Gas Sensor Heater Oxidation Prevention via Selective Sealing
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Solution Overview
Problem
Existing gas sensors face measurement errors due to oxidation of the heater, which is difficult to avoid for gas permeability, affecting sensitivity and selectivity, and also face challenges in moisture proofing.
Innovation Solution
A gas sensor structure with a silicon support, a cavity on the back side, a heater embedded in a dielectric layer on the front side, and a sealing layer on the back side covering the cavity, using materials like silicon nitride and polyamide to prevent moisture ingress and oxidation of the heater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heater is exposed for gas permeability, then gas sensing function is improved, but heater oxidation occurs causing measurement error
Solution Approach 1:
The device is divided into two functional regions: the cell region where the heater and sensing element are exposed to gas for sensing, and the peripheral region where the heater is protected from oxidation. This segmentation allows the heater to serve dual purposes - gas sensing in the cell region and oxidation protection in the peripheral region.
Solution Approach 2:
Different regions of the heater serve different functions: the portion in the cell region is exposed for gas permeability and sensing, while the portion in the peripheral region is protected from oxidation. The sealing layer is applied selectively to protect only the peripheral region heater from oxidation while maintaining gas access in the cell region.
2Volume of moving object
If the support structure is made thin for compact design, then device size is reduced, but wafer bending occurs
Solution Approach 1:
The stress characteristics of the sealing layer are utilized to counteract wafer bending. By selecting appropriate sealing layer materials and thickness (500-10000 angstroms), the layer provides compensating stress that prevents bending in thin supports, enabling compact design without sacrificing structural stability.
3Reliability
If the sealing layer is made thick for better moisture proofing, then moisture protection is improved, but device complexity and fabrication difficulty increase
Solution Approach 1:
Rather than making the entire heater structure thick for protection, the sealing layer is applied selectively only to the peripheral region where oxidation protection is needed. This partial application provides sufficient moisture proofing while minimizing fabrication complexity and maintaining device compactness.
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 solution provides improved moisture proofing and prevents heater oxidation, enhancing the accuracy and reliability of gas measurements while maintaining a compact design and reducing wafer bending issues.
Implementation Method 1
a sensitive film, a physical value of which is changed by adsorption, desorption or the like of a gas
Implementation Method 2
a heater is provided in the vicinity of the film and the temperature of the film is controlled to a specific temperature (300° C. to 500° C.)
Implementation Method 3
a sensitive film, a physical value of which is changed by adsorption, desorption or the like of a gas
Data Source
AI summary
The present invention provides a structure of a gas sensor, comprising: a support, having a front side, a back side opposite to the front side, a cell region, and a peripheral region circling the cell region; a cavity, formed on the back side of the support in the cell region; a heater, disposed on the front side of the support covering the cavity; a sensing element, disposed on the heater; and a sealing layer, formed on the back side of the support covering inside the cavity.