SAW Resonator Parallel Capacitor Tuning for Stable TCF
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Solution Overview
Problem
Existing multilayer piezoelectric substrate (MPS) devices face challenges in achieving high Q, high coupling coefficient (keff2), and small temperature coefficient of frequency (TCF) while maintaining high power durability, particularly in lithium tantalate (LT) based SAW filter packages, which require thick silicon dioxide layers that limit Q performance.
Innovation Solution
Incorporating an additional capacitor in parallel with the series surface acoustic wave resonator and an interdigital transducer (IDT) structure, with specific capacitance ranges and configurations, to shift the anti-resonant frequency and improve TCF, while embedding the IDT structure partially or fully within the piezoelectric layer to enhance static capacitance and reduce size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick silicon dioxide layers are used in lithium tantalate based SAW filter packages to achieve high power durability, then power durability is improved, but Q performance deteriorates
Solution Approach 1:
The patent changes the material parameter from silicon dioxide to silicon oxyfluoride, which has different acoustic and electrical properties. This material substitution allows achieving the required acoustic isolation and power durability without the need for thick layers, thereby preserving the Q performance of the piezoelectric substrate.
Solution Approach 2:
The patent uses silicon oxyfluoride as a composite material that combines the benefits of acoustic isolation (like silicon dioxide) with lower acoustic velocity and improved electrical properties. This composite approach enables thinner layer designs that maintain power durability while reducing the negative impact on Q performance.
2Reliability
If thick silicon dioxide layers are used to achieve high power durability, then power durability is improved, but device size increases
Solution Approach 1:
By changing the material from silicon dioxide to silicon oxyfluoride, the patent achieves the same acoustic isolation function with a thinner layer. The silicon oxyfluoride's lower acoustic velocity and different impedance characteristics allow for reduced layer thickness while maintaining the required power durability and isolation performance.
Solution Approach 2:
The patent applies the silicon oxyfluoride layer with optimized local thickness and positioning to achieve acoustic isolation at the critical interfaces. This localized optimization allows the layer to be thinner overall while still providing the necessary acoustic and electrical isolation for high power durability.
3Reliability
If conventional SAW resonator structures are used to achieve high coupling coefficient, then coupling coefficient is improved, but temperature coefficient of frequency increases
Solution Approach 1:
The patent introduces an additional capacitor element that changes the electrical parameters of the resonator circuit. This additional capacitance allows for adjusting and optimizing the temperature coefficient of frequency while preserving the high coupling coefficient achieved by the embedded IDT structure. The capacitor provides an extra degree of freedom for temperature compensation.
Solution Approach 2:
The patent creates a composite resonator structure that combines the embedded IDT (for high coupling) with an additional capacitor (for TCF optimization). This composite approach allows each element to contribute its strengths: the embedded IDT provides high coupling coefficient while the additional capacitor enables TCF adjustment and stabilization.
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 achieves improved temperature stability and reduced size with enhanced coupling coefficient and Q performance, addressing the limitations of existing LT-based MPS SAW filter packages without the need for thick silicon dioxide layers.
Implementation Method 1
A surface acoustic wave resonator can include an interdigital transducer (IDT) electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transducer electrode is disposed.
Implementation Method 2
a capacitor coupled in parallel with the series surface acoustic wave resonator, the capacitor resulting in a shifted anti-resonant frequency for the series surface acoustic wave resonator
Data Source
AI summary
An acoustic wave filter package with a surface acoustic wave resonator having a capacitor coupled in parallel with the surface acoustic wave resonator. The capacitor results in a shifted anti-resonant frequency.