The expansion of mobile phone services and networks, drives the need for progressively wider and higher frequency bands. New services currently going into operation require frequencies in the range of 3.3–3.8 GHz (B78), 3.3–4.2 GHz (B77), 4.4–5.0 GHz (B79), 24.25–29.5 GHz (B257, B258, B261), and 37–40 GHz (B260), with much wider absolute and relative bandwidths than legacy services. Since modern mobile phones must operate in many frequency bands, they demand a large number (20+) of compact, high-performance filters.
Currently, for frequencies below 3 GHz, these filters are realised using ladder filters based on surface acoustic wave (SAW) resonators or bulk acoustic wave (BAW) resonators. For the 3–5 GHz range, SAW devices require increasingly narrower electrodes resulting in a higher loss, reduced power handling, and more expensive lithography. BAWs have relatively small piezoelectric coupling and have difficulty supporting the wider bandwidths required. Thus, new acoustic wave filter solutions addressing the loss, power, and bandwidth needs above 3 GHz will be attractive. This paper shows a potential path to such solutions. It is inspired by Kadota’s results on Lamb modes in thin LiNbO3 layers, by Murata’s Incredibly High Performance (IHP) wafer technology for SAW devices and by recent developments in MEMS.
