Pinned Photodiode shape design with high demodulation contrast for high-speed time-of-flight image sensors

Abstract

A two-tap pinned photodiode (PPD) pixel using standard CMOS processes for high-speed time-of-flight (ToF) sensors is proposed in this paper. The buried n-well of this PPD can be realized by only one ion implantation, which effectively reduces the process complexity and realization difficulty of the PPD. TCAD simulation results verify that this PPD, based on a special shape design, generates a stable lateral charge transfer electric field when different taps are opened, which greatly improves the charge transfer speed and efficiency, i.e., the demodulation contrast of the pixel at high frequency can be effectively improved. Simulation results show that this PPD pixel achieves 83.5% demodulation contrast at a frequency of 50MHz and 74.6% demodulation contrast at a frequency of 100MHz, which can be applied to high-speed ToF sensors to effectively improve the depth measurement accuracy of the sensors.