Characterizationof Delayed Crosstalk of SiPM
Hiroyasu Tajima, Akira Okumura,
Yusuke Kuroda, Kazuhiro Furuta,
Nagoya Hidaka
Institute for Space–Earth Environmental Research
Nagoya University

16aS41-3

15pSF-11

Japan Physical Society Meeting
September 15, 2020

Photon Sensor❖ Silicon Photomultiplier is chosen as a photon sensor for many
experiments✤ Cost per channel✤ Tolerance against high rate environment✤ Photon detection efficiency✤ Reliability

Dark pulses
credit: HPK website❖ Major drawback of SiPM
✤ Optical crosstalk (OCT)✤ Gain dependence on the temperature❖ Main objective of this study✤ Suppress OCT while retaining photon detection efficiency (PDE)
Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

2 /17

Suppressing OCT with Trench❖ Optical crosstalk is caused by photons produced in primaryavalanche❖ Trench is implemented to prevent photons from crossing
cell boundary✤ Narrower trench gives better fill factor
Poly strip
resistor

Metal

NUV-SiPM

High-field region

High-field region
Cell 1NUV-HD SiPM

Cell 2Cell 1~ 4.5 µm

< 2 µmCharacterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

Cell 2Cell 3

Trenchcredit: FBK

3 /17

Suppressing OCT with Trench❖ Optical crosstalk is caused by photons produced in primaryavalanche❖ Trench is implemented to prevent photons from crossing
cell boundary✤ Narrower trench gives better fill factor
NUV-SiPM

High-field region
Cell 1

Cell 2Cell 1~ 4.5 µm

Optical Crosstalk Rate (%)

Poly
60strip
resistor

Metal

NUV-HD SiPM

5050 µm cell, 3 mm, no

High-field region

40

Cell 2Cell 330

Trench< 2 µm

75 µm cell,credit:
6 mm,FBK

20

50 µm cell, 6 mm,
10

50 µm cell, 3 mm,
00Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

1

2

3

4

5

6

7

8

9

10

Over Voltage (V)3 /17

Effect of Resin Coating on OCT❖ Thicker coating or no coating give lower crosstalk
Crosstalk Rate vs Over Voltage
25
LCT5-3050 Epoxy 100 µm #1
LCT5-3050 Epoxy 100 µm #2
LCT5-3050 Epoxy 300 µm #665
LCT5-3050 Epoxy 300 µm #666
LCT5-3050 Silicone 450 µm #965
LCT5-3050 Silicone 450 µm #966
LVR2-6050 No coating #15
LVR2-6050 No coating #14
LVR2-7050 No coating #11

Optical Crosstalk Rate (%)

20

15

100 µm300 µm450 µm10
No coating

5

0
0

2

4

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

6Over Voltage (V)

8

10

4 /17

Propagation of Crosstalk Photons❖ No coating (or very thin coating)✤ Reflected photons come back to the original cell

❖ Intermediate thickness✤ Photons reflected by the air interface may produce avalanches
in other cells❖ Very thick coating✤ Photons reflected by the air interface may get out of the device✤ Smaller device may have lower crosstalk rate

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

5 /17

Propagation of Crosstalk Photons❖ No coating (or very thin coating)✤ Reflected photons come back to the original cell

❖ Intermediate thickness✤ Photons reflected by the air interface may produce avalanches
in other cells❖ Very thick coating✤ Photons reflected by the air interface may get out of the device✤ Smaller device may have lower crosstalk rate

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

5 /17

Propagation of Crosstalk Photons❖ No coating (or very thin coating)✤ Reflected photons come back to the original cell

❖ Intermediate thickness✤ Photons reflected by the air interface may produce avalanches
in other cells❖ Very thick coating✤ Photons reflected by the air interface may get out of the device✤ Smaller device may have lower crosstalk rate

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

5 /17

Propagation of Crosstalk Photons❖ No coating (or very thin coating)✤ Reflected photons come back to the original cell

❖ Intermediate thickness✤ Photons reflected by the air interface may produce avalanches
in other cells❖ Very thick coating✤ Photons reflected by the air interface may get out of the device✤ Smaller device may have lower crosstalk rate

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

5 /17

OCT Dependence on Device/Cell Sizes❖ We have systematically investigated the OCT rate withvarying device size, cell size, and with and without coating✤ OCT rate is expected to be proportional to the number ofelectron-holes pairs (=charge) produced in an avalanche✦ proportional to a product of [cell capacitance] and [over voltage]✤ Find out propagation properties of crosstalk photons
Product ID

Device size

Cell size

Coating

Fill factor

S14520-3050VS

3 mm

50 µm

300 µm74%

S14520-3050VN

3 mm

50 µm

None

74%

S14520-3075VS

3 mm

75 µm

300 µm82%

S14520-3075VN

3 mm

75 µm

None

82%

S14520-6050VS

6 mm

50 µm

300 µm74%

S14520-6050VN

6 mm

50 µm

None

74%

S14520-6075VS

6 mm

75 µm

300 µm82%

S14520-6075VN

6 mm

75 µm

None

82%

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

6 /17

SiPM Measurement Setup at Nagoya❖ Take waveform data by digital oscilloscope
8✤ Offline data analysis❖ Light output is monitored❖ Wavelength is fixed at 405 nm
for this measurement
Pulse Generator
Tektronix AFG 3251

LED

ND filter

6

V (mV)✦ Digital filter to minimize
the effect of pile ups✦ Fit the data with multiple pulses

fiber

5
4
3
2
1
0
−1

Oscilloscope
Tektronix MSO4054B

diffuser— Raw data
— Filtered data

7

0

50

100

150

200

250

300

350

400

450

500

t (ns)

SiPM(Monitor)
ZFL-500LN-S+

collimator

SiPM (DUI or Reference)climate chamber (25°C)
Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

7 /17

SiPM Measurement Setup at Nagoya❖ Take waveform data by digital oscilloscope✤ Offline data analysis❖ Light output is monitored❖ Wavelength is fixed at 405 nm
for this measurement
Pulse Generator
Tektronix AFG 3251

LED

ND filter

fiber

2.4 ns

30
20
10
0

−10

Oscilloscope
Tektronix MSO4054B

diffuser

1.1 ns40

V (mV)✦ Digital filter to minimize
the effect of pile ups✦ Fit the data with multiple pulses

50

0

10

20

30

40

50

t (ns)

SiPM(Monitor)
ZFL-500LN-S+

collimator

SiPM (DUI or Reference)climate chamber (25°C)
Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

7 /17

PDE Measurements❖ We measure number of photons for short LED (or laser) pulses✤ Current measurement does not provide accurate PDE due tooptical crosstalk, delayed cross talk and after pulse❖ Number of photo electrons (p.e.) does not follow Poisson distribution
due to optical crosstalk✤ Probability of 0 p.e. is used to obtain the average to avoid effects of
optical crosstalk✤ Effect of dark count still need
to be taken into accountP (n) = e µ µn /n!
P (0) = e µµ = ln(P (0))
Ptrue (0) = PON (0)/POFF (0)0 p.e.

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

1 p.e.

2 p.e.

3 p.e.

8 /17

PDE vs Over Voltage❖ PDEs were measured for 2 devices for each type
❖ PDEs were measured twice for some devices❖ Measured PDEs were very consistent, which indicatesvarying light intensity is properly compensated by themonitor SiPM
Avalanche probability
PDE/(Fill factor) = PDEmax · (1Average p.e.

Averege p.e. for Monitor SiPM
0.45
0.44
0.43
0.42
0.41
0.4
0.39
0.38
0

20

40

60

80

100

120

140

160 180 200 220
Measurement number(Photon Detection Efficiency)/(Fill Factor) (%)<latexit sha1_base64="yW2He5m1fbspoYOy2EDwn/6bw9Q=">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</latexit>

exp[ Cdepth VOV /VBR ])

90
80
70
60
50

— 3 mm— 6 mm
50 µm
75 µm○ no coating

40
30
20
10
0
0

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

0.05

0.1

0.15
0.2
0.25
(Over Voltage)/(Breakdown Voltage)

9 /17

Optical Crosstalk Measurements❖ Assume 1 p.e. peak of dark signal is dominated by dark count✤ 2 p.e. peak consists of optical crosstalk from 1 p.e. and chancecoincidence of dark counts within ∆tPS (~3 ns in our setup)
Probability to have no optical crosstalkN(N(

1.5 p.e.)
Poisson probability to have no
fDC tPS= 1 (1 ROCT )eoverlapping dark count within ∆tPS
0.5 p.e.)✓◆N ( 1.5 p.e.)
ROCT = 1
1/e fDC tPS
N ( 0.5 p.e.)<latexit sha1_base64="CtKuJlq36iMZ8HPcThLvX+ECQb4=">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</latexit>N(≧0.5 p.e.)N(≧1.5 p.e.)ƒDC: Dark count rate∆tPS: Double-pulse separation time

0 p.e.

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

1 p.e.

2 p.e.

3 p.e.

10 /17

Crosstalk Rate vs. Over Voltage❖ Optical crosstalk rate should be proportional to the gain andavalanche trigger probability
Avalanche probability

0exp[ Cdepth
VOV /VBR ])ROCT /(Gain) = COCT · (1<latexit sha1_base64="Qjye2sH6LwOAvWuPOitHYqDlBnA=">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</latexit>✤ Cdepth tends to be small without resin coating

Product ID

COCT

Cdepth

S14520-3050VS

16

17

S14520-6050VS

20

14

S14520-3075VS

14

23

S14520-6075VS

18

22

S14520-3050VN

4.5

9(Optical Crosstalk Rate)/(Gain) (%/pC)✦ Avalanche seed is produced in the region where it is harder totrigger avalanche
20
18
16
14

10
8
6

S14520-6050VN

50

0.4

S14520-3075VN

3

11

2

S14520-6075VN

7

3

0
0

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

— 3 mm— 6 mm
50 µm
75 µm○ no coating

12

4

1

2

3

4

5

6

7

8
9
Over Voltage (V)

11 /17

Crosstalk Rate vs. Over Voltage❖ Optical crosstalk rate should be proportional to the gain andavalanche trigger probability
Avalanche probability

0exp[ Cdepth
VOV /VBR ])ROCT /(Gain) = COCT · (1<latexit sha1_base64="Qjye2sH6LwOAvWuPOitHYqDlBnA=">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</latexit>✤ Cdepth tends to be small without resin coating

Product ID

COCT

Cdepth

S14520-3050VS

16

17

S14520-6050VS

20

14

S14520-3075VS

14

23

S14520-6075VS

18

22

S14520-3050VN

4.5

9(Optical Crosstalk Rate)/(Gain) (%/pC)✦ Avalanche seed is produced in the region where it is harder totrigger avalanche
20
18
16
14

10
8
6

S14520-6050VN

50

0.4

S14520-3075VN

3

11

2

S14520-6075VN

7

3

0
0

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

— 3 mm— 6 mm
50 µm
75 µm○ no coating

12

4

1

2

3

4

5

6

7

8
9
Over Voltage (V)

11 /17

Propagation of Crosstalk Photons❖ No coating (or very thin coating)✤ Reflected photons come back to the original cell

❖ Intermediate thickness✤ Photons reflected by the air interface may produce avalanches
in other cells❖ Very thick coating✤ Photons reflected by the air interface may get out of the device✤ Smaller device may have lower crosstalk rate

❖ How about the crosstalk thorough the backside?
Initially fired pixel

Isolation
trenchNeighboring pixel

AP-diff

CT-diff

delayed crosstalk
Minority
carrier

Si substrate
Characterization of Delayed Crosstalk of SiPM

arXiv: 1409.4564

Figure 1: Physicalprocesses
JPS
Meeting, considered
SEP 15, 2020in the analysis. Top: Afterpulsing due to carriers

12 /17

Measurement of Delayed Crosstalk❖ Distribution of the time difference between two pulses show
two exponential component with different time constants✤ Relatively long time constant is due to dark counts✤ Short time component is mainly due to delayed crosstalk✦ Short time constant is not heavily dependent on the over voltage✦ Afterpulse is negligible in these SiPMs

τS = 19.1 ns
τS = 19.8 ns

τL = 105 ns

τL = 431 ns

S14520-3050VN @ V=48V∆t (ns)Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

S14520-6050VN @ V=48V∆t (ns)13 /17

Measurement of Delayed Crosstalk❖ Distribution of the time difference between two pulses show
two exponential component with different time constants✤ Relatively long time constant is due to dark counts✤ Short time component is mainly due to delayed crosstalkτS = 19.8 ns

τL = 431 ns

S14520-3050VN @ V=48V∆t (ns)Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

Delayed Cross Talk Time Constant (ns)✦ Short time constant is not heavily dependent on the over voltage✦ Afterpulse is negligible in these SiPMs
30

τS = 19.1 ns τDCT = 20.5−0.067VOV
25

20

τL—=3 105
mm ns

15

— 6 mm⌧L
50 µm⌧S = ⌧DCT
75 µm⌧DCT + ⌧L5○ no coating
S14520-6050VN @ V=48V

10

0
0

1

2

3

4

5

∆t (ns)6789Over Voltage (V)

13 /17

Delayed Crosstalk Rates❖Delayed crosstalk rate (RDCT) is calculated as
NS: # of event with short time constant
NL: # of event with long time constant❖There is no significant difference due to coating❖CDCT is smaller for 75 µm cells (smaller crosstalk efficiency)❖CDCT is larger than COCT, which means total amount of delayedcrosstalk is larger than optical cross talkCharacterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

30
14/17
/17

Delayed Crosstalk Rates❖Delayed crosstalk rate (RDCT) is calculated as
NS: # of event with short time constant
NL: # of event with long time constant❖There is no significant difference due to coating❖CDCT is smaller for 75 µm cells (smaller crosstalk efficiency)❖CDCT is larger than COCT, which means total amount of delayedcrosstalk is larger than optical cross talk
Product ID

CDCT

CDepth

S14520-3050VS

59

3.4

S14520-3050VN

53

3.6

S14520-6050VS

55

4.7

S14520-6050VN

62

3.2

S14520-3075VS

37

4.5

S14520-3075VN

27

8.6

S14520-6075VS

26

6.6

S14520-6075VN

23

7.2

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

31
14/17
/17

Missing Events❖ There are some missing events for ∆t < 6 ns
✤ These events may be recognized as “prompt” crosstalk❖ Ratio of (Missing Event Rate)/(Apparent Optical Crosstalk)✤ Ratio is more than 1 and constant for SiPMs without coating✤ Apparent crosstalk may be accounted for by missing events
NMissing N ( 1.5p.e.)
for SiPMs without coating/
Missing events

S14520-3050VN @ V=48V∆t (ns)Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

(Missing Event Rate)/(Apparent Optical Crosstlak Rate)

NS + N L N (0.5p.e.)

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0

1

2

3

4

5

6

7

8
9
Over Voltage (V)15 /17

Temperature Dependence❖ No visible dependence on temperature for

Delayed Crosstalk Rate (%)

Delayed Cross Talk Decay Time (ns)✤ delayed crosstalk time constant✤ delayed crosstalk rate

120

100

80

60

60

50

40

30

40

20

20

10

0
0

1

2

3

4

5

6

7

8
9
Over Voltage (V)Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 2020

5 °C
15 °C
20 °C
25 °C
35 °C

0
0

1

2

3

4

5

6

7

8
9
Over Voltage (V)

16 /17

Summary❖ Optical crosstalk rate is significantly affected by resin
coating✤ Seed photons propagate through resin coating✤ Smaller device size and thicker coating reduce OCT rate
✤ Larger cell size increase OCT rate due to larger gain
✤ No coating significantly reduces OCT rate

❖ Delayed crosstalk rate is greater than the optical crosstalk✤ Delayed crosstalk is indecent of the resin thickness✤ Time constant of delayed crosstalk is ~20 ns and independentof the over voltage✦ Apparent cross talk will increase if the pulse width is not much
shorter than 20 ns✤ Early component of the delayed crosstalk may account for theremaining crosstalk for SiPMs without resin coating

Characterization of Delayed Crosstalk of SiPM
JPS Meeting, SEP 15, 202017 /17