Bulk Acoustic Wave Resonator Sealing Layer Moisture Ingress
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Solution Overview
Problem
Bulk acoustic wave resonators face challenges in preventing moisture permeation, which affects their reliability, especially due to micropores in the bonding agent used in the manufacturing process.
Innovation Solution
A bulk acoustic wave resonator design that includes a substrate with a resonating part, a piezoelectric layer, and electrodes, where a sealing layer and connective conductor are formed using a titanium-copper alloy, and an external electrode is formed using a double layer of gold-nickel metals, with the nickel layer being thicker than the gold layer, to prevent moisture ingress and enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a bonding agent is used to bond the cap to the substrate, then the cap can be securely attached, but micropores in the bonding agent allow moisture to permeate into the resonator
Solution Approach 1:
A sealing layer is introduced as an intermediary component between the bonding agent and the external environment. This sealing layer specifically targets and blocks the micropores in the bonding agent, preventing moisture permeation while allowing the bonding agent to maintain its bonding function. The sealing layer acts as a mediator that resolves the contradiction between bonding strength and moisture resistance.
Solution Approach 2:
The patent uses a composite structure combining the bonding agent and the sealing layer. The bonding agent provides strong adhesion between the cap and substrate, while the sealing layer (formed by electroless plating of metal materials) provides moisture barrier properties. This composite approach allows both bonding strength and moisture resistance to be achieved simultaneously.
2Ease of manufacture
If a single-layer metal coating is used for the sealing layer, then the manufacturing process is simple, but it cannot effectively prevent moisture permeation through micropores
Solution Approach 1:
The sealing layer is formed as a composite structure with multiple metal layers (e.g., copper layer and nickel layer) deposited by electroless plating. Each layer contributes different properties: the copper layer provides base sealing, while the nickel layer enhances corrosion resistance and moisture barrier properties. This multi-layer composite structure achieves effective moisture protection while maintaining manufacturing feasibility through a single electroless plating process.
3Quantity of substance
If the nickel layer is made thinner than the gold layer in the double layer structure, then the manufacturing cost is reduced, but the moisture protection effectiveness is compromised
Solution Approach 1:
The patent optimizes the thickness parameters of the metal layers in the sealing structure. Specifically, the nickel layer thickness is set to be greater than the gold layer thickness, which is a parameter change from conventional designs. This parameter optimization ensures that the nickel layer provides sufficient moisture barrier protection while the overall material quantity and cost are controlled. The specific thickness ratio is determined based on the required moisture resistance performance.
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 moisture permeation, thereby improving the reliability and performance of the bulk acoustic wave resonators by using a titanium-copper alloy for the sealing layer and a gold-nickel double layer for the external electrode, ensuring consistent operation.
Implementation Method 1
when an electrical field is induced in the piezoelectric layer by applying electrical energy to the first and second electrodes, the electrical field causes a piezoelectric phenomenon in the piezoelectric layer. Such a piezoelectric phenomenon causes the resonating part to vibrate in a predetermined direction. As a result, bulk acoustic waves are generated
Data Source
AI summary
In examples, there is provided a bulk acoustic wave resonator including a substrate; a resonating part including a first electrode, a piezoelectric layer, and a second electrode, laminated on an upper surface of the substrate, a cap bonded to the substrate by a bonding agent; and a sealing layer formed on an externally exposed surface of the bonding agent. This structure provides for a bulk acoustic wave resonator with improved reliability.