FBAR Packaging Structure With Elastic Bonding for Stable Resonance
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Solution Overview
Problem
The existing packaging process for film bulk acoustic resonators (FBARs) is complex, costly, and introduces gold-related pollution, with insufficient mechanical strength due to the Au—Au bonding process and passivation layer gaps, leading to reliability risks.
Innovation Solution
A packaging method using an elastic bonding material layer to bond a resonant cavity main structure with a resonator cover, featuring a groove and through holes for electrical connections, which minimizes step height differences and avoids Au—Au bonding, ensuring reliable and stable bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Au—Au bonding process is used to bond the carrier wafer with the resonant cavity main structure, then bonding strength is improved, but manufacturing complexity and cost increase, and gold-related pollution is introduced
Solution Approach 1:
The patent extracts and removes the carrier wafer after bonding, replacing the complex Au—Au bonding process with a simpler bonding method. The carrier wafer is taken out after serving its purpose as a support during fabrication, eliminating the need for expensive gold bonding layers while maintaining structural integrity.
Solution Approach 2:
The carrier wafer is treated as a disposable component that serves its function during fabrication and is then removed. This replaces the expensive and complex Au—Au bonding process with a simpler, more cost-effective approach that doesn't require gold materials or complex bonding equipment.
2Reliability
If passivation layer is deposited to protect the silicon dioxide layer, then protection is improved, but gaps in holes are created and mechanical strength is reduced
Solution Approach 1:
Instead of depositing a passivation layer that creates gaps and weakens the structure, the patent inverts the approach by filling the holes with conductive material and then depositing the passivation layer over the entire surface, including over the filled holes. This ensures continuous mechanical strength while providing protection.
Solution Approach 2:
The patent uses composite material structures where conductive material fills the holes and the passivation layer is deposited over both the surface and the filled holes, creating a composite structure that maintains both electrical functionality and mechanical strength without gaps.
3Ease of operation
If carrier wafer is removed through backside thinning process, then access to gold surface is improved, but process complexity and equipment cost increase
Solution Approach 1:
The patent performs preliminary actions during the bonding process itself, where the carrier wafer is bonded and then removed in a simplified manner. The backside thinning and gold surface exposure are achieved through preliminary process planning that avoids complex multi-step procedures and expensive equipment.
Solution Approach 2:
The patent replaces complex mechanical processes (backside thinning, precise etching) with simpler chemical or thermal processes that achieve the same result of exposing the gold surface without requiring sophisticated equipment or multi-step mechanical operations.
4Ease of operation
If thinner passivation layer is used to maintain hole access, then electrical connection is improved, but mechanical strength and reliability are reduced
Solution Approach 1:
The patent solves the contradiction by moving from a two-dimensional thin layer approach to a three-dimensional solution where holes are filled with conductive material. This dimensional change allows the passivation layer to be deposited uniformly over the entire surface while maintaining electrical connectivity through the filled holes, achieving both electrical connection and mechanical strength.
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 method simplifies the packaging process, reduces costs, eliminates gold-related pollution, and enhances the mechanical strength and reliability of the FBAR by using an elastic bonding material that adapts to step height differences, improving the stability and resonance performance of the resonator.
Implementation Method 1
bonding the resonant cavity main structure and the resonator cover together through the elastic bonding material layer, and removing elasticity of the elastic bonding material layer
Implementation Method 2
forming through holes penetrating the resonator cover and exposing corresponding electrical connection portions of the bulk acoustic resonant structure
Implementation Method 3
forming a conductive interconnection layer on surfaces of the through holes and on a portion of a surface of the resonator cover at a periphery of the through holes
Data Source
AI summary
The present disclosure provides a packaging method and packaging structure of an FBAR. A second cavity in a resonator cover provided includes a groove in a second substrate and a space surrounded by an elastic bonding material layer. The elastic bonding material layer bonds the resonator cover to a resonant cavity main structure, and elasticity of the elastic bonding material layer is removed after the bonding. Through holes and a conductive interconnection layer on inner surfaces of the through holes are formed on the resonator cover. Since the second cavity includes the groove in the second substrate and the space surrounded by the elastic bonding material layer, which can avoid problems that performance of the elastic bonding material layer is unstable with temperature and humidity changes when the second cavity is entirely surrounded by the elastic bonding material layer, that is, the stability of the resonator is improved.