Thermal Conductivity Sensor Gap Control via Sacrificial Layer
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Solution Overview
Problem
Existing thermal conductivity sensors face challenges in achieving high sensitivity when measuring gas concentrations, particularly when the thermal conductivity of the target gas is close to that of a reference gas, as the efficiency of heat transfer needs to be enhanced to ensure satisfactory sensitivity.
Innovation Solution
The thermal conductivity sensor comprises a substrate with a semiconductor layer, an intermediate layer, and a dielectric membrane with a heater. The sensor features a precisely controlled gap between the membrane and the substrate, which enhances heat transfer efficiency by allowing a very small and uniform gap, thereby increasing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gap between the membrane and substrate is made very small to increase heat transfer efficiency, then sensitivity is improved, but manufacturing precision becomes more difficult to control
Solution Approach 1:
A sacrificial layer is introduced as an intermediary element between the membrane and substrate. This layer is deposited with controlled thickness and then selectively removed to create the gap. The sacrificial layer acts as a temporary mediator that enables precise gap formation without requiring direct precision control during final assembly, resolving the contradiction between small gap size and manufacturing feasibility
Solution Approach 2:
The gap is formed through preliminary action by depositing and then removing the sacrificial layer before final device operation. This preliminary removal creates the precise gap geometry needed for high heat transfer efficiency, while the gap thickness is predetermined by the sacrificial layer thickness rather than requiring precision control during final assembly
2Measurement precision
If the gap thickness is precisely controlled to increase heat transfer through gas, then sensitivity improves, but the risk of membrane contact with substrate increases
Solution Approach 1:
The sacrificial layer serves as a mediator that defines the gap thickness. By controlling the sacrificial layer thickness, the minimum safe gap distance is established, preventing membrane contact while maintaining sufficiently small gap for high heat transfer efficiency. The mediator approach decouples the conflicting requirements of small gap size and adequate separation margin
Solution Approach 2:
The gap thickness parameter is precisely controlled through control of the sacrificial layer deposition parameters. By changing the sacrificial layer thickness parameter, the optimal balance between heat transfer efficiency (requiring small gap) and membrane separation reliability (requiring adequate gap margin) is achieved
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 precise control of the gap thickness in the thermal conductivity sensor significantly increases the percentage of heat transferred through the gas, leading to improved sensitivity and reliability while ensuring manufacturing precision.
Implementation Method 1
increase the percentage amount of heat transferred through the gas in the gap, from the heater and through the membrane, to the surface of the gap opposite to the membrane
Data Source
AI summary
A thermal conductivity sensor for measuring a concentration of a gas, the sensor comprising: a substrate portion; an intermediate layer disposed on the substrate portion; a semiconductor layer disposed on the intermediate layer, and a dielectric layer comprising a dielectric membrane, the dielectric membrane provided with a heater; wherein the dielectric membrane is located over a gap, the gap being located in the semiconductor layer. Methods for manufacturing a thermal conductivity sensor are also described.