High $T_c$ $YBa_2Cu_3O_{7-x}$(YBCO) superconducting thin films were deposited on (100) MgO substrate by pulsed laser deposition. Using two step process, which is consist of a first step deposition at low temperature and consequentively second step deposition on the firstly deposited film at higher temperature. In this work, preferred texture and microstructure of YBCO thin films prepared by various deposition conditions have investigated by XRD, SEM and cross sectional TEM.
Decreasing deposition temperature, (100) plane was more preferred texture than (001) plane and oxygen concentration reduced. At the deposition temperature 650℃, the relative intensity I(200)/I(006) was 2 and "a"and "c" parameter were 3.874Å and 11.82Å, respectively. At deposition temperature 700℃, c-axis films grow dominantly. The "a"and "c"parameter were 3. 836Å and 11.79Å, respectively. As deposition temperature is increased above 700℃, the surface morphology shows smooth surface with rectangular grains. However, the film deposited at 650℃ shows densely packed fine grains of submicron sized.
After in-situ annealing at 500℃ for 1 hr, XRD patterns for the film deposited at low temperature show that (103) peak stricktly increases and (001) peak decreases. The morphology of surface shows long grains like mountain-shape.
We observed that the texture of second deposited film depends on the texture of first deposited film in two step processed films. And reorientation occurred only during in-situ annealing.
From the cross sectional TEM study, c-axis oriented epitaxial films grow firstly upto 10 nm on (100) MgO substrate, and then a-axis oriented grains and [301] oriented grains grow on the c-axis oriented epitaxial film. Intermediate layer was not observed at their three major interfaces between c-axis oriented grains and substrate, a-axis oriented grains and c-axis oriented grains, and [301] oriented grains and c-axis oriented grains.
