BAW Resonator Superlattice Buffer for High-Sc ScAlN Growth
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Solution Overview
Problem
The deposition of ScAlN piezoelectric material with high Scandium composition directly on a bottom electrode of a BAW resonator results in poor crystalline quality, which lowers the coupling coefficient of the resonator.
Innovation Solution
Incorporating a superlattice buffer with alternating AlN and SLAIN layers between the bottom electrode and the piezoelectric material to improve the crystalline quality of the ScAlN piezoelectric material with high Sc composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ScAlN piezoelectric material with high Scandium composition is deposited directly on a bottom electrode, then the coupling coefficient increases, but the crystalline quality deteriorates
Solution Approach 1:
A multilayer buffer structure consisting of alternating AlN and ScAlN layers is introduced between the bottom electrode and the high-Sc piezoelectric layer. This intermediary buffer structure provides a gradual transition in lattice constant, enabling the deposition of high-Sc piezoelectric material with improved crystalline quality while maintaining the desired coupling coefficient.
Solution Approach 2:
The buffer layer is segmented into multiple alternating layers of AlN and ScAlN with different lattice constants. This segmentation creates a superlattice structure that gradually transitions the lattice mismatch, allowing each layer to accommodate the strain progressively rather than abruptly, thereby improving overall crystalline quality.
2Manufacturing precision
If a single layer AlN buffer is used to improve crystalline quality, then the crystalline quality improves, but the coupling coefficient decreases
Solution Approach 1:
The buffer structure is designed as a composite multilayer system combining AlN and ScAlN layers. This composite structure leverages the beneficial properties of both materials: AlN provides lattice matching and crystalline quality improvement, while ScAlN layers maintain the high coupling coefficient characteristic of scandium-rich piezoelectric materials.
Solution Approach 2:
Different regions of the buffer structure have different local compositions and properties. The AlN layers provide lattice matching and structural stability, while the ScAlN layers contribute to the piezoelectric coupling. This local differentiation of material properties allows simultaneous optimization of both crystalline quality and coupling coefficient.
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 use of a superlattice buffer enhances the crystalline quality of the ScAlN piezoelectric material, thereby increasing the coupling coefficient of the BAW resonator while maintaining high Sc composition.
Implementation Method 1
The multilayer buffer includes two or more pairs of alternating layers. A first pair of the two or more pairs includes a first layer of crystalline material having a first lattice constant, and a second layer of crystalline material having a lattice constant that is distinct from the first lattice constant.
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 wave resonator includes a substrate, and a stack that is supported by the substrate. The stack includes a first electrode, a multilayer buffer, a piezoelectric layer, and a second electrode. The multilayer buffer is disposed between the first electrode and the piezoelectric layer, and the piezoelectric layer is disposed between the multilayer buffer and the second electrode. The multilayer buffer includes two or more pairs of alternating layers. A first pair of the two or more pairs include a first layer of crystalline material having a first lattice constant, and a second layer of crystalline material having a lattice constant that is distinct from the first lattice constant.