Tracking detector should have timing information for all hits!

• Tentative Requirement– 30ps timing resolution &~o(10)um spatial resolution– (hadron collider) ~o(1016)neq/cm2 radiation tolerance

4D tracking！

Particle identification
β=1

β = 0.95

150ps difference at R=1m
Solve pileup hits in an event
TCHoU meeting

Mass spectrum for new particle

K+ π+ separation

β measurement to obtain mass
e.g. Mass measurementfor Long lived chargeno
12/28/2023

5

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 very
high Electric Field at the surface.
→ Good timing resolution.
30ps timing resolution achieved already in 2015.
Signal drivers : Gain Holes-- - n+ - eee--h
eeh
h
e
-h
----ehee-h hehhhhheh
p++
h
e
e- h
e
e- h hGain measurement :Gain=26.7@ best timing resolutionp-Electric field
TCHoU meeting

12/28/2023

6

Charge Collection Noise (Landau Noise)
For Minimum Ionization Particle (MIP), charge deposition is not
uniform depth profile.

Non-Uniform charge deposition
Geant4 simulation

This effect makes timing resolution get worse.
The slower turn on for charge at deep region. (the thinner sensor the better)
Signal increase by depth but saturated at some point (25um in simulation)

TCAD simulation

𝐼𝑖𝑛𝑑 = ෍ 𝒒𝒊 𝑣Ԧ𝑑𝑟𝑖𝑓𝑡,𝑖 ∙ 𝐸𝑤,𝑖𝑖Thinner active thickness will help to reduce the effect50um thick sensor : ~30ps CCN → 35ps in actual device achieved.
20um thick sensor : ~15ps CCN → 20ps in actual device achieved.
➔10um thick sensor?
Smaller signal size (worse jitter) but better CCN.
TCHoU meeting

12/28/2023

7

Radiation tolerance of LGAD detector
Interstitial Boron
Like normal silicon device
Bulk damage (NIEL) : Si lattice damage

Substitutional Boron

Surface damage (TID) : charge up at SiO2-Si

In addition ”Acceptor Removal”
p+ in Gain layer reduced

Acceptor removal (low p+ concentration) introduce weaker field :→ Need higher voltage to keep high electric field at gain layer

P+ doping concentration measured by Bulk C

Lower p+ doping
After NIEL
1.5e15neq/cm2

TCHoU meeting

12/28/2023

8

The issue is :Why “Acceptor removal” is an issue?

Active shallow acceptors are no longer active by defect.
Increase gain voltage by fluence.

Non-irrad(-20oC conv.)

Possible maximum operation voltage
Single Event Burnout (SEB) happens if MIP particle deposited
relatively high(~10MeV) energy at high electric field region.

1e14neq/cm2(-20oC)

5e14neq/cm2(-20oC)

Non-irrad (20oC)

This happened only “>12V/um average E field” independently
by the gain layer concentration or radiation fluence.

Single Event Burnout

TCHoU meeting

12/28/2023

9

New idea for improvement of Radiation Tolerance?
Protection of p+ gain layer is a key point to reduce Acceptor removal-- - n+ - eee--hehehhe- -e-hee-h hehhhhheh
p++
h
e
e- h
e
e- h hNew ideas
Carbon annealing (confirmed by FBK)
Improvement is just a factor of 2 or so…

Compensation method
Add Boron + Phosphorus

Electric fieldIf acceptor removal is smaller than donner removal this method should work!

Partially activated Boron (PAB)
Large number of Bi at the beginning to clean up Oi

TCHoU meeting

12/28/202310p-Interstitial Boron

Carbon annealing
ATLAS HGTD people studied a lot about carbon doping on p+ layer

Substitutional Boron

Sensors with Carbon survive up to 2e15neq/cm2 : Vop can be below 550V
~300V lower Vop after 2e15neq/cm2 irradiation.
HPK don’t process carbon dope so far. (→now trying with us though)

TCHoU meeting

Carbon annealing

12/28/2023

11

Compensation method

Compensation

Both Boron(p+) and Phosphorus(n+) are doped.

p+

Due to the mass difference of Boron and Phosphorus, depth
profile of p+ and n+ are slightly different. (effective dope is not
simple Gaussian like depth profile)n+=Effective p+

NormalOperating with effective p+ (difference of p+ and n+)Compensation
Dopingdepth

It should work if donor removal is faster than acceptor removal-

Same effective p+

Slower decrease of eff. p+?

Donor removal / Acceptor removal

decrease ｐ

Decrease both ｐ and ｎ
Effective Dopen+ dope elec.
n+ dope gainp+ dope gain

HPK could successfully produced working LGAD
with a few types of compensation parameters.
Performed a couple of Irradiation Campaign at CYRIC
1B (reference), 1.5B+0.55P, 2.5B+1.5P, 5B+4.05P, 10B+9.2P
B : Boron
P : Phosphorus

Difficulty of
doping profile :Depth

TCHoU meeting

12/28/2023

12

Compensation results

Non-irrad

6 x 1014
3 x 1015

Tested different compensation ratio
1B (reference)
1.5B+0.55P : No visible improvement
2.5B+1.5P : No visible improvement
5B+4.05P : See slight improvement (~50V)

10B+9.2P : No significant signal observed

What does this mean?

2.5B+1.5P
1.5B+0.55P
5B+4.05P

TCHoU meeting

12/28/2023

13

Ref.

Compensation results

Non-irrad

6 x 1014
3 x 1015

Tested different compensation ratio
1B (reference)
1.5B+0.55P : No visible improvement
2.5B+1.5P : No visible improvement
5B+4.05P : See slight improvement (~50V)

10B+9.2P : No significant signal observed

What does this mean?
Small compensation doesn’t work, because….
→ acceptor and donor removal roughly the same.

2.5B+1.5P
1.5B+0.55P
5B+4.05P

TCHoU meeting

12/28/2023

14

Ref.

Compensation results

Non-irrad

6 x 1014
3 x 1015

Tested different compensation ratio
1B (reference)
1.5B+0.55P : No visible improvement
2.5B+1.5P : No visible improvement
5B+4.05P : See slight improvement (~50V)

10B+9.2P : No significant signal observed

What does this mean?
Small compensation doesn’t work, because….
→ acceptor and donor removal roughly the same.

Large Compensation works, because…

2.5B+1.5P
1.5B+0.55P
5B+4.05P→ larger doping concentration have smaller acceptor removal

TCHoU meeting

12/28/2023

15

Ref.

Compensation results

Non-irrad

6 x 1014
3 x 1015

Tested different compensation ratio
1B (reference)
1.5B+0.55P : No visible improvement
2.5B+1.5P : No visible improvement
5B+4.05P : See slight improvement (~50V)

10B+9.2P : No significant signal observed

What does this mean?
Small compensation doesn’t work, because….
→ acceptor and donor removal roughly the same.

Large Compensation works, because…

2.5B+1.5P
1.5B+0.55P
5B+4.05P→ larger doping concentration have smaller acceptor removal

However larger compensation have risk of reduction of signal size
→ larger implantation makes smaller signal size

TCHoU meeting

12/28/2023

16

Ref.

Compensation results

Non-irrad

6 x 1014
3 x 1015

Tested different compensation ratio
1B (reference)
1.5B+0.55P : No visible improvement
2.5B+1.5P : No visible improvement
5B+4.05P : See slight improvement (~50V)

10B+9.2P : No significant signal observed

What does this mean?
Small compensation doesn’t work, because….
→ acceptor and donor removal roughly the same.

Large Compensation works, because…

2.5B+1.5P
1.5B+0.55P
5B+4.05P→ larger doping concentration have smaller acceptor removal

However larger compensation have risk of reduction of signal size
→ larger implantation makes smaller signal size

TCHoU meeting

We have new compensation sample with Carbon→ Shipped to JSI for irradiation.

12/28/2023

17

Ref.

Partially-Activated Boron

Interstitial Boron

If non-activated Boron are remaining:

Probably Oi is cleaned up by Bi+Oi->BiOi process.

Doped larger Boron but baked with lower temperature not Substitutional Boronto activate all Boron. (i.e. lots of Bi with some Bs)
First prototype shows very low Vbd before irradiation. (i.e.
too much active Bs) : x2.5 Boron doped, baked at 500oC
No signal observed.

Partially activated Bolons (PAB)

PAB2022
1B+1PAB

1B+0.5PAB

Partial Activate

NormalSecond prototype : 1B completely baked. Dope additional 0.5
or 1 Boron without baking. (i.e. 1B+0.5PAB, 1B+1PAB)

Bs
Bs
Bi

Bs
Bi
BiO

Bs
Bi
BiO

Increase Bi byradiation damage

Bs

In-Active Boron
clean up O in the beginning

Bi
BiO

Donnor level

Not increase
donnor level defect

S.Oosterhoff et. al. Solid-State Electronics, 28(5) 1985

TCHoU meeting

12/28/2023

18

All different type of PAB samples don’t show significant improvement.
May be assumption was wrong?
Recently observed very high Oxygen contamination in the Epi layer by SIMS.
Not enough Non-Active Boron?
Does this work for the wafers with smaller Oxygen contamination?

Non-irrad

What we expected

As a results of PAB samples :Reality

Partially-Activated Boron results

Bs

Bs

Bi
BiO

Bi
BiO

Bs

Bs
BiO

BiO
OxygenOxygen6 x 1014

3 x 1015

TCHoU meeting

12/28/2023

19

Readout Electronics
Various ASIC developed for ATLAS/CMS/EIC detector(i.e. ALTIROC/ETROC/EICROC)

t
t

B

A

50% threshold
50% thresholddiscriminator signal for A
discriminator signal for Bt

Low noise pre-amplifier and Comparator with time walkcorrection is important for timing resolution.
Still signal size based time walk correction is popular method
Recently Constant Fraction Discriminator is implemented to
the ASIC by Fermilab group.

Low noise pre-amplifire

TCHoU meeting

Comparator
Time walk correction

12/28/2023

20

Si-Ge ASIC
Si-Ge Bi-CMOS ASIC : IHP 130nm process designed by Uni. Geneva
Originally the architecture developed for monolithic detector.
100um x 100um pitch 10x10 input electrodes.

There are 3ch analog readout and 1ch discriminator output.
Fulvio Martinelli et. al. Si-Ge Bi-CMOS
ASIC

Readout Setup @ Univ Geneva

GPIO Board
dev. by Uni.Ge
ALTERA FPGA

Chip Card

TCHoU meeting

Copy createdat KEK

12/28/2023

21

Si-Ge ASIC test
Use analog channels to readout signal and check by Oscillo scope.
Design issue : input resistor located under WB pad →short in very high probability…
Only one channel connected to Discriminator output is working!

X

Differential discriminator signal has been observed.
Will try to solve WB issue.

analog analog
analog Discri
Resistance
TCHoU meeting

Capacitance

12/28/2023

22

Conclusion & Future
ACLGAD with 80um pitch strip sensor
Good S/N ratio : 99.98% at 1e-4 noise rate
ACLGAD with 100um x 100um pixel sensor
Larger signal than strip sensor!!

Large prototype
20mm x 20mm sensor flip-chipped to
ITkpix chip. → Gain Uniformity

Better timing resolution
Need 10um thick AC-LGAD

20um thick ACLGAD successfully developed
We achieved ~20ps level time resolution!
→ Need to test pixelated LGAD

LGAD detector with Radiation tolerance
Tested Compensation and Partially activated
Boron : both are not promising→Next Compensation with carbon
TCHoU meeting

Small signal → Low noise ASIC development
Monolithick AC-LGAD

Hybrid AC-LGAD• Low material (for e+e-)• Fast production rate.
• No bonding Capacitance.

• Adapt high speed output• Good Radiation hardness

12/28/2023

23

Conclusion & Future
ACLGAD with 80um pitch strip sensor
Good S/N ratio : 99.98% at 1e-4 noise rate
ACLGAD with 100um x 100um pixel sensor
Larger signal than strip sensor!!

Large prototype
20mm x 20mm sensor flip-chipped to
ITkpix chip. → Gain Uniformity

Better timing resolution
Need 10um thick AC-LGAD

20um thick ACLGAD successfully developed
We achieved ~20ps level time resolution!
→ Need to test pixelated LGAD

LGAD detector with Radiation tolerance
Tested Compensation and Partially activated
Boron : both are not promising→Next Compensation with carbon
TCHoU meeting

Small signal → Low noise ASIC development
Monolithick AC-LGAD

Hybrid AC-LGAD• Low material (for e+e-)• Fast production rate.
• No bonding Capacitance.

• Adapt high speed output• Good Radiation hardness

SOI monolithic AC-LGAD
12/28/2023

24

backupTCHoU meeting

12/28/2023

25

How to improve the timing resolution?
Two reasons which make worse timing resoulution :1. Time walktA

Solution:
The effect will be negligibleusing constant fraction thr.

thresholdtBtt

discriminator signal for A

A

discriminator signal for B

2. Time jitter
tr

S

𝒕

discriminator signal for Bt

This is a matter of arrival time definition.

𝜎𝑛
𝜎𝑛
𝑡𝑟
𝜎𝑗 =
=
=
𝑆
𝑆
𝑑𝑉
𝑡𝑟
𝜎𝑛
𝑑𝑡

Slope of vol.
𝝈𝒏Size of signal
Ramping time

discriminator signal for At

Different arrival time
for small and large signals

B

50% threshold
50% threshold

Size of noise𝝈𝒋

Arrival time is randomlychange by noise.

Solution :To make smaller jitter
1. Smaller noise
2. Larger signal
3. Faster ramping time

Faster signal turn on and good S/N ratio
should be the key to improve timing resolution
TCHoU meeting

12/28/2023

26

Two approach
Readout ASIC (amplifier) with smaller noise
3D detector with CMOS ASIC
Time Spot
RD53 ASIC (28nm)

Monolithic detector with Si-Ge BiCMOS
Monolith (Univ. of Geneva) by IHPSize of noise

𝜎𝑛
𝜎𝑛
𝑡𝑟
𝜎𝑗 =
=
=
𝑆
𝑆
𝑑𝑉
𝑡𝑟
𝜎𝑛
𝑑𝑡
Slope of vol.

Size of signal
Ramping time

Making sensor with larger signal and faster turn on
Low Gain Avalanche Diode (LGAD)

These two approaches may realize at the same time.
TCHoU meeting

12/28/2023

27

Timing resolution of LGAD sensor full picture2
𝜎𝑡2 = 𝜎𝑡𝑤
+ 𝜎𝑗2 + 𝜎𝐿2

𝜎𝑡𝑤 :Time walk𝜎𝑗 : Jitter (electronics)

𝜎𝐿 : Charge collection noise
Charge Collection noise :50um thick sensor : ~30ps timing resolution
20um thick sensor : ~15ps timing resolution
Thinner sensor should have better timing resolution.
TCHoU meeting

𝜎𝑛
𝜎𝑛
𝑡𝑟
𝜎𝑗 =
=
=
𝑆
𝑆
𝑑𝑉
𝑡𝑟
𝜎𝑛
𝑑𝑡

S : pulse height
σn : Noisetr : rise time

Pros and Cons of Low Gain Avalanche Detector• Pros• LGAD have gain : x35 times larger signal size
• Should be a lot better jitter.
• Having slightly faster turn on (To be confirmed)• Cons• LGAD have Charge Collection noise• Thinner sensor have smaller noise• But thinner sensor have smaller signal• Finally important point is jitter of ASIC i.e. 𝜎𝑛• If smaller 𝜎𝑛 possible, 10um thick LGAD with
10ps resolution may be possible?
12/28/2023

28

Spatial resolution of LGAD
Segmented LGAD :To have spatial resolution, strip sensors has beenprocessed.

Need Junction termination extension(JTE) and p-stop
structure to have individual gain layer →Low fill factor(20% for 80um strip)

TCHoU meeting

Al SiO2

Normal-LGAD
n++

n+
p+

--

ne+- --eee-ehh-heh-e-h n+eee- - e-h- h h
p-+ehhhhhhe hh p+
e

n+
p+

JTE

ee-

eh

n+
p+

n+
p+

Low fill factor

h

h

p+

12/28/2023

29

n++

Spatial resolution of LGAD
Segmented LGAD :To have spatial resolution, strip sensors has beenprocessed.

Al SiO2

Normal-LGAD
n++Need Junction termination extension(JTE) and p-stop
structure to have individual gain layer →Low fill factor(20% for 80um strip)

n+
p+

--

ne+- --eee-ehh-heh-e-h n+eee- - e-h- h h
p-+ehhhhhhe hh p+
e

n+
p+

JTE

ee-

e-

n+
p+

n+
p+

n++

Low fill factor

h

h

h

p+

Uniform gain layer with AC-Coupled electrode.
(AC-LGAD)
Signal shared on neighboring electrodes.

Al

AC-LGADIn principle, 100% fill factor.

DC elecn++

SiO2

AC elec-eee- - e- ee-e--- - eeh-hhh-hhe hh
e ehhhhehe- h h hn++Need optimization of n+ resistivity

eee-

n+

n++

n++

p+

h

h

h

P-

TCHoU meeting

12/28/2023

30

AC-LGAD collaboration
Collaboration for EICROCEICROC
28nm ATLAS ASIC

Bi-CMOS ASIC
Si-Ge BiCMOS Monistic

HGTD ASIC

AC-LGAD sensor

collaboration

collaboration
AC-LGAD sensor

collaboration

collaboration
Bi-CMOS ASIC for EIC

HGTD (ATLAS LGAD)

Will focus on HPK AC-LGAD in this seminar
TCHoU meeting

Sensor Development
ASIC Development
12/28/2023

31

AC-LGAD sensors• Read out principle of AC-LGAD
CinputCinputCint

Ccp

Charge split : Impedance ratio

CinputCint

Ccp

Assuming ZCbulk,Zcint>>ZCcp…

Ccp
n+

Rimp

Rimp
signal readoutcrosstalk/sharing

Rimp

p++

Rimp

𝑄=

𝑍𝑅𝑖𝑚𝑝
𝑍𝑅𝑖𝑚𝑝 + 𝑍𝐶𝑐𝑝

𝑄0

Amount of produced charge:Q0
Readout Charge :Q

Cbulk• Additional cross talk is expected due to the inter electrode capacitance Cint
– Amount of cross talk may also depend on input capacitance on the electronics.
– Effect must be understood → Sensor with smaller Cint should be important
TCHoU meeting

12/28/2023

32

How small electrode could we achieve?
Used thinner di-electric layer (Oxide layer)→ Electrode capacitance increased by factor of 5 !!
Pixel sensor➢ Various of pitch
200um

150um

100um

50um

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

E120

E240

E600

400

C120

C240

C600

50um pitch electrode sensor has not been yet tested
due to difficulty of wire bonding.

Ccp [pF/mm2]
TCHoU meeting

12/28/2023

33

• 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

Signal MPV [V]– 100/150/200um pitches are compared.

Signal size comparison by Ccp/Rimp
150um pixel

Rimp [𝛀/□]How small electrode could we achieve?
1600

E120

E240

E600

400

C120

C240

C600
Ccp [pF/mm2]

Pulse height comparison by pixel pitches
100 um pitch pixel

Noise

Signal MPV: 122.4±5.5mV

Ccp [pF/mm2]
TCHoU meeting

Successfully developed
Good S/N 100um pitch
pixel detector!
12/28/2023

34

Measurement of timing resolution
Measurement of timing resolution for fine electrode sensors are challenging.
Taking time if we use two layer coincidence
Photek PMT 240 (90Sr source)~9ps timing resolution

Infra-Red (pico sec) laser
5ps timing jitter

Timing resolution2
𝜎𝑡2 = 𝜎𝑡𝑤
+ 𝜎𝑗2 + 𝜎𝐿2

𝜎𝑡𝑤 :Time walk𝜎𝑗 : Jitter (electronics) MIP IR
𝜎𝐿 : Landau noise

MIP• Photek PMT240 (MCP-PMT)– Mes. Of timing resolution to MIP– 9ps PMT240 resolution (reference)– Don’t know injecting position.

• Infra-red (pico sec) laser– Known injecting position(Size：1.8um)– 5ps jitter– No landau noise

TCHoU meeting

12/28/2023

35

Timing resolution results• Timing resolution measurement by two methods
Infra-red laser (Edep~ a few times MIP)
𝝈𝟐𝒕 = 𝝈𝟐𝒕𝒘 + 𝝈𝟐𝒋 + 𝝈𝟐𝑳

𝜎𝑛
𝜎𝑛
𝑡𝑟
𝜎𝑗 =
=
=
𝑆
𝑆
𝑑𝑉
𝑡𝑟
𝜎𝑛
𝑑𝑡

Beta-ray measurement
𝝈𝟐𝒕 = 𝝈𝟐𝒕𝒘 + 𝝈𝟐𝒋 + 𝝈𝟐𝑳

By laser measurement,
calculated noise for each Volt.
Calculate jitter for MIP meas.
Evaluated Landau term.

10ps timing resolution!!

31.2±0.4ps@105V

38.8±0.4ps@190V

20um sensor have smaller landau term in timing resolution.
Scattering effect of beta-ray measurement should be affected → Testbeam measurement
TCHoU meeting

12/28/2023

36

Timing resolution measurement at testbeam

Results for 2x2 pad sensors with 50um, 30um and 20um thickness
Signal size (amplitude) is smaller in thinner sensors.

20um thick sensor has the best timing resolution : ~20ps
Uniform timing resolution at the gap region as well.

~35ps

~25ps
~20ps

TCHoU meeting

12/28/2023

37

Two approaches to have good spatial resolution
Fine pitch electrode approach
For High occupancy experiment like hadron collider.
Reduce crosstalk (charge sharing)High n+ implant resistivity

Pros. : smaller occupancy and smaller data size like
digital readout

Cons. : Limitation of spatial resolution by electrodesize. # of channels get huge…

• Charge sharing approach– For lepton collider or other low occupancy
colliders.
– Reconstruct particle position using charge sharing(charge fraction to next channels)• Relatively low n+ implant resistivity– Pros. : Very good spatial resolution if highresolution ADC used.
– Cons. : Smaller signal size. Need high resolution
ADC.

Fine pitch strip with narrow Al(to reduce inter strip cap.)

HPK strip/pixel approach
TCHoU meeting

HPK pad and BNL sensor approach
12/28/2023

38

Is Strip type electrode possible?
For collider experiments, outer layers should use Strip type electrode to reduce readout channels.
However, the signal size is much smaller than pixel sensors(c.f.)

80um pitch Strip

100 um pitch pixel

Noise

Signal MPV: 122.4±5.5mV
MPV 34mV

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

TCHoU meeting

Why so small signal?
How much effect of interstrip capacitance?
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 ofsignal readout.
12/28/2023

39

Inter strip capacitance (Cint) effectlong strip

short strip
Signal size [V]Strip sensor with cut line
CutlineEffect of interstrip capacitance

reduced by 60%➢ Strip sensor which has different electrodelength (to study inter electrode cap.)

Strip length [mm]Pattern diagram
16 strips x 2

TCHoU meeting

Where signal disappeared?

12/28/2023

40

Inter strip capacitance (Cint) effectlong strip

short strip
Signal size [V]Strip sensor with cut line

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

Pattern diagram

Crosstalk size
both neighbors/leading

CutlineEffect of interstrip capacitance

reduced by 60%
Where signal disappeared?
→ Cross talk via Cint

Strip length [mm]16 strips x 2

Strip length [mm]TCHoU meeting

12/28/2023

41

Removal of Dopant

Donor removal

Active dopant will reduce by exponential function by fluence (Φ)

𝑁𝐴 (∅) = 𝑁𝐴 (0) ∙ 𝑒 −𝐶𝐴 ∅𝑁𝐷 (∅) = 𝑁𝐷 (0) ∙ 𝑒 −𝐶𝐷 ∅Any idea of CA and CD from past measurement?

Acceptor removal

CD=2.4 x 10-13 cm2 for phosphorus and CA=2.0 x 10-13 cm2 for boron
in very high resistivity p-type and n-type materials (>1kΩcm).
→ How about lower resistivity ? (like 1 x 1016 cm-3 p+ concentration)

Compensated effective p+ gain layer will change by following formula𝑁𝐴 ∅ − 𝑁𝐷 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴 ∅ − 𝑁𝐷 (0) ∙ 𝑒 −𝐶𝐷 ∅TCHoU meeting

12/28/2023

42

How to understand results?

If CA>CD ? If CA<CD ?

If CA=CD ?
𝑁𝐴 ∅ − 𝑁𝐷 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴 ∅ − 𝑁𝐷 (0) ∙ 𝑒 −𝐶𝐷 ∅𝑁𝐴 ∅ − 𝑁𝐷 ∅ = (𝑁𝐴 0 − 𝑁𝐷 0 ) ∙ 𝑒 −𝐶𝐴 ∅reference

Shorter life time

CA/CD=1.5

𝑁𝐴 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴∅
Slightly longer life time
Reduction of effective p+ must be
Not detreated performance until some point the same as non-compensated case
CA/CD=0.8

CA/CD=1.01

Most likely…
This is the case
If this is true,compensation is not promising.

TCHoU meeting

12/28/2023

43

Radiation tolerance results of Compensation LGAD
Three different conditions are compared
Boron and Phosphorus doping

non-irrad

6E14 n/cm2

2.5B+1.5P

3E15 n/cm2

1.5B+0.55P
1B (reference)

3 different fluence points (non-irrad, 6e14, 3e15 neq/cm2)

Result shows not very promising
All three samples show very similar IV.
This probably means CA=CD
𝑁𝐴 ∅ − 𝑁𝐷 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴 ∅ − 𝑁𝐷 (0) ∙ 𝑒 −𝐶𝐷 ∅𝑁𝐴 ∅ − 𝑁𝐷 ∅ = (𝑁𝐴 0 − 𝑁𝐷 0 ) ∙ 𝑒 −𝐶𝐴 ∅reference𝑁𝐴 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴∅
Reduction of effective p+ must be the sameas non-compensated case
TCHoU meeting

Next step:
Compensation with Carbon dope should be promising
Carbon effect :Reduce Accepter removal
Accelerate Donner removal
12/28/2023

44

Idea for monolithic AC-LGAD detector

TCHoU meeting

12/28/2023

45