Multilayer-Base BAW Resonator for Crystal Alignment Stability
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Solution Overview
Problem
Conventional bulk acoustic wave resonators have polycrystalline piezoelectric thin films with less than desired piezoelectric effects due to crystal growth in various directions, leading to suboptimal performance.
Innovation Solution
A bulk acoustic resonator design featuring a multilayer base with alternating layers of crystalline materials having different lattice constants, which relaxes crystal lattice strains and improves the alignment of crystal orientations in the piezoelectric layer, resulting in higher quality piezoelectric films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional sputter deposition is used to create piezoelectric thin films, then the manufacturing process is simple and cost-effective, but the crystal growth occurs in various directions resulting in polycrystalline structure with less than desired piezoelectric effects
Solution Approach 1:
The base structure is segmented into multiple alternating layers of crystalline materials with different lattice constants. This segmentation allows each layer to contribute differently to the overall strain relaxation, enabling improved crystal orientation alignment in the piezoelectric film without requiring a complete redesign of the entire device structure.
Solution Approach 2:
The patent employs composite materials by combining multiple crystalline materials with different lattice constants in an alternating layered structure. This composite base structure creates a gradient strain environment that promotes better crystal orientation alignment, achieving higher manufacturing precision while maintaining the benefits of sputter deposition processing.
2Manufacturing precision
If a single-layer base is used, then the device structure is simple, but the crystal lattice strains are not effectively relaxed leading to poor piezoelectric layer quality
Solution Approach 1:
The patent changes the lattice constant parameter by using alternating layers of crystalline materials with different lattice constants. This parameter variation creates a gradient strain environment that effectively relaxes crystal lattice strains and improves piezoelectric layer quality, achieving better manufacturing precision through controlled material composition changes.
3Reliability
If polycrystalline piezoelectric films are used, then the fabrication process is straightforward, but the resonance frequency shifts significantly due to temperature changes
Solution Approach 1:
The patent applies local quality by creating specific regions with different crystal orientation qualities. The alternating layered base structure produces areas with varying strain conditions, leading to locally optimized crystal growth orientations that collectively improve resonance frequency stability while maintaining overall fabrication simplicity.
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 multilayer base structure enhances the quality of the piezoelectric layer, leading to improved performance and characteristics closer to single crystal layers, with reduced resonance frequency shifts due to temperature changes.
Implementation Method 1
The piezoelectric layer has improved alignment of crystal orientations due to the effectiveness of the multilayer base in relaxing the strains caused by the different lattice constants of different materials in the BAW stack
Implementation Method 2
When an oscillating electrical signal is applied between the top and bottom electrodes, the piezoelectric thin film layer converts the oscillating electrical signal into bulk acoustic waves
Data Source
AI summary
A bulk acoustic (BAW) resonator having a multilayer base and method of fabricating the bulk acoustic resonator is disclosed. A BAW resonator comprises a substrate having a cavity and including a frame around the cavity, a multilayer base adjacent the cavity and supported by the frame. The multilayer base includes a first layer of crystalline material having a first lattice constant and a second layer of crystalline material having a second lattice constant that is distinct from the first lattice constant. The BAW resonator further includes a stack over the multilayer base. The stack includes a first electrode formed on the multilayer base, a piezoelectric layer having a first side coupled to the first electrode and a second side opposite to the first side of the piezoelectric layer, and a second electrode coupled to the second side of the piezoelectric layer.