Framed BAW Resonator Structure for Acoustic Wave Loss Reduction
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Solution Overview
Problem
Bulk acoustic wave resonators experience a reduction in quality factor due to acoustic wave loss in both width and thickness directions, making it challenging to maintain high performance and precise frame formation using existing lift-off methods, which often result in residual protrusions and difficulty in achieving linear characteristics.
Innovation Solution
A resonator design featuring a frame that covers the outer end portion of the second electrode, with an air gap between the substrate and the resonating portion, and a membrane layer to support the structure, along with a manufacturing method that includes laminating electrodes and piezoelectric layers, forming a frame layer with higher etching selectivity than the second electrode, and using an etch stop layer to prevent residual issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frame is provided to reduce acoustic wave loss and improve quality factor, then resonator performance is improved, but manufacturing precision deteriorates due to residual protrusions and difficulty in achieving linear characteristics with lift-off methods
Solution Approach 1:
The patent introduces an etch stop layer as an intermediary between the frame layer and the second electrode. This etch stop layer acts as a mediator that allows for precise control of the frame formation process, enabling the frame to be formed with accurate dimensions and linear characteristics without residual protrusions, thus resolving the manufacturing precision issue while maintaining the quality factor improvement benefit
Solution Approach 2:
The patent changes the etching parameters by selecting materials with different etching rates. The frame layer material is chosen to have a different etching rate compared to the second electrode material, and the etch stop layer is specifically selected to have appropriate etching characteristics. This parameter change enables selective etching that achieves precise frame dimensions and eliminates residual protrusions, resolving the manufacturing precision contradiction
2Power
If acoustic waves are generated in width direction according to piezoelectric layer characteristics, then resonance occurs, but loss increases reducing quality factor
Solution Approach 1:
The patent extracts or removes the harmful acoustic wave propagation in the width direction by providing a frame structure that confines the acoustic waves. The frame acts as a barrier that takes out the unwanted lateral acoustic wave energy, preventing it from causing loss, while allowing the desired thickness-direction resonance to continue, thus improving quality factor without sacrificing resonance generation
Solution Approach 2:
The patent converts the harmful lateral acoustic wave energy into beneficial reflected energy by using the frame as a reflective boundary. Instead of allowing acoustic waves to propagate laterally and cause loss, the frame reflects them back into the resonating region, converting what would be energy loss into useful resonant energy, thereby improving quality factor while maintaining resonance
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 solution significantly reduces acoustic wave loss, improves reflective characteristics, and enhances the quality factor and electro-mechanical coupling coefficient, leading to improved resonator performance and precise frame dimensions, thereby increasing bandwidth and data transmission efficiency.
Implementation Method 1
Bulk acoustic wave (BAW) resonators (BAWR) generating resonance using acoustic waves in a thickness or depth direction of a substrate
Implementation Method 2
a frame provided at an outer edge of the resonating portion, a portion of the frame covering an outer end portion of the second electrode
Data Source
AI summary
A resonator includes a resonating portion including a first electrode, a second electrode, and a piezoelectric layer positioned between the first electrode and the second electrode; and a frame provided at an outer edge of the resonating portion, at least a portion of the frame covering an outer end portion of the second electrode.