Angled Silicon Springs for MEMS Resonant Frequency Matching
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Solution Overview
Problem
Conventional motion sensors, such as angular rate sensors, face issues with mismatches in resonant frequency between primary and secondary flexure nodes, high mass, and sensitivity to vibration, limiting their performance.
Innovation Solution
A silicon motion sensor design featuring a silicon sensing ring supported by angled silicon springs, with specific orientations to match the modulus of elasticity, and a manufacturing method using a silicon-on-insulator substrate that includes forming trenches for isolation and anti-stiction bumps to prevent sticking, enhancing frequency matching and reducing vibration sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional micromachining techniques are used to manufacture MEMS sensors, then the sensors can be produced with standard manufacturing processes, but the sensors suffer from mismatches in resonant frequency between primary and secondary flexure nodes
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the crystalline orientation of silicon springs at specific angles (20-25° and 65-70°) to match the modulus of elasticity. This precise parameter control ensures that both primary and secondary flexure nodes have matched resonant frequencies, resolving the frequency mismatch problem while maintaining compatibility with standard MEMS manufacturing processes
Solution Approach 2:
The patent implements local quality by orienting different silicon springs at different specific angles relative to the crystalline orientation of the silicon substrate. This localized variation in spring orientation creates the necessary modulus of elasticity matching at specific locations, enabling precise resonant frequency control without affecting the entire device structure
2Ease of manufacture
If conventional sensor designs are used, then the manufacturing process is simpler, but the sensors suffer from relatively high mass
Solution Approach 1:
The patent employs thin silicon structures and flexible spring elements to create a low-mass sensing mechanism. The silicon springs and sensing elements are fabricated as thin films or microstructures that provide the necessary mechanical flexibility while minimizing mass, thereby improving sensitivity without complicating the manufacturing process
3Device complexity
If conventional sensor structures are used, then the device design is simpler, but the sensors exhibit undesirable sensitivity to vibration
Solution Approach 1:
The patent utilizes mechanical vibration principles by designing the silicon sensing ring to resonate at specific frequencies determined by the oriented silicon springs. The matched resonant frequencies of primary and secondary flexure nodes create a controlled vibration pattern that is less susceptible to external vibrations, thereby reducing vibration sensitivity while maintaining structural simplicity
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 design achieves improved sensitivity and reduced errors by matching the resonant frequencies and modulus of elasticity, resulting in a more accurate and robust motion sensing capability.
Implementation Method 1
a plurality of silicon support springs connecting the substrate to the ring, wherein the support springs are located at an angle to substantially match a modulus of elasticity of the silicon support springs
Implementation Method 2
a silicon sensing ring formed within and supported by the substrate and having a flexural resonance
Implementation Method 3
at least one drive electrode including drive capacitive plates for applying electrostatic force on the ring to cause the ring to resonate
Implementation Method 4
at least one sense electrode including sense capacitor plates for sensing a change in capacitance indicative of the vibration nodes of resonance of the ring so as to sense motion
Data Source
AI summary
A motion sensor in the form of an angular rate sensor and a method of making a sensor are provided and includes a support substrate and a silicon sensing ring supported by the substrate and having a flexive resonance. Drive electrodes apply electrostatic force on the ring to cause the ring to resonate. Sensing electrodes sense a change in capacitance indicative of vibration modes of resonance of the ring so as to sense motion. A plurality of silicon support rings connect the substrate to the ring. The support rings are located at an angle to substantially match a modulus of elasticity of the silicon, such as about 22.5 degrees and 67.5 degrees, with respect to the crystalline orientation of the silicon.