The electrical and material properties of high temperature superconducting (HTSC) thin films have improved dramatically in recent months. However, a fabrication process capable of producing Josephson junctions in finite yields has yet to be developed. Some demonstration devices have been made which indicate that the 77 K noise levels of dc SQUIDs made from thallium-barium-calcium-copper-oxide are low enough for many applications. Unfortunately, a basic understanding of the processing protocol needed to reproducibly achieve suitable I-V characteristics is lacking. The objective of this Phase I program is to establish the basic processing technology required for reliable weak link fabrication in thallium-boricum-calcium- copper-oxide. A novel approach will be investigated which takes advantage of the high volatility of thallium oxide. The current- voltage characteristics of the weak links will be measured and optimum processing conditions developed. These results will establish the feasibility of reproducibly fabricating links in microbridges of thallium-barium-calcium-copper-oxide. These results will provide the key component required to fabricate active HTSC devices such as SQUIDS and microwave mixers in the Phase II Program.
