All Silicon Capacitive Pressure Sensor Thermal Mismatch
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Solution Overview
Problem
Traditional capacitive pressure sensors face issues of thermal mismatch between materials and high parasitic capacitance, leading to accuracy errors and signal dilution.
Innovation Solution
An all-silicon capacitive pressure sensor design with an electrically isolated silicon sensing node minimizes thermal mismatch and reduces parasitic capacitance by using a silicon on insulator structure with a small, central gap, reducing the bond area and thus minimizing unwanted capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass electrode wafer is used for the second electrode, then electrical separation between electrodes is achieved, but thermal mismatch and thermal hysteresis occur reducing measurement precision
Solution Approach 1:
The patent uses an all-silicon construction where both the diaphragm and the second electrode are made of silicon material, eliminating the thermal mismatch between dissimilar materials. The silicon substrate serves as both the structural base and the electrode material, ensuring homogeneous thermal expansion properties throughout the device.
Solution Approach 2:
The patent replaces the glass electrode with a silicon-based electrode structure that copies the functional role of the glass electrode while using the same material as the substrate. This silicon electrode is formed through standard semiconductor fabrication processes, creating an electrically conductive layer on the silicon substrate that maintains electrical separation while matching thermal properties.
2Measurement precision
If silicon on insulator wafer with thin oxide dielectric is used for the second electrode, then thermal mismatch is avoided, but large parasitic capacitance occurs causing signal dilution
Solution Approach 1:
The patent removes the thick oxide dielectric layer that causes parasitic capacitance while retaining the essential silicon-silicon interface. By using a thin oxide layer or alternative isolation structures, the design extracts only the necessary electrical isolation function without the harmful capacitive effect of thick dielectric layers.
Solution Approach 2:
The patent changes the dielectric thickness parameter from thick to thin, fundamentally altering the capacitance characteristics. By reducing the oxide layer thickness to a minimal value, the parasitic capacitance is dramatically reduced while still providing sufficient electrical isolation between the diaphragm and the second electrode.
3Measurement precision
If diaphragm structure is used for capacitive pressure sensing, then pressure detection is enabled, but only the small central portion contributes to measurement while the rest creates parasitic capacitance
Solution Approach 1:
The patent segments the electrode structure into distinct functional zones: a central sensing area where the diaphragm interfaces with the second electrode for pressure measurement, and peripheral areas that are electrically isolated or structured to minimize parasitic capacitance. This segmentation allows the useful sensing area to be separated from the parasitic capacitance-generating areas.
Solution Approach 2:
The patent applies different structural qualities to different regions of the device. The central region maintains the diaphragm structure for pressure sensing, while the peripheral regions use different configurations (such as raised structures, different electrode patterns, or isolation structures) that minimize parasitic capacitance contribution while still providing structural support.
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 design enhances accuracy and reliability by eliminating thermal stress, reducing parasitic capacitance to less than 10% of base capacitance, and providing stable, high-performance pressure readings.
Implementation Method 1
When pressure is applied to a pressure diaphragm, the diaphragm deforms and the gap changes, allowing the pressure sensor to detect the pressure change
Implementation Method 2
the first electrode is separated from the second electrode by a dielectric layer
Implementation Method 3
Capacitive pressure sensors are made of two electrodes separated by a gap. When pressure is applied to a pressure diaphragm, the diaphragm deforms and the gap changes, allowing the pressure sensor to detect the pressure change
Data Source
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AI summary
A method of making a capacitive pressure sensor comprising depositing a nitride layer on a silicon on insulator wafer, etching a sensing node on a first side of the silicon on insulator wafer, etching primary and secondary cavities on a second side of the silicon on insulator wafer opposite the first side, selectively removing the protective nitride layer, bonding a sensing wafer to the first side of the silicon on insulator wafer opposite the second side, bonding a backing wafer to the sensing wafer opposite the silicon on insulator wafer and depositing metal onto the primary cavities.