Multi-dimensional Time Correlated Single Photon Counting has nowadays reached a prominent position among analytical techniques employed in the medical and biological fields. The development of instruments able to perform simultaneously temporal and spectral fluorescence analysis (sFLIM) is strongly related to the performances of single-photon detector arrays and currently available solutions cannot satisfy simultaneously all the requirements.

To face this rising quest, we develop a fully-parallel eight channel module, based on a monolithic Single Photon Avalanche Diode (SPAD) array where every pixel maintains the performance of the best single channel photo-detector such as: great temporal resolution, high active area (diameter of 50 µm), high Photon Detection Efficiency (50% @ 550 nm, 15% @ 800 nm) and low Dark Counting Rate (DCR).

The system relies on a novel architecture of the single pixel, based on the integration of the timing pick-up circuit next to the photo-detector, making the negative effects of electrical and optical crosstalk on photon timing performances negligible. To this aim, the custom technological process used to fabricate the SPAD has been modified, allowing the integration of MOS transistors without impairing the performances of the detector.

The single channel is complemented by an external Active Quenching Circuit, fabricated in a standard CMOS technology, that ensures high maximum counting rate (> 5 MHz) and low afterpulsing probability(< 1.5% with dead time of 80 ns). Finally, the output timing signals are read and conditioned by a proper CMOS electronics. The complete pixel shows a very good temporal resolution of about 45 ps (FWHM), which is maintained in parallel operation conditions. The module also includes a double-stage Peltier, driven by a closed loop controller that allows a minimum operation temperature of about -15°C, and a liquid cooling system.

Finally, being the architecture of the first 8x1 prototype modular and easily extendable, the number of pixels can be increased in order to fabricate arrays with higher dimension to completely exploit the advantages of parallelization; actually we are working on the design of a 32x1 complete module.

Publications

• I. Rech, A. Gulinatti, M. Crotti, C. Cammi, P. Maccagnani, and M. Ghioni:
  "Towards picosecond array detector for single-photon time-resolved multispot parallel analysis."
  Journal of Modern Optics, vol. 58, issue 3&4, pages 233 – 243.
  Jan. 2011
• I. Rech, C. Cammi, F. Panzeri, A. Gulinatti and M. Ghioni:
  "Parallel fluorescence photon timing module with monolithic SPAD array."
  paper presented at SPIE Photonics West 2011 – BIOS – Single Molecule Spectroscopy and Imaging IV, San Francisco (Ca, US), Proc. SPIE 7905, 790504 (2011).
  January 22-27, 2011.
  
• C. Cammi, I. Rech, A. Gulinatti, F. Panzeri and M. Ghioni:
  "Compact eight-channel SPAD module for photon timing applications."
  SPIE Defense, Security and Sensing, Orlando (Florida).
  April 25-29, 2011

Contacts

Massimo Ghioni - ghioni@elet.polimi.it
Ivan Rech - rech@elet.polimi.it
Angelo Gulinatti - gulinatt@elet.polimi.it