title: Microlens performance limits in sub-2mum pixel CMOS image sensors.
abstract: CMOS image sensors with smaller pixels are expected to enable digital imaging systems with better resolution. When pixel size scales below 2 mum, however, diffraction affects the optical performance of the pixel and its microlens, in particular. We present a first-principles electromagnetic analysis of microlens behavior during the lateral scaling of CMOS image sensor pixels. We establish for a three-metal-layer pixel that diffraction prevents the microlens from acting as a focusing element when pixels become smaller than 1.4 microm. This severely degrades performance for on and off-axis pixels in red, green and blue color channels. We predict that one-metal-layer or backside-illuminated pixels are required to extend the functionality of microlenses beyond the 1.4 microm pixel node.
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Yijie
authors.initials: Y
authors.lastname: Huo
authors.forename: Christian C
authors.initials: CC
authors.lastname: Fesenmaier
authors.forename: Peter B
authors.initials: PB
authors.lastname: Catrysse
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007909:Lenses; D008904:Miniaturization; D010781:Photography / Q000295:instrumentation*; D012666:Semiconductors; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D014159:Transducers