YBCO Films and YSZ Buffer Layers Grown in Situ on Silicon by Pulsed Laser Deposition

Abstract

Attempts to grow high quality YBCO (Y1Ba2Cu3O7−δ) films on bare silicon substrates have been hindered by substrate-film reactions, which are substantial even at growth temperatures as low as 550 C (Fenner et al., 1990b). In an effort to circumvent this problem, buffer layers have been introduced as part of the thin film growth process. Recently, we have shown that YSZ |(Y2O3)x (ZrO2)1−x| is a most promising buffer-layer (Connell et al., 1989). It has two ideal properties: first, at temperatures below 800 C, reactions with Si and YBCO are minimal under appropriate conditions; second, for compositions in the range 0.08 < x < 0.4, bulk YSZ exists in the cubic fluorite structure and at x =0.1 has a lattice constant that is within 6% of both the near neighbor distance between Si atoms on the (100) surface and the basal plane dimensions in YBCO (Golecki et al., 1983). Table 1, which summarizes our earlier results on surface morphology, interface Table 1 Variation of structural and electrical parameters with x in YSZ [(Y2O3)x (ZrO2)1−x] . The surface roughness and intensity of the [005] 2θ diffraction peak are measued relative to the parameters for the x = 0 film x [mole fraction] 0 0.05 0.1 0.2 Surface Roughness 1 0.2 0.1 0.1 Intensity [005]-Peak 1 90 100 110 Tco [K] Insulating 62 77 70 ∆Tc [K] Insulating 28 13 20 P300 [μΩ.cm] Insulating 24,000 6,300 13,000 P300/P100 Insulating 1.8 2.2 1.85 and crystal structure, and conductivity, demonstrates that the value of x plays a critical role in preparing the YSZ buffer layer for the subsequent growth of YBCO. That many of the properties were optimized near x =0.1 is suggestive that the cubic YSZ phase is forming, lattice matched and oriented relative to the Si. Our electron microscopy results supported this conjecture, albeit under the deposition conditions used, the cubic and tetragonal phases were intermixed and had a high density of defects, and there was only weak preferred orientation.