Silicon Angular Rate Sensor Spring Orientation
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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 silicon springs oriented at specific angles to match the modulus of elasticity, along with a method of manufacturing on a silicon-on-insulator substrate that includes forming trenches for isolation and anti-stiction bumps to prevent sticking, ensuring accurate resonance and reduced vibration sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional micromachining techniques are used to manufacture MEMS sensors, then the sensors can be precisely manufactured, but mismatches in resonant frequency between primary and secondary flexure nodes occur
Solution Approach 1:
The patent changes the physical parameters of the support springs by orienting them at specific angles (20-25° and 65-70°) relative to the silicon crystalline orientation. This parameter change in spring orientation compensates for manufacturing variations and achieves matched resonant frequencies between primary and secondary flexure nodes, resolving the contradiction between manufacturing precision and measurement precision.
2Measurement precision
If conventional sensor designs are used, then the sensors can detect motion, but they suffer from relatively high mass
Solution Approach 1:
The patent employs a thin silicon sensing ring structure supported by flexible silicon springs, replacing conventional bulkier metal or silicon plate designs. This flexible thin-film structure reduces the mass of the sensing element while maintaining its motion detection capability, resolving the contradiction between measurement precision and weight.
3Measurement precision
If conventional sensors are used, then they can measure angular rate, but they exhibit undesirable sensitivity to vibration
Solution Approach 1:
The patent introduces asymmetric orientation angles for the support springs (20-25° and 65-70° relative to crystalline orientation) rather than symmetric arrangements. This asymmetric configuration creates differential responses to various vibration modes, allowing the sensor to distinguish between desired angular rate signals and unwanted vibration interference, thereby reducing vibration sensitivity while maintaining angular rate sensing accuracy.
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 solution provides improved sensitivity and reduced errors in angular rate sensing by matching the resonant frequencies and minimizing the effects of vibration, resulting in a more precise and robust motion sensing device.
Implementation Method 1
at least one drive electrode including drive capacitive plates for applying electrostatic force on the ring to cause the ring to resonate
Implementation Method 2
a plurality of silicon support springs connecting the substrate to the ring
Implementation Method 3
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
Data Source
Figure 1
Figure 2
Figure 2A
AI summary
A motion sensor in the form of an angular rate sensor (10) and a method of making a sensor are provided and includes a support substrate (12) and a silicon sensing ring (14) supported by the substrate and having a flexural resonance. Drive electrodes (20A) apply electrostatic force on the ring (14) to cause the ring to resonate. Sensing electrodes (20B) sense a change in capacitance indicative of vibration modes of resonance of the ring (14) so as to sense motion. A plurality of silicon support rings (16) connect the substrate (12) to the ring (14). The support springs (16) have portions (B1 and B2) are located at an angle to substantially match a modulus of elasticity of the silicon, such as about 22.5° and 67.5°, with respect to the crystalline orientation of the silicon. Also disclosed is a method of making a silicon integrated sensor.