MEMS Tuning Fork Arms with SiO2 Layer for TCF Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing MEMS vibrating devices face challenges in sufficiently reducing the absolute value of the temperature coefficient of resonant frequency (TCF), which affects their temperature characteristics.
Innovation Solution
The proposed vibrating device incorporates a base portion with multiple tuning fork arms, featuring a Si layer made of a degenerate semiconductor, a silicon oxide layer, and a piezoelectric layer, with specific thickness ratios and doping, to achieve reduced TCF. The silicon oxide layer is laminated on the Si layer, and electrodes are applied to the piezoelectric layer to induce flexural vibrations, with the thickness of the silicon oxide layer set within a specific range to minimize TCF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide layer is laminated on the Si layer, then the temperature coefficient of resonant frequency is reduced, but the manufacturing precision requirement increases due to specific thickness ratio constraints
Solution Approach 1:
The patent applies parameter changes by establishing a specific mathematical relationship between the thickness of the silicon oxide layer (T2) and the Si layer (T1). The thickness ratio T2/(T1+T2) is controlled within a specific range defined by the formula (−0.0002x2−0.0136x+0.0014)±0.05, where x represents the TCF when the silicon oxide layer is not provided. This quantitative parameter control enables systematic optimization of temperature characteristics while providing clear manufacturing guidelines.
Solution Approach 2:
The patent employs composite materials by laminating a silicon oxide layer on a degenerate semiconductor Si layer. This composite structure combines materials with different thermal properties to achieve reduced temperature coefficient of resonant frequency. The silicon oxide layer (with low TCF) compensates for the temperature drift of the Si layer, creating a composite structure with superior temperature stability.
2Reliability
If the silicon oxide layer thickness is increased to reduce TCF, then temperature characteristics improve, but the device structure becomes more complex
Solution Approach 1:
The patent resolves the complexity issue by providing a clear mathematical formula that directly determines the optimal silicon oxide layer thickness based on the Si layer thickness and initial TCF value. This parameter-based approach transforms a complex design problem into a straightforward calculation, enabling engineers to determine the exact thickness ratio needed without requiring complex simulations or trial-and-error processes.
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 effectively reduces the absolute value of the temperature coefficient of resonant frequency to within ±5 ppm/°C, providing improved temperature characteristics and stability across a range of temperatures.
Implementation Method 1
an excitation portion including a piezoelectric thin film is constituted on a Si semiconductor layer
Implementation Method 2
a method of reducing an absolute value of the TCF by laminating Si and SiO2
Data Source
AI summary
A vibrating device having tuning fork arms extending in a first direction that are joined to a base portion and are arranged side by side in an second direction. Each of the tuning fork arms has a structure that a silicon oxide layer is laminated on a Si layer made of a degenerate semiconductor, and that an excitation portion is provided on the silicon oxide layer. When a total thickness of the Si layer is denoted by T1, a total thickness of the silicon oxide layer is denoted by T2, and the temperature coefficient of resonant frequency (TCF) when the silicon oxide layer is not provided on the Si layer is denoted by x, a thickness ratio T2/(T1+T2) is within a range of (−0.0002x2−0.0136x+0.0014)±0.05.