Buffer Layers for High-Quality Epitaxial YBCO Films on Si

Efforts aimed at producing device quality YBa2Cu3O7-delta (YBCO) films on Si have resulted in films with properties comparable to what can be achieved with conventional oxide substrates such as SrTiO3. Epitaxial YBCO films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia (YSZ). Both layers are grown via an entirely in situ process by pulsed laser deposition (PLD). The large difference in thermal expansion coefficients between silicon and YBCO causes strain at room temperature. Thin (<500 angstrom) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Ion channeling reveals a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal state resistivity is 250-300 mu Omega . cm at 300 K; the critical temperature, Tc (R =0), is 86-88 K with a transition width (Delta Tc) of 1 K. Critical current densities of 2 x 10(7) at 4.2 K and 2.2 x 10(6) at 77 K have been achieved. Noise measurements indicate that these films are suitable for use in highly sensitive far infrared bolometers. Applications of this technology to produce in situ reaction patterned microstrip lines is discussed.