BAW Resonator Electrode Flap Structure for Spurious Mode Suppression
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Solution Overview
Problem
BAW resonators face spurious mode excitation and reduced quality factor due to termination regions, which can lead to lower resonator performance and energy leakage, especially in frequency filtering applications.
Innovation Solution
A BAW resonator design featuring a top electrode with an outer flap and a low acoustic impedance step-forming material between the piezoelectric layer and the flap, along with optimized thickness and dimensions, to enhance the quality factor and suppress spurious modes. This design includes a Bragg mirror for energy containment and uses materials like SiO2, Al, and heavy metals to achieve improved lateral boundary conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional termination regions are used in BAW resonators, then the resonator can be manufactured with standard processes, but spurious mode excitation occurs and quality factor is reduced
Solution Approach 1:
The top electrode is segmented into an inner electrode region and an outer flap region that are electrically connected but spatially separated. The outer flap extends laterally beyond the piezoelectric layer boundaries, creating distinct functional zones that suppress spurious modes while maintaining manufacturability through standard deposition processes
Solution Approach 2:
The solution transitions from a two-dimensional electrode plane to a three-dimensional structure by extending the outer flap laterally beyond the piezoelectric layer boundaries. This additional lateral dimension creates acoustic boundary conditions that suppress spurious modes propagating in lateral directions
2Reliability
If the top electrode is extended laterally beyond the piezoelectric layer, then spurious modes are suppressed, but the device complexity increases
Solution Approach 1:
The outer flap serves multiple functions simultaneously: it acts as an acoustic boundary to suppress lateral spurious modes, provides electrical connection to the inner electrode, and can be integrated with existing interconnect structures. This multi-functionality reduces the need for additional separate components
3Loss of energy
If termination regions are optimized to reduce spurious mode excitation, then energy is contained within the resonator, but the manufacturing process becomes more complex
Solution Approach 1:
The electrical connection between inner electrode and outer flap is achieved by controlling the deposition parameters of the top electrode material. By adjusting deposition conditions, the material naturally forms conductive pathways at the interface, eliminating the need for separate connection structures while maintaining energy containment
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 results in a significantly improved quality factor of approximately 1800-3000 at 2 GHz, effectively minimizing spurious signals and enhancing resonator performance by reducing lateral modes and energy leakage, thereby improving both in-band and out-of-band filter performance.
Implementation Method 1
The step forming material comprises a structured layer of a material having an acoustic impedance that is low w.r.t. the acoustic impedance of the top electrode and the piezoelectric layer
Implementation Method 2
a piezoelectric layer and a top electrode
Implementation Method 3
a Bragg mirror for energy containment
Data Source
AI summary
A BAW resonator is provided wherein the top electrode (TE) has an outer flap (OF). The flap extends away from the active resonator region (AR) and has a projecting section that runs at a level above the piezoelectric layer (PL) that is higher than the level of the top electrode at any of the inwardly located areas enclosed by the outer flap. The higher level is formed by an intermediate step-forming material (SM) arranged between piezoelectric layer and top electrode in the outer flap. The step forming material comprises a structured layer of an acoustic impedance that is low w.r.t. the impedance of the top electrode and the piezoelectric layer.