A Backside-Illuminated 3.5 μm Pixel With 86% Demodulation Contrast at 1.0 V Voltage Swing for Indirect Time-of-Flight Image Sensors

This article presents a
$3.5 ~\mu \text{m}$
stacked backside-illuminated (BSI) indirect time-of-flight (i-ToF) pixel fabricated in a 65-nm CMOS image sensors (CIS) process. Transfer gate-induced lateral electric field control of charge transfer is one of the most relied techniques for implementing i-ToF image sensors. However, the transfer gate as modulated gate usually needs a high voltage swing to achieve high demodulation contrast (DC). We introduce a photonic demodulator pixel that utilizes a new lateral electric field modulation technology to achieve a 1.0 V modulation voltage swing while maintaining a high DC of 86% at 100 MHz modulation frequency. The proposed method employs a gate-controlled junction field effect transistor (JFET) to control the drain-induced barrier lowering (DIBL) effect to modulate the lateral electric field. In addition, the photonic demodulator can be also fully depleted with an N-type epitaxy for 22% quantum efficiency (QE) enhancement at 940 nm. This development can greatly lower the power consumption for high-resolution i-ToF sensor applications.