32 × 32 SOI CMOS image sensor with pinned photodiode on handle wafer

Abstract

We have fabricated a 32 × 32 silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) active pixel image sensor with a pinned photodiode on a handle wafer. The structure of one pixel is a four-transistor type active pixel sensor (APS) which consists of a reset and a source follower transistor on a seed wafer, and is comprised of a photodiode, a transfer gate, and a floating diffusion on the handle wafer. The photodiode could be optimized for better quantum efficiency and low dark currents because its process on the handle wafer is independent of that of transistors on a seed wafer. Most of the wavelengths are absorbed within the visible range, because the optimized photodiode is located on the handle wafer. The image has been captured by the fabricated 32 × 32 SOI CMOS image sensor with array pixels, vertical scanner, horizontal scanner, and delta-difference sampling circuit.