Engineering picogram level detection using high frequency surface acoustic wave chemical and biological sensors based on multilayered Diamond/AlN/LiNbO<inf>3</inf> substrates

Operating SAW devices in the GHz frequency range can enable detection of single molecules by imparting high sensitivities and low detection limits. In the present work, we used 3-D coupled field structural as well as fluid-solid interaction finite element models to study the acoustic wave propagation characteristics of diamond/AlN/LiNbO ₃ multi-layered piezoelectric surface acoustic wave devices under the influence of fluid loading for applications in chemical and biological sensing. These devices were studied as a method to increase device frequency and sensitivity, and maintain standard fabrication procedures. The operating frequency of SAW devices is directly proportional to the substrate's acoustic wave velocity; hence the highest acoustic wave velocity material (diamond) is needed for fabrication of MEMS GHz frequency devices. The aluminum nitride piezoelectric layer also has a very high acoustic wave velocity and a fairly large piezoelectric coupling coefficient along its c-axis, in comparison to other piezoelectric materials. Although recent experimental investigations have realized GHz frequency devices based on such multilayered substrates, very little is known about the acoustic wave propagation characteristics in these devices. Identifying the optimum configuration and thickness of the various layers involved still represents a challenge, which is addressed in this work.