Ceramic SAW Substrate Structure for Back Reflection Suppression
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Solution Overview
Problem
Acoustic wave filters using high impedance support substrates like silicon experience spurious responses due to back reflections, degrading frequency response, while existing ceramic substrates do not effectively scatter back reflections and maintain desirable thermal dissipation.
Innovation Solution
Implementing a ceramic substrate, such as polycrystalline spinel, which scatters back reflections and maintains smoothness, combined with a piezoelectric layer and temperature compensating layers to suppress spurious modes and improve thermal dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high impedance support substrates like silicon are used, then thermal dissipation is improved, but spurious responses occur due to back reflections
Solution Approach 1:
A roughness layer is introduced as an intermediary between the piezoelectric layer and the silicon substrate. This roughness layer acts as a mediator that scatters acoustic waves to prevent back reflections while allowing the silicon substrate to provide thermal dissipation. The roughness layer with controlled surface topology disrupts the acoustic wave paths, preventing them from reflecting back into the piezoelectric layer, thus eliminating spurious responses while maintaining the thermal management benefits of the silicon substrate.
2Object-generated harmful factors
If ceramic substrates are used to scatter back reflections, then spurious responses are reduced, but thermal dissipation performance deteriorates
Solution Approach 1:
The support structure is segmented into two distinct functional layers: a silicon substrate layer for thermal dissipation and a roughness layer for acoustic wave scattering. Instead of using a single ceramic substrate that performs both scattering and thermal management (with compromised performance), the solution divides the support structure into separate layers, each optimized for its specific function. The silicon substrate provides excellent thermal dissipation while the roughness layer on its surface provides effective acoustic wave scattering.
3Device complexity
If the piezoelectric layer is made thinner to reduce device complexity, then manufacturing is simplified, but frequency response stability worsens
Solution Approach 1:
The roughness layer creates a copied or replicated surface topology that is transferred to the piezoelectric layer through bonding. This copied roughness pattern on the piezoelectric layer surface helps to scatter acoustic waves at the interface, preventing back reflections. This allows the use of thinner piezoelectric layers without compromising frequency response stability, as the scattered waves reduce the impact of thickness variations on acoustic wave propagation.
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 enhances frequency response and thermal dissipation, ensuring stable performance in carrier aggregation applications and meeting 5G frequency band specifications by reducing back reflections and maintaining structural integrity.
Implementation Method 1
Implementing a ceramic substrate, such as polycrystalline spinel, which scatters back reflections
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
Implementation Method 3
a temperature compensating layer over the interdigital transducer electrode
Data Source
AI summary
A surface acoustic wave device is disclosed. The surface acoustic wave device can include a ceramic substrate, a piezoelectric layer over the ceramic substrate, and an interdigital transducer electrode over the piezoelectric layer. The ceramic substrate can be a polycrystalline spinel substrate. The surface acoustic wave device can also include a temperature compensating layer over the interdigital transducer electrode.