Collection efficiency and charge transfer optimization for a 4-T pixel with multi n-type implants

In order to increase collection efficiency and eliminate image lag, multi n-type implants were introduced into the process of a pinned-photodiode. For the purpose of improving the collection efficiency, multi n-type implants with different implant energies were proposed, which expanded the vertical collection region. To reduce the image lag, a horizontal gradient doping concentration eliminating the potential barrier was also formed by multi n-type implants. The simulation result shows that the collection efficiency can be improved by about 10% in the long wavelength range and the density of the residual charge is reduced from 2.59 x 10 super(9) to 2.62 x 10 super(7) cm super(-3).