Effect of Thickness on Properties of MgB₂ Thin Films

Superconducting MgB2 films have been fabricated on sapphire substrate by the method of hybrid physical-chemical vapor deposition (HPCVD). The film thickness ranges from 75 nm to 3 mu m. The investigation on the physical properties, such as the transition temperature, T-C, the transition width, Delta T, and the critical current density, J(C), has indicated that the optimum film thickness is about 1 mu m. At this thickness, T-c(onset) = 40.3 K and Delta T-c = 0.15 K. At T = 5 K without external field, J(C) has been estimated as 5.6x10(5) A/cm(2) according to the Bean model. The film quality begins to degrade as the thickness exceeds 1 mu m. This work has demonstrated that HPCVD is a simple but effective technique for the application in the production of MgB2 wires.