PREPARATION, MICROWAVE AND MAGNETIC FIELD RESPONSE OF YBaCuO THIN FILM MICROBRIDGES

Abstract

SummaryOn YBaCuO thin films, which were deposited at ambient temperature and were superconducting after post-deposition annealing in oxygen, microbridges and d.c. superconducting quantium interference devices (SQUIDS) were constructed by lift-off. Over a temperature range from 4.2 to >70 K the devices show well-developed Josephson-like behaviour when irradiated with microwaves.Also, SQUID operation can be observed in this temperature range.Thin superconducting films of YBaCuO were sputtered by r.f.-mag-. netron onto MgO substrates from a stoichiometric ceramic target [ 11. During the deposition, the films were kept at ambient temperature. The films were then annealed at 920 "C in flowing oxygen, after which they show electrical transitions to superconductivity with zero resistance at about 80 K. As a result of the low deposition temperatures, standard photoresist can be used for construction of the thin films by lift-off technique [2]. In that way, single microbridges as well as d.c. superconducting quantum interference devices (SQUIDS) and flux transformers were made. The width of the microbridges was below 10 pm, the thickness of the films typically being 400 nm. The operating temperature of the resulting devices reveals that almost no degradation of the film properties takes place during this lithographic process.For microbridge applications, low critical current densities Jc are desirable. Typically, films with critical current densities of 2 x lo5 A cm ' at 4.2K and 10"A cm ' at 74 K were used for our measurements (Fig. I), determined after construction of the devices and including the small degradation of the superconducting properties by the lithographic process.