How The MEMS Gas Sensor Works
With the development of industrialization and urbanization, issues such as air pollution and environmental degradation have become increasingly severe. Gas detection has become one of the important means to solve these problems. Due to their high accuracy, small size, and low power consumption, MEMS gas sensors have become one of the important technologies in the field of gas detection. In fields such as air quality monitoring, smart homes, and automobile exhaust emission detection, MEMS gas sensors have played an important role. This article aims to introduce the working principle of MEMS gas sensors and provide reference and assistance to users.
1. Overview of MEMS technology
MEMS, short for Micro-Electro-Mechanical Systems, also known as microelectromechanical systems, microsystems, micromachines, etc., refer to high-tech devices with dimensions ranging from a few millimeters to even smaller. MEMS is a micro device or system that integrates micro sensors, micro actuators, micro mechanical structures, micro power sources and energy, signal processing and control circuits, high-performance electronic integrated devices, interfaces, communications and other components into one.
MEMS technology is based on traditional semiconductor technology such as photolithography, etching, and packaging, and is integrated with ultra-precision machining, combining knowledge and technology from various disciplines such as physics, chemistry, optics, biology, etc., enabling tiny MEMS devices to have precise and complete mechanical, electronic, and other characteristic structures.
In brief, MEMS chips are made using microfabrication techniques on a chip basis to create small mechanical structures for detecting and measuring physical and chemical quantities. What are these chips used for? Usually, they are used to carry sensing functions, such as acceleration sensors, pressure sensors, optical sensors, and the gas sensors introduced in this article.
2. What is a MEMS Gas Sensor?
MEMS gas sensors are a type of gas detection sensor based on micro-electro-mechanical system (MEMS) technology. They are capable of detecting various gas components in the air, such as CO2, NOx, SO2, and formaldehyde. These sensors are characterized by their small size, light weight, low cost, low power consumption, high reliability, suitability for mass production, ease of integration, and implementation of intelligence. In addition, their micrometer-scale feature size allows them to achieve functions that cannot be realized by some traditional mechanical sensors. Therefore, MEMS gas sensors have a wide range of applications in areas such as environmental monitoring, industrial production, security testing, and medical diagnosis.
3. Working principle of MEMS gas sensor
The fundamental principle of MEMS gas sensors lies in detecting the presence and concentration of various gases in the air by utilizing the changes in the interaction between gas molecules and the sensor surface. When gas molecules come into contact with the sensor surface, they cause changes in the surface morphology, which can be measured using various sensor technologies, thus calculating the composition and concentration of the gas being detected. Common measurement techniques include electrochemical, infrared absorption, and thermal conductivity methods.
The detection principle of MEMS gas sensors is based on the electrochemical reaction of gas molecules on the electrode surface, where the change in gas concentration is detected by measuring the potential difference or current variation between electrodes. Typically, the electrodes of the sensor are made of precious metals (such as Pt, Au) or semiconductor materials (such as SnO2, W02). The interaction between different gas molecules and electrode materials causes differences in electrochemical reactions, leading to changes in potential difference or current, thereby outputting corresponding gas concentration signals.
Therefore, the operational process of MEMS gas sensors typically involves the following steps:
- Device preheating: The sensor is heated to a specific temperature by an internal micro-heater.
- Gas adsorption: When the gas to be detected enters the sensor, gas molecules are adsorbed on the sensor surface and react chemically with the active materials on the sensor surface, causing changes in the electrical, optical, or thermal properties of the sensor surface.
- Signal detection: The sensor converts the changes in surface properties caused by adsorbed gas into electrical, optical, or thermal signals, which are then transmitted to the detection circuit for processing.
- Signal amplification and processing: The detection circuit usually amplifies and filters the signals to improve the signal-to-noise ratio and increase sensitivity. After amplification and filtering, the sensor signals undergo a series of signal processing algorithms to determine gas composition and concentration.
- Data output: Finally, the sensor outputs the measurement results of gas composition and concentration in the form of digital signals, typically transmitted to external devices via serial ports, Bluetooth, Wi-Fi, etc., for further analysis and application.
4. Basic structure of MEMS gas sensor
The fundamental structure of MEMS gas sensors typically consists of three parts: the sensor chip, packaging, and ASIC chip.
The sensor chip is the most critical component of the MEMS gas sensor, made using microfabrication technology and typically uses principles such as the piezoresistive effect or capacitance effect to detect gases.
Due to its fragile nature, the sensor chip is often designed with a covered packaging to protect it from external interference and damage. This enclosed packaging involves sealing the sensor chip in a covered metal or ceramic box and connecting it to the external circuit through multiple pins.
The ASIC chip serves as the control center of the MEMS gas sensor, primarily used for controlling the sensor's operating state and signal processing. The ASIC chip usually contains analog circuits, digital circuits, and microprocessors modules, which can amplify, filter, convert the ADC, and process digital signals of the sensor, thus enhancing its accuracy and stability.
5. Technical advantages of MEMS gas sensors
Compared to traditional gas sensors, MEMS gas sensors have various technological advantages. Here are some specific advantages:
- Miniaturization: MEMS devices are small in size, with dimensions of individual MEMS sensors measured in millimeters or even micrometers. This miniaturization not only makes the sensors more lightweight and portable, but also expands their applications into more fields.
- High sensitivity: MEMS gas sensors employ micrometer-level microstructures and possess higher sensitivity. In gas detection, they can detect lower concentrations of gas, thus improving the accuracy and reliability of detection.
- Low power consumption: MEMS gas sensors typically require very little power to operate normally. This is because they use microcircuits to collect and process signals, and can prolong battery life through sleep or low power modes.
- Fast response: Due to their extremely small structure, MEMS gas sensors can respond to gas changes in milliseconds. This fast response enables the sensors to promptly detect gas leaks or other dangerous situations, thereby reducing the likelihood of accidents.
- Integrability: MEMS gas sensors can be integrated with other MEMS devices (such as accelerometers and gyroscopes) into a single chip, thereby achieving multiple sensing functions simultaneously. This integrability makes the design of MEMS gas sensors more flexible and diverse.
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