Gas sensors play an important role in environmental monitoring.
At present, there are many methods and means for gas sensors to monitor gas, including: electrochemical method, gas chromatography, thermal conductivity method, infrared absorption method, contact combustion method, semiconductor gas sensor detection method, optical fiber method, etc. However, from the perspective of the application range, popularity and practicability of materials, the application of semiconductor gas sensors undoubtedly occupies half of the gas sensors.
What is a semiconductor gas sensor?
To understand what a semiconductor sensor is, we should first know what a semiconductor is.
A semiconductor refers to a material whose electrical conductivity is between that of a conductor and an insulator at room temperature. Semiconductors are used in integrated circuits, consumer electronics, communication systems, photovoltaic power generation, lighting applications, high-power power conversion and other fields. For example, a diode is a device made of semiconductors. Whether from the perspective of technology or economic development, the importance of semiconductors is very huge.
the classification of semiconductor sensors
Semiconductor sensors include non-resistive gas sensors and resistive gas sensors.
1. Non-resistive gas sensors mainly use some physical effects and device characteristics to detect gases, such as the volt-ampere characteristics of Schottky diodes and the characteristics of metal oxide semiconductor field effect transistor threshold voltage changes.
2. The resistive gas sensor uses the change of its resistance value to detect the gas concentration. This type of sensor has the advantages of high sensitivity, convenient operation, small size, low cost, short response time and recovery time, etc. The common semiconductor gas sensors on the market are mostly resistive gas sensors.
Working principle of semiconductor gas sensor
In a vacuum (when there is no external interference), there are many electrons inside the semiconductor material that can conduct electricity. After the semiconductor contacts the air, it will adsorb oxygen, and oxygen will capture and fix those electrons in the semiconductor. Let’s take monitoring methane as an example: In this state Next, if the semiconductor comes into contact with a gas such as methane, the methane will react with the oxygen, and those electrons captured by the oxygen will be freed and returned to the semiconductor, improving its electrical conductivity. This process is the exchange of electrons between oxygen and semiconductors. When the electrons are fixed by oxygen, the resistance of the semiconductor increases; when the methane reacts with oxygen, and the electrons return to the semiconductor, the resistance of the semiconductor decreases. The resistance change is related to the methane concentration. By measuring the resistance change of the semiconductor, the corresponding amount of methane can be known
What materials are suitable for semiconductor gas sensors?
1. The raw materials are easy to obtain;
2. It has a good adsorption capacity for oxygen and target gas at a lower temperature, and the two have a good chemical reaction capacity, and have a good desorption capacity for the reaction product at this temperature;
3. It has good compatibility, chemical stability, and suitable micro-defect conductivity with other auxiliary materials after molding.
Common materials that meet this condition are tin dioxide, tungsten oxide, indium oxide, zinc metastannate, etc.
the future prospects of semiconductor gas sensors
Among many gas sensor categories, semiconductor sensors are very promising gas sensors. The reason is that its working principle and sensing process are extremely simple, that is, the gas information can be turned into an electrical signal in one step; the second is that the sensing carrier is stable; and the cost is relatively cheap. The above features not only provide a clear path and space for its evolution, but also provide economic feasibility for large-scale deployment in the future.
