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This paper demonstrates low-loss acoustic delay lines based on shear-horizontal waves in thin-film LiNbO3 for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here we show that shear-horizontal waves in LiNbO3 thin films are also excellent for implementing low-loss acoustic delay lines based on unidirectional transducers. The high acoustic reflections and large transducer uni-directionality induced by the mechanical loading of the electrodes on a LiNbO3 thin film provide a great trade-off between delay line insertion loss and bandwidth. The directionality for two different types of uni-directional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3 dB bandwidth of 16 MHz centered at 160 MHz (FBW=10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed.

This work presents a new class of micro-electro-mechanical system (MEMS) resonators toward Ka band (26.5-40 GHz) for fifth-generation (5G) wireless communication. Resonant frequencies of 21.4 and 29.9 GHz have been achieved using the fifth and seventh order asymmetric (A5 and A7) Lamb-wave modes in a suspended Z-cut lithium niobate (LiNbO3) thin film. The fabricated device has demonstrated an electromechanical coupling (kt 2 ) of 1.5% and 0.94% and extracted mechanical Qs of 406 and 474 for A5 and A7 respectively. The quality factors are the highest reported for piezoelectric MEMS resonators operating at this frequency range. The demonstrated performance has shown the strong potential of LiNbO3 asymmetric mode devices to meet the front-end filtering requirements of 5G.

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