The upgrade programme of the CMS Tracker at SLHC

The CMS experiment at LHC is planning a major upgrade of its tracking system to adapt to expected increases in luminosity of the accelerator. Present ideas suggest it will be achieved in two stages, with a major long shutdown after the experiments have reached their design lifetimes, about ten years after start-up. At this time the accelerator will increase the luminosity to 10$^{35}$ cm$^{-2}$s$^{-1}$. The new tracker will then have to cope with several hundred interactions per bunch crossing and fluxes of thousands of charged particles emerging from the 40MHz collisions. This will require major developments of detector technology and RandD has begun to address the expected challenges. Among the most important are the radiation tolerance of sensors and other components, the provision and distribution of power for both electronics and sensors, the removal of heat loads, which may significantly exceed those in the present detector, and the development of low power, but highly performing electronics in more advanced technologies. CMS has also identified another novel requirement, which is to utilise tracker data in the first level trigger, which must maintain the 100kHz rate for compatibility with existing sub-detector systems while increasing the decision latency by only a few $\mu$sec. The motivations for the upgrade and recent progress in several aspects of the R\&D are described.