SAW Protective Cap Structure for Moisture-Resistant Transducers
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Solution Overview
Problem
Conventional surface acoustic wave devices using polyimide materials for protection suffer from reduced moisture resistance in high temperature or high humidity environments, leading to oxidation of interdigital transducers, which compromises their functionality.
Innovation Solution
A surface acoustic wave device and fabrication method that replaces polyimide materials with a conductive surrounding structure and cap layer, such as a solder or epoxy resin, to enhance moisture resistance and prevent oxidation, using electroplating and reflow processes to form a protective metal or molded plastic structure around the interdigital transducers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polyimide material is used for cap structure, then the device can be manufactured with simple process, but the moisture resistance deteriorates in high temperature or high humidity environment
Solution Approach 1:
The patent employs a composite protective structure combining organic material layer (polyimide or acrylic) with inorganic material layer (alumina or silica). This composite approach leverages the advantages of both material types: the organic layer provides good adhesion and stress relief, while the inorganic layer provides superior moisture barrier properties. The combination resolves the contradiction by achieving both ease of manufacture (through established coating processes) and high reliability (through enhanced moisture resistance of the composite structure).
Solution Approach 2:
The patent modifies the protective layer structure by introducing an additional inorganic material layer with specific physical parameters (low moisture permeability, controlled porosity). By changing the material parameters and layer configuration, the system achieves improved moisture resistance while maintaining manufacturability through standard thin-film deposition techniques. The inorganic layer's specific surface area and pore size parameters are optimized to block moisture diffusion paths.
2Device complexity
If polyimide material is used for cap structure, then the device structure can be simplified, but the protection function deteriorates due to oxidation of interdigital transducers
Solution Approach 1:
The composite structure of organic and inorganic layers works synergistically to prevent oxidation. The inorganic layer (alumina or silica) forms a dense, oxidation-resistant barrier that protects the interdigital transducers from environmental oxygen and moisture. The organic layer provides a stable substrate that prevents delamination. This composite approach maintains structural simplicity while dramatically improving oxidation resistance compared to polyimide alone.
Solution Approach 2:
The inorganic material layer acts as an intermediary barrier between the interdigital transducers and the harsh environment. It mediates the interaction by providing a chemically stable interface that blocks oxygen and moisture diffusion, thereby protecting the sensitive transducer elements from oxidation without requiring complex structural modifications.
3Ease of manufacture
If conventional cap structure with polyimide is used, then the fabrication process is simple, but the protection effectiveness deteriorates in high temperature or high humidity environment
Solution Approach 1:
The patent implements a multi-layer composite protective structure where an organic material layer (polyimide or acrylic) is combined with an inorganic material layer (alumina or silica). This composite design maintains fabrication simplicity by using established thin-film deposition and coating techniques, while simultaneously achieving superior protection effectiveness through the synergistic properties of the combined materials that resist moisture penetration and thermal degradation.
Solution Approach 2:
The patent changes the protective layer parameters by introducing an inorganic material layer with specific physical and chemical properties (low moisture permeability, high thermal stability, controlled porosity). This parameter modification enables the system to maintain protection effectiveness in high temperature and high humidity environments while keeping the fabrication process relatively simple through standard semiconductor manufacturing techniques.
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 solution effectively prevents oxidation of interdigital transducers by improving moisture resistance, ensuring the reliable operation of surface acoustic wave devices in challenging environmental conditions.
Implementation Method 1
performing an electroplating process for forming a conductive surrounding structure
Implementation Method 2
the cap layer is a reflow solder layer to close the opening
Data Source
AI summary
A surface acoustic wave (SAW) device including a substrate is provided. Multiple surface acoustic wave elements are disposed on the substrate. A conductive surrounding structure includes: a wall part, disposed on the substrate and surrounding the surface acoustic wave elements; and a lateral layer part, disposed on the wall part. The lateral layer part has an opening above the surface acoustic wave elements. A cap layer covers the lateral layer part and closes the opening.