Developments in MOS CCDs for X-ray astronomy

MOS CCDs with excellent X-ray spectroscopic performance have been supplied to both the EPIC and RGS instruments on XMM. Future X-ray astronomy instruments are planned with larger focal planes, for use with high throughput optics. To perform useful imaging spectroscopy, the array will require large area devices, optimised for the application and operated at significantly higher data rates than in previous instruments, but with similar noise performance. Most of the enabling technologies for the realisation of such arrays have been demonstrated in MOS CCDs. This paper will provide examples of advances that have already been demonstrated since X-ray CCDs of the current generation were designed and will describe developments which can be expected in the near future. In particular, we will refer to device size, construction of multi-chip arrays, read noise and quantum efficiency.