Controlling the axis orientation in REBa2Cu3Oy (RE123; RE meaning Nd, Sm, Gd, Y and Yb) thin films is an important problem for many superconducting applications since RE123 materials have anisotropic properties (e.g., irreversible field, critical current density and so on) along their crystallographic axes. To obtain the RE123 thin films with excellent superconducting properties, we systematically studied the orientation, mechanism of orientation control and superconducting properties in RE123 thin films. We found that the preferred orientation of RE123 thin film on MgO and SrTiO3 is c-axis orientation. RE123 thin films with RE/Ba substitution (RE=Sm, Gd) showed that the substrate temperature corresponding to the boundary line between the c-axis and a, c-axis mixed orientation decreased as RE/Ba substitution increased. These facts imply that the orientations of RE123 thin film are principally determined by their peritectic temperatures. The highest critical current densities of RE123 thin films so far are 7.93 MA/cm2 for Sm123, 3.03 MA/cm2 for Gd123 and 1.85 MA/cm2 for Yb/Nd123.
The micro-miniature JT cooler is a promising cooling device as an element of the micro-thermal system for semiconductor devices, which dissipate an incredible amount of heat. In particular, the thermal management of laser diodes is a serious problem because they require a large amount of power but must maintain a fixed temperature. Considering such a situation, the performance of a micro-miniature JT cooler was calculated under the assumption of a countercurrent heat exchanger operating with a laminar gas flow, and the guidelines of a micro-miniature JT cooler for optimizing pump power and size were designed from the viewpoint of minimizing the cost. The authors present the results in this paper. A micro-miniature JT cooler was fabricated from Si wafer using a photolithographic process, which is available for operation with C2H6 from 3 MPa to 0.1 MPa. It is shown that a cooling power of 2.1 W was obtained at 239 K with a mass flow of 51.7 mg/s.