Design and Characterization of Enhanced Angle Sensitive Pixels

Stacks of metal gratings placed above a photodiode have been demonstrated to show a strong sinusoidal response to angle. Although these devices, called angle sensitive pixels (ASPs), enable new imaging modalities on CMOS, such as light field capture, their optical sensitivity is limited by the metallic gratings. In this paper, we provide a detailed characterization of the angular response of ASPs and report on a new set of optically efficient structures for angle detection. By analyzing the properties of the Talbot effect, we present a quantitative model for the angular sensitivity, β, of an ASP and qualitatively describe the dependence of modulation depth, m, on the grating parameters. We then describe structures that employ phase gratings and interleaved diffusion diodes to provide angle sensitivity while improving the quantum efficiency by 4×. A post-CMOS process flow for the fabrication of phase gratings is described. Finally, we show that ASPs that use p
⁺
diffusion diodes embedded in an n-well diode improve their modulation efficiency by over 50% compared with interleaved diodes that share the p-substrate.