Capacitive Pressure Sensor Segmented Electrodes Parasitic Capacitance
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Solution Overview
Problem
Conventional capacitive pressure sensors face issues with parasitic capacitance acting as noise during pressure detection, limiting their ability to measure micro-pressure and realizing a micro-sensor due to the expansion of the polycrystalline silicon film over the cavity and the need for thick silicon oxide and nitride films.
Innovation Solution
A capacitive pressure sensor design featuring a substrate with a first insulating film, a cavity, a second insulating film with openings, a conductive sealing film in an anchor shape to seal the cavity, and an upper electrode electrically separated from the sealing film, minimizing parasitic capacitance and reducing sensor thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the polycrystalline silicon film is expanded to cover the cavity area, then the electrode coverage is improved, but parasitic capacitance increases acting as noise
Solution Approach 1:
The electrode structure is segmented into two separate conductive layers: a bottom electrode layer formed before cavity formation, and a top electrode layer formed after cavity formation. This segmentation ensures that the electrodes only overlap in the intended sensing area above the cavity, eliminating parasitic capacitance from areas outside the cavity while maintaining sufficient coverage for effective pressure detection.
Solution Approach 2:
The bottom electrode is formed preliminarily before the cavity is created, allowing precise control of its position and area. This preliminary formation ensures that the electrode coverage is optimized for the final sensing configuration, preventing excessive coverage that would generate parasitic capacitance noise while ensuring adequate coverage for effective operation.
2Strength
If thick silicon oxide film is deposited to cover the electrode and bury openings, then structural integrity is improved, but sensor thickness increases limiting micro-sensor realization
Solution Approach 1:
The protective and insulating function is segmented across multiple thin layers rather than relying on a single thick layer. The structure uses alternating layers of silicon oxide and silicon nitride, where each layer contributes specific properties (insulation, stress compensation, protection), achieving structural integrity with reduced overall thickness compared to a single thick oxide layer.
Solution Approach 2:
The patent employs composite material structure with alternating layers of silicon oxide and silicon nitride. This composite approach combines the advantages of both materials: silicon oxide provides insulation and protection, while silicon nitride provides stress compensation and additional protection, achieving structural integrity with thinner overall thickness.
3Stability of the object's composition
If additional silicon nitride film is formed for stress compensation, then membrane stability is improved, but sensor thickness increases making micro-sensor realization more difficult
Solution Approach 1:
The stress compensation function is merged into the existing multi-layer structure by incorporating silicon nitride layers within the sequence of silicon oxide and silicon nitride alternating layers. This integration ensures that stress compensation is provided without requiring additional thickness beyond what is already needed for the protective and insulating structure.
Solution Approach 2:
The alternating composite structure of silicon oxide and silicon nitride layers provides both mechanical stability through stress compensation and electrical insulation, achieving membrane stability with minimal additional thickness. The intrinsic stress properties of silicon nitride are utilized to counterbalance the compressive stress of silicon oxide layers.
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 minimizes parasitic capacitance, allowing for accurate micro-pressure detection and the realization of a micro-sensor by limiting the cavity area affecting pressure detection and reducing the overall sensor thickness.
Implementation Method 1
a parallel plate capacitor is positioned between a silicon thin film membrane and a support. This capacitive pressure sensor uses the principle that the capacitance value varies as a gap between two electrodes changes by the deflection of a silicon thin film diaphragm (that is, deformation of the membrane) according to pressure applied from the outside
Implementation Method 2
The silicon nitride film 40 has the tensile stress property to compensate the compressive stress of the silicon oxide film 36
Data Source
AI summary
The capacitive pressure sensor comprises: a substrate functioning as a lower electrode; a first insulating film formed on the substrate; a cavity formed on the first insulating film; a second insulating film formed on the first insulating film to have openings communicated with the cavity and to cover the cavity; a sealing film formed of a conductive material to seal the openings and to extend partially into the cavity through the openings; and an upper electrode formed on the second insulating film to be electrically separated from the sealing film and to overlap the cavity.