Serge Charlebois1, Réjean Fontaine1, Jean-François Pratte1 3D Digital SiPM with High Single Photon Timing Resolution for Radiation Instrumentation and Photon Science Frédéric Nolet1 , Nicolas Roy1, Frédérik Dubois1, Samuel Parent1, William Lemaire1, Marc-Olivier Mercier1, Fabrice Retière2, Serge Charlebois1, Réjean Fontaine1, Jean-François Pratte1 1Interdisciplinary Institute for Technological Innovation (3IT), Université de Sherbrooke 2Triumf, Vancouver

D = ? Timing resolution Time-of-flight Detector Laser William.lemaire@usherbrooke.ca

Time-of-Flight in Applications High Energy Physics (TORCH, TiCAL) Medical Imaging (Positron emission tomography) LabPET, Université de Sherbrooke Info sur les applications: In PET, ToF can determine the position of the annihilation which would increase significantly the image contrast. If coincidence timing resolution (CTR) in the range of tens of ps FWHM could be achieved, this would provide millimetric precision along the line of response, improving significantly the contrast in the image of pre-clinical PET scanners [16]-[17]. Au niveau de la science, de nombreuses applications en physique des hautes énergies au \textit{Large Hadron Collider} (LHC) au CERN bénéficieraient également d'un détecteur possédant une précision temporelle de 10~ps. Par exemple, le détecteur "Time of internally Reflected CHerenkov light" (TORCH), a pour objectif de développer un détecteur possédant une précision temporelle de 15~ps par événement incident afin d'identifier des kaons de 10 GeV/c et plus \cite{Adinolfi2013}. Un second exemple de projet est le projet de \textit{Time-Imaging Calorimeter 4D} (TiCAL) qui tente de mesurer trajectoire des particules émises lors des collisions dans le LHC, ce qui permet d'identifier ces dites particules. De plus, dans la prochaine itération du LHC, l'augmentation de l'intensité des collisions créera un problème d'empilement des événements \cite{Cox2007}. Un détecteur possédant une précision temporelle de l'ordre de 10~ps permettra la mitigation de l'empilement \cite{White2007, White2013}. http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev Requires picoseconds timing resolution for : Improving constrast Particle identification William.Lemaire@USherbrooke.ca

Time-to-digital converter Time-of-Flight in PET Time-of-Flight Stop Time-to-digital converter Δ time = Δ distance Patient PET Scanner + - Start In both applications we want to integrate time of flight to improve the performances PET scan is a medical imaging modality used in oncology to detect cancer cells To improve the contrast in the image or reduce the time to aquire an image, we want to integrate time of flight Time of flight is measuring the distance travelled by the photon by measuring the its time of flight let’s see an animation to better understand the principle of time of flight. When an annihilation occurs, two photon are emitted in opposed direction. The first photon starts the TDC (the chronometer) and the second one stop the measurements. The difference in time represents the difference between the distance travelled To obtain a precision of 3 mm required by pre-clinical scanner, a timing precision of 10 ps is required. 3 mm = 10 ps timing resolution State of the art detectors: ~100 ps William.Lemaire@USherbrooke.ca

Single Photon Avalanche Diode (SPAD) SPAD (Geiger mode) Gain = 104-106 Vbias > VBreakdown Photodiode Gain = 1 Vbias < VBreakdown Current Vbias oltage Voici les trois régimes d’une photodiode polarisé à l’inverse. La photodiode linéaire qui possède un gain de 1. La photodiode avalanche (APD) qui est utilisé dans les scanners labPET présentement développé. (possède un gain de 10-1000) permet de détecter plusieurs photons à la fois etc. Et finalement le SPAD (photodiode en mode Geiger) qui est au dessus de la tension de claquage de la diode. L’état est métastable. Le gain permet e produire un signal détectable avec un seul photon. Par contre, il faut un circuit pour le contrôler pour que la diode ne s’emballe pas et ne s’endommage pas. William.Lemaire@USherbrooke.ca

How SPAD works Quenching circuit Vbias 3: Recharge A C 2 3 1 1: Hit C’est ici qu’entre en jeu le circuit d’étouffement. Voici l’animation Attente de photon, lorsque détecter on passe a B. donc un fort courant se développe dans la diode. Le circuit d’étouffement étouffe la diode en diminuant la tension aux bornes de la diode pour se rendre au point C. La diode n’est plus en mode Geiger et ne peu pas faire feu (il est possible ici d’ajouter un temps mort volontaire. Afin de minimiser un bruit corrélé intrinsèque a la diode, on ne rentre pas plus dans les détails) Et ensuite le circuit d’étouffement revient polarisé la diode. B William.Lemaire@USherbrooke.ca

How to Achieve ps Timing Resolution? Digital SiPM Our Approach Analog SiPM SiPM are very popular because of low cost, low complexity and high photosensitive area Timing resolution limited by : SPAD to SPAD skew and high output capacitance To overcome the limitations of the SiPM, the solution proposed is a digital SiPM with individual TDC. One challenge remains, obtaining a high fill factor for low light events.: … To overcome the low sensitive area with the 2D approach is the 3D integration High output capacitance Skew between channels Not suitable for ps timing resolution High output capacitance Skew between channels  Photosensitive area William.Lemaire@USherbrooke.ca

How to Achieve ps Timing Resolution? TSV TDC SPAD Digital readout QC 3D Integration Maximize Photosensitive Area CMOS or Optoelectronics CMOS 65 nm Our group is also working on 3D integration in collaboration with Teledyne Dalsa to obtain a 3D integrated photodector (3D digital SiPM) The top layer is a custom process optimized for photodetector performance The bottom layer can be developped in different process to optimize the performance (either low power or high timing for example) In this case, to obtain high timing performance, a CMOS 65 nm node was selected. 50 µm 50 µm William.Lemaire@USherbrooke.ca

3D digital SiPM architecture 256 Pixels (1 mm2): 1 Photodetector (SPAD) 1 readout circuit (QC) 1 Time-to-digital Converter (TDC) The 3D digital SiPM can be divided in two section: First, each pixel is composed of a photodetector, a readout circuit and a TDC. This way, the information of each photon detected is quickly digitalized and the timing performance is then improved The second section of the detector is the array readout. First each pixel is calibrated in real time and correction are applied is necessary The ASIC can combined the timing information and photon counting to build timing and energy histogram It is really important for radiation instrumentation where the energy deposited as well as the timing information is required in the measurements Each pixel as an adresse and a frame rate mode can be activated to obtain an image similar to a 3D camera (image with z information) Time and energy calculation William.Lemaire@USherbrooke.ca

Experimental Setup Femtoseconds laser Photon starved environment (<1 photon per pulse) For the SPAD single photon timing resolution (SPTR) measurements, the SPAD was illuminated by a Newport MaiTai 80 MHz Ti:sapphire pulsed laser. The light was attenuated with neutral density filter to ensure that the measure was done in a photon starved environment. The beam intensity was measured using an 818-UV Newport diode and a 1918-R Newport power meter to evaluate the number of photons hitting the SPAD. William.Lemaire@USherbrooke.ca

Timing precision of circuits Single photon timing resolution SPAD and electronics only 7.8 ps FWHM Time-to-digital converter only 6.9 ps rms (~16 ps FWHM) Full pixel 20 ps FWHM The pixel can be separated in 2 sections, the SPAD and its electronic readout and the chronometer (TDC). The timing performance is the Single photon timing resolution, the timing precision when detecting a single photon since the number of photon affect the timing performance (the higher number of photon the better) The measurements was done with a femtosecond laser pulse and a 8 ps FWHM precision was measured For the TDC, each code of the dynamic range of the chronomter was measured and the timing precision varies from 1 ps to 9 ps rms. The measurements was also done considering a single event uncorralted to the code and the timing precision for a single event is about 6.9 ps rms (or 16 ps rms) The pixel is the combination of the two circuits presented in the previous slide. ( the SPAD and its electronic readout and the chronometer (TDC).) The timing performance is also the Single photon timing resolution and the measurements were performed using a femtosecond laser The pixel performance varies from 16.5 to 21.5 FWHM depending on the TDC code for a SPTR of 20 ps. William.Lemaire@USherbrooke.ca

Benefits of ps timing resolution? Time measurement in Positron emission tomography ~ 100 x image contrast improvement Patient Today I will present you my master project which consists of designing... … The photodetectors need to have ps timing resolution William.Lemaire@USherbrooke.ca

Conclusion 3D digital SiPM for time-of-flight Pixel results SPAD 7.8 ps FWHM Full pixel : 20 ps FWHM Applications PET scanner detector High energy physics Your application? We are looking for collaborations! Today I will present you my master project which consists of designing... … The photodetectors need to have ps timing resolution William.Lemaire@USherbrooke.ca

Acknowledgement Thank you for you attention William.Lemaire@USherbrooke.ca

Benefits of ps timing resolution? Range finding Distance measurement with mm precision in a single image frame Simulated LIDAR image of an angled plane Detector Laser Today I will present you my master project which consists of designing... … The photodetectors need to have ps timing resolution 0 mm 100 mm Measured distance William.Lemaire@USherbrooke.ca

Time-of-Flight in Applications 1 Intro TEP + requis 10 ps 2 Intro HEP + requis 10 ps 3 Limitation des SiPM pour atteindre 10 ps 4 3D Digital SiPM 5 EXTRA pour intro 6 3D digital SiPM architecture (shéma bloc) 7 energy estimation and photon counting 8 Calibration – Correction - dark noise suppression –timing estimation 9 EXTRA pour architecture 10 current measurement 8 ps FWHM SPAD/QC + TDC at 8 ps bin/ 8 ps FWHM 11 Pixel = 20 ps FWHM 12 conclu sur possibilité pour autres applications Today I will present you my master project which consists of designing... … The photodetectors need to have ps timing resolution William.Lemaire@USherbrooke.ca

Materials ASIC Interface PCB TSMC CMOS 65 nm Data Acquisition PCB TDC2 The TDC has designed in TSMC CMOS 65 nm… … 2 test structures, with dPLL and without dPLL to know its optimum performances TDC2 Controlled with External Controls TDC1 Controlled with a Digital PLL Nicolas.Roy6@USherbrooke.ca

Open Circuits and High Impedance Paths Between SPAD and READOUT Under Bump Metalization (UBM) Bumps SPAD TSV UBM (Ti-Cu) Bump (Cu-In) Jean-Francois.Pratte@USherbrooke.ca

TDC Resolution Selection Better compromise ~ 15 ps We have measured the TDC’s jitter vs the TDC’s resolution… … So the better compromise is situated at 15 ps. Nicolas.Roy6@USherbrooke.ca