Challenges and prospects for multi-chip microlens imprints on front-side illuminated SPAD imagers

The overall sensitivity of frontside-illuminated, silicon single-photon avalanche diode (SPAD) arrays has often suffered from fill factor limitations. The fill factor loss can however be recovered by employing microlenses, whereby the challenges specific to SPAD arrays are represented by large pixel pitch (> 10 µm), low native fill factor (as low as ∼10%), and large size (up to 10 mm). In this work we report on the implementation of refractive microlenses by means of photoresist masters, used to fabricate molds for imprints of UV curable hybrid polymers deposited on SPAD arrays. Replications were successfully carried out for the first time, to the best of our knowledge, at wafer reticle level on different designs in the same technology and on single large SPAD arrays with very thin residual layers (∼10 µm), as needed for better efficiency at higher numerical aperture (NA > 0.25). In general, concentration factors within 15-20% of the simulation results were obtained for the smaller arrays (32×32 and 512×1), achieving for example an effective fill factor of 75.6-83.2% for a 28.5 µm pixel pitch with a native fill factor of 28%. A concentration factor up to 4.2 was measured on large 512×512 arrays with a pixel pitch of 16.38 µm and a native fill factor of 10.5%, whereas improved simulation tools could give a better estimate of the actual concentration factor. Spectral measurements were also carried out, resulting in good and uniform transmission in the visible and NIR

Super resolution microscopy with SPAD imagers

Cytoskeleton (microtubuli) of a cell with resolution down to 30 nm.<br>Reference: <br><p>Antolovic, I. M., Burri, S., Bruschini, C., Hoebe, R. A., & Charbon, E. (2017). SPAD imagers for super resolution localization microscopy enable analysis of fast fluorophore blinking. <i>Scientific Reports</i>, <i>7</i>. https://doi.org/10.1038/srep44108</p

High frame rate SPAD camera videos

3 videos with different frame rates showing glass breaking:<br>1)156 frames per second<br>2)2604 frames per second<br>3)15625 frames per second<br><br>One can note that the moving objects appear blurred at lower frame rates because of their high speed. High frame rate exhibit higher noise due to lower number of detected photons - shot noise is in this case a dominant noise source. Interestingly, on the 2nd video (60 binned) you can see the glass "levitating" between 0:50 and 1:20. <br><br>More information on:<br>1) https://www.osapublishing.org/oe/abstract.cfm?uri=oe-22-14-17573<br>2) http://ieeexplore.ieee.org/document/7177073/?arnumber=7177073&tag=1<br>3) http://www.mdpi.com/1424-8220/16/7/1005<br><br

Light microscope with photon-counting detector elements and imaging method

A light microscope comprises a light source (10) for illuminating a specimen (35), a photon-counting detector array (60) with a plurality of photon-counting detector elements (61-64) for measuring detection light (15) coming from the specimen (35), wherein the photon-counting detector elements (61-64) are configured to output respective measured photon count rates, and a control device (70) for controlling the photon-counting detector array (60). The control device (70) is configured to individually influence the measurable photon count rates which are simultaneously measurable with different photon-counting detector elements (61-64) and/or which are consecutively measurable with the same photon-counting detector element (61). Furthermore, in an imaging method the measurable photon count rates of photon-counting detector elements are individually influenced to increase the signal-to-noise ratio for the photon-counting detector array