Packaged Acoustic Wave Substrate Layout for Crack-Resistant Reliability
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Solution Overview
Problem
Packaged acoustic wave components face reliability issues due to stress-induced cracking during heat cycle testing, and existing solutions fail to adequately reduce parasitic surface conduction and mechanical stress on the piezoelectric layer.
Innovation Solution
A packaged acoustic wave component design featuring a substrate with a trap-rich layer, a functional layer covering the substrate, a recessed piezoelectric layer, and metal layers to reduce stress and parasitic surface conduction, while maintaining thermal insulation and high electromechanical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the piezoelectric layer is completely covered by a dielectric layer, then the device structure is simplified and manufacturing is easier, but stress concentration occurs during heat cycle testing leading to cracking
Solution Approach 1:
The dielectric layer is selectively removed from the peripheral portion of the functional layer, creating different dielectric coverage conditions in different regions. The central region maintains full dielectric coverage for simplified manufacturing, while the peripheral region has reduced dielectric coverage to relieve stress concentration and prevent cracking during heat cycle testing.
2Object-generated harmful factors
If the trap-rich layer is uncovered to reduce parasitic surface conduction, then PSC is reduced, but the silicon surface becomes susceptible to oxidation that can reactivate PSC
Solution Approach 1:
The trap-rich layer is selectively uncovered only in the peripheral portion where it does not generate significant parasitic surface conduction, while the central region maintains full dielectric coverage to protect the trap-rich layer from oxidation. This localized approach allows PSC reduction without exposing the silicon surface to oxidative environments.
3Reliability
If the piezoelectric layer is recessed from the lateral edge, then stress on the piezoelectric layer is reduced, but the device complexity increases
Solution Approach 1:
The piezoelectric layer is recessed only from the lateral edges of the functional layer, while maintaining full coverage in the central region. This localized recession reduces stress concentration at the edges during heat cycle testing without requiring complete reconfiguration of the entire layer structure, thus limiting the increase in device complexity.
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 design enhances the reliability and mechanical ruggedness of the packaged acoustic wave components by reducing stress and parasitic surface conduction, enabling their use in high-power applications and improving thermal dissipation.
Implementation Method 1
These traps are configured as crystal defects which act as recombining centers. They can trap carriers, thus decreasing parasitic surface conduction (PSC)
Implementation Method 2
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer
Data Source
AI summary
A packaged acoustic wave component comprises a substrate having a trap-rich layer arranged at a surface of the substrate, a functional layer disposed over the surface of the substrate such as to cover that surface, a piezoelectric layer disposed over the functional layer and covering the functional layer with the exception of a peripheral portion of the functional layer, a first metal layer comprising an electrode structure disposed over the piezoelectric structure, and a second metal layer disposed partially in contact with the first metal layer and partially in contact with the peripheral portion of the functional layer.