Count rate of 30035 and 30020 SiPM
Count rate/dynamic range of 30035
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Fig 1 shows the dynamic range of 30035 when a bias voltage of 28 V was applied at the SiPM.
Wavelength = 405 nm (L405P150). dc light (circular guassian beam ≥ 20 cm at 0 degree AOI using diffuser)
was transmitted at the SiPM
Intensity of the light was varied with wire-grid polariser and monitored by Newports’ calibrated PD
At each intensity, the SiPM bias current/photocurrent was measured using Keithley digital ammeter (195A)
The measured SiPM photocurrent against a range of irradiance is shown in Fig. 1 (dashed line)
The measured photocurrent can be converted into average counts (dotted line in Fig. 1) using the following
realtion
(1.1)
where Idark equals to 0.53 µA at 28 V
Ndark is the average number of dark counts equal to approximately 1 Gcps measured using peak counting
method
ISiPM is the average photocurrent at a given irradiance and Nph_det is the average number of detected counts
per second
At higher values of irradiance the SiPM bias current or photocurrent starts to saturate, which means that the
count rate will also saturate accordingly
Fig. 1 SiPM bias current and count rate against irradiance at the SiPM of 30035
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The count rate (dotted line) in Fig. 1 saturates at around 54 Gcps.
Model for 30035
1. SensL[1]
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Equation 1.2 gives the number of fired microcell (Nfired) against the number incident photons, which can be
used to predict the output of a SiPM
𝑁𝑓𝑖𝑟𝑒𝑑 = 𝑀𝑒𝑓𝑓 (1 − 𝑒
-
−𝑃𝐷𝐸×𝑁𝑝ℎ
𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡
𝑀𝑒𝑓𝑓
)
(1.2)
where PDE is the photon detection efficiency of the SiPM, Nph_incident is the number of incident photon per
unit of time over activer area of a SiPM and Meff is the effective number of microcells, which depends
upon the microcell recovery time (Trecovery), the pulse duration (Tpulse), and the total number of microcells.
The effective number of microcell is given as
𝑀𝑒𝑓𝑓
𝑁𝑆𝐴𝑃𝐷𝑠 ,
= { 𝑇𝑝𝑢𝑙𝑠𝑒
,
𝑇𝑝𝑢𝑙𝑠𝑒 < 𝑇𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦
𝑇𝑝𝑢𝑙𝑠𝑒 > 𝑇𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦
𝑇𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦
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The microcell recovery time (Trecovery) is given as
𝑇𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦 = 𝐶µ𝑐𝑒𝑙𝑙 (𝑅𝑄 + 𝑅𝑆 × 𝑁𝑆𝑃𝐴𝐷𝑠 )
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-
(1.3)
(1.4)
where Cµcell is the effective capacitance of the microcell, RS is the series resistance, and RQ is the quenching
resistance
To predict the output of the 30035 SiPM, the SiPM has NSPADs = 5676, PDE = 46% at 28 V, Trecovery = 85 ns
with Rs = 50 Ω (Evaluation Board), calculated from Equation 1.4 with Cµcell = 164 fF at 40 degree celcius
[N.otte.A et al], RQ = 220 kΩ, calculated from Equation 1.4 with known Trecovery = 37 ns with Rs = 1 Ω.
Fig. 2 shows the output of the 30035 SiPM in terms of the number of fired microcell estimated with
Equation 1.2
Fig. 2 The number of fired microcell against a range of irradiance for the 30035 SiPM. The dashed line shows the
number of fired microcell when the Trecovery = 85 ns and solid line when Trecovery = 104 ns
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The number of fired microcell saturates at approx: at 66 Gc/s when Trecovery = 85 ns and saturates at approx:
54 Gc/s when Trecovery = 104 ns
If the number of fired microcell per second is equal to the number of detected photons per second then the
effective recovery time is equal to 104 ns (i.e. 1.2×RC or 70% of max amplitude), as the Equation 1.2
shows the number of fired microcell equal to approx: 54 Gc/s, when the recovery time is 104 ns.
Particularly, the max count rate calculated using equation 1.1 is also approximately equal to 54 Gcps
2. Max count rate of a passively quenched SiPM[2],[3]
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For a passive quenching SPAD array, the maximum count rate can be calculated [2],[3]
𝑇
×𝑁𝑆𝑃𝐴𝐷𝑠
𝐶𝑚𝑎𝑥 = exp𝑝𝑢𝑙𝑠𝑒
(1)×𝑇
𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦
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(1.5)
Table 1 shows the number of fired microcell based on Equation 1.2 and the maximum count rate based on
Equation 1.5 for various recovery times, and the maximum count rate calculated using Equation 1.1
Maximum number of fired
microcell
Gc/s
(Equation 1.2)
ON Semi
SiPM
Trecovery = 85 ns
RS = 50 Ω
T’recovery = 104 ns
Micro30035
66
54
Maximum
count rate
Gcps
(Equation 1.1)
Maximum count rate
Gcps
(Equation 1.5)
Trecovery = 37 ns
(Datahseet
RS = 1 Ω)
Trecovery = 45 ns
(Datasheet
RS = 1 Ω)
Trecovery = 85 ns
(Equation 1.4
RS = 50 Ω)
56.4
46.4
24.5
54.5
Trecovery = 15 ns
Trecovery = 59 ns
(Datahseet
(Equation 1.4
137.8
RS = 1 Ω)
RS = 50 Ω)
244.2
138.6
353
89.8
Table 1: Number of maximum fired pixel (Equation 1.2), max count rate (Equation 1.5), and the max count rate
(Equation 1.1)
Micro30020
Trecovery = 59 ns
RS = 50 Ω
T’recovery = 104 ns
Count rate of 30020
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Fig. 2 shows the dynamic range of 30020 when a bias voltage of 28 V was applied at the SiPM.
Wavelength = 405 nm (L405P150). dc light (circular guassian beam ≥ 20 cm at 0 degree AOI using diffuser)
was transmitted at the SiPM
Intensity of the light was varied with wire-grid polariser and monitored by Newports’ calibrated PD
At each intensity, the SiPM bias current/photocurrent was measured using Keithley digital ammeter (195A)
The measured SiPM photocurrent against a range of irradiance is shown in Fig. 2 (triangular marker)
The measured photocurrent can be converted into average counts (solid line in Fig. 1) using Equation 1.1
where Idark equals to 0.15 µA at 28 V
Ndark is the average number of dark counts equal to approximately 0.6 Gcps measured using peak counting
method
ISiPM is the average photocurrent at a given irradiance and Nph_det is the average number of detected counts
per second
Since 300320 has a large number of microcells compared to the 30035 (2.5 times the 30035), so ideally, the
30020 should be linear at higher irradiance
As expected, the 30020 saturates at higher values of irradiances compared to the 30035 and accordint to
Equation 1.1, the number of counts saturates at around 137 Gcps as shown in Fig. 2.
Fig. 2 SiPM bias current and count rate against irradiance at the SiPM of 30020
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Fig. 3 shows the count rate of 30020 and 30035 measured using Equation 1.1
Fig. 3 Comparison of count rate of 30020 and 30035
Model for 30035
1. SensL[1]
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To predict the output of the 30020 SiPM, the SiPM has NSPADs = 14410, PDE = 30% at 28 V, Trecovery = 59
ns with Rs = 50 Ω (Evaluation Board), calculated from Equation 1.4
where Cµcell = 62 fF can be calculated using the following relation[1]
𝑒
𝐶𝑢𝑐𝑒𝑙𝑙 = 𝐺 ×
𝑉𝑜𝑣
o e is the elementary charge and G is the gain and Vov is the overvoltage applied at the SiPM
RQ = ~220 kΩ can be calculated from Equation 1.4 with known Trecovery = 15 ns with Rs = 1 Ω.
Fig. 4 shows the output of the 30020 SiPM in terms of the number of fired microcell estimated with Eq: 1.2
Fig. 4 The number of fired microcell against a range of irradiance for the 30035 SiPM. The dashed line shows the
number of fired microcell when the Trecovery = 59 ns and solid line when Trecovery = 104 ns
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The number of fired microcell saturates at approx: at 244 Gc/s when Trecovery = 85 ns and saturates at
approx: 138 Gc/s when Trecovery = 104 ns
If Nfired per second is equal to the number of detected photons per second then the effective recovery time is
equal to 104 ns (i.e. 1.2×RC or 70% of max amplitude), as the Equation 1.2 shows the number of fired
microcell equal to approx: 138 Gc/s, when the recovery time is 104 ns. Moreover, the max count rate
calculated using equation 1.1 is also approximately equal to 138 Gcps
Tentative conclusion/summary
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Summary of the number of fired microcells per second and the count rate of 30035 and 30020 SiPM has
been shown in Table 1.
Ratio of the total number of microcells of 30020 to the total number of microcells 30035 ≈ 2.5
Ratio of measured count rate of 30020 to the measured max count rate of 30035 using Equation 1.1 ≈ 2.5
Fig. 5. Dark count results by Will