Overview:
Polysilazanes, highly reactive polymers with Si-N bonds as their backbone, react violently with water, oxygen, and various polar substances. This has led to their widespread application in a variety of fields, including ceramics, aviation, aerospace, and coatings. Polysilazanes can be divided into two categories: organic and inorganic. Organic polysilazanes have organic groups on their side chains, while inorganic polysilazanes, also known as perhydropolysilazanes (PHPS), consist solely of silicon, nitrogen, and hydrogen. Due to its simple structure and high market value, PHPS is often used in the manufacture of ceramic precursors and thermal insulation materials. Because it lacks organic groups, PHPS can be converted at relatively low temperatures using various methods and exhibits excellent adhesion to substrates. The resulting coatings exhibit multiple advantages, including corrosion resistance, high and low temperature resistance, gas barrier properties, long-term durability, transparency, and scratch resistance, thus finding widespread application in coating preparation. PHPS polysilazane has the following properties:
High Reactivity: PHPS polysilazane exhibits high reactivity and can be converted into inorganic materials such as SiCNO, silicon carbide nitride (SiCN), or silica ceramics at high temperatures.
High-Temperature Resistance: PHPS polysilazane exhibits excellent high-temperature resistance, reaching temperatures exceeding 1800°C. At high temperatures, its cured hardness can reach 9H.
Chemical Inertness: The highly stable and chemically inert Si-N bonds in its molecular structure give PHPS polysilazane low surface energy and high thermal stability.
Excellent Adhesion: PHPS polysilazane exhibits excellent adhesion to most substrates and can be converted at low temperatures using a variety of methods. The resulting coating exhibits multiple advantages, including corrosion resistance, high and low-temperature resistance, gas isolation, long-term durability, transparency, and scratch resistance. These properties make PHPS polysilazane widely used in many fields, including ceramic precursors, thermal insulation materials, anti-corrosion coatings, adhesives and composite materials.
Applications:
As a dielectric layer
Silicon dioxide dielectric layers prepared using the liquid-phase method of PHPS have gained popularity because they effectively overcome the limitations of traditional methods such as thermal oxidation, chemical vapor deposition (CVD), and plasma-enhanced chemical vapor deposition (PECVD). The molecular structure of PHPS significantly influences the properties of the dielectric layers produced. For example, one study used PHPS within a specific molecular weight range to prepare a coating composition. Upon heating, this composition formed a siliceous film that penetrated deep into the gaps, thereby improving the performance of the dielectric layer. Furthermore, the content of specific elements or groups in PHPS has also attracted considerable attention. For example, PHPS compositions that are free of N-H and C but rich in Si can, under specific conditions, combine with catalysts to produce low-shrinkage oxide films, making them ideal for filling semiconductor gaps. Furthermore, PHPS with specific 1H NMR spectral characteristics, under specific ratios, can produce silicon dioxide layers with excellent thickness uniformity. Finally, the PHPS used in the preparation process has a molecular weight of 8,000 to 15,000 and a nitrogen content of 25% to approximately 30% by weight. The resulting silicon dioxide layer exhibits excellent etch resistance.
Application as a Barrier Layer
Barrier layers, particularly coatings that offer excellent barrier properties against gases such as water vapor, play a key role in surface protection for electronic and optical devices. PHPS has also attracted significant attention in this field. An earlier patent disclosed a barrier layer prepared using PHPS with a surface density controlled between 4 and 0 g·cm⁻³, and oxygen, nitrogen, and silicon composition ratios of 60% to 75%, 0% to 10%, and 25% to 35%, respectively, achieving high gas barrier performance. Furthermore, by adjusting the PHPS structure, such as increasing the ratio of SiH₃ to SiH₂ to 1:(10 to 30), the stability of the barrier film under high temperature and high humidity conditions can be further optimized. Besides using PHPS alone, combining it with other modifying materials, such as the metal compound tri-sec-butoxyaluminum, can produce silicon-containing films with the structure SiOxNyMz, demonstrating excellent stability in high-temperature and high-humidity environments. Furthermore, the introduction of specific additives, such as hydrocarbon-substituted guanidines and oxygen- and nitrogen-containing crown ether amines, can significantly enhance the gas barrier properties of barrier films.
The composition of the solution also significantly influences the performance of the PHPS barrier layer. By defining specific structural units and the ratio of Si-R bonds to Si-H bonds in PHPS, it can be dissolved in aliphatic hydrocarbon solvents, thereby producing silica-glass-like barrier layers with low water vapor transmission rates.
Applications in Optical Films
PHPS plays a key role in the preparation of optical films and is often combined with modifying raw materials to form composite materials suitable for optical film production. For example, combining PHPS with organic polymers containing silazanes, siloxysilazanes, or ureasilazanes can produce low-refractive-index films. Furthermore, by mixing a PHPS-containing solution with a fluoropolymer solution and then coating it, a high-strength, oleic acid-resistant, and slippery silica optical film can be obtained. Furthermore, using a xylene solution of PHPS as a precursor, a spiropyran (SP)-doped silica coating can be prepared. During this process, the color of the film changes from transparent light yellow to red as PHPS transforms into silica, accompanied by an increase in absorbance at 500 nm. After light exposure, the color of the film deepens further, demonstrating reversible photochromic properties, demonstrating the significant potential of PHPS in optical film applications.