Effect of Bi and Ce co-doping in garnet-based materials: Impact on microwave device performance

Abstract

Microwave devices in the modern era are rapidly integrating new substrates for passive devices such as filters, phase shifters, isolators, and circulators, etc. Garnet ferrites doped with rare-earth elements have emerged as promising candidates for reciprocal and nonreciprocal microwave devices using direction-dependent information transfer. This study demonstrates how Bi and Ce co-doping in yttrium iron garnet enhances microwave device functionality, including operating frequency, phase shift, and isolation. A flip-chip-based FMR configuration with a S-type microstrip line enabled a reciprocal notch filter design with 100 % tunability for 0.4 cerium concentration. The linewidth of the device was observed to be cerium concentration-dependent with a maximum for 0.6. A maximum differential phase shift of approximately 114°/cm was achieved for the Ce = 0.2 sample at an external magnetic field of 6.6 kOe. A straight microstrip line in parallel configuration facilitated nonreciprocal wave propagation in the Bi and Ce co-doped YIG. The nonreciprocal isolation was significantly enhanced with the applied DC bias magnetic field. Experimental results were validated using HFSS simulations, confirming the potential use of substrates made from Bi and Ce co-doped yttrium iron garnet for the fabrication of reciprocal and non-reciprocal microwave devices.