MEMS Resonator Silicon Oxide Layer Thickness Control
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Solution Overview
Problem
Existing resonators with MEMS structures and piezoelectric thin films on Si semiconductor layers face challenges in achieving favorable frequency temperature characteristics due to unclear configurations of silicon oxide layers, leading to inconsistent performance.
Innovation Solution
A resonator design incorporating a base material with a first silicon oxide layer and a second silicon oxide layer, where the thickness of the second layer is greater than the first, and the etching rate of the second layer is higher, allowing for improved temperature coefficient of frequency (TCF) control and reduced variation, enhancing frequency stability across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single silicon oxide layer is used in the resonator structure, then the device complexity is reduced, but the frequency temperature characteristic cannot be sufficiently improved
Solution Approach 1:
The silicon oxide layer is segmented into multiple distinct layers (first silicon oxide layer and second silicon oxide layer) with different thicknesses and etching rates. This segmentation allows each layer to contribute differently to the overall frequency temperature characteristic, enabling fine-tuned control that cannot be achieved with a single uniform layer.
Solution Approach 2:
Different regions of the silicon oxide structure are assigned different properties: the first silicon oxide layer has a specific thickness and etching rate, while the second silicon oxide layer has different thickness and etching rate characteristics. This local differentiation of properties enables optimized frequency temperature compensation throughout the resonator structure.
2Manufacturing precision
If the thickness of silicon oxide layers is increased to improve frequency stability, then the manufacturing precision is improved, but the etching time is prolonged reducing productivity
Solution Approach 1:
The second silicon oxide layer is designed with a higher etching rate compared to the first layer, allowing it to be removed more quickly during manufacturing processes. This local quality differentiation enables the use of thicker oxide layers for improved frequency stability while maintaining reasonable etching times through selective removal of the higher-etching-rate layer.
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 resonator achieves a more stable and improved frequency temperature characteristic, reducing the variation in resonance frequency over a temperature range from -25°C to +75°C, thereby enhancing the performance of oscillators, electronic apparatuses, and vehicles.
Implementation Method 1
by setting the ratio of the sum of the thickness of the Si layer and the thickness of the silicon oxide layer to the thickness of the Si layer to a predetermined condition, the temperature coefficient of frequency (TCF) is decreased
Implementation Method 2
an excitation section including a piezoelectric thin film is formed on an Si semiconductor layer
Data Source
AI summary
A resonator includes a surface silicon layer as a base material, a first silicon oxide layer disposed on a first surface of the surface silicon layer, and a second silicon oxide layer disposed on the opposite side to the surface silicon layer of the first silicon oxide layer, wherein when the thickness of the surface silicon layer is represented by tsi, the thickness of the first silicon oxide layer is represented by ta, and the thickness of the second silicon oxide layer is represented by tb, the following relationships are satisfied: 0.138×tsi<ta<0.268×tsi and 0.189×tsi<tb<0.527×tsi.