Silica-Based Angular Velocity Sensor
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Solution Overview
Problem
Conventional Coriolis-type angular velocity sensors made from silicon face limitations in quality factor due to thermoelastic damping and frequency matching challenges, which are exacerbated by manufacturing imperfections and temperature variations.
Innovation Solution
The use of a silica-based material for the vibrating ring structure, combined with interdigitated conductive electrodes on both the ring and support layers, allows for improved thermal stability and precise electrostatic force application, enabling higher quality factors and reduced bias errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon is used for the vibrating ring structure, then the material provides good mechanical properties and ease of manufacture, but it suffers from high thermoelastic damping that limits the quality factor
Solution Approach 1:
The patent changes the material parameter (thermal expansion coefficient) by replacing silicon with silica-based material. Silica has a thermal expansion rate of only 0.5 ppm/°C compared to silicon's 3 ppm/°C, which directly reduces thermoelastic damping and increases the quality factor by up to 36 times.
2Reliability
If silica-based material is used for the vibrating ring structure, then thermoelastic damping is reduced and quality factor increases, but the insulating nature of silica prevents direct electrical connection for driving and sensing
Solution Approach 1:
The patent transitions from planar electrodes to three-dimensional interdigitated comb electrodes with axial spacing. The moveable electrodes are positioned on the ring structure while fixed electrodes are on the support layer, creating an axial dimension for electrical connection that overcomes the insulating property of silica.
Solution Approach 2:
The patent introduces conductive interdigitated electrodes as intermediaries between the electrical signal source and the silica-based ring structure. These electrodes provide the necessary electrical connection for driving and sensing without requiring the silica itself to be conductive.
3Ease of manufacture
If conventional planar electrodes are used on silica, then manufacturing is simplified, but precise electrostatic force application is difficult due to the insulating nature of silica
Solution Approach 1:
The patent employs interdigitated comb electrodes with fingers extending in the axial direction, creating a three-dimensional electrode structure. This configuration provides precise electrostatic force application through controlled axial spacing between moveable and fixed electrodes, enabling accurate driving and sensing forces.
4Manufacturing precision
If silicon ring structures are manufactured, then high manufacturing accuracy is achieved, but frequency splitting between primary and secondary modes occurs due to geometric imperfections
Solution Approach 1:
The patent changes the material from silicon to isotropic silica-based material. This material parameter change eliminates the anisotropic properties of silicon that cause stress-induced frequency splitting, resulting in better frequency matching between degenerate modes despite manufacturing tolerances.
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 results in a 36 times lower thermoelastic damping and potentially 36 times greater quality factor, leading to significantly smaller bias errors and enhanced sensitivity, while overcoming the insulating nature of silica through the use of conductive electrodes.
Implementation Method 1
a plurality of conductive electrodes, each electrode comprising a first set of moveable conductive electrode tracks formed on a surface of the planar ring structure and a second set of fixed conductive electrode tracks formed on a surface of the insulative support layer
Implementation Method 2
When the sensor undergoes rotation about an axis perpendicular to the plane of the ring structure, Coriolis forces are generated which couple energy into the secondary vibration mode (in-plane)
Implementation Method 3
this is limited by thermoelastic damping (TED), which is principally set by the thermal expansion rate of the semiconductor material (about 3 ppm/° C.). silica has a thermal expansion rate of only 0.5 ppm/° C., resulting in thermoelastic damping (TED) that is 36 times lower than for silicon
Data Source
AI summary
An angular velocity sensor comprises: an insulative support layer (10); a substrate layer (8) formed of a silica-based material and comprising a planar ring structure (2) mounted to vibrate in-plane; and a plurality of conductive electrodes (14), each comprising a first set of moveable conductive electrode tracks (14a) formed on a surface of the planar ring and a second set of fixed conductive electrode tracks (14b) formed on a surface of the insulative support layer axially spaced from the surface of the planar ring. The first and second sets of conductive electrode tracks are interdigitated with a lateral spacing between them in a radial direction. Each moveable conductive electrode track has a radial offset from a median line between adjacent fixed conductive electrode tracks such that each moveable conductive electrode track has a different lateral spacing from two different adjacent fixed conductive electrode tracks in opposite radial directions.