Al₂O₃ Porous Nanosolid Prepared By SHP Method And Its Dielectric Properties

In this thesis,Al₂O₃ and BN porous nanosolid were prepared by the hydro-thermal hot press method and solvo-thermal hot press method(SHP),and their porosity,stability, mechanical strength and dielectric properties were tested and analysed as well.In addition,we successfully prepared Al₂O₃/Polyimide composite to lower its k and increase its stability,and researched on its mechanical strength and dielectric properties.Comparing with Al₂O₃ ceramic,Al₂O₃ porous nanosolid,has preponderance both at preparing conditions and dielectric properties to satisfy the low-k requirement of the integrated circuit.So firstly we systematically analysed the influence caused by the thermal treatment to the structure and dielctric properties of AlOOH porous nanosolid. The thermal treatment can regenerate Al₂O₃ dehydrated from AlOOH,which was the reaction product of the solvothermal hot press process.At the same time,the connection of the Al₂O₃ particulates was strengthened,thereby the mechanical strength of porous nanosolid was improved,and the dielctric properties of the sample was changed according to the variety of its structure.The k value of a material can be reduced by introducing pores into it,however,it is quite difficult to be further reduced because of the intrinsic dipole moment.Besides,the high activity of Al₂O₃ particulate cause the instability of porous nanosolid.Considering all of above,a organic solvent 1,4-dioxane,which can form coordination bond with Al₂O₃ and reduce its intrinsic dipole moment,was used as the pore-forming agent.On the other hand,the formation of coordination bond also lowered the reactivity of Al₂O₃ nanoparticles,and improved the stability of the porous nanosolid.In addition, 1,4-dioxane can fit for a wide range of press when form the the porous nanosolid.So we can control the porosity of porous nanosolid simply by regulating the press.Furthermore,Samples prepared with the two pore-forming agents---deionized water and 1,4-dioxane,can only perform advantage other on mechanical strength or on porosity.However the two solvent can be mixt together without reaction,so the mixture of deionized water and 1,4-dioxane was selected as the new pore-forming agent,in order to prepare samples with good mechanical strength and high porosity.According to the experimental results,the porosity of the Al₂O₃ porous nanosolid increased with increasing the content of 1,4-dioxane in the mixed solvent,and it decreased with the increase of water content.At the same time,both the k value and mechanical strength varied in the opposite way.The porous nanosolid has lower k value than the corresponding solid ceramics,but its stability is harmed by introducing pores at the same time.As an organic low-k material with high performance,poyimide(PI)has been introduced into the preparation of organic/inorganic composite porous nanoslids,with improved both low k and high stability.The starting materials for synthesizing PI were dissolved into DMF,which can also used as pore-forming agent.During the process of solvothermal hot press,PI is generated,and the low-k material—poyimide/Al₂O₃ composite porous nanosolid was prepared.The results indicate that the composite porous nanosolid possesses low k value and much higher stability.Because of the high intrinsic molecular polarity of Al₂O₃,it is difficult to further lower the k of porous nanosolid.So we chose BN nanoparticulate with low intrinsic k (3--5)as the start material,used deionized water,1,4-dioxane and cyclohexane as pore-forming agents,and prepared three kinds of BN porous nanosolid.The test results showed that all the three samples are porous structure,which lead to their dielectric constants lower than the BN bulk crystal,and decrease with the increasing of their porosity.