Interdiffusion studies on high - T , superconducting YBa , Cu , O , _ , thin films on Si ( 111 ) with a NiSi , / ZrO , buffer layer

Interdiffusion studies on high-T, superconducting YBasCu,O,_s thin films with thicknes~s in the range of 2000-3000 A, on a Si(ll1) substrate with a buffer layer have been performed. The buffer layer consists of a 400 A thick epitaxial Nisi, layer, covered with 1200 A of polycrystalline 210,. YBa,Cu,O,_s films were prepared using laser ablation. The YBa,Cu,O,_, films on the Si/NiSi,/ZrOs substrates are of good quality; their critical temperatures T’,, and 7”*,,,=, have typical values of 85 and 89 K, respectively. The critical current density j, at 77 K equaled 4 X lo4 A/cm*. 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 ZrOs buffer layer prevents severe Si diffusion to the YBa,Cu,O,_a layer, the Si concentration in the ZrO, 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 mm) no severe interface reactions occur. The interfaces are sharp and well defined. However, during long deposition times (t a 30 mm), some Cu diffuses from the YBa,CusO,_, layer to the interface between the Zr02 layer and the Nisi, layer. Also indications for the formation of BaZrO, at the interface between the YBa,Cu,O,_s layer and the ZrO, layer have been found. Finally, Ni diffusion into the Si substrate and Ni segregation to the surface of the ZrO, 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’, superconducting YBa,Cu,O,_, thin films on a Si(ll1) substrate with a NiSi,/ZrO, buffer layer.