High-Density-cell (HD) NUV Silicon Photomultipliers produced at FBK F. Acerbi, A. Ferri, G. Zappalà, A. Gola, G. Paternoster, N. Zorzi, C. Piemonte
Silicon ph Silicon phot otom omult ultipliers ipliers Flash of 3 photons current 3X elementary http://www.ketek.net/ pulse http://advansid.com/ time photon arrival few tens of m m size Performance parameters: 1. Photon-detection efficiency (PDE) • 2. Primary noise (primary DCR) Fill Factor 3. Correlated noise: • GAIN 1. Afterpulsing • Semiconductor properties 2. Optical Crosstalk 4. Photon number resolution … Timing & Energy resolution 5. Jul. 2015 Fabio ACERBI - PhotoDet 2015 2
SiPM SiPM te tech chno nolog logy y at at FB FBK RGB SiPM NUV SiPM SPAD size: 40 m m SPAD size: 40 m m Fill factor: 60% Fill factor: 60% Peak PDE: 33% Peak PDE: 40% Max PDE @ 400nm Max PDE @ 550nm ENF: ~1.7 ENF: ~1.5 DCR: < 100kHz DCR ~ 300 kHz RGB-HD SiPM p-on-n junction Jul. 2015 Fabio ACERBI - PhotoDet 2015 3
New New NUV NUV SiP SiPM M – tech techno nologica logical l improveme improvements nts DiCT DeCT & AP AP primary pulse Old substrate new substrate • Improved substrate Minority carrier lifetime reduced ~ 2 order of magnitude lower delayed correlated noise F. Acerbi et. al., IEEE T. Nucl. Sci., vol. 62, n. 3, 2015 Jul. 2015 Fabio ACERBI - PhotoDet 2015 4
SiPM SiPM te tech chno nolog logy y at at FB FBK RGB SiPM NUV SiPM SPAD size: 40 m m SPAD size: 40 m m Fill factor: 60% Fill factor: 60% Peak PDE: 33% Peak PDE: 40% Max PDE @ 550nm Max PDE @ 400nm ENF: ~1.7 ENF: ~1.5 DCR ~ 300 kHz DCR: < 100kHz RGB-HD SiPM NUV-HD SiPM Combine benefits of the HD technology (high FF & PDE, low correlated noise and high cell-density) with the advantages of p-on-n approach for detection at short wavelength Jul. 2015 Fabio ACERBI - PhotoDet 2015 5
NUV NUV-HD HD SiPM SiPM te tech chno nolog logy Poly strip Metal NUV NUV-HD HD Si SiPM PM NU NUV SiPM SiPM resistor High-field region High-field region n - epi-Si Cell 2 Cell 1 Cell 3 n ++ Substrate ~4,5µm <2µm Trench • Small cells Gain reduction afterpulsing and CT reduction • Redesigned border structure Trenches between cells Optical and electrical cell isolation Dead border reduction (< 2 µm) increased FF Small Cell Size without FF reduction Jul. 2015 Fabio ACERBI - PhotoDet 2015 6
NUV NUV-HD HD SiPM SiPM te tech chno nolog logy Trench < 1 um Cell Pitch = 15 µm • Narrow trench, width < 1 um • High aspect ratio • Filled with silicon dioxide • Electrical and optical cell isolation Jul. 2015 Fabio ACERBI - PhotoDet 2015 7
Small Small cells cells 1. lower gain (lower Cd) lower ENF external scintillator cross-talk 1. afterpulsing reduction 2. direct- and delayed- Optical CT reduction high-field region active direct cross-talk 3. external Optical CT - - layer + + (with scintillator) reduction - + - + delayed cross-talk 2. Larger dynamic range substrate 3. Faster recharge time 1. reduced pile-up 2. useful with «slow» scintillators (CsI) for further dynamic range … but only if we have a high fill factor!! need also high PDE Jul. 2015 Fabio ACERBI - PhotoDet 2015 8
NUV NUV-HD HD SiPMs SiPMs pr prot otot otyp ypes es 100% Cell size 90% NUV-HD 80% (L<2µm) 70% NUV SiPM Fill factor 60% (L=4.5µm) L 50% 40% 30% 20% 10% 0% 0 10 20 30 40 50 60 70 Cell Pitch FF Cell Density Cell size (µm) ~4444 cells/mm 2 15 µm 55 % 20 μm 66 % 2500 cells/mm 2 Devices with 4 different CS have 25 μm 1600 cells/mm 2 73 % been produced and tested ! 30 μm ~1111 cells/mm 2 77 % Jul. 2015 Fabio ACERBI - PhotoDet 2015 9
Functional characterization Jul. 2015 Fabio ACERBI - PhotoDet 2015 10
Functional characterization GAIN an GAIN and d rec recha harge rge-time time 7V 7V • Reduced gain ~ 7·10 5 at 7V for 15µm cell (vs. ~4.5·10 6 of NUV SiPM) • Fast cell recharge reduced pile-up ~ 20÷25 ns recharge time constant for 15µm cell Also available SiPM with 15µm cell and halved Rq lower recharge time Jul. 2015 Fabio ACERBI - PhotoDet 2015 11
Functional characterization Ph Photo oton n de detec tection tion efficie efficienc ncy y (PDE) (PDE) 7V 30µm cell pitch PDE at 400nm • PDE peaked in the blue region of the spectrum (~400nm): – PDE >50% for 30µm cell, with 7V – PDE ~33% for 15µm cell, with 7V Jul. 2015 Fabio ACERBI - PhotoDet 2015 12
Functional characterization Noise Noise 7V • Primary noise in the order of 100kcps/mm 2 no increment due to trench and additional processes • Very Low afterpulsing + delayed CT Only few percent at max excess bias (<1% for 15µm cell) Jul. 2015 Fabio ACERBI - PhotoDet 2015 13
Functional characterization Compariso Comp arison a n as a fun s a functio ction o n of PDE f PDE PDE=50% • Prim. DCR of 100÷200 kcps/mm 2 with PDE=50% • ENF <1.4 with PDE=50% Jul. 2015 Fabio ACERBI - PhotoDet 2015 14
NUV NUV-HD: HD: Lo Low w en ener ergy gy Ga Gamma mma 𝑒𝐹 1 𝐹𝑂𝐺 𝐹 = ∙ 𝑄𝐸𝐹 × 𝜁 + ⋯ 𝑂 𝑡𝑑𝑗𝑜𝑢 ENF measured on SiPMs without scintillator LaBr NaI l = 400nm Good results expected for energy resolution at 350nm÷450nm Jul. 2015 Fabio ACERBI - PhotoDet 2015 15
NUV-HD: NUV HD: TOF TOF-PE PET T ap applica plicatio tion • Minimum achieved CRTs are: – ~100ps FWHM for the 5 mm crystal – ~150ps FWHM for the 22 mm crystal Jul. 2015 Fabio ACERBI - PhotoDet 2015 16
Co Conc nclusio lusions ns HD technology was successfully applied to NUV SiPMs investigating many SPAD sizes. Very promising results: • PDE > 50% • Average DCR ~100 kcps/mm2 • Low ENF (1.2 ÷ 1.4) • Fast recharge time-constant = few tens of ns Very good time resolution with scintillator & good energy resolution expected Future Development new technological features to further increase FF and reduce the crosstalk Jul. 2015 Fabio ACERBI - PhotoDet 2015 17
High-Density-cell (HD) NUV Silicon Photomultipliers produced at FBK F. Acerbi, A. Ferri, G. Zappalà, A. Gola, G. Paternoster, N. Zorzi, C. Piemonte http://iris.fbk.eu/silicon-photomultipliers http://srs.fbk.eu
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