BAW Filter Electrode Layout to Reduce Frame Reflection Loss
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Solution Overview
Problem
The Q performance of bulk acoustic wave resonators in BAW filters deteriorates due to reflection loss caused by the insulating layer deposited on the outer surface of the frame, leading to leakage of resonant energy.
Innovation Solution
An acoustic wave filter device design where the insulating layer exposes portions of the upper electrode, including the frame portion, to reduce reflection loss by selectively patterning and etching the insulating layer, thereby improving the Q performance by trapping resonant energy in the active area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating layer is deposited over the entire bulk acoustic wave resonator including the frame, then electrical insulation is improved, but reflection loss increases and Q performance deteriorates
Solution Approach 1:
The insulating layer is selectively deposited only on specific regions of the upper electrode that require electrical insulation, while leaving the frame surface exposed. This local differentiation allows the frame to reflect lateral waves effectively without being covered by the insulating layer, thus reducing reflection loss while maintaining necessary electrical insulation properties.
2Ease of manufacture
If the insulating layer covers the frame outer surface, then manufacturing simplicity is improved, but resonant energy leakage occurs
Solution Approach 1:
The insulating layer deposition process is segmented into selective regions rather than covering the entire resonator surface. The frame area is excluded from insulating layer deposition, creating a distinct zone that maintains acoustic reflection functionality while other areas receive insulation as needed.
3Manufacturing precision
If the frame is formed to reflect lateral waves, then frequency selectivity is improved, but Q performance deteriorates due to insulating layer reflection loss
Solution Approach 1:
The frame is designed with localized acoustic reflection properties by excluding the insulating layer from its surface, allowing it to effectively reflect lateral waves. This local acoustic optimization maintains frequency selectivity while preventing the reflection loss that would occur if the frame were covered by the insulating layer.
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 effectively reduces reflection loss and enhances the Q performance of the bulk acoustic wave resonators by exposing specific surfaces of the frame portion, improving frequency selectivity and reducing energy loss.
Implementation Method 1
a piezoelectric layer (140) disposed on the lower electrode (130)
Implementation Method 2
a frame is formed at a circumference of the bulk acoustic wave resonator to reflect lateral waves generated at the time of resonance to an inner portion of bulk acoustic wave resonators, thereby trapping resonant energy in the active area
Implementation Method 3
The insulating layer exposes portions of the upper electrode... to reduce reflection loss by selectively patterning and etching the insulating layer, thereby improving the Q performance by trapping resonant energy in the active area
Data Source
AI summary
An acoustic wave filter device includes a lower electrode disposed between a substrate and a piezoelectric layer, an upper electrode disposed on the piezoelectric layer, and an insulating layer disposed on the upper electrode. The insulating layer exposes portions of the upper electrode.