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Relationship Between Loaded Quality Factor and Responsivity for NbN-Based MKIDs Using Dual-Function Spiral Strip

2014; IEEE Council on Superconductivity; Volume: 25; Issue: 3 Linguagem: Inglês

10.1109/tasc.2014.2367459

1558-2515

A. Saito, Kensuke Nakajima, K. Hayashi, Yasunobu Ogawa, Y Okuyama, Daichi Oka, Seiichiro Ariyoshi, H. Yamada, Tohru Taino, Chiko Otani, Jongsuck Bae, Shigetoshi Ohshima,

Microwave Engineering and Waveguides

We investigated the relationship between loaded quality factor (QL) and responsivity of microwave kinetic inductance detectors (MKIDs) using a dual-function spiral strip (DFSS). Three types of DFSSs with different QL values were designed, and the S 21 properties were simulated when kinetic inductance of a superconductor was changed by using a 2.5-dimentional simulator. The simulated results showed that a very high Q L value was not necessarily required. The resonator frequencies of the 25-MKID array using a better type of DFSS (Q L ~ 3500) were adjusted to be separated by 5 MHz around 2.0 GHz. The 25-MKID array were fabricated using 20-nm thick niobium nitride films deposited on r-plane sapphire substrates. We clearly observed 25 half-wavelength resonances around 2.0 GHz at 2.245 K. The optical responses were also confirmed using hot and cold radiation. The dependence of the responsivity on the Q L indicated that the Q L value of approximately 2000 could obtain higher responsivity.