Single-Crystal BAW Resonator Structure for Low Acoustic Leakage
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Solution Overview
Problem
Traditional bulk acoustic wave resonators face issues such as corrosion, low quality factor, and high insertion loss due to structural defects and polycrystalline piezoelectric materials, which limit their performance in high-frequency and miniaturized applications.
Innovation Solution
A single crystal film bulk acoustic wave resonator is designed with a substrate, Bragg reflection layer, bonding layers, silicon oxide layers, and a piezoelectric layer made of AlN or lithium niobate, featuring air holes to enhance acoustic wave reflection and mechanical reliability, and a preparation method involving magnetron sputtering and hot pressing bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional polycrystalline piezoelectric material is used, then the resonator structure is easier to manufacture, but the quality factor is low due to high defect density
Solution Approach 1:
The patent changes the crystal structure parameter from polycrystalline to single crystal, fundamentally altering the material's internal structure to eliminate grain boundaries and reduce defect density. This parameter change directly addresses the quality factor issue while the established single crystal growth techniques maintain manufacturing feasibility
Solution Approach 2:
The patent creates a composite structure combining single crystal piezoelectric material with carefully designed bonding layers and Bragg reflection layers. This composite approach leverages the superior properties of single crystal material while using the layered structure to manage acoustic wave reflection and bonding reliability
2Reliability
If traditional bulk acoustic wave resonator structure is used, then the device is simpler in structure, but the resonator is easily corroded by solution from sacrificial layer due to structural defect
Solution Approach 1:
The patent performs preliminary protective actions by designing bonding layers with extended coverage that protrude beyond the electrode edges before corrosion can occur. This preliminary structural arrangement prevents direct contact between corrosive solutions and the piezoelectric material, addressing the corrosion issue before it manifests
Solution Approach 2:
The patent introduces protective bonding layers and extended structural elements that act as cushioning barriers against corrosion. These layers are positioned in advance to intercept and protect the vulnerable piezoelectric material from corrosive solutions released during device operation or processing
3Reliability
If traditional film bulk acoustic wave resonator is used, then the device is miniaturized, but acoustic waves leak into surrounding substrate through piezoelectric material resulting in low quality factor
Solution Approach 1:
The patent converts the potentially harmful acoustic wave leakage into a beneficial reflection by implementing Bragg reflection layers with specific acoustic impedance characteristics. These layers are designed to reflect acoustic waves back into the resonator cavity, transforming what would be energy loss into useful acoustic confinement that enhances the quality factor
Solution Approach 2:
The patent introduces Bragg reflection layers as intermediary structures between the piezoelectric material and the substrate. These intermediary layers serve as acoustic mirrors that prevent direct coupling of acoustic energy into the substrate, thereby reducing leakage losses while maintaining the miniaturized device structure
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 significantly improves the quality factor and reduces power loss, achieving a higher electromechanical coupling coefficient and lower insertion loss compared to traditional polycrystalline resonators, making it suitable for high-frequency and miniaturized scenarios.
Implementation Method 1
The film bulk acoustic wave resonator converts an electrical signal with an extremely large wavelength into an acoustic signal with a small wavelength through a piezoelectric effect
Implementation Method 2
A Bragg reflection layer, a first bonding layer, a second bonding layer, a piezoelectric layer and an electrode layer sequentially from bottom to top
Implementation Method 3
a preparation method involving magnetron sputtering and hot pressing bonding
Implementation Method 4
a preparation method involving magnetron sputtering and hot pressing bonding
Data Source
AI summary
A single crystal film bulk acoustic wave resonator includes a substrate layer, a Bragg reflection layer, a first bonding layer, a second bonding layer, a piezoelectric layer and an electrode layer; a width of the electrode layer is smaller than that of the piezoelectric layer. The resonator further includes a first silicon oxide layer and a second silicon oxide layer, which surround the first bonding layer and the second bonding layer respectively, and a plurality of first air holes horizontally arranged and a plurality of second air holes horizontally arranged are respectively formed in the first silicon oxide layer and the second silicon oxide layer. Each of the plurality of first air holes corresponds to and is communicated with a respective one of the plurality of second air holes. The piezoelectric layer is made of AlN or lithium niobate.