SiC Gas Sensor Mid-Transition-Metal Oxide Barrier
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Solution Overview
Problem
Existing silicon carbide (SiC) based field effect gas sensors face reliability issues at high temperatures due to oxidation of ohmic contact layers and structural integrity problems, limiting their use in harsh environments and high-temperature applications.
Innovation Solution
The use of mid-transition-metal oxides, such as iridium oxide (IrO2) and rhodium oxide (RhO2), as barrier layers to protect ohmic contact layers from oxidation, providing structural integrity and resistance to oxygen diffusion at temperatures up to 750°C, thereby extending the operational temperature range of SiC-based field effect gas sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional metal barrier layers are used to protect ohmic contact layers, then protection is provided at temperatures up to 450°C, but oxidation occurs at temperatures above 500°C
Solution Approach 1:
The patent employs a composite barrier layer structure consisting of multiple materials (e.g., tungsten silicide combined with other refractory materials) to achieve both low resistivity and high-temperature oxidation resistance. This composite approach allows the barrier layer to maintain protective function at temperatures exceeding 500°C where conventional single-material barriers fail.
Solution Approach 2:
The invention changes the material parameters of the barrier layer by selecting materials with specific properties: refractory metals and their silicides that exhibit stable crystalline structures and low oxygen diffusion coefficients at high temperatures. This parameter optimization enables operation in the 600-750°C range while preventing oxidation of the underlying ohmic contact layers.
2Reliability
If barrier layers are added to protect ohmic contact layers, then oxidation resistance improves, but device complexity increases
Solution Approach 1:
The barrier layer materials selected in the patent serve multiple functions simultaneously: they provide oxidation protection, maintain low electrical resistivity for signal integrity, and offer thermal stability at high operating temperatures. This multi-functionality reduces the need for additional separate protective structures, thereby limiting the increase in device complexity.
3Reliability
If mid-transition-metal oxides are used as barrier layers, then resistance to oxygen diffusion improves at high temperatures, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies the barrier layer selectively in regions where ohmic contact layers are present and oxidation protection is needed, rather than uniformly across the entire device. This localized application reduces the total material deposition required and allows for more controlled, precise manufacturing in critical areas while simplifying non-critical regions.
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
This solution ensures long-term stability and reliability of SiC-based field effect gas sensors at temperatures above 600°C, enabling their use in applications like exhaust emission monitoring and control, with improved durability and accuracy in detecting gases like ammonia and nitrogen oxides.
Implementation Method 1
at least one barrier layer formed by an electrically conducting mid-transition-metal oxide covering the ohmic contact layer
Implementation Method 2
protect ohmic contact layers from oxidation, providing structural integrity and resistance to oxygen diffusion at temperatures up to 750°C
Implementation Method 3
SiC based field effect sensors may also be tailored for the detection of different gaseous substances
Implementation Method 4
change an electrical property of the SiC semiconductor structure
Data Source
Figure 1~2
Figure 3
Figure 4a~4c
AI summary
A field effect gas sensor, for detecting a presence of a gaseous substance in a gas mixture, the field effect gas sensor comprising: a SiC semiconductor structure (2, 3); an electron insulating layer (7) covering a first portion of the SiC semiconductor structure; a first contact structure (12) at least partly separated from the SiC semiconductor structure by the electron insulating layer; and a second contact structure (8b) conductively connected to a second portion of the SiC semiconductor structure, wherein at least one of the electron insulating layer (7) and the first contact structure (12) is configured to interact with the gaseous substance to change an electrical property of the SiC semiconductor structure; and wherein the second contact structure comprises: an ohmic contact layer (9) in direct contact with the second portion of the SiC semiconductor structure; and a barrier layer (10) formed by an electrically conducting mid-transition-metal oxide covering the ohmic contact layer.