Bulk Acoustic Wave Resonator Cavity Bonding for Structural Stability
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Solution Overview
Problem
Bulk acoustic wave resonators in prior art suffer from poor structure stability due to the need for large cavities to form acoustic isolation regions, which compromises the device's integrity.
Innovation Solution
A fabrication method for a bulk acoustic wave resonator that involves forming a cavity on a lower surface around the resonant piezoelectric stack through bonding, rather than etching away a large portion of the silicon substrate, thereby enhancing structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large cavity is etched on the silicon substrate to form an acoustic isolation region, then acoustic wave confinement is improved, but structure stability deteriorates
Solution Approach 1:
The device is divided into two separate wafers: a first wafer containing the cavity and a second wafer containing the resonant piezoelectric stack. This segmentation allows the cavity to be formed without compromising the structural integrity of the resonator components, as they are fabricated on separate substrates and subsequently bonded together.
Solution Approach 2:
The resonant piezoelectric stack is positioned over the cavity opening, effectively nesting the active device components above the acoustic isolation region. This arrangement allows the cavity to provide acoustic confinement while the piezoelectric stack remains structurally supported by the second wafer.
2Object-affected harmful factors
If a large area of silicon wafer is etched away to form the back side cavity, then acoustic isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The fabrication process is segmented into independent steps for each wafer. The cavity is formed on the first wafer using standard etching techniques, while the resonant piezoelectric stack is fabricated on the second wafer separately. This segmentation simplifies the overall manufacturing process by avoiding the need for complex deep etching through the entire device structure.
Solution Approach 2:
The cavity is prepared in advance on the first wafer before the resonant piezoelectric stack is fabricated on the second wafer. This preliminary action allows both components to be optimized independently and then assembled together, reducing the overall fabrication complexity.
3Object-affected harmful factors
If a large cavity is formed under the resonant piezoelectric stack, then acoustic wave confinement is improved, but device reliability deteriorates
Solution Approach 1:
By separating the cavity formation from the resonator fabrication, the structural integrity of the resonant piezoelectric stack is maintained. The cavity serves its acoustic isolation function without creating stress concentrations or structural weaknesses that would compromise device reliability.
Solution Approach 2:
A bonding layer is introduced as an intermediary between the first wafer (containing the cavity) and the second wafer (containing the resonant piezoelectric stack). This bonding layer provides mechanical support and ensures reliable electrical connections while allowing the cavity to function as an acoustic isolation region.
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 method results in a more stable device structure compared to traditional etching methods, while also simplifying the fabrication process and reducing equipment costs, leading to improved quality factors.
Implementation Method 1
a resonant piezoelectric stack including a piezoelectric film, and a first electrode and a second electrode that are in contact with the piezoelectric film
Data Source
AI summary
Disclosed are a bulk acoustic wave resonator and a fabrication method for the bulk acoustic wave resonator. The fabrication method includes: preparing a cavity with a top opening on a first silicon wafer; preparing an insulating layer on an upper surface of a second silicon wafer, and preparing a resonant piezoelectric stack on an upper surface of the insulating layer; preparing a first silicon dioxide layer on an upper surface of the resonant piezoelectric stack; bonding a surface where the top opening of the cavity is located with an upper surface of the first silicon dioxide layer; and preparing a lead out pad of the first electrode and the second electrode.