Capacitive Humidity Sensor with Differential Electrode Gaps
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Solution Overview
Problem
Capacitive humidity sensors with detection and reference capacitive devices on the same substrate face challenges in improving sensitivity while minimizing size, as the presence of humidity-sensitive films in both devices reduces sensitivity and increases size due to the need for larger electrode gaps for optimal performance.
Innovation Solution
The capacitive humidity sensor design includes detection and reference capacitive devices with humidity-sensitive films made from the same material and thickness, where the electrode gaps are set to maximize the sensitivity ratio of the detection device while minimizing the size by keeping the reference device's electrode gap smaller than the peak value, thereby enhancing sensitivity and reducing overall sensor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the electrode gap is increased to optimize sensitivity ratio, then the sensitivity improves, but the sensor size increases
Solution Approach 1:
The patent applies different electrode gap dimensions to different functional regions: the detection capacitive device uses a first electrode gap optimized for sensitivity (0.5-2.0 μm), while the reference capacitive device uses a second electrode gap optimized for size reduction (0.1-0.5 μm). This local differentiation allows each region to operate at its optimal performance point without compromising the other.
Solution Approach 2:
The sensor is segmented into two distinct capacitive devices with independently optimized parameters. The detection device and reference device are structurally separated and functionally differentiated, allowing the electrode gaps to be independently controlled. This segmentation enables the detection device to achieve high sensitivity while the reference device maintains compact dimensions.
2Measurement precision
If the reference capacitive device has no humidity-sensitive film, then the sensitivity improves, but the reliability deteriorates due to electrode deterioration
Solution Approach 1:
The humidity-sensitive film is selectively applied only to the detection capacitive device, creating a local quality difference between the detection and reference regions. The detection device has both the humidity-sensitive film and protection film for optimal sensitivity, while the reference device has only the protection film to maintain electrode stability and prevent deterioration.
Solution Approach 2:
The humidity-sensitive film is extracted from the reference capacitive device structure, leaving only the protection film. This extraction eliminates the sensitivity-reducing effect in the reference device while maintaining the protective function against electrode deterioration. The reference device thus serves as a stable baseline without the interfering humidity response.
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 the sensitivity of the capacitive humidity sensor while reducing its size by optimizing the electrode gaps and maintaining the humidity-sensitive films' protective and capacitive properties, effectively addressing the trade-off between sensitivity and size in existing designs.
Implementation Method 1
A relative permittivity of the detection humidity-sensitive film changes when the detection humidity-sensitive film absorbs water
Implementation Method 2
a capacitive humidity sensor includes a detection capacitive device and a reference capacitive device formed on the same substrate. A capacitance of the detection capacitive device changes with a change in ambient humidity
Data Source
AI summary
A humidity sensor includes a detection device with a capacitance changing with humidity at a first ratio and a reference device with a capacitance changing with humidity at a second ratio smaller than the first ratio. The detection device has detection electrodes facing each other with a first gap and a detection humidity-sensitive film covering the detection electrodes. The reference device has reference electrodes facing each other with a second gap and a reference humidity-sensitive film covering the reference electrodes. The detection humidity-sensitive film and the reference humidity-sensitive film are made from the same material and have the same thickness. The detection electrodes and the reference electrodes are made from the same material and have the same width and thickness. The second ratio peaks when the second gap is equal to a predetermined value. The second gap is smaller than the first gap and the predetermined value.