Introduction to the research direction of gas sensors

A surface acoustic wave (SAW) type gas sensor SAW gas sensor is fabricated on a substrate of a piezoelectric material, the surface of one end being an input sensor and the other end being an output sensor. A region between the two deposits a polymer film capable of adsorbing VOC. The adsorbed molecules increase the mass of the sensor, causing the velocity or frequency of sound waves to travel on the surface of the material to change, and measuring the volume fraction of the gas by measuring the velocity or frequency of the sound wave. The main gas sensing materials are polyisobutylene, fluoropolypolyol, etc., which are used to measure organic vapors such as styrene and toluene. The advantages are high selectivity, high sensitivity, stability over a wide temperature range, low humidity response and good repeatability. The SAW sensor output is a quasi-digital signal, so it can be easily interfaced to the microprocessor. In addition, the SAW sensor uses a semiconductor planar process, which makes it easy to combine the sensor with the matching electronics to achieve miniaturization and integration, thereby reducing measurement costs.

4) Quartz vibrator gas sensor

The quartz vibrator microbalance (QCM) consists of a quartz vibrating plate with a diameter of several micrometers and electrodes fabricated on both sides of the disc. When an oscillating signal is applied to the device, the device will be at its characteristic frequency. ~30MHz) Resonance occurs. An organic polymer is deposited on the vibrating plate. After the polymer adsorbs the gas, the mass of the device is increased, thereby causing the resonance frequency of the quartz oscillator to decrease, and the gas is identified by measuring the change in the resonant frequency.

The polymer gas sensor has high sensitivity to specific gas molecules, good selectivity, simple structure, can be used at normal temperature, supplements the shortage of other gas sensors, and has a good development prospect.

3 processing technology

In the sensor technology, there are many manufacturing processes for gas sensors, but for the characteristics and materials of gas sensors, microelectromechanical technology (MEMT) is mainly used.

Microelectromechanical technology is a new technology based on microelectronics technology and micromachining technology. It is divided into bulk micromechanical technology, surface micromechanical technology and X-ray deep lithography electroforming (LIGA) technology. The body micro-mechanical technology is mainly made of bulk silicon single crystal, and the processing thickness is tens to hundreds of micrometers. The key technology is corrosion technology and bonding technology. The advantages are simple equipment and process, but poor reliability; surface micro-mechanical technology utilizes semiconductor Processes, such as oxidation, diffusion, photolithography, thin film deposition, sacrificial layer and stripping, are processed to a thickness of a few microns. The advantage is that they are compatible with IC processes, but the vertical dimension is small and cannot meet the requirements of high aspect ratio. It is greatly affected by high temperature; LIGA technology uses traditional X-ray encapsulation, thick photoresist as mask, electroforming process, processing thickness of several micrometers to tens of micrometers, and can achieve high-volume production with high repeatability. .

Microelectromechanical technology is to explore components and systems with new principles and functions through miniaturization and integration of systems.

4 Development direction

In recent years, research and development of gas sensors have become increasingly important due to the increasing requirements for accuracy, performance, and stability of gas sensors in industrial production, home safety, environmental monitoring, and medical fields. With the application of advanced science and technology, the trend of gas sensor development is miniaturization, intelligence and multi-functionality. In-depth study and master the characteristics and interactions of organic, inorganic, biological and various materials, understand the working principle and mechanism of various gas sensors, correctly select sensitive materials of various sensors, and flexibly use micro-machining technology and sensitive film formation Technology, microelectronics technology, fiber optic technology, etc., to optimize sensor performance is the development direction of gas sensors.
4.1 Research and development of new gas sensitive materials and production processes

Studies on gas sensor materials have shown that metal oxide semiconductor materials Zn0, SIlo2, Fe203, etc. have become more mature, especially in the detection of C ratio, C2H5OH, CO and other gases. At present, there are two main directions in this work: First, the chemical modification method is used to dope, modify and surface modification the existing gas sensitive membrane materials.

The film formation process is improved and optimized to improve the stability and selectivity of the gas sensor. Second, the development of new gas sensitive membrane materials, such as composite and hybrid semiconductor gas sensing materials, polymer gas sensing materials, etc. The new materials have high sensitivity, high selectivity and high stability for different gases. Organic polymer sensitive materials have become a research hotspot because of their rich materials, low cost, simple film forming process, easy compatibility with other technologies, and work at room temperature.

4.2 Development of a new gas sensor

Following the traditional principle of action and some new effects, the use of crystalline materials (silicon, quartz, ceramics, etc.) is preferred, and advanced processing techniques and microstructure design are used to develop new sensors and sensor systems, such as optical waveguide gas sensors and polymer sounds. Development and use of surface wave and quartz resonant gas sensors, research on microbial gas sensors and biomimetic gas sensors. With the application of new materials, new processes and new technologies, the performance of gas sensors is more perfect, which makes the miniaturization, miniaturization and multi-function of sensors have the advantages of long-term stability, convenient use and low price.

4.3 Gas sensor intelligence

With the continuous improvement of people's living standards and the increasing emphasis on environmental protection, the detection of various toxic and harmful gases, the monitoring of air pollution, industrial waste gas and the detection of the quality of food and living environment have all raised higher on gas sensors. Requirements. The successful application of new materials development technologies such as nanometer and thin film technology provides a good precondition for gas sensor integration and intelligence. Gas sensors will be developed on the basis of multi-disciplinary integrated technologies such as micromachine and microelectronics, computer technology, signal processing technology, sensing technology, fault diagnosis technology, and intelligent technology. The development of fully automatic digital intelligent gas sensors capable of simultaneously monitoring multiple gases will be an important research direction in this field.