Design of low-loss one-pole synchronous lithium niobate surface acoustic wave resonators for sensing applications

The surface acoustic wave (SAW) device has been used in many applications, such as using as resonators, to replace the inductance-capacitance (LC) filters, chemical or gas sensors. Our objectives in this work are to increase insertion loss (IL) and Q factor. The new improved device has applications in RF engineering as well as in sensors. They are used to sense the additional particles on the surface, which have a good potential for biological sensors.;In this work, a synchronous low-loss one-pole SAW resonator is designed to improve the existing SAW filter design. The mass-sensing applications of SAW resonators indicate the different potential for applications in biosensors. There are three objectives studied in this work. The first objective is to develop a low-loss and one-pole frequency response for SAW resonators. The insertion loss, which is the receiving power in the output transducer, is typically smaller than -6dB. Our goal is to achieve a low-loss response (>-3dB), and then it is necessary to improve the performance of SAW as a filter and as a biosensor. The bidirectional SAW resonator on the LiNbO3 piezoelectric substrate have two-pole frequency response and low a Q factor. An improved frequency response with high Q factor is introduced in this work. The second objective in this research is to develop a SAW mass sensor on the LiNbO 3 substrate. When the additional mass is deposited on the surface, it results in a decrease in velocity and center frequency of acoustic waves. This decrease of the center frequency, or frequency shift, is linearly related to the additional mass. A frequency shift, due to the additional mass, can be observed by the low-loss and one-pole response in the output. This mechanism allows a synchronous low-loss one-pole SAW resonator to have potential application in sensors; however, it is easier to determine the frequency shifts if the SAW resonator has a one-pole response in the output interdigital transducer (IDT). The mass sensitivity in this work is 8.23e12 Hz˙mm 2/g for 978MHz SAW mass sensor. The third objective in this work is to use the SAW mass sensor operational in a liquid-phase environment for mass detection. The acoustic waves are excited by conductive electrodes on the piezoelectric surface; the signal on these electrodes becomes shorted when the SAW device is in liquid. In order to protect the electrodes, a polymer coating is applied to the surface in order to avoid the short circuit. This polymer-coated SAW mass sensor makes it possible to sense antibody-antigen reactions in liquid.