Metal Thin-film Dosimetry Technology for the Ultra-high Particle Fluence Environment of the Future Circular Collider At CERN

The Future Circular Collider (FCC) design study aims to assess the physics potential and technical feasibility of a new synchrotron accelerator expected to reach an energy level of 100 TeV colliding proton beams circulating in a 100 km tunnel located in the Geneva area in Switzerland. Inside the FCC detectors, over the 10 years of scheduled operation, unprecedented radiation levels will presumably exceed several tens of MGy with more than 10^17 particles/cm^2. Current dosimetry technologies, such as silicon pin diodes, are not capable of integrating this particle fluence, thus requiring a new type of sensor to be used as dosimeter in future irradiation facilities and, at a later stage, in the FCC accelerator. As a solution for the Ultra High Fluence monitoring, we have focused our research on metal nanolayers. The technology consists of thin film resistive structures deposited on silicon wafers, where sensitivity to displacement damage, measurable in a variation of their electrical properties, can be trimmed by variating geometrical (thickness, W, L) and physical (material) properties of the nanolayers. The first prototypes of these new dosimeters have been fabricated at EPFL Centre of Micronanotechnology, and specific high-fluence irradiation tests (with gamma, protons, neutrons) have been carried out in several facilities inside and outside CERN. In this paper, after presenting the process flow for the fabrication of these dosimeters, we show the results of annealing tests performed on devices previously irradiated with 23 GeV protons. These measurements suggest the occurrence of an oxidation process that was enhanced by the radiation damage.