To date, the semiconductor properties of SiCN ceramics have been widely studied, and the sensor applications based on the semiconductor properties of SiCN have also been relatively maturely studied.
Polymer conversion ceramics (PDCs) technology is a technology for preparing inorganic ceramics by high-temperature pyrolysis of organic polymers. Common ceramic systems include binary systems such as SiC, Si3N4, BN, and AlN, ternary systems such as SiCN, SiCO, and BCN, and quaternary systems such as SiCNO, SiBCN, SiBCO, SiAlCN, and SiAlCO.
Polymer conversion ceramics technology is a breakthrough in the traditional powder sintering method for preparing ceramics. Traditional ceramic sintering technology generally uses corresponding ceramic powders for molding and high-temperature sintering. For covalently bonded ceramic materials such as SiC and Si3N4, sintering is difficult, and sintering aids and very high sintering temperatures are usually required. Compared with traditional powder sintering technology, polymer conversion ceramics technology has many advantages such as low preparation temperature, good molding processability, strong precursor molecular design, and good high-temperature performance of ceramics. It is an important technology for the preparation of advanced ceramics.
Among many ceramic systems, polymer-converted SiCN ceramics show good high-temperature stability, oxidation resistance, creep resistance and other properties, and have good high-temperature semiconductor properties, excellent piezoresistive effect, etc. At the same time, polymer-converted SiCN technology is also an important means to prepare SiC/Si3N4 composite materials and has been widely studied. The basic process of preparing polymer-converted SiCN ceramics includes: synthesis of organic Si/C/N polymers, cross-linking molding of polymers, high-temperature cracking of polymers, etc. The cracking process is generally completed between 900-1100℃. The ceramics after cracking are generally amorphous ceramics. Crystalline SiC/Si3N4 composite ceramics can be prepared by heat treatment at higher temperatures. According to the basic structural unit of the skeleton in the precursor, SiCN ceramic precursors can be mainly divided into two categories: polysilazane and polysilicon carbon nitride. The skeleton unit of the polysilazane precursor is Si-N-Si structure, and the skeleton unit of polysilicon carbon nitride is Si-N=C=N-Si structure. Compared with polysilazane, polysilicon carbon nitride is highly sensitive to air and has high requirements for preparation and storage conditions. It has only been used in the preparation of SiCN ceramics in the past two decades, and its development is relatively late. The synthesis process of polysilazane is mature, the raw materials are simple, and it is a relatively mature precursor. It has now achieved commercial production.
To this day, the semiconductor properties of SiCN ceramics have been widely studied, and the application of sensors based on the semiconductor properties of SiCN has also been relatively mature. For example, some researchers have prepared aluminum-modified and graphene-modified SiCN bulk ceramic temperature sensors by powder sintering, and realized the conversion of temperature to output voltage through a voltage divider circuit. The sensor shows good stability and repeatability. In addition, since the resistance of SiCN ceramics is also very sensitive to temperature changes, how to effectively separate the temperature signal and the pressure signal and eliminate the interference of temperature when used at high temperatures is one of the difficulties in the application of SiCN ceramics in the field of high-temperature pressure sensors.
