Variable Thickness MEMS Resonator for Sensitivity Loss
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Solution Overview
Problem
Existing inertial sensors face challenges in miniaturization, leading to increased mass and reduced sensitivity due to homothetic size reduction, and require burdensome transfer of substrates in volume technology, limiting their application in mass-production industries like automobiles and mobile telephones.
Innovation Solution
The development of MEMS sensors using 3D planar technology with multiple thickness areas, allowing for separate optimization of resonators, hinges, and seismic masses, and the integration of electronics close to the sensor for improved sensitivity and reduced size, achieved through differentiated etching steps in semiconductor substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If homothetic size reduction is applied to miniaturize sensors, then the size of the sensor is reduced, but the sensitivity is significantly lost
Solution Approach 1:
The patent applies local quality by creating a resonator with non-uniform thickness distribution, where different regions have different thicknesses optimized for their specific functions. The resonator includes a thinner detection region for enhanced sensitivity and a thicker mass region for sufficient seismic mass, allowing each part to have the local properties needed for its function rather than using uniform homothetic scaling
Solution Approach 2:
The patent transitions from two-dimensional planar resonators to three-dimensional resonators with variable thickness. By introducing the thickness dimension as a design parameter, the resonator can simultaneously achieve small footprint area for miniaturization while maintaining adequate mass and sensitivity through vertical dimension optimization
2Length of stationary object
If volume technology is used to produce resonators, then the resonator thickness can be reduced for beam vibration mode, but the process requires transfer of two substrates which is burdensome
Solution Approach 1:
The patent merges the resonator structure and the substrate into a single integrated component. The resonator is formed directly in the substrate through selective etching, eliminating the need for separate substrate fabrication and transfer operations. This integration simplifies the manufacturing process while maintaining the ability to control resonator thickness
Solution Approach 2:
The patent extracts only the necessary portions of the substrate to form the resonator structure, leaving the rest of the substrate intact. By selectively removing material in the resonator region through etching, the design achieves thin resonator sections for vibration while avoiding the complexity of transferring entire substrates
3Length of moving object
If the resonator is placed at the surface of the substrate to minimize the gap with excitation electrode, then the gap is minimized, but the resonator cannot be optimally positioned near the hinge to enhance the lever principle
Solution Approach 1:
The patent resolves the positioning conflict by utilizing the vertical thickness dimension. The resonator is positioned at an optimal height above the hinge axis, and its variable thickness profile is designed so that the detection region extends closer to the hinge while maintaining adequate gap for excitation. This three-dimensional positioning allows simultaneous optimization of both gap distance and lever arm length
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 approach enables the creation of highly sensitive inertial sensors with reduced size, overcoming sensitivity loss during miniaturization and allowing for efficient integration with processing electronics, suitable for mass-production applications.
Implementation Method 1
Resonant sensors can be produced... resonator vibrates in a plane
Implementation Method 2
The inertial sensors made of volume technology are based on electrostatic excitation outside the plane of the resonator
Implementation Method 3
achieved through differentiated etching steps in semiconductor substrates
Data Source
AI summary
The invention relates to a surface-type MEMS resonant sensor, comprising a resonator (4) with excitation in a plane, which sensor comprises:a first, so-called thick area (2), having a first thickness (E1), forming a seismic mass; anda second, thin area (4), having a second thickness (E2), lower than the first, for detection.