Abstract
Single-photon avalanche photodiode (SPAD) image sensors offer time-gated photon counting, at high binary frame rates of >100 kFPS and with no readout noise. This makes them well-suited to a range of scientific applications, including microscopy, sensing and quantum optics. However, due to the complex electronics required, the fill factor tends to be significantly lower (< 10%) than that of EMCCD and sCMOS cameras (>90%), whilst the pixel size is typically larger, impacting the sensitivity and practicalities of the SPAD devices. This paper presents the first characterisation of a cylindrical-shaped microlens array applied to a small, 8 micron, pixel SPAD imager. The enhanced fill factor, ≈50% for collimated light, is the highest reported value amongst SPAD sensors with comparable resolution and pixel pitch. We demonstrate the impact of the increased sensitivity in single-molecule localisation microscopy, obtaining a resolution of below 40nm, the best reported figure for a SPAD sensor.
Highlights
Single Photon Avalanche Diode (SPAD) arrays offer a widefield approach to more traditional scanning imaging modes for the detection and timing of individual photons of light
We have here demonstrated that by applying a custom-designed microlens array to such a SPAD imager, the effective fill factor can be further increased by almost a factor of two
The resulting fill factor of the 320×240, 8 μm pixel pitch sensor is around 50%, which is the highest reported value for SPADs with similar resolution and pixel pitch (Table 2.)
Summary
Single Photon Avalanche Diode (SPAD) arrays offer a widefield approach to more traditional scanning imaging modes for the detection and timing of individual photons of light. An alternative approach for raising the fill factor is to use a back-side illumination (as commonly seen in conventional CMOS imagers) so as to prevent metallisation layers from obscuring the photo-sensitive area, and to adopt a stacked a structure, moving the pixel electronics to a separate tier This has recently been demonstrated in a 7.8 μm pitch SPAD device attaining 45% fill factor, albeit at the cost of a reduced spectral response across the blue-green wavelengths [8]. The microlens array features cylindrical rather than the typical circular-shaped elements, and achieves a fill factor of 50% We apply this technology to an exemplar application of single-molecule localisation microscopy, and show optical resolutions of below 40 nm, not viable in the non-microlensed array
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
