Optically Transduced MEMS Gyroscope with Bulk Micromachined Proof Mass
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Solution Overview
Problem
Vibratory gyroscopes face limitations in achieving large proof mass dimensions and high capacitive coupling due to constraints in thin film micromachining techniques, which restrict their sensitivity and performance metrics.
Innovation Solution
A bulk micromachined vibratory gyroscope with a proof mass of bulk substrate thickness and multi-layer sub-wavelength gratings for optical displacement transduction, enabling increased mass dimensions and high inertial sensitivity while minimizing cross-talk with non-optical drive elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thin film micromachining techniques are used to achieve large capacitive coupling by minimizing gap spacing, then capacitive coupling is improved, but proof mass dimensions are limited to tens of microns in thickness
Solution Approach 1:
The patent replaces the mechanical capacitive sensing system with an optical transduction system. Optical beams are used to detect the position and motion of the proof mass, eliminating the need for close capacitive coupling. This substitution allows the proof mass to be much thicker (bulk dimensions) without compromising sensing capability, as optical methods can detect displacement over larger gaps without requiring nanometer-scale spacing.
2Volume of moving object
If bulk micromachining techniques with deep substrate etches are used to increase proof mass dimensions, then proof mass volume is improved, but lateral dimensions of deep trenches are limited to many tens of microns due to anisotropic etch performance
Solution Approach 1:
The patent transitions from two-dimensional planar sensing to three-dimensional bulk structures. By using optical transduction, the system can accommodate deep trenches and thick proof masses that would be impossible with planar capacitive sensing. The optical method senses motion in the vertical dimension through the bulk structure, enabling proof masses with thicknesses of hundreds of microns or more while maintaining manufacturing feasibility with standard deep substrate etching techniques.
3Measurement precision
If optical displacement transduction with multi-layer sub-wavelength gratings is implemented, then sensitivity is improved and cross-talk with non-optical drive elements is reduced, but device complexity increases
Solution Approach 1:
The patent introduces multi-layer sub-wavelength gratings as an intermediary between the proof mass and the optical detection system. These gratings modulate the optical signal in response to proof mass displacement, providing high sensitivity detection. The grating structure acts as a transducer that converts mechanical displacement into optical signal modulation, enabling precise measurement while maintaining electrical isolation between drive and sense elements, thus reducing cross-talk despite the increased structural complexity.
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 allows for enhanced sensitivity and reduced cross-talk, enabling the achievement of superior inertial sensing capabilities with larger proof mass dimensions and improved performance metrics compared to conventional thin film MEMS gyroscopes.
Implementation Method 1
optical displacement transduction is performed with multi-layer sub-wavelength gratings for high sensitivity and low cross-talk with non-optical drive elements
Implementation Method 2
at least one capacitive drive element. A plurality of drive electrodes may further be utilized... to capacitively impart the drive force to a face of the proof mass
Implementation Method 3
when the gyroscope experiences a rotation, the Coriolis effect couples energy from the from the excited resonance to an orthogonal (sensed) dimension
Data Source
AI summary
A bulk micromachined vibratory gyro in which a proof mass has a bulk substrate thickness for a large mass and high inertial sensitivity. In embodiments, optical displacement transduction is with multi-layer sub-wavelength gratings for high sensitivity and low cross-talk with non-optical drive elements. In embodiments, the vibratory gyro includes a plurality of multi-layer sub-wavelength gratings and a plurality of drive electrodes to measure motion of the proof mass induced by drive forces and/or moments and induced by the Coriolis Effect when the gyro experiences a rotation. In embodiments, phase is varied across the plurality gratings and a multi-layer grating having the best performance is selected from the plurality.