Flexible Transparent Devices Research Articles

Flexible transparent memory cell: bipolar resistive switching via indium–tin oxide nanowire networks on a poly(dimethylsiloxane) substrate

This report describes the fabrication and resistive switching (RS) characteristics of a novel flexible transparent (FT) resistive random access memory (ReRAM) device with a Ag/indium–tin oxide (ITO) nanowire network/ITO capacitor deposited on a PDMS substrate. The transmittance of the device is ∼70% in the visible region, and it exhibits a stable high-resistance state (HRS) to low-resistance state (LRS) ratio (HRS/LRS ratio) in different bending states. The RS characteristics are attributed to the congregate state of oxygen vacancies at different voltages, and the difference between positive and negative bending is mainly contributed by the effect of stress on the conductive layer. The FT-ReRAM can be used as nonvolatile memory element in future flexible transparent devices.

Graphene transfer with self-doping by amorphous thermoplastic resins

The wet transfer of graphene requires sacrificial layer, which can support graphene during the removal of metallic substrate and prevent mechanical damage of thin graphene. However, the used polymer layer leaves an amounts of debris or residue on the graphene surface. The typical amorphous thermoplastic resins that consist of macromolecular chains with no crosslinks between the chains have been investigated as sacrificial layers for transferring graphene grown on metallic substrate. We have observed that the strong interaction of graphene and polymer provides clean surface without a chuck of residues and largely diminishes wrinkles and folds of transferred graphene. In addition, due to the increased substrate coupling as well as uniform plausible covalent bonding, we have achieved significant amount of electron transfer from graphene. Thus, polymer-self-doped-graphene during the transfer process has no need for the additional doping process or annealing process in order to obtain clean and flat surface with reduced sheet resistance. No thermal budget makes graphene available towards flexible transparent device application.

Preparation on transparent flexible piezoelectric energy harvester based on PZT films by laser lift-off process

The piezoelectric energy generation properties of transparent flexible devices (TFD) based on PbZr0.52Ti0.48O3 (PZT) films, which were fabricated by laser lift-off (LLO) process, were studied for a piezoelectric energy harvester. Through the introduction of indium-tin-oxide (ITO) and polyethylene terephthalate (PET) substrates, TFDs were implemented, respectively. The TFDs based on PZT films generated an AC-type output signal and output power of 8.4nW/cm2, at periodically bending and releasing motion. In addition, inverted output signals were observed when the manufactured TFDs were connected to the measuring equipment in reverse and were bended to the reverse direction, demonstrating that the generating signals originated from the piezoelectric effect of TFDs. The experimental results clearly showed that the TFDs based PZT film have potential for use in next generation of electronic devices applications such as flexible devices, transparent electronics, and energy harvester.

Novel optoelectronic devices based on single semiconductor nanowires (nanobelts)

Semiconductor nanowires (NWs) or nanobelts (NBs) have attracted more and more attention due to their potential application in novel optoelectronic devices. In this review, we present our recent work on novel NB photodetectors, where a three-terminal metal–semiconductor field-effect transistor (MESFET) device structure was exploited. In contrast to the common two-terminal NB (NW) photodetectors, the MESFET-based photodetector can make a balance among overall performance parameters, which is desired for practical device applications. We also present our recent work on graphene nanoribbon/semiconductor NW (SNW) heterojunction light-emitting diodes (LEDs). Herein, by taking advantage of both graphene and SNWs, we have fabricated, for the first time, the graphene-based nano-LEDs. This achievement opens a new avenue for developing graphene-based nano-electroluminescence devices. Moreover, the novel graphene/SNW hybrid devices can also find use in other applications, such as high-sensitivity sensor and transparent flexible devices in the future.

Simple fabrication of transparent flexible devices using SnO2 nanowires and their optoelectronic properties

A SnO2 nanowire-based transparent flexible device was fabricated via a simple transfer method and its optoelectronic properties were investigated. SnO2 nanowires grown on an Au-patterned Si substrate by thermal evaporation were simply transferred to a polyester film with an adhesive followed by screen printing of Ag electrodes. The fabricated flexible device exhibited good ohmic behaviors in the dark state as well as a high photoconductivity and a good on/off ratio of 104 under the UV irradiation with a wavelength of 254nm.

Low-temperature soluble InZnO thin film transistors by microwave annealing

Low-temperature solution-deposited thin film transistors (TFTs) involving sol–gel derived indium zinc oxide (IZO) as active layers is reported. Microwave annealing is shown to afford the fabrication of low-temperature processable TFTs. Solution-processed IZO-TFTs prepared at 150 °C by microwave irradiation have shown enhanced device characteristics of 0.1 cm 2 V −1 s −1 mobility and a ∼10 6 on/off current ratio, a threshold voltage of 8.1, and a subthreshold slope of 3.3 V/decade. From the results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), we confirmed that the device improvement originates from better crystallization at low temperature made possible by the use of microwave irradiation. Our findings suggest that solution-processable oxide semiconductors have potential for low-temperature and high-performance applications in transparent flexible devices.

Multicolor graphene nanoribbon/semiconductor nanowire heterojunction light-emitting diodes

We report novel graphene nanoribbon (GNR)/semiconductor nanowire (SNW) heterojunction light-emitting diodes (LEDs) for the first time. In the device, the GNR and SNW have face-to-face contact with each other, which has the merits of a larger active region and smaller series resistance, and may benefit high-efficiency electroluminescence and even electrically driven lasers in the future. ZnO, CdS, and CdSe NWs were employed in our case. At forward biases, the GNR/SNW heterjunction LEDs could emit light with wavelengths varying from ultraviolet (380 nm) to green (513 nm) to red (705 nm), which were determined by the band-gaps of the involved SNWs. The mechanism of light emitting for the GNR/SNW heterojunction LEDs was discussed. Our work opens new routes to developing diverse graphene-based nano-optoelectronic devices, which are basic components in integrated optoelectronic system. Besides, the novel graphene/SNW hybrid devices, by taking advantage of both graphene and SNW, will be promising candidates for use in applications such as high-sensitivity sensor and transparent flexible devices in the future.

Low-Temperature Solution-Deposited Oxide Thin-Film Transistors Based on Solution-Processed Organic–Inorganic Hybrid Dielectrics

We describe low-temperature, solution-deposited, oxide semiconductor thin-film transistors (TFTs) with a solution-processed gate dielectric in this study. The sol–gel-derived indium zinc oxide (IZO) semiconductor matched well with the organic–inorganic hybrid dielectric annealed at 200 °C, forming a coherent interface between the semiconductor and the dielectric without evidence of chemical damage. The IZO-TFTs made with a 420-nm-thick hybrid dielectric layer showed good performance: a low off-current on the order of <10-10 A, a field-effect mobility of 3.3×10-2 cm2 V-1 s-1, and a low threshold gate voltage of ∼2.4 V. Spin-coating of the IZO semiconductor on a hybrid dielectric/glass substrate results in TFTs optically transparent in the entire visible region (∼90%). Our solution-processable materials of the semiconductor and the gate dielectric can open the possibility of realizing flexible transparent devices using all-solution processing.

Fabrication and Evaluation of Large Flexible Transparent GZO-ReRAM

Fabrication of Flexible Transparent Resistive Random Access Memory (FT-ReRAM) which consists of Ga-doped ZnO (GZO) film not only as a memory layer but also as electrodes on the large Poly Ethylene Naphthalate (PEN) sheet was attained by introducing RF plasma assist DC magnetron sputtering method. The averaged transmittance in the visible region (400-800 nm) was 72%. The resistance change effect without morphological change was confirmed by using conducting atomic force microscope (C-AFM). Stable and repeatable bi-polar resistive switching by applying the voltage less than 2.5 V was confirmed in the all-GZO-FT-ReRAM. The present work showed the high applicability of the all-GZO-FT-ReRAM to achieve flexible transparent devices for the next generation.