A 92k SPAD Time-Resolved Sensor in 0.13µm CIS Technology for PET/MRI Applications International Image Sensors Workshop (IISW), 13-16 th June 2013 Richard Walker , Ahmet T. Erdogan, Robert K. Henderson The University of Edinburgh, Scotland, U.K. Leo H. C. Braga, Leonardo Gasparini, Nicola Massari, Matteo Perenzoni, David Stoppa Fondazione Bruno Kessler (FBK), Trento, Italy. Lindsay A. Grant Imaging Division, STMicroelectronics, Edinburgh, UK.
PET Imaging Background 2 • MRI/CT: • Provide structural information • PET: • Provides functional information • Patient administered with radiotracer • Areas of high metabolic activity visible: applications in oncology & neurology etc. • Goal: • Enabler for multi-modal imaging International Image Sensors Workshop 13th-16th June 2013
Goal: Simultaneous Combined PET+MRI 3 • Several advantages over PET+CT: • MRI does not involve X-ray dose. • MRI provides improved soft tissue contrast. • However, not cost effective at present. • Magnetic field of MRI scanner incompatible with current PET systems. International Image Sensors Workshop 13th-16th June 2013
PET Imaging Background 4 4 Source: Sun Source: Ramsey Badawi, University of Washington International Image Sensors Workshop 13th-16th June 2013
Data Extraction in a PET Module 5 5 • Each time a Gamma photon strikes the scintillator... scintillator crystal gamma pulse photon arrival photons Coincidence time, τ scintillation event detection and visible photon τ τ τ τ burst time (ns) Rejection of photons pulse low-energy Energy, E scattered gamma time (ns) photons Image pulse spatial CMOS reconstruction position x-y SPAD sensor International Image Sensors Workshop 13th-16th June 2013
Typical PET System Detectors 6 • Photomultiplier tubes (PMT) • Classic detector of choice • Bulky, fragile… • Incompatible with magnetic fields • Avalanche photo-diodes (APD) • Analog gain – sensitive to voltage/temperature • Silicon-Photomultipliers (i.e. SPAD arrays): • Analog (aSiPM) • Digital (dSiPM) – emerging trend International Image Sensors Workshop 13th-16th June 2013
The SPADnet Sensor Concept 7 The design challenge - The solution: a new sensor which: • Is MRI compatible • Silicon based • Is mass-manufacturable at • Standard CMOS imaging low cost process • Potential to extract more • Leverage ability to information per photon integrate time-stamping circuits and logic. • Meets existing PET • Sensitive fully-digital SPAD system requirements array International Image Sensors Workshop 13th-16th June 2013
The SPADnet Sensor Concept 8 International Image Sensors Workshop 13th-16th June 2013
Sensor Architecture 9 • Two operating modes: • Real time energy histogramming • Pixel data readout (spatial image data & TDC values) counts time International Image Sensors Workshop 13th-16th June 2013
Sensor Architecture 10 • On-chip discriminator: • Recognises valid events • Controls integration (programmable integration time) counts time International Image Sensors Workshop 13th-16th June 2013
Sensor Architecture 11 International Image Sensors Workshop 13th-16th June 2013
Sensor Architecture 12 International Image Sensors Workshop 13th-16th June 2013
Sensor Architecture 13 International Image Sensors Workshop 13th-16th June 2013
Logic per SPAD (Restricted Fill Factor) 14 Cross section PMOS NMOS NMOS PMOS NMOS ½g ½g d ½g ½g ½g ½g Logic Logic Logic Logic Logic p+ n+ n+ n+ S S S S S S T T T T T T P-well P I I I I I I N-well P-well N-well N-well P-well N-well P-well N-well Guard ring Deep retrograde N-well Multiplication region P-substrate International Image Sensors Workshop 13th-16th June 2013
SiPM Arrays (Fill Factor Improved) 15 Cross section NMOS PMOS NMOS d ½g ½g d ½g ½g ½g ½g Logic Logic Logic p+ p+ n+ n+ n+ S S S S S S T T T T T T P-well P-well P I I I I I I N-well N-well P-well N-well P-well N-well Guard ring Deep retrograde N-well P-substrate International Image Sensors Workshop 13th-16th June 2013
Implemented Device 16 0.61mm 5.425mm 0.57mm 9.85mm International Image Sensors Workshop 13th-16th June 2013
Characterisation Overview 17 • Multiple TDCs improve system timing resolution International Image Sensors Workshop 13th-16th June 2013
Summary 18 • 92k SPAD PET image sensor in 0.13µm CIS technology: • 8 × 16 pixel array • 0.57 × 0.61mm pixel • 43% array fill factor • TDCs per pixel for improved timing resolution • 100MHz real-time energy histogram output for event recognition • On-chip discriminator for improved efficiency. International Image Sensors Workshop 13th-16th June 2013
Thank you for your attention 19 Acknowledgements: Sensor design Module assembly Industrial partners www.SPADnet.eu This work, conceived within the SPADnet project (www.spadnet.eu), has been supported by the European Community within the Seventh Framework Programme ICT Photonics. Disclaimer: This publication reflects only the authors’ views. The European Community is not liable for any use that may be made of the information contained herein. International Image Sensors Workshop 13th-16th June 2013
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