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Vertical channel thin film transistors (VTFTs) have been expected to be exploited as one of the promising three-dimensional devices demanding a higher integration density owing to their structural advantages such as small device footprints. However, the VTFTs have suffered from the back-channel effects induced by the pattering process of vertical sidewalls, which critically deteriorate the device reliability. Therefore, to reduce the detrimental back-channel effects has been one of the most urgent issues for enhancing the device performance of VTFTs. Here we show a novel strategy to introduce an In–Ga–Zn–O (IGZO) bilayer channel configuration, which was prepared by atomic-layer deposition (ALD), in terms of structural and electrical passivation against the back-channel effects. Two-dimensional electron gas was effectively employed for improving the operational reliability of the VTFTs by inducing strong confinement of conduction electrons at heterojunction interfaces. The IGZO bilayer channel structure was composed of 3 nm-thick In-rich prompt (In/Ga = 4.1) and 12 nm-thick prime (In/Ga = 0.7) layers. The VTFTs using bilayer IGZO channel showed high on/off ratio (4.8 × 109), low SS value (180 mV dec−1), and high current drivability (13.6 μA μm−1). Interestingly, the strategic employment of bilayer channel configurations has secured excellent device operational stability representing the immunity against the bias-dependent hysteretic drain current and the threshold voltage instability of the fabricated VTFTs. Moreover, the threshold voltage shifts of the VTFTs could be suppressed from +5.3 to +2.6 V under a gate bias stress of +3 MV cm−1 for 104 s at 60 °C, when the single layer channel was replaced with the bilayer channel. As a result, ALD IGZO bilayer configuration could be suggested as a useful strategy to improve the device characteristics and operational reliability of VTFTs.

Based on density functional theory calculations and non-equilibrium Green’s function method, we study the photovoltaic effect of monolayer MoSe2–WS2 lateral heterojunction under vertical irradiation. Combined with the differential charge density, it predicts the stability of the MoSe2–WS2 heterojunction and the high possibility of charge transfer from MoSe2 to WS2. As a result, such MoSe2–WS2 lateral heterojunction breaks the spatial inversion symmetry thus leading to a photocurrent. The resultant photocurrent increases from close to zero to a maximum value in the range of photon energy of 1.7 eV–2.8 eV. The photocurrent response fits the cosine function with respect to the polarization angle. The peak photocurrent is obtained when the photon energy is 2.8 eV, and can be attributable to the large density state peaks near −1.3 eV in the valence band and 1.5 eV in the conduction band. Meanwhile, the single-layer MoSe2–WS2 lateral heterojunction exhibits higher polarization sensitivity that is characterized by an extinction ratio of up to 9.6. These results suggest possible applications of the single-layer MoSe2–WS2 lateral heterojunction in next generation optoelectronic devices.

Three-dimensional (3D) vertical architecture transistors represent an important technological pursuit, which have distinct advantages in device integration density, operation speed, and power consumption. However, the fabrication processes of such 3D devices are complex, especially in the interconnection of electrodes. In this paper, we present a novel method which combines suspended electrodes and focused ion beam (FIB) technology to greatly simplify the electrodes interconnection in 3D devices. Based on this method, we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al2O3 gate-oxide both grown by atomic layer deposition. Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires, which avoid cumbersome steps in the traditional 3D structure fabrication technology. Both single pillar and arrays devices show well behaved transfer characteristics with an I on/I off current ratio greater than 106 and a low threshold voltage around 0 V. The ON-current of the 2 × 2 pillars vertical channel transistor was 1.2 μA at the gate voltage of 3 V and drain voltage of 2 V, which can be also improved by increasing the number of pillars. Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.

Aluminium alloy motor shell is the core part of the new energy vehicle powertrain. It has a complex structure with an average wall thickness of 4∼5mm, a side wall with 6∼7mm spiral water jacket, and the bottom of the shell inlaid with cast steel bearing bushing. Because of its complex structure characteristics, as well as higher internal quality requirements and air tightness requirements, the casting process of motor housing is very difficult. This paper introduces the structural characteristics and common casting defects of the motor shell. On this basis, the typical casting process scheme of motor shell with sand core casting technology and the application of computer simulation technology in the development of motor shell casting process are discussed and shared.

The spatially continuous control of the physical properties in semiconductor materials is an important strategy in increasing electron-capturing or light-harvesting efficiencies, which is highly desirable for the application of optoelectronic devices including photodetectors, solar cells and biosensors. Unlike the multi-layer growth of chemical composition modulation, local strain offers a convenient way to continuously tune the physical properties of a single semiconductor layer, and open up new possibility for band engineering within the 2D plane. Here, we demonstrate that the gradient refractive index and bandgap can be generated in atomically thin transition metal dichalcogenide flakes due to the effect of thermal strain difference. A highly resolved confocal scanning optical microscopy is used to perform a real-space light-reflection mapping of suspended atomically thin WSe2 flakes at the low temperature of 4.2 K, in which the parabolic light-reflection profiles have been observed on suspended monolayer and bilayer WSe2 flakes. This finding is corroborated by our theoretical model which includes the effect of strain on both the refractive index and bandgap of nanostructures. The inhomogeneous local strain observed here will allow new device functionalities to be integrated within 2D layered materials, such as in-plane photodetectors and photovoltaic devices.

We investigate the electronic transport properties in Weyl semimetals (WSM) in the presence of unidirectional and torsional strains. We show that unidirectional and torsional strains induce an effective pseudomagnetic field which influences the tunneling transport through a barrier in a Weyl semimetal. The perfect transmission rings and arcs are shown to be highly sensitive to the application of unidirectional and torsional strains. Interestingly, the profile of the perfect transmission rings and arcs are different under tensile and compressive strains of the same magnitude. These results, together with the fact that the precise control of strain has been demonstrated in Weyl semimetals, open an exciting prospect towards all-Weyl semimetal electronics.

The effects of the atomic composition of Ge2Sb2Te5 (GST), especially the Sb-excess phase, on device reliability were investigated for applications of spatial light modulator (SLM) devices using phase-change materials. Sb-excess GST phases were prepared by cosputtering with two target systems. For Sb-excess GST thin films, amorphous phases were found to be more directly crystallized to more conductive hexagonal-close-packing phases at higher crystallization temperatures without the appearance of a less conductive face-centered-cubic phase with increasing amount of incorporated Sb. The marked changes in crystallization behavior and improved thermal stability were suggested as critical benefits for enhancing the device durability during cyclic operations, considering that the interdiffusion within the GST could be the main origin of the final device failure. The number of cyclic operations of the unit pixel device was markedly improved to more than 103 when the amount of excess Sb was modulated from 0 to 21 at. %.

In this work, a switchable plasmonic structure is proposed for reflection-type spatial light modulation in the visible range with subwavelength resolution. This structure is based on a metallic grating in which each resonant cavity couples the incident light into a gap surface plasmon mode and then reflects the light modulated in the cavity. By incorporating an ultrathin layer of the phase-change material Ge2Sb2Te5 at the entrance of the cavity, the optical modulation characteristic of the structure can be switched between two modes. Numerical investigations are conducted to verify the proposed structure, with the focused analysis of two common types of binary modulations: amplitude-only and phase-only modulations.

Top-emission organic light-emitting diodes (TEOLEDs) using chromium anode have been fabricated by employing two techniques: direct-current magnetron sputtering and e-beam evaporation. Atomic force microscopy and work function taken on the chromium film surfaces obtained from both techniques revealed that using dc magnetron sputtering is advantageous over e-beam evaporation in terms of surface characteristics particularly when the film is deposited. The anode having a triple-layer structure of Cr/Al/Cr was deposited on a Si wafer. The device structure of the TEOLED was Cr (20 nm)/Al (100 nm)/Cr (20 nm)/α-napthylphenylbiphenyl diamine (NPB) (60 nm)/tris(8-hydroxyquinoline) aluminum (Alq3) (60 nm)/LiF (1 nm)/Al (2 nm)/Ag (20 nm)/NPB (200 nm). The TEOLED containing the Cr layer deposited by dc magnetron sputtering method showed higher luminance and efficiency than that containing the Cr layer deposited by e-beam evaporation. The superior device characteristics of the TEOLED containing the chromium layer deposited by dc magnetron sputtering have been investigated.

Nowadays the micro direct methanol fuel cell (μDMFC) has received much attention as a leading candidate for portable power of the future. This paper presents a novel modification method of the commercial proton exchange membrane Nafion®117 to produce an improved polymer electrolyte membrane for the μDMFC. The method involves using γ-ray radiation and electroless palladium deposition on a Nafion®117 membrane. Specific scopes of the γ-ray radiation dose may cause membrane crosslinking, thus reduce the membrane swelling ratio and decrease methanol crossover. The electroless palladium deposition on the γ-ray radiation modified Nafion®117 further decreases methanol crossover. The modified membrane was characterized using a scanning electron microscope (SEM), an energy dispersive x-ray spectrometer (EDX) and x-ray diffraction (XRD). Water uptake, methanol permeability and membrane conductivity tests were also carried out. By reducing the membrane swelling ratio and methanol permeation, the single μDMFC with the modified Nafion®117 membrane produced reasonable power density performance as high as 4.9 mW cm−2 under 2 M methanol solution at room temperature.

Fully vacuum-sealed triode-type active-matrix field emission display (AMFED) having an active-matrix cathode on soda-lime glass substrate was designed and fabricated. Each pixel in the active-matrix cathode has the monolithically integrated structure of an amorphous–silicon thin-film transistor (a-Si TFT) and triode-type field emitter array with conical Mo-tips just on the drain of the a-Si TFT. Experimental data indicate that the emission currents of the fabricated active-matrix cathode could be successfully controlled by the a-Si TFT gate voltage. We demonstrated that an emitting image of a moving picture from the fully vacuum-sealed 2-inch AMFEDs could be achieved by switching the low bias-voltage of the a-Si TFT gate to a value below 25 V.

Fine-pitched carbon nanotube (CNT) pixels for field emitter arrays were patterned using a lift-off process. Compared with the conventional screen-printing method, this lift-off process provides a small feature size of 195 µm×80 µm pixels in emitter arrays. The field emission properties of patterned pixels are highly dependent on surface morphology. The buried carbon nanotubes from the surface barely contribute to field emission in a low electric field range. By using a proper formulation of carbon nanotube slurry for emitters in the patterning layer, we were able to obtain carbon nanotube pixels in which most of carbon nanotubes protruded from the surface layer of patterns after a final heat treatment, to burn out the organic binders at 300°C. Their turn-on field was determined to be less than 2.2 V/µm and the current density was 3.2 mA/cm2 at 3.7 V/µm. This lift-off process has the potential for use as an inexpensive patterning method for fine-pitched emitter array on a large substrate.

A novel method is proposed for simulating free space field propagation from a source plane to a destination plane that is applicable for both small and large propagation distances. The angular spectrum method (ASM) was widely used for simulating near field propagation, but it caused a numerical error when the propagation distance was large because of aliasing due to under sampling. Band limited ASM satisfied the Nyquist condition on sampling by limiting a bandwidth of a propagation field to avoid an aliasing error so that it could extend the applicable propagation distance of the ASM. However, the band limited ASM also made an error due to the decrease of an effective sampling number in a Fourier space when the propagation distance was large. In the proposed wide range ASM, we use a non-uniform sampling in a Fourier space to keep a constant effective sampling number even though the propagation distance is large. As a result, the wide range ASM can produce simulation results with high accuracy for both far and near field propagation. For non-paraxial wave propagation, we applied the wide range ASM to a shifted destination plane as well.

We proposed a bilayered etch-stop layer (BiESL) composed of Al2O3/SiO2 for the high-mobility oxide thin-film transistor (TFT) fabricated with low-resistivity Cu electrodes. The In–Ga–Zn–O TFT employing the BiESL showed no marked degradation in its high mobility and transfer characteristics even after the conventional passivation process using SiN x film, which causes hydrogen incorporation into the active channel. Excellent barrier properties of atomic-layer-deposited Al2O3 film could provide the feasibility for the direct deposition of organic planarization film without the need for an extra passivation layer. The proposed BiESL structure was also suggested to be compatible with the simple patterning process of Cu electrodes.

The light stability of top gate indium gallium zinc oxide (IGZO) thin film transistor (TFT) has been investigated under gate bias and constant current stress to explore the possibility of active matrix display applications. While the halogen lamp irradiation onto the device under positive gate bias stress caused just -0.18 V of threshold voltage shift (ΔV th), it resulted in -15.1 V shift under negative gate bias stress. When the white light extracted from the halogen lamp of 100 µW/cm2 power illuminated the device under constant current stress, operation voltage shifted just -0.05 V for 21 h. The result shows good promise for the application of highly stable IGZO TFT to active matrix organic light emitting diodes (AMOLEDs).

Two inverter architectures are proposed to be integrated on panels for flat panel display applications using only n-type amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFTs). The proposed cross-coupled (CC) inverter uses the positive feedback effect of its CC structure to reduce the static current and increase the output voltage swing when using depletion mode n-type amorphous IGZO TFTs. The other proposed cross-coupled and bootstrapping (CCB) inverter also uses the cross-coupled structure and includes a capacitor for the bootstrapping effect to increase the operating frequency. The measured results show that the output voltage swing of the proposed CC inverter is from 0 to 14.50 V and that of the CCB inverter is from 0.15 to 14.57 V when V DD is 15 V at 20 kHz and the load capacitance is 103.0 pF. The power consumption of the CC and CCB inverters are 1.4 and 2.5 mW, respectively, which are 29.3 and 53.4% of the power consumption of the ratioed inverter.

Organic–inorganic hybrid-type nonvolatile memory thin-film transistors using an organic ferroelectric gate insulator and an oxide semiconducting active channel are a very promising solution to the memory devices having both features of low-cost and high-performance, which are embeddable into the next-generation flexible and transparent electronics. In this paper, we discuss some important issues for this proposed device, such as device structure design, process optimization and memory array integration. Promising feasible applications and remaining technology issues to solve were also discussed.

The combination of a ferroelectric polymer and an oxide semiconductor is a very promising solution to realize embeddable nonvolatile memory thin-film transistors (TFTs) for novel electronic devices. Memory TFTs with a gate structure of Al/80 nm-poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)]/4 nm Al2O3/5 nm ZnO were fabricated and their programming characteristics were investigated. Good performances in memory and transistor behaviors were successfully confirmed. When the voltage pulses of ± 15 V and 990 ms were employed, a memory on/off ratio of 4400 was obtained. It was found that the initial memory on/off ratio was closely related to the applied programming conditions such as pulse amplitude and width of programming voltage signals. Retention behaviors were also sensitively affected by the programming conditions. The initial memory on/off ratio of approximately 300 decreased to 3.4 after a lapse of 104 s when the programming voltage, pulse duration, and gate bias during the retention period were set to be ± 18 V, 500 ms, and open, respectively.

DC–DC converters integrated into a panel are proposed for mobile display applications using indium gallium zinc oxide (IGZO) thin film transistors (TFTs). The proposed positive DC–DC converter uses cross-coupled and diode-connected structures for a high output voltage and a high power efficiency, while the proposed negative DC–DC converter uses also a cross-coupled structure but with separated pumping capacitors for a negative output voltage and a high power efficiency. The simulated results show that the output voltage and power efficiency are 21.3 V and 69.5% for the positive DC–DC converter and -5.1 V and 56.1% for the negative DC–DC converter, respectively, at a supply voltage of 10 V and a load current of 250 µA. The measured results show that the output voltage and power efficiency of the proposed positive DC–DC converter are 20.8 V and 66.6%, respectively, under the same conditions as those for the simulated results.

Ensuring the sound ferroelectric behaviors of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] after various fabrication processes routinely performed for the device integration is very important for the practical nonvolatile memory applications using P(VDF-TrFE). In this work, the changes in the electrical and physical properties of the P(VDF-TrFE) thin film were investigated, assuming that some chemical treatments are involved in the fabrication processes for P(VDF-TrFE)-based memory devices. Although the treatments in the conventional developer and acids fortunately caused no critical damage to the film, it was found that the use of some resist strippers provides harsh conditions to the film. They caused the degradation in the crystallinity and surface roughness, and hence large increases in coercive field and leakage current were observed. Among the chemicals tested in this work, we proposed 1-methoxy-2-propanol as the best resist stripper. Metal–ferroelectric–metal capacitors and metal–ferroelectric–insulator–semiconductor diodes were also fabricated using the proposed patterning methods, in which no critical degradation in ferroelectric memory effects was observed when the size of capacitor decreased to 30 ×30 µm2. We conclude that these experimental studies can give us a useful solution to realizing memory arrays and related integrated circuits by exploiting P(VDF-TrFE)-based nonvolatile memory devices.

Using a double-layered gate insulator [SiO2 (100 nm)/Al2O3 (10 nm)] and a dry-etching process for the channel layer, we could obtain high mobility top-gate SnO2 and ZnO–SnO2 (ZTO) transparent thin-film transistor (TTFT). After annealing at 300 °C, for 1 h in O2 ambient, the saturated mobility of SnO2 TTFT was 17.4 cm2 s-1 V-1, and that of ZTO TTFT was 50.4 cm2 s-1 V-1. Generally, both devices operated in the enhancement mode with a drain current on-off ratio of ~106.

In this study, for the first time, Ag-doped SnO2 and Mo-doped ZnO films for transparent electrodes was explored by using a direct co-sputtering method in a non-oxidizing atmosphere, and successfully applied to source and drain electrodes of transparent thin-film transistors. Ag (~4%)-doped SnO2 films has the low resistivity of 3.8 ×10-4 Ω cm, but the relatively low transmittance of ~50%, after 300 °C for 1 h post-annealing in an O2 ambient. On the other hand, a shallow coating of Mo (2.3 nm) on Mo-doped ZnO electrode caused a hard-saturation behavior even at the low drain voltage (~2 V), which can provide effective tools to current-driving devices, for example, active matrix-organic light emitting display (AM-OLED).

Transparent conductive, Al-doped ZnO films (ZnO:Al) have been deposited by means of an atomic layer deposition method with the surface chemical compositions of ZnO (film A) and Al2O3 (film B). The sheet resistance, surface work function, and structure characteristics of ZnO:Al films have been investigated. Organic light emitting diodes (OLEDs) were fabricated on glass substrates using two different ZnO:Al anodes. The devices fabricated with them exhibited higher current and luminance with higher external quantum efficiencies below approximately 5000 cd/m2, than those fabricated with a conventional tin-doped indium oxide (ITO) anode. The external quantum efficiencies of the devices with film A, film B, and ITO were 1.86, 1.97, and 1.74%, respectively.