NEXT GENERATION ACOUSTIC AND MAGNETIC RESONATORS FOR RADIO FREQUENCY COMMUNICATION

This dissertation focuses primarily on the development of next generation acoustic and magnetic resonators for radio frequency communication. Through novel design and fabrication techniques, acoustic and magnetic devices with improved performance are demonstrated.

Chapter 1 begins with an introduction to the current wireless communication industry and the roles of resonators in RF front-end architecture, as well as the requirements for next generation resonators to meet the needs of 5G technology.

Chapter 2 describes our work on lithium niobate acoustic MEMS resonators. The theory section introduces the general working principles of acoustic resonators utilizing piezoelectricity, and is followed by an overview of various types of commonly used acoustic resonators. Subsequently, the design, modeling, fabrication, and measurement of Al-IDT driven laterally vibrating LN resonator on LN-on-LN platform are presented. With novel fabrication techniques, resonators with competitive quality factor and superior thermal stability have been achieved. Specifically, we demonstrate S0 and SH0 mode LN thin-film resonators with a quality factor (Q) ranging from more than 500 up to 2600 and from 2% to 11.6% with a constant temperature coefficient of frequency in various power ranges (-12dBm to -1dBm) with device dimensions of only .

Chapter 3 presents the design, fabrication, and characterization of octave-tunable magnetostatic wave YIG resonators on a chip, starting with an introduction to spin wave theory. At 4.77GHz, the 0.68mm² resonator has achieved a Q >5000 with a bias field of 987Oe. We also demonstrate YIG resonator tuning by more than one octave from 3.63GHz to 7.63GHz by applying an in-plane external magnetic field. The measured quality factor of the resonator is consistently greater than 3000 above 4GHz. We achieved this technological breakthrough by developing a YIG film etching process and fabricating a thick aluminum coplanar waveguide inductor loop around each resonator to individually address and excite magnetostatic waves. The micromachining technology enables the fabrication of multiple single-port and two-port YIG resonators on the same chip, with all resonators demonstrating octave tunability and high Q, thus allowing for potential monolithic high order MSW filters and multiplexers as a chip-scale SHF multiplexing solution.

Chapter 4 presents the first MSW YIG resonator on YIG-on-insulator, taking advantage of the YIG film layer transfer technique that we developed by using surface activated bonding and ion slicing for heterostructure integration. Surface and crystalline structure characterization is presented to demonstrate applicability to device fabrication. The YIG resonator is measured with a magnetic bias changing from 560Oe to 3610Oe, thus resulting in a resonance ranging from 2.6GHz to 13.2GHz. With the removal of substrate constraints, this technology enables a chip-scale multiplexing solution as well as new possibilities for low damping magnetic quantum computing components.

Chapter 5 presents our preliminary results in three active research areas. First, the design of a strain-tunable free standing MSW YIG resonator is presented, together with batches of fabrication process optimization. Second, the thermal strain induced anisotropy frequency tuning from the thermal mismatch between YIG film and Si substrate is measured with in-plane ferromagnetic resonance at different in-plane orientations. Third, a YIG circulator on a silicon chip is proposed with high isolation, low insertion loss, and a size 1000 times smaller than that of the state-of-the-art commercial product.