Kapton Substrate Research Articles

Development of a 2.45 GHz Antenna for Flexible Compact Radiation Dosimeter Tags

Numerous medical operations employ blood transfusions, requiring X-ray irradiated blood for safety concerns. Current irradiation techniques can be significantly improved by replacing standard visual indicators with wireless dosimeter tags that automate the process, reducing inefficiencies, and eliminating blood wastage. A key requirement of the proposed dosimeter tag is flexible and efficient antennas that can be mounted on blood bags. This paper presents the design of a low-cost inkjet-printed dipole antenna on flexible Kapton substrate for a 2.45 GHz radio frequency identification (RFID) dosimeter tag. The tag is to be used in a lossy blood environment, which can severely affect antenna radiation performance. To mitigate this, the concept of artificial magnetic conductor (AMC) unit cells is investigated for best impedance and gain performance. When integrated with a dipole radiator, the fabricated AMC-backed antenna maintains broadside radiation with gains of 4.1–4.8 dBi under planar and bending conditions, and on a lossy blood bag. In a rectenna configuration, the antenna can power sensors for ranges up to 1 m. Measured output dc voltages up to 1.7 V are achieved across a 25 $\text{k}\Omega $ resistor. This antenna design is flexible, compact, efficient on lossy structures, and suitable for direct integration with biomedical sensing chips.

3D nanotube-structured Ni@MnO2 electrodes: Toward enhanced areal capacitance of planar supercapacitors

Rationally engineering three dimensional (3D) architrctures of transition-metal oxides (TMOs) is of great concern for the effective enhancement of electrochemical capacity, nevertheless, it is still challenging to selectively construct well-defined 3D architectured electrode materials in planar-configuration supercapacitors (SCs). Herein, we demonstrated a novel 3D nanotube-structured Ni@MnO2 electrode with interdigital configuration for high-performance planar supercapacitors. By combining transfer printing, alloying-dealloying and electrodeposition methods, 3D architecture of nanotube-structured Ni@MnO2 was subtly built on flexible Kapton substrate. The highly conductive Ni nanotubes embedded in MnO2 nanoflakes offer efficient electron collection paths, endowing the 3D electrodes with low internal resistance. Simultaneously, this 3D nanotube architecture provides multiple channels for electrolyte penetration and large active surface for Faradaic reactions. For these reasons, 3D SCs deliver remarkably enhanced areal capacitance of 10.75 mF cm−2, 2.4 times of the pristine SCs without 3D architecture. Moreover, 3D SCs exhibit desirable flexibility under different bending conditions, which indicates the potential feasibility of planar-configuration SCs as energy-storage components for wearable electronics.

Enhanced thermoelectric properties in vacuum-annealed Bi0.5Sb1.5Te3 thin films fabricated using pulsed laser deposition

Localized cooling in microelectronics and nanoelectronics as well as energy autonomy in applications such as wireless sensor networks and wearable electronics could be well served by thin-film thermoelectric devices fabricated on rigid and/or flexible substrates. Bi0.5Sb1.5Te3 is considered to be a state-of-the-art p-type thermoelectric material at the desired temperature range, i.e., near room temperature (RT). Fabrication of Bi0.5Sb1.5Te3 thin films with bulklike thermoelectric properties (∼3900 μW/mK2 at 380 K) remains, however, a great challenge. In this study, we have successfully fabricated Bi0.5Sb1.5Te3 thin films on fused silica and Kapton substrates using a two-step process. The films were deposited at RT using pulsed laser deposition and then subjected to a postdeposition ex situ vacuum annealing process. The as-grown films were nearly amorphous. However, the annealing process enhanced both their crystallinity and texture, resulting in thin films with bulklike thermoelectric power factor values. Bi0.5Sb1.5Te3 thin films grown on fused silica and annealed at 350 °C for 16 h exhibit a power factor of 3750 μW/mK2 at 380 K. In addition, Bi0.5Sb1.5Te3 films grown on Kapton and annealed at 250 °C for 5 h and also grown on Kapton substrates at 250 °C exhibit a power factor of 2600 μW/mK2 at 390 K. Both of these power factor values are among the highest reported in the literature to date for Bi0.5Sb1.5Te3 thin films grown on fused silica and Kapton substrates, respectively.

Preparation and growth mechanism of solidified TiO2 film on polyimide by SILAR at room temperature

In order to further expand the applications of polyimide, titanium oxide (TiO2) was deposited on flexible Kapton substrate by successive ionic layer adsorption and reaction (SILAR) method at room temperature. The growth process was systematically investigated by analyzing the changes of surface structures, film thickness, water wettability and adhesion work during film deposition. The results showed the SILAR TiO2 films growth initializes in an island-like pattern and then gradually transforms into a 2D layered manner after 10 deposition cycles with a growth rate of about 0.5 nm/cycle. With the increase of cycle number, the water wettability and adhesion work increased to ensure the deposition process to be continued. Interestingly, the obtained TiO2 film exhibits weak crystallinity, which is attributed to the surface graphitized structure of Kapton induced by the ultraviolet (UV) activation in ambient. However, no information of the crystalline phase was detected when TiO2 films were deposited on glass or polyethylene (PE) substrates without the special graphit-like structures under the same conditions. Hence, the growth mechanisms as the surface reactions, film formation and continuous growth behaviors of TiO2 film on Kapton substrate were discussed in details.

Novel Electronic Packaging Method for Functional Electronic Textiles

A novel packaging method that enables the reliable mounting and protection of bare die within a textile yarn has been investigated. The reliability of electronic textiles is highly challenging given the flexibility of the fabric and the rigors of typical applications. Achieving reliable operation requires novel packaging approaches. In order to maximize the reliability and to minimize stresses in the electronic package, the die should be located as close as possible to the central axis of the overall assembly. The die is bonded to a bottom Kapton substrate that contains patterned conductive interconnects and bond pads forming the functional circuit. The circuit is protected by a molded Kapton film that has recesses formed where the die is located. This approach has been compared with three other traditional packaging technologies during washing, twisting, and cyclical bending tests. The novel electronic packaging method shows the best performance in all tests surviving up to 45 wash cycles.

Mechanical Characterization of Reduced Graphene Oxide Using AFM

Nanoindentation coupled with Atomic Force Microscopy was used to study stiffness, hardness, and the reduced Young’s modulus of reduced graphene oxide. Oxygen reduction on the graphene oxide sample was performed via LightScribe DVD burner reduction, a cost-effective approach with potential for large scale graphene production. The reduction of oxygen in the graphene oxide sample was estimated to about 10 percent using FTIR spectroscopic analysis. Images of the various samples were captured after each reduction cycle using Atomic Force Microscopy. Elastic and spectroscopic analyses were performed on the samples after each oxygen reduction cycle in the LightScribe, thus allowing for a comparison of stiffness, hardness, and the reduced Young’s modulus based on the number of reduction cycles. The highest values obtained were after the fifth and final reduction cycle, yielding a stiffness of 22.4 N/m, a hardness of 0.55 GPa, and a reduced Young’s modulus of 1.62 GPa as compared to a stiffness of 22.8 N/m, a hardness of 0.58 GPa, and a reduced Young’s modulus of 1.84 GPa for a commercially purchased graphene film made by CVD. This data was then compared to the expected values of pristine single layer graphene. Furthermore, two RC circuits were built, one using a parallel plate capacitors made of light scribed graphene on a kapton substrate (LSGC) and a second one using a CVD deposited graphene on aluminum (CVDGC). Their RC time constants and surface charge densities were compared.

Inkjet-Printed Human Body Temperature Sensor for Wearable Electronics

This paper presents an all-printed human body temperature sensor developed on a plastic substrate with high deformation characteristics. The sensors are developed on $50~\mu \text{m}$ thick Kapton substrate with structural configuration of silver interdigital electrodes (IDEs) fabricated through inkjet material printer DMP 2850 and the sensing film based on carbon black deposited through doctor blade coating. Interdigital distance of the IDEs were optimized by evaluating sensors’ performance against changing the fingers spacing within a close range of 0.1–1 mm. Good sensitivity i.e. 0.00375 °C −1 is achieved at a temperature range of 28 to 50 °C with response and recovery times of 4 and 8.5 sec, respectively. Robustness of the sensor was also evaluated for a period of 50 days and a negligible drift ( $1\Omega$ ) in the base resistance was recorded. The sensor exhibited bendability down to 5 mm and was also characterized for the chemical and electrical properties i.e. resistance variation, surface morphology and Raman shift analysis of the carbon black. This wearable sensor can potentially be applied on human body for continuous temperature monitoring as well as on the artificial skin for social and industrial robotic applications.

Highly Efficient and Ultrasensitive Large-Area Flexible Photodetector Based on Perovskite Nanowires.

Hybrid organic-inorganic perovskites have shown exceptional semiconducting properties and microstructural versatility for inexpensive, solution-processable photovoltaic and optoelectronic devices. In this work, an all-solution-based technique in ambient environment for highly sensitive and high-speed flexible photodetectors using high crystal quality perovskite nanowires grown on Kapton substrate is presented. At 10 V, the optimized photodetector exhibits a responsivity as high as 0.62 A W-1 , a maximum specific detectivity of 7.3 × 1012 cm Hz1/2 W-1 , and a rise time of 227.2 µs. It also shows remarkable photocurrent stability even beyond 5000 bending cycles. Moreover, a deposition of poly(methyl methacrylate) (PMMA) as a protective layer on the perovskite yields significantly better stability under ambient air operation: the PMMA-protected devices are stable for over 30 days. This work demonstrates a cost-effective fabrication technique for high-performance flexible photodetectors and opens opportunities for research advancements in broadband and large-scale flexible perovskite-based optoelectronic devices.

Design and Experimentation of a Batteryless On-Skin RFID Graphene-Oxide Sensor for the Monitoring and Discrimination of Breath Anomalies

Real-time and comfortable monitoring of the human breathing could allow identifying anomalies in the rhythm and waveform to be correlated with several pathologic disorders of respiratory and cardiovascular systems. A wireless sensor based on a flexible Kapton substrate, suitable to be stuck over the face skin like a plaster and provided with a graphene-oxide (GO) electrode, is here proposed for application to the monitoring of the moisture emitted during inhalations and exhalations. The GO-based electrode increases its dc resistance when exposed to humidity with a sensitivity of $60~\Omega $ /RH. The device is compatible with the radiofrequency identification (RFID) standard in the UHF band. When used in battery-less mode, it can be read up to 60 cm. The RFID sensor has been successfully experimented in a measurement campaign involving 10 volunteers asked to reproduce a set of predefined normal and pathological breaths. The resulting resistance traces permit to well clusterize the breath patterns with respect to the respiration rate (extracted by a fast Fourier transform) and to the average peak variation of the sensor’s resistance with an accuracy close to 90%.

Fabrication, electrical characterization and mechanical flexibility test of back gated carbon nanotube thin film transistors on polyimide substrate

This work demonstrates the scalable method of fabricating back gated carbon nanotube thin film transistors (CNTTFTs) on a polyimide (kapton) substrate using photo lithography and lift-off process for patterning gate dielectrics and metals deposited for electrodes , and dip coating method for single walled carbon nanotubes deposition on functionalized dielectric surface. The CNTTFTs of varying dimensions are fabricated and electrical characterizations are done at room temperature and the CNTTFTs have exhibited p-type behaviour. The CNTTFT of channel length(L) 3 μm, width(W) 10 μm exhibits on-off current ratio of 9.219 × 105, carrier mobility of 4.9 cm2 V−1 s−1, trans conductance of 26 μS and on current of 472 μA when the substrate is kept flat (not bent). The mechanical flexibility test of CNTTFTs is done by conducting electrical characterization of CNTTFTs with the substrate bent to different diameters. Irrespective of the channel length, CNTTFTs have exhibited minimal change in the electrical characteristics when bent to 14 mm diameter. However, short channel CNTTFT (L = 3 μm) has shown considerable change in electrical characteristics when bent to 8 mm diameter compared to long channel length CNTTFT (L = 75 μm). The fabricated back gated flexible CNTTFTs work as CNTTFTs when bent up to the diameter of 8 mm, demonstrates that the CNTTFTs can be used for practical applications in the area of flexible electronics.

Fully Inkjet‐Printed VO2‐Based Radio‐Frequency Switches for Flexible Reconfigurable Components

AbstractFrequency‐reconfigurable radio‐frequency (RF) components are in high demand due to multiple frequency bands in wireless devices as well as varying frequency‐spectrum standards across the world. An important part of reconfigurable components is a switch; however, existing switches are very expensive, particularly for higher frequencies (≈10s of dollars). In this regard, metal–insulator transition (MIT) materials are attractive, as they can change their phase and can be used as switches. Vanadium dioxide (VO2) is one such material that features a transition temperature of only 68 °C. The cost of the switch can be brought down considerably (≈cents) if MIT materials such as VO2 can be inkjet‐printed; however, no ink of this sort is commercially available. In this work, VO2 ink and fully printed RF switches (shunt and series configurations) through this ink are presented for the first time. Both thermal and electrical triggering mechanisms are investigated in this work. These switches have shown decent performance up to 40 GHz. A more than 102 ON/OFF ratio and a switching speed of 0.4 µs are achieved. Finally, a frequency‐reconfigurable antenna, printed on a flexible Kapton substrate along with a printed VO2 switch, is demonstrated as a proof of concept.

Magnetodielectric Nanocomposite Polymer-Based Dual-Band Flexible Antenna for Wearable Applications

One of the major challenges in wireless communication technologies is the antenna design. In this paper, a wideband flexible antenna made by covering a Kapton substrate with a flexible magnetodielectric polymer-based nanocomposite layer is proposed. This novel magnetodielectric polymer-based nanocomposite relies on carbon-coated cobalt (CCo) and is coated with a conjugated polymer, polyaniline (PANI). The nanocomposite (PANI/CCo) fabrication, whose morphology was studied via scanning electron microscopy, demonstrates a relative permeability, a dielectric permittivity, and a conductivity of 5.5, 4.3, and 7500 S/m, respectively. In this paper, two frequency bands are of interest [1.8–2.45 GHz (personal communication service and wireless local area network) and 5.15–5.825 GHz (wireless networks)]. The functioning of the antenna in free space and on body is numerically and experimentally investigated. The average specific absorption rate is also discussed. Thanks to its performance this magnetodielectric nanocomposite polymer (PANI/CCo) antenna has been found to be a good candidate for wearable applications where complex bending situations are encountered.

Multicracking and Magnetic Behavior of Ni80Fe20 Nanowires Deposited onto a Polymer Substrate.

This work presents the effect of large strains (up to 20%) on the behavior of magnetic nanowires (Ni80Fe20) deposited on a Kapton substrate. The multicracking phenomenon was followed by in situ tensile tests combined with atomic force microscopy measurements. These measurements show, on the one hand, a delay in crack initiation relative to the nonpatterned thin film and, on the other hand, a saturation of the length of the nanowire fragments. The latter makes it possible to retain the initial magnetic anisotropy measured after deformation by ferromagnetic resonance. In addition, the ferromagnetic resonance line profile (intensity, width) is minimally affected by the numerous cracks, which is explained by the small variation in magnetic anistropy and the low magnetostriction coefficient of Ni80Fe20.

A Combined Experimental and Computational Study of Gas Sensing by Cu3SnS4 Nanoparticulate Film: High Selectivity, Stability, and Reversibility for Room Temperature H2S Sensing

AbstractSeveral binary sulfides are used for sensing of gases such as NH3, NO2, and H2, but not for H2S, especially at room temperature, because of the relative inactivity of metal sulfide surface bonds for this gas. The situation can be entirely different in the ternary case, however, due to the possible synergy of interactions involving dual cation surface chemistry. This is borne out by the present work wherein the Cu3SnS4 material, the Cu‐rich ternary sulfide used for the first time in the gas sensing context, not only senses H2S at room temperature but also remarkably does so with high selectivity and stability. Thus, a combined experimental and computer modeling study on the use of nanocrystalline orthorhombic Cu3SnS4 phase is reported for H2S sensing. The material shows sensitivity for a wide range of H2S concentrations (from 10 to 2000 ppm). The performance of the sensing device fabricated on Kapton substrate remains intact even after several days and multiple bending cycles. Importantly, these experimental findings are consistent with the results of density functional theory calculations for binding energies for different gases, namely, H2S, NO2, NH3, and CO, on Cu3SnS4 surface.

Laser-Induced Graphene by Multiple Lasing: Toward Electronics on Cloth, Paper, and Food.

A simple and facile method for obtaining patterned graphene under ambient conditions on the surface of diverse materials ranging from renewable precursors such as food, cloth, paper, and cardboard to high-performance polymers like Kevlar or even on natural coal would be highly desirable. Here, we report a method of using multiple pulsed-laser scribing to convert a wide range of substrates into laser-induced graphene (LIG). With the increased versatility of the multiple lase process, highly conductive patterns can be achieved on the surface of a diverse number of substrates in ambient atmosphere. The use of a defocus method results in multiple lases in a single pass of the laser, further simplifying the procedure. This method can be implemented without increasing processing times when compared with laser induction of graphene on polyimide (Kapton) substrates as previously reported. In fact, any carbon precursor that can be converted into amorphous carbon can be converted into graphene using this multiple lase method. This may be a generally applicable technique for forming graphene on diverse substrates in applications such as flexible or even biodegradable and edible electronics.

Kron–Branin modelling of ultra-short pulsed signal microelectrode

An uncommon circuit modelling of microelectrode for ultra-short signal propagation is developed. The proposed model is based on the Tensorial Analysis of Network (TAN) using the Kron–Branin (KB) formalism. The systemic graph topology equivalent to the considered structure problem is established by assuming as unknown variables the branch currents. The TAN mathematical solution is determined after the KB characteristic matrix identification. The TAN can integrate various structure physical parameters. As proof of concept, via hole ended microelectrodes implemented on Kapton substrate were designed, fabricated and tested. The 0.1-MHz-to-6-GHz S-parameter KB model, simulation and measurement are in good agreement. In addition, time-domain analyses with nanosecond duration pulse signals were carried out to predict the microelectrode signal integrity. The modelled microstrip electrode is usually integrated in the atom probe tomography. The proposed unfamiliar KB method is particularly beneficial with respect to the computation speed and adaptability to various structures.

Stress Analysis and Optimization of a Flip Chip on Flex Electronic Packaging Method for Functional Electronic Textiles

A method for packaging integrated circuit silicon die in thin flexible circuits has been investigated that enables circuits to be subsequently integrated within textile yarns. This paper presents an investigation into the required materials and component dimensions in order to maximize the reliability of the packaging method. Two die sizes of $3.5 \,\,\text {mm} \times 8 \,\,\text {mm} \times 0.53\,\, \text {mm}$ and $2 \,\,\text {mm} \times 2\,\,\text {mm} \times 0.1 \,\,\text {mm}$ have been simulated and evaluated experimentally under shear load and during bending. The shear and bending experimental results show good agreement with the simulation results and verify the simulated optimal thickness of the adhesive layer. Three underfill adhesives (EP30AO, EP37-3FLF, and Epo-Tek 301 2fl), three highly flexible adhesives (Loctite 4860, Loctite 480, and Loctite 4902), and three substrates (Kapton, Mylar, and PEEK) have been evaluated, and the optimal thickness of each is found. The Kapton substrate, together with the EP37-3FLF adhesive, was identified as the best materials combination with the optimum underfill and substrate thickness identified as 0.05 mm.

Investigating Sintering Mechanisms for Additive Manufacturing of Conductive Traces

Additive Manufacturing (AM) processes enable the fabrication of miniaturized and flexible devices on complex geometries. This paper explores a hybrid additive manufacturing technology that integrates micro-extrusion and PICO-jetting methods. Conductive slurries and colloidal inks were optimized for their rheological properties to aid their precise deposition. A variety of conductive materials which include carbon, silver, nano-particle silver and nickel were deposited on both rigid (glass) and flexible (Kapton) substrates. The deposited traces were cured using two sintering mechanisms which include furnace heating and in situ laser irradiation. The effect of curing mechanism on the conductance of deposited traces was evaluated. The results indicated that traces could be cured successfully with the laser curing mechanism. Nickel and silver laser cured traces had lower resistivity than the furnace sintered traces. An increase in the laser power resulted in lower resistivity of the traces. The lowest resistivity was achieved at 40W laser power with a single laser pass. Scanning electron microscopy and energy dispersive spectroscopy were used to characterize the trace morphology and elemental compositions. Higher power laser curing resulted in better bonding of the particles. Laser cured samples had minimal oxidation to the cross-section region of the traces as compared to furnace cured samples. This research lays the foundation for the fabrication of electronic components for a high level of freeform 3D electronics using a hybrid additive manufacturing technology.

Flexible UWB organic antenna for wearable technologies application

New generations of printed flexible antennas are playing an important role in wireless communication systems. The ultra wide band and wearable possibilities are critical aspects of these kinds of antennas. In this study, the proposed antenna is an elliptical monopole fed by a coplanar waveguide; it uses a kapton substrate and it is optimised to work from 1 to 8 GHz. In the case of copper, a conductive nanocomposite material based on a polymer (polyaniline: PANI) and charged by multiwalled carbon nanotubes (MWCNTs) is exploited. The flexibility of both the kapton substrate and the nanocomposite (PANI/MWCNTs) provides the ability to crumple the antenna paving the way to potential applications for body-worn wireless communications systems. In this study, the performance of the antenna is investigated in terms of return loss, radiation patterns and gain for both crumpled and uncrumpled antennas. The results confirm that performance remains at a good level when the antenna is crumpled.

Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films.

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000. Various elements e.g., F, Ti, Mo and W are utilized for doping and co-doping of VO. All the spin coated films are heat treated in a vacuum. Other than the doping elements the existence of only V4+ and V5+ species is noticed in the present films. Transmittance as a function of wavelength and the optical band gap are also investigated for doped and co-doped VO thin films grown on a Kapton substrate. The highest transparency (∼75%) is observed for the Ti, Mo and F (i.e., Ti–Mo–FVO) co-doped VO system while the lowest transparency (∼35%) is observed for the F (i.e., FVO) doped VO system. Thus, the highest optical band gap is estimated as 2.73 eV for Ti–Mo–FVO and the lowest optical band gap (i.e., 2.59 eV) is found for the FVO system. The temperature dependent phase transition characteristics of doped and co-doped VO films on both Kapton and Al6061 are studied by the differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition is noticed in the range of −24 to −26.3 °C.