CHARACTERISTICS OF ALL-NB THIN-FILM MICROBRIDGES FABRICATED BY NANOMETER PROCESS

We have fabricated all-Nb thin film microbridges by nanometer process using new resist developed by us, electron beam lithography (EBL) and reactive ion etching (RIE) using CBrF3 gas. The resistance against CBrF3 plasma of this EB resist is 4 - 10 times as strong as poly-(methyl methacrylate) PMMA. The merit of RIE using CBrF3 gas is an anisotropic etching and high selectivity about resist and target. Trench of about 20 nm width was fabricated. Using this technique, the bridge with 40 nm length and 50 nm width was fabricated, and the thickness of bridge was 100 nm. The capacitance of the junction was estimated as 0.004 pF. Because of this small capacitance, fabricated samples are suitable for detection of submillimeter wave. The critical current I(c)(T) of fabricated samples was proportional to (1 - T/T(c)3/2 like variable thickness bridge (VTB). Moreover, Shapiro step up to the 11th under the millimeter wave radiation (70 GHz) was observed.