Improvement of timing resolution andradiation tolerance for finely segmented
AC-LGAD sensors
S. Kita, T. Imamura, K. Hara – U. Tsukuba
K. Nakamura – KEK
Acknowledgement:
Hamamatsu Photonics, ELPH & CYRIC (Tohoku U.), FNAL FTBF
US-Japan Science and Technology Cooperation Program in HEP (KN – A. Apresyan)
JSPS Kakenhi No.19H05193, 19H04393, 21H0073 and 21H01099
FJPPL (France Japan Particle Physics Laboratory)AC-LGAD : parameters to optimize
High granularity achieved by AC electrodes achieving uniform LGAD gain

• Performance evaluated ofthree sensor types
Strip (80um pitch x 1cm)Ccp (pF/mm2)

Hamamatsu Photonics:
n+ implant resistivity(W/sq)40

130 400 800 1600

✔

✔

✔

✔

120

✔

✔

240

✔

✔

600

✔

✔

80

Pixel (1x1mm active:
50,100,150,200um□)✔

4ch Pad(2x2 500um□)- w/ slits for laser- p+ implantation adjusted to Vgain<160~190V (50umt)- active thickness : 50um, 20um
- electrode gap varied slightly• Q larger for larger Ccp, Rimp
• large Rimp to suppress X-talkMeasurement system@ bench (20℃)• Beta-ray• IR laser

KATANA10(1064nm, 35ps PW, Jitter ~ 5 ps)

16-ch amp
(2-stage GALI-S66+, BW~3GHz)• Time referenceorPhotek PMT240(40mmf,Jitter<10ps)

2 sensors aligned fortiming resolution study• DAQDT5742(16ch,5GS/s)or
Waverunner8208HD(2GHz, 8ch,10GS/s)

collimatedPulse height

HV@ max V below noise increases

Max PH/trigger in on-timing region

Vop=160V=190V

Nice signal, rms noise~1.5-2.0 mV
Q larger for larger Ccp, Rimp , as expected
X-talk smaller for larger Rimp

X-talk distance@V/Vmax~1/ebut• PH(strip)<PH(pixel)• weak Ccp(strip) dependence.

Strip Pulse Height• PH(strip)<PH(pixel)• weak Ccp(strip) dependence

PH dependence on strip length
studied w/ a dedicated sample

MPV pulse height [V]X-talk ratio =(P-1+P+1)/P080um pitch
Rimp=1.6kW/sq• PH reduced by 60% by inter-strip capacitance at 10 mm, dominatingover Ccp dependence• X-talk increase with length

100 um pitch

MPV pulse height [V]Pixel Pulse Height

Strip1 mmL
80um pitch
CCP=600 pF/mm250 um pitch• PH weakly depends on the pitch• Signal seen also for 50um pitch pixel(as wirebonds are at 100um pitch, readout isnot similar to the others; we expect largersignal from TCAD)

90Sr

Including PMT jitter

Time resolution ns]

Time Resolution (β)

34.4±0.4ps(105V)
MCP-PMT240
Jitter<10ps38.4±0.4ps(185V)

2x2 pad• Time resolution is (slightly) better w/ 20um
• Not as good as FTBF measurement@70%CF

σΔT(PMT-sensor) [ns]50umtInstrumentation? Beam?
⇒ Currently testing @ FTBF

R. Heller et. al., JINST 17 P05001, 2022

laser: free from Landau effect as
Timing resolution (laser) IRcharge
deposit is uniform along depth

𝝈𝟐𝒕 = 𝝈𝟐𝒕𝒘 + 𝝈𝟐𝒋 + 𝝈𝟐𝑳

2: drift velo.
saturate
3:noise1: gain

Laser jitter included

Time-walk is small
for larger signal andCFD method…
cf: PH=50mV for β w/
strip (50um) at 180V

20um→80% CF
50um→60% CF@ best time resolution↑ IR laser(1.8um)8um slit

4chPad

Strip

20um

8.54±0.03ps @105V

10.69±0.03ps @110V

50um

9.81±0.03ps @180V

10.83±0.03ps @185V8um slit

Timing resolution contributions in β
𝝈𝟐𝒕 = 𝝈𝟐𝒕𝒘 + 𝝈𝟐𝒋 + 𝝈𝟐𝑳
50umt

20umt

𝛔𝐭𝛔𝐣

38.4ps

34.4ps

26.8ps

30.7ps𝝈𝑳27.1 ps

15.5 psmeasured tr /Stranslated to 𝝈𝒋
subtractionof above

Timing resolution deterioration
due to Landau effect is smaller
for 20 um thick sensor

Time resolution w/ laser for varied HV
tr /S calculated for tr=20%-80% of S

tr

Dependence
as expected as3/1/2023
𝒕𝒓
𝝈𝒋 =𝝈𝝈𝒋𝑺 𝒏(Vnoise)(Tjitter)measuredw/ beta (p7)9S𝝈𝒏3D TCAD - signal dependence on depth✓ 20 um thickness has smaller Landau
contribution than 50 um

5x5 100um pitch pixels

Signal shapes forcharges created atspecific depths(D = 2 to 45 um)(ns)
Pulse height

Arrival time

pulse height / rise time

tr : 20%-80% of S
CFD=50%✓ PH almost saturated for D>20 um✓ Landau fluctuation⇒signal shape deteriorated by late arrival time for D>20um

Radiation tolerance improvement – trial1
HPK is investigating to improve their (poor) radiation hardness !

HAB = Half Activated Boron
dope Boron more than required -> insufficient annealing process->Borons not in Si lattice work to suppress “acceptor removal” e.g. capture O

Samples: HGTD prototype(DC-LGAD)

non-irrad• Quite promising results• Vgain at non-irrad needs
to tune higher

6E14 n/cm2
3E15 n/cm2

Radiation tolerance improvement – trial2Compensation

Result not promising….
Not much change by two
different compensation
parameters
2.5B+1.5P
1.5B+0.55P
Initial comensation works perfect

What does this mean?

Nonirrad6e143e15

How should we understand the results?
Previous data𝑁𝐴 ∅ − 𝑁𝐷 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴 ∅ − 𝑁𝐷 (0) ∙ 𝑒 −𝐶𝐷 ∅Donor removal

If CA=CD𝑁𝐴 ∅ − 𝑁𝐷 ∅ = (𝑁𝐴 0 − 𝑁𝐷 0 ) ∙ 𝑒 −𝐶𝐴 ∅reference𝑁𝐴 ∅ = 𝑁𝐴 0 ∙ 𝑒 −𝐶𝐴∅

Reduction of effective p+
must be the same as noncompensated caseAcceptor removal

CA/CD=1.01

Conclusion• AC-LGAD sensor parameters are tuned: β signals observed forstrip sensor of 80 um pitch
pixel sensors down to 50 um pitch• Time resolution evaluated w/ β- time resolution obtained w/ IR laser is used to decompose
𝝈𝑳𝒂𝒏𝒅𝒂𝒖 and 𝝈𝒋𝒊𝒕𝒕𝒆𝒓
20um thick sensor has smaller 𝝈𝑳𝒂𝒏𝒅𝒂𝒖
more reliable estimate will be soon available from FTBF

• 3D TCAD is ready for qualitative evaluation on time resolution• HPK is investigating radiation tolerant LGAD: half-activated boron
is promising : initialUSJAPAN
trial ofMEETING
compensation was not promising
3/1/2023

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backup

TCAD3D model
5x5 Pixel

Z=0

3/1/2023

IV simulation @ -20degC

dopingconcentration

USJAPAN MEETING

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Signal size pitch dependence
Compared different pitch (50, 100, 150, 200um)
Pulse shapesimulation

measurement✓ signal size is similar to each pitches.
✓ simulation and measurement are consistent✓ signal size of 50um pitch may be ~90mV?
3/1/2023

USJAPAN MEETING

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Pixel crosstalk
Change MIP injection point to y axis

pulse height

pulse height ratio

Y0

actualmeasurement
3/1/2023✓ pulse height ratio is 1 between two electrode✓ ±30um area is <30% of xtalk
USJAPAN MEETING

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