  For experiments at the European X-Ray Free-Electron Laser (XFEL) the Adaptive
Gain Integrating Pixel Detector (AGIPD) is under development. The particular
requirements for the detector are a high dynamic range of 0, 1 - to more than
10E4 12.4 keV photons per pixel within an XFEL pulse duration of < 100 fs, and
a radiation tolerance of doses up to 1 GGy for 3 years of operation. The
detector will have 1024 x 1024 p+ pixels with a pixel size of 200 um x 200 um
and will be manufactured on 500 um thick n-type silicon. The design value for
the operating voltage is 500 V, however, for special applications an operation
up to ~ 1000 V should be possible. Experimental data on the dose dependence of
the surface density of oxide charges at the Si-SiO2 interface and the
surface-current density have been implemented in the SYNOPSYS TCAD simulation
program in order to optimize the design of the pixel and guard-ring layout. The
methodology of the sensor design, the optimization of the most relevant
parameters and the layout are demonstrated. Finally the simulated performance,
in particular the breakdown voltage, dark current and inter-pixel capacitance
as function of the X-ray dose will be presented.
