Porous Electrode Parallel Plate Capacitive Sensor
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Solution Overview
Problem
Capacitive humidity sensors face limited sensitivity due to a weak function of capacitance in relation to the sensing film permittivity, as most fields from the interdigitated capacitor do not pass through the sensing film, making it difficult to read relative humidity changes effectively.
Innovation Solution
A parallel plate capacitive sensor configuration is adopted with a porous top electrode to allow reagent gases to penetrate and interact with the sensing film, enhancing sensitivity by ensuring nearly all fields pass through the sensing film, and using inkjet printing to pattern the top electrode over a topographic surface, allowing for a permeable structure that facilitates gas diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an interdigitated capacitor configuration is used, then the sensor can be constructed with a planar structure, but most fields do not pass through the sensing film resulting in limited sensitivity
Solution Approach 1:
The patent inverts the traditional interdigitated capacitor configuration by placing one electrode above the sensing film and the other below it, creating a parallel plate structure. This inversion ensures that the electric field passes directly through the sensing film, maximizing sensitivity while maintaining manufacturability through standard semiconductor fabrication processes.
Solution Approach 2:
The patent transitions from a planar two-dimensional interdigitated configuration to a three-dimensional parallel plate structure with electrodes positioned on opposite sides of the sensing film. This dimensional change creates a vertical electric field that penetrates the sensing film completely, resolving the contradiction between ease of manufacture and measurement precision.
2Device complexity
If a non-porous electrode is used, then the electrode structure is simple, but reagent gases cannot penetrate to interact with the sensing film
Solution Approach 1:
The patent employs a porous top electrode that allows reagent gases to penetrate through it and reach the sensing film. The porous structure is achieved through standard semiconductor fabrication techniques such as etching or deposition of porous materials, maintaining electrode simplicity while enabling reliable gas interaction.
3Measurement precision
If a parallel plate configuration with porous electrode is used, then sensitivity and signal-to-noise ratio improve, but the fabrication process becomes more complex
Solution Approach 1:
The patent utilizes parameter changes in the fabrication process, such as controlling porosity levels, electrode thickness, and material composition, to optimize the parallel plate configuration. These parameter adjustments are achieved through standard semiconductor fabrication techniques, improving signal-to-noise ratio while managing fabrication complexity.
Solution Approach 2:
The patent employs composite materials, particularly porous conductive materials for the electrodes and specialized sensing films, to achieve the desired parallel plate configuration with optimal performance. These composite materials can be deposited using standard fabrication processes, balancing improved measurement precision with manageable device complexity.
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 configuration significantly improves the signal-to-noise ratio and reduces the sensor area by up to two orders of magnitude, simplifying circuit requirements and enhancing the sensitivity of the sensor, enabling more accurate humidity and gas detection.
Implementation Method 1
using inkjet printing to pattern the top electrode over a topographic surface, allowing for a permeable structure that facilitates gas diffusion
Implementation Method 2
Capacitive integrated circuit (IC) based gas/humidity sensors are typically constructed with a planar interdigitated capacitor, which is then covered by a sensing film that varies in electrical permittivity based on reagent exposure
Implementation Method 3
Changes in the electrical permittivity of the sensing film cause a change in the capacitance of the interdigitated capacitor as the fringing fields from the interdigitated capacitor pass through the sensing film
Data Source
AI summary
An integrated circuit (IC) with an impedance sensor fabricated on a surface of the substrate is disclosed. The impedance sensor includes a bottom conductive plate formed on the substrate. A sensing membrane is formed on the bottom conductive plate. A top conductive plate is formed on the sensing membrane, in which the top conductive plate is a fusion of conductive nanoparticles having a random three dimensional porosity that is permeable to a reagent.