SAW Resonator Passivation Structure for Frequency Shift Suppression
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Solution Overview
Problem
Surface acoustic wave (SAW) resonators experience frequency shifts and spurious responses due to exposure to oxygen plasma during backend processes, and there is a need for reliable passivation and frequency adjustment in wireless devices.
Innovation Solution
A SAW resonator configuration with a piezoelectric substrate, interdigital transducer electrodes, a dielectric temperature compensation layer, and a dielectric passivation layer, where the oxide passivation layer has a sound velocity greater than the temperature compensation layer, and includes trench regions to reduce thickness and suppress transverse signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxynitride (SiON) passivation layer is used to protect the SiN layer, then reliability is improved, but frequency shift occurs due to oxidation by oxygen plasma
Solution Approach 1:
The patent changes the material parameter of the passivation layer from silicon oxynitride (SiON) to aluminum oxide (Al2O3). This material substitution fundamentally alters the chemical properties, making the passivation layer immune to oxidation by oxygen plasma while maintaining protective functions. The Al2O3 layer has superior oxidation resistance compared to SiON, thereby preventing the frequency shift issue caused by plasma-induced oxidation.
Solution Approach 2:
The patent replaces the SiON passivation layer with an Al2O3 layer that forms a more stable and permanent protective barrier. The Al2O3 material provides long-term protection without degrading under plasma exposure, effectively eliminating the need for frequent recalibration or replacement due to frequency drift.
2Reliability
If the passivation layer thickness is increased to improve protection, then reliability is improved, but spurious responses from high-order transverse modes increase
Solution Approach 1:
The patent introduces trench regions within the Al2O3 passivation layer, creating local variations in thickness. The passivation layer is thinner in certain areas (trench regions) and thicker in others, allowing the design to simultaneously achieve adequate overall protection while minimizing the generation of spurious responses from high-order transverse modes. This local quality variation optimizes both protection capability and signal purity.
Solution Approach 2:
The passivation layer is segmented into different thickness regions through the introduction of trenches. This segmentation divides the uniform layer into zones with different acoustic properties, which helps suppress unwanted transverse modes while maintaining protective coverage. The trenches create acoustic path differences that interfere with the propagation of spurious signals.
3Object-generated harmful factors
If the sound velocity of the passivation layer is increased to suppress transverse signal transmission, then spurious response is reduced, but frequency characteristics become harder to adjust
Solution Approach 1:
The patent makes the passivation layer structure dynamic and adjustable by incorporating trenches with variable dimensions. The depth, width, and spacing of the trenches can be modified to tune the acoustic characteristics of the layer. This dynamic structural design allows optimization of sound velocity for suppressing transverse modes while retaining the ability to adjust frequency characteristics through geometric parameter changes.
Solution Approach 2:
The patent utilizes geometric parameter changes in the trench structures (depth, width, spacing) to achieve both high sound velocity for transverse mode suppression and adjustable frequency characteristics. By varying these physical parameters, the system can be optimized for different frequency requirements while maintaining effective spurious response suppression.
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 prevents frequency shifts and suppresses spurious responses from high-order transverse modes, ensuring reliability and allowing for adjustable frequency characteristics, even when exposed to oxygen plasma.
Implementation Method 1
the oxide passivation layer has a sound velocity greater than the temperature compensation layer, and includes trench regions to reduce thickness and suppress transverse signal transmission
Implementation Method 2
interdigital transductor (IDT) electrodes 113 are formed on an upper surface of a piezoelectric substrate 111 of LiNbO3
Implementation Method 3
The temperature compensation layer 115 may have a positive temperature coefficient of frequency to compensate the frequency temperature characteristics of the piezoelectric substrate 111 having a negative temperature coefficient of frequency
Data Source
AI summary
Aspects of this disclosure relate to a surface acoustic wave resonator. The surface acoustic wave resonator includes a piezoelectric substrate, interdigital transducer electrodes formed on an upper surface of the piezoelectric substrate, a dielectric temperature compensation layer formed on the piezoelectric substrate to cover the interdigital transducer electrodes, and a dielectric passivation layer over the temperature compensation layer. The passivation layer may include an oxide layer configured to have a sound velocity greater than that of the temperature compensation layer to suppress a transverse signal transmission.