$320 \times 240$ Back-Illuminated 10- $\mu \text{m}$ CAPD Pixels for High-Speed Modulation Time-of-Flight CMOS Image Sensor

Abstract

A $320\times 240$ back-illuminated (BI) time-of-flight CMOS image sensor with 10- $\mu \text{m}$ current-assisted photonic demodulator (CAPD) pixels has been developed. The BI pixel structure maximizes fill factor, allows for flexible transistor positioning, and makes the light path independent of the metal layers. The BI-CAPD pixel, which has relatively thinner substrate than that of front-illuminated CAPD, makes it possible to generate steeper electric-potential gradient in the vertical direction of the substrate, and results in 80% modulation contrast at 100-MHz modulation frequency. A higher modulation contrast contributes to suppress system power consumption as the sensor integration time for reaching specific signal-to-noise ratio is reduced. Alternatively, it contributes to improve depth accuracy when integration time is fixed.