Ie situ processed high Tc superconducting devices using a low temperature FIB system

摘要

A Focused Ion Beam (FIB) system has been equipped with a low temperature sample holder mount, compatible with electron scanning microscopy and I-V measurements on the device under test, during the FIB milling operation. The use of this FIB system enables the patterning of micro and nanobridges (resolution down to 50 nm) in a reproducible way. We detail in this paper a possible application in the field of superconducting thermometry. It uses the Ic(T) dependence in order to enlarge the operating range of classical R(T) thermometers and that of microbridges elaborated with standard photolithography (2 μm resolution). This were proved to operate with a high sensitivity parameter SiT=dIc/dT (above a few mA/K) in a narrow temperature range a few K below Tc. Using in situ controlled thinning of YBCO microbridges maintained at 82 K during FIB operation, we were able to obtain various sensitivities from the μiA/K to the mA/K range, extending the operating range down to liquid helium temperature. Besides, it will be shown that the low temperature part of the Ic(T) may be fitted by the flux creep model, leading to estimation of the effective bridge film thickness.