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It is usually difficult to realize high mobility together with a low threshold voltage and good stability for amorphous oxide thin-film transistors (TFTs). In addition, a low fabrication temperature is preferred in terms of enhancing compatibility with the back end of line of the device. In this study, α-IGZO TFTs were prepared by high-power impulse magnetron sputtering (HiPIMS) at room temperature. The channel was prepared under a two-step deposition pressure process to modulate its electrical properties. X-ray photoelectron spectra revealed that the front-channel has a lower Ga content and a higher oxygen vacancy concentration than the back-channel. This process has the advantage of balancing high mobility and a low threshold voltage of the TFT when compared with a conventional homogeneous channel. It also has a simpler fabrication process than that of a dual active layer comprising heterogeneous materials. The HiPIMS process has the advantage of being a low temperature process for oxide TFTs.

The concept of nanosatellite technology becomes a viable platform for earth and space observation research to minimize cost and build time for the payload. The communication approach is the essential fundamental attribute of a satellite, of which the antenna is a crucial component for forming a communication link between the nanosatellite and the earth. The nanosatellite antenna must comply with some special requirements like compact size, lightweight, and high gain with a space-compatible structure. This paper proposes a compact metamaterial-based Ku-band antenna with circular polarization for the nanosatellite communication system. The designed antenna obtained an impedance bandwidth of 2.275 GHz with a realized gain of 6.74 dBi and 3 dB axial beamwidth of 165° at 12.10 GHz. The overall antenna size of the designed is 0.51λ × 0.51λ × 0.17λ, which is fabricated on Rogers 5880 substrate material. The antenna results performance has been examined with a 1 U nanosatellite structure and found suitable to integrate with metallic and nonmetallic surfaces of any miniature nanosatellite structure.

Hafnium oxide (HfO 2 ) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO 2 films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO 2 films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD-HfO 2 films were obtained by capacitance-voltage and current-voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO 2 films. The crystallinity of HfO 2 films has a major effect on electrical properties of the films. HfO 2 thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

The promising functional tin oxide (SnOx) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnOx can be described as common n-type SnO2 and p-type Sn3O4. In this study, the functional SnOx films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO2 and oxygen-deficient Sn3O4 phases coexisting in PEALD SnOx films were found. The PEALD SnOx films are composed of intrinsic oxygen vacancies with O-Sn4+ bonds and then transformed into a crystalline SnO2 phase with increased substrate temperature, revealing a direct 3.5−4.0 eV band gap and 1.9−2.1 refractive index. Lower (<150 °C) and higher (>300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnOx films near an estimated 1.74 suggests the highest mobility of 12.89 cm2 V−1 s−1 at 300 °C.

Indium tin oxide (ITO) thin films were prepared by high power impulse magnetron sputtering (HiPIMS) and annealed in hydrogen-containing forming gas to reduce the film resistivity. The film resistivity reduces by nearly an order of magnitude from 5.6 × 10 -3 Ω·cm for the as-deposited film to the lowest value of 6.7 × 10 -4 Ω·cm after annealed at 700 °C for 40 min. The role of hydrogen (H) in changing the film properties was explored and discussed in a large temperature range (300-800 °C). When annealed at a low temperature of 300-500 °C, the incorporated H atoms occupied the oxygen sites (H o ), acting as shallow donors that contribute to the increase of carrier concentration, leading to the decrease of film resistivity. When annealed at an intermediate temperature of 500-700 °C, the H o defects are thermally unstable and decay upon annealing, leading to the reduction of carrier concentration. However, the film resistivity keeps decreasing due to the increase in carrier mobility. Meanwhile, some locally distributed metallic clusters formed due to the reduction effect of H 2 . When annealed at a high temperature of 700-800 °C, the metal oxide film is severely reduced and transforms to gaseous metal hydride, leading to the dramatic reduction of film thickness and carrier mobility at 750 °C and vanish of the film at 800 °C.

Amorphous Gallium oxide (Ga 2 O 3 ) thin films were grown by plasma-enhanced atomic layer deposition using O 2 plasma as reactant and trimethylgallium as a gallium source. The growth rate of the Ga 2 O 3 films was about 0.6 Å/cycle and was acquired at a temperature ranging from 80 to 250 °C. The investigation of transmittance and the adsorption edge of Ga 2 O 3 films prepared on sapphire substrates showed that the band gap energy gradually decreases from 5.04 to 4.76 eV with the increasing temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that all the Ga 2 O 3 thin films showed a good stoichiometric ratio, and the atomic ratio of Ga/O was close to 0.7. According to XPS analysis, the proportion of Ga 3+ and lattice oxygen increases with the increase in temperature resulting in denser films. By analyzing the film density from X-ray reflectivity and by a refractive index curve, it was found that the higher temperature, the denser the film. Atomic force microscopic analysis showed that the surface roughness values increased from 0.091 to 0.187 nm with the increasing substrate temperature. X-ray diffraction and transmission electron microscopy investigation showed that Ga 2 O 3 films grown at temperatures from 80 to 200 °C were amorphous, and the Ga 2 O 3 film grown at 250 °C was slightly crystalline with some nanocrystalline structures.

We demonstrate the growth of ultra-thin (~5 nm) indium ytterbium oxide (In-Yb-O) thin film using a simple vacuum-free aqueous solution approach for the first time. The influences of Yb addition on the microstructural, chemical, optical, and electrical properties of In 2 O 3 are well investigated. The analyses indicate that Yb dopant could suppress oxygen vacancy defects effectively owing to the lower standard electrode potential, lower electronegativity, and stronger metal-oxide bond strength than that of In. The optimized In-Yb-O thin-film transistors (TFTs) exhibit excellent electrical performance (mobility of 8 cm 2 /Vs and on/off ratio of ~10 8 ) and enhanced stability. The triumph of In-Yb-O TFTs is owing to the high quality In 2 O 3 matrix, the remarkable suppressor of Yb, and the nanometer-thin and atomically smooth nature (RMS: ~0.26 nm) of channel layer. Therefore, the eco-friendly water-induced ultra-thin In-Yb-O channel provides an excellent opportunity for future large-scale and cost-effective electronic applications.

Thin-film transistors (TFTs) made of solution-processable transparent metal oxide semiconductors show great potential for use in emerging large-scale optoelectronics. However, current solution-processed metal oxide TFTs still suffer from relatively poor device performance, hindering their further advancement. In this work, we create a novel ultrathin crystalline indium-boron-oxide (In-B-O) channel layer for high-performance TFTs. We show that high-quality ultrathin (~10 nm) crystalline In-B-O with an atomically smooth nature (RMS: ~0.15 nm) could be grown from an aqueous solution via facile one-step spin-coating. The impacts of B doping on the physical, chemical and electrical properties of the In 2 O 3 film are systematically investigated. The results show that B has large metal-oxide bond dissociation energy and high Lewis acid strength, which can suppress oxygen vacancy-/hydroxyl-related defects and alleviate dopant-induced carrier scattering, resulting in electrical performance improvement. The optimized In-B-O (10% B) TFTs based on SiO 2 /Si substrate demonstrate a mobility of ~8 cm 2 /(V s), an on/off current ratio of ~10 6 and a subthreshold swing of 0.86 V/dec. Furthermore, by introducing the water-processed high-K ZrO 2 dielectric, the fully aqueous solution-grown In-B-O/ZrO 2 TFTs exhibit excellent device performance, with a mobility of ~11 cm 2 /(V s), an on/off current of ~10 5 , a subthreshold swing of 0.19 V/dec, a low operating voltage of 5 V and superior bias stress stability. Our research opens up new avenues for low-cost, large-area green oxide electronic devices with superior performance.

Tantalum (Ta)-doped titanium oxide (TiO 2 ) thin films are grown by plasma enhanced atomic layer deposition (PEALD), and used as both an electron transport layer and hole blocking compact layer of perovskite solar cells. The metal precursors of tantalum ethoxide and titanium isopropoxide are simultaneously injected into the deposition chamber. The Ta content is controlled by the temperature of the metal precursors. The experimental results show that the Ta incorporation introduces oxygen vacancies defects, accompanied by the reduced crystallinity and optical band gap. The PEALD Ta-doped films show a resistivity three orders of magnitude lower than undoped TiO 2 , even at a low Ta content (0.8-0.95 at.%). The ultraviolet photoelectron spectroscopy spectra reveal that Ta incorporation leads to a down shift of valance band and conduction positions, and this is helpful for the applications involving band alignment engineering. Finally, the perovskite solar cell with Ta-doped TiO 2 electron transport layer demonstrates significantly improved fill factor and conversion efficiency as compared to that with the undoped TiO 2 layer.

In this study, silicon oxide (SiO 2 ) films were deposited by remote plasma atomic layer deposition with Bis(diethylamino)silane (BDEAS) and an oxygen/argon mixture as the precursors. Oxygen plasma powers play a key role in the quality of SiO 2 films. Post-annealing was performed in the air at different temperatures for 1 h. The effects of oxygen plasma powers from 1000 W to 3000 W on the properties of the SiO 2 thin films were investigated. The experimental results demonstrated that the SiO 2 thin film growth per cycle was greatly affected by the O 2 plasma power. Atomic force microscope (AFM) and conductive AFM tests show that the surface of the SiO 2 thin films, with different O 2 plasma powers, is relatively smooth and the films all present favorable insulation properties. The water contact angle (WCA) of the SiO 2 thin film deposited at the power of 1500 W is higher than that of other WCAs of SiO 2 films deposited at other plasma powers, indicating that it is less hydrophilic. This phenomenon is more likely to be associated with a smaller bonding energy, which is consistent with the result obtained by Fourier transformation infrared spectroscopy. In addition, the influence of post-annealing temperature on the quality of the SiO 2 thin films was also investigated. As the annealing temperature increases, the SiO 2 thin film becomes denser, leading to a higher refractive index and a lower etch rate.

Indium oxide (In 2 O 3 ) film has excellent optical and electrical properties, which makes it useful for a multitude of applications. The preparation of In 2 O 3 film via atomic layer deposition (ALD) method remains an issue as most of the available In-precursors are inactive and thermally unstable. In this work, In 2 O 3 film was prepared by ALD using a remote O 2 plasma as oxidant, which provides highly reactive oxygen radicals, and hence significantly enhancing the film growth. The substrate temperature that determines the adsorption state on the substrate and reaction energy of the precursor was investigated. At low substrate temperature (100-150 °C), the ratio of chemically adsorbed precursors is low, leading to a low growth rate and amorphous structure of the films. An amorphous-to-crystalline transition was observed at 150-200 °C. An ALD window with self-limiting reaction and a reasonable film growth rate was observed in the intermediate temperature range of 225-275 °C. At high substrate temperature (300-350 °C), the film growth rate further increases due to the decomposition of the precursors. The resulting film exhibits a rough surface which consists of coarse grains and obvious grain boundaries. The growth mode and properties of the In 2 O 3 films prepared by plasma-enhanced ALD can be efficiently tuned by varying the substrate temperature.

In this study, spatial atomic layer deposition (sALD) is employed to prepare titanium dioxide (TiO 2 ) thin films by using titanium tetraisopropoxide and water as metal and water precursors, respectively. The post-annealing temperature is varied to investigate its effect on the properties of the TiO 2 films. The experimental results show that the sALD TiO 2 has a similar deposition rate per cycle to other ALD processes using oxygen plasma or ozone oxidant, implying that the growth is limited by titanium tetraisopropoxide steric hindrance. The structure of the as-deposited sALD TiO 2 films is amorphous and changes to polycrystalline anatase at the annealing temperature of 450 °C. All the sALD TiO 2 films have a low absorption coefficient at the level of 10 -3 cm -1 at wavelengths greater than 500 nm. The annealing temperatures of 550 °C are expected to have a high compactness, evaluated by the refractive index and x-ray photoelectron spectrometer measurements. Finally, the 550 °C-annealed sALD TiO 2 film with a thickness of ~8 nm is applied to perovskite solar cells as a compact electron transport layer. The significantly enhanced open-circuit voltage and conversion efficiency demonstrate the great potential of the sALD TiO 2 compact layer in perovskite solar cell applications.

Zinc oxide (ZnO) attracts much attention owing to its remarkable electrical and optical properties for applications in optoelectronics. In this study, ZnO thin films were prepared by spatial atomic layer deposition with diethylzinc and water as precursors. The substrate temperature was varied from 55 to 135 °C to investigate the effects on the optical, electrical, and structural properties of the films. All ZnO samples exhibit an average transmittance in visible and near-infrared light range exceeding 80% and a resistivity in the range of (3.2-9.0) × 10 -3 Ω·cm when deposited on a borosilicate glass with a refractive index of ≈1.52. The transmittance, band gap, refractive index, and extinction coefficient are rarely affected, while the resistivity only slightly decreases with increasing temperature. This technique provides a wide process window for depositing ZnO thin films. The results revealed that the films deposited at a substrate of 55 °C were highly crystalline with a preferential (1 0 0) orientation. In addition, the grains grow larger as the substrate temperature increases. The electrical properties and reliability of ZnO/PET samples are also studied in this paper., Competing Interests: The authors declare no conflict of interest.

In this study, needle-like and pyramidal hybrid black silicon structures were prepared by performing metal-assisted chemical etching (MACE) on alkaline-etched silicon wafers. Effects of the MACE time on properties of the black silicon wafers were investigated. The experimental results showed that a minimal reflectance of 4.6% can be achieved at the MACE time of 9 min. The height of the nanostructures is below 500 nm, unlike the height of micrometers needed to reach the same level of reflectance for the black silicon on planar wafers. A stacked layer of silicon nitride (SiN x ) grown by inductively-coupled plasma chemical vapor deposition (ICPCVD) and aluminum oxide (Al 2 O 3 ) by spatial atomic layer deposition was deposited on the black silicon wafers for passivation and antireflection. The 3 min MACE etched black silicon wafer with a nanostructure height of less than 300 nm passivated by the SiN x /Al 2 O 3 layer showed a low surface recombination rate of 43.6 cm/s. Further optimizing the thickness of ICPCVD-SiN x layer led to a reflectance of 1.4%. The hybrid black silicon with a small nanostructure size, low reflectance, and low surface recombination rate demonstrates great potential for applications in optoelectronic devices.

In this study, inorganic silicon oxide (SiO x )/organic silicon (SiC x H y ) stacked layers were deposited by a radio frequency inductively coupled plasma chemical vapor deposition system as a gas diffusion barrier for organic light-emitting diodes (OLEDs). The effects of thicknesses of SiO x and SiC x H y layers on the water vapor transmission rate (WVTR) and residual stress were investigated to evaluate the encapsulation capability. The experimental results showed that the lowest WVTR and residual stress were obtained when the thicknesses of SiO x and SiC x H y were 300 and 30 nm, respectively. Finally, different numbers of stacked pairs of SiO x /SiC x H y were applied to OLED encapsulation. The OLED encapsulated with the six-pair SiO x /SiC x H y exhibited a low turn-on voltage and low series resistance, and device lifetime increased from 7 h to more than 2000 h.