Achieving Lower Insertion Loss and Higher Sensitivity in a SAW Biosensor via Optimization of Waveguide and Microcavity Structures

Achieving low power consumption and high sensitivity is a major obstacle in realizing the potential of surface acoustic wave (SAW) devices in portable sensing applications. In this paper, we demonstrate that an optimal combination of a microcavity structure filled with a low acoustic impedance material in the delay path combined with a suitable wave guide lowers power consumption substantially and improves sensitivity. 3-D finite-element method (FEM) simulations were employed to systematically evaluate the effect of various filling and waveguide materials for similar to 100 MHz devices in ST quartz. Based on the simulated device designs, trends in device performance, and ease of fabrication, SAW sensors were fabricated in ST quartz with tantalum filling of the microcavity array along with an optimal SiO2 wave guide to achieve improvements on the order of 5 dB in insertion loss and nearly ten times the sensitivity compared with an SAW device without these modifications. This paper allows for the possibility of designing and realizing robust SAW sensors for detection at concentration levels of relevance to clinical diagnosis, i. e., sub-ng to ng/mL levels.