Development of an Antenna-coupled Al Superconducting Tunnel Junction for a detection of cosmic microwave background B-mode polarization H. Ishino 4, M. Yoshida 1, M. Hazumi 2, M. Hasegawa 2, T. Higuchi 2, S. Ishimoto 2, N. Sato 2, K. Sumisawa 2, T. Suzuki 2, O. Tajima 2, T. Tomaru 2, Y. Ushiroda 2, T. Morishima 3, H. M. Shimizu 3, A. Kibayashi 4, S. Mima 4, S. Ariyoshi 5, H. Sato 5, M. Hattori 6 1) Accelerator laboratory, KEK 2) Institute of particle and nuclear studies, KEK 3) Institute of material structure science, KEK 4) Department of physics, Okayama University 5) RIKEN 6) Astronomical institute, Tohoku University Abstract We present our recent development of a new Aluminum Superconducting Tunnel Junction (STJ) detector for future measurements of the cosmic microwave background (CMB) polarization. We have successfully fabricated the Al STJs. The measured IV characters are within expectations. Introduction astro-ph/ How the inflation happened in the early universe is one of the fundamental questions still unresolved. One way to elucidate the inflation mechanism is to detect CMB polarization pattern, called B-mode, generated by the primordial gravitational waves. As shown in the right figure, the B-mode signal is overlaid by huge foregrounds: dust and synchrotron. In order to subtract those with reduced systematic uncertainties, we need a detector that makes use of a single technology and is able to cover the frequency range over 90GHz. → The aluminum STJs is one of the solutions. About STJ E gap =2  S I S The STJ has a sandwich structure of superconductor-insulator- superconductor. 1. a photon breaks a Cooper pair. The procedure how to detect a photon. 2. quasi-particles are produced in the conducting band. 3. go through the insulator with the tunneling effect. 4. measure the output current. Material candidates Video detection Photon detection Energy gap (2  ) TCTC Elements The antenna-coupled aluminum STJ can cover the frequency of > 40GHz. Fabrication substrate superconductor thin film photoresist dry-etching, remove the photoresist We have fabricated the Al STJs in the clean rooms at RIKEN and KEK. We employ the photolithography technique. The fabrication procedure is based on that of the Nb STJ. Etching procedure is carefully tuned so as not to damage the photoresist. Evaluation GND Al antenna Nb strip 7μm readout SIS junction Nb strip SIS junction TEM images of the cross section Nb Al 2 O 3 Al Al 2 O 3 We successfully fabricate the antenna-coupled Al STJ. assume r=0.01 We use a 3 He sorption cryostat able to cool down to 0.3K and measure IV curves. ~0.05μm 5x5mm 2 I V 2/e2/e Real case (T>0K): leak current in the subgap region due to thermal excitation. Ideal case (T=0K) Measurement results 4  /e =650  V gap due to serial connection of two STJs. R n = 0.3  I leak =  V Comparison with the theoretical calculation measurements on two different SIS junctions at two temperatures. temperature [K] The magnitude of the leakage current is within expectation. Summary and Future We have successfully fabricated the antenna-coupled Al STJ. The measured performance is within expectation. We will try to irradiate milliwave light to the detector in near future.