Relative permittivity and dielectric loss tangent of substrate materials for high-Tc superconducting film

We measure the relative permittivityεr and dielectric loss tangent tanδ of substrate materials for high-Tc superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. Theεr values are 10–30 and become almost constant below about 50 K. The tanδ values decrease with decreasing temperature and are below 1×10−5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tanδ values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-Tc superconducting films. It is also demonstrated that the tanδ of the substrate material is strongly affected by impurities.