SPAD array sensitivity enhancement by diffractive microlens

Jérôme Vaillant (1) , Lilian Masarotto (2) , Romain Paquet (2) , Véronique Lecoutre (2) , Catherine Pellé (2) , Norbert Moussy (2) , Sébastien Jouan (3)

1 DOPT - Département d'Optronique
2 CEA-LETI - Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information
3 ST-CROLLES - STMicroelectronics [Crolles]

In this paper we present sensitivity improvement of SPAD pixel using diffractive microlens. We designed microlens structures based on rigorous optical simulations, then we developed the process for thick optical spacer and thin amorphous silicon deposition, on which diffractive structures were defined by lithography and etching. These microlenses have been implemented two SPAD designs available on STMicroelectronics 40nm CMOS testchips (32 × 32 SPAD array). Circuits were characterized and we demonstrated, depending on SPAD design, high optical gain at 850nm (×3 to ×8) and significant gain at 940nm (×2 to ×2.5).

Domaines: Optique [physics.optics]; Micro et nanotechnologies/Microélectronique

Jérôme Vaillant, Lilian Masarotto, Romain Paquet, Véronique Lecoutre, Catherine Pellé, et al.. SPAD array sensitivity enhancement by diffractive microlens. IISW 2017 - 2017 International Image Sensor Workshop, International Image Sensor Society, May 2017, Hiroshima, Japan. ⟨hal-04235027⟩