Recessed frames in thickness mode piezoelectric resonators
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Solution Overview
Problem
Piezoelectric devices face performance degradation due to electrical and mechanical dissipation factors, leading to increased heat generation and energy leakage through unwanted lateral modes in thickness mode resonators like BAW, DBARs, SMRs, and FBARs, which affects the quality factor (Qp) at parallel resonance frequency (fp).
Innovation Solution
A piezoelectric resonator design featuring a metal frame that is partially recessed into the piezoelectric material layer, with recesses and extensions configured to suppress spurious modes, thereby reducing lateral energy leakage and enhancing energy containment within the resonator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional planar electrode structure is used in thickness mode piezoelectric resonators, then the device structure is simple and easy to manufacture, but unwanted lateral modes are generated that leak energy out of the resonator, decreasing the quality factor (Qp) at parallel resonance frequency
Solution Approach 1:
The patent transitions from a conventional planar (2D) electrode structure to a three-dimensional recessed frame structure. The metal frame is recessed into the piezoelectric material layer at multiple locations, creating a 3D configuration that provides lateral confinement and suppresses unwanted mode generation while maintaining manufacturability through standard semiconductor fabrication processes.
Solution Approach 2:
The electrode structure is segmented into multiple discrete metal frame segments recessed at different locations within the piezoelectric material layer. These segmented frames work collectively to suppress lateral modes while allowing independent optimization of each segment's position and dimensions to target specific unwanted modes.
2Loss of energy
If the piezoelectric material layer is extended laterally to increase energy containment, then energy leakage is reduced, but the device area increases and lateral modes may still be generated
Solution Approach 1:
Instead of extending the piezoelectric material layer laterally in the plane, the patent uses vertical recesses into the material layer to create confinement. This 3D approach provides effective lateral mode suppression without increasing the planar footprint of the device.
Solution Approach 2:
The metal frame structures are nested within the piezoelectric material layer by recessing them into the material. This nesting configuration allows the frames to be positioned at optimal depths to maximize their effectiveness in suppressing lateral modes while minimizing their impact on the overall device area.
3Reliability
If deeper recesses are made in the piezoelectric material layer to improve mode suppression, then spurious mode attenuation increases, but manufacturing complexity and difficulty increase
Solution Approach 1:
The patent optimizes the recess parameters (depth, width, spacing) to achieve effective mode suppression at practical manufacturing depths. By carefully selecting these parameters, the design achieves spurious mode attenuation without requiring excessively deep or complex recesses that would be difficult to manufacture.
Solution Approach 2:
The metal frames are recessed partially into the piezoelectric material layer rather than completely through it. This partial recess configuration provides sufficient mode suppression effectiveness while maintaining simpler fabrication processes compared to through-silicon vias or deep trench structures.
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 design improves the resonator's quality factor (Qp) at parallel resonance frequency (fp) by attenuating spurious energy propagation, leading to increased energy containment and reduced heat generation, thus enhancing the overall performance of the piezoelectric device.
Implementation Method 1
a piezoelectric material layer having a first side and a second side that is opposite the first side, the piezoelectric material layer first side abutting the first metal layer, the piezoelectric material layer second side having recesses
Implementation Method 2
the confinement of energy around fp is related to the quality factor (Qp) of the resonance. A factor that may lead to a decrease in Qp includes the setup and sustainment of unwanted modes in a lateral (e.g., longitudinal) direction which may leak energy out of the resonator
Data Source
AI summary
In some examples, an apparatus includes a first metal layer having a thickness, a piezoelectric material layer having a first side and a second side that is opposite the first side, the piezoelectric material layer first side abutting the first metal layer, the piezoelectric material layer second side having recesses, and a second metal layer abutting the piezoelectric material layer second side, the second metal layer having extensions that fill the recesses to form a metal frame that is at least partially recessed into the piezoelectric material layer. The first metal layer, the piezoelectric material layer, and the second metal layer form a resonator body. The metal frame has a shape governing a resonant mode of the resonator body.