A sensor for measuring current in a conductor has a substrate in the form of a stratified plate having a first metallization layer, a second metallization layer and an isolation layer between the first metallization layer and the second metallization layer, the substrate having a coil that winds along a coil axis parallel to the first metallization layer, having at least one winding. Each winding has a first track in the first metallization layer connected by a via through the first isolation layer to a second track in the second metallization layer, and the substrate has a measurer to measure the current in the coil, and having at least one winding only winding around non-magnetic material.