Fabrication and Properties of Josephson Junction Cantilevers for Terahertz Applications

Abstract

Josephson cantilevers are employed to measure the three-dimensional radiation distribution at microwave frequencies and up to the terahertz regime. Epitaxial YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> Josephson junctions with high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> products are required at these frequencies. The commonly used epitaxial Josephson junctions on LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> bicrystal substrates fulfill these requirements but exhibit significant variance in their electronic properties. In addition, the substrate losses have to be minimized and, therefore, only substrate materials with low relative permittivity ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and loss tangent tan δ in the microwave regime are suitable. The fabrication is realized by optimized pulsed laser deposition of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> . The separated devices are automatically characterized including the electric I-V curves and temperature dependence. In addition, the microwave properties are determined in our terahertz microscope at 762 GHz with a far infrared laser system and low-noise measurement electronics. The Josephson cantilevers are used to measure the spatial power distribution of the laser beam by differential resistance analysis and by Hilbert transform of the first Shapiro step. The latter approach shows a good agreement with the expected beam profile.