J.E. Lefebvre

Acoustic wave propagation in continuous functionally graded plates: an extension of the Legendre polynomial approach

The propagation of guided waves in continuous functionally graded plates is studied by using Legendre polynomials. Dispersion curves, and power and field profiles are easily obtained. Our computer program is validated by comparing our results against other calculations from the literature. Numerical results are also given for a graded semiconductor plate. It is felt that the present method could be of quite practical interest in waveguiding engineering, non-destructive testing of functionally graded materials (FGMs) to identify the best inspection strategies, or by means of a numerical inversion algorithm to determine through-thickness gradients in material parameters.

Integration of RF filters on GaAs substrate

Up to now, RF front-end and interstage surface acoustic wave (SAW) filters for mobile communication are mainly fabricated on LiNbO/sub 3/ and LiTaO/sub 3/ substrates. A monolithic integration of these filters on semiconductor substrates is highly desirable to miniaturize the outer dimensions of the cellular phones. Direct realization of SAW filters on non piezoelectric or weakly piezoelectric substrates is impossible. One alternative is the deposition of a piezoelectric film on the semiconductor substrate. In this paper, we present an analysis and realization of a ladder SAW filter built up on a two-layered structure made up of a ZnO film on a GaAs substrate in the 900 MHz frequency range.

Two true surface acoustic waves and other acoustic modes in (110) plane of Li2B4O7 substrate

The surface acoustic waves (SAWs) and other acoustic modes propagating in the (110) plane of Li2B4O7 are investigated by means of the effective surface permittivity (ESP). It is demonstrated that the velocity of all piezoactive SAWs, both true and pseudo, as well as surface skimming bulk waves (SSBWs) can be numerically determined by computing the ESP as a function of acoustic trace slowness. A physical phenomenon not reported has been found for certain propagation directions, namely, simultaneous existence of two true SAWs, both being of the generalized Rayleigh type, together with a pseudo SAW of similar polarization. Propagation velocity, electromechanical coupling coefficient, and decay factor have been verified and confirmed by using two different sets of material constants and two numerical methods. The obtained values and accuracy of SAWs parameters are compared, and the validity conditions discussed. The generalized slowness diagram, plotted for the sagittal plane, enables to determine the total n...

Modeling of bulk acoustic wave devices built on piezoelectric stack structures: Impedance matrix analysis and network representation

The fundamental electro-acoustic properties of a solid layer are deduced in terms of its impedance matrix (Z) and represented by a network for modeling the bulk acoustic wave devices built on piezoelectric stacked structures. A piezoelectric layer is described by a three-port equivalent network, a nonpiezoelectric layer, and a short- or open-circuit piezoelectric layer by a two-port one. Electrical input impedance of the resonator is derived in terms of the Z-matrix of both the piezoelectric layer and an external load, the unique expression applies whether the resonator is a mono- or electroded-layer or a solidly mounted resonator (SMR). The loading effects of AZ-electrodes on the resonating frequencies of the piezoelectric ZnO-layer are analyzed. Transmission and reflection properties of Bragg mirrors are investigated along with the bulk radiation in SMR. As a synthesizing example, a coupled resonator filter (CR.F) is analyzed using the associated two-port equivalent network and by calculating the power transmission to a 50 Omega-load. The stacked crystal filter is naturally included in the model as a special case of CRF. Combining a comprehensive matrix analysis and an instructive network representation and setting the problem with a full vectorial formalism are peculiar features of the presented approach.

Wave propagation in layered piezoelectric rectangular bar: an extended orthogonal polynomial approach.

Wave propagation in multilayered piezoelectric structures has received much attention in past forty years. But the research objects of previous research works are only for semi-infinite structures and one-dimensional structures, i.e., structures with a finite dimension in only one direction, such as horizontally infinite flat plates and axially infinite hollow cylinders. This paper proposes an extension of the orthogonal polynomial series approach to solve the wave propagation problem in a two-dimensional (2-D) piezoelectric structure, namely, a multilayered piezoelectric bar with a rectangular cross-section. Through numerical comparison with the available reference results for a purely elastic multilayered rectangular bar, the validity of the extended polynomial series approach is illustrated. The dispersion curves and electric potential distributions of various multilayered piezoelectric rectangular bars are calculated to reveal their wave propagation characteristics.

Modeling of MEMS resonator piezoelectric disc by means of an equicharge current source method.

The Legendre polynomial method has been extended to the modeling of MEMS resonator disc with current excitation (equicharge current source). Formulation is given that allows the electric current source to be taken into account. A unique formalism has been developed which allows for both harmonic and modal analyses. Numerical results such as normalized electric input impedance, resonant and anti-resonant frequencies, dispersion curves and displacement profiles are presented and compared with those obtained by using voltage excitation in order to check the accuracy and range of applicability of the proposed approach.

Polynomial approach to analyze guided waves in anisotropic solid cylinders

We present a polynomial approach for studying guided acoustic waves in infinite homogeneous solid cylinders with the crystalline axis Z coincident with the cylinder axis. Axisymmetric and flexural modes in an isotropic cylinder and axisymmetric modes in a cylindrically orthotropic cylinder are calculated and the results are compared against other calculations from the literature to assess the accuracy and efficiency of the proposed approach.

Analysis of 900 MHz SAW filters on ZnO/GaAs structures

Up to now, RF front-end and interstage surface acoustic wave (SAW) filters for mobile communication are mainly fabricated on LiNbO/sub 3/ and LiTaO/sub 3/ substrates. A monolithic integration of these filters on GaAs or Si substrates is highly desirable to miniaturize the outer dimensions of the cellular phones. Direct monolithic integration of SAW filters is impossible with Si which is non piezoelectric, and difficult with GaAs which is weakly piezoelectric. One alternative is the deposition of a piezoelectric film on the semiconductor substrate. In this paper, we present an analysis of a ladder SAW filter built up on a two-layered structure made up of a ZnO film on a GaAs substrate in the 900 MHz frequency range.

Modelling of heterojunction acoustic charge transport devices

Abstract A method of modelling heterojunction acoustic charge transport (HACT) in GaAs has been developed. This model allows for nonuniform impurity doping profile, variable epitaxial layer configuration, and arbitrary structural design of the input electrode. The acoustic wave potential is incorporated as a time- and space-varying doping density that adds directly to the impurity doping density. The wave-induced doping density is obtained from the piezoelectric displacement charge that accompanies the acoustic wave. The method uses a solution of the two-dimensional Poisson equation to obtain the potential and charge distribution in the charge injection region of an HACT device.

Acoustic phonons in a piezoelectric [111] GaAs/AlAs superlattice

Dispersion, transmission (T), and reflection (R) properties of acoustic phonons in a [111] GaAs/AlAs superlattice are numerically investigated. Both classical dispersion curves and Floquet slowness diagrams are given to show the edges of the Brillouin zones. Locations and widths of the stop bands inside the folded zones, as well as T- and R-rates, are studied as a function of frequency and incident angle. General expressions for T- and R-rates are derived, including mode conversion. Due to interaction between modes, T and R rates exceed unity for certain frequencies.