Doped Silicon MEMS Resonators for Temperature-Stable Oscillators
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Solution Overview
Problem
MEMS resonant elements exhibit significant variation in resonant frequency due to temperature changes, which affects their stability and performance in various applications.
Innovation Solution
The fabrication of MEMS resonant elements with specific dopant concentrations and orientations, combined with temperature compensation circuits, to stabilize frequency across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature compensation circuits are added to stabilize resonant frequency, then frequency stability improves, but device complexity increases
Solution Approach 1:
The patent modifies physical parameters of the resonant element itself (dopant concentration, crystal orientation, geometry) to inherently compensate for temperature effects, eliminating the need for external compensation circuits. This resolves the contradiction by achieving frequency stability through parameter optimization rather than adding complex circuitry.
Solution Approach 2:
The resonant element is designed to self-compensate for temperature variations through its inherent material properties and structural characteristics. The doped semiconductor material and specific crystal orientations provide automatic temperature compensation without requiring external circuits, thus maintaining frequency stability while avoiding increased device complexity.
2Reliability
If dopant concentration is increased to reduce temperature sensitivity, then frequency stability improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses composite material structures combining doped semiconductor regions with undoped or differently doped regions. This composite approach allows temperature compensation through material property interactions while using standard dopant concentrations that are within normal manufacturing capabilities, avoiding excessive precision requirements.
Solution Approach 2:
Different regions of the resonant element have different dopant concentrations optimized for their specific functions. The doped regions provide temperature compensation while undoped or lightly-doped regions maintain high mechanical quality factor. This localized quality differentiation achieves frequency stability without requiring uniform high-precision dopant control throughout the entire structure.
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
Stabilizes the resonant frequency of MEMS elements by minimizing temperature sensitivity, ensuring consistent performance across operating temperatures.
Implementation Method 1
thermally induced changes to the Young's modulus (or other variables) tend to change the mechanical stiffness of the structure
Implementation Method 2
fabricating the resonant element from a doped semiconductor material
Data Source
AI summary
The present inventions, in one aspect, are directed to micromachined resonator comprising: a first resonant structure extending along a first axis, wherein the first axis is different from a crystal axis of silicon, a second resonant structure extending along a second axis, wherein the second axis is different from the first axis and the crystal axis of silicon and wherein the first resonant structure is coupled to the second resonant structure, and wherein the first and second resonant structures are comprised of silicon (for example, substantially monocrystalline) and include an impurity dopant (for example, phosphorus) having a concentrations which is greater than 1019 cm−3, and preferably between 1019 cm−3 and 1021 cm−3.