Microwave Surface Resistance of Superconducting YBa₂Cu₃O_7-δ Thin Films

Abstract

One of the serious material problems with high T_c superconductors is their granularity which greatly affects their microwave transmission (as well as absorption) properties. High quality near-epitaxial thin films of these oxide superconductors have been found to be advantageous for microwave devices due to their low conduction loss. Pulsed laser ablation deposition (PLAD) technique has been extensively used for the growth of high quality films of oxide superconductors. Work carried out at TIFR during the last several years has convincingly shown that significant improvement in microstructure, and consequently, in microwave transmission properties of YBa₂Cu₃O_7-δ (YBCO) thin films can be realised by incorporating a small quantity (about 5%) of Ag in the YBCO target used for PLAD. Microwave surface resistance of YBCO films has been measured using microstrip resonator configuration at various temperatures in the range 15-88K and in the frequency range 1.5 to 12 GHz. Due to the much improved microstructure, Ag-YBCO films have not only shown a low surface resistance but also a good power handling capability. Au-YBCO films too have shown improved properties with the added advantage of much improved environmental stability. This paper reviews significant advances in the growth and microwave measurements of Ag-YBCO and Au-YBCO thin films and show why they would be of great advantage for microwave passive devices operating at 77K.

Indexing terms:

• YBa₂Cu₃O_7-δ thin films
• Microwave surface resistance
• Oxide superconductors
• Pulsed laser deposition
• Microwave devices

Additional information

Notes on contributors

R Pinto

R Pinto, has been actively engaged in research at the Tata Institute of Fundamental Research since 1964. He obtained PhD Degree in Physics in 1972 from TIFR/University of Bombay, India. He has served as a member of national committees for the development of advanced devices such as charge coupled imagers and magneto-optic devices, and was awarded the 1997 MRS (India) Medal. Currently, Professor Pinto heads the high T_c thin film microwave device program in collaboration with Society for Applied Microwave Electronic Engineering and Research (SAMEER), Mumbai, India and Space Applications Centre (SAC), Ahmedabad, India.

S P Pai

S P Pai obtained his MSc (Physics) degree from Bombay University in 1981 by topping the merit list of that year. Since then he is involved in research related activity at the Tata Institute of Fundamental Research, Mumbai. His current interest is in High T_c superconductors and materials and devices related to them.

P R Apte

Prakash R Apte was born in Indore, India on March 23, 1947. He received his BE degree in Electrical Engineering in 1968 from Indore University, the MTech degree in Electrical Engineering from IIT Kanpur and the PhD degree from Bombay University.

Since 1970 he has been with the Solid State Electronics Group at the Tata Institute of Fundamental Research, Mumbai. He was at Stanford University Integrated Circuit Laboratory as a visiting research associate during 1977–78. His current interest is in fabrication and modelling of high temperature superconducting thin film devices. His other interest is in micromatching of silicon for microsensors, actuators and MicroElectroMechanical systems (MEMS).

B K Sarkar

B K Sarkar passed BTech in 1967, MTech in 1969 and PhD in 1981 from IIT Medras, NT Kharagpur and IIT Bombay respectively, initially he joined the Tata Institute of Fundamental Research, Mumbai where he worked as Scientific Officer from 1969 to 1985,. Subsequently, he was transferred to Society for Applied Microwave Electronics Engineering and Research (SAMEER) under the Department of Electronics, Government of India, at present, he is holding the post of Associate Director. He has worked for the last 30 years on Semiconductor devices and its applications, antenna and special purpose radar systems. He has published as many as 95 papers in the journals and proceedings of symposia in India and abroad. He is a senior member of Society of EMC Engineers, India.