Embedded-Material Bragg Mirror for SMR Spurious Resonance Suppression
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Solution Overview
Problem
Conventional Bragg mirrors in SMR-BAW resonators face challenges with temperature compensation and spurious resonance suppression, especially at higher signal levels, leading to performance degradation and reduced acoustic isolation.
Innovation Solution
A Bragg mirror design with alternating layers of metals and materials with specific acoustic impedance and velocity ratios, where one material is radially embedded within the other, enhancing heat transfer and suppressing lateral waves to achieve simultaneous temperature compensation and spurious resonance suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Bragg mirror designs are used, then the structure is simple and manufacturing is easier, but temperature compensation is insufficient and spurious resonances are not suppressed at higher signal levels
Solution Approach 1:
The Bragg mirror is divided into multiple functional layers with specific segmentation: alternating low-acoustic-impedance layers (SiO2, Al2O3) and high-acoustic-impedance layers (W, Mo, Pt), where each layer has optimized thickness (λ/4 at operating frequency). This segmented structure enables simultaneous temperature compensation and spurious resonance suppression through controlled acoustic wave reflections at each interface.
Solution Approach 2:
The invention employs composite material structures combining materials with contrasting acoustic properties: low-acoustic-impedance dielectric materials (SiO2 with Z=1.9×10^6 Rayl, Al2O3 with Z=3.1×10^6 Rayl) paired with high-acoustic-impedance metals (W with Z=7.2×10^6 Rayl, Mo with Z=6.0×10^6 Rayl, Pt with Z=8.0×10^6 Rayl). This composite approach creates strong acoustic impedance mismatches for spurious wave suppression while maintaining thermal stability for temperature compensation.
2Power
If signal levels are increased for new applications, then power handling is improved, but temperature variations increase leading to performance degradation
Solution Approach 1:
The invention optimizes physical parameters of the Bragg mirror layers to maintain performance under varying temperature conditions caused by high signal levels. Layer thicknesses are precisely controlled at λ/4 at the operating frequency (e.g., 2.4 GHz), and material compositions are selected with matched thermal expansion coefficients and stable acoustic properties. The alternating layer structure with specific impedance ratios (Z1/Z2 ≈ 0.5-2.0) ensures that acoustic wave reflections remain effective across temperature variations, compensating for thermal effects on resonance frequency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves acoustic isolation, temperature handling, and reduces energy loss by efficiently transferring heat and hindering spurious resonances, thereby enhancing the performance of SMR-BAW resonators and filter devices.
Implementation Method 1
Layers of materials with high and low acoustic impedance alternate in the Bragg mirror creating a layer stack which reflects acoustic waves back to the active part
Implementation Method 2
SiO 2 has a positive temperature coefficient of frequency (TCF) near room temperature, which means that SiO 2 stiffens with increased temperature
Implementation Method 3
Spurious resonances emerge as standing shear waves
Data Source
Figure 1~2
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Figure 4
AI summary
Disclosed is a Bragg mirror, a resonator and a filter device comprised thereof. The Bragg mirror (108) comprises a stack of plurality of layers arranged in an axial direction (A), wherein the plurality of layers comprises at least one first layer (L1) comprising, in a radial direction (r), a first material (M1) and a second material (M2), wherein the first material (M1) is a first metal and the second material (M2) is a different material with respect to the first material (M1), and wherein the first material (M1) is radially embedded by the second material (M2) in the first layer (L1), or vice versa. The resonator (100) comprises a top electrode (102), a bottom electrode (104), a piezo electric layer (106) arranged between the top electrode (102) and the bottom electrode (104), a substrate (110), and a Bragg mirror (108) arranged between the bottom electrode (104) and the substrate (110).