Increasing Operational Frequency in Microwave Devices by Using [SmCo/NiFe] Multilayered Structures

We present here the application of an exchange spring multilayer system in an on-chip microwave device. The microwave devices were made in a coplanar geometry using a [SmCo/NiFe]₁₀ sputtered multilayer structure as the active material. At low fields we find an up shift of the operational frequency by more than 15 GHz for the multilayer system compared to the NiFe alone. For higher fields (above 2 kOe) the increase in operational frequency is about 8-10 GHz. In contrast to previous results using an oriented SmCo film, we find in our polycrystalline film that there is not a large difference between frequencies measured with positive magnetic field compared to those measured with negative magnetic field. We studied multilayer systems with different thicknesses of NiFe. Magneto-optical Kerr effect measurements show a distinct uniaxial anisotropy for structures with 30-nm NiFe. Thinner NiFe films did not result in a clear anisotropy. Nonetheless, a substantial frequency shift was measured for all the samples. These measurements indicate that exchange coupled structures can substantially increase the frequency of signal processing devices