In planar micro inductors with magnetic cores, an important problem is to deduce the demagnetization in order to increase the inductance per unit area. From this point of view, planar inductors containing thin film magnetic open and solid closed circuit cores are made and discussed. On the basis of these results, we propose a new type planar inductor. In the new type inductor, 24–72 small solid magnetic closed cores are connected and excited by two turn coils. The resonant frequency from this device is higher than that of a planar inductor containing the same magnetic core volume.