Kapton Polyimide Film Research Articles

Flexible subterahertz metamaterial absorber fabrication using inkjet printing technology

In this study, a flexible metamaterial (MM) absorber was designed at 0.1 THz and fabricated using inkjet printing technology. The unit cell of the MM absorber was designed using a finite element method-based full-wave simulation. The unit cell comprised square rings, and it was printed with silver nanoparticle ink on flexible Kapton polyimide film. The fabrication processes were performed using a material printer. The absorber’s reflection coefficient was measured using a vector network analyzer and a WR-10 waveguide. The absorption ratio was 93.5 % at 0.102 THz. Therefore, we demonstrated the possibility of inkjet printing at a subterahertz band.

Preparation of solution-processable colorless polyamide-imides with extremely low thermal expansion coefficients through an in-situ silylation method for potential space optical applications

AbstractSeveral tough and flexible fluorinated polyamide-imide films were prepared from trimellitic anhydride chloride and 2,2′-bis(trifluoromethyl)benzidine through a facile one-pot in-situ silylation method. By incorporating fluorinated side groups, the solubility of the prepared polyamide-imide was greatly enhanced. Meanwhile, due to their linear chain configuration and the existence of hydrogen bonding, the prepared polyamide-imide films revealed high tensile strength, high tensile modulus, high glass transition temperature (Tg) and most interestingly, very low coefficient of thermal expansion (CTE) of 11 ppm/°C. Copolymerization with pyromellitic dianhydride (PMDA) led to an extremely low CTE of 4 ppm/°C which should be among the lowest values available for soluble polyamide-imides. The optical homogeneity and stress homogeneity of the obtained polyamide-imide films were also tested. After non-contact with substance and thermal treatment at 300°C, they revealed a better optical homogeneity and stress homogeneity than that of the commercially available Kapton polyimide (PI) films, with a PV value of 0.915 λ and RMS value of 0.163 λ. Thus, these colorless and soluble polyamide-imide films simultaneously possessing promising optical imaging performance are good candidates as novel diffractive membrane optical system architectures.

Multiple Cracking of Metallized Polyimide Kapton Films

Mechanical behaviour of metallized polyimide Kapton films was studied. The adhesion of metallized films to Kapton films is approximately hundred-folds higher than that of coatings made by usual sputter deposition of a metal on a polymer substrate. Multiple cracking of a metallized film was observed. Cracks<br />of two different scale levels are observed. The cracks of the first type (microcracks) are short with 1-2 μm length. The cracks of the second type are much longer and have length of several hundreds microns. The cracks of this type appear at higher strains as compared with the shorter ones. In thinner 7-μm-thick samples<br />long cracks were not observed.

Effect of infill patterns on print quality of dispenser‐printed electronic ink

The effect of six different infill patterns on the print quality of a dispenser-printed silver ink on Kapton polyimide film is investigated. The results indicate that improved and more complex printed electronic structures can be produced due to the improvement in print homogeneity. Dispenser printing is a rapid manufacturing process using direct write technology that can be used to deposit a broad range of inks onto substrates irrespective of their surface geometry. Standard three-dimensional printer infill patterns known as line, rectilinear, concentric, honeycomb, Hilbert curve and Archimedean chords were tested at densities of 30, 50 and 70%. The prints were timed allowing comparison of print speed. After curing, the coverage was checked and the surface roughness ( R a ) was measured. The results showed that only the rectilinear infill pattern at 50% density print, and the rectilinear and honeycomb infill patterns at 70% density achieved 100% coverage. The 50% rectilinear print was the fastest of the 100% coverage prints, and the 70% honeycomb print had the lowest surface roughness. The rectilinear pattern at 50% is recommended if there is only one layer to print. The honeycomb pattern is recommended for multilayer prints, where surface roughness is the key.

Room temperature deposition of alumina-doped zinc oxide on flexible substrates by direct pulsed laser recrystallization

In this study, a method combining room temperature pulsed laser deposition (PLD) and direct pulsed laser recrystallization (DPLR) is introduced to deposit transparent conductive oxide (TCO) layer on low melting point flexible substrates. Alumina-doped zinc oxide (AZO), as one of the most promising TCO candidates, has now been widely used in solar cells. However, to achieve optimal, electrical, and optical properties of AZO on low melting point, flexible substrate is challenging. DPLR technique is a scalable, economic, and fast process to remove crystal defects and generate recrystallization at room temperature. It features selective processing by only heating up the TCO thin film and preserve the underlying substrate at low temperature. In this study, AZO thin film is pre-deposited by PLD on flexible and rigid substrates. DPLR is then introduced to achieve a uniform TCO layer on these substrates, i.e., commercialized Kapton polyimide film, micron-thick Al-foil, and sold lime glass (SLG). Both finite element analysis simulation and designed experiments are carried out to demonstrate that DPLR is promising in manufacturing high quality AZO layers without any damage to the underlying flexible substrates. The hall mobility of AZO after DPLR on Kapton and SLG reached 198 cm2/v · s and 398 cm2/v · s respectively, while the carrier concentrations are reduced to 2.68 × 1018 and 4.3 × 1019/cm−2, respectively. These characteristics are exactly what an ideal TCO layer should carry: high conductivity and high transmission. The property changes are due to the reduction of defect density after DPLR.

Flexible Substrate Antennas

Flexible electronics can currently be considered a wellestablished technology that has reached a certain degree of maturity in meeting the requirements of tightly assembled electronic packages, providing reliable electrical connections where the assembly is required to flex during its normal use or where board thickness, weight, or space constraints are driving factors. In this context, flexible substrate antennas (FSAs) play a key role in the integration and packaging of wireless communication devices and sensor networks. Those antennas, which are designed such that the resonant peak frequency remains unaffected after bending, stretching, or twisting, are currently being embedded into materials such as textile fabrics, bandages, stickers, and bendable displays. FSAs are rapidly emerging as a popular choice for radio frequency identification (RFID) tags, multisystem wireless communication gadgets, wearable computer systems, and smart clothing and spurring new applications in wireless sensing such as monitoring of civil construction, health care supervision, or the integration in search and rescue satellite systems. The introduction of new design concepts, new materials and new fabrication processes is adding momentum and interest to the development of flexible antennas for consumer electronics. Researchers are continuingly relying on flexible antenna technology to solve the problems of efficiency, reliability, cost, weight, shape, and reproducibility. There is also the need of using environmentally friendly and lowcost materials and production processes, in order to allow for the easy disposal of a massive number of those devices. This special issue aims at reflecting current research trends and new approaches in FSAs, collecting 13 peer-reviewed articles (with an acceptance ratio of 52%) reporting original research coming from 46 authors of 19 institutions of 14 countries. Authors of this special issue used a variety of materials such as silver nanoparticle ink printed on Kapton polyimide film, ceramic-polymer and carbon-epoxy composites, conductive polymers such as PEDOT or PPy, metamaterialbased artificial magnetic conductor structures, or a copperplated nylon fabric that acts as a conductive electrotextile material. They addressed a number of technologies located in different frequency bands, including near field communications (13,56MHz), UHF RFID tag antennas (860MHz), global navigation satellite systems (L2 band at 1.227GHz and L1 band at 1.575GHz), L-band DVB-H (1452–1492MHz), GSM1800 (1710–1880MHz), PCS1900 (1859–1990MHz), UMTS (1900–2170MHz), wireless local area networks such as WiFi and WiMAX (2.4-, 3.6-, and 5-GHz), Bluetooth (2.4GHz), ultra-wideband (3.1 to 10.6GHz), and even scientific applications at the Ku-band (12–18GHz). This diversity reflects the lively momentum that research of FSAs is experiencing, as corroborated by the number of scientific publications on the topic shown in Figure 1.

Development of a flexible three-axial tactile sensor array for a robotic finger

In this paper, we propose a flexible three-axial tactile sensor array for measuring both normal and shear loads. The sensor array has 16 tactile sensor units based on piezoresistive strain gauge. It is constructed on a Kapton polyimide film using advanced polymer micromachining technologies. Thin metal strain gauges are embedded in polyimide to measure normal and shear loads, which are tested by applying forces from 0 to 1 N. The developed sensor unit had a hysteresis error of about 9% and repeatability error of about 1.31%. The sensor showed a good resulting image when pressed by a circle-shaped object with 10 N loads. The proposed flexible three-axial tactile sensor array can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a robotic finger.

Tests and Performance Analysis of Coreless Inductive HTS Fault Current Limiters

Superconducting fault current limiters (SFCL) are designed to protect the electrical grid from faults that result from lightning strikes, downed power lines and other system interruptions. The rapid increase of impedance of the SFCL reduces the short current in the circuit. Several coreless constructions of inductive SFCLs have been tested. The space between the windings is the thick of the polyimide film kapton insulation to increase the coupling and reduces the leakage reactance. Both primary and secondary windings have been immersed in liquid nitrogen. The presented solutions reduce the size and the weight of the device. A few limiters based on HTS 1G and HTS 2G tapes has been described, tested and compared.

Degradation kinetics of polyimide film

Through the use of thermogravimetry (TG), this work explores the thermal degradation mechanism and kinetics of Kapton (polyimide) film. Isoconversional kinetic methods, which provide activation energy as a function of degradation, present insight into the development of a five-step competitive and consecutive kinetic model. To evaluate the accuracy and validity of the model, a statistical analysis of the implemented kinetic model is also presented. Coupled TG-mass spectroscopy and TG-Fourier transform infrared analysis were used to investigate the decomposition mechanism and to more fully explain the complex, heating-rate-dependent, decomposition pathway of Kapton.

Flexible In-plane Photonic Devices Based on Transferrable Si Nanomembranes on Polyimide Film

The flexible electronics and photonics have attracted a lot of attentions in past decade because of their potentially wide applications. A general method to fabricate nanomembrane flexible device involves two steps. At first, a nanomembrane on top of a sacrificial layer is patterned. Then, the nanomembrane is freed by high selective etching of the sacrificial layer and then weakly bonds to the handle substrate by Vander Waals forces. Later on, the released devices are transferred to the target flexible substrates. Notable successes include paper-like display, flexible silicon integrated circuits, photonic crystal filter and sensor skins, and so on. However, the progress in flexible photonic device is still limited to surface-normal devices such as photonic crystal filter. This type of devices usually has a large area and/or same dimensions which makes the transfer much easier than in-plane photonic device. This paper reports the transfer of in-plane Silicon nanomembrane photonic devices on polyimide flexible film. Employing a slightly modified transfer process, passive optical components, such as optical waveguide and multimode multimode interferometer, are successfully transferred on to Kapton polyimide film.

Development and Evaluation of the Time-Resolved Heat and Temperature Array

The development and evaluation of a differential style heat flux gauge is presented. The sensor is constructed from spot-welded foils of copper and constantan on either side of a thin Kapton polyimide film and is capable of measuring the heat flux and surface temperature at ten locations simultaneously. Analytical modeling was performed to estimate the sensor’s sensitivity and time response. Calibrations were performed in conduction and radiation yielding an average heat flux sensitivity of 20.4 μV/(kW/m2). Time response measurements were also performed, which gave an average 63% time response of 168 ms. The capabilities of the sensor are demonstrated by showing its use in ongoing convection research.

Protecting Polymers in Space with Atomic Layer Deposition Coatings

Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. Atomic layer deposition (ALD) techniques can produce films that mitigate many of the current challenges for space polymers. We have studied the efficacy of various ALD coatings to protect Kapton polyimide, FEP Teflon, and poly(methyl methacrylate) films from atomic-oxygen and vacuum ultraviolet (VUV) attack. Atomic-oxygen and VUV studies were conducted with the use of a laser-detonation source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings protected the underlying substrates from atomic-oxygen attack, and the addition of TiO2 coatings protected the substrates from VUV-induced damage. The results indicate that ALD coatings can simultaneously protect polymers from oxygen-atom erosion and VUV radiation damage.

Polymer Micromachined Flexible Tactile Sensor for Three-Axial Loads Detection

A flexible three-axial tactile sensor was fabricated on Kapton polyimide film using polymer micromachining technology. Nichrome (Ni:Cr = 8:2) strain gauges were positioned on an etched membrane to detect normal and shear loads. The optimal positions of strain gauges were determined through strain distribution from finite element analysis. The sensor was evaluated by applying normal and shear loads from 0 N to 0.8 N using an evaluation system. Sensitivity of the tactile sensor to normal and shear loads was about 206.6 mV/N and 70.1 mV/N, respectively. The sensor showed good linearity, and its determination coefficient (<TEX>$R^2$</TEX>) was about 0.982. The developed sensor can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a robotic fingertip.

Numerical simulation on atomic oxygen undercutting of Kapton film in low earth orbit

A Monte Carlo model describing the interaction between atomic oxygen undercutting with polyimide Kapton film of spacecraft surfaces in low earth orbit is presented. The physical process of atomic oxygen undercutting is elaborated and a binary chained list optimization technique is used to reduce computations. In order to analyze the impact–reaction probability in three-dimensional space, a new mathematical impact–reaction probability based on the mapping theory is established to be the important reaction parameter for predicting the difference of undercutting patterns between two-dimensional and three-dimensional spaces. Numerical simulations are carried out with different initial defect widths, orbit inclination angles, thermal assimilation–reaction coefficients and thickness of protective layers, as well as their combining action conditions. Results agree well with the NASA long duration exposure facility experimental data. The maximum undercutting depth is larger than the maximum undercutting width at all times, which reduces with increase in orbit inclination angle, thermal assimilation–reaction coefficient, three-dimensional space and thickness of the protective layer. Comparing three- and two-dimensional spaces, the maximum depth is decreased by approximately 20% for 28.5° orbit inclination angle.

MEMS-Based Electronically Steerable Antenna Array Fabricated Using PCB Technology

In this paper, a MEMS-based electronically steerable antenna array (ESA) fabricated using printed circuit processing techniques is reported. A Kapton polyimide film is used as the structural layer for fabricating MEMS varactors. The MEMS varactors have been used in the bistable mode to design loaded- line-type MEMS phase shifters. These MEMS phase shifters have been monolithically integrated with the ESA on a Duroid substrate using printed circuit processing techniques. For proof-of-concept demonstration of the proposed MEMS-based ESA, a 3-bit MEMS phase shifter has been monolithically integrated with a two- element double-folded slot-antenna array on a Duroid substrate. An X-band ESA prototype with a beam steering angle of 20deg at 9.1 GHz is presented.

A microelectromechanical accelerometer fabricated using printed circuit processing techniques

A microelectromechanical systems (MEMS) capacitive-type accelerometer fabricated using printed circuit processing techniques is presented. A Kapton polymide film is used as the structural layer for fabricating the MEMS accelerometer. The accelerometer proof mass along with four suspension beams is defined in the Kapton polyimide film. The proof mass is suspended above a Teflon substrate using a spacer. The deflection of the proof mass is detected using a pair of capacitive sensing electrodes. The top electrode of the accelerometer is defined on the top surface of the Kapton film. The bottom electrode is defined in the metallization on the Teflon substrate. The initial gap height is determined by the distance between the bottom electrode and the Kapton film. For an applied external acceleration (normal to the proof mass), the proof mass deflects toward or away from the fixed bottom electrode due to inertial force. This deflection causes either a decrease or increase in the air-gap height thereby either increasing or decreasing the capacitance between the top and the bottom electrodes. An example PCB MEMS accelerometer with a square proof mass of membrane area 6.4 mm × 6.4 mm is reported. The measured resonant frequency is 375 Hz and the Q-factor in air is 0.52.

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

Hydrogels are a continuously expanding class of pharmaceutical polymers designed for sustained or controlled drug release. The structure and intermolecular interactions in such systems define their macroscopic properties. The aim of this study was to investigate the mechanism of swelling, drug impregnation, and drug release from poly(ethylene oxide) (PEO) gel crosslinked by urethane bonds. A combination of SAXS/WAXS/SANS techniques enabled us to determine the phase transition between lamellar and extended gel network, and to apply different descriptions of crystallinity, based on lamellar and crystal lattice structures. It is shown that even low (1-7% w/w) loading of model drugs acetaminophen and caffeine, produced significant disorder in the polymer matrix. This effect was particularly pronounced for acetaminophen due to its specific ability to form complexes with PEO. The drug-release profiles were analyzed using a general cubic equation, proposed for this work, which allowed us to determine the gel hydration velocity. The results indicate that the release profiles correlate inversely with the polymer crystallinity.

A MEMS-based electrostatically tunable circular microstrip patch antenna

This paper reports a MEMS-based electrostatically tunable circular microstrip patch antenna. This antenna is fabricated using printed circuit processing techniques. The microstrip patch antenna is patterned on the top side of a Kapton polyimide film which is suspended above the ground plane. The resonant frequency of the antenna is tuned electrostatically by applying a dc bias voltage between the patch and the ground plane. The movable patch deflects downward toward the fixed ground plane due to electrostatic force of attraction caused by the applied dc bias voltage. This deflection decreases the air gap thereby increasing the effective permittivity of the antenna. This increase in effective permittivity results in a downward shift in the resonant frequency. The patch is inductively coupled to a coplanar waveguide (CPW) feed line via a slot in the ground plane. A 6 mm diameter circular patch antenna tunable from 16.91 GHz at 0 V to 16.64 GHz at 165 V, a tuning range of 270 MHz, is presented in this paper.

MEMS-Based Frequency Switchable Microstrip Patch Antenna Fabricated Using Printed Circuit Processing Techniques

This letter reports a microelectromechanical systems (MEMS)-based electrostatically actuated frequency switchable microstrip patch antenna fabricated on Kapton polyimide film using printed circuit processing techniques. A 6 $times$ 6-mm microstrip patch antenna with resonant frequency switchable from 18.34 GHz at 0-V bias to 17.95 GHz at 268-V bias is discussed. The return loss is 40.6 dB and 20.1 dB at 18.34 and 17.95 GHz, respectively. The bandwidth of the antenna is about 0.9 GHz for return loss better than 10 dB in both states.

&lt;SUP&gt;111&lt;/SUP&gt;Cd(&amp;larr;&lt;SUP&gt;111&lt;/SUP&gt;In) Time Differential Perturbed Angular Correlation (TDPAC) Spectroscopy in Fe/Ag Films

We have investigated the magnetic properties of Cd atoms decayed from 111 In at the interfaces of Fe/Ag evaporated films. In order to determine the magnetic properties of the films, we have measured 111 Cd( 111 In) time differential perturbed angular correlation (TDPAC) spectra at room temperature as a function of distance from the interface. Fe and Ag were evaporated using electron beam evaporation, and small amounts of radioactive 111 In were evaporated by resistance-heating. The evaporated films had the following stacking orders on kapton polyimide film substrate: (1) polyimide/Fe 50 nm/ 111 In/Fe x nm/Ag 20 nm (x¼ 0:2; 0:3; 1; 3; 5; 10), (2) polyimide/Fe 50 nm/Ag x nm/ 111 In/Ag 20 nm (x¼ 0; 0:2; 1). We used an Ag layer as a cap layer in order to prevent oxidation in air. TDPAC spectra were measured using a four-detector arrangement. The hyperfine magnetic field tends to be slightly larger when 111 In is close to the interface of the Fe/Ag layer. The intensity of perturbation damps rapidly as 111 In is close to the interface of Fe and Ag. These behaviors are thought to depend on electric field gradients and the influence of the surface roughness.