Imaging systems with improved near-infrared detection pixels

Abstract

An imaging device may have an array of image sensor pixels that includes infrared image pixels. Backside and frontside reflectors may be incorporated into the infrared pixels to increase effective thicknesses of photosensitive regions within the pixels. In other words, light incident on each pixel may be reflected and traverse the photosensitive region multiple times, thereby allowing silicon in the photosensitive region to absorb infrared light more efficiently. The backside reflector may be interposed between the silicon and a microlens, which may have a toroidal shape to direct light around the backside reflector. If desired, the toroidal lens may have a concave opening. Alternatively, the backside reflector may be ring-shaped, and a spherical microlens may focus light through a center portion of the reflector. A top surface of the silicon layer may be curved to focus light toward the center of the photosensitive region and improve pixel efficiency.