WO3 Cr2O3 Diffuse p-n Junction Sensor for Breath NO Detection
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Solution Overview
Problem
Current gas sensors face challenges in achieving selectivity and sensitivity for nitric oxide (NO) detection in harsh environments, particularly in discriminating NO from other gases like carbon monoxide (CO), and are often bulky and inefficient for applications such as breath analysis.
Innovation Solution
A sensor system utilizing a diffuse p-n junction formed by adjacent WO3 and Cr2O3 regions, with electrodes connected to measure resistance changes, allowing for high sensitivity to NO at ppb levels while minimizing the effect of CO, even at concentrations several orders of magnitude higher, through a calibration curve correlation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gas sensors are used to detect NO, then sensitivity can be achieved, but selectivity against other gases like CO deteriorates
Solution Approach 1:
The sensor system is segmented into multiple independent sensing elements, each made from different metal oxide materials (e.g., SnO2, ZnO, TiO2, WO3) with distinct sensitivities to various gases. This segmentation allows the system to detect multiple gases simultaneously and discriminate between them through pattern recognition algorithms, resolving the contradiction between NO sensitivity and gas selectivity.
Solution Approach 2:
The invention employs composite material strategies by combining multiple metal oxide semiconductors with complementary gas sensing properties. Each oxide material responds differently to various gases, and their composite arrangement creates a fingerprint pattern that enables selective NO detection even in the presence of interfering gases like CO at higher concentrations.
2Measurement precision
If chemiluminescence analyzers are used for breath analysis, then high sensitivity to NO can be achieved, but device size and complexity increase
Solution Approach 1:
The invention replaces the complex mechanical chemiluminescence analyzer system with a solid-state electronic sensor array based on metal oxide semiconductors. This substitution maintains high NO detection sensitivity while dramatically reducing device size, eliminating the need for ozone generation systems, and enabling portable breath analysis applications.
Solution Approach 2:
The sensor array operates by detecting changes in electrical resistance or conductivity of metal oxide materials when exposed to different gases. By monitoring resistance changes across multiple oxide materials with different sensitivities, the system achieves ppb-level NO detection capability in a compact form factor, replacing the bulky chemiluminescence approach.
3Device complexity
If single metal oxide sensors are used, then simple structure can be maintained, but ability to discriminate against multiple gases deteriorates
Solution Approach 1:
Instead of using a single complex sensor, the invention segments the sensing function across multiple simple metal oxide elements. Each oxide material (SnO2, ZnO, TiO2, WO3, etc.) has a simple individual structure but collectively they provide complex discrimination capability through their different responses to various gases, maintaining structural simplicity while achieving high selectivity.
Solution Approach 2:
The metal oxide sensor array achieves multi-functionality by detecting and discriminating against hundreds of different molecules in breath using the same basic sensing mechanism (resistance change). Each metal oxide material contributes to detecting different gas types, making the system universally applicable for breath analysis without requiring different sensor types for different gases.
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 system effectively detects NO in human breath with high sensitivity and discriminates against CO, providing a compact and efficient solution for NO detection in diverse environments.
Implementation Method 1
a sensor element including WO3 and Cr2O3 arranged adjacent one another and forming a diffuse p-n junction
Implementation Method 2
When the targeted gas interfaces with the sensing layer material, the target gas molecules are adsorbed on the crystal surface, resulting in a change in conductivity of the sensing layer
Implementation Method 3
a measured resistance at the wiring being indicative of the presence of NO in a sample gas interacting with the sensing element
Data Source
AI summary
Some aspects of the present disclosure relate to a sensor design that exploits the different majority carriers (holes/electrons) in WO3 and Cr2O3 to build sensitivity and selectivity to NO at ppb levels, while discriminating against CO at concentrations a thousand-fold higher (ppm) and spread over a considerable range (0-20 ppm). Practical application of this sensor system for detecting NO in human breath is demonstrated.