An Investigation on Efficient Acoustic Energy Reflection of Flexible Film Bulk Acoustic Resonators

This paper investigates the issues on acoustic energy reflection of flexible film bulk acoustic resonators (FBARs). The flexible FBAR was fabricated with an air cavity in the polymer substrate, which endowed the resonator with efficient acoustic reflection and high electrical performance. The acoustic wave propagation and reflection in FBAR were first analyzed by Mason model, and then flexible FBARs of 2.66 GHz series resonance in different configurations were fabricated. To validate efficient acoustic reflection of flexible resonators, FBARs were transferred onto different polymer substrates without air cavities. Experimental results indicate that efficient acoustic reflection can be efficiently predicted by Mason model. Flexible FBARs with air cavities exhibit a higher figure of merit (FOM). Our demonstration provides a feasible solution to flexible MEMS devices with highly efficient acoustic reflection (i.e. energy preserving) and free-moving cavities, achieving both high flexibility and high electrical performance.