Transverse magnetooptic effect in multilayers applied to mapping of microwave currents

A sensor capable of mapping microwave (mw) currents in semiconductor circuits can be realized by exploiting magneto-optic effects (MO) at transverse magnetization (M⊥) in ultrathin ferromagnetic or ferrimagnetic films. In the sensor, M⊥would be induced in the magnetic film by the fringing fields of mw currents flowing in the semiconductor circuit along the plane of incidence. In this work, an evaluation of MO sensor performance was made for nanostructures consisting of ultrathin Fe layers sandwiched between AlN dielectric layers. The multilayer thin film stacks were grown on Si wafer substrates. The performance of the sensor systems is characterized in terms of magnetization-induced changes in the MO multilayer reflection coefficients, expressed analytically. Sensor configurations which optimize the operation at the laser wavelength of 410 nm, and which are still easy to fabricate, are proposed. Modeling predicts the strongest MO enhancement in a sensor incorporating two Fe nanolayers, each of a different thickness, formed by the layer sequence AlN/Fe/AlN/Fe/AlN/Au/Si. The use of ferrimagnetic hexagonal ferrite films with the in-plane c-axis as an alternative sensor material is also discussed.