Preparation Of Low Dielectric Constant Polyimide/Pure Silica Zeolite Hybrid Films

Polyimide (PI) possesses remarkable thermal stability, mechanical strength, durability andsolvent resistance, and has been widely applied in the electrical and electronic industries. Withthe rapid development of ultra large scale integrated circuit (ULSIC), the increasing density ofwire and decreasing size of device in ULSIC make a requirement for the dielectric materialwith lower dielectric constant. Constrained by the higher intrinsic dielectric constant, PI stillcan not meet the requirement of modern microelectronic industry. Therefore, the preparationof a new generation of PI with low dielectric constant and excellent overall performances is aresearch focus in the field of materials in the recent year.In this paper, MEL-type pure silica zeolite nanocrystal (PSZN) and amino-derivative ofPSZN (A-PSZN) were synthesized, and then the inorganic filler was introduced into PI matrixvia solution blending with PI-precursor (PAA) and subsequently thermal imidization toprepare a series of PI/A-PSZN hybrid films, and the performances of hybrid films werestudies in detailed.1. PSZN was synthesized from tetraethyl orthosilicate (TEOS) by usingtetrabutylammonium hydroxide (TBAOH) as template and alkali via the static hydrothermalcrystallization and then was surface modified to prepare A-PSZN byγ-aminopropyltriethoxysilane coupling agent (KH550) in acid medium. By making effort tooptimize the experimental parameters of synthesizing PSZN, the suitable experimentalcondition to synthesize uniform PSZN with regular morphology was obtained and showed asfollow: the solution with a molar ratio of1TEOS/0.3TBAOH/20H2O was stirred for24h at25°C, after pre-hydrolization, the solution was transferred into a Teflon-lined autoclave andwas further heated at110°C for24h crystallization. Meanwhile, the studies show that KH550tend to graft onto the (101) crystal face of PSZN and the surface modification does not bringsignificant impact on the morphology, crystallinity and microporous properties of sample, theamount of KH550grafted onto the surface of PSZN is3.10%.2. PSZN and A-PSZN were incorporated respectively into pyromellitic dianhydride(PMDA)-4,4’-diaminodiphenyl ether (ODA) type PI matrix to preparedPI(PMDA-ODA)/PSZN composite films and PI(PMDA-ODA)/A-PSZN hybrid films. The studies show that A-PSZN can be uniformly dispersed in the matrix with the aid of thereaction between amino group of A-PSZN and anhydride of PI and form the crosslinkedstructure within the hybrid, while PSZN tend to agglomerate due to the poor compatibilitybetween PSZN and PI, thus PI(PMDA-ODA)/A-PSZN hybrid film possesses more excellentoverall performances compared with PI(PMDA-ODA)/PSZN composite film; when theaddition of A-PSZN is5wt%, the dielectric constant (1MHz) of PI(PMDA-ODA)/A-PSZNhybrid film decreases from3.52of matrix to3.11, moreover, hybrid film possesses increasedthermal and mechanical properties, as well as improved hydrophobicity with respect to matrix;however，when excessive A-PSZN is added, agglomeration will occur, and therefore resultingin worse overall performance.3. The dielectric constant of PI matrix can be reduced by incorporated–CF3into PImain-chain, and the addition of A-PSZN not only can reduce the dielectric constant offluorinated PI, but also can improved the poor thermal and mechanical properties offluorinated PI. Using2,2-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA),4,4’-diaminodiphenyl ether (ODA) and2,2’-bis(trifluoromethyl)-4,4’-diaminobiphen (TFDB)as monomer, the hybrid films of PI(6FDA-ODA)/A-PSZN and PI(6FDA-TFDB)/A-PSZNwere prepared through the solution blending of A-PSZN with precursor of fluorinated PI. Thestudies show that when the addition of A-PSZN is7wt%, the hybrid film ofPI(6FDA-ODA)/A-PSZN and PI(6FDA-TFDB)/A-PSZN have the lowest dielectric constant,are2.73and2.56(1MHz), respectively; on the other hand, storage modulus, glass transitiontempera(Tg) and decomposition temperature(Tdec) of PI(6FDA-ODA)/7wt%A-PSZN increase0.59GPa,14.7°C and2.6°C than that of matrix, respectively, while Young’s modulus andtensile strength of PI(6FDA-TFDB)/7wt%A-PSZN improves0.88GPa and27.1MPa thanthat of matrix, respectively.4. PI(PMDA-ODA) fiber membrane and corresponding A-PSZN hybrid fiber membranewere fabricated by electrospinning technology. The studies show that the optimizedelectrospinning is carried out with the feeding rate of0.5mL/h at applied voltage of15kV atambient temperature of25°C and relative humidity of40%, while PAA concentration andcollective distance is set to be15wt%and15cm, respectively; since moisture absorptionfrom the internal porous structure, PI(PMDA-ODA) fiber membrane possesses a dielectric constant of1.61(1MHz), which is higher than the theoretical dielectric constant of1.22calculated by Maxwell-Garnett equation; although the addition of A-PSZN does not affect thedielectric constant, but improved the mechanical properties, tensile strength ofPI/7wt%A-PSZN hybrid fiber membrane is improve to41.3MPa from29.4MPa of matrix.