J Low Temp Phys (2008) 151: 500–505 DOI 10.1007/s10909-007-9681-6 Advances in Fabrication of TES μ-Calorimeter Arrays and Associated Filter Structures for AC-Biased Read Out M.P. Bruijn · M.L. Ridder · L. Gottardi · H.F.C. Hoevers · P.A.J. de Korte · J. van der Kuur Received: 23 July 2007 / Accepted: 5 October 2007 / Published online: 17 January 2008 © Springer Science+Business Media, LLC 2008 Abstract In this paper we describe microfabrication developments for a 1024 pixel calorimeter array, to be used in future X-ray spectroscopic space missions. We report on an optimization study of high packing factor, mushroom shaped, Cu/Bi absorbers, for which a sputter deposition technique into a new type of photoresist mould has been developed. We have fabricated a prototype 32 × 32 array where 98 representable pixels are potentially functioning TESs. To gain more control on the detector pixel performance a new procedure was developed to couple absorber and thermometer, utilizing a thin insulating layer. Advances are reported in the fabrication of supercon- ducting LC resonating circuits, needed for frequency domain multiplexed read out. A quality factor Q ∼ 4000 @ 2.6 MHz has been measured, which was limited by critical current in the circuit. Keywords Transition edge sensors · X-ray astronomy · Micro machining · MEMS · Superconducting resonators PACS 85.25 Oj · 95.55.Ka 1 Introduction Transition Edge Sensor arrays are one of the most promising cryogenic detectors for future X-ray spectroscopic space missions, like XEUS (X-ray Evolving Universe Spectrometer) [1] and EDGE (Explorer of the Diffuse emission and Gamma-ray burst Explosions) [2]. A typical array size foreseen is 32 × 32 pixels. SRON, together M.P. Bruijn ( ) · M.L. Ridder · L. Gottardi · H.F.C. Hoevers · P.A.J. de Korte · J. van der Kuur SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands e-mail: M.P.Bruijn@sron.nl