FocusThe activity is focused on the development of single-photon avalanche diodes (SPADs) and associated electronic systems for low-light-level detection, with special attention to applications in lifescience such as micro and nano-analytical techniques for biomedical and genetic diagnostics. A driving force is the widespread interest to rapid and efficient detection of fluorescent emission from extremely small biological samples down to single molecules of DNA and proteins. Main goal is the development of new miniaturized detection systems that overcome drawbacks and limitations of existing systems, which rely on bulky and costly equipment and discrete sensors. High attention and remarkable efforts are devoted to imaging with ultrafast time-resolved capability at single-photon level with array detectors in linear and 2D geometries.
Risutati principali della ricerca
Monolithic SPAD array detectors with wide pixel size
The first monolithic arrays of SPAD detectors with wide pixel area (50µm diameter), high photon detection efficiency (50% @ 550nm ) and on-chip timing electronics were developed. A compact 6x8 array system with multiplexed readout was implemented for protein microarray analysis. A 60-element array system with fully parallel output and capability of operation at 20kframes/s was developed for adaptive optics in astrophysics. A 8x1 array was experimented in high-throughput FCS measurements for single-molecule spectroscopy in collaboration with UCLA.
Resonant-cavity-enhanced (RCE) SPAD detectors
We developed the first RCE SPAD detectors on a reflecting silicon-on-insulator (SOI) substrate. The substrate incorporates a two-period distributed Bragg reflector developed in collaboration with Boston Univerity. The RCE SPAD detectors have peak photon detection efficiency (PDE) ranging from 42% at 780 nm to 34% at 850 nm and time resolution of 35-ps full-width at half-maximum. These detectors are suitable for demanding photon counting applications where both high PDE and picosecond time resolution are required.
Fully-programmable 1.55µm photon-counting module for InGaAs/InP SPADs
We conceived, designed, fully characterized and validated in actual experiments a state-of-the-art near-infrared photon-counting module. The module exploits at best the performance of InGaAs/InP SPADs for detection of very fast and faint optical signals in the infrared range up to 1.7 μm; it is flexible and suitable for various advanced applications thanks to a user-friendly interface and a user-adjustable setting of all the parameters of operation. We validated the actual electronics and detector performance in nanosecond-gated operation up to 133 MHz gate repetition frequency, verifying excellent photon-timing performance (time jitter better than 100 ps) and detector operation at controlled low temperature.
CMOS SPAD imagers for 2D single photon counting
We developed cost-effective fully-CMOS compatible SPAD arrays in a 0.35µm CMOS technology. The array has smart-pixels composed by a SPAD detector, analog sensing and avalanche quenching electronics, in-pixel digital processing for counting the incoming photons and in-pixel memory and buffer stages for global-shutter readout with nil dead-time. The 32x32 2D-imager can operate up to 100,000 frames/s with 8bit photon-counting dynamics. The 32x1 array provides 50ps resolution in photon-timing. The advanced performances have already enabled new scientific results, like sub-Reyleigh imaging via N-photon detection.