Flux Pinning Films

In the weak magnetic field region (0.6 T), the experimental results are not in agreement with the intrinsic pinning model. In this case, the flux pinning at the film surface becomes more dominant than the intrinsic pinning by the ab planes. 

K. These differences are manifested in a enhancement in sputtered versus CVD-derived films which is presumably due to a larger density of flux pinning centers occurring at grain boundaries. 

Calculated and measured critical currents for a sputtered NbsGe thin film are given in Fig. 3. The measured critical currents at 10 T, which corresponds to B/Bc2(0) = 03, and, at zero field, have been fitted to the corresponding calculated curve at r = 0.5 by adjusting /c(0X Whereas the agreement between measured and calculated critical currents at 10 T is fair, the prediction of Ic fails at zero external field. Evidently, the critical currents are limited by mechanisms other than flux pinning in the self-field measurements. 

Fig. 34. True critical current densities in various oxygen-deficient thin films versus reduced temperature. The solid lines correspond to flux pinning due to spatial fluctuations of the mean fiee path and the dashed line to pitming due to spatial variations of the transition temperature (van Dalen et al. 1996).

Fig. 43. Effects of heavy-ion irradiation under different angles on flux pinning in Y-I23 superconductors (a) hysteresis loops at (top) 5 K and (bottom) 70 K of an Y-123 single crystal irradiated with 580 MeV Sn ions under an angle of 30° with respect to the c-axis and measured with the field at +30° or -30° from the c-axis (cf. the schematic of the field and track orientations, from Civale 1997) (b) angular dependence of the transport critical current densities in Y-123 thin films irradiated under various angles with respect to the c-axis (top parallel to the c-axis, 340 MeV Xe middle 30°, 770 MeV Pb bottom 60°, 340 MeV Xe from Kraus et al. 1994b) (c) angular dependence of the transport critical current densities in an Y-123/Pr-123 multilayer system irradiated by 770 MeV Pb ions under an angle of 30° with respect to the c-axis (Kraus et al. 1994b).

Izumi T (2007) Metal organic deposition of YBCO films high Ic and long-length results. In Paranthaman MP, Selvamanickam V (eds) Flux pinning and ac loss studies on YBCO coated conductors, 1st edn. Nova Publishers, Hauppauge, NY, pp 153-169... 

A similar principle to pin transfer is used for the application of flux on the solder ball of FC components for DCA (See Fig. 40.14). The die is immersed into a thin film bath of flux. The flux depth allows only the balls to be coated so that, in effect, the solder balls become the pin, taking up the flux. The flux on the solder balls is transferred with the die to the circuit board, where it provides the tack function as well as fluxing action for the solder balls during the reflow step. 

Lattice mismatch. In semiconductor systems lattice mismatches of only a few percent, or less, are desired to reduce the number of dislocations in the film. In ceramic thin films larger mismatches (generally <15%) are tolerated because higher defect densities in the film are acceptable. In some situations a certain number of defects are actually beneficial to film properties (they can provide pinning sites in high-temperature superconductors that can trap magnetic flux lines). 

---