Slide 1: Silicon Photomultiplier: Operation, Performance & Possible Applications
Silicon Photomultiplier Operation, Performance & Possible Applications Slawomir Piatek Technical Consultant, Hamamatsu Corp.
Slide 2: Introduction
Introduction Very high intrinsic gain together with minimal excess noise make silicon photomultiplier (SiPM) a possible choice of a photodetector in those applications where the input light is in the photon-counting range. 2
Slide 3: Introduction
Introduction This webinar is a high-level review of SiPM’s structure, operation, and opto-electronic characteristics, followed by a discussion of some possible applications. 3
Slide 4: Outline
Outline • Structure and operation • Opto-electronic characteristics • Applications + Automotive ToF LiDAR + Flow cytometry + Radiation detection and monitoring • Summary and conclusions 4
Slide 5: Structure and Operation of a SiPM
SiPM Structure and Operation of a SiPM Portraits of SiPMs (images not to scale) 5
Slide 6: SiPM structure
SiPM structure Top view RQ oxide = n+ APD Side view p+ π SiPM is an array of microcells p+ electrical equivalent circuit of a microcell Single microcell 6
Slide 7: SiPM structure
SiPM structure Cathode RQ ... APD Anode single microcell All of the microcells are connected in parallel 7
Slide 8: SiPM specifications
SiPM specifications Active area: 1.3×1.3 − 6×6 mm2 Microcell size (pitch): 10×10, 15×15, 25×25, 50×50, 75×75 μm2 Number of microcells: (active area)/(microcell size), from 100’s to 10,000’s Overvoltage: ΔV = VBIAS – VBD; recommended by the manufacturer 8
Slide 9: SiPM operation
SiPM operation VBIAS > VBD Amplitude [mV] K A ×G time [ns] RL Example of single-photoelectron waveform (1 p.e.) Gain = area under the curve in electrons 9
Slide 10: SiPM operation
SiPM operation RC time constant of the slow component Fast component depends on microcell size (all else being equal) Amplitude [mV] Recovery time tR ≈ 5 times the RC time constant Slow component tR is on the order of 10’s to 100’s ns but in practical situations, it is also a function of detection b
Slide 11: SiPM operation
SiPM operation Current pulses due to photons Arb. time The output of an SiPM is a chronological superposition of current pulses SiPM also outputs current pulses even in absence of light: dark counts (dark current) 11
Slide 12: Dark Counts
Dark Counts Current pulses due to photons and dark counts are indistinguishable Arb. time Dark-count pulses are indistinguishable from those due to photons The rate of dark counts depends on overvoltage, temperature, and size of the active area 12
Slide 13: Crosstalk
Crosstalk 2 p.e. crosstalk event Arb. time Primary discharge can trigger Crosstalk probability depends on a secondary discharge in neighboring microcells. This is overvoltage crosstalk. 13
Slide 14: Operation
Operation VBIAS If the pulses are distinguishable, SiPM can be operated in a photon 1, 2, 3,…. counting mode. counter light VBIAS If the pulses overlap, the SiPM can be 0 100 operated in an analog mode. The measured output is voltage or current. SiPM V or I 14
Slide 15: SiPM detection circuits
SiPM detection circuits VBIAS VBIAS R C R C RF SiPM SiPM V/V Vout + TIA RL - Vout 15
Slide 16: Performance and characteristics
SiPM Performance and characteristics 16
Slide 17: Characteristics of a SiPM
Characteristics of a SiPM • Photon detection efficiency • Gain • Temperature effects • Crosstalk probability • Dark current & dark counts • Linearity & dynamic range 17
Slide 18: Photon detection efficiency
Photon detection efficiency • Photon detection efficiency (PDE) is Photon detection efficiency [%] a probability that an incident photon is detected. It depends on: - wavelength - overvoltage - microcell size Peak PDE 20% − 50% wavelength [nm] 18
Slide 19: Photon detection efficiency
Photon detection efficiency Examples of PDE curves for Photon detection efficiency [%] 30 25 SiPMs optimized for NIR, VIS, 20 and UV response. 15 10 5 wavelength [nm] 19
Slide 20: Gain
Gain • Gain of SiPM is comparable to that of a PMT. Crosstalk prob. & PDE S13720, 1.3×1.3 mm2 25 μm Excess noise very low: Gain F ~ 1.1, mostly due to crosstalk • Gain depends linearly on overvoltage Overvoltage [V] 20
Slide 21: Gain versus temperature
Gain versus temperature Does gain of an SiPM depend on temperature? Yes – if the bias voltage is fixed Gain [×106] Otte et al. (2016) Reverse bias voltage [V] 21
Slide 22: Gain versus temperature
Gain versus temperature Does gain of an SiPM depend on temperature? Gain variation [%] No – if the overvoltage is fixed Fixed overvoltage Temperature [°C] 22
Slide 23: Crosstalk
Crosstalk PCT increases with overvoltage Crosstalk prob. & PDE S13720, 1.3×1.3 mm2 Crosstalk is the main contributor to 25 μm excess noise F ≈ (1+PCT) Overvoltage [V] 23
Slide 24: Dark Current
Dark Current S13720, 1.3×1.3 mm2 Example of dark current versus overvoltage 25 μm Dark current [A] DCR = ID/eμ ID = 1×10-7 A (at 7 V) μ = 1.2×106 (at 7 V) -> DCR ≈ 520 kHz or once per about 2 μs Overvoltage [V] 24
Slide 25: Linearity and dynamic range
Linearity and dynamic range S13720, 1.3×1.3 mm2 Example of output current versus incident light 25 μm level. Photon irradiance (at 850 nm) = 4.3×1018× P[W] Output current [A] P = 10-8 W −> 4.3×1010 photons per second Linearity depends on the number of microcells for a given active area Incident ligh
Slide 26: SiPM, PMT & APD
SiPM, PMT & APD This webinar will compare and contrast SiPM with a photomultiplier tube (PMT) and APD. Let’s briefly review the operation of a PMT and APD Examples of a PMT (left) and APD (right). 26
Slide 27: Operation of a PMT
Operation of a PMT Rf K P e− D6 IP D1 D2 D3 D4 D5 IK 100 mV/div C1 C2 C3 R1 R2 R3 R4 R5 R6 R7 Typical voltage V ~ 1000 V divider 2 ns/div 27
Slide 28: SiPM versus PMT
SiPM versus PMT • Solid state versus vacuum tube • Comparable photosensitivity in the technology spectral overlap region • Comparable gains • Greater optimization for PMTs • Comparable excess noise • Dark count rate per unit active area larger in SiPM • E & B field immunity in SiPM 28
Slide 29: Operation of an APD
Operation of an APD self-quenching avalanche APD biased below breakdown voltage photon Single photon can lead up to about holes electrons 100 of electron-hole pairs Thus gain up to ~100 IPH RL Avalanche is self-quenching VBIAS 29
Slide 30: SiPM versus APD
SiPM versus APD • Differ in construction log(Gain) • GainSiPM >> GainAPD linear Geiger Gain = 1 • FSiPM << FAPD region region VBD VBIAS APDs SiPMs 30
Slide 31: Possible applications of SiPMs
Possible applications of SiPMs • Automotive time-of-flight LiDAR • Flow cytometry • Radiation detection and monitoring 31
Slide 32: Automotive time-of-flight LiDAR
Automotive time-of-flight LiDAR How far is this tree? LiDAR LiDAR = Light Detection and Ranging 32
Slide 33: Automotive ToF LiDAR: basic concept
Automotive ToF LiDAR: basic concept “start” pulse “fast” photodetector emitted pulse laser w = cτ beam splitter emission optics to target timer returned pulse after Δt “stop” pulse collection optics 33
Slide 34: Automotive ToF LiDAR: basic concept
Automotive ToF LiDAR: basic concept Measure round-trip time-of-flight Δt Range (distance to the reflection point) = cΔt/2; here c is the speed of light By scanning the surroundings, a 3D map can be constructed 34
Slide 35: Characteristics of received light
Characteristics of received light • Wavelength: 905 nm or 1550 nm • Pulse: duration 2 – 5 ns • No. of photons per returned pulse: 100’s – 10,000’s on detector’s active area • Repetition frequency: kHz - MHz • DC photon background 35
Slide 36: Photodetector requirements
Photodetector requirements • High quantum efficiency at 905 nm and/or 1550 nm (affects detection range) • High detector (intrinsic) gain (reduces importance of electronic noise) • Small excess noise (affects timing error) • Small time jitter (affects distance resolution) APD has been a default detec
Slide 37: Photosensitivity
Photosensitivity Photon detection efficiency [%] S13720 SiPM S10341 Si APD Quantum efficiency [%] Wavelength [nm] Wavelength [nm] 37
Slide 38: Intrinsic gain
Intrinsic gain Gain Gain S13720 SiPM S10341 Si APD Overvoltage [V] Reverse voltage [V] 38
Slide 39: Excess noise
Excess noise S10341 Si APD Crosstalk probability [%] Excess noise factor S13720 SiPM Overvoltage [V] Gain F ≈ 1+PCT = 1.06 F ≈ (Gain)0.3 = 3.2 for gain = 50 39
Slide 40: Time jitter
Time jitter There are two contributions to timing jitter: 1. “Classical” jitter – variation in response time, often reported for a single photon illumination. This contribution is on the order of 100 ps for SiPMs and APDs 2. Time-walk effect. For a constant trigger level, timing depends gain variati
Slide 41: Time jitter
Time jitter arb. For a given light level SiPM has smaller time-walk effect because of its lower excess noise. trig. level Different trigger times: time time walk effect 41
Slide 42: Take-away points
Take-away points 1. SiPMs are likely to compete successfully with APDs at 905 nm because of their higher gain and much lower excess noise. Empirical evidence is forthcoming. 2. Sensitivity at 905 nm will improve in a new generation SiPMs 3. SiPMs with sensitivity at 1550 nm are being developed. 42
Slide 43: Flow cytometry
Flow cytometry Studying biological cells with light 43
Slide 44: Flow cytometry (basic concept)
Flow cytometry (basic concept) Side-scatter photodetector flow Data processing Laser Forward-scatter photodetector flow 44
Slide 45: Flow cytometry
Flow cytometry fluorescent dye Excitation light Fluorescent light cell Flow cytometry also uses fluorescence tagging to study cells 45
Slide 46: Flow cytometry
Flow cytometry • Used to study and sort biological cells • Side-scatter signal vs. forward scatter signal depends on cell properties • Fluorescence is also employed (dyes attached to cells) to produce a variety of plots using fluorescence signal(s) • The optical system employs a combination of laser
Slide 47: Flow cytometry data
Flow cytometry data Side scatter vs. forward scatter plot – the most fundamental in flow cytometry Side scatter signal Cell’s characteristics such as size, complexity, or refractive index affect the relative strengths of side scatter and forward scatter signals Forward scatter signal 47
Slide 48: Characteristics of received light
Characteristics of received light • Wavelength: can be selected depending on cell sizes and fluoresce • Pulses − duration dependent on sheath flow speed and cell size and is on the order of μs. • No. of photons per pulse varies from few to thousands • Rate of pulses in kHz 48
Slide 49: Side-scatter photodetector requirements
Side-scatter photodetector requirements • High photodetection efficiency (affects S/N of detection) • High intrinsic gain (reduces importance of electronic noise) • Minimal excess noise (affects accuracy of the scatter plots; random noise) • High linearity (affects accuracy of the scatter plot; syst
Slide 50: Photosensitivity
Photosensitivity Cathode radiant sensitivity [mA/W] S13360 H10720 3×3 mm2, 25 μm 14,400 microcells QE ≈ 28% PDE [%] at 450 nm Wavelength [nm] Wavelength [nm] 50
Slide 51: Gain
Gain H10720 S13360 3×3 mm2, 25 μm 14,400 μcells Gain Gain Overvoltage [V] Control voltage [V] 51
Slide 52: Excess Noise
Excess Noise F ≈ 1+PCT (SiPM) Excess noise increases with gain F ≈ δ/(δ – 1) (PMT; δ – gain of the first dynode ) Excess noise decreases with gain 52
Slide 53: Linearity/dynamic range (PMT)
Linearity/dynamic range (PMT) H10720 10% nonlinearity: 75 mA, TP = 500 ns Gain = 2×106, QE = 28% Deviation [%] No. of incident photons at 450 nm: 4.2×105 Output current [mA] 53
Slide 54: Linearity/dynamic range (SiPM)
Linearity/dynamic range (SiPM) Ntot = 14,400; PDE = 25%, tr = 50 ns Nγ.PDE = 1.1×105 (ideal response) Nfired = 0.75×105 or 32% below an ideal response 54
Slide 55: Take-away points
Take-away points 1. The major weakness of SiPMs in flow cytometry is limited dynamic range and linearity 2. However, out of dozens of optical channels in a flow cytometer, SIPM can be suitable for some 3. There is a great interest in using SiPMs in flow cytometry but little published work on this su
Slide 56: Radiation monitoring and spectroscopy
Radiation monitoring and spectroscopy 56
Slide 57: Radiation monitoring (basic idea)
Radiation monitoring (basic idea) radiation events Ionizing Output radiation trigger level Scintillator Photodetector time An event is registered if the output signal exceeds the threshold level. 57
Slide 58: Radiation monitoring (basic idea)
Radiation monitoring (basic idea) 1,2,3… Amplifier Discriminator Counter • Used to detect the presence of specific radiation • Monitoring devices are often portable and hand-held. • Information provided: radiation rate (flux can be derived) 58
Slide 59: Characteristics of received light
Characteristics of received light • Wavelength dependent on the choice of scintillator often in the 300 nm – 500 nm range • Pulses • Number of photons per pulse depends on energy of ionizing radiation and type of scintillator • Duration of the pulse depends on the size and type of the scintillator (
Slide 60: Photodetector requirements
Photodetector requirements • High photodetection efficiency • High intrinsic gain • Large active area • Ability to couple to a scintillator • Suitable for portable hand-held devices 60
Slide 61: Radiation spectroscopy
Radiation spectroscopy R Charge integrator C Ionizing radiation Scintillator Photodetector 61
Slide 62: Radiation spectroscopy (basic idea)
Radiation spectroscopy (basic idea) V/V A/D Charge Discriminator Computer integrator FWHM Resolution = E No. of events FWHM Resolution is affected by the properties of the photodetector and the scintillator. E Energy 62
Slide 63: Photodetector requirements
Photodetector requirements • High photodetection efficiency (affects S/N of the detection and thus resolution) • High intrinsic gain (reduces the importance of electronic noise and, thus, better count rate and measurable lower energy levels) • Low excess noise (affects energy resolution) • High line
Slide 64: Radiation detection photodetectors
Radiation detection photodetectors PMTs used to dominate the detector choice in radiation detection, monitoring, and spectroscopy. SiPMs are becoming a viable alternative. Due to a multitude of possible detection scenarios, it is best to perform a side-by-side comparison between an SiPM and a PMT. 6
Slide 65: SiPM vs. PMT in γ-ray detection
SiPM vs. PMT in γ-ray detection SiPM PMT Number of counts Number of counts Energy [MeV] Energy [MeV] Example of energy spectra from Grodzicka et al. 2017 [Nuclear Inst. and Methods in Physics Research, A 874 (2017) 137–148] 65
Slide 66: SiPM vs. PMT in γ-ray detection
SiPM vs. PMT in γ-ray detection SiPM – PMT comparison for different energies and scintillators from Grodzicka et al. 2017 [Nuclear Inst. and Methods in Physics Research, A 874 (2017) 137–148] 66
Slide 67: Take-away points
Take-away points 1. SiPMs provide comparable performance to PMTs in radiation monitoring and spectroscopy 2. It is likely that the majority of hand-held devices will employ SiPMs 3. Side-by-side comparison is the best approach in deciding if an SiPM or a PMT should be used for a given detection appl
Slide 68: Summary and conclusions
Summary and conclusions • High gain, low excess noise, magnetic immunity, and ease of use are some of the highly desirable characteristics of SiPMs • There is a great interest in using SiPMs instead of APDs and PMTs in a variety of applications • New generation SiPMs will have improved characteristi
Slide 69: Visit Booth #521 & Presentations at PW18
Visit Booth #521 & Presentations at PW18 Development of an InGaAs SPAD 2D array for Flash LIDAR Presentation by Takashi Baba, January 29, 2018 (11:00 AM - 11:30 AM) Development of an InGaAs MPPC for NIR photon counting applications Presentation by Yusei Tamura, January 30, 2018 (5:50 PM - 6:10 PM) P
Slide 70: Thank you for listening!
Thank you for listening! Slawomir Piatek piatek@njit.edu 70