Sensing characteristics of high-frequency shear mode resonators in glycerol solutions

Film bulk acoustic resonators (FBAR) vibrating in shear mode and operating at around 830 MHz have been fabricated. They were tested in air and water–glycerol solutions. With a sensitivity of 1 kHz cm2/ng, these devices are attractive for gravimetric sensing applications. The FBARs are solidly mounted on acoustic mirrors and use 16° c  -axis inclined ZnO thin films realized by reactive sputtering. An analysis of the performance in liquids with different viscosities has been done and the effect on quality factor and resonance frequency has been shown. Effective coupling coefficients Keff2 of up to 1.7% and quality factors of up to 380 and 199 were determined in air and deionized water, respectively. The obtained characteristics are sufficient for gravimetric sensing applications in liquid environments and the FBARs can be used as high frequency viscosity sensors for liquids of viscosities up to 10 mPa s.