Magnetron sputter deposition of a 48-member cuprate superconductor library: Bi_2Sr_2Y_xCa_(1-x)Cu_2O_(8+δ) (0.51≤x≤ 1) linearly varying in steps of △x=0.01

摘要

Using magnetron sputtering, a spatial composition spread approach was applied successfully to obtain 48-member libraries of the Bi_2Sr_2Y_xCa_(1-x)Cu_2O_(8+δ) (0.5≤x≤1) cuprate superconducting system. The libraries of each system were deposited onto (100) single crystal MgO, mounted on a water cooled rotating table, using two targets: the antiferromagnetic insulator Bi_2Sr_2YCu_2O_(8+δ) (P = 98 W rf) and the hole doped superconductor Bi_2Sr_2CaCu_2O_(8+δ) (P = 44 W dc). A low chamber pressure of 0.81 mTorr argon was used to reduce scattering by the process gas. To minimize oxygen resputtering a substrate bias of -20 V was used, as well as a process gas free of oxygen. A rapid thermal processor was used to post-anneal the amorphous deposited films. A step annealing regime was used, with a ramp rate of 5℃/s for heating and cooling, with a first plateau at 780℃ held for 200 s, and a second at 875℃ held for 480 s. X-ray diffraction reveals that the films develop crystalline order with the c-axis lattice parameter contracting linearly from 30.55 A (x = 0.5) to 30.24 A (x = 1.0) with increasing Y-content, consistent with bulk values. The crystallized films are polycrystalline, developing preferred orientation (c-axis parallel to the substrate) for thinner members of the library. There is a change of 0.01 in doping per library member which will enable further studies to densely map phase space.