Dielectric Properties of MgO, Al ₂ O ₃ , and LaAlO ₃ From 0.22 to 3 THz at Different Temperatures

With moderate cooling requirements, YBCO-based superconducting detectors are promising for space applications from microwave to the terahertz regime. Their sensitivities, however, are still rather limited. The dielectric loss of the substrate on which YBCO films are deposited might play an important role in the detector performance. This study systematically characterizes the dielectric properties of three common commercially available substrates for YBCO film, i.e., Sapphire (Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>), Lanthanum aluminate (LaAlO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>), and Magnesium oxide (MgO), from 0.22 to 3 THz at 300 K, 77 K, and 20 K. It has been found that both Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and MgO substrates exhibit significantly reduced loss tangents (tanδ < 1×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup>) at cryogenic temperatures (77 K and 20 K), whereas LaAlO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> maintains high dielectric loss tangents (tanδ > 3×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>) across all measured temperatures and frequencies