MEMS Force Sensor Segmentation and Sealing for Debris Protection
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Solution Overview
Problem
Current MEMS force sensors are large, fragile, and susceptible to debris, lacking robustness and efficiency in force measurement due to their design and environmental sensitivity.
Innovation Solution
A microelectromechanical (MEMS) force sensor with compact sensing elements positioned on the periphery of the die, featuring a flexure and piezoresistive strain gauges, and a sealed design with retaining walls to prevent debris entry, utilizing a bonded cap and base wafer structure with an air gap for overload protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact pads are positioned around the diaphragm in current MEMS force dies, then the sensing function is achieved, but the device size becomes relatively large
Solution Approach 1:
The patent divides the sensing function into multiple compact sensing elements positioned on the periphery of the die rather than using a single large central diaphragm. Each sensing element is comprised of a flexure and a piezoresistive strain gauge, allowing the force measurement function to be distributed across smaller components that fit within a reduced die area.
Solution Approach 2:
The patent transitions from a planar arrangement of contact pads around a central diaphragm to a three-dimensional configuration where sensing elements are positioned on the periphery of the die, utilizing the edge space and vertical dimension to achieve compact packaging while maintaining measurement capability.
2Measurement precision
If current MEMS force dies use traditional diaphragm structures, then force sensing is achieved, but the devices become fragile and susceptible to debris
Solution Approach 1:
The patent uses flexible flexure elements instead of fragile thin diaphragms. The flexures are designed to be mechanically robust while still providing the necessary deformation for force measurement. The retaining walls and sealed cavity structure further protect these flexible elements from debris and mechanical damage.
Solution Approach 2:
The patent incorporates retaining walls and a sealed cavity structure that prevent debris from entering and damaging the sensing elements. The air gap between the cap and base wafer provides cushioning space that prevents direct contact between external debris and the internal flexure and strain gauge components.
3Ease of manufacture
If current MEMS force dies lack sealed structures, then manufacturing is simpler, but debris from the external environment can enter and clog the overload stop
Solution Approach 1:
The patent segments the device into distinct sealed compartments: a sealed cavity containing the sensing elements, retaining walls that form barriers, and an air gap that provides protection. This segmentation allows each component to be manufactured separately and then assembled, maintaining manufacturing feasibility while providing comprehensive debris protection.
Solution Approach 2:
The patent introduces retaining walls and sealed cavity structures as intermediary elements between the external environment and the internal sensing components. These intermediary structures prevent direct contact between debris and the flexure and strain gauge elements, while still allowing force transmission through the designed pathways.
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 results in a smaller, more robust, and sealed force sensor that effectively measures forces while preventing debris interference and mechanical overload, enhancing sensitivity and durability.
Implementation Method 1
Each sensing element is comprised of a flexure and a piezoresistive strain gauge
Data Source
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AI summary
Described herein is a miniaturized and ruggedized wafer level MEMS force sensor composed of a base and a cap. The sensor employs multiple flexible membranes, a mechanical overload stop, a retaining wall, and piezoresistive strain gauges.