Study of MgB2 Ultrathin Films in Submicron Size Bridges

We discuss a custom built hybrid physical chemical vapor deposition system for MgB
₂
ultrathin film deposition: construction, deposition process development, and optimization. Achieved films on SiC substrates have a critical temperature (T
_c
) ranging from 35 K (10-nm-thick films) to 41 K (40-nm-thick films). The 20-nm-thick unpatterned film had a room temperature resistivity of 13 μ Ω·cm, whereas it becomes 50 μΩ·cm in submicrometer size bridges with a critical current density J
_c
(4.2 K) up to 1.2 × 10
⁸
A/cm
²
. The lower value of resistivity corresponds to the higher of both T
_c
and J
_c
. The surface roughness, measured with an atomic force microscope, is approximately 1.5 nm.