Near-infrared cut-off filters based on CMOS nanostructures for ambient light sensors and image sensors

Abstract

Silicon based photodiodes provide spectral response in the visible wavelength range (VIS) but also in the near-infrared (NIR). For ambient light sensors (ALS) and image sensors with high color reproducibility the sensitivity in the NIR is unwanted as it impairs the sensing performance. Typically, external thin film filters are applied as near-infrared cut-off filters added to the photodiode or image sensor. We demonstrate plasmonic nanostructures fabricated directly within an extended CMOS (complementary metal-oxide- semiconductor) process. Designs in one and two metal layers are used and enable ambient light sensors as well as image sensors with pixel level NIR-blocking filters for color vision and additional NIR-sensitive pixels for simultaneous acquisition of VIS and NIR images

Resonant waveguide vs Fabry-Perot cavity: A comparative study for CMOS spectral sensor technology

“…Thanks to miniaturization, driving the ubiquitous use of smartphones and associated cameras in all environments, there is a rapidly growing demand for integrated spectral sensors with various functions [1,2,3,4,5]. Among these, ambient light sensors (ALS), especially for operation in the far red + near-infrared ranges, are of interest in smartphone cameras, color correction, screen-brightness adjustment and intended surveillance and monitoring systems [6,7,8,9,10,11,12,13]. The embedded filters that come atop each large pixel of an ALS could be made by variable thickness Fabry-Perot, but this choice incurs too costly multiple deposition+masking processes for more than 3-5 channels in the CMOS context that is unavoidable to get low-cost mass production [14,15,16].…”

Highly Angular Tolerant Transmission Filters for Narrow-Band Image Sensors

“…There are three challenging aspects for these filter technologies [4]: 1) to go to robust materials, such as ultraviolet-robust ones; 2) to ease mass fabrication, by changing in-plane nanostructure parameters rather than sequentially depositing numerous filters; 3) to perform better or new photonic functions, such as narrow-band and/or highly angular-tolerant filtering. This last point is the main motivation of this paper, especially for (ALS) sensors [5]. While these devices in the most common version just capture ambient light to correct smartphone displays, the present study rather addresses the more advanced versions that have multispectral capability (e.g.…”

Large area manufacturing of plasmonic colour filters using substrate conformal imprint lithography

“…Since the discovery of the phenomenon of 'extraordinary optical transmission' (EOT) by Ebbesen et al [1] in 1998, the use of subwavelength metal nanoapertures as colour filters has been discussed in numerous publications. Authors have investigated the use of different metals (Au [2], Ag [3][4][5][6][7][8], Al [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]) and various aperture forms such as lines [4,5,10,24], circles [7, 9, 11, 14-16, 21, 25], triangles [12] and crosses [17,18,23]. Alternatively, a similar filtering behaviour can also be achieved by the formation of subwavelength metal islands [8,20].…”

“…Authors have investigated the use of different metals (Au [2], Ag [3][4][5][6][7][8], Al [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]) and various aperture forms such as lines [4,5,10,24], circles [7, 9, 11, 14-16, 21, 25], triangles [12] and crosses [17,18,23]. Alternatively, a similar filtering behaviour can also be achieved by the formation of subwavelength metal islands [8,20].…”

“…However, unlike commercially available polymer filter solutions, plasmonic filters for the visible regime require a lithographic solution with a resolution capability of a few 100 nm or less. Very often serial techniques like focused ion beam (FIB) [3,10,15,21], electron beam lithography [9,11,12,14,24,25] or advanced optical lithography [22,26] as well as x-ray lithography [8] have been used in the fabrication process, including their intrinsic limitations in terms of patterning area or process time. Other approaches rely on parallel lithography techniques like nanoimprint lithography (NIL) [4,18] or laser interference lithography (LIL) [16], thereby enabling the time efficient patterning of larger areas.…”