本研究は，Si基板上にNbN-HEBMを構築する手法を検討し，高い(100)配向性を有するMgO薄膜の成膜方法を確立，MgO薄膜をバッファ層として用いることで，優れた超伝導特性を有するNbN極薄膜を室温で形成できることを見出している．そしてこのNbN成膜技術を用いてSi基板上に3 THz帯HEBMを設計・試作し，良好なミキサ雑音温度特性が得られたので報告する。

Hot electron bolometer mixers (HEBM) are expected to be used as low-noise heterodyne mixers in the terahertz frequency range. We are developing quasi-optical HEBMs for applications such as atmospheric remote sensing and radio astronomy in the terahertz frequency range. Therefore,, we developed a fabrication method using niobium nitride (NbN) ultrathin films deposited on a silicone (Si) substrate for terahertz applications. First,, a magnesium oxide buffer layer 50 nm thick was deposited on a Si substrate at approximately 525 °C. After deposition of this layer,, NbN ultrathin films were deposited at ambient temperature. Using the buffer layers,, we found the transition temperature of the 3.5-nm-thick NbN thin films to be approximately 10 K. The same method was applied to fabricate NbN-HEBMs on a Si substrate. The fabricated quasi-optical mixers were designed to operate at 3.1 THz. The receiver noise temperature was found to be approximately 1930 K (DSB) at 3.1 THz.

doi: 10.2221/jcsj.49.433