  We describe a process route to fabricate arrays of Ultra-low-Noise MoAu
Transition Edge Sensors (TESs). The low thermal conductance required for space
applications is achieved using 200 nm-thick Silicon Nitride (SiNx ) patterned
to form long-thin legs with widths of 2.1 {\mu}m. Using bilayers formed on SiNx
islands from films with 40 nm-thick Mo and Au thicknesses in the range 30 to
280 nm deposited by dc-sputtering in ultra-high vacuum we can obtain tunable
transition temperatures in the range 700 to 70 mK. The sensors use large-area
absorbers fabricated from high resistivity, thin-film beta-phase Ta to provide
impedance-matching to incident radiation. The absorbers are patterned to reduce
the heat capacity associated with the nitride support structure and include Au
thermalizing features to assist the heat flow into the TES. Arrays of 400
detectors at the pixel spacing required for the long-wavelength band of the
far-infrared instrument SAFARI are now being fabricated. Device yields
approaching 99% are achieved.

Instrumentation and Detectors