Bulk Acoustic Wave Resonator Cavity Layout for Stiction Control
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Solution Overview
Problem
The challenge in manufacturing bulk acoustic wave resonators is the occurrence of stiction between resonant portions and substrates due to sacrificial layer thickness, which increases the size of the device and leads to characteristic deterioration and process accuracy issues.
Innovation Solution
A bulk acoustic wave resonator design featuring a substrate with a cavity groove and a convex membrane layer, where the cavity groove is sized to correspond with the convex portion, forming a larger first space that prevents stiction and reduces the length of the inclined surface, using a support layer and passivation to maintain structural integrity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the sacrificial layer is increased to reduce stiction between resonant portions and substrates, then the occurrence of stiction is reduced, but the size of the overall filter device and resonator increases
Solution Approach 1:
The cavity formation process is segmented into two independent parts: (1) a cavity groove formed in the substrate before depositing the sacrificial layer, and (2) the sacrificial layer deposited only in the remaining space. This segmentation allows the cavity groove to provide initial stiction prevention while the sacrificial layer fills only the necessary space, preventing excessive device size increase.
Solution Approach 2:
The cavity groove is formed in the substrate before the sacrificial layer is deposited. This preliminary action creates a pre-defined cavity space that prevents stiction from the outset, allowing the subsequent sacrificial layer to be thinner since it only needs to fill the remaining space rather than providing the entire cavity volume.
2Reliability
If the thickness of the sacrificial layer is increased to reduce stiction, then the occurrence of stiction is reduced, but the length of the inclined surface increases leading to characteristic deterioration
Solution Approach 1:
The cavity structure is segmented into a vertical cavity groove component and an inclined sacrificial layer component. The cavity groove provides the primary cavity depth, while the sacrificial layer only forms a thinner inclined portion, significantly reducing the total inclined surface length compared to a single thick sacrificial layer approach.
Solution Approach 2:
The cavity formation transitions from a single-dimensional thick sacrificial layer approach to a two-dimensional structure combining a vertical cavity groove with a thinner inclined sacrificial layer. This dimensional change allows cavity volume to be maintained while reducing the inclined surface length that causes characteristic deterioration.
3Reliability
If the thickness of the sacrificial layer is increased, then the occurrence of stiction is reduced, but the size of the step increases causing negative properties in process accuracy
Solution Approach 1:
The sacrificial layer deposition is segmented to occur only after the cavity groove is formed, allowing the layer to be deposited as a thinner film that conforms to the groove structure. This eliminates the need for thick layer deposition and subsequent planarization, maintaining process accuracy throughout.
Solution Approach 2:
The cavity groove is formed preliminarily before sacrificial layer deposition, creating a pre-defined cavity space. This preliminary structure allows the sacrificial layer to be deposited as a thin conformal coating rather than requiring a thick layer, thereby maintaining small step sizes and high process accuracy in subsequent manufacturing steps.
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 design effectively prevents stiction between the substrate and membrane layer, reduces the overall size of the resonator, and maintains process accuracy by increasing the volume of the cavity space, thereby addressing the issues caused by sacrificial layer thickness increases.
Implementation Method 1
a piezoelectric layer configured so that a portion of the piezoelectric layer may be disposed above the convex portion
Data Source
AI summary
A bulk acoustic wave resonator includes a substrate including a cavity groove, a membrane layer disposed above the substrate and including a convex portion. And a lower electrode including a portion thereof disposed on the convex portion. The bulk acoustic wave resonator also includes a piezoelectric layer configured so that a portion of the piezoelectric layer is disposed above the convex portion, and an upper electrode disposed on the piezoelectric layer. A first space formed by the cavity groove and a second space formed by the convex portion form a cavity, the cavity groove is disposed below an active region, and the convex portion comprises an inclined surface disposed outside of the cavity groove.