Thin LN-LT Acoustic Resonators for Parasitic Mode Suppression
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications networks, such as those proposed for future wireless communications systems, which require improved performance and wider communication channel bandwidths.
Innovation Solution
The development of Y-cut film bulk acoustic resonators (YBARs) and solidly-mounted Y-cut film bulk acoustic resonators (SM YBARs) using piezoelectric materials like lithium niobate, with specific crystal orientations and configurations, including rotated Y-cuts and acoustic Bragg reflectors, to enhance frequency response and reduce parasitic modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used, then current communication systems operate effectively, but they cannot meet the requirements for higher frequency bands (up to 28 GHz) and wider communication channel bandwidths
Solution Approach 1:
The patent changes the crystal orientation parameter from conventional cuts to Y-cut (with specific Euler angles α, β, γ) to enable operation at higher frequencies. This parameter change in the piezoelectric material's crystal structure allows the resonator to achieve the required frequency response and bandwidth for future communication systems up to 28 GHz
Solution Approach 2:
The invention uses composite layered structures including piezoelectric layers (lithium niobate, lithium tantalate), acoustic Bragg reflectors with alternating high and low acoustic impedance layers, and suspended membrane configurations. These composite materials and structures enable enhanced frequency selectivity and suppression of parasitic modes at higher frequency bands
2Adaptability or versatility
If Y-cut film bulk acoustic resonators with rotated Y-cuts and acoustic Bragg reflectors are implemented, then frequency selectivity and performance at higher frequencies improve, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The resonator is segmented into distinct functional layers: piezoelectric layers with specific Y-cut orientations, acoustic Bragg reflector layers with alternating impedance materials, suspended membrane sections, and electrode patterns. This segmentation allows each layer to be optimized independently for its specific function while managing overall device complexity
Solution Approach 2:
The Y-cut piezoelectric plate with rotated orientation serves multiple functions simultaneously: it provides the piezoelectric effect for acoustic wave generation, establishes the desired frequency response through crystal orientation, and suppresses parasitic modes through the specific Euler angle configuration. The acoustic Bragg reflector also serves dual purposes of frequency selection and parasitic mode suppression
3Adaptability or versatility
If Y-cut film bulk acoustic resonators with rotated Y-cuts and acoustic Bragg reflectors are implemented, then frequency selectivity and performance at higher frequencies improve, but manufacturing precision requirements increase
Solution Approach 1:
The crystal orientation (Euler angles α, β, γ) is predetermined and established during the wafer fabrication stage before device assembly. This preliminary action ensures that the piezoelectric layers are pre-aligned to the required Y-cut orientation, reducing the need for post-processing alignment and simplifying subsequent manufacturing steps
Solution Approach 2:
By changing to Y-cut with specific Euler angles, the patent optimizes the piezoelectric coefficients and acoustic wave propagation characteristics to achieve better frequency response. This parameter change in crystal orientation also provides more tolerant manufacturing windows compared to other cut configurations, as the Y-cut geometry naturally suppresses certain parasitic modes
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
These resonators provide improved frequency selectivity and reduced parasitic modes, enabling effective operation in higher frequency bands with enhanced performance and adaptability to different filter specifications.
Implementation Method 1
Y-cut film bulk acoustic resonators (YBARs) and solidly-mounted Y-cut film bulk acoustic resonators (SM YBARs) using piezoelectric materials like lithium niobate
Implementation Method 2
acoustic Bragg reflectors
Data Source
AI summary
Acoustic resonator devices, filter devices, and methods of fabrication are disclosed. A resonator device includes a substrate having a surface and a single-crystal piezoelectric plate including one of rotated Y-cut lithium niobate and rotated Y-cut lithium tantalate. The single-crystal piezoelectric plate has a front surface and a back surface opposite the front surface, wherein the back surface is coupled to the surface. A floating back-side conductor pattern is formed on a portion of the back surface. A front-side conductor pattern consisting of two electrodes is formed on a portion of the front surface opposite the back-side conductor, wherein a radio frequency applied between the two electrodes excites a primary acoustic mode in the single-crystal piezoelectric plate.