Kapton HN Research Articles

Characterization of Magnetron Sputtered BiTe-Based Thermoelectric Thin Films.

Thermoelectric (TE) technology attracts much attention due to the fact it can convert thermal energy into electricity and vice versa. Thin-film TE materials can be synthesized on different kinds of substrates, which offer the possibility of the control of microstructure and composition to higher TE power, as well as the development of novel TE devices meeting flexible and miniature requirements. In this work, we use magnetron sputtering to deposit N-type and P-type BiTe-based thin films on silicon, glass, and Kapton HN polyimide foil. Their morphology, microstructure, and phase constituents are studied by SEM/EDX, XRD, and TEM. The electrical conductivity, thermal conductivity, and Seebeck coefficient of the thin film are measured by a special in-plane advanced test system. The output of electrical power (open-circuit voltage and electric current) of the thin film is measured by an in-house apparatus at different temperature gradient. The impact of deposition parameters and the thickness, width, and length of the thin film on the power output are also investigated for optimizing the thin-film flexible TE device to harvest thermal energy.

Modeling Electrical Aging of Polyimide Kapton HN Under High-Voltage High-Frequency Pulse Waveforms

Large voltage transients due to power electronic inverters are one of the major factors influencing the insulation lifetime. This article studies the effect of square voltage transients and switching frequency on insulation breakdown time based on the series of voltage endurance tests. A medium-voltage power-electronics inverter testbed is built to stress polyimide films Kapton HN with square waveforms at different frequencies. The voltage endurance test data are used to develop behavioral aging models and identify the effect of voltage transients and switching frequencies on insulation breakdown time. Results show a new correlation between switching frequency, insulation thickness, and voltage stress that have not been covered in the literature before.

Threshold voltage reliability in flexible amorphous In–Ga–ZnO TFTs under simultaneous electrical and mechanical stress

Flexible amorphous In–Ga–ZnO (a-IGZO) thin film transistors (TFTs) have been successfully demonstrated on 50 µm thick freestanding polyimide (PI) with µ sat around 10 cm2 V−1 s−1. In the literature, common characterization of flexible TFTs consist of measuring their electrical response at different bending radius or under positive and negative gate bias stress (PBS and NBS). However, there are few studies where the flexible TFTs have been measured with a simultaneous mechanical and electrical stress. In this work, simultaneous testing under electrical and mechanical stress were carried out with a gate bias stress voltage of ±6 V during 3600 s, and with a tensile bending radius of 1, 2 and 4 mm. a-IGZO TFTs bottom gate-top contacts were fabricated on commercial Kapton HN PI by a complete photolithography process. All the PBS and NBS characteristics presented an abnormal threshold voltage left shift which was mainly explained by the adsorption/desorption of water molecules at the back channel. This V th shift was modeled with the stretched exponential equation. Analyzed TFTs were stable under simultaneous stress until a 4 mm bending radius with electrical parameters V th, subthreshold slope, µ sat and I on/I off in the order of 0.7 V, 340 mV dec−1, 6 cm2 V−1 s−1 and 5 × 108, respectively.

All Inkjet-Printed Temperature Sensors Based on PEDOT:PSS

This paper develops a simple, cost-effective, fully Inkjet-printed flexible temperature sensor with easy fabrication steps using PiXDRO LP50 inkjet printer. The thermistor sensor employed a Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT: PSS) as a temperature-sensitive layer with silver nanoparticles (AgNps) as a contact electrode. The sensor performance was evaluated on different dimensions and types of substrates. Epson Glossy paper with 255 μm thickness and Polyimide (Kapton HN) with 50 μm thickness were used over temperatures ranging from room temperature up to 50 °C and 90 °C for paper and Kapton substrates, respectively. The sensor developed over Glossy paper showed the best sensitivity of -1.67 %/°C in the chosen temperature range while the sensor showed +0.113%/°C on PI substrate.

210Pb measurements at the André E. Lalonde AMS Laboratory: Potential for the radioassay of materials used in rare event search detectors

210Pb (T1/2=22.2 y) is an important source of background in rare event searches, such as neutrinoless double-β decay and dark matter direct detection experiments. In this paper, the capabilities of the A.E. Lalonde AMS Laboratory at the University of Ottawa for 210Pb measurements are discussed.For fluoride targets, the blank 210Pb/206Pb ratio was in the 10−14 to 10−13 range, but (PbF3)− current output was lower and less stable. For oxide targets, (PbO2)− current output showed better stability, despite a significant difference in current output for commercial PbO and processed samples, and background studies suggested a background not much higher than that of the fluoride targets. Both target materials showed, therefore, good performance for 210Pb Accelerator Mass Spectrometry assay.Measurements of Kapton ultra-thin films were performed. 90% C.L. upper limits for the 210Pb specific activity in the range of 0.74–2.8 Bq/kg were established for several Kapton HN films.

Antidelaminating, Thermally Stable, and Cost-Effective Flexible Kapton Platforms for Nitrate Sensors, Mercury Aptasensors, Protein Sensors, and p-Type Organic Thin-Film Transistors.

The inkjet printing of metal electrodes on polymer films is a desirable manufacturing process due to its simplicity but is limited by the lack of thermal stability and serious delaminating flaws in various aqueous and organic solutions. Kapton, adopted worldwide due to its superior thermal durability, allows the high-temperature sintering of nanoparticle-based metal inks. By carefully selecting inks (Ag and Au) and Kapton substrates (Kapton HN films with a thickness of 135 μm and a thermal resistance of up to 400 °C) with optimal printing parameters and simplified post-treatments (sintering), outstanding film integrity, thermal stability, and antidelaminating features were obtained in both aqueous and organic solutions without any pretreatment strategy (surface modification). These films were applied in four novel devices: a solid-state ion-selective (IS) nitrate (NO3-) sensor, a single-stranded DNA (ssDNA)-based mercury (Hg2+) aptasensor, a low-cost protein printed circuit board (PCB) sensor, and a long-lasting organic thin-film transistor (OTFT). The IS NO3- sensor displayed a linear sensitivity range between 10-4.5 and 10-1 M (r2 = 0.9912), with a limit of detection of 2 ppm for NO3-. The Hg2+ sensor exhibited a linear correlation (r2 = 0.8806) between the change in the transfer resistance (RCT) and the increasing concentration of Hg2+. The protein PCB sensor provided a label-free method for protein detection. Finally, the OTFT demonstrated stable performance, with mobility values in the linear (μlin) and saturation (μsat) regimes of 0.0083 ± 0.0026 and 0.0237 ± 0.0079 cm2 V-1 S-1, respectively, and a threshold voltage (Vth) of -6.75 ± 3.89 V.

Traps energy distribution in Kapton HN polyimide films through surface potential decay model under humidity conditions

In this paper, an experimental study and analysis of the effects of environmental relative humidity (RH %) on the transport mechanisms of electrical charges in 50 μm thick Kapton HN polyimide (PI) films have been presented. The evolution of the surface potential decay with time after negative corona charge deposition have been investigated and analyzed by examining the tdV/dt characteristics to straightly obtain information about trap energy distribution in PI films for different relative humidity levels (35, 50, 70 and 90%). The calculating method of trap energy distribution is based on the double exponential fitting analysis of surface potential decay measurements. Two peaks were observed in the trap charge density distribution curve with trap levels, which is agreed with the presence of the shallow and deep traps. The results indicate that for different charging voltage levels, the surface potential decays faster in humid air (RH = 90%) than in relatively dry ones (RH = 35%). The recorded corona charging current confirms the interpretation of surface potential decay measurements. In addition, the density and depths of both shallow and deep traps change with charging voltage and relative humidity levels. Both shallow and deep trap distribution moves towards lower energy levels, indicating an increase in the film's electrical conductivity.

Material erosion measurements and expected operational lifetime of a deployable photon sieve payload

Spacecraft operating in low-Earth orbit are subjected to a number of hazardous environmental constituents that can lead to decreased system performance and reduced operational lifetimes. Due to their thermal, optical, and mechanical properties, polymers are used extensively in space systems; however they are particularly susceptible to material erosion and degradation as a result of exposure to the LEO environment. The focus of this research is to examine the material erosion and mass loss experienced by a custom Kapton-like polyimide due to exposure in a simulated low-earth orbit environment. The deployable membrane telescope design discussed in this research is named Peregrine and is the scientific payload for FalconSat-7, a 3U cubesat designed and developed at the United States Air Force Academy (USAFA) for the purpose of demonstrating the capability of deployable membrane telescope technology on a nano-satellite platform. In addition to the polymer samples, chrome, silver and gold specimens will be examined to measure the oxidation rate and act as a control specimen, respectively. A magnetically filtered atomic oxygen plasma source has previously been developed and characterized for the purpose of simulating the low-Earth orbit environment. The plasma source can be operated at a variety of discharge currents and gas flow rates, of which the plasma parameters downstream of the source are dependent. The characteristics of the generated plasma were examined as a function of these operating parameters to optimize the production of O+ ions with energy relevant to LEO applications. The erosion yield of the Kapton-like polyimide was experimentally determined to be 2.84 × 10−24 cm3 per atom which is in close agreement when compared to the on-orbit measurement for reaction efficiency of Kapton HN. The experimentally determined reaction rate for the Kapton-like polyimide was used to estimate the operational lifetime of the photon sieve during the solar conditions expected beginning in May 2019. The effective lifetime is estimated between 126 and 153 days.

Data-Dense and Miniature Chipless Moisture Sensor RFID Tag for Internet of Things

A novel and miniaturized semi-elliptical 20-bit fully passive chipless RFID sensor tag is proposed in this article. The realized sensor tag is made up of semi-elliptical shaped open-end slots within the compact size of 25 mm × 17 mm. The multi-substrate analysis of the proposed tag is examined using non-flexible and flexible materials. The articulated tag configuration is capable of monitoring moisture levels when the largest resonator is covered by a heat-resistant sheet of Kapton HN (DuPontTM). The proposed tag functions in the operational frequency band of 4.1 GHz–16 GHz and possesses the overall bit density of 4.70 bit/cm2. The structure is composed of a thin passive substrate layer topped with an active layer of conductive path and is considered as a potential candidate for low-cost identification of the tagged objects. In addition to that, its moisture sensing property and flexible nature make it a reliable smart sensor for conformal applications.

Perfect Absorption by an Array of Lossy Dipoles Located Close to a Ground Plane

This paper presents a thin absorbing structure comprising an array of finitely conductive terminal-loaded dipoles spaced about half a wavelength apart and located above a ground plane. We show that if the antennas are terminated with proper load impedance, instead of a conjugate-matched one, a perfect absorption can be attained even when the array lies close to the ground plane. We also identify a threshold height below which the absorption efficiency rapidly drops and perfect absorption cannot be realized. The idea is illustrated via a concrete example of array of dipoles printed with conductive ink technology on a Kapton HN flexible film backed by a rigid Rogers 4350B substrate. The array is designed for perfect absorption at 3.45 GHz when it is located one-tenth of a wavelength above the ground plane. Good agreement between simulation and measurement results is demonstrated.

Reliability Challenges in Fabrication of Flexible Hybrid Electronics for Human Performance Monitors: A System-Level Study

Flexible hybrid electronics (FHE) interface rigid electronic components with flexible sensors, circuits, and substrates. This paper reports the reliability improvement of an FHE human performance monitor (HPM), designed to monitor electrocardiography (ECG) signals. The $50.8 {\,\,\mathrm {mm}} \times 50.8 {\,\,\mathrm {mm}}$ HPM is fabricated on Kapton HN polyimide (PI) substrate with flexible gold (Au) ECG electrodes on one side of the substrate and rigid electronic components for signal processing and communication mounted on the other side of the substrate. Our previously reported HPMs demonstrated reliability issues due to: 1) cracking of the copper (Cu) circuitry and 2) thinning and lack of adhesion at the printed Au and plated Cu interface that connected printed sensors to the Cu circuitry. Both failure mechanisms resulted in electrical opens in the circuit, which caused device failure. We explored effects of different design parameters, such as PI substrate thickness (50 versus $125~\mu \text{m}$ ), Cu circuit thickness (2 versus 6 $\mu \text{m}$ ), solder reflow temperature [205 °C for Tin-Lead (Sn-Pb) versus 175 °C for Tin-Bismuth (Sn–Bi) solder], solder pad design, and optimized inkjet printing (printing on bare Cu versus Au-plated Cu) on improving FHE reliability. Test vehicles (TVs) with different combinations of these factors were fabricated and bend-tested to determine the most robust configuration. TVs with 50- $\mu \text{m}$ -thick PI substrate, 6- $\mu \text{m}$ -thick Cu circuit, Sn–Bi solder, redesigned solder pads with rounded corners, and printed Au traces on Au plated Cu pads demonstrated the best reliability results.

Microwave Sensing Schemes of CPW Resonators Fully Printed on Humidity Sensitive Substrates

This letter investigates the humidity sensing schemes of the transmission line-based resonators printed on the hygroscopic sheets. A serial resonator in the coplanar waveguide technology was designed, simulated, screen-printed with only one silver layer on a Kapton HN foil, and tested under variable humidity conditions. Sensing schemes in frequency and phase paradigm for integration within resonant or transmitting microwave systems were proposed and experimentally validated. The resonant frequency and $S_{21}$ phase were used as the measurement variables. The sensor was proven highly sensitive and wide range. In the 60–100 %RH range, the frequency sensitivity of the sensor reached 3.88 MHz/%RH, and its phase sensitivity reached 1.25°/%RH.

Dielectric Properties of Substrates for InkJet Technology in GHz Area

This paper is focused on investigation of dielectric properties of various substrates for InkJet printing technology. In addition this paper included investigation of dielectric properties' homogeneity. Dielectric constant and loss tangent of polymeric flexible substrates (Polyimide DuPont Kapton HN, PET Mylar A, PEN Teonex Q51) and insulation paper (Nomex 410) were measured in GHz frequency area. Measurements were done by combination of vector network analyzer and split cylinder resonator. This measuring method provides dielectric properties at frequency around 10 GHz, the exact value of frequency may vary depends on specific material and its resonant frequency. Experiments included two types of samples, 6 x 6 cm which is recommended area for measurements of dielectric properties by split cylinder resonator and 12 x 12 cm for measurements of dielectric properties' homogeneity (one sheet contains 9 overlapping measuring areas 6 x 6 cm). All measured values of dielectric constant and dielectric losses were statistically processed and depicted by SigmaPlot software. The paper shows values of dielectric properties at GHz frequency area as they are lacking in datasheets from manufacturers and evaluate homogeneity of measured substrates.

Role of filler and its heterostructure on moisture sorption mechanisms in polyimide films

Moisture sorption and diffusion exacerbate hygrothermal aging and can significantly alter the chemical and mechanical properties of polymeric-based components over time. In this study, we employ a multi-pronged multi-scale approach to model and understand moisture diffusion and sorption processes in polyimide polymers. A reactive transport model with triple-mode sorption (i.e., Henry’s, Langmuir, and pooling), experiments, and first principles atomistic computations were combined to synergistically explore representative systems of Kapton H and Kapton HN polymers. We find that the CaHPO4 processing aid used in Kapton HN increases the total moisture uptake (~0.5 wt%) relative to Kapton H. Henry’s mode is found to play a major role in moisture uptake for both materials, accounting for >90% contribution to total uptake.However, the pooling mode uptake in Kapton HN was ~5 times higher than in Kapton H. First principles thermodynamics calculations based on density functional theory predict that water molecules chemisorb (with binding energy ~17–25 kcal/mol) on CaHPO4 crystal surfaces. We identify significant anisotropy in surface binding affinity, suggesting a possible route to tune and mitigate moisture uptake in Kapton-based systems through controlled crystal growth favoring exposure of CaHPO4 (101) surfaces during manufacturing.

An AZ31 magnesium alloy coating for protecting polyimide from erosion-corrosion by atomic oxygen

A continuous and uniform AZ31 magnesium alloy coating was deposited by magnetron sputtering to protect flexible polyimide substrate (Kapton HN) from atomic oxygen (AO) erosion-corrosion in low earth orbit. The AO erosion yield of the coated Kapton was determined to be 8.87 × 10−26 cm3 atom−1 after exposure to AO fluence of 1.47 × 1021 atoms cm−2, about 34 times lower than that of blank Kapton. XPS analysis results showed that an oxide layer of MgO formed on the surface of the coating after AO exposure, which is the main reason for the enhanced AO erosion-corrosion resistance of the AZ31 Mg-alloy coating.

Temperature effect on electrical characteristics of negative DC corona charged polyimide films

The study of the effect of sample temperature on the electric properties of PI films has been investigated. Surface potential decay (SPD) measurements on PI (Kapton HN, thickness: 50 μm) films were measured, after negative corona discharge, as a function of sample temperature varying from 27 to 80 °C. The measurements showed significant increase in the SPD rate with increasing sample temperature. Surface potential profile, return potential appearing after charge neutralization and charging current characteristics have been experimentally recorded for different sample temperatures in order to interpret SPD evolution at high sample temperature. The SPD curves were analyzed by fitting a bi-exponential decay Equation according to the presence of two different decay mechanisms related to shallow and deep traps. The distributions of trapped charges are obtained for different sample temperatures.

1-D Physical Model of Charge Distribution and Transport in Dielectric Materials Under Space Radiations

In this paper, the development of a 1-D physical and numerical model is presented for the description of charge transport and ionization processes of irradiated space used polymers (Teflon FEP and Kapton HN). This model extends the previous circuit model described by Hanna et al. and relies on solid-state physics. This model aims at predicting the charging behavior of space used dielectric materials under space radiation conditions. A physical validation is carried out through crossed comparisons with the experimental data on surface potentials, conductivity and bulk charge distribution. For this physical validation, different irradiation conditions and several materials are presented. The interest of this 1-D model is to obtain a more realistic prediction of dielectric charging behavior as a function of time as well as a better bulk charge description.

Miniaturized humidity and temperature sensing RFID enabled tags

A compact 27-bit linearly polarized chipless radio frequency identification tag is presented in this research. The proposed tag is designed with an overall tag dimension of 23 × 23 mm2. The tag comprises of metallic (copper) rings-based structure loaded with slots. These slots correspond to a particular sequence of bits. The circular tag is analysed using 2 different substrates, that is, Rogers RT/duroid/5870 and flexible Rogers RT/duroid/5880. The radar cross-section response of frequency signatured tag is analysed for humidity and temperature sensor designs. Humidity sensing is achieved by deploying a DuPont Kapton HN heat resistant sheet on the shortest slot of the tag, that is, the sensing slot. Temperature sensing is attained using Rogers RT/duroid/5870 and Stanyl polyamide as a combined substrate. Hence, the miniaturized, robust, and flexible tag can be deployed over irregular surfaces for sensing purposes.

Thin film growth into the ion track structures in polyimide by atomic layer deposition

High-aspect ratio porous structures with controllable pore diameters and without a stiff substrate can be fabricated using the ion track technique. Atomic layer deposition is an ideal technique for depositing thin films and functional surfaces on complicated 3D structures due to the high conformality of the films.In this work, we studied Al2O3 and TiO2 films grown by ALD on pristine polyimide (Kapton HN) membranes as well as polyimide membranes etched in sodium hypochlorite (NaOCl) and boric acid (BO3) solution by means of RBS, PIXE, SEM-EDX and helium ion microcopy (HIM). The focus was on the first ALD growth cycles.The areal density of Al2O3 film in the 400 cycle sample was determined to be 51±3×1016at./cm2, corresponding to the thickness of 55±3nm. Furthermore, the growth per cycle was 1.4Å/cycle. The growth is highly linear from the first cycles.In the case of TiO2, the growth per cycle is clearly slower during the first 200 cycles but then it increases significantly. The growth rate based on RBS measurements is 0.24Å/cycle from 3 to 200cycles and then 0.6Å/cycle between 200 and 400cycles. The final areal density of TiO2 film after 400 cycles is 148±3×1015at./cm2 which corresponds to the thickness of 17.4±0.4nm. The modification of the polyimide surface by etching prior to the deposition did not have an effect on the Al2O3 and TiO2 growth.

Manufacture and mechanical characterisation of high voltage insulation for superconducting busbars – (Part 1) Materials selection and development

It is planned that the high voltage electrical insulation on the ITER feeder busbars will consist of interleaved layers of epoxy resin pre-impregnated glass tapes (‘pre-preg’) and polyimide. In addition to its electrical insulation function, the busbar insulation must have adequate mechanical properties to sustain the loads imposed on it during ITER magnet operation. This paper reports an investigation into suitable materials to manufacture the high voltage insulation for the ITER superconducting busbars and pipework. An R&D programme was undertaken in order to identify suitable pre-preg and polyimide materials from a range of suppliers. Pre-preg materials were obtained from 3 suppliers and used with Kapton HN, to make mouldings using the desired insulation architecture. Two main processing routes for pre-pregs have been investigated, namely vacuum bag processing (out of autoclave processing) and processing using a material with a high coefficient of thermal expansion (silicone rubber), to apply the compaction pressure on the insulation. Insulation should have adequate mechanical properties to cope with the stresses induced by the operating environment and a low void content necessary in a high voltage application. The quality of the mouldings was assessed by mechanical testing at 77K and by the measurement of the void content.