We report our studies on electrical current pulse perturbation of superconducting YBa2Cu3O7-x (YBCO) epitaxial thin films. When a current pulse is applied to a YBCO microbridge, a voltage develops across it that depends on the amplitude of the input current pulse. For a total current (input current pulse plus the dc bias) that is lower than the critical current Ic, an inductive voltage response is observed. When the total current exceeds Ic, a resistive response is generated and is observed after a certain delay time td. The origin of the resistive response was analyzed using the Geier and Schon model, which is based on the time-dependent Ginzburg-Landau equation. Our experimental samples consisted of 200-nm-thick epitaxial YBCO films, patterned into coplanar-strip (CPS) transmission lines, containing either two-microbridge or single-microbridge test structures. For the two-microbridge samples, a train of 100-fs-duration optical pulses was used to excite the larger microbridge and generate 2-ps-duration electrical pulses, which were then applied to perturb the smaller microbridge, which was independently biased in the superconducting state. In this case, an electro-optic sampling system was used to measure the YBCO kinetic-inductive voltage responses with the picosecond time resolution. For the single-microbridge structures, an electronic pulse generator was employed to supply the input current pulse, and a 14-GHz sampling oscilloscope was used to monitor the microbridge responses. The latter signals were in very good agreement with the model of Geier and Schon, assuming that the quasiparticle dynamics process that resulted from the nanosecond-wide current excitation was bolometric and followed the phonon escape time τes.

It is necessery to investigate the buckling mechanism in order to obtaining good performance from various sensors composed of resistors and microbridges or membranes. Especially for flow sensors, a convex formed bridge has an advantage over a flat or concave bridge with respect to heat transfer coefficient. We have fabricated various shapes of bridges and have prepared SiNx sputtered films as the support films of microbridges and Pt sputtered or evaporated films as resistors. We have achieved deformation control for both the longitudinal axis and transverse axis of Pt/SiNx double layered microbridges by appropriate selection of the total residual stress of Pt/SiNx structures and of the stress gradient between the Pt film and SiNx film. The deformation direction of the longitudinal axis of bridges for the beam bridge (Type ) are all the same as that of cantilevers and may be predicted via the stress gradient between the Pt and SiNx filmes of the bridges. The deflection of the transverse axis of the table bridge supported by four beams (Type ) changes linearly with the total stress of the Pt/SiNx structure and the deformation changes for the transverse axis are the same as that of completely free films as predicted from the stress gradient between the Pt film and the SiNx film. The interesting result is that the deformation direction for the longitudinal axis of Type is opposite to that of Type with the same film structure. We discuss the reason for this opposition via differences in the progress of the anisotropic etching. We consider that this result will expand the range of manufacturable shapes and film structures of microbridges.