Capacitive Pressure Sensor Bonding and Electrode Design
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Solution Overview
Problem
Existing capacitive pressure difference sensors face challenges with sensitivity, resolution, linearity, and overload protection due to complex structures, large dimensions, and difficulties in reducing the constant capacitor value, which affects measurement accuracy and suitability for small spaces.
Innovation Solution
A capacitive pressure difference sensor is designed using a three-layer wafer bonding method with metal eutectic bonding, featuring intrinsic silicon and silicon oxide layers, and patterned doped silicon, which allows for adjustable capacitance values and improved linearity, sensitivity, and overload protection by optimizing the spacing and contact area between capacitor plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick ceramic layer is used as an insulating layer to ensure spacing between electrodes, then bonding reliability is improved, but device dimension increases and suitability for small spaces deteriorates
Solution Approach 1:
The patent changes the insulating layer material from ceramic to silicon oxide, and adjusts the thickness parameter to 1-10μm (optimally 3-7μm), achieving both reliable bonding and compact dimensions suitable for small spaces
Solution Approach 2:
The patent uses a composite structure combining silicon oxide insulating layer with metal eutectic bonding layers (such as Au-Sn or Cu-Sn), creating a multi-layer composite that provides both electrical insulation and mechanical bonding strength
2Measurement precision
If the constant capacitor value is reduced by extending electric field line path and reducing cross-sectional area, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent transitions from planar capacitor structure to three-dimensional stacked capacitor structure by forming upper and lower capacitors above and below the intermediate-layer movable diaphragm, effectively utilizing vertical space to reduce constant capacitor value without increasing lateral complexity
3Strength
If silicon-silicon direct bonding or anode bonding is used to ensure cavity air tightness, then bonding strength is improved, but manufacturing process difficulty increases
Solution Approach 1:
The patent introduces metal eutectic bonding layers (such as Au-Sn or Cu-Sn) as intermediary bonding layers between silicon wafers, which serve as mediators to achieve strong bonding with lower process difficulty compared to direct silicon-silicon bonding or anode bonding
4Ease of manufacture
If pressure guide holes are located directly above and below the center of the intermediate-layer movable diaphragm, then manufacturing simplicity is improved, but overload protection capability deteriorates
Solution Approach 1:
The patent positions pressure guide holes asymmetrically at offset locations rather than directly at the center, creating an asymmetric layout that provides overload protection by preventing excessive diaphragm displacement while maintaining manufacturing simplicity through standardized hole positioning
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 enhances sensitivity, resolution, and linearity while providing stronger overload protection and a simpler lead structure, making it suitable for small spaces and improving measurement accuracy.
Implementation Method 1
A manner of the bonding is metal eutectic bonding; the metal eutectic bonding includes an upper metal bonding layer and a lower metal bonding layer
Implementation Method 2
a pressure difference between the two pressure cavities makes the intermediate-layer movable diaphragm shift to a side thereof with a weak pressure
Implementation Method 3
The upper electrode and the lower electrode respectively form two capacitors with the intermediate-layer movable diaphragm. The shifting of the intermediate-layer movable diaphragm makes a spacing between the intermediate-layer movable diaphragm and an electrode with a weak pressure side decrease and makes a spacing between the intermediate-layer movable diaphragm and an electrode with a strong pressure increase. Correspondingly, one of capacitances of two capacitors on both sides of the intermediate-layer movable diaphragm becomes larger, and the other becomes smaller, which results in a capacitance difference
Data Source
AI summary
Provided are a pressure difference sensor, and a manufacturing method and an application thereof. A manner of bonding three layers of wafers is adopted, and the sensor includes an upper structure, an intermediate structure and a lower structure. Each of the upper structure and the intermediate structure is manufactured by a silicon-on-insulator (SOI) wafer, the lower structure is manufactured by patterned doped intrinsic silicon; and a lead pad of each of the upper electrode, and the intermediate electrode and the lower electrode is located on a corresponding one of three-stepped steps at a side of the pressure difference sensor. Annular through holes are formed around the upper electrode and the lower electrode. A constant capacitance of a capacitance signal outputted by an upper capacitor of the sensor by extending an electric field line path of the constant capacitor part.