Synchronous One-Pole $\hbox{LiNbO}_{3}$ Surface Acoustic Wave Mass Sensors

Mass-loading-effect surface acoustic wave (SAW) devices with center frequencies at 121 and 978 MHz have been investigated. Two types of SAW mass sensors, the dual- and single-track interdigital transducers with synchronous shorted reflection gratings, are fabricated on the 128° Y-X LiNbO
₃
substrate. The center frequencies of SAW mass sensors are shifted due to the additional mass on the electrodes. The 128° Y-X LiNbO
₃
piezoelectric material has a high velocity-shift coefficient so that its frequency shift due to the additional mass is enhanced. Experimental results show the good linearity and high sensitivity between the frequency shift and mass density. The minimum detectable mass densities are 24.3 ng/mm
²
from the 978-MHz SAW mass sensors and 152 ng/mm
²
from the 121-MHz SAW mass sensors, with 200- and 20-kHz frequency shifts, respectively. Furthermore, the mass sensitivities are 1.315 × 10
¹¹
and 8.23 × 10
¹²
Hz·mm
²
/g, respectively.