Microacoustic Cavity Stack Filter Using AlScN Plate-Mode Deposition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Designing a cost-effective filter that supports frequencies between 500 MHz and 2.6 GHz while maintaining sufficient electromechanical coupling and quality factors is challenging, especially with increasing wafer sizes.
Innovation Solution
A microacoustic filter with a cavity stack using a piezoelectric material that excites a plate mode, specifically aluminium scandium nitride, with a buffer layer enabling epitaxial growth, allowing direct deposition without layer-removal or transfer processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface-acoustic-wave filters use lithium niobate or lithium tantalate piezoelectric material with bulk wafer material, then filtering performance is achieved, but manufacturing cost increases significantly for wafer sizes of 150 millimeters or more
Solution Approach 1:
The patent changes the piezoelectric material from traditional lithium niobate or lithium tantalate to aluminium scandium nitride, which enables direct deposition on silicon substrates. This material substitution allows for direct growth on standard silicon wafers without requiring expensive bulk wafer materials or complex transfer processes, thereby reducing manufacturing costs while maintaining filtering performance
Solution Approach 2:
The patent replaces the mechanical transfer and layer-removal processes traditionally required for piezoelectric filter fabrication with a direct epitaxial growth process. By using aluminium scandium nitride that can be directly deposited on silicon substrates, the complex mechanical manipulation steps are eliminated, simplifying manufacturing and reducing costs for large wafer sizes
2Reliability
If layer-removal process or transfer process is used to deposit piezoelectric layer, then filtering performance is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the unnecessary layer-removal and transfer processes from the manufacturing workflow. By selecting aluminium scandium nitride as the piezoelectric material, the invention allows direct deposition on the final silicon substrate, removing intermediate steps involving temporary substrates, layer transfer, and selective removal operations
Solution Approach 2:
The patent performs preliminary preparation of the silicon substrate surface and establishes appropriate growth conditions before directly depositing the aluminium scandium nitride piezoelectric layer. This preliminary action ensures proper epitaxial growth and crystal orientation, eliminating the need for subsequent layer removal or transfer operations that would add complexity
3Ease of manufacture
If acoustic wave is not confined within the filter structure, then manufacturing is simpler, but electromechanical coupling factor and quality factor decrease
Solution Approach 1:
The patent employs a composite structure combining aluminium scandium nitride piezoelectric layer with silicon substrate and carefully designed cavity geometry. This composite approach creates intrinsic acoustic wave confinement through the interaction of acoustic impedance mismatches at material interfaces and the cavity boundary conditions, achieving high electromechanical coupling and quality factors while maintaining manufacturing feasibility
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 microacoustic filter achieves a competitive price point compared to surface-acoustic-wave filters, with higher electromechanical coupling and quality factors due to intrinsic acoustic wave confinement within the cavity stack.
Implementation Method 1
The piezoelectric material has a crystal orientation that enables excitation of a plate mode (e.g., a Lame mode) with an orientation that is normal to a surface of the piezoelectric layer
Implementation Method 2
A top layer of the cavity stack and the buffer layer enable epitaxial growth of the piezoelectric layer such as aluminium scandium nitride
Data Source
AI summary
An apparatus is disclosed for implementing a microacoustic filter with a cavity stack. In an example aspect, the apparatus includes a microacoustic filter with an electrode structure, a cavity stack, a buffer layer, and a piezoelectric layer. The cavity stack comprises a conductive layer, a substrate layer, and at least two pillars extending past a plane defined by a surface of the substrate layer and towards the conductive layer to form a cavity between the substrate layer and the conductive layer. The buffer layer is disposed between the conductive layer of the cavity stack and the electrode structure. The piezoelectric layer is disposed between the buffer layer and the electrode structure.