Towards Energy-Dispersive Particle Detection with sub-eV Energy Resolution: Metallic Magnetic Calorimeters with Direct Sensor Readout

Metallic magnetic calorimeters are energy-dispersive cryogenic particle detectors providing an excellent energy resolution, a fast signal rise time, a high quantum efficiency as well as an almost ideal linear detector response. To surpass the present record resolution of 1.6 eV (FWHM) for 6 keV photons, we have started to develop integrated detectors for which the paramagnetic temperature sensor monitoring the temperature rise of the detector is integrated directly into the pickup loop of the superconducting quantum interference device. Due to the greatly enhanced magnetic flux coupling and consequently the reduced contribution of SQUID noise to the overall noise spectrum, this kind of devices should push the resolution to a value well below 1 eV. Here, we discuss the design and performance of a prototype 64 pixels metallic magnetic calorimeter based detector array with integrated detectors that rely on first-order parallel gradiometric SQUIDs with two meander-shaped pickup coils onto which planar temperature sensor made of Ag:Er are deposited.