Design Optimization Of New Silicon-based Micro-hot Plates

Industry drives economic development and increases people's living standards.Gas detection is being used more widely in human's life and production.As an important part of gas detection,the gas sensor can effectively measure the type and concentration of gas.It can convert the detected signal into an electrical signal.Gas sensors play an important role in air pollution detection,indoor environmental testing and food odor detection.The microstructured gas sensor has obvious advantages in various gas sensors.And it meets the challenge of integration and miniaturization.In microstructured gas sensors,micro-hot plates are an important component that provides the corresponding temperature for materials.Therefore,it is necessary to consider whether the micro-hot plate can provide enough heat to work on the materials at the same heat generation rate.That is to say,it's important for the surface state of the micro-hot plate to have high temperature and uniform distribution.The thermal steady state can be analyzed by ANSYS which is a simulation software using finite element.In this thesis,the structure of the micro-hot plate is designed and optimized by ANSYS.The micro-hot plate is divided into three parts: a substrate,an insulating layer and an electrode from bottom to top.The substrate plays a supporting role in the entire structure.Heat lost can be prevented by the insulating layer.The electrodes are further divided into a heating electrode and a measuring electrode.The heating electrode is energized to generate Joule heat to energize the micro-hot plate,and the measuring electrode is used to detect the change in resistance of the gas-sensitive material before and after contact with the gas needed to be measured.In this thesis,three new micro-hot plate structures are proposed from three aspects: substrate,insulating layer and electrode.The first structure consists of a etched silicon substrate plus a ‘silicon island',a silicon dioxide insulating layer and an interdigital electrode.The second structure consists of a complete silicon substrate,a porous silicon insulating layer and an interdigital electrode.The third structure consists of a complete silicon substrate,a silicon dioxide insulating layer and edge-type electrodes.The results show that all of three optimized micro-hot plates can reach higher temperature at the same heat generation rate,and the temperature distribution of the whole micro-hot plate is more uniform.After the application of a layer of gas-sensitive material tin dioxide in combination with the actual,the overall temperature of the three new structures can also reach the working temperature of tin dioxide.In these three new types of micro-hot plates,thetemperature and temperature difference of the third structure is better than the other two structures,so the third optimized structure can reduce power consumption and improve work efficiency.The third structure can also reduce the interference of the accompanying magnetic field on the measuring electrode because its electrode is not in the middle of the micro-hot plate.In the last part of the thesis,the fabrication process of the micro-hot plate is introduced in detail,including the cleaning preparation of the silicon wafer,the preparation of the insulating layer and the preparation of the electrode.