Fabrication and sensing behavior of piezoelectric microbridge transducer for nanobalance

We have fabricated a highly sensitive mass sensor based on piezoelectrically driven microbridge transducers. We have used the resonant-frequency change of the microbridge transducer upon mass increase. Finite-elcment-method (FEM) simulation was carried out to estimate the resonant property of the microbridge. The microbridge transducer was fabricated by using the micro-electro-mechanical-system (MEMS) technique. The microbridge employs a sol-gel derived Pb(Zr _0.52,Ti _0.48)O ₃ (PZT) film capacitor fabricated on a low-stress SiN _x elastic layer. The first harmonic bending frequency of the microbridge was in the range of 250 kHz to 260 kHz. The microbridge exhibited a mass sensitivity of ca. 91 Hz/ng, which enables its application to a nanobalance to detect bio-molecules or gas molecules in a nanogram regime. The gravimetric sensitivity factor of the bare microbridge transducer was 377.3 cm ²/g, which is higher compared with conventional acoustic mass sensors using surface acoustic wave (SAW) or thickness shear mode (TSM).