Propagation Of Bulk Acoustic Waves In Piezoelectric Thin Film Structure With Tilted C-Axis Orientation

Researching on acoustic waves in layered piezoelectric structures has very importantsignificance in designing the electronic components such as piezoelectric sensors, filters andresonators. It is necessary to consider the interaction between the piezoelectric structure and theliquid or viscoelastic layer for the technology of surface acoustic waves applied in the field of thebio-chemical sensors. Due to the demand of high frequency and low power consumption, thedevelopment of the piezoelectric thin film bulk acoustic resonators causes great interest. The bulkacoustic waves in piezoelectric thin film structures of hexagonal crystal system with tilted c-axis,such as ZnO and AlN play an important role and have promising application prospect in thefields of bio-sensing and chemical sensors. Based on piezoelectric theory, combined withviscoelastic mechanics and electric field theory, we investigate the propagation properties ofacoustic waves in piezoelectric structures, including the bulk acoustic waves in piezoelectric thinfilm with tilted c-axis and the surface acoustic waves in layered piezoelectric structure.(1) We propose and analyze a new piezoelectric gyroscope operating with TSh modes of atwo-layered plate (bimorph). We use a two-layered AlN plate with inclined c-axes as a gyroscope.The output voltage is sensitive to various parameters which is useful in design. Its dimensions canbe much smaller than those of conventional piezoelectric gyroscopes of quartz, lithium niobate,and polarized ceramics. The proposed structure can also be used for other6mm crystals orpolarized ceramics with properly inclined c-axes or poling directions.(2) We analyze the thickness vibration of c-axis inclined ZnO FBARs carrying an array ofmicrobeams. The microbeams are perfectly bonded to a thin piezoelectric substrate. For theflexural motion of the beams, we use the Euler-Bernoulli theory of bending. We focus on theeffects of the geometric dimension including the diameter and the length of the microbeams on thefrequency spectrum.(3) An analytical approach is taken to investigate SH-SAW propagation in a layeredviscoelastic/piezoelectric structure. We introduce the complex shear modulus to express the viscouseffect of the viscoelastic layer. The imperfect degree of the interface is described by the so-calledshear-lag model. And then we also assume the elastic coefficient, density and the viscouscoefficient of the viscoelastic layer are functionally graded, respectively. The influence of thenonconductive liquid is investigated at last. The numerical results are presented and discussed.