Papers by Keyword: Flexible Substrate

Abstract: Conductive and flexible electronics have attracted great demands and attention in the field of stretchable and wearable electronic devices. In this work, polydimethylsiloxane (PDMS) was composited with different drops of graphene solution to produce flexible, conductive and optically transparent PDMS/Graphene composite using the drop-cast method. The dielectric constants of PDMS and PDMS/Graphene composite were measured using Agilent dielectric probe. I-V characterization was used to measure the conductivity of the flexible substrate in flat and bending conditions. The UV-VIS was used to measure the transmittance properties of the substrate. Comparing the electrical properties of the pristine PDMS substrate with graphene composited PDMS substrates, the current shows a slight decrease due to the physical morphology of PDMS/Graphene composite that creates a small hole on the surface. No significant changes can be found between 1 drop, 2 drops, 3 drops and 4 drops of graphene in PDMS solution. For the dielectric measurement, the result of composited PDMS/Graphene sample had shown a lower value of dielectric constant (1.1 F/m) compared to pure PDMS (2.33 F/m). This shows that the existence of graphene in PDMS reduces the dielectric constant of pristine PDMS. The result of UV-VIS shows the samples with 4 drops of graphene having the lowest visible transmittance. The PDMS/Graphene composite can be concluded as a dielectric material with a lower dielectric constant. It has the potential to be used as a conductive substrate for further flexible interconnect materials since it has a unique electrical feature and robust mechanical strength.

Abstract: Inkjet printing is a promising technique for fabricating printed electronics. This technique acquires the utilization of conductive ink to form a fine and thin resolution conductive structure on a flexible substrate. The challenges are to design a stable conductive ink with a controlled properties to prevent nozzle clogging. Furthermore, a fine structure construction often demonstrated poor device performance due low mechanical durability. In this work, we have characterized morphology of the newly developed inkjet-printable nanosilver conductive ink (Mi-Ag) in our laboratory. The ink shows a stable colloidal ink zeta potential of-79.1 mV with nanoparticle size less than 100 nm properties has been tailored for compatibility with inkjet printing of conductive pattern on polyethylene terephthalate (PET) flexible substrate. It has been ascertained that the flexible electronic form factor affects the quality of the physical and electrical properties of printed pattern and the device performance. Hence, the bending test of the printed RFID patterns fabricated with different layer of thicknesses was investigated. Electrical properties of the samples were monitored by in-situ conductivity and resistivity measurement under cyclic bending testing. Pattern with thinnest layer of 1.31μm (1X) had the smallest electrical properties percentage drop (38.4%) at 12,000 bending cycles due to the fact that in thick layer, the interparticle network started to change during bending and became weaker due to the large amount of the particles in the dense printed layer. In contrast, printed device exhibited minimal increase in resistivity. Consequently the particle gap increased which allowed the movement of electrons, leading to the increased of electrical resistance. The device endurance characteristic is crucial to satisfy future design requirement of flexible electronic applications.

Abstract: The fabrication of novel semiconductor seed crystals using hetero-epitaxial growth on substrates such as Si, sapphire, and SiC, which have been successfully grown to large diameter and high quality, is very attractive as a breakthrough technology. However, a critical issue in heteroepitaxial growth is the formation of cracks due to thermal stress caused by the difference in the thermal expansion coefficient between the substrate and the growth layer during the cooling process after growth. In this study, we propose a method to reduce thermal stress by using a "Flexible substrate," which is a substrate with mechanical flexibility enhanced by removing more than 80% of its volume with periodic through holes. Using this method, we obtained an AlN hetero-epitaxial growth layer with absolutely no cracks observed. This method is applicable not only for AlN on SiC but also for the fabrication of various new semiconductor materials.

Abstract: The methods of obtaining the base layers of cadmium telluride to create effective solar cells are considered. At present, two groups of methods are distinguished for the preparation of base layers of cadmium telluride for high-efficiency PECs: low-temperature and high-temperature. If a polyimide film with a temperature stability of 450 °C is used as a substrate, then deposition should be carried out at a temperature of about 430 °C. Therefore, to create base layers of cadmium telluride on a flexible polyimide substrate, it is necessary to use low-temperature methods for producing base layers. It has been established that the formation of base layers of solar cells based on cadmium telluride on flexible polyimide substrates must be carried out by direct current magnetron sputtering.

Abstract: In this report, indium nitride (InN) thin films were deposited on kapton polyimide flexible substrate by reactive radio frequency (RF) sputtering method using an indium target in a mixture of Ar and N₂ gases. The effects of the Ar:N₂ gas ratio on the properties of the deposited InN thin films were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and energy dispersive (EDX) spectroscopy. The XRD revealed that the deposited films composed of polycrystalline wurtzite InN. The FESEM and AFM surface morphologies showed smooth and uniform surface of gas ratio at 60:40 compare to others gas ratio. Overall, the characteristics of the InN thin films were effectively improved with combination the N₂:Ar gas ration at 60:40. The results showed that the gas ratio plays an important role in improving the properties of the InN thin films.

Abstract: Nowadays, flexible electronic is an important technology to produce flexible electronic devices due to it offers the attractive features such as possibility of product types and designs, with reducing size and weight, and low cost. Poly (3,4-ethelenedioxythiophene):poly (stylenesulfonate) (PEDOT:PSS) is a conductive polymer which possess high conductivity, high electrochemical, and low redox potential. PEDOT:PSS and PEDOT:PSS/Graphene (GP)/Dimethyl sulfoxide (DMSO) conductive ink ware deposited on Polyethylene terephthalate (PET) flexible substrate using desktop inkjet printer. Conductivity and thickness of conductive pattern at 1, 3, 5, 10, 20 layers were investigated in this study. It is observed that sheet resistivity of the conductive pattern is influenced by number of printed layers. Addition of GP at 20 layers of PEDOT:PSS/GP/DMSO conductive pattern exhibits the lowest sheet resistivity at 44 ohm/󠇯󠇯sq compared to PEDOT:PSS conductive pattern of 1.81×10⁴ ohm/󠇯󠇯sq.

Abstract: Sol-gel precursor has been prepared by using zinc acetate (ZnAC) as starting material dissolved in isopropanol (IPA), diethanolamine (DEA) and distilled water (H₂O) were added to produce a homogeneous and stable solution. The sol-gel precursor was deposited on ITO/PET substrate by spin-coat route. Oxidation process was held in deionized water at 90 °C for a specific time. The (100) and (101) ZnO planes were formed as the preferred orientation. RMS values of ZnO samples found to be 280 nm, 272 nm and 241 nm for 8 h, 12 h and 16 h, respectively by hot water treatment (HWT). ZnO nanorods-hourglass-like, nanosheet-leafs-like and nanorods-oval-like were obtained with different HWT time.

Abstract: The study signifies the radio-frequency (RF) sputtering growth and characterizations of indium nitride (InN) thin films deposited on flexible substrates. A three-inch diameter indium (In) sputtering target with purity of 99.999% was used. The deposition was carried out at room temperature and with substrate temperature of 200 °C. The surface morphologies, structural and optical properties of the deposited thin films were examined by using field-emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction as well as Fourier transform infrared spectroscopy. All the results revealed that InN thin films have been successfully deposited on the flexible substrates in the gas mixture ambient of argon and nitrogen.

Abstract: Silicone rubber composites filled with fused silica were prepared through sigma mixing followed by hot pressing. Filling fraction of fused silica in the silicone rubber matrix was varied from 0-0.51 volume fraction (V_f) and its effects on dielectric properties at different frequencies, thermal properties and moisture absorption were investigated. The results indicate that with the increase of filler volume fraction the relative permittivity increases and dielectric loss decreases. The coefficient of thermal expansion decreased and the moisture absorption increased marginallyas the filler loading increased.

Abstract: Photonic crystals are dielectric materials with different refractive index or permittivity periodically. Photonic crystals have widely application for future technology such as waveguide, optical transistor, cavity of laser and biosensor. Photonic crystals can be fabricated in three types i.e 1D, 2D and 3D structure. In this paper, we report the successful fabrication of 3D photonic crystal from polystyrene particles. The fabrication process began with the synthesis of polystyrene particles followed by deposition on glass and flexible substrate using self-assembly method. We obtained polystyrene monodispered particles which have a uniform shaped with diameter 320 nm. Self-assembly method resulted to the arrangement of polystyrene particles on glass and flexible substrate. Stop band which is related to its optical property are at wavelength of 721 nm and 631 nm for photonic crystal on glass and flexible substrate, respectively. We found that filling fraction of photonic crystal on flexible substrate is lower than that of glass substrate due to some defects.