The Future Circular Collider (FCC) is the envisioned particle accelerator to be installed in the Geneva area (Switzerland). It could achieve an energy of 100 TeV by colliding proton beams (FCC-hh) travelling through a 100 km tunnel. Unprecedented radiation levels inside the FCC detectors will presumably exceed several tens of MGy with more than 10e17 particles/cm2. Current solid-state dosimetry technologies based on silicon, are not capable of withstanding such radiation, thus requiring a new type of sensor to be used as dosimeter in the future irradiation facilities and, at a later stage, in the accelerator itself. The aim of this thesis is to develop a Radiation Dependent Resistor (RDR) as novel candidate technology for ultra-high radiation monitoring, and to study the radiation effects that are responsible for the measured increase of resistance of the RDR. Following theoretical and experimental selection processes, copper was chosen as the best candidate material as thin film for the active layer of such radiation sensor. Such approach was never attempted before. The RDR was developed via four experimental phases each including: the micro-fabrication at the CMi Center of MicroNanoTechnology (EPFL), the irradiation tests with protons at the IRRAD Proton Facility (CERN) and neutrons at the TRIGA nuclear reactor (Jožef Stefan Institute), and the characterisation at CERN and EPFL. As result, the RDR was fully prototyped with an optimized process flow, a compact chip layout, a radiation hard Printed Circuit Board (PCB), and an online and remote readout system. By analyzing the electrical data and cross-sectional images of the irradiated samples, the conventional theory of high-temperature copper oxidation has proven useful in proposing a new concept of room temperature oxidation which is considerably amplified by radiation (Radiation Enhanced Oxidation). This new interpretation has been implemented in behavioural, analytical and empirical models and validated against experimental data. Through the knowledge gathered in the framework of this thesis, the RDR technology was demonstrated to be compatible with the radiation levels expected in high energy physics experiments such as the HL-LHC and FCC. Additionally, these copper RDR sensors could also be used as dosimeters in particularly radioactive environments such as nuclear and fusion reactors.