Micro-machined Cap Layer for Thermal Conductivity Sensor Sensitivity
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Solution Overview
Problem
Existing thermal conductivity sensors face challenges in sensitivity due to the close thermal conductivity values between target gases and reference gases, leading to inefficient heat transfer and reduced sensor sensitivity.
Innovation Solution
The thermal conductivity sensor incorporates a micro-machined cap layer with a second gap between the cap layer and the dielectric membrane, allowing for precise control of the heat transfer path and increasing the percentage of heat transferred through the gas, thereby enhancing sensor sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional sensor structure without a micro-machined cap layer is used, then the manufacturing process is simpler, but the heat transfer efficiency through the gas is insufficient and sensor sensitivity is reduced
Solution Approach 1:
The device is segmented into distinct functional layers including a micro-machined cap layer, dielectric membrane with heater, and substrate portion. The cap layer is separated from the dielectric membrane by a precisely controlled second gap, creating distinct thermal pathways that segment the heat transfer process and improve gas thermal conductivity measurement sensitivity.
Solution Approach 2:
A second gap is introduced in the vertical dimension between the cap layer and dielectric membrane, creating a new thermal pathway dimension. This additional dimensional space allows optimized heat transfer through the gas phase, enhancing the sensor's ability to detect gas thermal conductivity changes.
2Adaptability or versatility
If the thermal conductivity of target gas is close to that of reference gas, then the sensor can measure a broader range of gases, but the heat transfer efficiency decreases and sensitivity is reduced
Solution Approach 1:
The thermal conductivity measurement parameters are enhanced by introducing the micro-machined cap layer and optimizing the second gap dimensions. This structural parameter change increases the heat transfer efficiency through the gas, amplifying the sensitivity response even when target gas thermal conductivity is close to reference gas thermal conductivity.
Solution Approach 2:
The sensor employs a composite structure combining the micro-machined cap layer (potentially metallic or high thermal conductivity material) with the dielectric membrane and gas medium. This composite architecture creates optimized thermal pathways that enhance the detection capability for gases with similar thermal conductivity values.
3Measurement precision
If the second gap thickness is reduced to increase heat transfer through gas, then sensor sensitivity increases, but manufacturing precision requirements become more stringent
Solution Approach 1:
The micro-machined cap layer is formed with the second gap dimensions predetermined during the fabrication process. By performing the micro-machining operation in advance with precise control, the optimal gap thickness is achieved without requiring post-fabrication adjustments, balancing sensitivity enhancement with manufacturing 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 implementation of a micro-machined cap layer significantly increases the sensitivity of the thermal conductivity sensor by optimizing heat transfer through the gas, even when the thermal conductivity of the target gas is close to that of the reference gas.
Implementation Method 1
The cap layer can provide a route for heat transfer from the heater through the gas and to the ambient, so allowing to increase the percentage of heat transferred through the gas
Implementation Method 2
the distance between the dielectric membrane and the cap layer surface (i.e. the thickness of the second gap) is within the distance of the device thermal boundary layer
Data Source
AI summary
A thermal conductivity sensor for measuring a concentration of a gas, the sensor comprising: a substrate portion; a dielectric layer comprising a dielectric membrane, wherein the dielectric membrane is provided with a heater; a first gap between the substrate portion and the dielectric membrane wherein the primary dielectric membrane is located above the first primary gap; and a micro-machined cap layer; a second gap located between the cap layer and the dielectric membrane. A method of manufacturing a thermal conductivity sensor is also described.