BAW Resonator Electrode Layout for Higher Q at High Frequencies
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Solution Overview
Problem
Conventional bulk acoustic wave resonator devices using polycrystalline piezoelectric thin films face challenges in maintaining quality factor at higher frequencies due to degradation in film quality as thickness decreases below 0.5 um, and existing single crystal solutions face manufacturing and transfer difficulties.
Innovation Solution
The implementation of an anti-symmetrical configuration for bulk acoustic wave resonator devices, featuring partial mass-loaded structures on both front-side and back-side electrodes, which are spatially configured to provide a symmetric acoustic impedance profile and lower electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polycrystalline piezoelectric thin films are used in BAW resonators, then manufacturing is easier and cost is lower, but film quality degrades quickly as thickness decreases below 0.5 um, limiting operation to frequencies up to 3 GHz
Solution Approach 1:
The patent applies asymmetry by introducing a mass-loaded structure only on the back-side electrode rather than symmetrically on both electrodes. This asymmetric configuration creates a specific acoustic impedance profile that improves quality factor while maintaining compatibility with polycrystalline thin films, resolving the contradiction between ease of manufacture and reliability.
2Reliability
If single crystal piezoelectric thin films are used to maintain quality at high frequencies, then film quality and piezoelectric performance improve even at very thin thicknesses, but manufacturing and transfer challenges arise
Solution Approach 1:
The patent applies local quality by introducing a mass-loaded structure at a specific location (back-side electrode) rather than uniformly across the entire device. This localized modification improves acoustic impedance matching and quality factor without requiring complex single crystal manufacturing processes, thus maintaining ease of manufacture while improving reliability.
3Ease of manufacture
If conventional symmetric electrode configurations are used, then manufacturing is simpler, but acoustic impedance mismatch and higher electrical resistance reduce quality factor
Solution Approach 1:
The patent deliberately introduces asymmetry in the electrode configuration by adding a mass-loaded structure only to the back-side electrode. This asymmetric design creates a tailored acoustic impedance profile that reduces mismatch and electrical resistance, improving quality factor while remaining manufacturable with standard processes.
4Speed
If electrode thickness is reduced to enable higher frequency operation, then resonator size decreases and frequency increases, but electrical resistance increases and quality factor deteriorates
Solution Approach 1:
The patent applies local quality by concentrating the mass-loaded structure at the back-side electrode region, creating localized acoustic impedance optimization. This allows the use of thinner piezoelectric films for high-frequency operation while the localized mass-loading compensates for the increased electrical resistance, maintaining quality factor.
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 configuration enhances the quality factor of the resonator devices by providing a symmetric acoustic impedance profile, reducing misalignment issues, and achieving lower electrical resistance, while being compatible with arbitrary resonator shapes and manufacturable in a cost-effective manner.
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)
Implementation Method 2
Each of the front-side electrode (230) and the back-side electrode (240) includes a partial mass-loaded perimeter (233, 243). The front-side electrode (230) and the back-side electrode (240) are spatially configured in an anti-symmetrical manner
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.