A key point for the project success is the development of a device capable to detect electrons with an energy resolution lower than 0.05 eV. Micro-calorimeters based on transition-edge sensors (TES) are among the best candidates since they already reach 0.11 eV of energy resolution for telecomm photons. To further increase the energy resolution, while maintaining a suitable saturation energy, it is necessary to reduce the transition temperature. This could be achieved by proximity effect of a normal-superconducting bilayer. To this aim, TiAu very thin films are under development to demonstrate the feasibility of reaching 0.05 eV energy resolution for light pulses of few eV. Thanks to the high electron stopping power of metals, the penetration depth of low energy incident electrons is limited to few nanometers and, with respect to visible light, we expect a high detection efficiency, while keeping similar dark counts and energy resolution.