2D and 3D-integrated image sensor

Abstract

This work develops a 2 Dimension (2D)/ 3 Dimension (3D)-integrated image sensor that adopts the same photodiode under different biased voltages and integrated sensing circuitry. By using the TSMC CMOS technology, four different photodiodes, N-well_P-substrate, P-diffusion_N-well, Pdiffusion_ N-well_P-substrate and N-diffusion_P-substrate, are available. Since P-substrate is used for grounding and P-diffusion_N-well has poor quantum efficiency, only the photodiode of P-diffusion_N-well_P-substrate can be employed by biasing two different voltages to P-diffusion. If the photodiode is driven by little smaller than its breakdown voltage, it functions at the Geiger mode to work for 3D depth sensing. Otherwise, this photodiode performs 2-D gray-level sensing. In the sensing circuitry, a feed-back mechanism is employed to yield a charge supply for a high dynamic range of 2-D sensing, and a feed-back inverter is adopted to boost the processing speed of 3-D sensing. These two feedbacks are effectively integrated in an active pixel to establish 2D/3D image sensor. Based on the TSMC 0.35µm 2P4M technology, a 352×288-pixel 2D/3D image sensor was implemented where its dynamic range can reach 134dB under photocurrents from 10–13A to 5×10−7A and sensing time can be accelerated to 16.3ns. The proposed image sensor can effectively capture 2D and 3D information of an object at the same location without additional alignment and post-processing.