FBAR Recessed Frame Electrode Structure for Spurious Wave Suppression
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Solution Overview
Problem
Film bulk acoustic wave resonators (FBARs) face degradation in frequency response due to spurious acoustic waves generated by transverse waves perpendicular to the main acoustic wave, which are undesirable and reduce the quality factor of the device.
Innovation Solution
The FBAR design incorporates recessed frame regions with a thinner electrode and dielectric material layer compared to the central region, and raised frame regions with a thicker electrode, creating a discontinuity in acoustic wave velocity to scatter and reflect transverse waves, thereby preventing them from entering the main active domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrode thickness is uniform across the entire device, then the manufacturing process is simple, but spurious acoustic waves are generated that reduce the quality factor
Solution Approach 1:
The electrode is designed with different thicknesses in different regions: a first thickness in the central region and a second (greater) thickness in the frame region. This local variation in electrode thickness creates corresponding variations in acoustic wave velocity, forming a velocity profile that directs acoustic energy away from the edges and reduces spurious wave generation, thereby improving the quality factor without requiring complete redesign of the device architecture.
2Reliability
If the dielectric material layer thickness is uniform, then the manufacturing process is simplified, but transverse waves are not effectively scattered
Solution Approach 1:
The dielectric material layer is configured with a first thickness in the central region and a second (greater) thickness in the frame region. This local thickness variation creates corresponding variations in acoustic wave velocity, forming a velocity profile that directs acoustic energy away from the edges and reduces spurious wave generation, thereby improving the quality factor without requiring complete redesign of the device architecture.
3Speed
If recessed frame regions are created with thinner electrode and dielectric layers, then acoustic wave velocity increases in those regions, but manufacturing precision requirements increase
Solution Approach 1:
The invention modifies the thickness parameters of the electrode and dielectric material layer to create regions of different acoustic wave velocities. By controlling the thickness parameters (first thickness in central region, second greater thickness in frame region), the acoustic wave velocity is adjusted to create a velocity profile that directs acoustic energy away from edges, reducing spurious waves while maintaining manufacturability through standard thin-film deposition techniques.
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 design enhances the quality factor of the FBAR by reducing spurious acoustic waves and improving frequency response, with the recessed frame regions exhibiting higher acoustic velocity and raised frame regions showing lower velocity, effectively creating a barrier to transverse waves.
Implementation Method 1
a piezoelectric film disposed in a central region defining a main active domain in which a main acoustic wave is generated during operation
Implementation Method 2
creating a discontinuity in acoustic wave velocity to scatter and reflect transverse waves, thereby preventing them from entering the main active domain
Implementation Method 3
the recessed frame regions exhibiting higher acoustic velocity and raised frame regions showing lower velocity, effectively creating a barrier to transverse waves
Data Source
AI summary
A film bulk acoustic wave resonator (FBAR) includes a piezoelectric film disposed in a central region defining a main active domain in which a main acoustic wave is generated during operation and in recessed frame regions disposed laterally on opposite sides of the central region, and an electrode disposed on an upper surface of the piezoelectric film, the electrode having a lesser thickness in the recessed frame regions than the thickness of the electrode in the central region to increase a quality factor of the FBAR.