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TT: Fachverband Tiefe Temperaturen

TT 9: SC: Poster Session

TT 9.56: Poster

Montag, 22. März 2010, 14:00–18:00, Poster A

Micro-fabrication of metallic magnetic calorimeters — •S. Schäfer, S. Kempf, A. Pabinger, C. Pies, J-P. Porst, F. v. Seggern, T. Wolf, L. Gastaldo, A. Fleischmann, and C. Enss — Kirchhoff Institut für Physik, INF 227, 69120 Heidelberg

Metallic magnetic calorimeters (MMC) are energy dispersive particle detectors with very high resolving power that are operated at temperatures below 100 mK. Our presently fabricated MMCs consist of a particle absorber made of electroplated gold, in tight thermal contact to a temperature sensor. The sensor is made of the paramagnetic alloy Au:Er and placed in a weak magnetic field. A temperature rise upon the absorption of a particle is detected via the change of the sensor’s magnetization monitored by a dc-SQUID. A planar meander shaped coil made of niobium underneath the sensor is used to generate the necessary bias magnetic field and to pick-up the change of magnetization. An on-chip persistent current switch with Au:Pd heater is used to inject the field generating current. We describe the fabrication steps for the Au:Er sputter target and the co-sputter process for the deposition of the sensor material. We discuss the challenge of electroplating high quality gold into a mold of photo resist to fabricate overhanging absorbers on top of the sensors and present the processes for the sputter deposition and micro-structuring of niobium, SiO_x and Au:Pd. We report on measurements of all relevant material properties at low temperatures, e.g. the critical current density of the niobium structures as well as the specific heat and the magnetization of the sensor material, and compare them to those of the corresponding bulk materials.