Recent advances in silicon single photon avalanche diodes and their applications

Transcription

1 Recent advances in silicon single photon avalanche diodes and their applications Massimo Ghioni Politecnico di Milano, Dipartimento di Elettronica e Informazione

2 Outline 2 Single photon counting: why, what and how SPAD device technology: origin and evolution Single element SPAD detectors recent advances custom SPAD vs standard CMOS technology application cases SPAD array detectors application cases Conclusions

3 Why single photon counting? 3 For ultimate sensitivity in optical signal measurement! straight digital technique overcomes limits of analog measurements (circuit noise) photon timing with picosecond precision measurement of ultrafast optical signals by Time Correlated Single Photon Counting (TCSPC)

4 Why high sensitivity? 4 Low sample concentration Minute samples Short exposure time Photon losses (poor collection, absorption, etc.) Low excitation power Greater magnification Ultra-weak emission (Raman scattering etc.)

5 Photon counting/timing applications 5 bioluminescence single molecule detection medical imaging\ lighting displays entertainment detector calibration hyper-spectral imaging Biotechnology Electronics primary radiometric scales Metrology Metrology photon counting quantum standards Quantum Information Processing Medical Physics quantum imaging quantum cryptography quantum computing single photon sources medical / non interactive imaging neutrino/ cherenkov/ dark matter detection Space Applications Meteorology Meteorology IR detectors robust imaging remote sensing lidar devices environmental monitoring Military Military radioactivity nuclear night vision security chemical bio agent detection source:

6 Available detectors 6 Vacuum Tube PMT Currently used in photon counting/timing applications Limited quantum efficiency Solid State APD (ordinary Avalanche PhotoDiodes) No single photon detection Special CCD (EM-CCD, I-CCD) Photon counting possible only at low frame rates Limited time resolution SSPD (Superconducting Single Photon Detector) Limited active area Need to be operated at < 4 K SPAD (Single Photon Avalanche Diode) Best suited for photon counting/timing applications

7 SPAD: reverse I-V characteristic 7 No avalanche V BD V REV [V] I REV [ma] Avalanche

8 APD vs. SPAD 8 APD SPAD ON Quenching Avalanche Reset Avalanche PhotoDiode Single-Photon Avalanche Diode Bias: slightly BELOW breakdown Linear-mode: it s an AMPLIFIER Gain: limited < 1000 Bias: well ABOVE breakdown Geiger-mode: it s a TRIGGER device!! Gain: meaningless!!

9 for SPAD operation 9 mandatory to avoid local Breakdown, i.e. edge breakdown guard-ring feature microplasmas uniform area, no precipitates etc. but for good SPAD performance... further requirements!!

10 Earlier Diode Structures 10 Haitz s planar diode (early 60 s) n+ 5µm metal oxide 5µm n - guard ring p metal Avalanche physics investigation operated at low voltage (a few tens of Volt) limited power dissipation during the avalanche (a few hundred milliwatt) fabricated in ordinary silicon wafer with a planar technology R.Haitz, J.Appl.Phys. 35, 1370 (1964), J.Appl.Phys. 36, 3123 (1965) M. Ghioni Pavia, April 3, 2007

11 Earlier Diode Structures 11 RCA reach-through diode (circa 1970) operated at high voltage (a few hundred Volts) high power dissipation during the avalanche (around ten watt) proprietary non-planar technology on a ultra-pure high-resistivity silicon wafers R. McIntyre, H. Springings, P.Webb, RCA Engineer 15, 1970 M. Ghioni Pavia, April 3, 2007

12 Haitz s planar diode 12 Deep diffused guard ring causes the photon detection efficiency (PDE) to be non uniform in the active zone PDE = QE x η - QE = quantum efficiency - η = avalanche triggering probability

13 Haitz s planar diode 13 - Haitz s structure has drawbacks in applications requiring high-resolution photon-timing - Long diffusion tail - Multi-exponential tail makes deconvolution more difficult G. Ripamonti and S. Cova, Solid State Electron. 28, 925 (1985) T.A.Louis et al, Rev.Sci.Instrum. 59, 1148 (1988). M. Ghioni Pavia, April 3, 2007

14 Epitaxial SPAD structure Counts Time (ns) - Shorter tail duration - p+ implantation for V BD control - Fully isolated devices on wafer - Guard Ring still employed non-uniform PDE, non-exponential tail M.Ghioni, S.Cova, A.Lacaita, G.Ripamonti, Electron. Lett. 24, 1476 (1988)

15 Double-epitaxial SPAD structure Counts Time (ns) Short diffusion tail with clean exponential shape Active area defined by p+ implantation No guard-ring (uniform PDE) Adjustable V BD and E-field SUITABLE for array fabrication neutral p layer thickness w tail lifetime τ = w 2 / π 2 D n A.Lacaita, M.Ghioni, S.Cova, Electron.Lett. 25, 841 (1989)

16 Double-junction SPAD structure 16 FWHM = 35ps hν n+ FW(1/100)M = 125ps p++ p-epi p + p++ FW(1/1000)M = 214ps n-substrate Patterned p++ buried layer No Tail (no carrier collection from neutral layer) Suitable for small area devices (Φ ~ 10µm) A.Spinelli, M.Ghioni, S.Cova and L.M.Davis, IEEE J. Quantum Electron. QE-34, 817 (1998) M. Ghioni Pavia, April 3, 2007

17 Device technology: prospect 17 Two different approaches standard CMOS technology custom SPAD technology have to face most requested improvements: higher photon detection efficiency (especially in the red region) larger active area (~ 100 µm) shorter diffusion tail

18 Custom SPAD technology 18 Full process flexibility makes it possible to address the most demanding requirements 0.7 p p+ n hν + n p+ Photon Detection Efficiency Wavelength (nm) Excess Bias Voltage 10 V 7 V 5 V Top epi-layer thickess/doping adjusted to increase PDE

19 Custom SPAD technology hν + n 10 3 FWHM = 35 ps p p+ p+ Counts 10 2 FW1/100M = 370 ps n Time (ps) Bottom epi-layer thickess adjusted to achieve short diffusion tail

20 Custom SPAD technology 20 hν + n heavy phosphorus diffusion p/p+ segregation gettering p p+ n p+ Specific designed gettering processes for removing transition metal impurities responsible for: - thermal carrier generation (dark count rate - DCR) - carrier trapping (afterpulsing effect) M. Ghioni Pavia, April 3, 2007

21 Dark Count Rate (primary noise) 21 Thermally generated carriers trigger avalanche pulses Shot noise, equivalent to dark current in PINs / APDs Thermal Generation via GR centers Field-Enhanced Generation M. Ghioni Pavia, April 3, 2007

22 Field-enhanced generation 22 Coulombic well Dirac well Poole-frenkel effect barrier height lowered Phonon-assisted tunneling barrier width decreased Phonon process is thermally activated Tunneling is temperature independent Overall temperature dependence is a function of electric field M. Ghioni Pavia, April 3, 2007

23 Custom SPAD technology hν + n 1000 SPAD with "standard" electric p p+ n p+ Counts (c/s) SPAD with "engineered" electric field Temperature ( C) Electric field engineered to avoid band-to band tunneling Field-enhanced generation less intense DCR strongly reduces with temperature M. Ghioni Pavia, April 3, 2007

24 Large area SPADs: dark count rate 24 Counts (c/s) µm 100 µm 50 µm Dark Count Rate (DCR) Avalanche pulses triggered by thermally generated carriers Equivalent to the dark current in PINs and APDs Practical Exploitation of DCR vs T Peltier cooling to -20 C is simple / cheap / rugged Temperature ( C) reduces DCR by a factor Typical excess bias voltage M. Ghioni Pavia, April 3, 2007

25 Large area SPADs: afterpulsing 25 Afterpulsing Effect Carriers trapped during avalanche Carriers released later trigger the avalanche Increases noise and affects correlation measurements Characterization of afterpulsing 200 µm detector 80ns deadtime Time Correlated Carrier Counting (TCCC) method Afterpulsing negligible after 1 µs Total afterpulsing probability: ~ RT ~ -25 C M. Ghioni Pavia, April 3, 2007

26 Large area SPADs: time response 26 Counts (c/s) FWHM = 35 ps λ = 820 nm By using a current pick-up circuit* and sensing the avalanche current at very low level (< 100 µa): FWHM not dependent on the detector diameter Time (ns) 35ps FWHM checked for 200µm device at room temperature Very stable response up to 4 Mc/s - clean exponential tail with 240 ps lifetime * S.Cova, M.Ghioni, F.Zappa, US patent No. 6,384,663 B2, 2002 A.Gulinatti et al, Electron. Lett. 41, 272 (2005) M. Ghioni Pavia, April 3, 2007

27 Custom SPAD technology: pros & cons 27 PROs Flexibility: designer can modify process parameters & conditions Optimization of device structure can be pursued High-performance SPADs demonstrated with diameter up to 200 µm Progress of technology driven by detector requirements CONs Monolithic integration of detector and electronics requires circuit components specifically designed in the detector technology Dedicated silicon foundry is required

28 CMOS based SPAD 28 standard HV-CMOS technology deep n-well to cut off the diffusion tail p+n junction (intrinsically low PDE) A. Rochas et al, Rev. Sci. Instrum. 74, 3263 (2003)

29 CMOS-SPAD: experimental results 29 PDE DCR low nm fairly high V exc >3V (φ = 12µm) DCR decreases slowly with T F. Zappa et al, Optics Letters 30, 1327 (2005) S.Tisa et al, IEEE-IEDM, 815 (2005) 0.8 µm HV-CMOS M. Ghioni Pavia, April 3, 2007

30 CMOS-SPAD: experimental results 30 Afterpulsing Time response Afterpulsing Probability Density (1/ns) 1E-02 1E-03 1E-04 1E-05 1E-06 55ns hold-off Time (ns) 2.6% total afterpulsing 55ns hold-off 35 ps time resolution FWHM long diffusion tail F. Zappa et al, Optics Letters 30, 1327 (2005)

31 CMOS-SPAD: pros & cons 31 PROs Standard fabrication in silicon foundry, mature technology Straightforward integration: on-chip detector & electronics Small parasitic capacitance small avalanche charge for small detectors but NOT for wide devices (higher junction cap: 100 µm diam. C J ~ 1pF ) CONs High voltage CMOS process required No flexibility in processing SPAD s with diameter > 50 µm not yet demonstrated Progress of technology driven by circuit requirements M. Ghioni Pavia, April 3, 2007

32 32 Quenching circuits

33 Quenching circuits 33 Passive quenching is simple... but suffers from not well defined deadtime τ reset > 100 ns for (C d +C s )> 1 pf photon timing spread et al τ reset =R L (C d +C s )

34 Quenching circuits 34 Active quenching......provides: short, well-defined deadtime high counting rate > 1 Mc/s good photon timing standard logic output Output Pulses P.Antognetti, S.Cova, A.Longoni IEEE Ispra Nucl.El.Symp. (1975) Euratom Publ. EUR 5370e

35 iaqc: integrated Active Quenching Circuit 35 Practical advantages Miniaturization mini-module detectors Low-Power Consumption portable modules Rugged and Reliable Plus improved performance Reduced Capacitance Improved Photon Timing Reduced Avalanche Charge Reduced Afterpulsing Reduced Photoemission reduced crosstalk in arrays F.Zappa, S.Cova, M.Ghioni, US patent 6,541,752 B2, 2003 (prior. March 9, 2000) F.Zappa et al., IEEE J. of Solid State Circuits 38, 1298 (2003)

36 Signal pick-up for improved photon-timing Time resolution FWHM (ps) µm active area diameter Avalanche current sensing at very low level (< 100 µa) Can be added to any existing AQC Threshold voltage (mv) S.Cova, M.Ghioni, F.Zappa, US patent No. 6,384,663 B2, 2002 (prior. March 9, 2000) A.Gulinatti et al., Electron. Lett. 41, (2005)

37 Improved i-aqc with on-chip current pick-up and timing circuit 37 A. Gallivanoni, I. Rech, D. Resnati, M. Ghioni, and S. Cova, Optics Express 14, 5021 (2006)

38 38 Single element SPAD: application cases Single molecule fluorescence spectroscopy Fluorescence Lifetime Imaging (FLIM)

39 Single molecule fluorescence spectroscopy 39 Fre-FAD complex Conformational dynamics of of biomolecules is crucial to their biological functions Electron transfer used as a probe for angstrom-scale structural changes Measure fluorescence lifetimes (down to < 100ps) to gauge conformational dynamics H. Yang, G. Luo, P. Karnchanaphanurach, T.M. Louie, I. Rech, S.Cova, L. Xun, and X. Sunney Xie, Science, 302(5643), 2003

40 Single molecule fluorescence spectroscopy 40 Yang, H., et al., Science, 302(5643), 2003 Correlation analysis revealed conformational fluctuation at multiple time scales spanning from hundreds of microsecond to seconds

41 Single Photon Timing Module SPTM 41 Compact (82x60x30mm) Single power supply (+15V) Controlled Temperature (Peltier cell) Software controlled settings On-board fast counters RS-232 data transmission Time-resolution: 60ps Dark Counts: down to 5 c/s PDE: 500nm I.Rech et al., IEEE J. of Sel. Topics in Quantum Electronics, vol.10, 788 (2004)

42 SPTM performance in the Harvard set-up 42 Time-resolution: 60ps Dark Counts: down to 5 c/s Quantum Efficiency: 500nm Instrument Response Function (IRF) with SPTM and with PerkinElmer SPCM I.Rech et al., IEEE J. of Sel. Topics in Quantum Electronics, vol.10, 788 (2004) M. Ghioni Pavia, April 3, 2007

43 Fluorescence Lifetime Imaging (FLIM) 43 FLIM image of the autofluorescence of daisy pollen grains 64 µm x 64 µm area (256 pixels/axis) 0.6 ms/pixel acquisition time 2 min total measurement time Courtesy of Picoquant GmbH, Germany M. Ghioni Pavia, April 3, 2007

44 44 SPAD arrays

45 SPAD arrays 45 Two approaches - Dense CMOS-based SPAD arrays 3D imaging - SPAD arrays with limited pixel number (< 100) and large pixel area Photon Counting in Adaptive optics in astronomy Parallel Fluorescence Correlation Spectroscopy Multiphoton multifocal microscopy Chemiluminescent assay analysis Photon Timing in Fluorescence lifetime imaging Basic goals - increase throughput - miniaturization, lower system cost M. Ghioni Pavia, April 3, 2007

46 SPAD arrays and optical crosstalk 46 Origin: hot-carrier luminescence 10 5 avalanche carriers 1 photon emitted A. Lacaita et al, IEEE TED (1993) Approach: Optical isolation between pixels Avalanche charge minimization

47 47 SPAD arrays: application cases Tip-tilt and curvature sensors for adaptive optics Large element SPAD array for protein microarray detection

48 Adaptive Optics 48 STRAP Adaptive-Optics System of the VLT Observatory (Chile) European Southern Observatory - ESO D.Bonaccini et al, Proc. SPIE Vol. 3126, p , Adaptive Optics and Applications; R.K.Tyson, R.Q.Fugate Eds., 1997 STRAP = System for Tip-tilt Removal with Avalanche Photodiodes

49 Hybrid four-quadrant SPAD module 49 2x2 lenslet array Spacer Ceramic Centering Ceramic Peltier Quenching, protection circuit and other electronics developed by Polimi and Microgate Courtesy of A. Silber (ESO) 4 SPAD chips supplied by PerkinElemer

50 Monolithic four-quadrant SPAD detector µm, 80µm, 50µm pixel diameter Replace the single SPAD chips in STRAP modules

51 SPAD-Array (SPADA) element array with circular geometry Fully parallel 20 kfps 4 sets of pixels - Curvature sensor for AO systems F. Zappa et al, IEEE PTL 17, 657 (2005)

52 SPADA detector head 52

53 6x8 SPAD array detector 53 Chemiluminescent protein microarray for in-vitro allergy diagnosis 50 µm pixel diameter 240 µm pitch

54 2-D photon counting module: optics 54 Collecting Ottica di raccolta optics Ottica Focusing di focalizzazione optics NA = 0.3 FOV = 2,064 mm Microarray Optical Filtri ottici filters SPADA η ~ 8% Magnification 1:1

55 2-D photon counting module: mechanics 55 Slide tray X Y θ 17cm 8.5cm 20cm Filter holder

56 Conclusion 56 SPADs in planar silicon technology offer high performance at low-cost HV-CMOS industrial technologies produce remarkable devices: Single SPAD s (< 50µm diam); SPAD Arrays (<10% FF), Integrated PC-Systems Custom CMOS-compatible technologies provide today s top-performance SPAD s and flexibility to sustain continuing evolution and progress Monolithic iaqcs open the way to miniaturized modules (down to the chip scale) Remarkable results obtained in diversified applications: DNA and Protein Analysis; Single-Molecule Spectroscopy; Wavefront Sensors in Adaptive Optics; etc. Results of decades of research made widely available by a new spinoff company