Semiconductor gas sensor working principle and application

What is a semiconductor gas sensor?

At present, gas sensor plays an important role in environmental monitoring. There are many methods and methods of gas sensor monitoring, including: electrochemical method, gas chromatography, heat conduction method, infrared absorption method, contact combustion method, semiconductor gas sensor detection method, optical fiber method, etc. However, from the application range, popularity and practicability of materials, the application of semiconductor sensor undoubtedly occupies half of the gas sensor.

Semiconductor gas sensor
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 change of threshold voltage of metal oxide semiconductor field effect transistors.

2、The resistive gas sensor uses its resistance change to detect 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. Most of the common semiconductor gas sensors on the market are resistive gas sensors.

3、The working principle of semiconductor gas sensor

Semiconductor sensor

In vacuum (when there is no external interference), there are many electrons inside the semiconductor material that can conduct electricity. After the semiconductor is in contact with air, oxygen will be adsorbed, and the oxygen will be captured and fixed For those electrons in semiconductors, let’s take the monitoring of methane as an example: in this state, if the semiconductor comes into contact with a gas like methane, methane will react with oxygen, and those electrons captured by oxygen will regain their freedom and return to the semiconductor. , Improve its electrical conductivity. This process is a process in which electrons are exchanged between oxygen and semiconductors. When electrons are fixed by oxygen, the resistance of the semiconductor becomes larger; when methane reacts to oxygen, when the electrons return to the semiconductor, the resistance of the semiconductor becomes smaller. The resistance change is related to the methane concentration, and the corresponding methane content can be known by measuring the semiconductor resistance change.

gas sensor
What materials are suitable for semiconductor gas sensors?

1、The raw materials are easy to obtain;

2、It has good adsorption capacity for oxygen and target gas at lower temperature, and both have good chemical reaction ability, and react at this temperature. The product has good desorption ability;

3、After forming with other auxiliary materials, it has good compatibility, chemical stability, and suitable micro-defect electrical conductivity.

Common materials that meet this condition are tin dioxide, tungsten oxide, indium oxide, zinc metastannate, etc.

The future prospects of semiconductor gas sensors

Among the many gas sensor categories, semiconductor sensors are very promising gas sensors. The reason is that its working principle and the sensing process are extremely simple, that is, 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 characteristics not only provide a clear path and space for its evolution, but also provide economic feasibility for future large-scale deployment.

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