Multi-Layer Movable Combs for MEMS Gyroscope Bias Reduction
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Solution Overview
Problem
Micro-electro-mechanical system (MEMS) gyroscopes face bias and scale factor errors due to drive-induced bias caused by electric fringing fields in near drive or pickoff combs, which affect the accuracy of rotation rate measurements.
Innovation Solution
The MEMS sensor design incorporates interleaved combs with multiple conductive layers electrically isolated by non-conductive layers, allowing individual voltage application to each conductive layer to balance fringing electric fields and reduce motion along the sense axis, thereby minimizing drive-induced bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional single-layer combs are used in MEMS gyroscopes, then the device structure is simple, but drive-induced bias errors occur due to unbalanced fringing electric fields
Solution Approach 1:
The comb structure is segmented into multiple conductive layers (at least two layers per comb: first conductive layer and second conductive layer) separated by non-conductive layers. Each layer can be independently biased to create opposing fringing electric fields that cancel each other out, eliminating drive-induced bias errors while maintaining measurement precision
Solution Approach 2:
Different regions of the comb structure have different electrical properties through the multi-layer design. The first and second conductive layers are positioned at different locations (e.g., top and bottom surfaces) and can be assigned different bias voltages to create localized electric fields that balance fringing effects in specific regions, improving overall measurement accuracy
2Measurement precision
If multiple conductive layers are added to screen fringing fields, then drive-induced bias is reduced, but device complexity increases
Solution Approach 1:
The multi-layer comb structure nests conductive and non-conductive layers within each other in an interleaved configuration. Each comb consists of alternating conductive layers and non-conductive layers, creating a compact nested structure that screens fringing fields without requiring excessive space or complexity in the overall device architecture
Solution Approach 2:
The multi-layer comb structure creates equipotential surfaces through the conductive layers that are biased to equalize electric field distributions. By adjusting the bias voltages on different conductive layers, the fringing electric fields are balanced to create a more uniform potential distribution, reducing measurement errors while maintaining structural feasibility
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 drive-induced bias errors, enhancing the accuracy of rotation rate measurements by balancing fringing electric fields and minimizing out-of-plane forces, leading to improved performance in MEMS gyroscopes and accelerometers.
Implementation Method 1
A vibratory Micro-electro-mechanical system (MEMS) gyroscope typically consists of two proof masses vibrating along a line (the drive axis) in a plane. Rotation of the device around an axis perpendicular to the drive axis creates a Coriolis Force vibration in a direction (the sense axis) perpendicular to both the drive and rotation axes.
Implementation Method 2
Rotation of the device around an axis perpendicular to the drive axis creates a Coriolis Force vibration in a direction (the sense axis) perpendicular to both the drive and rotation axes. The sense axis vibration amplitude is proportional to the rotation rate.
Data Source
AI summary
A MEMS sensor comprises a substrate and at least one proof mass having a first plurality of combs, wherein the proof mass is coupled to the substrate via one or more suspension beams such that the proof mass and the first plurality of combs are movable. The MEMS sensor also comprises at least one fixed anchor having a second plurality of combs. The first plurality of combs is interleaved with the second plurality of combs. Each of the combs in the first plurality of combs and the second plurality of combs comprises a plurality of conductive layers electrically isolated from each other by one or more non-conductive layers. Each conductive layer is individually coupled to a respective electric potential such that fringing electric fields are screened to reduce motion of the first plurality of combs along a sense axis due to the fringing electric fields.