Study On Ceramic-based Micro-hotplate Gas Sensors Array And Detection System

China has been one of the biggest production and consumption countries for energy and chemical raw materials in the world. There is a pressing need to enhance efficient detection ways, in view of the frequent leakage and explosion of hazardous chemicals and the serious air pollution due to the emission of toxic and harmful gases from industry and agriculture. Due to the shortcomings of big volume, high power and low integration, conventional sensor detection cannot satisfy the detection requirements for modern intelligence and network security. However, microelectromechanical systems sensors array technology can meet the detection requirements of miniaturization, integration and low cosumption.MEMS Si-based technology is mainly suitable for micromechanical sensors, but when it is applied in Si-based micro-hotplate gas sensors and arrays, there exist many defects such as complex process, poor compatibility and big thermal mismatch. While ceramic-based mictro-hotplate sensors and array technology possesses advantages of simple process, good adhesion and good thermal match. Therefore, it is beneficial to the adhesion of nano-sensing materials, and the machining properties have been improved.Based on the abovementioned issues, the ceramic micro-hotplate sensors array was prepared by Al N ceramic-based MEMS technology in this thesis, which can solve the thermal interference of ceramic micro-hotplate sensors array. The photolithography lift-off process and etching technique of the ceramic-based MEMS can be explored to prepare Al N-based ceramic micro-hotplate gas sensors array. The toxic and harmful gases are hence detected, and the gas sensing characteristics and mechanism are disscussed and analyzed. The main contents of this thesis are as following.1. The thermal structure of Al N ceramic micro-hotplate sensors array was designed. Since the thermal structure of ceramic micro-hotplate has size effect and it is hard to realize directional wet etching for ceramic, thermal isolation structure is designed by laser micromachining etching technique. The geometric factor of thermal conduction structure can be decreased via thermal isolation trapezoid throughholes. The thermal loss is hence decreased. The steady and transient characteristics of thermal structure and thermal stress coupling are investigated and analyzed. In addition, the thermal structure and thermal stress are simulated by ANSYS software.2. In-Nb composite semicondctor sensing material was prepared and its charateristics were investigated and analyzed. In order to meet the detection requirements of high concentration, wide range and low temperature detection for the strong oxidizing gases such as Cl2, In-Nb composite semicondctor sensing material was prepared and investigated. X-ray diffraction(XRD) and scanning electron microscope(SEM) were used to characterize the nanostructure variation with temperature. The gas sensing characteristics and conduction characteristics were also discussed.3. Prepation process of Al N ceramic micro-hotplate sensors array was investigated. The flexible mechanical lift-off process and laser micromachining technology were used to solve the following problems, for example, the forming process of metal with complex surface morphology is difficult to achieve and ceramic substrate is hard to machining. Through the flexible mechanical lift-off process, the stripping effect of the conventional photolithography lift-off process has been improved. Compared with inversion photoresist lift-off process, the stripping procedures of the flexible mechanical lift-off process have been simplified. The cost of preparation process is hence reduced.4. The thermal instability and gas sensitivity characteristics of Al N ceramic micro-hotplate sensors array were investigated and analyzed. According to the thermal coupling characteristics among the sensors array units, four kinds of thermal interference modes of sensors array units were proposed and the thermal interference tests were performed under the four kinds of thermal interference modes. The comparison of the thermal response characteristics before and after thermal isolation was carried out. There are three kinds of thermal response mechanism under the effect of thermal modulation. The gas sensing and sensitivity characteristics of Cl2, NO2, SO2 and CO were investigated and analyzed.On the basis of the Al N ceramic micro-hotplate sensors array, the data acquisition detection system of ARM Cortex-M3 microprocesser is designed. The closed test system platform can be employed to detect the toxic and harmful gases, which satisfies the requirements of in-situ online signal detection for the ceramic micro-hotplate sensors array. The testing results show that the design of the ceramic micro-hotplate gas sensors array is reasonable. The research work prepares the ground for the development of the micro-system technology of ceramic micro-hotplate sensors array.