Flexible Polyimide Films Research Articles

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride, self-orientation behavior during solution casting, and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high Tg's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.

Flexible and transparent polyimide films containing two-dimensional alumina nanosheets templated by graphene oxide for improved barrier property.

Unique two-dimensional alumina nanosheets (Alns) using graphene oxide (GO) as templates are fabricated and successfully incorporated with organo-soluble polyimide (PI) to obtain highly transparent PI nanocomposite films with improved moisture barrier property. The effects of filler types and contents on water vapor transmission rate (WVTR) and transparency of PI are systematically studied. The hydroxyl groups on GO react with aluminum isopropoxide via sol-gel process to obtain alumina coverd-GO (Al-GO), and then thermal decomposition is applied to obtain Alns. Alns are the most efficient fillers among others to restrict the diffusion of water vapor within PI matrix and simultaneously maintain the transparency of PI. XRD pattern, TEM, and AFM images confirm the sheet-like morphology of Alns with ultrahigh aspect ratio. With only 0.01 wt % of Alns, the PI nanocomposite film exhibits the most significant reduction of 95% in WVTR as compared to that of pure PI film. Most importantly, the resultant PI/Alns-0.01 film exhibits excellent optical transparency and high mechanical strength and great thermal stability.

Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

Flexible polyimide films hybrid with functionalized boron nitride and graphene oxide simultaneously to improve thermal conduction and dimensional stability.

Coupling agent-functionalized boron nitride (f-BN) and glycidyl methacrylate-grafted graphene (g-TrG) are simultaneously blended with polyimide (PI) to fabricate a flexible, electrically insulating and thermally conductive PI composite film. The silk-like g-TrG successfully fills in the gap between PI and f-BN to complete the thermal conduction network. In addition, the strong interaction between surface functional groups on f-BN and g-TrG contributes to the effective phonon transfer in the PI matrix. The thermal conductivity (TC) of the PI/f-BN composite films containing additional 1 wt % of g-TrG is at least doubled to the value of PI/f-BN and as high as 16 times to that of the pure PI. The hybrid film PI/f-BN-50/g-TrG-1 exhibits excellent flexibility, sufficient insulating property, the highest TC of 2.11 W/mK, and ultralow coefficient of thermal expansion of 11 ppm/K, which are perfect conditions for future flexible substrate materials requiring efficient heat dissipation.

Novel high Tg, organosoluble poly(ether imide)s containing 4,5-diazafluorene unit: Synthesis and characterization

The synthesis of aromatic poly(ether imide)s containing 4,5-diazafluorene units in the polymer backbone is described. 9,9-di[4-(4-Aminophenoxy)phenylene]-4,5-diazafluorene (3), which was used as a new monomer, was synthesized with 4,5-diazafluoren-9-one as the starting material. This diamine monomer was employed in reactions with a variety of aromatic dianhydrides to furnish poly(ether imide)s. These 4,5-diazafluorene-based polymers showed solubility in polar amidic solvents such as NMP, DMAc and DMF, good optical transparency, and high thermal stability. The glass transition temperatures (Tg) of these poly(ether imide)s were recorded between 325 and 356°C with the help of differential scanning calorimetry (DSC), and the Tg determined by dynamic mechanical thermal analyses (DMA) stayed in the range of 329–363°C, and the 10% weight-loss temperatures all occurred above 560°C in both nitrogen and air atmospheres. In addition, the flexible polyimide films possessed tensile strengths in the range of 64–101MPa, tensile modulus of 1.8–2.1GPa, and elongations at break of 6–13%.

Frequency tunable terahertz filter based on dual layered split-ring resonator array

Terahertz frequency tunable filter based on the dual layered split-ring resonator (SRR) array was fabricated on flexible polyimide film using conventional photolithography techniques. The fabricated SRR array was measured by terahertz time-domain spectroscopy (THz-TDS) and compared with the simulation data. We found that the center frequency could be controlled from 1.04 to 1.65 THz by the dipole coupling effect between upper and lower SRR layers. The bandwidth of the fabricated filter is also confirmed to be tuned validly ranging from 1.04 to 1.72 THz. By using the extracted field distribution, we verified that the localized field enhancement could be manipulated by changing the coupling distance between adjacent layers.

Synthesis and characterization of novel polyimides derived from 3,6-bis(4-aminophenoxy)pyridazine

Pyridazine-containing aromatic diamine monomer, 3,6-bis(4-aminophenoxy)pyridazine (APPD), was successfully synthesized by a nucleophilic substitution reaction of 3,6-dichloropyridazine with para-aminophenol. The aromatic heterocyclic diamine was employed to synthesize a series of polyimides (PIs) by polycondensation with various commercially available aromatic dianhydrides in N, N-dimethylacetamide via the conventional two-step method and further thermal imidization forming polyimides. The inherent viscosities of the resulting poly (amic acid)s were in the range of 0.47–1.51 dL g−1. Meanwhile, strong and flexible PI films were obtained, which had good thermal resistance, with the glass transition temperatures of 214–305°C and the temperature at 5% weight loss of 421–463°C under nitrogen atmosphere, as well as outstanding mechanical properties with tensile strengths of 61–102 MPa and elongations at break of 2.8–64.7%. The cutoff wavelength of the PI films were ranged in 357–413 nm.

Glucose Fuel Cells with a MicroChannel Fabricated on Flexible Polyimide Film

In this work, a glucose fuel cell was fabricated using microfabrication processes assigned for microelectromechanical systems. The fuel cell was equipped with a microchannel to flow an aqueous solution of glucose. The cell was fabricated on a flexible polyimide substrate, and its porous carbon-coated aluminum (Al) electrodes of 2.8 mm in width and 11 mm in length were formed using photolithography and screen printing techniques. Porous carbon was deposited by screen printing of carbon black ink on the Al electrode surfaces in order to increase the effective electrode surface area and to absorb more enzymes on the electrode surfaces. The microchannel with a depth of 200 μm was fabricated using a hot embossing technique. A maximum power of 0.45 μW at 0.5 V that corresponds to a power density of 1.45 μW/cm2 was realized by introducing a 200 mM concentrated glucose solution at room temperature.

Graphene nanosheets as ink particles for inkjet printing on flexible board

Stable ink containing highly dispersed graphene nanosheets (GNSs) for inkjet printing on polyimide (PI) film has been successfully prepared by the adsorption of sodium n-dodecyl sulphate (SDS) and adjusting the pH value to 10 by ammonia. Conductive features on a flexible PI film were fabricated by inkjet printing the stable ink directly on a substrate. With higher number of printing cycles, the loading weight of GNS on PI film showed a linear increase up to printing 200 times, when the conductivity reached the saturation value of 6Sm−1. Sintering the printed GNS at 400°C can effectively lead to the elimination of excess SDS on the GNSs and increase the CC content. The data provided by a four-point probe show that the conductivity of the sintered film can be improved to 121.95Sm−1.

초발수 현상을 이용한 나노 잉크 미세배선 제조

This study is carried out to develop the new process for the fabrication of ultra-fine electrodes on the flexible substrates using superhydrophobic effect. A facile method was developed to form the ultra-fine trenches on the flexible substrates treated by plasma etching and to print the fine metal electrodes using conductive nano-ink. Various plasma etching conditions were investigated for the hydrophobic surface treatment of flexible polyimide (PI) films. The micro-trench on the hydrophobic PI film fabricated under optimized conditions was obtained by mechanical scratching, which gave the hydrophilic property only to the trench area. Finally, the patterning by selective deposition of ink materials was performed using the conductive silver nano-ink. The interface between the conductive nanoparticles and the flexible substrates were characterized by scanning electron microscope. The increase of the sintering temperature and metal concentration of ink caused the reduction of electrical resistance. The sintering temperature lower than <TEX>$200^{\circ}C$</TEX> resulted in good interfacial bonding between Ag electrode and PI film substrate.

High-Performance Current Saturating Graphene Field-Effect Transistor With Hexagonal Boron Nitride Dielectric on Flexible Polymeric Substrates

Graphene transistors using hexagonal boron nitride as the gate dielectric are implemented on mechanically flexible polyimide films. Current saturation is observed for the first time in graphene transistors on a plastic substrate. An atomically smooth insulating surface is achieved with the proposed capture-release process and two-step annealing process, resulting in subnanometer surface roughness. The device shows strong electrical performance: Extracted mobility exceeds 2300 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s for both electron and hole transport, and drive current is over 300 μS/μm. This transport symmetry affords frequency doublers with high spectral purity and a conversion gain of - 29.5 dB and output power of -22.2 dBm, representing the highest performance for graphene transistors on flexible substrates.

Fabrication and Characterization of Cu-Plated Fine Pitch Patterns on Flexible Polyimide

The thin flexible Polyimides (PI) films have desirable properties for use in the electrical and electronics industry because their good thermal stability, high flexibility, low dielectric constants, excellent mechanical strength, low loss tangent, low relative permittivity and electrical insulating properties. In order to determine the process window of the surface metallization of PI, the fine traces with 50 micron pitch (25micron line /space) built on a flexible 50 micron thick PI film using wet fabrication process are reported in this paper. The thick copper (Cu) film was obtained from the Cu plating process using evaporated thin film of Cu as the adhesion layer. The fabricated fanout fine patterns are further investigated using scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and X-ray spectrometry technologies. The experiment is conducted to study the effect of the process parameters on the Cu film surface properties. The results obtained in this work can be applied to the fabrication of flexible microelectronic devices.

Fabrication and Characterization of Glucose Fuel Cells with a Microchannel Fabricated on Flexible Polyimide Film

Fabrication and Characterization of Glucose Fuel Cells with a Microchannel Fabricated on Flexible Polyimide Film

Printable fabrication of Pt-and-ITO free counter electrodes for completely flexible quasi-solid dye-sensitized solar cells

Low-cost bendable photoanodes and counter electrodes (CEs), as well as gel electrolytes, are potentially desired for the mass production of completely flexible dye-sensitized solar cells (DSSCs). In this work, via printing at low temperature, we fabricated titanium carbide (TiC)-functionalized conductive-carbon (CC) on flexible polyimide (PI) films to replace traditional and expensive Pt/ITO/PEN CEs. Morphology characterization revealed this composite CE was highly porous and homogeneous. Electrochemical investigations demonstrated that this Pt-and-ITO free flexible CE exhibited a high electro-catalytic activity. Finally, the conversion efficiencies of the all flexible quasi-solid DSSCs using this low-cost TiC-CC/PI CE achieved 86% of that based on a Pt/CC/PI CE. Thus, the facile fabrication process of this novel CE, along with its notable performance, are quite promising for the future roll-to-roll production of completely flexible DSSCs.

Microfluidic origami: a new device format for in-line reaction monitoring by nanoelectrospray ionization mass spectrometry

Microfluidics is an attractive platform for chemical synthesis because it offers fast reaction times, reduced reagent usage, and the ability to integrate multiple functions on a single device. Digital Microfluidics (DMF) is particularly well-suited for microscale chemical synthesis, as it permits discretized sample handling, allowing for total process control. However, a limitation of DMF-based synthesis is analysis, which is often performed offline. To this end, we have developed "microfluidic origami", a new device format that integrates DMF with in-line analysis by mass spectrometry (MS). This format comprises a DMF platform and a folded nanoelectrospray ionization (nanoESI) emitter formed on a single flexible polyimide film substrate. Additionally, the device contains a two-plate-to-one-plate DMF interface, which allows for straightforward coupling of micro-reaction operations and product delivery to the emitter for analysis. The integrated platform was used to perform the Morita-Baylis-Hillman (MBH) reaction using DMF followed by inline MS analysis for monitoring the reaction progress in real-time. We propose that this platform has potential as a new tool for real-time monitoring of reaction rates and reaction pathways and could be a useful addition to the synthetic organic chemistry laboratory.

Vapor Phase Growth of Bismuth Telluride Nanoplatelets on Flexible Polyimide Films

We report the growth of bismuth telluride, Bi2Te3, nanoplatelets on flexible polyimide films (Kapton films), using a chemical vapor transport process. Hexagonal, triangular, and ribbon-shaped nanoplatelets can be routinely synthesized on Kapton films. We developed a dry transfer technique to transfer these as-grown nanoplatelets from the Kapton films onto SiO2(300 nm)/Si substrates for atomic force microscopy (AFM) characterization. The thickness of the as-grown nanoplatelets is 10–100 nm, and thinner than those grown on glass and silicon susbtrates. We further suggest the possible growth mechanism based on our AFM obervations.

Uniform Wafer-Scale Chemical Vapor Deposition of Graphene on Evaporated Cu (111) Film with Quality Comparable to Exfoliated Monolayer

This article demonstrated monolayer graphene grown on annealed Cu (111) films on standard oxidized 100-mm Si wafers with higher quality than existing reports. Large area Raman mapping indicated high uniformity (>97% coverage) of monolayer graphene with immeasurable defects (>95% defect-negligible) across the entire wafer. Key to these results is the phase transition of evaporated copper films from amorphous to (111) preferred crystalline, which resulted in subsequent growth of high quality graphene, as corroborated by X-ray diffraction and electron backscatter diffraction. Noticeably, such phase transition of the copper film was observed on a technologically ubiquitous Si wafer with a standard amorphous thermal oxide. A modified two-step etching transfer process was introduced to preserve the clean surface and electrical property of transferred monolayer graphene. The fabricated graphene field effect transistor on a flexible polyimide film achieved peak mobility over 4900 cm2/(V s) at ambient condition.

Synthesis and properties of new aromatic polyimides containing redox‐active anthraquinone moieties

AbstractA novel anthraquinone‐containing bis(ether amine) monomer, 2,6‐bis(4‐aminophenoxy)anthraquinone, was synthesized from readily available reagents. A series of novel aromatic polyimides were prepared from the newly synthesized diamine monomer with various aromatic tetracarboxylic dianhydrides. The intermediate poly(amic acid)s had inherent viscosities of 0.67–1.12 dL g−1, and those derived from less stiff dianhydrides could be solution‐cast and thermally cyclodehydrated into flexible and tough polyimide films. The polyimides exhibited glass transition temperatures between 270 and 297 °C, and they were fairly stable up to a temperature of 500 °C in air or nitrogen. The electrochemical and electrochromic properties of one of the polyimides were investigated. The polymer could undergo two reversible steps of electrochemical reduction, with a color change from a colorless neutral state to pink and rose‐red reduced states. © 2012 Society of Chemical Industry

Synthesis and characterization of novel semi-alicyclic polyimides from methyl-substituted tetralin dianhydride and aromatic diamines

The asymmetrical alicyclic dianhydride 3,4-dicarboxy-1,2,3,4-tetrahydro-6-methyl-1-naphthalene succinic dianhydride (MTDA, II) was synthesized from 4-methylstyrene and maleic anhydride under nitric oxide catalysis with a yield >70%. A series of semi-alicyclic polyimides (PIs) (PI–IIa∼PI–IId) were prepared by a one-step high temperature polycondensation procedure from MTDA and various aromatic diamines. For comparison, another series of PIs (PI–Ia∼PI–Id) were prepared from the analogous dianhydride 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride (TDA, I) and the same diamines. The asymmetrical molecular structure of MTDA endowed the derived PIs with good solubilities in common solvents and high optical transparencies in the ultraviolet and visible light regions by decreasing the intramolecular or intermolecular interactions of the polymer chains. The flexible and tough PI films exhibited good thermal stability up to 400 °C and showed glass transition temperatures in the range of 204–271 °C. The PI films exhibited good optical transparency with transmittances >80% at 400 nm, a cut-off wavelength <300 nm and a refractive index <1.54. A series of semi-alicyclic PIs have been synthesized from an alicyclic dianhydride MTDA and various aromatic diamines by a one-step high temperature polycondensation procedure. Flexible and tough PI films have been cast from their solution in common solvents. The PI films exhibited good thermal stability and good transparency in the ultraviolet-visible (UV-vis) light region.

Activity on Electrochemical Surface Area: Silver Nanoplates as New Catalysts for Electroless Copper Deposition

Electrochemical surface areas (ESAs) were used to estimate the specific activities of different-sized Ag nanoplates (NPLs), which were used as novel catalysts for electroless copper deposition (ECD). Based on the consideration of ESAs and deposition kinetics measured using an electrochemical quartz crystal microbalance, the mean specific activities of NPLs with sizes of 74 nm, 117 nm, and 162 nm were determined to be 0.107, 0.250, and 1.017 mg·cm−2, respectively. The largest NPLs showed the highest activity. Simultaneously, in the Tafel plot normalized to the ESA, the specific current density corresponding to 74 nm < 117 nm < 162 nm NPLs for formaldehyde oxidation in the high overpotential region was determined. This anodic reaction activated with various NPLs could thus be the rate-determining step in ECD. Additionally, an untypical open circuit potential curve containing two mixed potentials for two period depositions—Cu deposition on Ag NPLs and Cu on the deposited Cu layer—was observed. In the intended application, conductive Cu patterns on a flexible polyimide film using Ag NPL ink of 2.5 wt% solid content were successfully fabricated by inkjet printing combined with catalyzed ECD.