  CMOS pixel sensors with a small collection electrode combine the advantages
of a small sensor capacitance with the advantages of a fully monolithic design.
The small sensor capacitance results in a large ratio of signal-to-noise and a
low analogue power consumption, while the monolithic design reduces the
material budget, cost and production effort. However, the low electric field in
the pixel corners of such sensors results in an increased charge collection
time, that makes a fully efficient operation after irradiation and a timing
resolution in the order of nanoseconds challenging for pixel sizes larger than
approximately forty micrometers. This paper presents the development of
concepts of CMOS sensors with a small collection electrode to overcome these
limitations, using three-dimensional Technology Computer Aided Design
simulations. The studied design uses a 0.18 micrometer process implemented on a
high-resistivity epitaxial layer.
