Design and characterization of a new generation of single photon avalanche diodes (SPAD) array, manufactured by STMicroelectronics
in Catania, Italy, are presented. Device performances, investigated in several experimental conditions
and here reported, demonstrate their suitability in many applications. SPADs are thin p-n junctions operating above the
breakdown condition in Geiger mode at low voltage. In this regime a single charged carrier injected into the depleted
layer can trigger a self-sustaining avalanche, originating a detectable signal. Dark counting rate at room temperature is
down to 10 s-1 for devices with an active area of 10 μm in diameter, and 103 s-1 for those of 50 &mgr;m. SPAD quantum
efficiency, measured in the range 350÷1050 nm, can be comparable to that of a typical silicon based detector and reaches
the values of about 50% at 550 nm for bigger samples. Finally, the low production costs and the possibility of integrating
are other favorable features in sight of highly dense integrated 1-D or 2-D arrays.
New single photon avalanche detectors (SPAD), are presented. Device performances, as photo-detection efficiency, timing and dark counts, extracted in several experimental conditions and here reported, make them suitable in many applications. The integration possibility, in order to achieve a new concept of solid state photomultiplier, has been also successfully investigated within the 5x5 arrays manufacture.
In this paper we report the results relative to the design and fabrication of Single Photon Avalanche Detectors (SPAD) operating at low voltage in planar technology. These silicon sensors consist of pn junctions that are able to remain quiescent above the breakdown voltage until a photon is absorbed in the depletion volume. This event is detected through an avalanche current pulse.
Device design and critical issues in the technology are discussed.
Experimental test procedures are then described for dark-counting rate, afterpulsing probability, photon timing resolution, quantum detection efficiency. Through these experimental setups we have measured the electrical and optical performances of different SPAD technology generations. The results from these measurements indicate that in order to obtain low-noise detectors it is necessary to introduce a local gettering process and to realize the diode cathode through in situ doped polysilicon deposition. With such technology low noise detectors with dark counting rates at room temperature down to 10c/s for devices with 10mm diameter, down to 1kc/s for 50mm diameter have been obtained.
Noticeable results have been obtained also as far as time jitter and quantum detection efficiency are concerned.
This technology is suitable for monolithic integration of SPAD detectors and associated circuits. Small arrays have already been designed and fabricated. Preliminary results indicate that good dark count rate uniformity over the different array pixels has already been obtained.