A first insulating layer is formed on a support substrate. The first insulating layer includes a first portion and a second portion. The second portion has a thickness smaller than that of the first portion. A ground layer having electric conductivity higher than that of the support substrate is formed on the second portion of the first insulating layer. The ground layer is electrically connected to the support substrate. A second insulating layer is formed on the first insulating layer to cover the ground layer. A write wiring trace is formed on the second insulating layer to overlap with the first portion and the second portion of the first insulating layer.