A nano-patterning process is reported in this paper, which can achieve surface acoustic wave (SAW) devices with an extremely high frequency and a super-high mass sensitivity. An integrated lift-off process with ion beam milling is used to minimize short-circuiting problem and improve quality of nanoscale interdigital transducers (IDTs). A specifically designed PEC algorithm is applied to mitigate proximity effects occurring in the conventional electron-beam lithography process. The IDTs with a period of 160 nm and a finger width of 35 nm are achieved, enabling a frequency of 30 GHz on

Surface acoustic wave (SAW) devices are widely used for physical, chemical, and biological sensing applications, and their sensing mechanisms are generally based on frequency changes due to mass-loading effects at the acoustic wave propagation area between two interdigitated transducers (IDTs). In this paper, a new sensing mechanism has been proposed based on a significantly enhanced mass-loading effect generated directly on Au IDT electrodes, which enables significantly enhanced sensitivity, compared with that of conventional SAW devices. The fabricated ultrahigh-frequency SAW devices show a significant mass-loading effect on the electrodes. When the Au-electrode thickness increased from 12 to 25 nm, the Rayleigh mode resonant frequency decreased from 7.77 to 5.93 GHz, while that of the higher longitudinal leaky SAW decreased from 11.87 to 9.83 GHz. The corresponding mass sensitivity of 7309 MHz•mm 2 •μg −1 (Rayleigh mode) is ∼8.9 × 10 11 times larger than that of a conventional quartz crystal balance (with a frequency of 5 MHz) and ∼1000 times higher than that of conventional SAW devices (with a frequency of 978 MHz). Trinitrotoluene concentration as low as 4.4 × 10 −9 M (mol•L −1 ) can be detected using the fabricated SAW sensor, proving its giant mass-loading effect and ultrahigh sensitivity.

This paper explores to use graphene as transparent interdigital transducer (IDT) electrode for a fully transparent surface acoustic wave (SAW) device due to its extraordinary electrical, physical and mechanical properties. The number of graphene atomic layers was firstly optimized for its best performance as the SAW electrode, and a 4-layered graphene IDT electrode, with aluminum doped zinc oxide, AZO, as the bus bar and wire bonding pad, was selected to fabricate fully transparent ZnO/glass SAW devices. The SAW resonators exhibited obvious resonant response at different wavelengths, and resonance signals with amplitude up to 20 dB were obtained with the transparency above 80%. The graphene-based transparent SAW sensor has been used for different sensing applications. Temperature sensing tests showed that the frequencies increase linearly with the increase of temperature, which has an opposite trend compared to that obtained from a conventional LiNbO 3 SAW device. The humidity sensing and human breathing detection have been demonstrated, and discontinuous respiration measurement can be used to distinguish the human respiration at the normal state or the state after exercise. Strong acoustic streaming and particle concentration using the transparent SAW devices have been achieved, which are suitable for microfluidic and lab-on-chip applications.

This paper reports the development of high performance surface acoustic wave (SAW) devices by using graphene as a virtually massless interdigital transducer (IDT) to mitigate mass-loading effects. Different layers of graphene electrodes were made and their influences on the SAW device performance were experimentally and theoretically evaluated. Results showed that 4-layer graphene with a value of sheet resistance less than 77.6 Ω/sq. and graphene IDTs of at least 80 pairs are needed to obtain the optimum performance of graphene IDT SAW devices. Furthermore, the optimal ratio of aperture/wavelength for the graphene IDT electrode was found to be 5. Graphene based SAW devices, with a resonance frequency of 154 MHz, transmission signal amplitude of 30 dB and K 2 of 3.78%, were fabricated and successfully demonstrated for applications in breathing monitoring.