  In recent years, the progress on low temperature detector technologies has
allowed design of large scale experiments aiming at pushing down the
sensitivity on the neutrino mass below 1\,eV. Even with outstanding
performances in both energy ($\sim$eV on keV) and time resolution ($\sim
1\,\mu$s) on the single channel, a large number of detectors working in
parallel is required to reach a sub-eV sensitivity. HOLMES is a new experiment
to directly measure the neutrino mass with a sensitivity as low as 2\,eV.
HOLMES will perform a calorimetric measurement of the energy released in the
electron capture (EC) decay of 163Ho. In its final configuration, HOLMES will
deploy 1000 detectors of low temperature microcalorimeters with implanted 163Ho
nuclei. The baseline sensors for HOLMES are Mo/Cu TESs (Transition Edge
Sensors) on SiN\textsubscript{x} membrane with gold absorbers. The readout is
based on the use of rf-SQUIDs as input devices with flux ramp modulation for
linearization purposes; the rf-SQUID is then coupled to a superconducting
lambda/4-wave resonator in the GHz range, and the modulated signal is finally
read out using the homodyne technique. The TES detectors have been designed
with the aim of achieving an energy resolution of a few eV at the spectrum
endpoint and a time resolution of a few micro-seconds, in order to minimize
pile-up artifacts.
