Finite element simulation of Love wave resonator for DNA detection

The paper presents 3D finite element simulation of a Love wave resonator using coupled resonance with ZnO nanorods for biosensing application. The variation in mode shape, phase velocity, and coupling coefficient with rotation angle for a Y-cut LiTaO3 crystal is reported. At rotation angle of 36° the leaky SAW is transformed into a perfect shear horizontal surface wave with high coupling coefficient. Mass sensitivity and electromechanical coupling coefficient of Love wave resonator are calculated for different guiding layer materials (ZnO, SiO2 and PMMA) of varying thickness. The mass sensitivity provided by PMMA is about 15 times that of SiO2 layer but coupling coefficient falls rapidly as its thickness increases, offering a narrow range of thickness of the guiding layer. Simulations are performed for ZnO nanorods of varying height (300–1800 nm) present over 315.605 MHz Love wave resonator having 4.7 μm thick SiO2 waveguide layer. The addition of double stranded DNA is simulated by applying its equivalent surface mass density on the sensor surface. Coupled resonance occurs when the resonance frequency of ZnO nanorods is close to the device operating frequency and causes frequency shift of about 10.5 MHz which is about 20 times greater than the value obtained in the absence of coupled resonance. Love wave device with resonant nanostructures operating in coupled resonance is a promising candidate for designing highly sensitive biosensor.