Experimental evidence of resputtering of the yttria layer in a YBa₂Cu₃O_7−x/Y₂O₃/YBa₂Cu₃O_7−x trilayer film

Using transmission electron microscopy and energy dispersive x‐ray spectroscopy analysis, the microstructure and composition of a YBa₂Cu₃O_7−x/Y₂O₃/YBa₂Cu₃O_7−x trilayer film deposited on MgO by off‐axis sputtering at 670 °C and 100 mTorr was investigated. The YBa₂Cu₃O_7−x layer in contact with the substrate was found to be mainly single phase. However, the top YBa₂Cu₃O_7−x layer was embedded with 5–10 nm crystalline Y₂O₃ (yttria) particles, which disturbed the local microstructure. The top YBa₂Cu₃O_7−x layer also had barium copper oxide particles covering its surface. The partial decomposition of the top YBa₂Cu₃O_7−x layer may have been due to resputtering of the yttria layer which locally altered the deposition conditions. In particular, the oxygen pressure in the vicinity of the growing film may have increased due to sputtering of the yttria layer by plasma gas atoms and the sputtered target atoms. As a result, deposition occurred under conditions away from the thermodynamic stability line.