A high-fill-factor SPAD array cell with a shared deep N-well

This paper presents a high-fill-factor (FF, is the ratio of photo-sensitive area to total imaging or pixel area) array cell of single photon avalanche diodes (SPADs), where the four basic SPAD devices share a same deep N-well in deep sub-micron CMOS technology. A honeycomb structure is also used in this array cell to improve the fill factor. By calculation the overall fill-factor of the array cell is up to 57%. Various methods, such as the virtual guard ring, are also used in this structure to reduce the crosstalk caused by the shared deep n-well. The key parameters such as Dark Count Rate (DCR) and Photon Detection Efficiency (PDE), are calculated to analyze the important statistical performances of the proposed SPAD array cell.