The LHC is undergoing an upgrade process to accomplish its transition to the high-luminosity phase, which is foreseen from 2027 onward, and the CMS experiment is thus having major upgrades to withstand the high radiation flux. The Pisa-CMS group is involved in the upgrade of the inner pixel tracker of the experiment, which is located closest to the interaction point and thus susceptible to the highest amount of radiation. Since the present tracker will be completely replaced with a new and highly radiation-tolerant subdetector, new designs and materials are being studied for the same. Studies of planar and three-dimensional silicon pixels of varying dimensions were carried out for the innermost part of the detector. Double and quad modules are also under investigation. Modules are being irradiated at high fluences, and beam test studies are being done before and after irradiation to study the performance in realistic conditions. In addition to this, I am actively involved in studying the behaviour of different modules under X-rays, which reveal further interesting results.