FBAR Resonator Electrode Thickness Variation
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Solution Overview
Problem
Film bulk acoustic resonators (FBARs) face insertion loss due to mechanical energy conversion into thermal or acoustic energy, which is exacerbated by electrode conductivity, increasing fabrication costs when attempting to reduce this loss by thickening or using high-conductivity materials.
Innovation Solution
A resonator design where the electrodes in the active region have varying thicknesses, with a metal film added to the non-active region to enhance conductivity without increasing thickness or using costly materials, and a fabrication method involving layer formation and patterning to achieve these thickness differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electrode thickness is increased or high-conductivity materials are used to reduce insertion loss, then electric conductivity is improved, but fabrication cost increases
Solution Approach 1:
The electrode is designed with non-uniform thickness, featuring a thicker first electrode in the non-active region and a thinner second electrode in the active region. This local variation optimizes electrical conductivity where needed (non-active region) while maintaining resonance characteristics in the active region, thereby reducing insertion loss without requiring expensive high-conductivity materials throughout the entire electrode structure.
2Loss of energy
If a frame-like layer is formed to prevent bulk acoustic wave leakage, then resonance characteristic is improved, but the effective piezoelectric coefficient is changed
Solution Approach 1:
Instead of forming a frame-like layer that modifies the entire edge region, the invention uses localized thickness variation of the electrode itself - thicker in the non-active region to contain acoustic waves and thinner in the active region to preserve piezoelectric coefficients. This approach achieves acoustic wave containment without interfering with the resonance characteristics in the active region.
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 improves resonance characteristics and reduces insertion loss by preventing bulk acoustic wave leakage and enhancing electric conductivity, as demonstrated by reduced deviation in passing characteristics on Smith's charts.
Implementation Method 1
when electric energy is applied to the first and the second electrodes, an electric field is incited in the piezoelectric film. The electric field incites a piezoelectric phenomenon to the piezoelectric film, so that the resonating unit oscillates in a predetermined direction.
Implementation Method 2
a bulk acoustic wave is produced in the same direction as the oscillating direction of the resonating unit to cause resonances
Data Source
AI summary
A resonator including a substrate, and a resonating unit having an active region that causes resonances and a non-active region that does not cause resonances, and having a first electrode, a piezoelectric film, and a second electrode layered in turn on the substrate. At least one of the first and the second electrodes is formed, so that at least a portion of a non-active region portion thereof has a thickness different from that of an active region portion thereof.