A device includes an interposer, a plurality of conductive through vias (TVs), a conductive element, and a redistribution line (RDL). The conductive TVs extend from a bottom surface of the interposer to a top surface of the interposer. The conductive element is over the bottom surface of the interposer. The RDL is over the top surface of the interposer. The RDL, the conductive TVs, and the conductive element are connected to form an inductor.