Over the last few years, MOX, otherwise known as metal oxide sensors, or semiconductor gas sensors, have been shrinking furthermore into very effective designs, and today, they even cut down their energy consumption. Thanks to new production techniques, miniaturized gas sensors are very affordably producible in bulk today. We understand the mechanism behind it.
What is a gas sensor?
Gas sensors are commonly employed to detect small concentrations of flammable, explosive, or toxic gases and to monitor environmental pollution. Gas, moisture, and humidity monitoring is equally important for the environment around us, medicine, industrial processes, and agriculture. One good example of gas sensor applications is sensing hydrogen (H2)-the lightest of all elements is colorless, odorless, and tasteless in ambient standard pressures and temperatures. Therefore, sensory organs cannot detect hydrogen. H2 is a highly combustible and flammable gas that forms an explosive mixture with air, which spontaneous reactions can ignite. In addition, industries use hydrogen as fuel and propellant in hydrogen-powered vehicles and aerospace operations.
Principles
The two most frequently employed gas sensing principles are via semiconductor methods as well as electrochemical principles. The former one relies on gas adsorption in interaction with the metal oxide surface while the latter relies on the oxidation-reduction of gas on the sensing electrodes.
Work Mechanism
SnO2 is one of the most prominent N-type semiconductors sensing materials whose sensing mechanism is based on the change in the conductivity due to the interaction of the gas molecules. oxygen species in the atmosphere adsorbs the sensing material free electrons in the gas testing environment. Consequently, the concentration of electrons is decreased, the sensor resistance and the thickness of space charge layer is increased. When the target gas molecule approaches the sensor, it releases the electrons back to the sensing material by reacting with the oxygen ions. This whole process reduces the thickness of the space charge layer thus reduces the resistance.
NiO is used as P type Semiconductor. Metals like oxide react with oxygen during atmospheric conditions and gives the conduction with a hole-accumulation layer (HAL). At the second stage, the absorbed electrons travel back to the metal oxide when the target gas strike the sensor. These electrons unite with the hole in the accumulation up to reduced charge concentration and increased resistance. Performance sensing for the change of resistance before and after interaction with target gas.
Applications
Gas sensors and sensor nodes are some of the major actuators of advanced communication technologies such as internet of things (IoT), cloud computing, and so on. It’s all interconnected-with each other in technology: it connects various hardware (smart appliances, smart gadgets, and more generally, wearable and mobile consumer devices) through middleware to the cloud of thing (CoT).
Today, the automobile actually has the electronic control unit (ECU) that automatically closes and opens the fresh air flaps, based on the ambient gas concentration measured inside the intake manifold at the hood of the vehicle. Engineers typically monitor combustion-related gases. Hence, they regularly insert a pair of sensitive CO and NO₂ sensors into a damper system to determine the “outside air quality level.”
Researchers urgently require deep learning-based analytics in semiconductor gas sensors to profile noise and analyze hidden signals. These advancements are expected to greatly improve the sensitivity and selectivity of the sensors.
