Low-k and superior comprehensive property hybrid materials of a fluorinated polyimide and pure silica zeolite

Abstract

In this study, various amounts of an amino-derivative of pure silica zeolite nanocrystals (A-PSZN) were blended with fluorinated poly(amic acid) (FPAA) to form a FPAA/A-PSZN precursor solution, and the fluorinated polyimide (FPI)/A-PSZN hybrid films were prepared via spin-coating and following thermal imidization of the FPAA/A-PSZN solution. A series of FPI/A-PSZN hybrid films were investigated scientifically based on the dielectric constant (k), water absorption, dynamic mechanical and thermal and mechanical properties. It is found that the k value decreases from 3.11 for pristine FPI to 2.65 for the FPI/7 wt% A-PSZN hybrid, which is attributed to the air within the micropore of A-PSZN and the inhibited molecular polarization originating from the internal cross-linking structure of hybrids. Due to the effective phase interconnection and the inherent excellent property of A-PSZN, on the other hand, the incorporation of A-PSZN results in the improvement of the storage modulus, glass transition temperature, thermal stability, Young's modulus, tensile strength and the decrease of water absorption, and thermal expansion coefficients for materials. The results indicate that the incorporation of A-PSZN is a promising approach to reduce the k value and improve the comprehensive properties of FPI, and the FPI/A-PSZN hybrid materials are potentially useful in the microelectronic industry.

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Introduction

In the microelectronic industry, insulator materials with low dielectric constants (k) are urgently needed for resolving the serious technological problems in high packing density integrated circuits, such as the resistance–capacitance delay, crosstalk noise and power dissipation, etc.^1,2 Generally speaking, in addition to a low-k, high thermal stability, a low thermal expansion coefficient, low moisture uptake, high mechanical strength, chemical inertness and good processability also must be satisfied for ideal insulator materials.³

Polyimide (PI), an aromatic polymer with rigid imide functional group, possesses outstanding thermal, mechanical, dielectric properties and chemical stability, and thereby is a desirable and promising dielectric material for the microelectronic industry.⁴ However, the conventional PI has the k value of 3.1–3.5 that limits its application in high-density integrated circuit.⁵ In view of the C–F bond with small dipole and low polarization, the introduction of trifluoromethyl group with greater free volume on PI chain is able to reduce the k value, and the fluorinated PI (FPI) has been developed rapidly.^6,7 On the other hand, concerning the dielectric constants of air (k ≈ 1), the incorporation of controlled porous structure in matrix can obtain low-k porous PI, which includes PI nanofoam and PI/nanoporous inorganic hybrid materials.⁸ Fu et al. prepared PI nanofoam with the k value of about 2.00 by heat-induced decomposition of thermally labile unit of polyacrylamide on PI main-chain.⁹ Leu et al. introduced polyhedral oligomeric silsesquioxanes (POSS) into PI matrix to construct PI-chain-end tethered POSS,¹⁰ PI-side-chain tethered POSS¹¹ and PI-tethered POSS nanocomposites¹² by different methods, and the k value of those materials are 3.09, 2.40 and 2.30, respectively. However, the complex purification and very low yield are the key problems to restrict the real applications of POSS.⁸ As an alternative, porous silica shows obvious advantage on preparation and has widely used to prepare low-k PI/nanoporous inorganic hybrid materials. For example, the incorporation of 5 wt% silica nanotube,¹³ 10 wt% silica mesoporous particles¹⁴ and 5 wt% silica hollow spheres¹⁵ can obtain PI composites with the k value of 2.95, 2.60 and 2.20, respectively.

Since the polarity and the porosity are independent factors on affecting the k value of materials, the construction of nanoscale porous structure in low polarity PI matrix is a promising approach to obtain lower-k value.⁶ However, some drawbacks for FPI and PI nanofoam, such as poor mechanical and thermal properties, have to be overcome before commercial application of materials.^12,16 In view of that, the preparation of FPI/inorganic hybrids by appropriate incorporation of rigid porous inorganic fillers is of great interest, which can further decrease the k value and improve overall performance of FPI.

As microporous silica, pure silica zeolite nanocrystal (PSZN) possesses high heat conductivity and mechanical strength and hydrophobicity due to its high crystalline nature, which are the advantages over its amorphous counterparts.^17,18 Most importantly, many studies show that the PSZN films prepared by suspensions spin-on method have the k value in the range of 1.5–2.1.^19–21 Therefore, it is believed that PSZN films can meet the requirement of insulator materials in microelectronic industry, but the complex preparation procedure and the brittleness of PSZN films are the technical challenge that must be faced. Take into account the good processability and flexibility of polymer matrix, the combination of PSZN and FPI would be expected to obtain low-k dielectric materials with good performance. Against this background, PSZN was surface modified to synthesized amino-derivative (A-PSZN), and then introduced into FPI matrix to prepared FPI/A-PSZN hybrid film, the influence of A-PSZN on dielectric, water absorption, dynamic mechanical, thermal, mechanical properties of hybrid film were evaluated in this study.

Experimental part

Materials

Tetrabutylammonium hydroxide (TBAOH) (40 wt% aqueous solution), tetraethylorthosilicate (TEOS) (98.6 wt%) and aminopropyl triethoxysilane (KH550) (98 wt%) were purchased from Aladdin Industrial Inc. (Shanghai, China) and used without further purification. 2,2-Bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 4,4′-oxydianiline (ODA) were supplied by Alfa Aesar (Ward Hill, MA, USA) and vacuum-dried prior to use. N-Methyl-2-pyrrolidone (NMP) of analytical grade was purified by distillation under reduced pressure over phosphorus pentoxide.

Preparation and surface modification of PSZN

The TBAOH aqueous solution was dropwise added to TEOS under vigorous stirring. The mixture was stirred for pre-hydrolization in a sealed polypropylene bottle at 25 °C, and a solution with molar composition of 0.3TBAOH/1SiO₂/4EtOH/20H₂O was formed after 24 h. The precursor solution was subsequently transferred into Teflon-lined autoclave and heated at 100 °C for 24 h with the purpose of crystallization. After completion of synthesis, the suspension was centrifuged to obtain the nanoparticle product, which was washed with deionized water, freeze-dried, calcined at 450 °C in air for 2 h to remove the structure-directing-agent, and finally get PSZN.

The mixture of 1 g of PSZN, 5 g of deionized water and 95 g of ethanol was ultrasonically vibrated for 1 h, and then a certain amount of KH550 was added into the mixture under stirring. The resulting new mixture was adjusted to pH of 4–5 by acetic acid and stirred at refluxed temperature for 2 h. When the system was cooled down, the produce was collected by centrifugation and washed with ethanol several times, subsequently freeze-dried. Thus, the aminepropyl groups were introduced onto the surface of PSZN, and the resultant sample is called A-PSZN.

Preparation of FPI/A-PSZN hybrid films

3 mmol ODA was added into a three-necked flask containing 11.2 mL NMP, and the mixture was mechanically stirred along with N₂ at 25 °C. After ODA was completely dissolved, 3.06 mmol 6FDA was added into the flask under vigorous stirring over a period of 1.5 h. Until the viscosity of the system increased abruptly, an additional 12 h of stirring was carried out in the system, and finally a viscous fluorinated poly(amic acid) (FPAA) solution was obtained.

Varied amount of A-PSZN was dispersed into NMP by ultrasonic vibration and mechanically blended with above FPAA solution for 12 h in nitrogen atmosphere at 25 °C. Subsequently, the obtained mixture was cast on glass slide and cured with specific heat treatment procedure of 80 °C/1 h, 100 °C/1 h, 200 °C/1 h and 300 °C/2 h. Finally, the hybrid film with the thickness of around 100 μm was peeled off from the glass slide and used for measurement. The additions of A-PSZN in a series hybrid films are 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt% and 15 wt%, respectively.

The synthesis procedure of FPI/A-PSZN hybrid film is shown in Scheme 1.

Scheme 1 Synthesis procedure of FPI/A-PSZN film.

Characterization

The Fourier transition infrared (FTIR) spectra of nanoparticles were recorded by FTIR spectrophotometer (Netzsch 870). Zeta potentials and Z-average particle size of nanoparticles were tested on dynamic light scattering (DLS) instrument (Malvern Nano-ZS90). The morphologies of nanoparticles and the cross-section of films were observed using scanning electron microscope (HITACHI S-4800). The X-ray diffraction (XRD) patterns of nanoparticles were recorded by X-ray diffractometer (Bruker D8 ADVANCE) with CuKα radiation (λ = 0.1542 nm). The N₂ adsorption–desorption isotherms of nanoparticles were measured by Micromeritics system (ASAP2020), and the micropores properties of samples were determined by Horvath–Kawazoe (H–K) analysis, BET analysis and t-plot analysis. The transmittance spectrums of films were scanned with UV-vis spectrophotometer (Foundry Master, WAS Co., Germany) in the range of 300–900 nm. The k value of films was measured on a LCR meter (hp 4284A) in 40% relative humidity at 25 °C, and measure frequency range is 50 kHz to 1 MHz. Prior to the test, gold electrodes were vacuum-deposited on both surfaces of the dried films. The water absorption of films (w_wa) was calculated by (m_s − m_d)/m_d × 100%, where m_d and m_s are the weight of dry film and the weight of film soaked in deionized water for 24 h, respectively. The dynamic mechanical properties of films were analyzed through dynamic mechanical analyzer (Netzsch 242C) with the heating rate of 5 °C min⁻¹ and the frequency of 1.0 Hz in the temperature range of 50–310 °C. The thermal decomposition temperatures (T_dec, defined as 5% weight loss) of films were determined by thermogravimetric analyzer (Netzsch 209F1) with the heating rate of 20 °C min⁻¹ in the temperature range of 50–900 °C under nitrogen atmosphere. The in-plane coefficients of thermal expansion (CTE) of films were measured via thermal mechanical analyzer (Netzsch 402F3) with the heating rate of 5 °C min⁻¹ and the tension force of 0.05 N under nitrogen atmosphere. The mechanical properties of films were studied by mechanical testing machine (INSTRON 3365). Five measurements were carried out for each test and the average value was adopted.

Results and discussions

Characterization of PSZN and A-PSZN

The surface modification of PSZN to prepare A-PSZN is based on the reaction between silanol groups on the surface of PSZN²² and KH550.

Fig. 1 is the FTIR spectra of PSZN and A-PSZN. Due to the same framework, the stretching vibration adsorption peaks of Si–O–Si at 1230 cm⁻¹ and 1090 cm⁻¹ are found both for two samples. Before the surface modification, a weak broad peak around 3440 cm⁻¹, which attributed to the O–H stretching vibration, can be observed for PSZN. After the surface modification, two peaks are found at 1550 cm⁻¹ and around 3465 cm⁻¹ can be assigned to the bending vibration and the stretching vibration of N–H in amino-group, respectively. The difference of FTIR spectra between PSZN and A-PSZN indicates that KH550 has been successfully grafted onto the surface of PSZN.

Fig. 1 FTIR spectra of (a) PSZN and (b) A-PSZN.

Fig. 2 shows the zeta potentials of PSZN and A-PSZN are −46.8 mv (pH ≈ 9) and 33.7 mv (pH ≈ 2), respectively. PSZN possesses negative charge due to the ionization of surface silanol groups in base system. After surface modification, aminopropyl groups are introduced onto the surface of PSZN and get A-PSZN. Because amino group can be protonated to form cation in acid environment, the charge of A-PSZN is positive. The difference of zeta potential between PSZN and A-PSZN further confirms that KH550 has been successfully grafted onto the surface of PSZN.²³

Fig. 2 Zeta potentials of PSZN and A-PSZN.

The SEM images in Fig. 3 show that PSZN and A-PSZN possess similar morphology with aspect ratio of 2 : 1 and uniform size, but inconspicuous difference in size. DLS measurement shows that the Z-average particle size of A-PSZN (167.6 nm) is slightly bigger than that of PSZN (145.9 nm). This indicates that the surface modification does not lead to the agglomeration since KH550 mainly just graft on the surface of single PSZN.

Fig. 3 SEM images of (a) PSZN and (b) A-PSZN.

The XRD patterns (Fig. 4) of nanoparticles show that PSZN and A-PSZN possess same crystal structure and high crystallinity according to the four strong diffraction peaks (2θ = 8.0°, 8.9°, 23.3° and 24°), which correspond to (101), (200), (501) and (303) lattice planes of pure silica zeolite (MEL-type topology),²⁰ respectively. However, one can observe the obviously different intensity in the diffraction peaks of 2θ = 8.0° between PSZN and A-PSZN. The comparatively higher value of A-PSZN may be attributed to the tendentious graft of KH550 on (101) lattice plane.

Fig. 4 XRD patterns of (a) PSZN and (b) A-PSZN.

Fig. 5 shows the N₂ adsorption–desorption isotherms of PSZN and A-PSZN. The uptake at low relative pressures and no hysteresis loop at higher relative pressure indicate the presence of micropores and inexistence of mesopores for PSZN and A-PSZN. The more detailed analysis of the isotherms is present in Table 1. Compare to PSZN, the micropores size, surface area and volume of A-PSZN exhibit a little drop, which might be due to the blocked effect of modifier on micropores. This slight decrease in micropores data illustrates that the graft of KH550 on the surface of PSZN does not change its micropores characteristic.

Fig. 5 N₂ isotherm adsorption–desorption plots of PSZN and A-PSZN.

Table 1 Micropores properties of PSZN and A-PSZN

Sample	Micropore size (nm)	Micropore surface area (m^2 g^−1)	Micropore volume (cm^3 g^−1)
PSZN	0.535	182	0.103
A-PSZN	0.525	163	0.083

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Morphology of FPI/A-PSZN hybrid film

Fig. 6 shows the SEM images of the cross-section of FPI/A-PSZN hybrid films with A-PSZN addition of 5 wt% (a), 10 wt% (b) and 15 wt% (c). From the SEM images, one can not find any obvious phase separation on the cross-sections of hybrid films. This indicates the strong interaction between surface amino groups of A-PSZN and functional groups of FPI (terminal anhydride and –CF₃ groups) results in good compatibility between two phases.²⁴

Fig. 6 SEM images of cross-section of FPI/A-PSZN hybrid films with different addition of A-PSZN: (a) 5 wt%, (b) 10 wt% and (c) 15 wt%.

The good compatibility between FPI and A-PSZN in hybrids can be confirmed further by the effect of filler on the transmittance of films. As shown in Fig. 7, the transmittance of film decreases gradually with increasing the addition of A-PSZN in hybrid film due to the light scattering caused by the filler. However, FPI/15 wt% A-PSZN hybrid film with well transmittance is still observed, which suggests that fillers are evenly dispersed over matrix and do not form agglomerates.²⁴

Fig. 7 UV-visible transmittance spectroscopy of FPI/A-PSZN with different addition of A-PSZN.

Dielectric properties of FPI/A-PSZN hybrid film

The k (1 MHz) value of FPI/A-PSZN hybrid films as a function of the addition of A-PSZN is presented in Fig. 8. As can be seen, the effect of A-PSZN on the k value of hybrids demonstrates a decreasing first and increasing afterwards trend with the addition of A-PSZN, namely, the k values decrease from 3.11 of pristine FPI to 2.65 of FPI/7 wt% A-PSZN hybrid, and then increase to 3.07 of FPI/15 wt% A-PSZN hybrid. This is attributed to the structural characteristics of PSZN and hybrids. First of all, PSZN has been demonstrated to possess promising low-k due to the microporous structure and high crystallinity,¹⁸ and hence the introduction of A-PSZN into FPI matrix favor reduces the k of materials. Meanwhile, the reaction between the surface amino group of A-PSZN and the terminal anhydride of FPI chain generates the internal cross-linking structure of hybrids, which makes for inhibiting the molecular polarization of materials under applied electric field and thus contributes to obtain the hybrids with low-k.²⁵ When the terminal anhydride of FPI chain was consumed, however, excess A-PSZN without the chemical bond with FPI chain results in the increase of the polarity of hybrids originated from the free polar amino groups on the surface of A-PSZN. Therefore, the orientation polarization of dipole enhances under the applied electric field, which has an advantage over the effect of air within the micropore of A-PSZN on the k, and thus the k value of hybrids increases. Consequently, there is a optimal addition for the effect of A-PSZN on the k value of hybrids, after the addition of A-PSZN exceeds 7 wt% in hybrids, the k value of FPI/A-PSZN hybrid film increases with further increasing the content of A-PSZN.

Fig. 8 Dielectric constant (1 MHz) of FPI/A-PSZN hybrid films at 1 MHz as a function of the addition of A-PSZN.

Fig. 9 represents the k value of pristine FPI film and FPI/A-PSZN hybrid films varied with the frequency in the range of 50–1000 kHz. It is can be seen that the k value of films decreases slightly with increasing the test frequency, on the other hand, the higher content of A-PSZN in hybrids, the more obvious frequency dependency of the k value can be observed. This can be attributed to the frequency dependency of polarization mechanism.²⁶ In various polarizable units (electron, atom, dipole and interface), the frequency range of orientation polarization for dipole is 10³ Hz to 10⁸ Hz, which is consistent with the frequency range of determining the k value of hybrids in this study. Within this frequency range, the orientation polarization of dipole decreases with increasing frequency, and thus makes a reduction in the k value of hybrids at high frequency. While increasing the content of A-PSZN, orientation polarization of dipole strengthens, and more obvious frequency dependency of the k value for hybrids is present.

Fig. 9 Frequency dependency of dielectric constants for FPI/A-PSZN hybrid films with different addition of A-PSZN: (a) 0 wt%, (b) 1 wt%, (c) 3 wt%, (d) 5 wt%, (e) 7 wt%, (f) 10 wt%, (g) 15 wt%.

Water absorption of FPI/A-PSZN hybrid film

The hydrophobicity is very important for the dielectric materials. Seen from Fig. 10, as the content of A-PSZN increases, the water absorption of film (w_wa) decreases. This suggests that the hydrophobicity of film is improved by introducing A-PSZN into FPI matrix. For hybrids, the chemical and physical interaction between surface amino group of A-PSZN and terminal anhydride and –CF₃ of FPI chain can result in denser surface of film, which can suppress the penetration of water into the film.

Fig. 10 Water absorption of FPI/A-PSZN hybrid films as a function of the addition of A-PSZN.

Dynamic mechanical properties of FPI/A-PSZN hybrid film

Dynamic mechanical properties of pristine FPI film and FPI/A-PSZN hybrid films with different addition of A-PSZN are displayed in Table 2 and Fig. 11. One can observe that incorporation of A-PSZN efficiently enhances the storage modulus (E′) of pristine FPI, and the hybrids with greater content of A-PSZN possess higher E′. For example, E′ at 50 °C for FPI/15 wt% A-PSZN hybrid is 3.68 GPa, showing about increase of 51% compared to that of pristine FPI. Such reinforcement indicates that the introduction of rigid filler and the resulting cross-linking structure help to improve the stiffness of hybrids. As the corresponding result, the activating threshold of segmental motion has also been elevated, and thus impels the maximum of hybrid's mechanical loss peak move to a higher temperature, as shown in Fig. 11. Therefore, T_gs of all hybrids are higher than that of pristine FPI, and an increase of 15.8 °C in T_g (from 279.0 °C to 294.8 °C) can be obtained when the addition of A-PSZN in hybrid films is increased to 15 wt%.

Table 2 Dynamical mechanical properties of FPI film and FPI/A-PSZN hybrid films with different addition of A-PSZN

Content of A-PSZN (wt%)	0	1	3	5	7	10	15
E′ (GPa at 50 °C)	2.44	2.66	2.85	2.974	3.03	3.32	3.68
Tg (°C)	279.0	292.0	292.4	293.0	293.7	294.0	294.8

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Fig. 11 Storage modulus and mechanical loss factors (tan δ) curves of pristine FPI film and FPI/A-PSZN hybrid films as a function of temperature.

Thermal properties of FPI/A-PSZN hybrid film

Table 3 and Fig. 12 present the thermal stability of FPI/A-PSZN hybrid films with different content of A-PSZN. As can be seen, T_dec of FPI/A-PSZN hybrid film is slightly higher than that of pristine FPT, which comes from inherently high thermal stability of inorganic filler and enhanced interface bonding between FPI and A-PSZN. However, one can still find that incorporation of A-PSZN will accelerate degradation above 555 °C and reduce weight residues at 900 °C, moreover, this thermal degradation phenomenon becomes obvious as increasing the content of A-PSZN within hybrids. The similar result has been noticed in the studies of other FPI hybrids,^27,28 but not found for the common PI hybrids.² Therefore, it can be conjectured that the role of fluorinated substituent is dominated to the thermal degradation phenomenon above. For the FPI hybrids, the backbone of matrix contains large number of –CF₃ groups, which play a negative role on the formation of the tight carbon layer during the quick thermal degradation. After the decomposition of organic attachment between filler and matrix, inorganic fillers with fine heat conductivity only serve as the wick and consequently speed up the decomposition of the loose carbon layer. Hence, the quicker degradation rate above 555 °C and less weight residues at 900 °C for FPI/A-PSZN hybrids are observed.

Table 3 Thermal properties of FPI film and FPI/A-PSZN hybrid films with different addition of A-PSZN

Content of A-PSZN (wt%)	0	1	3	5	7	10	15
Tdec (°C)	538.9	539.0	544.6	541.2	541.5	544.7	542.5
Residual mass at 900 °C (%)	53.6	53.5	53.0	52.3	52.0	51.8	51.7
CTE (μm m^−1 °C^−1)	71.7	68.2	66.0	64.7	61.2	59.2	57.4

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Fig. 12 TGA curves of pristine FPI and FPI/A-PSZN hybrid films.

As shown in Table 3, the CTE values of FPI/A-PSZN hybrids gradually decrease as increasing the content of A-PSZN, the more addition of A-PSZN, the lower CTE value of hybrids. As can be seen, the CTE value of the hybrid with 15 wt% A-PSZN (57.4 μm m⁻¹ °C⁻¹) shows a drop of 14.3 μm m⁻¹ °C⁻¹ than that of pristine FPI (71.7 μm m⁻¹ °C⁻¹). It has been well recognized that the CTE value of hybrids is related closed to the CTE of each phase and the interaction among phases.²⁹ In terms of the framework composition, A-PSZN is crystalline silica and has an extremely low CTE value of approximately 0.5 μm m⁻¹ °C⁻¹,¹⁴ therefore the incorporation of A-PSZN in FPI can reduce the CTE value of materials. As porous silica, however, the air within micropore of A-PSZN will expand as elevating temperature and has a disadvantage on reducing the CTE of hybrids. Considering that the strong interaction between A-PSZN and FPI can against the expansion of air within micropore and restrict segmental motion of polymer, hybrid materials show the lower CTE values than pristine FPI accordingly.

Mechanical properties of FPI/A-PSZN hybrid film

Fig. 13 shows the Young's modulus of FPI/A-PSZN hybrid films as a function of A-PSZN content. Compared to the pristine FPI film, the Young's modulus of FPI/A-PSZN hybrid films increases as increasing the content of A-PSZN, and the Young's modulus of FPI/15 wt% A-PSZN (2.73 GPa) shows 77.3% of increase than that of pristine FPI (1.54 GPa).

Fig. 13 Young's modulus of FPI/A-PSZN hybrid films as a function of the addition of A-PSZN.

The tensile strength and elongation at break as a function of A-PSZN content are shown in Fig. 14. Because of the chemical interaction between filler and matrix resulting in the cross-linking structure, one can see that the tensile strength is increased from 91.2 MPa of pristine FPI to 101.9 MPa of FPI/7 wt% A-PSZN hybrid. Due to the weak secondary bond formed between the surface amino groups of excess A-PSZN and –CF₃ groups of FPI, however, only a slight increase magnitude in tensile strength can be obtained when the addition of A-PSZN further increase from 7 wt% to 15 wt%. As also can be seen, the toughness of FPI/A-PSZN hybrids increases with the content of A-PSZN till it reaches 7 wt%, and then decreases. Concretely, the elongation at break of FPI/7 wt% A-PSZN hybrid is increase from 10.5% of pristine FPI to 15.3%, while the elongation at break of the hybrids with 10 wt% and 15 wt% of A-PSZN decreases to 14.0% and 9.7%, respectively. The decrease in toughness for the FPI/10 wt% A-PSZN and FPI/15 wt% A-PSZN may be due to the presence of large number of rigid inorganic fillers within materials.

Fig. 14 Tensile strength and elongation at break of FPI/A-PSZN hybrid films as a function of the addition of A-PSZN.

Conclusion

PSZN was synthesized and surface modification by KH550 to prepared A-PSZN, these two as-prepared nanocrystal particles were characterized in detailed. As filler, A-PSZN with various amounts was introduced into FPI matrix, synthesize from 6FDA and ODA, to prepare a series of low-k FPI/A-PSZN hybrid films. On account of inherent excellent properties of A-PSZN and the good interface interaction between matrix and filler, the incorporation of A-PSZN in FPI can lead to the improvement of the comprehensive properties of materials. The k value shows a reduction of 0.46 (from 3.11 to 2.65) when the addition of A-PSZN in hybrid films is increased to 7 wt%. FPI/15 wt% A-PSZN possesses 0.86% of w_wa, 3.68 GPa of E′, 294.8 °C of T_g, 542.5 °C of T_dec, 57.4 μm m⁻¹ °C⁻¹ of CTE, 2.73 GPa of Young's modulus, 103.1 MPa of tensile strength, compare to 1.20%, 2.44 GPa, 279 °C, 538.9 °C, 71.7 μm m⁻¹ °C⁻¹, 1.54 GPa, 91.2 MPa of pristine FPI, respectively. This research provides an alternative approach to prepare the low-k FPI/A-PSZN hybrid films with superior comprehensive properties for the application of microelectronic industry.

Acknowledgements

The authors are grateful to the support of the National Natural Science Foundation of China (No. 51173047) and the Project for Science and Technology of Chaozhou (No. 2014G06).

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