Ultrathin Polyimide Films Research Articles

Lightweight Broadband Phased Array Antenna Based on Ultra-Thin Polyimide Film

Lightweight Broadband Phased Array Antenna Based on Ultra-Thin Polyimide Film

Low dielectric constant ultrathin polyimide films alternated by poly(amic acid) salt/poly(allylamine hydrochloride)/imogolite through layer by layer deposition

Low dielectric constant ultrathin polyimide films alternated by poly(amic acid) salt/poly(allylamine hydrochloride)/imogolite through layer by layer deposition

The mechanism study of laser peeling of ultra-thin polyimide film from the transparent substrate

Laser peeling of ultra-thin polyimide (PI) film from transparent substrate is a critical technology in the flexible electronics industry. This paper studies the laser ablation and interface separation of the PI film to reveal the mechanism of laser peeling. In the laser ablation process, the supercritical environment is formed, and gas bubbles appear. Then the gas bubbles fuse together and become cavitation holes. These cavitation holes fuse together and produce sparse nanopillar structures that can be seen as a blister. In the interface separation process, the blister absorbs thermal energy and expands under laser irradiation. This paper proposes a discrete quasi-static method to analyze the separation of the PI film from the transparent substrate during the blister expansion. The cohesive zone model is also introduced to predict the peeling behaviors of the PI film. The results show that the blister profile is related to the laser influence, and the blister profile obtained by the theoretical model can fit well with the experiment. When the laser fluence is larger, the blister profile is steeper, and the pressure inside the blister is larger. This paper provides a new perspective for understanding the laser peeling mechanism of ultra-thin PI film from a transparent substrate.

Ultra-thin polyimide films play crucial role in protecting NASA telescope

Ultra-thin Kapton polyimide films from DuPont's Electronics & Industrial business are being used to protect the National Aeronautics Space Administration's (NASA) James Webb Space Telescope (JWST) from the sun's light and heat – enabling it to function properly in space.

Highly Foldable Perovskite Solar Cells Using Embedded Polyimide/Silver Nanowires Conductive Substrates

AbstractFoldable solar cells, with the advantages of size compactness and shape transformation, are attractive power sources for wearable and portable devices. The challenge for realizing highly foldable solar cells is to exploit highly foldable conductive substrates to replace brittle indium tin oxide. In this work, highly foldable and smooth polyimide (PI)/silver nanowires (AgNWs) conductive substrates are constructed by embedding AgNWs into ultrathin PI films to improve the interface binding force. As a result, the embedded PI/AgNWs complex shows a neglectable change in resistance after folding for 1000 cycles. The perovskite solar cells (PSCs) on PI/AgNWs substrates exhibit power conversion efficiency (PCE) of 11.8%. More importantly, beneficial from the highly foldable PI/AgNWs conductive substrates, the PSCs maintain 73.5% and 55.2% of the initial PCE after +180° and −180° folding for 1000 cycles, respectively, which is the first report on the foldable AgNWs‐based PSCs. In addition, the degradation mechanism of PSCs subjected to different folding conditions is tentatively exploited. This work paves the way toward realizing highly foldable PSCs for various practical applications.

Photoactivated high-k lanthanum oxide-aluminum oxide (La2O3–Al2O3) alloy-type gate dielectrics for low-voltage-operating flexible transistors

Low-temperature-processable gate dielectrics with high dielectric constants, low leakage current, and good electrical/mechanical stabilities are largely pursued in diverse electronics including flexible transistors, wearable sensors, integrated logic circuits, and various optoelectronic devices. Here, we report low-temperature photochemically activated gate dielectrics based on a lanthanum oxide-aluminum oxide (La2O3–Al2O3 or LAO) alloy system for a utilization in flexible metal-oxide thin-film transistors (TFTs). With proper alloying of La2O3 and Al2O3 at an optimal ratio, synergetic effects could be achieved from both gate dielectric materials, high dielectric constant and excellent insulating properties. With a La:Al ratio of 2:8, LAO gate dielectrics with high dielectric constant (k = 10.72), low surface roughness (0.517 nm), low leakage current density (1.7 × 10−10 A cm−2 @2 MV cm−1), and high breakdown field (∼4.8 MV cm−1) were achieved. By utilizing the photo-annealed LAO as a gate dielectric, low operating voltage (≤5 V) solution-processed indium-gallium-zinc-oxide (IGZO) TFTs having saturation mobility of 8.5 ± 3.25 cm2 V−1s−1, linear mobility of 10.8 ± 2.03 cm2 V−1s−1, subthreshold slope of 0.228 V dec−1, and on/off ratio of ∼105 are demonstrated. Furthermore, the fabricated IGZO TFTs exhibited negligible hysteresis characteristics (<0.1 V) and good bias stabilities (threshold voltage shift < ±0.1 V). Using an ultrathin (∼2 μm) polyimide film as a substrate, flexible IGZO TFTs successfully operating at a bending radius of 2 mm were realized.

New Approach for Fabricating of Deep Submicron Free-Standing Polyimide Thin Film

A new approach for manufacturing ultrathin free-standing polyimide film was proposed. This approach involves casting polyamic acid solution to a Al-doped zinc oxide film coated substrate sputtered at room temperature and to form polyamic acid film. The polyamic acid film was released from substrate in 0.5% diluted hydrochloric acid. Then polyamic acid was reattached to glass substrate and was transformed into polyimide film by thermal imidization with gradient heat treatment process. After that, thickness of the1000 nm polyimide film was reduced by KrF excimer laser ablation with 100 pulses at 45 mJ/cm2 and 30 pulses at 75 mJ/cm2, and 200 nm free-standing polyimide film was obtained. By this method, free-standing polyimide films of 1000 nm and 200 nm thickness were fabricated without and with excimer laser ablation reduction, respectively.

Theoretical and experimental studies of laser lift-off of nonwrinkled ultrathin polyimide film for flexible electronics

This paper theoretically and experimentally studies an innovative laser lift-off (LLO) technique that utilizes a line-shaped laser to scan the interfacial polyimide (PI) film through the transparent substrate to peel off the thin-film electronics. A comprehensive illustration of the mechanism of the occurrence of wrinkles in ultrathin PI films is provided, based on which the LLO process for ultrathin flexible electronics is optimized. A mechanical model is established to describe the deformation of the laser-induced blister and validated by experimental results. The results show that the wrinkles are due to the plastic deformation inside the film, which is caused by the instantaneous pressure of gas products generated by laser ablation. By measuring the instantaneous pressure through piezoelectric sensors, the maximum allowable laser fluence without inducing plastic deformation has been found, which decreases linearly with the film thickness. Accordingly, the process window of the traditional single-pass LLO has been obtained, which confirms that the wrinkles in ultrathin PI films (<5 μm) are inevitable through traditional LLO process. To obtain non-wrinkled ultrathin films, two optimization approaches are proposed, which are also verified through the tests of strain sensors.

Mechanically Robust and Highly Flexible Nonvolatile Charge‐Trap Memory Transistors Using Conducting‐Polymer Electrodes and Oxide Semiconductors on Ultrathin Polyimide Film Substrates

AbstractFlexible charge‐trap memory thin‐film transistors (CTM‐TFTs) are fabricated and characterized for next‐generation highly functional consumer electronics. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and 1.2‐µm‐thick polyimide (PI) films are introduced as source/drain electrodes and plastic substrates, respectively, to realize highly flexible CTM‐TFTs with conducting polymers. A uniquely structured sacrificial layer is suggested for the lithography‐compatible transfer and patterning processes of PEDOT:PSS on inorganic Al2O3 barrier layers are prepared on the PI substrates. The CTM‐TFTs show significantly improved device performance compared with those of the previous proto‐type devices, including a memory window (MW) of 16.8 V and program speed of 100 µs at a program pulse amplitude of ±20 V. Furthermore, the MWs and on/off current ratio do not shown remarkable degradation, and total variations within a range of less than 7.5% are observed even under harsh bending strains with a curvature radius of 1 mm. Additionally, the mechanical robustness of the fabricated CTM‐TFTs is quantitatively discussed based on the contributions of the conducting polymer electrode and the ultrathin PI film to further improve device performance of the flexible CTM‐TFTs.

Experimental study of laser lift-off of ultra-thin polyimide film for flexible electronics

It is increasingly crucial for flexible electronics to efficiently and reliably peel large-area, ultra-thin flexible films off from rigid substrate serving as substrates of flexible electronics device, especially in industrial production. This paper experimentally investigated the mechanism and technologic characteristics of laser lift-off (LLO) process of ultra-thin (~ 2 μm) polyimide (PI) film. It was found increasingly difficult to obtain desirable ultra-thin PI film by LLO with the decrease of the film thickness. The optimal process parameters were achieved considering laser fluence and accumulated irradiation times (AIT), which were found to be strongly correlative to the thickness of PI film. The process mechanism of LLO of PI film was disclosed that laser ablation of interfacial PI will result in the formation of gas products between the PI and glass substrate, enabling the change of interface microstructures to reduce the interface bond strength. The amount of gas products mainly determines the result of LLO process for ultra-thin PI film, from residual adhesion to wrinkles or cracking. The strategy of multi-scanning based on multiple irradiations of low-energy laser pulses was presented to effectively achieve a reliable LLO process of ultra-thin PI film. This study provides an attractive route to optimize the LLO process for large-scale production of ultra-thin flexible electronics.

Electrical Control of Electromagnetically Induced Transparency by Terahertz Metamaterial Funneling

AbstractElectromagnetically induced transparency (EIT) analogs using metamaterials have diverse applications, including nonlinear optics, telecommunications, and biochemical sensors. These EIT analogs can be actively controlled by embedding semiconducting materials into metamaterial structures, but most active EIT metamaterials require complex optical setups and complicated fabrication processes. Graphene‐based EIT metamaterials are some of the most promising active EIT systems because of their simple controllability by electrical bias, but related researches have so far been limited to theoretical or numerical studies. Here, experimentally verified graphene EIT metamaterials are provided by controlling the terahertz funneling of the unique metaatom structures. The proposed active EIT metamaterials are fabricated on flexible and ultrathin polyimide films to acquire the lowest substrate insertion losses and achieve a 1 ps group delay change at the transmission peak of the EIT analog. Moreover, because the proposed metamaterials exhibit resonance properties that vary depending on the polarization direction, the phase delay can be controlled up to 80° from the proposed metamaterials by rotating the incident polarization to the orthogonal direction. Overall, by controlling the group and phase delay of incident waves in a single metamaterial device simultaneously, a multifunctional active tuning system can be realized in the terahertz range.

Stability improvements of InGaZnO thin-film transistors on polyimide substrates with Al2O3 buffer layer

We investigate the effects of atomic layer deposition (ALD)-grown Al2O3 buffer layer on the device characteristics of flexible amorphous InGaZnO thin-film transistors (TFTs) fabricated on ultrathin polyimide (PI) films. The TFT with a buffer layer exhibited a saturation mobility of 8.6 cm2 V−1 s−1 and a subthreshold swing of 0.16 V dec−1 after annealing at 150 °C. Under negative bias temperature stress at 40 °C, the turn-on voltage instabilities of TFTs with and without the buffer layer were estimated to be −1.0 and −13.2 V, respectively. This marked difference is mainly due to the adsorption of water molecules on the PI film resulting in a positively charged surface.

Highly Efficient Rapid Annealing of Thin Polar Polymer Film Ferroelectric Devices at Sub-Glass Transition Temperature.

An unexpected rapid anneal of electrically active defects in an ultrathin (15.5 nm) polar polyimide film at and below glass transition temperature (T g) is reported. The polar polymer is the gate dielectric of a thin-film-transistor. Gate leakage current density (J g) through the polymer initially increases with temperature, as expected, but decreases rapidly at T g - 60 °C. After ≈2 min at T g, the leakage is reduced by nearly three orders of magnitude. A concomitant observation is that the drain current (I d)-gate voltage (V g) hysteresis decreases with temperature, reaching zero at nearly the same temperature at which J g collapses. As J g drops further, the drain current hysteresis increases again but in the opposite direction. This combination strongly supports the interpretation of rapid defect annealing.

Automation Highlights from the Literature

Automation Highlights from the Literature

Printable Ultrathin Metal Oxide Semiconductor-Based Conformal Biosensors.

Conformal bioelectronics enable wearable, noninvasive, and health-monitoring platforms. We demonstrate a simple and straightforward method for producing thin, sensitive In2O3-based conformal biosensors based on field-effect transistors using facile solution-based processing. One-step coating via aqueous In2O3 solution resulted in ultrathin (3.5 nm), high-density, uniform films over large areas. Conformal In2O3-based biosensors on ultrathin polyimide films displayed good device performance, low mechanical stress, and highly conformal contact determined using polydimethylsiloxane artificial skin having complex curvilinear surfaces or an artificial eye. Immobilized In2O3 field-effect transistors with self-assembled monolayers of NH2-terminated silanes functioned as pH sensors. Functionalization with glucose oxidase enabled d-glucose detection at physiologically relevant levels. The conformal ultrathin field-effect transistor biosensors developed here offer new opportunities for future wearable human technologies.

Low-Temperature Solution-Processed Gate Dielectrics for High-Performance Organic Thin Film Transistors.

A low-temperature solution-processed high-k gate dielectric layer for use in a high-performance solution-processed semiconducting polymer organic thin-film transistor (OTFT) was demonstrated. Photochemical activation of sol-gel-derived AlOx films under 150 °C permitted the formation of a dense film with low leakage and relatively high dielectric-permittivity characteristics, which are almost comparable to the results yielded by the conventionally used vacuum deposition and high temperature annealing method. Octadecylphosphonic acid (ODPA) self-assembled monolayer (SAM) treatment of the AlOx was employed in order to realize high-performance (>0.4 cm2/Vs saturation mobility) and low-operation-voltage (<5 V) diketopyrrolopyrrole (DPP)-based OTFTs on an ultra-thin polyimide film (3-μm thick). Thus, low-temperature photochemically-annealed solution-processed AlOx film with SAM layer is an attractive candidate as a dielectric-layer for use in high-performance organic TFTs operated at low voltages.

Fabrication and characterization of a novel poly(amide-urethane@imide) TFC reverse osmosis membrane with chlorine-tolerant property

A novel poly(amide-urethane@imide) reverse osmosis (RO) composite membrane with chlorine-tolerant property was prepared on a polysulfone supporting film through two-step interfacial polymerization. The crosslinking agent – 5-choroformyloxyisophaloyl chloride (CFIC) was first reacted with 4-methyl-phenylenediamine (MMPD) via interfacial polymerization to get the nascent poly(amide-urethane) base membrane (CFIC–MMPD) without curing treatment. Then the resultant base membrane contacted again with the second aqueous solution containing functional secondary amine – N,N′-dimethyl-m-phenylenediamine (DMMPD) to obtain the poly(amide-urethane@imide) TFC RO membrane (MMPD–CFIC@CFIC–DMMPD). X-ray photoelectronic spectroscopy (XPS) was combined with attenuated total reflectance infrared (ATR-IR) to verify that the ultrathin polyimide film (CFIC–DMMPD) has been successfully grafted on the surface of the MMPD–CFIC base membrane. The images of scanning electronic microscopy (SEM) and atomic force microscope (AFM) showed that the poly(amide-urethane@imide) membrane has much smoother, more hydrophilic surface than the poly(amide/imide-urethane) membrane (MMPD/DMMPD–CFIC) prepared by conventional one-step interfacial polymerization of CFIC and composite MMPD/DMMPD. However, the permeation experiment revealed that the poly(amide-urethane@imide) membrane has a slight loss in both salt rejection and water flux than the poly(amide/imide-urethane) membrane and conventional commercialized polyamide membrane (MPD–TMC), but exhibits better chlorine-tolerant property due to the introduction of ultrathin polyimide film (CFIC–DMMPD) on the outmost surface of the TFC RO membrane, and the combination of IR and XPS analyses shows a good agreement with the chlorine exposure results of membranes.

High modulus and high strength ultra-thin polyimide films with hot-stretch induced molecular orientation

This paper concerns uniaxially stretched ultra-thin polyimide (PI) films containing ether and ketone moieties. The stretched PI films exhibited remarkable high modulus (4.9 GPa) and high strength (258 MPa) in the stretch direction compared with commercial polyimides because of their high degree of molecular orientation induced by uniaxial hot stretch. The tensile strength of the stretched PI films is about 2.4 times of that of undrawn films and the coefficients of thermal expansion decreased by as much as 84%. Studies of birefringence and wide-angle X-ray diffraction all proved a high degree of molecular orientation and crystallization induced during the drawing process. The thickness of stretched PI films was reduced at least 75% as compared to unstretched PI films and the thinnest film is only 7 μm.

Flexible PVDF-TrFE pyroelectric sensor driven by polysilicon thin film transistor fabricated on ultra-thin polyimide substrate

In this work we present a flexible pyroelectric sensor composed by a PVDF-TrFE capacitor realized on ultra-thin polyimide film (5μm thick), integrated with a n-channel low temperature polysilicon thin film transistor also fabricated on ultra-thin polyimide (8μm thick). Exploiting a multi-foil approach, the pyroelectric capacitors and the transistors were attached one over the other reaching a final thickness of about 15μm. The bottom contact of the sensor capacitance was connected to the gate of the transistor by a silver ink, while, for bias and load resistances, we used external elements. The active sensor area was defined by a circular capacitor with a diameter of about 2mm. In order to enhance PVDF-TrFE pyroelectric properties, an external stepwise voltage was applied to the structure up to values of 160V at a temperature of about 80°C. The devices were then tested, at different working frequencies (up to 800Hz) under a specific infrared radiation provided by a He–Ne laser, with a wavelength of 632nm and maximum power of 5mW. An output signal of tens of millivolt was observed at 10Hz, exploiting the pre-amplification of polysilicon thin film transistor.

Flexible PVDF-TrFE Pyroelectric Sensor Integrated on a Fully Printed P-channel Organic Transistor

Abstract In this work we present a flexible pyroelectric capacitive sensor, based on PVDF-TrFE, fabricated on a ultra-thin polyimide film (8 μm thick) connected to a fully printed p-channel organic thin film transistor that is used to amplify the sensor signal. We fabricate a standalone device, exploiting a multi-foil approach, where the pyroelectric capacitor was glued on the organic TFT substrate, that consists of a PEN foil 125 μm thick, previously made in CEA-LITEN labs. The pyroelectric properties of the PVDF-TrFE capacitor were enhanced using a thermal poling procedure before the TFT integration. The sensor behavior was analyzed at different working frequencies (up to 500 Hz) under a specific infrared (IR) radiation provided by a He-Ne laser, with a wavelength of 632 nm and maximum power of 5 mW. An output signal of few millivolts was observed, exploiting the pre-amplification of the fully printed organic transistor.