Scaling limits of YIG gyrators

Yttrium Iron Garnet (YIG) gyrators are obtained from two perpendicular coils around a thin single-crystal YIG layer. The gyrator characteristics are defined by the Landau–Lifshitz–Gilbert equations and typical resonances are obtained in the range from 6 GHz to 48 GHz.

Gyrators can be useful for many applications, such as, directional couplers, sharp bandpass and notch filters, high-quality tunable oscillators and impedance transformations.

The performance of YIG gyrators is reported to be defined by the YIG layer thickness and is reported to be independent of the lateral dimensions. [1] Literature provides experimental characterization has been done for layers that are typically 2 micron thick and have that have mm-size lateral dimensions. The lateral dimensions studied in the past were as a consequence dominantly larger than the layer thickness, and the ferro-magnetic modes were indeed very much defined by the layer thickness.

However, when the lateral dimensions get submicron, and hence smaller than the vertical dimensions, the foundations for the former conclusions no longer exist, and a more in-depth study of the modes is required. The object of this PhD is the study of the scaled Gyrator modes. This investigation starts from the theoretical modelling of the ferro-magnetic modes (using the Landau–Lifshitz–Gilbert equations) for downscaled gyrators. Subsequently, also the student will also prepare the devices on Gadolinium Gallium Garnet substrates and measure them in the 6 GHz to 48 GHz frequency range.

[1] Nicolas J. Moll, “Coupling of Circuit Structures to Magnetostatic Modes of Ferromagnetic Resonators,” IEEE Transactions on Microwave Theory and Techniques, vol. 25, no. 11, pp. 933–938, Nov. 1977, doi: 10.1109/TMTT.1977.1129244.