As‐Grown Superconductivity of Bi‐System Thin Films Prepared by Magnetron Sputtering with Three Pb Doped Targets: (Bi 1.6 Pb0.4) 1 + a (SrCa)2 Cu3 O x, (Bi 1.6 Pb0.4) 1 (SrCa)2+c Cu3 Ox and (Bi 1.6 Pb0.4) 1 (SrCa)2Cu3+cOx (a = 0.5, b= 1,c= 1.5)