MEMS Pressure Sensor Trenches and Floating Electrode
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Solution Overview
Problem
Existing micromechanical pressure sensors face inaccuracies and mounting issues due to mechanical forces caused by temperature changes and external temperature variations, leading to thermal mismatch and mechanical stress.
Innovation Solution
The introduction of trenches around mechanical contact areas and the design of a floating bottom electrode, along with elongated sensor structures, to alleviate thermal mismatch and mechanical stress, allowing the bottom electrode to act as a sensing element and reducing mechanical contact points, thereby enhancing sensitivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the sensor is mounted to a frame or PCB-board, then mechanical connection and structural support are achieved, but mechanical stresses and thermal mismatch occur between the sensor and the mounting structure
Solution Approach 1:
The patent divides the mounting structure into separate functional zones: a rigid frame for structural support and a flexible membrane for sensing. The membrane is selectively attached to the frame at specific regions, creating a segmented connection that allows differential movement and reduces stress transmission to the sensing elements.
Solution Approach 2:
The patent applies different mechanical properties to different regions of the mounting structure. The frame maintains high rigidity for structural integrity, while the membrane regions have tailored flexibility to accommodate thermal expansion differences. This local differentiation of mechanical properties reduces overall stress while maintaining necessary connection strength.
2Stability of the object's composition
If the sensor structure is rigidly attached to eliminate movement, then mounting stability is improved, but thermal mismatch stresses increase due to temperature changes
Solution Approach 1:
The patent transitions from a static rigid mounting to a dynamic mounting system where the membrane can flex and deform in response to thermal changes. This dynamic capability allows the structure to adapt to temperature variations while maintaining stable sensor operation, as the membrane absorbs thermal stresses through controlled deformation rather than transmitting them to the sensing elements.
3Strength
If the bottom electrode is fixed to the substrate, then structural support is provided, but mechanical stresses interfere with the sensing function
Solution Approach 1:
The patent extracts the bottom electrode from direct mechanical connection to the substrate, releasing it from fixed mounting. This allows the bottom electrode to move independently with the membrane during pressure sensing, eliminating parasitic stresses that would otherwise interfere with the capacitive measurement. The electrode is held only by its electrical connections, which are sufficiently flexible to accommodate the mechanical motion.
4Strength
If mechanical contact areas are increased for better mounting, then connection strength is improved, but thermal mismatch and mechanical stresses increase
Solution Approach 1:
The patent segments the mechanical contact areas into specific localized regions rather than using large continuous contact surfaces. The membrane is attached to the frame at discrete points or regions that provide sufficient mechanical support while minimizing the total area subject to thermal mismatch stresses. This segmentation reduces the cumulative thermal stress while maintaining adequate connection strength.
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 significantly reduces mechanical stresses within the micromechanical structure and between the sensor and its mounting frame, improving sensitivity and long-term stability by isolating the sensor from thermal and mechanical influences.
Implementation Method 1
The pressure is detected in the change of capacitance between the top and bottom electrodes caused by bending of at least one of the electrodes
Implementation Method 2
The invention is based on that the micromechanical structure includes weakenings like trenches around the mechanical contact areas for eliminating the thermal mismatch between the active element of the micromechanical structure and the other structures
Data Source
AI summary
The present publication discloses a micromechanical structure including at least one active element, the micromechanical structure comprising a substrate, at least one layer formed on the substrate forming the at least part of the at least one active element, mechanical contact areas through which the micromechanical structure can be connected to other structures like printed circuit boards and like. In accordance with the invention the micromechanical structure includes weakenings like trenches around the mechanical contact areas for eliminating the thermal mismatch between the active element of the micromechanical structure and the other structures.