SnO2–WO3 Porous Gas Sensor for Low-Level NO Detection
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Solution Overview
Problem
Existing metal oxide semiconductor gas sensors are unable to detect nitric oxide (NO) at concentrations of 1 ppm or less efficiently and cost-effectively.
Innovation Solution
A metal oxide semiconductor gas sensor with a sensing layer composed of SnO2 and WO3, having a specific porosity range of 16.0% to 22.0%, a pore size of 70 nm to 150 nm, and a thickness of 1.0 um, with a porosity gradient satisfying φf - φn ≥ 1.0, enhances sensitivity and responsiveness to NO.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a metal oxide semiconductor gas sensor is used to detect NO at low concentrations, then the structure becomes small and simple, but the detection sensitivity at 1 ppm or less is insufficient
Solution Approach 1:
The sensing layer uses a composite material consisting of SnO2 and WO3 in specific volume ratios (SnO2: 60-80 vol%, WO3: 20-40 vol%). This composite structure combines the advantages of both materials to achieve high detection sensitivity for NO at concentrations of 1 ppm or less, while maintaining the simplicity of the metal oxide semiconductor sensor structure.
Solution Approach 2:
The invention introduces a porosity gradient within the sensing layer, where the porosity varies from the electrode interface toward the gas exposure surface. Specifically, the porosity increases from the electrode side to the gas exposure side, creating different local properties: the lower porosity near electrodes ensures good electrical contact, while the higher porosity at the gas exposure surface enhances gas diffusion and sensing sensitivity.
2Productivity
If the sensing layer porosity is increased to improve gas diffusion, then the responsiveness improves, but the mechanical strength and structural stability deteriorate
Solution Approach 1:
The invention optimizes the porosity parameter within a specific range (16.0% to 22.0%) and implements a porosity gradient distribution. This controlled parameter change ensures sufficient porosity for gas diffusion and responsiveness while maintaining structural integrity. The gradient distribution specifically addresses the contradiction by having lower porosity (better strength) near electrodes and higher porosity (better gas diffusion) at the gas exposure surface.
3Measurement precision
If the sensing layer thickness is increased to improve detection sensitivity, then the sensitivity improves, but the response time increases
Solution Approach 1:
The porosity gradient structure creates different functional zones within the sensing layer thickness. The region near the gas exposure surface has higher porosity for rapid gas diffusion and quick response, while the region near the electrodes has lower porosity for good electrical contact and signal transmission. This local differentiation allows the layer to achieve both high sensitivity and fast response time simultaneously.
Solution Approach 2:
The SnO2-WO3 composite material system provides synergistic effects that enhance detection sensitivity per unit thickness. The specific volume ratios (SnO2: 60-80 vol%, WO3: 20-40 vol%) create a composite structure with optimized electronic and gas interaction properties, allowing thin layers to achieve high sensitivity without sacrificing response speed.
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 sensor can detect NO at concentrations as low as 1 ppm with high sensitivity and responsiveness, suitable for applications such as home healthcare, while maintaining cost-effectiveness.
Implementation Method 1
a sensing layer 4 in contact with both the first electrode 2 and the second electrode 3. The sensing layer 4 includes pores so as to have an average porosity of 16.0% or more and 22.0% or less in addition to a metal oxide material.
Data Source
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AI summary
A metal oxide semiconductor gas sensor includes a first electrode, a second electrode, and a sensing layer in contact with the first electrode and the second electrode. The sensing layer includes SnO2 and WO3. A cross section of the sensing layer has an average porosity of 16.0% or more and 22.0% or less. SnO2 occupies 60 vol% or more and 80 vol% or less and WO3 occupies 20 vol% or more and 40 vol% or less in the sensing layer provided that pores are not counted as part of the sensing layer.