30 GHz Surface Acoustic Wave Transducers with Extremely High Mass Sensitivity

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 lithium niobate based SAW devices. Both centrosymmetric type and axisymmetric type IDT structures are fabricated and results show that the centrosymmetric type tends to excite lower-order Rayleigh waves, and the axisymmetric type tends to excite higher-order wave modes. A super-high mass sensitivity of ~388.2 MHzmm2/μg is demonstrated, which is 109 times larger than that of a conventional quartz crystal balance and 50 times higher than a conventional SAW device with a wavelength of 4 m.