Biblio

In this paper, an acoustic resonator with frequency \textbackslashtextgreater 5 GHz is designed, implemented, and measured with electromechanical coupling exceeding 15% and low temperature dependence compared to conventional Lamb-wave resonators. The acoustic resonator is optimized for the S4 mode Lamb waves in a bi-morph composed of Lithium Niobate and Silicon Dioxide. The resonator optimization is based on adjusting the thickness of different materials in the bimorph to maximize the coupling and minimize temperature dependence simultaneously. The achieved specifications are adequate for 5G sub-6 GHz frequency band n46 in addition to Wi-Fi new bands between 5 and 6 GHz.

Emerging next generation wireless communication devices call for high-performance filters that operate at 3-10 GHz frequency range and offer low loss, small form factor, wide bandwidth and steep skirts. Bulk and surface acoustic wave devices have been long used in the RF front-end for filtering applications, however their operation frequencies are mostly below 2.6 GHz band. To scale up the frequency of the filters, the thickness of the piezoelectric material needs to be reduced to sub-micron ranges. One of the challenges of such scaling is maintaining high electromechanical coupling as the film thickness decreases, which in turn, determines the filter bandwidth.Aluminum Nitride (AlN) - popular in today's film bulk acoustic resonators (FBARs) and mostly deposited using sputtering techniques-shows degraded crystal quality and poor electromechanical coupling when the thickness of AlN film is smaller than 1 μm.In this work, we propose using high-quality single-crystalline AlN and Scandium (Sc)-doped AlN epi-layers grown on Si substrates, wherein high crystal quality is maintained for ultra-thin films of only 400 nm thickness. Experimental results verify improved kt2 for 3-10 GHz resonators, with quality factors of the order of 250 and kt2 values of up to 5%based on bulk acoustic wave resonators. The experimental results suggest that single-crystal Sc-AlN is a great material candidate for 5G resonators and filters.