In the coming years, the LHC will be upgraded to provide much higher luminosity. This implies increased radiation damage, occupancy and pile-up for the ATLAS experiment and requires the replacement of the current Inner Detector with an improved all-silicon tracker. While standard silicon sensor technology appears to be capable of fulfilling the demanding HL-LHC requirements, new innovative technologies might offer significant advantages. Deep-submicron HV-CMOS processes feature moderate bulk resistivity and HV capability and are therefore good candidates for drift-based radiation-hard sensors. Thanks to the high electric field, charge collection is fast and nearly insensitive to radiation-induced trapping. Technically being ASICs, their production is industrialized and hence both fast and cost-effective. The seminar will outline the current ATLAS Inner Detector, the reasons for its replacement, the current layout concepts and the limitations of the current "baseline" sensor technologies before giving an overview of ideas and concepts for novel CMOS-based sensors. In addition, results obtained with first prototypes and the current roadmap towards full-size prototype modules will be shown.