Capacitive Pressure Sensor Recessed Diaphragm
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Solution Overview
Problem
Conventional capacitive pressure sensors face challenges in optimizing performance while maintaining competitive manufacturing costs, particularly due to residual stress and stiction issues during fabrication, which affect sensitivity and require complex bonding processes.
Innovation Solution
The design incorporates a recessed diaphragm structure within a cavity of a substrate, avoiding bonding interface stresses and simplifying the fabrication process by eliminating wet etching and stiction problems, using a contoured cavity and spring structures to enhance sensitivity and reduce acoustic noise, and employing isolation layers to minimize leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bonding processes are used to fabricate capacitive pressure sensors, then substrate bonding is achieved, but residual stress and stiction issues occur affecting sensitivity
Solution Approach 1:
The patent extracts the diaphragm structure from the bonding interface by forming it within a recessed cavity of the first substrate, away from the bonding surface. This separation eliminates the stiction and residual stress problems that occur when bonding interfaces contact the diaphragm, thereby maintaining bonding reliability while improving sensitivity
Solution Approach 2:
The patent introduces a vertical dimension by creating a recessed cavity into the substrate, positioning the diaphragm at a different depth level than the bonding interface. This three-dimensional arrangement allows the bonding process to occur at the surface level while the diaphragm operates independently within the cavity, resolving the conflict between bonding reliability and sensitivity
2Strength
If complex bonding processes are used to ensure substrate bonding, then bonding strength is achieved, but fabrication complexity increases
Solution Approach 1:
By extracting the diaphragm formation process from the bonding sequence and placing it within a pre-formed recessed cavity, the patent allows bonding to occur independently without requiring complex protective measures for the diaphragm, thereby maintaining bonding strength while reducing fabrication complexity
Solution Approach 2:
The recessed cavity is formed in the first substrate before bonding occurs. This preliminary action creates a protective structure that naturally shields the diaphragm during subsequent bonding processes, eliminating the need for additional complex fabrication steps while ensuring bonding strength
3Shape
If wet etching is used in fabrication, then cavity formation is achieved, but stiction problems occur
Solution Approach 1:
The patent converts the potential harm of wet etching by using it to create the recessed cavity structure that ultimately protects against stiction. The etching process forms the cavity with specific geometric features that prevent capillary action and liquid bridging, thereby transforming a potentially problematic process into a beneficial structural feature
4Ease of manufacture
If flat diaphragm structure is used, then fabrication is simplified, but sensitivity is reduced
Solution Approach 1:
The patent applies curvature to the diaphragm surface within the recessed cavity, creating a contoured or curved diaphragm structure that enhances sensitivity to pressure changes. This curved geometry increases the deflection response to applied pressure while still being compatible with standard fabrication processes, thereby improving sensitivity without significantly complicating manufacturing
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 improves sensitivity, reduces acoustic noise, and simplifies the fabrication process, leading to higher performance and lower manufacturing costs for capacitive pressure sensors.
Implementation Method 1
a movable plate at a bottom of a first cavity recessed into the substrate from the first surface
Implementation Method 2
The second substrate includes a fixed plate disposed over the movable plate to form a capacitor
Data Source
AI summary
Aspects of the disclosure provide a capacitive pressure sensor. The capacitive pressure sensor can include a first substrate having a first surface and a second surface, a movable plate at a bottom of a first cavity recessed into the substrate from the first surface, and a second substrate bonded to the first substrate over the first surface. A second cavity is formed between the movable plate and the second surface. The second substrate includes a fixed plate disposed over the movable plate to form a capacitor. The second substrate further includes a third cavity between a surface of the fixed plate opposite to the movable plate and a surface of the second substrate opposite to the first substrate.