Thin Flexible Substrate Research Articles

Rotman Lens-Based Wide Angular Coverage and High-Gain Semipassive Architecture for Ultralong Range mm-Wave RFIDs

In this letter, the authors demonstrate, for the first time, the implementation of a fully-flexible, energy autonomous Rotman lens-based backscattering RFID tag operating in the 28 GHz 5G band. The Rotman lens front end was designed, simulated, fabricated on a thin flexible substrate and its gain and differential radar cross section (RCS) tested. The structure displays a simultaneous high gain and wide angular coverage, resulting in a remarkable RCS, measured in both planar and severe bending conditions. A low power oscillator was then added to the retrodirective array to test its detectability as a backscatterer at an unprecedented range of up to 64 m while displaying a power consumption as low as 2.64 $\mu$ W, effortlessly supplied by its flexible solar cell in normal office indoor conditions. Enabled by the implementation of a high degree of focalizing retrodirectivity, this unique Rotman lens-based system could enable the birth of RFIDs with practical reading ranges exceeding 1.8 km.

High thermoelectric performance of p-type Bi0.5Sb1.5Te3 films on flexible substrate

Bi2Te3-based compounds are excellent candidates for the low-temperature thermoelectric application. In the present work, a technology for fabrication of p-Bi0.5Sb1.5Te3 films with high thermoelectric efficiency on a thin flexible polyimide substrate has been developed. The preparation of films was carried out by a flash evaporation method. A systematic study of the transport properties (Hall coefficient, Seebeck coefficient, electrical conductivity, transverse Nernst coefficient) over the entire temperature range of 80–400 K for p-Bi0.5Sb1.5Te3 films has been performed. The power factor (PF) for the Bi0.5Sb1.5Te3 (doped by 0.5 wt % Te) film reaches the value of ~30.4 μW cm−1K−2, which is among the highest values of the PF reported in the literature to date for a film on a flexible polyimide (amorphous) substrate. The measured thermal diffusivity along the film allowed us to accurately estimate the figure of merit Z for p-Bi0.5Sb1.5Te3 films considering the anisotropic effect of Bi2Te3-based materials. A significant enhancement of Z up to ~3.0 × 10−3 K has been obtained for these films, which is state-of-the-art even compared to bulk materials. This research can provide insight into the fabrication of p-type branch of the Film Thermoelectric Modules (FTEM), which could be a candidate for application in micro-scale thermoelectric generators.

Additive Manufacturing of a Flexible Carbon Monoxide Sensor Based on a SnO2-Graphene Nanoink

Carbon monoxide (CO) gas is an odorless toxic combustion product that rapidly accumulates inside ordinary places, causing serious risks to human health. Hence, the quick detection of CO generation is of great interest. To meet this need, high-performance sensing units have been developed and are commercially available, with the vast majority making use of semiconductor transduction media. In this paper, we demonstrate for the first time a fabrication protocol for arrays of printed flexible CO sensors based on a printable semiconductor catalyst-decorated reduced graphene oxide sensor media. These sensors operate at room temperature with a fast response and are deposited using high-throughput printing and coating methods on thin flexible substrates. With the use of a modified solvothermal aerogel process, reduced graphene oxide (rGO) sheets were decorated with tin dioxide (SnO2) nanoscale deposits. X-ray diffraction data were used to show the composition of the material, and high-resolution X-ray photoelectron spectroscopy (XPS) characterization showed the bonding status of the sensing material. Moreover, a very uniform distribution of particles was observed in scanning (SEM) and transmission electron microscopy (TEM) images. For the fabrication of the sensors, silver (Ag) interdigitated electrodes were inkjet-printed from nanoparticle inks on plastic substrates with 100 µm linewidths and then coated with the SnO2-rGO nanocomposite by inkjet or slot-die coating, followed by a thermal treatment to further reduce the rGO. The detection of 50 ppm of CO in nitrogen was demonstrated for the devices with a slot-die coated active layer. A response of 15%, response time of 4.5 s, and recovery time of 12 s were recorded for these printed sensors, which is superior to other previously reported sensors operating at room temperature.

Low-cost thin-film passive RFID circuits and detector system

AbstractThis paper discusses the design of chip-less RFID tags of a standard pocket size of 69 mm by 156 mm. These tags are based on lumped elements of copper metal traces constructed on a thin polyamide flexible substrate. Moreover, a low-cost single-chip Bluetooth detector circuit system is demonstrated. Two different detection methods: variable coil load coupling and optical light intensity detection were combined to yield 256 unique ID codes. In the first method, by utilizing simple 4 MHz digital drivers and an integrated analog to digital converter (ADC) in the reader controller; various inductively coupled resonant loads corresponding to multiple distinct tags could be differentiated, yielding eight different (3-bit) ID codes. The additional via-based hole pattern reflectometer method creates additional 32 distinct levels (5-bit) utilizing 650 nm visible light-emitting diode and a simple trans-impedance operational along with the same analog ADC pins of a Bluetooth controller. The printed circuit board trace coil on the two-layer low-cost FR-4 waterproof sealed detector unit is simultaneously used as a Qi wireless power receiver to charge the120 mAh 2450 Lithium Polymer (LiR) battery. The device could remain operational for more than a month with a single charge; remaining connected with a mobile device and enabling 10 readouts daily.

Microneedle Patterning of 3D Nonplanar Surfaces on Implantable Medical Devices Using Soft Lithography.

Micropatterning is often used to engineer the surface properties of objects because it allows the enhancement or modification of specific functionalities without modification of the bulk material properties. Microneedle arrays have been explored in the past for drug delivery and enhancement of tissue anchoring; however, conventional methods are primarily limited to thick, planar substrates. Here, we demonstrate a method for the fabrication of microneedle arrays on thin flexible polyurethane substrates. These thin-film microneedle arrays can be used to fabricate balloons and other inflatable objects. In addition, these thin-filmed microneedles can be transferred, using thermal forming processes, to more complex 3D objects on which it would otherwise be difficult to directly pattern microneedles. This function is especially useful for medical devices, which require effective tissue anchorage but are a challenging target for micropatterning due to their 3D nonplanar shape, large size, and the complexity of the required micropatterns. Ultrathin flexible thermoplastic polyurethane microneedle arrays were fabricated from a polydimethylsiloxane (PDMS) mold. The technique was applied onto the nonplanar surface of rapidly prototyped soft robotic implantable polyurethane devices. We found that a microneedle-patterned surface can increase the anchorage of the device to a tissue by more than twofold. In summary, our soft lithographic patterning method can rapidly and inexpensively generate thin-film microneedle surfaces that can be used to produce balloons or enhance the properties of other 3D objects and devices.

(Invited) A Leaf-Inspired Photon Management Scheme for Graphene/Silicon Solar Cells

Graphene/silicon (Gr/Si) Schottky junction solar cells have attracted much attention due to the ease and low cost of fabrication, along with the lucrative properties of high electron mobility, transparency and mechanical flexibility of graphene as a transparent conducting electrode.1 Utilizing its inherent mechanical flexibility, graphene can be integrated with thin flexible crystalline Si substrates opening up a new regime of applications in flexible and wearable electronics. Reducing Si absorber thickness below 50 um offers advantages of reduced material cost, along with mechanical flexibility and light weight.2 But Si at such thicknesses suffers from low photon absorption in the solar spectrum. To compensate for the low light absorption in such thin substrates, light management schemes become essential. Light trapping in Gr/Si solar cells is enabled by engineering the Si surface to form nanopillars, nanowires etc., which decreases the reflection loss and allows more light to couple in to the Si substrate. The structured Si absorber increases surface area and surface recombination, which is detrimental to the solar cell efficiency. Thus, it is imperative to use a light-trapping scheme devoid of Si structuring to enhance the photo-conversion efficiency. We present an all-dielectric light-trapping scheme on planar Gr/Si Schottky junction solar cells with the use of bottom layer of titania spheres and top layer of silica spheres.3 An optimal Si thickness coupled with an optimized light-trapping scheme leads to efficient electron-photon harvesting. The photo-conversion efficiency of a 20 um thick nanosphere-decorated Gr/Si solar cell improves to 9%, which is 1.3x higher than the pristine cell’s PCE of 7%. FDTD simulations are performed for optimizing the diameter of nanoparticles in each of the layers. The ratio of size of nanoparticles in the top to bottom layer plays a crucial role in advanced light management. An optimized structure of silica spheres, having diameter larger than that of titania spheres, suppresses reflection over wide angles of incidence and increases absorption in active Si layer over AM1.5G solar spectrum. The non-absorbing dielectric spheres can be easily realized by the well-known Stober technique. Additionally, the photovoltaic characteristic of the laminated solar cell shows negligible change after several bending cycles having bend radius ranging from 5 mm to 10 mm. After continuous bending and straightening, the ultra-thin solar cell can retain its performance, revealing the excellent stability and flexibility of the device. Such simple, low-cost light trapping schemes are universal in nature, devoid of recombination losses and are potentially viable for any solar cell technology. References 1 B Li, et al. Adv. Mater. 22, 2743 (2010). 2 K E Petersen, Proc. IEEE 70, 420 (1982). 3 S. Das, et al. Nano Energy 58, 47 (2019).

Mitigating early fracture of amorphous metallic thin films on flexible substrates by tuning substrate roughness and buffer layer properties

Ductility mismatch between brittle amorphous thin films and flexible polymer substrate often leads to limited elongation and early failure of the system. A combined experimental and computational study was carried out to investigate the roles of buffer layer material type, thickness, and substrate roughness on the fracture toughness of the amorphous thin film/polymer system. Experimentally, about 1 μm thick amorphous aluminum-manganese thin films were deposited on polyimide substrates and tested in tension. The reliability of such systems was found to be strongly influenced by the film/substrate interface adhesion. Several strategies to improve the adhesion of the interface were conducted, including roughening the surface of the substrate, and adding a buffer layer with a desired mechanical properties and thickness. Computationally, finite element simulations of the same system were carried out under tension. It was found that by introducing substrate roughness and adding a Cr buffer layer of 75 nm, the interface toughness of the film/substrate can be increased by almost twenty times. The results of the present work may shed light on the interfacial engineering strategies for improving reliability of future flexible electronics.

SAC305 Solder Reflow: Identification of Melting and Solidification Using In-Process Resistance Monitoring

The proper control of solder heating and melting leads to successful joining of surface-mount technology devices to the metallization of printed circuit boards. When developing new solder alloys for more miniaturized and lower temperature processes, the improved process control for the heating and melting during solder reflow can be beneficial. To find an optimized temperature profile efficiently, it is helpful to know the exact onset times of the physical mechanisms of soldering including sintering, melting, and solidification. In particular, to exactly know the time, the solder remains in the molten state can help to minimize the temperature exposure of sensitive substrates. To this end, we used standard lead-free SAC305 solder and a real-time resistance monitoring setup to observe the in-process resistance during the soldering of a 0805-type chip resistor to find out exact points in time when the soldering mechanisms occur. Cross-sectioning studies and microscopic observations were performed in parallel to explain three distinct resistance drops observed in the resistance signals. Sintering of solder balls resulted in drop 1, the collapse and melting of all the solder balls resulted in drop 2, and the solidification of solder resulted in drop 3, which actually consisted of two separate drops, one for each solder joint of the chip resistor. The observation of the resistance drop due to solder solidification was achieved because our newly improved setup reduced the signal noise to less than 0.012 $\text{m}\Omega $ (root mean square value). On average, the solder was in a liquid state for 17.6 min ± 0.18 min (seven samples). The solidification drop was 0.2 $\text{m}\Omega $ and happened at approximately 200 °C, indicating not more than 28 K of undercooling. Such an accurate measurement of melting and solidification times may prove useful in the future when optimizing the reflow temperature profiles for advanced soldering applications, e.g., to minimize the melting–solidification interval on heat-sensitive thin flexible substrates for wearables.

High sensitivity ammonia detection using metal nanoparticles decorated on graphene macroporous frameworks/polyaniline hybrid

In this paper, we presented the fabrication and properties of new ammonia (NH3) sensors with sensitive layer of nickel nanoparticles decorated on three-dimensional nitrogen-doped graphene-based frameworks/polyaniline (NiNPs@3D-(N)GFs/PANI) hybrid. The hybrid are synthesized through in-situ oxidative polymerization on flexible thin substrate. Synergetic behavior between both components manifested outstanding sensitivity (750.2 at 1000 ppm NH3) and quick response (95 s) and recovery (25 s) times and a lower limit of detection (~ 45 ppb) at room temperature. The sensitivity of NiNPs@3D-(N)GFs/PANI hybrid sensor was shown to be about 14 times more than its of pure PANI sensor at 1000 ppm of NH3. The excellent sensitivity of the as-prepared hybrid is mainly originated from the substantial rise of hole-like carriers by NiNPs@3D-(N)GFs as well as improved inter-molecule interactions via π- π electron networks. The obtained results revealed significant advantages for the synthesized hybrid sensor, making it a suitable choice for real-world applications of NH3 detection.

Broadband and Ultrathin Infrared Stealth Sheets

To effectively hide objects and render them invisible to thermographic detectors, their thermal signatures in the infrared (IR) region of the spectrum may be concealed. However, to conceal broadband spontaneous thermal emission of objects, covering the mid‐ and long‐IR is a major obstacle. Here, metallic‐dielectric nanostructures and microscale IR emitters are integrated and transferred onto thin flexible substrates to realize IR stealth sheets. The nanostructures absorb and scatter a broad band of IR wavelengths to reduce both reflection and transmission to below 5% across a wide range from 2.5 to 15.5 μm, and thus significantly attenuate the amount of IR signals propagating toward the detectors. Results show that the nanostructures with their unique properties can almost completely conceal the thermal emission from objects and blend them into their surroundings. In addition, micro‐emitters thermally isolated from the broadband absorbers can present false thermography to deceive IR detectors and heat‐sensing cameras.

Millimeter‐wave planar antenna on flexible polyethylene terephthalate substrate with water base silver nanoparticles conductive ink

AbstractA 60 GHz, mm‐wave array antenna, mounted on a thin flexible polyethylene terephthalate substrate is presented. The proposed 16 8 microstrip series fed array antenna prototype used with laboratory made silver nanoparticles conductive ink used in inkjet technology. The main fabrication problem for this prototype is addressed via ink formulation for printing a homogeneous layer with an excellent electrical conductivity. In comparison to the previous millimeter‐wave series feed structures, the proposed antenna feed network conductive traces 50% is reduced. Silver base conductive ink is prepared in the laboratory with a viscosity of 9–12 cP and a surface tension of 27–32 mN/m for use in Fujifilm DMP‐2831 series. The realized design validate performances of 16‐element linear series sub‐array fed by a three‐stage T‐junction power‐divider network that achieves a 24 dBi gain is presented.

Wideband CPW-Fed Flexible Bow-Tie Slot Antenna for WLAN/WiMax Systems

A bow-tie antenna based on a slot configuration in a single metal sheet on top of a very thin flexible substrate is introduced. The antenna is constructed from two slotted right-angle triangles fed by a coplanar waveguide transmission line. The topology is very simple and extremely easy to tune in order to reach the proper characteristics after mounting on a supporting structure. A prototype is designed, fabricated, and characterized experimentally. The tunability is proven by considering both the version in free space and the version for use on a brick wall. Measurements demonstrate good agreement with simulations. Both versions cover the wireless local area network (2.4 and 3.65 GHz) and WiMax (2.3, 2.5, and 3.5 GHz) spectra, with an overall impedance bandwidth of 1.79 GHz (57.7%) and 1.46 GHz (49.7%), respectively. The radiation of the antenna is bidirectional with maximum gains of 6.30 and 5.09 dBi for the free space and brick wall versions, respectively.

Tensile and fatigue behavior of polymer supported silver thin films at elevated temperatures

Tensile and fatigue tests were conducted at 50 and 70°C for evaluating the mechanical behavior of polyethylene-terephthalate (PET) supported silver (Ag) thin films. The strain amplitude-number of cycles (S-N) curves of Ag/PET at elevated temperatures were acquired for determining the failure life under in-situ heating condition. The stretchability at elevated temperature was found to be better than the tensile behavior at room temperature, whereas the fatigue behavior is worse at elevated temperature. The adhesion between silver and PET is better at elevated temperature. However, the tensile and fatigue characteristics were different results because the adhesion of silver and PET is not homogeneous at elevated temperatures. The good adhesion between thin metal films and flexible substrates is not always beneficial effect of the mechanical behavior. Therefore, we suggest a new fatigue failure mechanism for Ag/PET at elevated temperature.

Approaching ultimate flexible organic light-emitting diodes using a graphene anode

Ultimate flexible organic light-emitting diodes (OLEDs) should have an ultra-high device efficiency, a low-efficiency roll-off at a high luminance and excellent flexibility. Here, we realized flexible tandem OLEDs using a graphene anode with a very high electroluminescent efficiency of ~205.9 cd A−1, 45.2% (~396.4 cd A−1, 87.3% with a hemispherical lens) and a very low efficiency roll-off at a high luminance of ~6.6% at 10 000 cd m−2 (~3.8% with a hemispherical lens) by stacking two organic electroluminescence (EL) units. For the first time, we used an easily controlled and low-temperature processable charge generation layer with lithium nitride (Li3N). This simultaneously provided efficient stacking of EL units and enhanced compatibility of the flexible device on a thin plastic substrate. The flexible tandem OLEDs with a graphene anode also showed great flexibility against bending up to a bending strain of 6.7%. These results represent a significant advancement towards the production of next-generation flexible displays and solid-state lighting that use a graphene anode. Bendable displays with nearly unmatched strain resistance and device efficiency can be realized using graphene-based transparent electrodes. Organic light-emitting diodes (OLEDs) are integral to today's touch-screen technology, but future applications are limited by a reliance on brittle, indium tin oxide electrodes. Researchers led by Tae-Woo Lee from Pohang University of Science and Technology in South Korea have made an alternative OLED prototype that assembles multi-electroluminescent units of organic materials onto high-quality, graphene electrodes transferred to thin plastic substrates. The team improved on previous graphene OLED designs by inserting a charge-generation layer - an organic material mixed with lithium ions that can be evaporated at low temperatures - between separate electroluminescent stacks. This setup provides ample charge carriers and mechanical strength to keep the OLED efficiency high, even after 1,000 bending cycles. We realized highly flexible tandem OLEDs using a graphene anode with very high electroluminescent efficiency ~205.9 cd A−1, 45.2% (~396.4 cd A−1, 87.3% with a hemispherical lens) and very low efficiency roll-off at high luminance ~6.6% at 10 000 cd m−2 (~3.8% with a hemispherical lens) by stacking two organic electroluminescence units using a easily controllable and low-temperature processable charge generation layer on thin flexible plastic substrates. The flexible OLEDs showed great flexibility against bending stress up to bending strain of 6.7%.

Flexible substrate technology for millimeter wave wireless power transmission

In this paper, a technology based on thin flexible polyimide substrate (Kapton) to develop antennas for millimeter wave wireless power transmission is presented. Firstly, we characterize the Kapton polyimide (relative permittivity and loss tangent) using a ring resonator method up to V band. A 60 GHz patch antenna is designed, fabricated, and measured to validate our technology. Crossed-dipoles array antennas at Kuband and K band for energy harvesting are also designed, fabricated, and measured. Then a prototype of crossed-slot dipole antenna at V band is proposed. Finally, a resistivity characterization of Au bump used in flip-chip packaging is done, which leads us one step further toward aheterogeneous integration on flexible substrate of different components for Wireless Sensor Network nodes.

Biocompatibility and implant of a less invasive intraocular pressure sensor

We discussed the design and fabrication consideration for an Intraocular Pressure (IOP) systems according to surgical and biocompatibility implant limitations. A new less invasive IOP system is implanted successfully in the eye of a rabbit by a minimum invasive surgical procedure. The MEMS array is over a flexible, biocompatible polyimide substrate in a maximum 8×8mm area. The substrate flexibility allows it to fit a small surface of the eye. The implanted coil is under the conjunctiva, out of the interior chamber. However, the pressure sensor is deposed inside the interior chamber through a minimum invasive procedure. The capacitive sensor is fabricated considering a maximum area of 0.5×0.5mm2. Increasing sensor capacitance is achieved by a set of windows cavities getting a sensible reduction of the separation of its capacitor plates at the base of the windows anchored. The coil and pressure sensor consist of alternating layers of polyimide–metal–polyimide, patterned using reactive ion etching over a thin silicon wafer that is used only as a sacrificial layer. We pointed out the way micron-scale metal layers can be incorporated in a thin flexible plastic substrate to integrate into the same process both: the coil and the intraocular pressure sensor. The whole structure encapsulated in a biocompatible polymer fits into the shape of the ocular globe.

Scalable Frequency Selective Surface with Stable Angles of Incidence on a Thin Flexible Substrate

A band-stop scalable frequency selective surface (FSS) structure that provides stability for an angle of incidence and polarization is designed using the repetitive arrangement of a unit structure miniaturized on a thin dielectric substrate. The designed miniaturized FSS has a hexagonal unit cell of a minimum size of 0.081 λat 2.5 GHz in which a triangular loop is repeated. In addition to the frequency stability, the proposed structure reduces the design complexity that is the biggest shortcoming of the miniaturization techniques studied previously. A scalable FSS structure possessing stable frequency response characteristics over a wide band ranging from 2 to 8 GHz, which is achieved by the control of a single design variable, can be designed. For verification of the proposed structure, FSS structures that operate in the bands of 2.5 GHz, 5 GHz, and 8.2 GHz have been designed and fabricated on a very thin substrate. It has been confirmed that the results of the measurement and simulation correspond well with each other. The designed structures also demonstrate high stability for both the polarized wave and the incidence angle of the incident wave.

Implantable Wideband Low-Specific-Absorption-Rate Antenna on a Thin Flexible Substrate

This letter proposes an implantable wideband low-specific-absorption-rate (SAR) antenna on a flexible substrate. The proposed antenna structure was printed on a thin flexible substrate, which is suitable for implantable human body applications. A sigma-shaped monopole radiator and the C-shaped design excited fundamental and coupled modes that dominated the near E-field distribution evenly to achieve a low SAR. The proposed antenna was fabricated and measured on a flexible substrate. The smallest size (80 $~\hbox{mm}^{3}$ ) was achieved with low-profile flexible substrate compared to a state-of-the-art implantable antenna over 400 MHz, and 68% fractional bandwidth was achieved. The maximum peak value of the average SAR was approximately 230 W/kg when the input power was 1 W. The maximum input power of the proposed antenna was approximately 10 mW.

Comparison of continuous-flow and static-chamber μPCR devices through a computational study: the potential of flexible polymeric substrates

Two types of micro-PCR (polymerase chain reaction) devices, a continuous-flow and a static-chamber device, with specifications imposed from flexible printed circuit technology, are compared through a computational study. Models for laminar flow, heat transfer in both solid and fluid, mass conservation of species, Joule heating, PCR kinetics, and temperature control feedback are coupled. The comparison is performed under identical conditions: the same material stack, i.e., flexible thin polymeric films with metal layers for integration of microheaters, the same volume of PCR mixture, and the same PCR protocol. Performance is quantified in terms of DNA amplification, energy consumption, and total operating time. The calculations show that the efficiency of DNA amplification is almost the same in both devices. However, contrary to what is generally believed, the static-chamber device fabricated on thin substrates, despite the necessary temperature ramping up within each thermal cycle, requires (2–4 times) lower energy consumption compared to the continuous-flow device. The constant energy losses to the ambient continuously during the operation of the continuous-flow device overcome the energy required for the thermal cycling of the static-chamber device. However, this result is reversed when the substrate thickness increases above 1000 μm. Concerning the speed, the total time required for the static-chamber device is only 1.1–2 times greater than that of the continuous-flow device due to relatively rapid heating and cooling rates for such thin substrates. These advantages for static-chamber micro-PCR devices arise as a result of the small thickness of the substrate where microchannels and microheaters are closely spaced. Both the low energy consumption and the inherent protocol flexibility indicate an attractive potential for static-chamber micro-PCR devices realized on flexible thin substrates with integrated microheaters.

An indium tin oxide-free polymer solar cell on flexible glass.

Future optoelectronic devices and their low-cost roll-to-roll production require mechanically flexible transparent electrodes (TEs) and substrate materials. Indium tin oxide (ITO) is the most widely used TE because of its high optical transmission and low electrical sheet resistance. However, ITO, besides being expensive, has very poor performance under mechanical stress because of its fragile oxide nature. Alternative TE materials have thus been sought. Here we report the development of a multilayer TiO2/Ag/Al-doped ZnO TE structure and an ITO-free polymer solar cell (PSC) incorporating it. Electro-optical performances close to those of ITO can be achieved for the proposed TE and corresponding PSC with an additional advantage in their mechanical flexibility, as demonstrated by the fact that the cell efficiency maintains 94% of its initial value (6.6%) after 400 cycles of bending, with 6 and 3 cm maximum and minimum radii, respectively. Instead of common plastic materials, our work uses a very thin (0.14 mm) flexible glass substrate with several benefits, such as the possibility of high-temperature processes, superior antipermeation properties against oxygen and moisture, and improved film adhesion.