Ferroelectric Thin-Film Substrate with Adhesive Layer for Wire Bonding
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Solution Overview
Problem
Current lead-free niobate-based ferroelectric thin-film devices face challenges in achieving high bond strength during wire bonding, which is essential for mass production and long-term reliability, particularly with existing techniques using gold electrodes.
Innovation Solution
A ferroelectric thin-film laminated substrate structure is developed, featuring a platinum lower electrode layer, a sodium potassium niobate ferroelectric thin-film layer, a gold upper electrode layer, and an upper electrode adhesive layer made from metals like nickel, cobalt, tungsten, or molybdenum, which form a solid solution alloy with gold, enhancing bond strength through controlled deposition processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a gold upper electrode layer is used for wire bonding, then electrical conductivity and ease of operation are improved, but bond strength is insufficient for mass production requirements
Solution Approach 1:
The patent applies composite materials by creating a multi-layer electrode structure consisting of a gold upper electrode layer combined with an adhesive layer made of nickel, cobalt, tungsten, or molybdenum. This composite structure combines the electrical conductivity advantages of gold with the high bond strength of the adhesive metal layer, resolving the contradiction between ease of wire bonding and sufficient bond strength for mass production
Solution Approach 2:
The adhesive layer acts as an intermediary between the gold electrode layer and the ferroelectric thin film. This intermediate layer provides the necessary mechanical strength for wire bonding while allowing the gold layer to maintain its electrical conductivity function, thus mediating between the conflicting requirements of bond strength and electrical performance
2Reliability
If lead-free niobate-based ferroelectric materials are used, then environmental compliance and reliability are improved, but piezoelectric properties and manufacturing maturity are insufficient compared to PZT
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratio of sodium and potassium in the niobate-based ferroelectric material to (Na0.5K0.5)NbO3, and by controlling the thickness parameters of each layer in the laminated structure. These parameter optimizations improve the piezoelectric properties of lead-free materials to approach PZT performance while maintaining environmental compliance
Solution Approach 2:
The patent applies local quality by creating a laminated structure where different layers have specialized functions: the ferroelectric thin film layer provides piezoelectric properties, the adhesive layer provides bond strength, and the gold layer provides electrical conductivity. This localized functional distribution allows each layer to be optimized independently, improving overall manufacturing feasibility and device performance
3Volume of moving object
If thin-film technology is used to reduce device size, then miniaturization is achieved, but bond strength and mechanical durability are reduced
Solution Approach 1:
The patent applies composite materials by creating a multi-layer electrode structure consisting of a gold upper electrode layer combined with an adhesive layer made of nickel, cobalt, tungsten, or molybdenum. This composite structure combines the electrical conductivity advantages of gold with the high bond strength of the adhesive metal layer, resolving the contradiction between ease of wire bonding and sufficient bond strength for mass production
Solution Approach 2:
The patent resolves the strength limitation of thin-film devices by adding a dimensional solution - introducing multiple thin layers in the vertical dimension. The adhesive layer and gold layer are deposited as separate thin films, creating a multi-dimensional structure that compensates for the reduced mechanical strength inherent in thin-film technology while maintaining miniaturization benefits
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 proposed structure achieves a bond strength of 60 mN or more, meeting the requirements for mass production and ensuring durability of the thin-film devices, while maintaining ferroelectric properties.
Implementation Method 1
the upper electrode adhesive layer is made of a metal which has less oxidizability than titanium and can make a solid solution alloy without generating an intermetallic compound with gold; and a part of the upper electrode adhesive layer and a part of the upper electrode layer are alloyed
Data Source
Figure 1~2
AI summary
There is provided a ferroelectric thin-film laminated substrate, including a substrate, and further including a lower electrode layer, a ferroelectric thin-film layer, an upper electrode adhesive layer, and an upper electrode layer being sequentially stacked on the substrate, in which: the lower electrode layer is made of platinum or a platinum alloy; the ferroelectric thin-film layer is made of a sodium potassium niobate (typical chemical formula of (K1-xNax)NbO3, 0.4 ≤ x ≤ 0.7); the upper electrode layer is made of gold; the upper electrode adhesive layer is made of a metal that has less oxidizability than titanium and can make a solid solution alloy without generating an intermetallic compound with gold; and a part of the upper electrode adhesive layer and a part of the upper electrode layer are alloyed.