Ruggedized Wafer Level MEMS Force Sensor with Tolerance Trench
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Solution Overview
Problem
Conventional MEMS force sensors are large, fragile, and susceptible to mechanical overload and environmental debris, lacking the robustness of other force sensing technologies.
Innovation Solution
A MEMS force sensor design featuring a cap and sensor bonded at peripheral edges, with a trench and cavity structure that enhances strength and sensitivity, using silicon or glass materials and piezoresistive elements for force measurement, and a method of manufacturing that includes silicon fusion bonding and etching techniques to create a robust and sealed device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS force dies use a diaphragm with four piezoresistive strain gauges positioned around it, then force sensing capability is achieved, but the device size becomes relatively large
Solution Approach 1:
The sensor die is segmented into functional zones: a central sensing area with the diaphragm and strain gauges, and a peripheral tolerance trench area. This segmentation allows the sensing function to be concentrated in a small central region while the trench provides necessary mechanical tolerance and bonding area at the periphery, reducing overall device size while maintaining force sensing capability.
Solution Approach 2:
The patent applies local quality by creating a tolerance trench only at the peripheral edges of the sensor die, while the central sensing diaphragm maintains its full thickness and structural integrity. This localized modification provides mechanical tolerance where needed at the bondsite without compromising the sensing area, enabling compact design while preserving measurement precision.
2Ease of manufacture
If conventional MEMS force dies are designed with contact pads around the diaphragm, then electrical connections are established, but the device becomes fragile and susceptible to mechanical overload
Solution Approach 1:
The tolerance trench is created beforehand during fabrication as a mechanical cushioning feature. This trench provides a compliant zone that absorbs mechanical stress and protects the fragile diaphragm and bonding interfaces from overload during assembly and operation, preventing damage before it occurs.
Solution Approach 2:
The sensor employs composite construction with the silicon diaphragm, metal strain gauges, and the tolerance trench structure working together. The trench acts as a mechanical composite feature that combines rigidity where needed with compliance for stress absorption, enhancing overall robustness while maintaining electrical connection capability.
3Ease of manufacture
If conventional MEMS force dies lack sealing structure, then fabrication is simpler, but the device is susceptible to debris from the external environment
Solution Approach 1:
The tolerance trench segments the sensor die into a sealed internal cavity and the external environment. This trench structure serves as a barrier that prevents debris penetration while allowing the interior to be sealed, protecting the sensitive diaphragm and strain gauges from environmental contamination without significantly complicating the fabrication process.
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 design results in a small, robust, and cost-effective MEMS force sensor with improved sensitivity and resistance to mechanical overload, capable of precise force measurement and protection from external debris.
Implementation Method 1
four piezoresistive strain gauges formed thereon
Implementation Method 2
silicon fusion bonding and etching techniques
Data Source
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AI summary
An example MEMS force sensor is described herein. The MEMS force sensor can include a cap for receiving an applied force and a sensor bonded to the cap. A trench and a cavity can be formed in the sensor. The trench can be formed along at least a portion of a peripheral edge of the sensor. The cavity, which can be sealed between the cap and the sensor, can define an outer wall and a flexible sensing element, and the outer wall can be arranged between the trench and the cavity. The sensor can also include a sensor element formed on the flexible sensing element. The sensor element can change an electrical characteristic in response to deflection of the flexible sensing element.