Tunable Non-Reciprocal Phase Shifter and Spin-Coated Ferrites for Adaptive Microwave Circuits

Tunable non-reciprocal components with ferrites that can be integrated using a foundry suitable process are key to achieving low-power adaptive microwave circuits. The current state-of-the-art still relies on electrical tuning or resistive absorbers to facilitate unidirectional propagation. Here, we demonstrate a novel process for spin-coating thick films of ferrites without the complexities of vacuum processes or high-temperature annealing. Composites of yttrium iron garnet (YIG) nanoparticles in a matrix spin-on-glass are spin-coated on silicon substrates, and magnetic properties comparable to bulk YIG are obtained in films exceeding 30 microns. We also propose a design for tunable phase shifter based on periodically serrated coplanar waveguide with a YIG cladding. A non-reciprocal phase difference of 20 - 60 degrees is obtained over a tunable band of 550 MHz between 3.85 - 4.4 GHz from a tuning magnetic field of 8 - 40 kA/m.