FBAR Top Electrode Frame Structure for Transverse Mode Suppression
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Solution Overview
Problem
Film bulk acoustic wave resonators (FBARs) suffer from spurious modes due to transverse acoustic waves generated by non-zero Poisson's ratio in the piezoelectric material, degrading their frequency response.
Innovation Solution
The FBAR design incorporates recessed and raised frame portions in the top electrode or piezoelectric film to control resonant frequencies and suppress transverse acoustic waves, reducing spurious mode generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional film bulk acoustic wave resonator structure is used, then the device is simple to manufacture, but spurious acoustic waves are generated that degrade frequency response
Solution Approach 1:
The top electrode is segmented into multiple regions with different thicknesses: a central region, a recessed frame portion, and a raised frame portion. This segmentation creates distinct acoustic impedance zones that suppress transverse wave propagation while maintaining manufacturing feasibility through selective etching and deposition processes
Solution Approach 2:
Different regions of the top electrode are given different local properties through varying thickness. The recessed frame portion has reduced thickness to create acoustic barriers, while the raised frame portion has increased thickness for enhanced suppression. This local quality variation targets specific transverse wave paths without affecting the entire electrode structure
2Reliability
If the piezoelectric film thickness is varied to control resonant frequency, then frequency response improves, but manufacturing precision requirements increase
Solution Approach 1:
The thickness of the top electrode is varied as a key parameter to control acoustic wave propagation. By changing the electrode thickness in different regions (recessed vs. raised portions), the acoustic impedance is modified to suppress transverse waves. This parameter change approach allows frequency response control through geometric modification rather than requiring extreme precision in piezoelectric film thickness
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 design effectively suppresses spurious modes, improving the frequency response and resonant characteristics of the FBARs.
Implementation Method 1
a piezoelectric film supported to oscillate in a direction opposite to a main surface of the substrate
Implementation Method 2
a recessed frame portion and a raised frame portion are formed to extend adjacent to each other along a periphery of an active area of the film oscillating during an operation
Data Source
AI summary
A film bulk acoustic wave resonator (FBAR) is disclosed with raised and recessed frame portions formed in a top electrode. The FBAR can include a substrate, a piezoelectric film supported to oscillate in a direction opposite to a main surface of the substrate, and a pair of top and bottom electrodes formed respectively on top and bottom surfaces of the film. The recessed frame portion and the raised frame portion can be formed to extend adjacent to each other along a periphery of an active region of the film oscillating during an operation of the film on a top surface of the top electrode.