MEMS Angular Rate Sensor with Bending Springs and Sealed Cavities
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Solution Overview
Problem
Existing angular rate sensors face challenges in achieving high precision and stability due to non-uniform characteristics, sensitivity to mechanical and thermal loads, and uncompensated quadrature signals, which affect their accuracy and reliability.
Innovation Solution
A fully symmetrical MEMS structure with a double-sided implementation using silicon-insulator composite wafers, featuring seismic masses, driving beams, and a bending spring, along with dedicated electrodes for frequency matching and quadrature compensation, is designed to enhance precision and stability. This structure includes stress-release means and a hermetically sealed cavity to minimize external interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electrostatic excitation is applied at right angles to the substrate surface, then the device is relatively easy to produce, but the gyroscopic scale factor is lower
Solution Approach 1:
The patent transitions from out-of-plane electrostatic excitation to in-plane electrostatic excitation, changing the dimension of the driving force application. This dimensional change enables the use of bending beams that can achieve large oscillation amplitudes while maintaining ease of manufacturing through standard silicon wafer processing techniques.
Solution Approach 2:
The patent changes the orientation parameter of the electrostatic excitation force from perpendicular to the substrate plane to parallel with the substrate plane. This parameter change allows the seismic masses to oscillate with larger amplitudes, thereby increasing the gyroscopic scale factor while maintaining compatibility with existing manufacturing processes.
2Measurement precision
If asymmetric beams are used to achieve large oscillation amplitudes, then primary motion with large amplitude is achieved, but non-uniform characteristics and built-in stress cause sensitivity to external mechanical and thermal loads
Solution Approach 1:
The patent employs asymmetric beam profiles that are optimized for bending in the plane of the substrate, achieving large oscillation amplitudes. The asymmetry is carefully designed to concentrate stress in controlled regions while maintaining overall structural balance to minimize sensitivity to external loads.
Solution Approach 2:
The patent applies local quality enhancement by introducing stress-release structures at specific locations where built-in stresses are most problematic. These localized modifications allow the beams to maintain their asymmetric shape for large amplitude oscillations while reducing sensitivity to external mechanical and thermal loads at critical stress points.
3Object-affected harmful factors
If stress-release structures and pedestals are used to address non-uniform characteristics, then sensitivity to external loads is reduced, but device complexity increases
Solution Approach 1:
The patent merges the functions of stress-release structures and pedestals into an integrated support system. The pedestals are designed to simultaneously provide mechanical support and incorporate stress-release features, thereby reducing sensitivity to external loads without significantly increasing device complexity.
Solution Approach 2:
The patent creates multi-functional elements where the same structural components serve multiple purposes: pedestals provide both support and stress management, while frame structures simultaneously enclose the sensing system and provide mechanical stability. This universality reduces the number of separate components needed.
4Measurement precision
If a hermetically sealed cavity is used to maintain vacuum and high quality factors, then large oscillation amplitudes are achieved, but manufacturing complexity increases
Solution Approach 1:
The patent employs a nested structure where the sensing system with seismic masses and beams is enclosed within a frame, which is in turn sealed within a hermetic cavity formed by bonding the silicon substrate to the glass wafer. This nested arrangement maintains vacuum for high quality factor oscillations while using standard bonding processes.
Solution Approach 2:
The patent uses composite material structures, specifically bonding silicon wafers to glass wafers, to create the hermetically sealed cavity. This composite approach leverages the complementary properties of silicon (for precise micromechanical structures) and glass (for hermetic sealing), achieving both high oscillation amplitudes and manufacturability.
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 achieves improved accuracy and stability by reducing sensitivity to mechanical and thermal interference, enabling reliable angular velocity measurement with enhanced precision and efficient space usage.
Implementation Method 1
a bending spring arranged to directly connect between, and synchronise a primary motion of, the two seismic masses
Implementation Method 2
when the device is subjected to an angular velocity around a third axis that is substantially in the plane of the silicon substrate and perpendicular to the longitudinal axis of the beams, a Coriolis force arises which causes the secondary oscillation of the seismic masses
Implementation Method 3
structures sealed in vacuum and exhibiting high quality factors
Data Source
AI summary
A micro-electromechanical system (MEMS) structure for an angular rate sensor includes seismic masses arranged to have a first degree of rotational freedom about an axis that is substantially perpendicular to the plane of a silicon substrate, and a second degree of rotational freedom about an axis substantially coincident with the longitudinal axis of driving beams to which the seismic masses are attached. A sensing system is arranged such that, when the structure is subjected to an angular velocity around a third axis that is substantially in the plane of the silicon substrate and perpendicular to the longitudinal axis of the beams, a Coriolis force arises which causes the secondary oscillation of the seismic masses.