Cryogenic characterization of potential high temperature superconducter substrates at microwave frequencies

Author

Sukhmani Kaur, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

5-31-1990

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Edip Niver

Second Advisor

Aly Fathy

Third Advisor

James R. Matey

Fourth Advisor

Kenneth Sohn

Abstract

The lack of characterization data for dielectric substrate materials at microwave frequencies and cryogenic temperatures hinders the development of high T_c superconducting circuits. Low loss (tanδ < 10^-4) substrates with dielectric constants in the range of 5-100 at cryogenic temperatures are needed to realize the advantages of superconductor circuits. Measurement techniques previously reported are either time consuming or inaccurate. We report an adaptation of Courtney's method for accurate, simple evaluation of complex dielectric constants (10 < ε_r < 100) at low temperatures. The fixture was calibrated using known properties of polycrystalline ZrSnTiO4. We measured er and tans on three potential substrate materials, Al₂O₃, MgO, and LaAlO₃ at 5-10 GHz in the temperature range 77-300K. No temperature hysteresis in either ε_r or tanδ was observed. The effects of inhomogeneity in the samples were studied, especially effects on the loss tangent. The accuracy of the ε_r measurements are 5%; the tans accuracy is ± 0.5 x 10^-5. Based on our results at 77K, alumina (tanδ = 0.229x10^-4, ε_r = 9.72) and MgO (tanδ = 0.414x10^-4, ε_r= 9.613) are suitable. Results on the loss tangent of LaAlO₃ were inconclusive because of inhomogeneities in the crystal.

Recommended Citation

Kaur, Sukhmani, "Cryogenic characterization of potential high temperature superconducter substrates at microwave frequencies" (1990). Theses. 2782.
https://digitalcommons.njit.edu/theses/2782