Humidity Sensor Diaphragm Thermal Isolation and Periodic Heating
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Solution Overview
Problem
Existing humidity sensors face challenges in providing fast and accurate measurements with minimal hysteresis while reducing power consumption, particularly in capacitive and resistive types that rely on water absorption and desorption properties of sensing materials.
Innovation Solution
The design incorporates a substrate with a recess forming a diaphragm, surrounded by a trench filled with thermally insulating material, featuring a resistive heater element and sensing electrodes with a sensing material that changes electrical properties in response to moisture, allowing for efficient humidity sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a resistive heater element is used to desorb water quickly, then measurement speed is improved, but power consumption increases
Solution Approach 1:
The heater element is activated periodically rather than continuously - turning on during measurement cycles to desorb water and turn off during idle periods. This periodic operation maintains fast measurement capability while significantly reducing average power consumption compared to continuous heating.
Solution Approach 2:
The heater element performs preliminary desorption of water from the sensing material before each measurement cycle begins. This preliminary action ensures the sensing material is in a ready state for immediate measurement, reducing the overall measurement time without requiring continuous high power consumption.
2Measurement precision
If the sensing material is heated to desorb water, then measurement accuracy is improved, but hysteresis increases
Solution Approach 1:
The heating is applied locally and selectively to the sensing material region through the heater element positioned directly beneath it. This localized heating ensures uniform desorption across the sensing area without creating thermal gradients that cause hysteresis, while maintaining measurement accuracy.
Solution Approach 2:
The patent replaces mechanical/thermal desorption methods with an electric field-based approach using the heater element to control water desorption. This substitution allows precise control of the desorption process, achieving accurate measurements while minimizing hysteresis effects through electrical rather than purely thermal means.
3Measurement precision
If the diaphragm is thermally isolated from the substrate, then sensing accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
An insulating layer is introduced as an intermediary between the diaphragm and the substrate to provide thermal isolation. This intermediate layer blocks heat transfer paths while maintaining the structural integrity of the device, achieving sensing accuracy without requiring complex thermal management structures.
Solution Approach 2:
The device structure is segmented into distinct functional layers with the insulating layer separating the diaphragm region from the substrate. This segmentation allows independent optimization of thermal properties for the sensing region while maintaining overall structural simplicity and ease of 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 configuration enables fast, accurate, and low-power humidity measurements with reduced hysteresis, improving the performance of humidity sensors.
Implementation Method 1
Some humidity sensors, such as capacitive and resistive type humidity sensors, rely on the ability of a sensing material to quickly absorb and desorb water. The absorbed water may alter measurable properties of the sensing material.
Implementation Method 2
Heaters may be used to more quickly desorb water between measurements.
Implementation Method 3
A trench in the second substrate extends around or substantially around the diaphragm and is at least partially filled with a thermally insulating material such as an oxide to help thermally isolate the diaphragm from a remainder of the second substrate.
Data Source
AI summary
A humidity sensor may include a first substrate having a recess formed in a first side, a second substrate and an insulating layer supported by the second substrate. The second substrate and the insulating layer may be supported by the first side of the first substrate and extend over the recess to form a diaphragm with the insulating layer facing the recess. The diaphragm may be at least partially thermally isolated from a remainder of the second substrate. A resistive heater element may be supported by the diaphragm. A pair of sensing electrodes are electrically separated from each other and supported by the diaphragm. A sensing material is disposed over the pair of sensing electrodes, wherein an electrical property of the sensing material changes in response to a change in moisture content of the sensing material.