Composite SAW Layer Stack for k2 and TCF Balance
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Solution Overview
Problem
Existing surface acoustic wave (SAW) devices face challenges in achieving optimal electromechanical coupling coefficient (k2) and temperature coefficient of frequency (TCF) characteristics, particularly when using a LT-quartz bonded substrate, where the TCF is degraded due to increased IDT thickness, leading to compromised device performance.
Innovation Solution
A SAW device configuration involving a quartz layer, an amorphous silicon oxide layer, and a piezoelectric layer, where the amorphous silicon oxide layer is laminated on the quartz layer, and the piezoelectric layer is laminated on the silicon oxide layer, with an Inter Digital Transducer formed on the piezoelectric layer, optimizing the thickness ratios of these layers to enhance k2 and TCF characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thickness of the LiTaO3 substrate is decreased to prevent TCF degradation, then the TCF is improved, but the k2 is degraded
Solution Approach 1:
The patent uses a composite substrate structure consisting of a LiTaO3 layer and an AT-cut quartz layer bonded together. This composite structure allows the device to achieve both improved TCF (through the quartz layer's temperature compensation properties) and maintained k2 (through the LiTaO3 layer's piezoelectric properties), resolving the contradiction between these two parameters that would otherwise require compromising the LiTaO3 substrate thickness.
2Reliability
If the thickness of the IDT is increased, then the k2 is improved, but the TCF is degraded
Solution Approach 1:
The composite LiTaO3-quartz substrate provides a stable foundation that compensates for the TCF degradation caused by thicker IDT electrodes. The quartz layer's low thermal expansion and stable acoustic properties counterbalance the TCF impact from increased IDT thickness, allowing optimization of k2 without severe TCF penalty.
Solution Approach 2:
The patent optimizes the thickness ratio between the LiTaO3 layer and quartz layer, as well as the IDT thickness, to achieve a balance between k2 and TCF. By carefully controlling these dimensional parameters within specific ranges, the device achieves both high electromechanical coupling and acceptable temperature stability.
3Reliability
If a LT-quartz bonded substrate is used to improve Q factor, then the Q factor is improved, but the TCF is degraded
Solution Approach 1:
The patent specifies optimal thickness ratios for the LiTaO3 and quartz layers to maximize Q factor while minimizing TCF degradation. By controlling the relative thicknesses and acoustic impedances of the bonded layers, the device achieves high Q factor through reduced energy leakage while the quartz layer's temperature compensation properties mitigate TCF degradation.
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 configuration significantly improves the Q factor, k2, and TCF characteristics, reducing the negative impact of IDT thickness on TCF, while maintaining a high Q factor and electromechanical coupling coefficient, thus enhancing the device's frequency and temperature stability.
Implementation Method 1
a temperature compensation effect by amorphous SiO2
Implementation Method 2
a piezoelectric layer, and an Inter Digital Transducer. The Inter Digital Transducer excites a surface acoustic wave on the piezoelectric layer
Implementation Method 3
a confinement of a vibration energy by AlN as a high-acoustic-velocity substrate
Data Source
AI summary
A surface acoustic wave device includes a quartz layer, an amorphous silicon oxide layer, a piezoelectric layer, and an Inter Digital Transducer. The amorphous silicon oxide layer is laminated on the quartz layer. The piezoelectric layer is laminated on the amorphous silicon oxide layer. The Inter Digital Transducer is formed on the piezoelectric layer. The Inter Digital Transducer excites a surface acoustic wave on the piezoelectric layer. Assuming that the surface acoustic wave has a wavelength λ,0.1≤a thickness of the amorphous silicon oxide layer/λ≤1, and0.08<a thickness of the piezoelectric layer/λ≤1.