  The ECHo experiment has been designed for the determination of the effective
electron neutrino mass by means of the analysis of the end-point region of the
Ho-163 electron capture spectrum. Metallic magnetic calorimeters enclosing
Ho-163 are used for the high energy resolution calorimetric measurement of the
Ho-163 spectrum. For the first phase of the experiment, ECHo-1k, a 72-pixel MMC
array has been developed. The single-pixel design has been optimised to reach
100% stopping power for the radiation emitted in the Ho-163 electron capture
process (besides the electron neutrino) and an energy resolution < 10 eV FWHM.
We describe the design of the ECHo-1k detector chip, the fabrication steps and
the characterisation at room temperature, at 4 K and at the final operation
temperatures. In particular, a detailed analysis of the results from these
tests allowed to define a quality check protocol based on parameters measurable
at room temperature. We discuss the performance achieved with the two ECHo-1k
detector chips - the first one with Ho-163 implanted in gold and the second one
with Ho-163 implanted in silver - which have been used for the high statistics
measurement of the ECHo-1k experiment. An average activity per pixel of 0.81 Bq
and 0.71 Bq and an average energy resolution of 6.07 eV FWHM and 5.55 eV FWHM
have been achieved with these two detectors, fulfilling the requirements for
the first phase of the ECHo experiment.
