Microlens testing on back-illuminated image sensors for space applications

Abstract

The optoelectronic properties of image sensors, among which are the photosensitivity and resolution, are key to the quality factors for imaging as well as spectrometry in Earth observation and scientific space exploration missions. Microlens arrays (MLAs) further improve state-of-the-art CMOS image sensors (CIS) by redirecting more photons into the photosensitive surface/volume of each pixel. This paper reports the design, deposition, optical characterization, and reliability assessment of such an MLA made from a UV-curable hybrid polymer and replicated on a packaged back-illuminated CIS having a pixel pitch of 15.5 µm. We find that such MLAs are highly stable to temperature variations, exposure to humidity, mechanical shocks and vibrations, as well as irradiation by gamma rays, while improving the parasitic light sensitivity by a factor of 1.8. Such MLAs can be applied on a large variety of image sensors, back-illuminated but mostly front-illuminated, with pixel pitches ranging from a few to several hundreds of micrometers, making them suitable for most specifications of the space industry.

High-efficiency fill factor recovery using refractive microlens arrays imprinted on 0.5–256 kpixel front-side illuminated SPAD imagers

“…Refractive microlens structures were manufactured using an improved process flow based on UV-replication (or UVimprinting) [4], [11], [12] . Photoresist masters are used to fabricate molds for imprints of UV curable hybrid polymers deposited on top of the SPAD arrays.…”

Bioinspired Artificial Compound Eyes: Characteristic, Fabrication, and Application

“…Using the converging effect of MLAs on light, it can be coupled with a CCD and CMOS to improve the luminous sensitivity of the sensors, thus improving their pixel quantum efficiency. [157] As early as the 1990s, Deguchi et al used a MLA to improve the imaging performance of the CCD. [158] The experimental results showed that the sensitivity of the CCD was improved three times compared to the CCD without coupling MLA.…”

“…Zanella et al fabricated microlens from a UV-curable polymer and replicated them on a back-illuminated CMOS image sensor (BI-CIS) with 2048 × 256 pixels on a 15.5 µm square pitch. [46] Compared to the pixels covered with microlens material, the microlens had greatly improved the performance of the BI-CIS. The average value of MTF increased from 0.577 to 0.594, QE increased from 83.1% to 85.7% (the spectrum from 400 to 700 nm), and 1/PLS increased from 565 to 1043 at the wavelength of 800 nm.…”

“…[22][23][24][25][26][27][28][29][30] Such MLAs compose of microscale lenses with the same surface feature and the regular arrangements are important microoptical components. The great light field (LF) regulation and focusing abilities of MLAs have made it essentially in various applications such as imaging, [31][32][33][34][35][36][37][38][39] dynamic target capture, [40][41][42] beaming homogenizing, [43][44][45][46] sensing, [47][48][49] light extraction…”

Mini-Review on Bioinspired Superwetting Microlens Array and Compound Eye

“…Microlens arrays (MLAs) and MLA-based artificial compound eyes (ACEs) play a key role in advanced micro-optical systems (Pan et al, 2007 ; Song et al, 2013 ; Gorzelak et al, 2014 ; Petsch et al, 2016 ; Lin et al, 2018 ). By taking advantages of small size, high integration, and striking optical capability, MLAs and ACEs are widely applied in light-field regulation (Deng et al, 2014 ; Wei et al, 2018 ; Zhou et al, 2018 ; Sohna et al, 2019 ), fiber coupling (Elsherif et al, 2019 ; Liu et al, 2019 ; Orth et al, 2019 ), lab-on-chip devices (Fei et al, 2011 ; Lv et al, 2016 ; Vespini et al, 2016 ), biochemical observation (Ma et al, 2014 ; Holzner et al, 2018 ), laser microfabrication (Bekesi et al, 2010 ; Li et al, 2020 ), solar cells (Chen Y. et al, 2013 ), sensors (Zanella et al, 2020 ), three-dimensional imaging (Li et al, 2016 ; Kim et al, 2019 ; Zhang et al, 2019 ; Joo et al, 2020 ; Qin et al, 2020 ; Zhao et al, 2020 ), and light extraction (Shin et al, 2018 ; Zhou et al, 2019a , b ). However, the normal use of the MLA is usually restricted by many limitations.…”