Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

Oxygen vacancy healing boosts the piezoelectricity of bone scaffolds

Although barium titanate (BaTiO3) presented tremendous potential in achieving self-powered stimulation to accelerate bone repair, pervasive oxygen vacancies restricted the full play of its piezoelectric performance. Herein, BaTiO3-GO nanoparticles were synthesized by the in situ growth of BaTiO3 on graphene oxide (GO), and subsequently introduced into poly-L-lactic acid (PLLA) powders to prepare PLLA/BaTiO3-GO scaffolds by laser additive manufacturing. During the synthesis process, CO and C-OH in GO would respectively undergo cleavage and dehydrogenation at high temperature to form negatively charged oxygen groups, which were expected to occupy positively charged oxygen vacancies in BaTiO3 and thereby inhibit the formation of oxygen vacancies. Moreover, GO could be partially reduced to reduced graphene oxide, which could act as a conductive phase to facilitate polarization charge transfer, thus further improving the piezoelectric performance. The results showed that the oxygen peak at the specific electron binding energy in O 1s declined from 54.4% to 14.6% and the Ti3+ peak that was positively correlated with oxygen vacancies apparently weakened for BaTiO3-GO, illustrating that the introduced GO significantly decreased the oxygen vacancy. As a consequence, the piezoelectric current of PLLA/BaTiO3-GO increased from 80 to 147.3 nA compared with that of PLLA/BaTiO3. The enhanced piezoelectric current effectively accelerated cell differentiation by upregulating alkaline phosphatase expression, calcium salt deposition and calcium influx. This work provides a novel insight for the design of self-powered stimulation scaffolds for bone regeneration.

High-κ Polyimide-Based Dielectrics by Introducing a Functionalized Metal-Organic Framework

In this work, novel metal-organic framework/polyimide (MOF/PI) composite films possessing dielectric properties were synthesized via a solution blending method. UiO-66 and UiO-66-NH₂ nanoparticles were first prepared by a hydrothermal method and added into PI to obtain the composite films. Compared with pure PI, the dielectric properties of the MOF/PI composites were substantially enhanced. The amine functionalization gave UiO-66-NH₂/PI composite films better dielectric properties in comparison with UiO-66/PI composite films because of improved interaction between PI and UiO-66-NH₂. It showed that the dielectric constant of the PI composite film containing 20 wt% UiO-66-NH₂ is 8.8 at 10² Hz, which was approximately 2.5 times that of the pure PI (3.5 at 10² Hz). The dielectric loss of the composite film was less than 0.034. Moreover, the breakdown strength of 20 wt% UiO-66-NH₂/PI composite films was found to be 208 kV/mm. We describe this new perspective for the preparation of high-performance polymer-based dielectric materials and their application as electrical materials.

Applicability of BaTiO3/graphene oxide (GO) composite for enhanced photodegradation of methylene blue (MB) in synthetic wastewater under UV-vis irradiation

Methylene blue (MB) is a dye pollutant commonly present in textile wastewater. We investigate and critically evaluate the applicability of BaTiO₃/GO composite for photodegradation of MB in synthetic wastewater under UV-vis irradiation. To enhance its performance, the BaTiO₃/GO composite is varied based on the BaTiO₃ weight. To compare and evaluate any changes in their morphologies and crystalline structures before and after treatment, BET (Brunauer-Emmett-Teller), XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy) and TEM (transmission electron microscopy) tests are conducted, while the effects of reaction time, pH, dose of photocatalyst and initial MB concentration on its photodegradation by the composite are also investigated under identical conditions. The degradation pathways and removal mechanisms of MB by the BaTiO₃/GO are elaborated. It is evident from this study that the BaTiO₃/GO composite is promising for MB photodegradation through ·OH. Under optimized conditions (0.5 g/L of dose, pH 9.0, and 5 mg/L of MB concentration), the composite with 1:2 dose ratio of BaTiO₃/GO has the highest MB degradation rate (95%) after 3 h of UV vis irradiation. However, its treated effluents still could not comply with the discharge standard limit of less than 0.2 mg/L imposed by national environmental legislation. This suggests that additional biological treatments are still required to deal with the remaining oxidation by-products of MB, still present in the wastewater samples such as 3,7-bis (dimethyl-amino)-10H-phenothiazine 5-oxide.

Fabrication and excellent electroresponsive properties of ideal PMMA@BaTiO3 composite particles

A series of core–shell-structured poly(methylmethacrylate)@BaTiO₃ (PMMA@BT) composite particles were constructed via the self-assembly of BT nanoparticles on the surfaces of PMMA cores through the covalent bonding of siloxane groups at room temperature. The PMMA@BT composite particles were characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, video-based optical contact angle measurement, thermogravimetric analysis, and impedance analysis. The electroresponses of the obtained PMMA@BT composite particles were all stronger than that of pure BT, and the electroresponse depended on the weight percentage of the BT shell. The PMMA@BT particles with the optimal core–shell structure contained 58.14 wt% of BT shell. The surface hydrophilicity of the optimal particles was close to that of pure BT, and the dielectric constant was the greatest among the series of synthesized PMMA@BT particles. Thus, the optimized PMMA@BT particles demonstrated the strongest electroresponsive behavior in gelatin hydrogel elastomer, as demonstrated by polarized microscopy and dynamic mechanical analysis. The excellent electroresponsive property of the optimal PMMA@BT particles is reflected by the large sensitivity of the increase in storage modulus for the gelatin hydrogel elastomer containing the composite particles (21% at E = 0.8 kV mm⁻¹ and a particle loading of 1.0 wt%), far greater than that of pure BT particles (4.7%). Based on the sensitive electroresponsive properties, the PMMA@BT particles have potential applications as electroresponsive materials.

A series of core–shell-structured poly(methylmethacrylate)@BaTiO₃ (PMMA@BT) composite particles were constructed via the self-assembly of BT nanoparticles on the surfaces of PMMA cores through the covalent bonding of siloxane groups at room temperature.

Sustainable in Situ Approach to Covalently Functionalize Graphene Oxide with POSS Molecules Possessing Extremely Low Dielectric Behavior

Incorporation of multifunctional inorganic additives into the commercial polymers still stands as the most captivating and effective way to realize new-generation electronic components. Here, we introduce a simple, cost-effective, and environmentally benign method to covalently functionalize graphene oxide (GO) with vinyl- and aminopropyl-functionalized hybrid silica spheres with a polyhedral oligomeric silsesquioxane (POSS)-siloxane composition. The reaction has been carried out in a mixture of ethanol and water (used as a medium) at ambient conditions with silane precursors. Later, the synthesized hybrid material has been tested for its dielectric properties after blending with syndiotactic polystyrene, a commercially available insulating semicrystalline polymer. It was observed that the dielectric constant decreases with the addition of GOPOSS up to 1.85 with a dielectric loss of 0.02 at 5 GHz. Significant improvements in the thermal properties of the composites were verified with minimal filler loading.

Using a novel rigid-fluoride polymer to control the interfacial thickness of graphene and tailor the dielectric behavior of poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) nanocomposites

A rigid liquid crystalline fluoride-polymer has been chosen to tailor the shell thickness of rGO to investigate the effect of interfacial thickness on the dielectric behavior of polymer conductive nanocomposites.

Enhancement of dielectric constant of polyimide by doping with modified silicon dioxide@titanium carbide nanoparticles

PI/SiO₂@TiC composites with enhanced dielectric constant are synthesized by hydrolysis of TEOS into microspheres forming a thin SiO₂layer on the TiC surface followed by mechanical blending of ODA and PMDA.