Optimized reflector stacks for solidly mounted bulk acoustic wave resonators (original) (raw)
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Opportunities for Shear Energy Scaling in Bulk Acoustic Wave Resonators
An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta 2 O 5 / SiO 2 stacks showing suppression of the spurious modes. Jose is with quality and reliability, nXP semiconductors, nijmegen, The netherlands. r. J. E. Hueting is with the Faculty
Design of High-Q Thin Film Bulk Acoustic Resonator Using Dual–Mode Reflection
In this paper, the Q-factor enhancement of the Thin Film Bulk Acoustic Wave Resonator (FBAR) with Type-II dispersion is investigated. Our purpose is to improve the Qfactors of the resonator, especially the one at anti-resonance frequency (f a ), by the application of a frame structure on its periphery. The frame performs as a lateral acoustic Bragg reflector, which is able to reflect two Lamb modes S 1 and S 0 upon the FBAR border region. These two modes are presumed to contribute the most to lateral acoustic leakage. The results of one of the modified FBARs exhibit a superior improvement of the Q factor at f a (Q a ) of about 1000 over the one without optimization.
Assessment of the Acoustic Shear Velocity in SiO2 and Mo layers for Acoustic Reflectors
We present a method to assess the shear acoustic velocity in SiO2 and Mo sputtered films, which are materials commonly used as low and high acoustic impedance layers in the acoustic reflectors of solidly mounted resonators. The method consists in the analysis of the frequency response of AlN-based resonators operating in the shear mode using acoustic mirrors specifically designed to obtain a half-wavelength resonance in the layer under study, the thickness of which is thickened to achieve a significant signal. After measuring the thickness and mass densities of all the layers composing the resonator, the fitting by Mason's model of the electrical response in a wide frequency range provides accurate values of both the longitudinal and the shear mode velocities. The shear acoustic velocities of porous SiO2 and Mo are 3150 m/s and 3450 m/s respectively. This method allows assessing the shear mode acoustic velocity of any material by adequately designing the test structure.
Investigation of spurious resonances in thin film bulk acoustic wave resonators
IEEE Ultrasonics Symposium, 2004, 2004
A Finite Element Analysis is performed to simulate Thin Film Bulk Acoustic Wave (FBAR) structures, and a coupled Finite Element Analysis / Boundary Integral Method (FEA/BIM) is used to accurately simulate a radiation medium, like a Bragg mirror underneath a resonator, without having to mesh it entirely. Displacement fields are extracted from these calculations and analysed. In particular, dispersion curves are obtained by a Fourier analysis of these fields and are used to explain phenomena arising at electrode edges, like standing wave resonances under the electrodes or mode conversions.
Sputtered SiO2 as low acoustic impedance material for Bragg mirror fabrication in BAW resonators
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2010
In this paper we describe the procedure to sputter low acoustic impedance SiO 2 films to be used as a low acoustic impedance layer in Bragg mirrors for BAW resonators. The composition and structure of the material are assessed through infrared absorption spectroscopy. The acoustic properties of the films (mass density and sound velocity) are assessed through X-ray reflectometry and picosecond acoustic spectroscopy. A second measurement of the sound velocity is achieved through the analysis of the longitudinal λ/2 resonance that appears in these silicon oxide films when used as uppermost layer of an acoustic reflector placed under an AlN-based resonator.
Guided acoustic wave resonators using an acoustic Bragg mirror
Applied Physics Letters, 2010
Lamb wave devices have recently gained an interest for providing narrow bandpass filters in wireless transmission systems. Their cointegration with film bulk acoustic wave resonators is a major advantage, enabling the possibility to provide simultaneously several radio frequency and intermediate-frequency filters in a single fabrication. Similarly, in this work, we report the fabrication of resonators using waves guided in a piezoelectric layer deposited atop a Bragg mirror. Such waves exhibit a behavior close to Lamb waves, thanks to the acoustic isolation provided by the mirror, while being cointegrated along with solidly mounted resonator structures.
Sputtered SiO2 as low acoustic impedance material for Bragg mirror fabrication in BAW resonators
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000
In this paper we describe the procedure to sputter low acoustic impedance SiO 2 films to be used as a low acoustic impedance layer in Bragg mirrors for BAW resonators. The composition and structure of the material are assessed through infrared absorption spectroscopy. The acoustic properties of the films (mass density and sound velocity) are assessed through X-ray reflectometry and picosecond acoustic spectroscopy. A second measurement of the sound velocity is achieved through the analysis of the longitudinal λ/2 resonance that appears in these silicon oxide films when used as uppermost layer of an acoustic reflector placed under an AlN-based resonator.
2021
This paper reports, the application of Taguchi Design of Experiments (DoE) and ANOVA (Analysis of Variance) for finding the optimal combinations and analysis of the effect of individual layer thickness on the performance of SMR sensor. The optimum combination of design parameters and its performance as a sensor have been predicted with DoE and validated through the finite element modeling (FEM) simulation. The optimization has been done to achieve enhancement in coupling coefficient of SMR sensor. The best optimized thickness of metal electrodes, piezoelectric, sensing, insulation low and high acoustic impedance layers have been found to be 0.2µm, 2µm, 0.68µm, 0.3µm, 1.028µm and 1.008µm, respectively. The results of the present study show that for the optimized dimension of SMR structure, simulated values of coupling coefficient (K2eff), Quality factor (Q) and figure of merit (FoM) are 0.075596 (or 7.5596%), 1171.6 and ≈ 88, respectively. Optimized structure performance has been com...
Journal of Microelectromechanical Systems
Most of the applications of solidly mounted resonator need the compensation of temperature coefficient of resonant frequency. The presence of materials with different properties in the stack makes it complicated to explain the influence of each material individually on temperature coefficient. To reduce design and fabrication costs, an accurate and precise modeling of the resonators is required. In this paper, Mason model and finite-element analysis are used to design the resonators and results for both models, which are almost similar, are presented. Different kinds of configuration (symmetric and asymmetric, according to the thickness of the layers) are designed to achieve the temperature coefficient of frequency as near-zero as possible with an optimized response. Such designs are fabricated and characterized obtaining measurements of the temperature coefficient of frequency. The result shows that useful and reliable information on the performance of resonators can be achieved with accurate modeling. Index Terms-Solidly mounted resonators (SMRs), temperature coefficient of frequency (TCF), mason model, finite element modeling (FEM).