  A metal-oxide film can be used as a hydrogen-isotope permeation barrier in
the fuel circulation system for nuclear fusion. We fabricated Er$_2$O$_3$ thin
film on a type 316L stainless-steel substrate by using a metal-organic chemical
vapor deposition technique for the purpose of hydrogen-isotope permeation
barrier. Electron microscopy based imaging and energy-dispersive X-ray
spectroscopy measurements indicate a sound film quality together with X-ray
diffraction experiments. We also measured deuterium permeation in the film at
high temperatures ranging from 600 $^{\circ}$C to 800 $^{\circ}$C. The
permeation reduction was most apparent at 650 $^{\circ}$C. Above 800
$^{\circ}$C, we confirmed that the film was damaged and did not work as a
permeation barrier.
