Interdiffusion studies on high- Tc superconducting YBa 2Cu 3O 7−δ thin films on Si(111) with a NiSi 2/ZrO 2 buffer layer

Abstract

Interdiffusion studies on high- T c superconducting YBa 2Cu 3O 7−δ thin films with thicknesses in the range of 2000–3000 Å, on a Si(111) substrate with a buffer layer have been performed. The buffer layer consists of a 400 Å thick epitaxial NiSi 2 layer, covered with 1200 Å of polycrystalline ZrO 2. YBa 2Cu 3O 7−δ films were prepared using laser ablation. The YBa 2Cu 3O 7−δ films on the Si/NiSi 2/ZrO 2 substrates are of good quality; their critical temperatures T c,zero and T c,onset have typical values of 85 and 89 K, respectively. The critical current density j c at 77 K equaled 4 × 10 4 A/cm 2. With X-ray diffraction analysis (XRD), only c-axis orientation has been observed. The interdiffusion studies, using Rutherford backscattering spectrometry (RBS) and scanning Auger microscopy (SAM) show that the ZrO 2 buffer layer prevents severe Si diffusion to the YBa 2Cu 3O 7−δ layer, the Si concentration in the ZrO 2 layer must be below the detectability limit of 1 at%, but Si diffusion along grain boundaries cannot be excluded completely. During short deposition times ( t ≈ 5 min) no severe interface reactions occur. The interfaces are sharp and well defined. However, during long deposition times ( t > 30 min), some Cu diffuses from the YBa 2Cu 3O 7−δ layer to the interface between the ZrO 2 layer and the NiSi 2 layer. Also indications for the formation of BaZrO 3 at the interface between the YBa 2Cu 3O 7−δ layer and the ZrO 2 layer have been found. Finally, Ni diffusion into the Si substrate and Ni segregation to the surface of the ZrO 2 layer may be expected. From the results we may conclude that, when using laser ablation, it is well possible to grow polycrystalline, c-axis-oriented high- T c superconducting YBa 2Cu 3O 7−δ thin films on a Si(111) substrate with a NiSi 2/ZrO 2 buffer layer.