A new compact snapshot multispectral mosaic imager with an improved deposition process

Abstract

Snapshot multispectral mosaic imagers are based on optical filters monolithically integrated directly on top of a standard CMOS image sensor, extending the traditional Bayer color imaging concept to multi- or hyperspectral imaging without a need for dedicated fore-optics. This overcomes the requirement for spatial or spectral scanning during acquisition by sensing an entire multispectral data cube at one discrete point in time, enabling the multispectral acquisition of scenes containing movement. The use of CMOS process technology based, monolithically integrated optical filters further enables the qualities of compactness, low cost, high acquisition speed, a limited spectral crosstalk and a high degree of design flexibility, differentiating it from other snapshot spectral cameras. However, the use of CMOS process technology also introduces process variability leading to peak wavelength variations and challenges in repeatable sensor-to-sensor behavior. In this paper we introduce a new compact snapshot multispectral mosaic imager with an improved deposition process. The new snapshot imager has 16 bands covering a wavelength range of 460-600nm, with a resolution of 272x512pixels for each band. The deposition process is based on in-line optical monitoring, dynamically compensating the depositions to reach a targeted optical performance. By depositing on a full batch of wafers in parallel on a rotating spindle, wafer-to-wafer variability is further reduced. Filter performance repeatability is further maximized by an improved intra-wafer layer thickness uniformity. Combining this with a deposition process tuned for optical materials also enables more complex filter stacks, such as multiple cavity and high OD filters.