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

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dc.contributor.authorBruschini, Claudio
dc.contributor.authorAntolovic, Ivan Michel
dc.contributor.authorZanella, Frédéric
dc.contributor.authorUlku, Arin C.
dc.contributor.authorLindner, Scott
dc.contributor.authorKalyanov, Alexander
dc.contributor.authorMilanese, Tommaso
dc.contributor.authorBernasconi, Ermanno
dc.contributor.authorPešić, Vladimir
dc.contributor.authorCharbon, Edoardo
dc.date.accessioned2023-07-13T07:00:25Z
dc.date.available2023-07-13T07:00:25Z
dc.date.issued2023-06-14
dc.description.abstractThe 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.en_US
dc.description.sponsorshipSchweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung; Nederlandse Organisatie voor Wetenschappelijk Onderzoek.en_US
dc.identifier.citationOptics Express 31 (13), 21935-21953en_US
dc.identifier.doi10.1364/OE.488177
dc.identifier.urihttps://hdl.handle.net/20.500.12839/1247
dc.language.isoenen_US
dc.subjectMicrolensesen_US
dc.subjectMicrolens arrayen_US
dc.subjectOn-chip lensen_US
dc.subjectSPADen_US
dc.subjectImageren_US
dc.titleChallenges and prospects for multi-chip microlens imprints on front-side illuminated SPAD imagersen_US
dc.typeJournal Articleen_US
dc.type.csemdivisionsBU-Ten_US
dc.type.csemresearchareasPhotonicsen_US
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