Magnetostatic wave resonators based on yttrium iron garnet (YIG) are a promising technology platform for future communication filters. Such devices have demonstrated better quality factors than acoustic resonators in the 7 GHz range and above. However, the coupling coefficients of these resonators have been limited to less than 3

This work reports a compact temperature compensating permanent magnet assembly to provide static bias for micro-machined distributed magnetostatic forward volume wave (MSFVW) resonators. The cuboid-shaped assembly is 8.2 mm x 8.2 mm x 6.3 mm and provides strong static magnetic field to bias MSFVW resonators at a frequency of 19.65 GHz. Compensated by the bias assembly, the resonator exhibits a temperature coefficient of frequency (TCF) of -26.81 ppm/K compared to uncompensated TCF of +359 ppm/K. The temperature compensated resonator shows a quality factor of 1050 and a coupling coefficient of 4% at room temperature.

The further development of 5G and 6G communication systems introduced new frequency allocations beyond 6 GHz, necessitating the development of compact bandpass filters that can operate over wide gigahertz frequency ranges. Herein, we report on the design, fabrication, and characterization of an edge-coupled magnetostatic forward volume wave bandpass filter (MSFVW). Using micromachining techniques, we fabricate both 2-pole and 4-pole filters from a yttrium iron garnet (YIG) film grown on a gadolinium gallium garnet (GGG) substrate with inductive transducers. By adjusting an out-of-plane magnetic field, we demonstrate linear center frequency tuning for a 4th-order filter from 4.5 GHz to 10.1 GHz while retaining a fractional bandwidth of 0.3%, an insertion loss of 6.94 dB, and a  - 35 dB rejection level. We characterize the filter nonlinearity in the passband and stopband with IIP3 measurements of  - 4.85 dBm and 25.84 dBm, respectively. In this work, we demonstrate a compact octave tunable narrowband channel-select filter with a significant degree of design flexibility and performance comparable to the state-of-the-art.

This work reports the design, fabrication, and characterization of coupling-enhanced magnetostatic forward volume wave (MSFVW) resonators with significant spur suppression. The fabrication is based on surface micromachining of yttrium iron garnet (YIG) film on a gadolinium gallium garnet (GGG) substrate with thick gold transducers. A distributed resonator is used to excite forward volume waves in YIG to realize a frequency-dependent coupling boost. Fabricated devices at 18 and 7 GHz show coupling coefficients as high as 13% and quality factors above 1000. Higher order magnetostatic mode suppression is experimentally demonstrated through a combination of transducer and YIG geometry design.

Microscale resonators are fundamental and necessary building blocks for modern radio communication filters for mobile devices. The resonator's Q factor (Q) determines the insertion loss while coupling (K_t^2) governs the fractional bandwidth. The product k_t^2 × Q is widely recognized as the definitive figure of merit for microresonators. Magnetostatic wave resonators based on Yttrium Iron Garnet (YIG) are a promising technology platform for future communication filters. They have shown considerably better performance in terms of Q when compared to the commercially successful acoustic resonators in the >7 GHz range. However, the coupling coefficients of these resonators have been limited to <3 space imposed by microfabrication challenges related to the patterning of gadolinium gallium garnet (GGG), the substrate material used for growing single crystal YIG. This paper reports novel resonator designs enabled by breakthrough bulk micromachining technology for anisotropic etching of GGG, leading to coupling >8 platform to show resonant enhancement of effective coupling, reaching up to 23 % at 10.5 GHz. The frequency of resonant coupling can be tuned by design during the fabrication process. The resonant coupling results in an unprecedented k_t^2 × Q figure of merit of 191 at 10.5 GHz and 222 at 14.7 GHz. The technology platform presented in this paper supports both tunable filter architecture and switched filter banks that are currently being used in consumer mobile devices.