FBAR Protection Layer Sealing for Stable Resonance Frequency
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Solution Overview
Problem
Conventional film bulk acoustic resonators (FBARs) face challenges such as damage to the upper electrode during manufacturing, permeation of foreign matter or moisture into air gaps, and variations in resonance frequency due to these issues, limiting their reliability and stability.
Innovation Solution
A non-cantilever FBAR structure is implemented, featuring a first protection layer that covers the upper electrode and extends downward along its side surface to seal the air gap between the upper electrode and the piezoelectric layer, using dielectric materials like SiOx and SiNx, and optionally a second protection layer to further enhance protection and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a membrane type FBAR is used to reduce power loss, then dielectric loss is reduced, but device-occupied area increases and structural stability decreases
Solution Approach 1:
The device is divided into separate functional layers: a substrate, a lower electrode, a piezoelectric layer, an upper electrode, and a protection layer. This segmentation allows each layer to perform its specific function independently, with the protection layer specifically addressing structural stability without affecting the power loss characteristics of the resonator core.
Solution Approach 2:
The FBAR structure combines multiple materials with different properties: piezoelectric materials (such as AlN or ZnO) for the active resonator layer, conductive materials for electrodes, and dielectric materials for the protection layer. This composite structure achieves both low power loss and high structural stability by selecting materials optimized for each specific function.
2Device complexity
If the upper electrode is exposed without protection, then the structure remains simple, but damage occurs during manufacturing and foreign matter permeates into air gaps
Solution Approach 1:
A protection layer is formed over the upper electrode before subsequent manufacturing steps. This preliminary protective action prevents damage during wire bonding and other packaging processes, while the protection layer is integrated into the overall device structure rather than added as a separate post-processing step.
Solution Approach 2:
The protection layer acts as an intermediary between the upper electrode and the external environment. It provides a barrier that prevents foreign matter and moisture from reaching the air gaps and electrode, while still allowing the device to function normally. This intermediary layer protects critical components without requiring complex sealing mechanisms.
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 prevents damage to the upper electrode and prevents foreign matter or moisture from affecting the resonance frequency, ensuring a stable and reliable frequency characteristic with variations of 25% or less compared to conventional FBARs.
Implementation Method 1
An FBAR is formed by depositing a piezoelectric film between both electrodes and generates resonance by causing a bulk acoustic wave
Implementation Method 2
a first protection layer which is formed above the upper electrode. Here, the first protection layer covers the upper electrode while extending downward along a side surface of one end of the upper electrode to cover a certain area of the piezoelectric layer
Data Source
AI summary
Disclosed is a film bulk acoustic resonator (FBAR) including a substrate, a lower electrode formed above the substrate, a piezoelectric layer formed above the lower electrode, an upper electrode formed above the piezoelectric layer, and a first protection layer formed above the upper electrode. Here, the first protection layer covers the upper electrode while extending downward along a side surface of one end of the upper electrode to cover a certain area of the piezoelectric layer.