  The soft X-ray imager (SXI) on the SMILE mission uses two large 4510x4510
back illuminated CCD370s to detect X-rays in the 0.2-2 keV range. These devices
take heritage from the optical imaging PLATO mission CCD270s and have been
optimised for low energy signals by including a parallel supplementary buried
channel (SBC) which should reduce the volume of the charge cloud and thereby
reduce the number of traps it interacts with as it is transferred through the
CCD. The charge transfer performance improvement between the CCD270 and the
CCD370 has been simulated using a combination of Silvaco and Matlab models to
predict its characteristics pre-fabrication over a 10^2-10^5 electron signal
range. Trap pumping measurements have been taken on both devices to count the
number of traps present and hence calculate the mean amount of trapsthat exist
per pixel across the range of signal levels. The trap pumping results are used
to calculate a charge transfer performance improvement that shows good
agreement with the simulated values, especially in the SXI science band.These
results bring added confidence to the early performance modelling of the SMILE
SXI instrument and is a good indicator that the simulations are accurate enough
to be used to model devices with more advanced geometries such as an SBC and
can be used in future CCD missions,where radiation-hardness and hence good
charge transfer characteristics are key.
