Humidity Sensor with Halogenated Surface Layer
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Solution Overview
Problem
Capacitive and resistive humidity sensors using bulk polyimide films exhibit significant hysteresis and slow response times due to adsorption, absorption, and desorption properties, necessitating a solution for reduced hysteresis and faster response times.
Innovation Solution
A humidity sensor design featuring a polymeric humidity sensing layer with a halogenated layer, such as fluorinated polyimide, and a substrate with electrode layers that include openings to increase the effective surface area, reducing hysteresis and enhancing response speed through halogenation and surface modification processes like plasma deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bulk polyimide films are used as humidity sensing material, then the sensor structure is simple and easy to manufacture, but the sensor exhibits significant hysteresis and slow response time
Solution Approach 1:
The patent applies local quality by modifying only the surface layer of the polyimide film with halogenated materials (fluorinated, chlorinated, or brominated compounds) rather than changing the entire bulk material. This creates a differentiated structure where the surface layer provides hydrophobicity to reduce hysteresis, while the bulk polyimide maintains its sensing functionality and ease of manufacture.
Solution Approach 2:
The patent creates a composite humidity sensing material by combining bulk polyimide with surface-modified halogenated layers. This composite structure integrates the advantages of both components: the polyimide provides structural integrity and sensing response, while the halogenated surface layer provides hydrophobicity to minimize hysteresis effects.
2Device complexity
If bulk polyimide films are used as humidity sensing material, then the sensor structure is simple, but the response time is relatively large
Solution Approach 1:
The surface modification with halogenated materials creates a hydrophobic layer that accelerates water molecule desorption from the sensing material surface. This local property change at the surface interface significantly reduces the time required for the sensor to respond to humidity changes without complicating the overall device structure.
3Measurement precision
If the polyimide humidity sensing layer is fluorinated to a depth less than the thickness of the layer, then the sensor achieves reduced hysteresis and faster response time, but the manufacturing process becomes more complex
Solution Approach 1:
The patent controls the fluorination depth parameter to be less than the total thickness of the polyimide layer, creating an optimized gradient structure. By adjusting this parameter (fluorination depth), the process achieves the desired hydrophobic surface properties while maintaining the bulk sensing characteristics, balancing performance improvement with process feasibility.
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 proposed solution achieves a significantly reduced hysteresis of 1% or less and faster response times, improving the sensitivity and accuracy of humidity sensing by making the sensor more hydrophobic and less susceptible to hysteresis effects.
Implementation Method 1
A halogenated layer may adjoin the non-halogenated humidity sensing layer... the sensing surface of the polyimide humidity sensing layer may be fluorinated to a depth that is less than the thickness of the polyimide humidity sensing layer
Implementation Method 2
making the sensor more hydrophobic and less susceptible to hysteresis effects
Implementation Method 3
Capacitive and resistive type humidity sensors rely on the ability of the sensing material to quickly absorb and desorb water molecules. The absorbed moisture changes the physical properties of the sensing material either by changing its resistance, permittivity, or stress
Implementation Method 4
The absorbed moisture changes the physical properties of the sensing material either by changing its resistance, permittivity, or stress
Implementation Method 5
the electrode layer may define a first capacitive plate and a second capacitive plate
Data Source
AI summary
Humidity sensors may exhibit a relatively small amount of hysteresis and/or a faster response time. In some cases, a humidity sensor may include a polymeric humidity sensing layer disposed over an electrode layer. The polymeric humidity sensing layer may include a halogenated layer disposed over the polymeric humidity sensing layer. The polymeric humidity sensing layer may, for example, include a polyimide and the halogenated layer may include a monolayer or less than a monolayer of a halogenated material such as a fluorinated material.