Film Bulk Acoustic Resonator Void Structure Without Substrate Etching
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Solution Overview
Problem
Existing methods for manufacturing film bulk acoustic resonators are complex and costly, often requiring intricate substrate processing that can lead to parasitic elements, stress concentration, and increased manufacturing costs.
Innovation Solution
A film bulk acoustic resonator design featuring a substrate with an oxide film and a laminated structure including a lower electrode, piezoelectric layer, and upper electrode, where a void is created between the substrate and the laminated film by removing part of the oxide film, allowing for easy and cost-effective production without substrate processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If substrate processing steps are performed to create gaps below electrodes, then manufacturing precision and control over parasitic elements improve, but device complexity and manufacturing cost increase
Solution Approach 1:
Instead of removing substrate material to create gaps (conventional approach), the patent inverts the approach by forming the gap space first using a sacrificial layer, then building the resonator structure on top. This eliminates complex substrate processing while achieving the same gap formation purpose.
Solution Approach 2:
The patent introduces a sacrificial layer as an intermediary material that temporarily occupies the gap space during manufacturing. This mediator enables simple planar deposition processes while the sacrificial layer is later removed to create the final gap structure, avoiding direct substrate modification.
2Reliability
If intricate substrate processing is performed to form gaps, then parasitic elements are reduced, but manufacturing cost and process time increase
Solution Approach 1:
The sacrificial layer is deposited in advance during the standard thin film stacking process, preparing the gap space before the electrode and piezoelectric layers are formed. This preliminary action integrates gap formation into the normal manufacturing flow without requiring post-processing or specialized substrate modification steps.
Solution Approach 2:
The sacrificial layer serves as a temporary structure that is deliberately discarded after serving its purpose of defining the gap space. Its removal creates the final gap structure, and this discarding process is simpler than conventional substrate processing because it involves removing a loosely-bound deposited layer rather than etching into the substrate.
3Reliability
If substrate material is removed to create gaps, then acoustic resonance performance improves, but structural strength decreases and warping increases
Solution Approach 1:
The patent segments the gap creation process from the substrate structure by using a separate sacrificial layer that can be independently deposited and removed. This segmentation allows the substrate to maintain its full thickness and strength while the gap is created in the overlying structure, eliminating the trade-off between gap formation and substrate strength.
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
This approach simplifies the manufacturing process, reduces parasitic elements, minimizes stress concentration, and lowers production costs while maintaining high strength and reducing warping, enabling efficient electrical resonance characteristics.
Implementation Method 1
a piezoelectric layer held between the first and the second electrodes
Data Source
AI summary
The present invention provides a technique for making a film bulk acoustic resonator with ease, at low cost. A film bulk acoustic resonator, according to one aspect of the present disclosure has: a substrate having a first main surface; an oxide film provided over the first main surface; and a laminated film provided over the oxide film and including a first electrode, a piezoelectric layer, and a second electrode laminated in this order, and, in this film bulk acoustic resonator, a void where the oxide film is removed is provided between the substrate and the first electrode, and the piezoelectric layer has a through-hole that communicates with the void.