BAW Resonator Guard Ring Recess for Spurious Mode Suppression
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators with traditional guard rings experience undesirable ripples around the parallel resonance frequency, leading to variations in quality factor and impedance, which affect system performance.
Innovation Solution
Incorporating a guard ring with a recessed space from the perimeter edge of the electrode, optimized in terms of thickness, width, and spacing, to minimize lateral standing waves and operate in piston mode, thereby reducing spurious modes and enhancing electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional guard ring is used in BAW resonator, then the resonator provides basic acoustic isolation, but it generates ripples around parallel resonance frequency causing quality factor and impedance variations
Solution Approach 1:
The guard ring structure is modified by creating a recessed region at its inner circumference, making different parts of the guard ring have different functions: the majority portion provides acoustic isolation while the recessed region eliminates lateral standing waves. This local structural differentiation resolves the contradiction by maintaining basic isolation functionality while adding spurious mode suppression capability.
Solution Approach 2:
The guard ring is segmented into functionally distinct regions: a majority portion for acoustic isolation and a recessed region for eliminating lateral standing waves. This segmentation allows each region to optimize its specific function, resolving the contradiction between maintaining isolation and eliminating spurious modes.
2Object-generated harmful factors
If guard ring spacing from electrode edge is increased, then lateral standing waves are reduced, but acoustic isolation effectiveness may be compromised
Solution Approach 1:
The recessed region creates a local geometric variation that specifically targets lateral standing wave elimination without requiring increased overall spacing. This localized modification maintains acoustic isolation effectiveness while suppressing spurious modes through the recessed geometry rather than through increased distance.
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 minimizes ripples around the parallel resonance frequency, ensuring stable quality factor and impedance, thereby improving the electrical performance of BAW resonators by eliminating lateral standing waves and achieving piston mode operation.
Implementation Method 1
A bulk acoustic wave (BAW) resonator is a MEMS device that includes a piezoelectric thin film sandwiched between two electrodes
Implementation Method 2
BAW resonators using piezoelectric films with thicknesses ranging from several micrometers down to tenth of micrometers resonate in the frequency range of roughly 100 MHz to 10 GHz
Data Source
AI summary
A micromechanical system (MEMS) acoustic wave resonator is formed on a base substrate. A piezoelectric member is mounted on the base substrate. The piezoelectric member has a first electrode covering a first surface of the piezoelectric member and a second electrode covering a second surface of the piezoelectric member opposite the first electrode, the second electrode being bounded by a perimeter edge. A first guard ring is positioned on the second electrode spaced apart from the perimeter edge of the second electrode.