  We report on the development of Thermal Kinetic Inductance Detectors (TKIDs)
suitable to perform X-ray spectroscopy measurements. The aim is to implement
MKIDs sensors working in thermal quasi-equilibrium mode to detect X-ray photons
as pure calorimeters. The thermal mode is a variation on the MKID classical way
of operation that has generated interest in recent years. TKIDs can offer the
MKIDs inherent multiplexibility in the frequency domain, a high spatial
resolution comparable with CCDs, and an energy resolution theoretically limited
only by thermodynamic fluctuations across the thermal weak links.
Microresonators are built in Ti/TiN multilayer technology with the inductive
part thermally coupled with a metal absorber on a suspended SiN membrane, to
avoid escape of phonons from the film to the substrate. The mid-term goal is to
optimize the single pixel design in term of superconducting critical
temperatures, internal quality factors, kinetic inductance and spectral energy
resolution. The final goal is to realize a demonstrator array for a next
generation thousand pixels X-ray spectrometer. In this contribution, the status
of the project after one year of developments is reported, with detailed
reference to the microresonators design and simulations and to the fabrication
process.
