Pixel structure with 10 nsec fully charge transfer time for the 20m frame per second burst CMOS image sensor

Abstract

ABSTRACT In this paper, we demonstrate the technologies r elated to the pixel structure achieving the fully charge transfer time of less than 10 nsec for the 20M frame per second burst CMOS image sensor. In this image sensor, t he size of the photodiode ( PD ) is 30.0 P m H u 21.3 P m V in the 32.0 P m H u 32.0 P m V pixel. In the pixel , the floating diffusion (FD) and the transfer -gate -electrode (TG) are place d at the bottom center of the PD . The n -layer for the PD consists of the semicircular regions centered on the FD and the sector -shaped portions extending from the edge s of the semicircular regions. To generate an electric field greater than the average of 400 V/cm toward the FD direction in the entire PD region, the n -layer width of the sector -shaped portions becomes narrower from the proximal -end to the distal -end. By using the PD structure, which include s the above mentioned n-layer shape and the PD dopant profile with the condition of three times n -type dopant imp lantation , w e achiev ed to collect 96 % of the charges generated in the PD at the FD withi n 10 nsec . An ult ra-high speed CMOS image sensor with the abovementioned pixel structure has been fabricated. Through t he experiments, we confirmed t hree key characteristics as follows; the image lag was below the measurement limit , the electron transit time in the PD was less than 10 nsec , and the entire PD region had equivalent sensitivit y. Keywords: burst CMOS image sensor , ultra -high speed , pixel structure, fully charge transfer