Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates. But metal-oxide formation by the sol-gel route requires an annealing step at relatively high temperature, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol-gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm(2) V(-1) s(-1) (with an Al(2)O(3) gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.

Photo and electrically stable transparent ZnO thin-film transistors for an active matrix organic light emitting diode (AM-OLED) panel are reported. Oxide semiconductor-based thin-film transistors (TFTs) have been extensively studied mainly to replace Si-based TFTs in electrical and optical devices. [1][2][3][4][5] Therefore, there have been many reports on oxide-based TFTs: transparent oxide TFTs, [6][7][8][9][10] amorphous oxide TFTs, [11][12][13][14][15] polycrystalline oxide TFTs, [16,17] and even photo-detecting oxide TFTs. [18] In particular, transparent ZnO-TFTs have attracted much attention as display drivers that possess some evident advantages over opaque Si-based TFTs.[19] Transparent TFTs (TTFTs) with a large energy bandgap channel of $3.3 eV would transmit a visible light signal to increase the aperture ratio even in the bottom emission OLED display, which could not be anticipated from any conventional opaque TFTs. Well-designed TTFTs would result in important benefits such as longer life time and lower fabrication price of OLEDs or TFT-LCDs. However, since the ZnO-TFTs usually contain defects in the ZnO channel and deep level defects in the channel/dielectric interface that generate unwanted photo-current during light transmission and device operation, [20,21] the very advantages of the transparent ZnO-TFTs have never been fully utilized or demonstrated for display panels, to the best of our limited knowledge. We recently developed an effective fabrication methodology to greatly reduce the number of defects in the channel and interfacial charge trap defects using a low temperature (200 8C) atomic layer deposition (ALD) for a ZnO semiconductor channel and Al 2 O 3 dielectric. We found that our transparent ZnO-TFTs with defect-controlled channel and channel/dielectric interface maintain good photo-stability during device operation without generating much detectable photocurrent. Our ZnO-TFTs showed a good mobility of $4 cm 2 V À1 s À1 and an excellent high on/off ratio of $10 7. The display back panels with our photo-stable and fully transparent ZnO-TFT array demonstrate a successful operation of a 2.5 inch-sized bottom emission AM-OLED panel under 15 V, which exhibited a high aperture ratio of $60%. Figure 1a and 1b show a microscopic plan view of our 2 TFT/1 storage capacitor (2T/1C) cell structure and a circuit diagram of the cell, respectively. (Please note that the size of a pixel cell was 210 mm 230 mm as measured under an optical microscope.) Based on this back plane composed of a 2T/1C cell matrix we fabricated OLED pixels to operate in a manner of bottom emission. Our TTFT exhibited a higher than 80% transmittance in the visible range as shown in Figure 1c. The schematic but detailed cross section of the cell is shown in Figure 2a, although it only displays our top-gate driving ZnO-TFT and storage capacitor here. In Figure 2a, the driving ZnO-TFT contains an initial 9 nm thin gate dielectric and next a 176 nm thick dielectric. The first thin dielectric was deposited on a ZnO channel at 200 8C...

Since the introduction of inorganic ZnO, typically in the form of nanoparticles (NPs), as an electron transport layer (ETL) material, the device performance of electrically driven colloidal quantum dot-light-emitting diodes (QLEDs), in particular, with either Cd-based II−VI or non-Cd-based III−V (e.g., InP) quantum dot (QD) visible-emitters, has been rapidly improved. In the present work, three Zn 1−x Mg x O (x = 0, 0.05, 0.1) NPs that possess different electronic energy levels are applied as ETLs of solution-processed, multilayered I−III−VI type QLEDs that consist of a Cu−In−S, Cu−In−Ga−S, or Zn−Cu−In−S QD emitting layer (EML) plus a common organic hole transport layer of poly(9-vinlycarbazole). The luminance and efficiency of those QLEDs are found to be strongly dependent on the type of ZnMgO NP ETL, resulting in the substantial improvements by means of alloyed ZnMgO ETL versus pure ZnO one. Ultraviolet photoelectron and absorption spectroscopic measurements on a series of ZnMgO NP films reveal that their conduction band minimum (CBM) levels are systematically closer to the vacuum level with increasing Mg content. Therefore, such beneficial effects of alloyed NPs on QLED performance are primarily ascribed to the reduced electron injection barrier between ETL and QD EML that is enabled by the upshift of their CBM levels.

Non-volatile memory (NVM) thin-film transistors (TFTs) with organic channels have been investigated with a ferroelectric gate material, poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] [1][2][3][4][5][6] under the basic principles from conventional Si-based ferroelectric field-effect transistors (FeFET), preparing the advent of transparent or flexible device technologies on glass and plastic substrates. Beta-phase crystalline P(VDF-TrFE) films generally have an induced remnant polarization of %10 mC cm À2 if polarized over their coercive electric field (E-field), formed through spin casting and subsequent optimum curing processes. [2,4,7] Researchers presented decent NVM properties of polymer channel NVM-TFT with P(VDF-TrFE) in their recent works: low leakage, relatively low switching voltage, [2] and a quite high switching speed. [1,2,6] They also reported the physical properties of the unit ferroelectric polymer layer. [8][9][10][11][12][13][14][15] Nonetheless, a challenging problem remains to be overcome prior to any practical application of this ferroelectric polymer towards NVM-TFT on flexible plastic or glass substrates: it is the inferior field mobility (less than %10 À2 cm 2 V À1 s À1) of present polymer-based NVM-TFTs, which is due to the intrinsic low channel mobility of polymer-based semiconductors and also due to the rough surface of spin-cast P(VDF-TrFE) layers. Moreover, obtaining low leakage current from spin-cast crystalline ferroelectric polymer films may require quite sensitive care [2] in the solvent selection and in the coating processes of purified polymers. Our previous report shows some high mobility (0.36 cm 2 V À1 s À1 ) ZnO-based NVM-TFTs with poly-4-vinylphenol (PVP)/P(VDF-TrFE) double layers, where the PVP overlayer suppressed current leakage of P(VDF-TrFE) but also caused poor retention, inducing depolarization electric field in the ferroelectric P(VDF-TrFE) layers.[16] Here, we adopt a single P(VDF-TrFE) layer of short-range-order crystalline phase as the nonvolatile memory component for a reproducible lowcurrent-leakage ferroelectric, to be applied onto high-mobility p-channel pentacene channels on flexible plastic substrates and also onto high-mobility n-channel ZnO channels on glass. Our limited-crystalline ferroelectric layer still showed good remnant polarization of maximum %7 mC cm À2, and the pentacene-and ZnO-based NVM-TFTs with such short-range-order crystalline P(VDF-TrFE) layer reproducibly demonstrated maximum field mobilities of 0.1 and 1 cm 2 V À1 s À1 , respectively, with low leakage current densities of a few nanoamperes (%1 Â 10 À6 A cm À2 ), low switching voltages of %20 V for write/erase (in 50 ms pulse), low operation (after switching) voltages of %5 V, and long retention of over 10000 s. In particular, our ZnO-based NVM-TFTs displayed a large memory window of 20 V, which is the maximum obtainable from 200 nm-thick P(VDF-TrFE).Device cross-sections in Figure 1a display our pentacene-and ZnO-based NVM TFTs with the short-range-order crystalline P(VDF-TrFE)...

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Crack-based strain sensor systems have been known for its high sensitivity, but suffer from the small fracture strain of the thin metal films employed in the sensor which results in its negligible stretchability. Herein, we fabricated a transparent (>90% at 550 nm wavelength), stretchable (up to 100%), and sensitive (gauge factor (GF) of 30 at 100% strain) strain gauge by depositing an encapsulated crack-induced Ag nanowire (AgNW) network on a hydroxylated poly(dimethylsiloxane) (PDMS) film. Stretching the encapsulated AgNWs/PDMS resulted in the formation of a percolation network of nanowire ligaments with abundant percolation paths. The encapsulating polymer was designed to adhere strongly to both the AgNW and PDMS. The improved adhesion ensured the resistance of the crack-induced network of AgNWs varied reversibly, stably, and sensitively when stretched and released, at strains of up to 100%. The developed sensor successfully detected human motions when applied to the skin.

Because of outstanding optical properties and non‐vacuum solution processability of colloidal quantum dot (QD) semiconductors, many researchers have developed various light emitting diodes (LEDs) using QD materials. Until now, the Cd‐based QD‐LEDs have shown excellent properties, but the eco‐friendly QD semiconductors have attracted many attentions due to the environmental regulation. And, since there are many issues about the reliability of conventional QD‐LEDs with organic charge transport layers, a stable charge transport layer in various conditions must be developed for this reason. This study proposes the organic/inorganic hybrid QD‐LEDs with Cd‐free InP QDs as light emitting layer and inorganic ZrO2 nanoparticles as electron transport layer. The QD‐LED with bottom emission structure shows the luminescence of 530 cd m−2 and the current efficiency of 1 cd/A. To realize the transparent QD‐LED display, the two‐step sputtering process of indium zinc oxide (IZO) top electrode is applied to the devices and this study could fabricate the transparent QD‐LED device with the transmittance of more than 74% for whole device array. And when the IZO top electrode with high work‐function is applied to top transparent anode, the device could maintain the current efficiency within the driving voltage range without well‐known roll‐off phenomenon in QD‐LED devices.

We report on the fabrication of pentacene-based nonvolatile memory thin-film transistors (NVM-TFTs) with thin poly(vinylidene fluoride/trifluoroethylene) ferroelectric gate insulators. Our NVM-TFT adopts flexible polyethersulfone substrate and operates under the low voltage write-erase (WR-ER) pulses of ±13∼±20 V with field effect mobilities of 0.1–0.18 cm2/V s, depending on the ferroelectric polymer thickness. Our NVM-TFT displays good memory window (ΔV) of 2.5–8 V and also exhibits WR-ER current ratio of 20–40. The retention properties persist over ∼10 000 s and the dynamic response for WR-ER pulses demonstrates clear distinction of WR-ER states under the short switching pulse of 50 ms.