MEMS Pressure Sensor Stress Isolation via Suspenders
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Solution Overview
Problem
Thermally-mismatched mechanical stress and vibrational dynamic stress adversely affect the accuracy of MEMS pressure sensing elements, leading to inaccuracy and noise in pressure measurements.
Innovation Solution
The use of flexible, electrically conductive suspenders formed from the same semiconductor material as the MEMS pressure sensing element, which are doped to provide mechanical support and signal pathways, and overlaid with a viscous gel to dampen vibrational stress, along with a stress-isolated design that includes a vacuum cavity and piezoresistors forming a Wheatstone bridge circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MEMS pressure sensing element is directly mounted on the support structure, then the device complexity is reduced, but thermally-mismatched mechanical stress and vibrational dynamic stress adversely affect the sensing element accuracy
Solution Approach 1:
The device is segmented into distinct functional modules: the MEMS pressure sensing element is separated from the support structure by compliant suspenders, and the sensing element is further isolated within a recessed cavity. This segmentation allows each component to perform its specific function while minimizing stress transmission, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
Compliant suspenders act as intermediary elements between the support structure and the MEMS pressure sensing element. These suspenders mechanically decouple the sensing element from thermally-mismatched stress and vibrational dynamic stress while maintaining positional stability and electrical connectivity, thereby improving pressure sensing accuracy without excessive complexity.
2Reliability
If compliant suspenders are used to support the MEMS pressure sensing element, then thermal and vibrational stress is reduced, but the device complexity increases
Solution Approach 1:
The compliant suspenders are designed to perform multiple functions simultaneously: they provide mechanical support for the MEMS pressure sensing element, isolate thermal stress, dampen vibrational dynamic stress, and maintain electrical connectivity. This multi-functionality improves reliability while minimizing the increase in device complexity by consolidating multiple requirements into a single component.
3Measurement precision
If the MEMS pressure sensing element is isolated in a recess with viscous gel overlay, then vibrational dynamic stress is dampened, but manufacturing complexity increases
Solution Approach 1:
The MEMS pressure sensing element is pre-positioned within a recessed cavity and surrounded by viscous gel before final assembly. This beforehand cushioning approach provides vibrational damping protection during the manufacturing process and operational phases, reducing vibrational dynamic stress without requiring complex post-assembly adjustments or specialized manufacturing equipment.
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 solution significantly reduces thermal and vibrational noise, enhancing the accuracy and reliability of MEMS pressure sensing by isolating mechanical stress and improving signal transmission.
Implementation Method 1
overlaid with a viscous gel to dampen vibrational stress
Implementation Method 2
piezoresistors forming a Wheatstone bridge circuit
Data Source
Figure 1A
Figure 1B~2
Figure 3
AI summary
Suspending a microelectromechanical system (MEMS) pressure sensing element inside a cavity using spring-like corrugations or serpentine crenellations, reduces thermally-mismatched mechanical stress on the sensing element. Overlaying the spring-like structures and the sensing element with a gel further reduces thermally-mismatched stress and vibrational dynamic stress.