  Thin planar silicon sensors with a pitch of 55um, active edge and various
guard ring layouts are investigated, using two-dimensional finite-element T-CAD
simulations. The simulation results have been compared to experimental data,
and an overall good agreement is observed. It is demonstrated that 50um thin
planar silicon sensors with active edge with floating guard ring or without
guard ring can be operated fully efficiently up to the physical edge of the
sensor. The simulation findings are used to identify suitable sensor designs
for application in the high-precision vertex detector of the future CLIC linear
$e^+e^-$ collider.
