BAW Resonator Thick Electrodes for Symmetric Acoustic Impedance
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Solution Overview
Problem
Conventional RF technologies face limitations in achieving high performance bulk acoustic wave resonators for frequencies above 5 GHz due to the degradation of polycrystalline piezoelectric films, and challenges in manufacturing single crystal piezoelectric thin films for improved resonator devices.
Innovation Solution
An anti-symmetrical configuration for bulk acoustic wave resonator devices with partial mass-loaded structures on both electrodes, using materials like molybdenum, ruthenium, and aluminum-copper, to achieve a symmetric acoustic impedance profile and lower electrical resistance, enhancing the Q factor and compatibility with arbitrary resonator shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polycrystalline piezoelectric thin films are used for BAW resonators, then manufacturing is easier and cost is lower, but the quality degrades quickly as thickness decreases below 0.5 um, limiting operation at frequencies around 5 GHz and above
Solution Approach 1:
The patent employs asymmetric electrode thickness design where the first electrode has a different thickness profile than the second electrode. Specifically, the first electrode has a mass-loaded region with greater thickness than its non-loaded region, while the second electrode has the opposite configuration. This asymmetric design compensates for the inherent asymmetries in the piezoelectric film structure and achieves symmetric acoustic impedance, thereby improving Q factor and enabling operation at frequencies above 5 GHz while maintaining manufacturing feasibility with polycrystalline films
2Reliability
If single crystal piezoelectric thin films are used to maintain quality at very thin thicknesses, then resonator performance improves for frequencies around 5 GHz and above, but manufacturing challenges and transfer difficulties increase
Solution Approach 1:
The patent applies local quality modification by introducing mass-loaded regions with different thicknesses at specific locations of the electrodes. Rather than requiring uniform high-quality single crystal films throughout, the invention uses localized thickness variations in the electrodes to compensate for polycrystalline film limitations. This allows the use of easier-to-manufacture polycrystalline films while achieving performance comparable to or exceeding single crystal films through strategic local structural modifications
3Adaptability or versatility
If conventional RF technology is used, then current applications are supported, but performance limitations prevent achievement of high performance at frequencies above 5 GHz
Solution Approach 1:
The patent changes critical physical parameters of the resonator structure, specifically the electrode thicknesses and the introduction of mass-loaded regions. By adjusting these geometric parameters, the acoustic impedance profile is modified to achieve symmetry, which directly improves the Q factor. This parameter optimization enables the resonator to operate effectively at frequencies above 5 GHz, expanding the frequency range while maintaining high performance that conventional designs cannot achieve
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 anti-symmetrical configuration provides improved Q factor and reduced misalignment issues, achieving a symmetric acoustic impedance profile and lower electrical resistance, enabling high performance at resonance frequencies while being cost-effective and compatible with conventional manufacturing methods.
Implementation Method 1
a piezoelectric layer (220) formed overlying a substrate member (210). A front-side electrode (230) is formed overlying the piezoelectric layer (220), while a back-side electrode (240) is formed underlying the piezoelectric layer (220)
Data Source
AI summary
A resonator circuit device. This device can include a piezoelectric layer having a front-side electrode and a back-side electrode spatially configured on opposite sides of the piezoelectric layer. Each electrode has a connection region and a resonator region. Each electrode also includes a partial mass-loaded structure configured within a vicinity of its connection region. The front-side electrode and the back-side electrode are spatially configured in an anti-symmetrical manner with the resonator regions of both electrodes at least partially overlapping and the first and second connection regions on opposing sides. This configuration provides a symmetric acoustic impedance profile for improved Q factor and can reduce the issues of misalignment or unbalanced boundary conditions associated with conventional single mass-loaded perimeter configurations.