SAW Device Post-Seal Frequency Trimming via Mass Deposition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
SAW devices face significant frequency shifts post-seal due to environmental stress, aging, and sealing processes, leading to reduced product yield, as existing frequency trimming methods are difficult and expensive to implement after the device is sealed.
Innovation Solution
A mass deposition device within the sealed casing, comprising a heated gold-plated tungsten wire that evaporates gold onto the acoustic channel, allowing for controlled frequency trimming by mass loading, even after the device is sealed, using a thin, non-conductive gold layer that does not interfere with transduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If frequency trimming is performed before sealing, then manufacturing precision is improved, but the device cannot be adjusted after sealing to compensate for frequency shifts
Solution Approach 1:
The patent pre-prepares the sealed cavity with all necessary components including the wire material source positioned above the acoustic channel. The sealing is performed with the trimming capability already in place, allowing post-seal frequency adjustment without compromising the sealed environment. This resolves the contradiction by enabling both preliminary sealing and subsequent frequency trimming.
Solution Approach 2:
The patent introduces a wire material source as an intermediary component within the sealed cavity that can be electrically activated to deposit material onto the acoustic channel. This intermediary enables frequency trimming after sealing by serving as a controllable mass deposition source that doesn't require breaking the seal.
2Ease of operation
If laser ablation is used for post-seal trimming, then frequency adjustment is possible, but the process becomes difficult and expensive to implement
Solution Approach 1:
The patent replaces the complex laser ablation system with a simple electrical resistance heating wire. Instead of using high-energy laser beams to ablate material, the wire is electrically heated to evaporate material onto the acoustic channel. This substitution dramatically simplifies the device complexity while maintaining post-seal frequency trimming capability.
Solution Approach 2:
The patent changes the physical state and deposition mechanism from laser-induced ablation to thermally-driven evaporation. By controlling the electrical current through the wire, the temperature and evaporation rate can be precisely controlled, enabling simple and cost-effective mass deposition for frequency trimming without the complexity of laser systems.
3Manufacturing precision
If mass is added to the acoustic channel, then frequency is trimmed downward, but the added material may interfere with electro-mechanical transduction
Solution Approach 1:
The patent applies mass deposition locally and selectively to specific regions of the acoustic channel rather than uniformly across the entire surface. By controlling the wire position and evaporation parameters, mass is added only where needed to achieve the desired frequency shift while leaving the transducer regions unaffected, thus maintaining transduction performance.
Solution Approach 2:
The patent utilizes controlled phase transition from solid to gas to solid deposition. The wire material is heated to evaporate (solid to gas), the vapor travels and condenses (gas to solid) onto the acoustic channel as a thin film. This phase transition process enables precise control over the deposited mass thickness and distribution, achieving frequency trimming without compromising transduction by keeping the deposited layer thin and controlled.
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 enables precise frequency adjustment with minimal factors contributing to frequency shift, achieving a frequency decrease of up to 1000 ppm, maintaining device performance and yield by allowing post-seal trimming in a sealed environment.
Implementation Method 1
a heated gold-plated tungsten wire to evaporate gold onto the acoustic channel
Implementation Method 2
using a carefully controlled DC or pulsed current through the Au/W wire
Implementation Method 3
Au is evaporated from the hot Au/W wire, diffused through gas and condensed on the SAW die surface
Data Source
AI summary
A surface acoustic wave (SAW) device includes a piezoelectric crystal substrate on which an acoustic channel is formed, at least one electro-mechanical transducer operatively associated with the acoustic channel, and an encapsulating casing having a cover spaced above the acoustic channel and thereby defining a sealed volume around the substrate. A mass deposition device within the casing is spaced between the acoustic channel and the cover, preferably as gold-coated heating wire spanning the acoustic channel and having ends that are connectable to an electric power source outside the casing. Stress and aging shifts can be induced after sealing of the cover. Tuning is achieved by evaporating metal molecules off the heated wire onto the acoustic channel as the frequency is monitored, until the mass loading of metal molecules on the transducer produces the target frequency.