Material Design And Electromechanical Properties Of Amorphous SiCN Ceramics For High Temperature Sensing

Multi-physical sensing and data acquisition in extreme environments such as gas turbine engines are always a challenge for existing testing technologies.In addition to being able to withstand extreme conditions such as high temperature,high pressure and severe corrosion,the internal sensors also need to maintain their stable functionality at all times.With the continuous development of space technology,higher requirements are put forward on the accuracy,stability,size,and ease of installation of the sensor as well.The development of micro-electro-mechanical system(MEMS)makes it possible to embed micro-sensors with high reliability and integration in extreme environment sy stems.However,the application of MEMS sensors in extreme environments strongly depends on the development of new materials.At present,the most commonly used MEMS sensors based on semiconductor Si and Si C can not exceed 500 °C.Polymer-derived Ceramics(PDCs)are a class of high-temperature ceramic derived from the high-temperature pyrolysis of polymer precursors,which have excellent high-temperature stability,oxidation/corrosion resistance,high creep resistance and high temperature multifunctionalities.In addition,the direct polymer-to-ceramic processing route of PDCs makes it much easier to be fabricated into various components/devices with complex shapes/structures.Therefore,PDCs can be used as a candidate for manufacturing MEMS temperature/pres sure sensors for extreme environments such as gas turbine engines.At present,the temperature sensor based on PDCs(>1000 °C)has been commercialized abroad,but the related research is still in its infancy in China.In addition,PDCs with high piezoresistivity also have great development potential in the application of pressure sensor technology.In this paper,the polymer-derived amorphous SiCN ceramics were taken as the research object.The application prospect for amorphous SiCN ceramics in MEMS sensors field in extreme environments was systematically analyzed from four aspects: material design,preparation and microstructure evolution,thermo-mechanical properties,and temperature/pressure sensing characteristics.It is expected to provide basic theoretical guidance and experimental basis for the preparation of MEMS temperature/pressure sensors used in extreme environments.A systematic composition design of the amorphous SiCN ceramics was carried out through the Si-C-N ternary composition diagram according to the microstructure characteristics of the amorphous SiCN ceramics.The atomic structure modeling method of amorphous SiCN ceramics was developed by using first-principles molecular dynamics.The radial distribution function obtained to describe the atomic structure characteristics is in good agreement with the experimental results,which proved the rationality of the modeling method.The effects of chemical composition on the atomic structure,electrical properties,and mechanical properties of amorphous SiCN ceramics were further studied.According to the sensitivity of the temperature-resistance effect and piezoresistance effect of amorphous SiCN ceramics,Si C0.7N0.9 was selected as the optimal research object.According to the composition design results of amorphous SiCN ceramics,PSN1 and PSN2 polysilazanes were selected as the research objects.The dense SiCN ceramics and SiCN ceramics with a continuous controllable porosity were prepared by liquid molding method and powder molding method,respectively.The cross-linking process and ceramicization process of the polysilazanes with different molecular structure were analyzed.The effects of heat treatment temperature,molecular structure of polysilazane and the porosity on the microstructure of amorphous SiCN ceramics were studied.Excellent mechanical properties and high temperature stability are the prerequisites for the application of amorphous SiCN ceramics to the sensing field under harsh environments.Firstly,the effects of the molecular structure of polysilazane and environmental pressure on high-temperature stability of amorphous SiCN ceramics were analyzed.Then,according to the actual service conditions,the high temperature stability of amorphous SiCN ceramics in inert atmo sphere during laser ablation was studied,and the relationship between oxidation resistance and high temperature stability of amorphous SiCN ceramics in atmospheric environment was further analyzed.Finally,the nano-indentation method was used to test the elastic modulus and hardness of SiCN ceramics with different pyrolysis temperatures,and the main factors affecting their mechanical properties were analyzed.Aiming at the semiconductor-metal interconnects during ultrahigh-temperature applications,a flexible carbon nanotube interconnects was proposed,which can meet the thermal-mechanical-electrical properties requirements of the SiCN ceramic/metal interface.The main factors controlling the conductivity of amorphous SiCN ceramics were obtained by analyzing the conductivity at room temperature of SiCN ceramics with different pyrolysis temperatures and different molecular structure of polysilazane.Finally,the temperature-resistance behavior of amorphous SiCN ceramics from room temperature to 1000 °C and the piezoresistance behavior at room temperature were tested,and the high-temperature conductive mechanism and piezoresistance mechanism of amorphous SiCN ceramics were discussed separately.