Fabrication Of High Temperature Resistant Flexible Conductive Films From Si₃N₄ Paper

With the development of science and technology,higher requirement has been put forward for the portability and wearability of electronic products,and traditional rigid electronic devices become difficult to meet people’s needs,and more and more people are looking at flexible electronic devices.Flexible films have excellent properties such as lightness,thinness and easy folding,so they are increasingly used in the preparation of flexible electronic devices.However,although researchers have done a lot of research on the preparation of flexible films,there are still many shortcomings in the existing preparation technologies.The preparation methods of flexible films can be divided into direct growth method and peel-transfer method according to the preparation process.The direct growth method directly prepares the film on a flexible substrate such as polymer or metal foil,which is simple but has problems such as the polymer is not resistant to high temperature and non-precious metal foil is easy to oxidize.The peel transfer method is to prepare the functional film on the traditional rigid substrate,and then transfer the functional film to the flexible substrate by etching the substrate or peeling the film,etc.,the film prepared by this method has a higher degree of crystallization and better performance,but the process is complex and has high requirements for the substrate,which is difficult to promote.In this thesis,LaNiO₃films and ZnO films are prepared on Si₃N₄ fiber papers by blade coating,which evaluates the feasibility of applying the paper as a substrate for fabricating flexible functional films and provides a new idea for the preparation and research of flexible films in the future.In this thesis,LaNiO₃/Si₃N₄ high-temperature flexible conductive films are prepared by annealing at different temperatures by blade coating LaNiO₃ sol on Si₃N₄ fiber papers,and the phases,surface morphologies,electrical and mechanical properties of the films are characterized and analyzed.The results show that after annealing at 650°C for 1h,LaNiO₃gains the highest crystallization degree.SEM analysis indicate that the film coated for 8 times has the best surface morphologies.The electrical properties of the film are tested and found that the film has low resistivity,and the resistivity is as low as 1.07 mΩ·cm after coating for8 times.The film has good mechanical properties and a minimum bending radius of up to 1mm.Under the condition of bending radius of 2 mm,the fatigue test of the film is carried out,and the resistivity rise to 1.89 mΩ·cm after 10,000 bends,which proves that the film has good fatigue resistance.These results show that PZT films can crystallize and form films on the substrate surface,and the PZT films prepared by magnetron sputtering have good morphologies and exhibit typical ferroelectricity,which evaluates the feasibility of LaNiO₃/Si₃N₄ films as flexible film substrates.ZnO/Si₃N₄ film varistors are prepared on Si₃N₄ fiber papers by the same preparation method as LaNiO₃/Si₃N₄ films,and the phases,surface morphologies and electrical properties of the films are tested.The results show that ZnO has the highest crystallization degree after annealing at 600°C for 1 h.The SEM analysis indicate that the ZnO/Si₃N₄ film coated for 10times has the best surface morphologies,and the fibers are covered completely without microcracks.The electrical properties of ZnO/Si₃N₄ film varistors annealed at 600℃for 1 h are measured and the I-V curve shows typical nonlinearity.The nonlinearity coefficient is 12.6,the varistor voltage is 7.1 V,and the leakage current is 63.6μA,showing obvious varistor properties.The results demonstrate the feasibility of Si₃N₄ fiber paper in the preparation of other flexible oxide films.