Fabrication of graphene oxide/montmorillonite nanocomposite flexible thin films with improved gas-barrier properties

Nanocomposites are potential substitutes for inorganic materials in fabricating flexible gas-barrier thin films. In this study, two nanocomposites are used to form a flexible gas-barrier film that shows improved flexibility and a decreased water vapor transmission rate (WVTR), thereby extending the diffusion path length for gas molecules. The nanoclay materials used for the flexible gas-barrier thin film are Na⁺-montmorillonite (MMT) and graphene oxide (GO). A flexible gas-barrier thin film was fabricated using a layer-by-layer (LBL) deposition method, exploiting electronic bonding under non-vacuum conditions. The WVTR of the film, in which each layer was laminated by LBL assembly, was analyzed by Ca-test and the oxygen transmission rate (OTR) was analyzed by MOCON. When GO and MMT are used together, they fill each other''s vacancies and form a gas-barrier film with high optical transmittance and the improved WVTR of 3.1 × 10⁻³ g per m² per day without a large increase in thickness compared to barrier films produced with GO or MMT alone. Thus, this film has potential applicability as a barrier film in flexible electronic devices.

Nanocomposites are potential substitutes for inorganic materials in fabricating flexible gas-barrier thin films.     

Efficient multi-barrier thin film encapsulation of OLED using alternating Al2O3 and polymer layers

Organic optoelectronic devices, especially for OLEDs, are extremely susceptibility to water vapor and oxygen which limit their widespread commercialization. In order to extend the shelf-lifetime of devices, thin film encapsulation is the most promising and challenging encapsulation process. In this study, dyad-style multilayer encapsulation structures based on alternating Al₂O₃ layer and parylene C have been discussed as gas diffusion barriers, in which dense and pinhole-free Al₂O₃ films were grown by atomic layer deposition (ALD) and flexible parylene C layers were deposited by chemical vapor deposition (CVD). We found the particle in ALD deposited Al₂O₃ films process is the key killer to barrier property. The thickness of Al₂O₃ films is the key factor which limit the amount of strain placed on barrier films. With three dyads of the optimal thickness of 30 nm Al₂O₃ film and 500 nm parylene C, WVTR value is lower than 10⁻⁵ g m⁻² per day. In addition, the lifetime of OLEDs with and without encapsulation was 190 h and 10 h, respectively. All the results show that this TFE structure has the effective encapsulated property and does not cause degradation of the OLED devices.

The work demonstrates the WVTR value of 3 dyads alternative 30 nm Al₂O₃ and 500 nm parylene C encapsulation structure is less than 10⁻⁵ g m⁻² per day. And this TFE technology successfully applies for OLED device encapsulation.     

Thin film encapsulation for quantum dot light-emitting diodes using a-SiNx:H/SiOxNy/hybrid SiOx barriers

A facile thin film encapsulation (TFE) method having a triple-layered structure of a-SiN_x:H/SiO_xN_y/hybrid SiO_x (ASH) on QD-LEDs was performed utilizing both reproducible plasma-enhanced chemical vapor deposition (PECVD) and simple dip-coating processes without adopting atomic layer deposition (ALD). The ASH films fabricated on a polyethylene terephthalate (PET) substrate show a high average transmittance of 88.80% in the spectral range of 400–700 nm and a water vapor transmission rate (WVTR) value of 7.3 × 10⁻⁴ g per m² per day. The measured time to reach 50% of the initial luminance (T₅₀) at initial luminance values of 500, 1000, and 2000 cd m⁻² was 711.6, 287.7, and 78.6 h, respectively, and the extrapolated T₅₀ at 100 cd m⁻² is estimated to be approximately 9804 h, which is comparable to that of the 12 112 h for glass lid-encapsulated QD-LEDs. This result demonstrates that TFE with the ASH films has the potential to overcome the conventional drawbacks of glass lid encapsulation.

The extrapolated T₅₀ at 100 cd m⁻² for the a-SiN_x:H/SiO_xN_y/hybrid SiO_x (ASH)-encapsulated QD-LEDs is estimated to be 9804 h, which is compatible to that of 12112 h for glass lid encapsulated QD-LEDs.     

Development of moisture-proof polydimethylsiloxane/aluminum oxide film and stability improvement of perovskite solar cells using the film

A method for enhancing the moisture barrier property of polydimethylsiloxane (PDMS) polymer films is proposed. This is achieved by filling the PDMS free volume with aluminum oxide (AlO_x). To deposit AlO_x inside PDMS, thermal atomic layer deposition (ALD) is employed. The PDMS/AlO_x film thus produced has a 30 nm AlO_x layer on the surface. Its water vapor transmission rate (WVTR) is 5.1 × 10⁻³ g m⁻² d⁻¹ at 45 °C and 65% relative humidity (RH). The activation energy of permeability with the PDMS/AlO_x film for moisture permeation is determined to be 35.5 kJ mol⁻¹. To investigate the moisture barrier capability of the PDMS/AlO_x layer, (FAPbI₃)_0.85(MAPbBr₃)_0.15/spiro-OMeTAD/Au perovskite solar cells are fabricated, and encapsulated by the PDMS/AlO_x film. To minimize the thermal damage to solar cells during ALD, AlO_x deposition is performed at 95 °C. The solar cells exposed to 45 °C-65% RH for 300 h demonstrate less than a 5% drop in the power-conversion efficiency.

A method for enhancing the moisture barrier property of polydimethylsiloxane (PDMS) polymer films is proposed. This is achieved by filling the PDMS free volume with aluminum oxide (AlO_x).     

Low-temperature atomic layer deposition of Al2O3/alucone nanolaminates for OLED encapsulation

Thin film encapsulation (TFE) is one of the key problems that hinders the lifetime and widespread commercialization of flexible organic light-emitting diodes (OLEDs). In this work, TFE of OLEDs with Al₂O₃/alucone laminates grown by atomic layer deposition (ALD) and molecular layer deposition (MLD) as moisture barriers were demonstrated. The barrier performances of Al₂O₃/alucone laminates with respect to the individual layer thickness and the number of dyads were investigated. It was found that alucone with suitable layer thickness could reduce the permeation to the defect zones of the inorganic layer by prolonging the permeation pathway, sequentially improving the moisture barrier performance. The water vapor transmission rate (WVTR) could be further lowered with increasing the number of dyads of the laminates, the WVTR value reached 1.44 × 10⁻⁴ g per m² per day for laminates with 5.5 dyads. These laminates were incorporated in OLEDs with pixel define layer (PDL), and were found to be able to evidently prolong the lifetime of the OLED.

Al₂O₃/alucone laminates were fabricated by atomic layer deposition (ALD) and molecular layer deposition (MLD), showing good barrier properties. These laminates were found to prolong the lifetime of organic light-emitting diodes (OLEDs) evidently.     

Atomic layer deposition of rhodium and palladium thin film using low-concentration ozone

Rhodium (Rh) and palladium (Pd) thin films have been fabricated using an atomic layer deposition (ALD) process using Rh(acac)₃ and Pd(hfac)₂ as the respective precursors and using short-pulse low-concentration ozone as the co-reactant. This method of fabrication does away with the need for combustible reactants such as hydrogen or oxygen, either as a precursor or as an annealing agent. All previous studies using only ozone could not yield metallic films, and required post treatment using hydrogen or oxygen. In this work, it was discovered that the concentration level of ozone used in the ALD process was critical in determining whether the pure metal film was formed, and whether the metal film was oxidized. By controlling the ozone concentration under a critical limit, the fabrication of these noble metal films was successful. Rhodium thin films were deposited between 200 and 220 °C, whereas palladium thin films were deposited between 180 and 220 °C. A precisely controlled low ozone concentration of 1.22 g m⁻³ was applied to prevent the oxidation of the noble metallic film, and to ensure fast growth rates of 0.42 Å per cycle for Rh, and 0.22 Å per cycle for Pd. When low-concentration ozone was applied to react with ligand, no excess ozone was available to oxidize the metal products. The surfaces of deposited films obtained the RMS roughness values of 0.30 nm for Rh and 0.13 nm for Pd films. The resistivities of 18 nm Rh and 22 nm Pd thin films were 17 μΩ cm and 63 μΩ cm.

Rh and Pd metallic thin films were fabricated by atomic layer deposition using Rh(acac)₃ and Pd(hfac)₂ precursors, and only low-concentration ozone as co-reactant.     

Effect of Fe ion implantation on the thermoelectric properties and electronic structures of CoSb3 thin films

In the present study, thin films of single-phase CoSb₃ were deposited onto Si(100) substrates via pulsed laser deposition (PLD) method using a polycrystalline target of CoSb₃. These films were implanted by 120 keV Fe-ions with three different fluences: 1 × 10¹⁵, 2.5 × 10¹⁵ and 5 × 10¹⁵ ions per cm². All films were characterised by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), Rutherford backscattering (RBS) spectrometry and X-ray absorption spectroscopy (XAS). XRD data revealed that the ion implantation decreased the crystalline nature of these films, which are recovered after the rapid thermal annealing process. The Seebeck coefficient S vary with the fluences in the temperature range of 300 K to 420 K, and is found to be highest (i.e., 254 μV K⁻¹) at 420 K for the film implanted with 1 × 10¹⁵ ions per cm². The high S and low resistivity lead to the highest power factor for the film implanted with 1 × 10¹⁵ ions per cm² (i.e., 700 μW m⁻¹ K⁻²) at 420 K. The changing of the sign of S from negative for the pristine film to positive for the Fe-implanted samples confirm that the Fe ions are electrically active and act as electron acceptors by replacing the Co atoms. XAS measurements confirm that the Fe ions occupied the Co site in the cubic frame of the skutterudite and exist in the 3+ oxidation state in this structure.

The power factor for the Fe ion-implanted samples is greater than that of the pristine sample with a value of 700 mW m⁻¹ K⁻² at 420 K for the I_1E15A sample.     

Atomic layer deposition of dielectric Y2O3 thin films from a homoleptic yttrium formamidinate precursor and water

We report the application of tris(N,N′-diisopropyl-formamidinato)yttrium(iii) [Y(DPfAMD)₃] as a promising precursor in a water-assisted thermal atomic layer deposition (ALD) process for the fabrication of high quality Y₂O₃ thin films in a wide temperature range of 150 °C to 325 °C. This precursor exhibits distinct advantages such as improved chemical and thermal stability over the existing Y₂O₃ ALD precursors including the homoleptic and closely related yttrium tris-amidinate [Y(DPAMD)₃] and tris-guanidinate [Y(DPDMG)₃], leading to excellent thin film characteristics. Smooth, homogeneous, and polycrystalline (fcc) Y₂O₃ thin films were deposited at 300 °C with a growth rate of 1.36 Å per cycle. At this temperature, contamination levels of C and N were under the detectable limits of nuclear reaction analysis (NRA), while X-ray photoelectron spectroscopy (XPS) measurements confirmed the high purity and stoichiometry of the thin films. From the electrical characterization of metal–insulator–semiconductor (MIS) devices, a permittivity of 13.9 at 1 MHz could be obtained, while the electric breakdown field is in the range of 4.2 and 6.1 MV cm⁻¹. Furthermore, an interface trap density of 1.25 × 10¹¹ cm⁻² and low leakage current density around 10⁻⁷ A cm⁻² at 2 MV cm⁻¹ are determined, which satisfies the requirements of gate oxides for complementary metal-oxide-semiconductor (CMOS) based applications.

In this work, the application of tris(N,N′-diisopropyl-formamidinato)yttrium(iii) [Y(DPfAMD)₃] as a precursor in a water-assisted thermal atomic layer deposition (ALD) process for the fabrication of device quality Y₂O₃ thin films is demonstrated.     

Improved interface passivation by optimizing a polysilicon film under different hydrogen dilution in N-type TOPCon silicon solar cells

The passivation properties of a polysilicon (poly-Si) thin film are the key for improving the photovoltaic performance of TOPCon silicon solar cells. In this work, we investigate the influence of the poly-Si microstructure on the interface passivation and photovoltaic performance in TOPCon solar cells. The poly-Si thin films are prepared from phosphorus-doped hydrogenated microcrystalline silicon (μc-Si:H) layers deposited via plasma enhanced chemical vapor deposition (PECVD) under different hydrogen dilutions and recrystallized by high temperature post-deposition annealing. The results revealed that, as the hydrogen dilution ratio increases, the microstructure of the pre-deposited films transforms from an amorphous phase to a microcrystalline phase. Meanwhile, the effective minority carrier lifetime of the symmetrically passivated contact structure shows a maximum value of 1.75 ms, implying that the efficient passivation at the c-Si interface is obtained which is mainly attributed to the joint enhancement of the improved field effect passivation from poly-Si films and the reduced defects density on the silicon surface. Consequently, the devices displayed excellent rectification behavior with a rectifying ratio of 3 × 10⁵, ascribed to the enhanced carrier transport with the high quality poly-Si film pre-deposited in the initial region of structural transition. Correspondingly, the obvious improvement of TOPCon solar cell performance was achieved, exhibiting an optimized conversion efficiency of 17.91%. The results provide an optimal design scheme for enhancing the photovoltaic properties of the TOPCon silicon solar cells.

The efficient passivation at the c-Si interface, and thus the enhanced photovoltaic performance in TOPCon silicon solar cells are obtained by appropriate hydrogen dilution of poly-Si film.     

Dual-gate low-voltage transparent electric-double-layer thin-film transistors with a top gate for threshold voltage modulation

Dual gate (DG) low-voltage transparent electric-double-layer (EDL) thin-film transistors (TFTs) with microporous-SiO₂ for both top and bottom dielectrics have been fabricated, both dielectrics were deposited by plasma-enhanced chemical vapor deposition (PECVD) at room temperature. The threshold voltage of such devices can be modulated from −0.13 to 0.5 V by the top gate (TG), which switches the device from depletion-mode to enhancement-mode. High performance with a current on/off ratio (∼2.1 × 10⁶), subthreshold swing (76 mV per decade), operating voltage (1.0 V), and field-effect mobility (∼2.6 cm² V⁻¹ s⁻¹) are obtained. Such DG TFTs are promising for ion-sensitive field-effect transistors sensor applications with low-power consumptions.

Dual gate (DG) low-voltage transparent electric-double-layer (EDL) thin-film transistors (TFTs) with microporous-SiO₂ for both top and bottom dielectrics have been fabricated, both dielectrics were deposited by plasma-enhanced chemical vapor deposition (PECVD).     

Effect of silane functionalized graphene prepared by a supercritical carbon dioxide process on the barrier properties of polyethylene terephthalate composite films

In this work, a simple and eco-friendly strategy to modify graphene nanoplatelets (GNs) with different silane coupling agents using a supercritical carbon dioxide (Sc-CO₂) process has been presented, and effect of the modified GNs on the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of GN/PET composite films was studied. FT-IR, SEM, EDX and TG results indicated that Sc-CO₂ process was an effective strategy to modify GNs with silane coupling agents. Addition of the modified GNs into PET matrix could greatly decrease the OTR and WVTR values of the GNs/PET composite films, and the WVTR of GNs560/PET composite film and OTR of GNs550/PET composite film were respectively decreased about 90.08% and 58.04%, as compared to those of GNs/PET composite film. It is found that the gas barrier property of GN/PET composites was attributed to not only the tortuous path effect caused by GNs themselves and the interfacial interaction, but also the affinity of binding bonds between GNs and the polymer to the gas molecules. It is believed that this work provided a strategy to design and prepare CN/polymer composites with high barrier properties.

Adding silane modified GNs prepared by a Sc-CO₂ process into a PET matrix could greatly enhance the barrier properties of the GNs/PET composites.The barrier performance of GNs/PET composites was greatly enhanced by modifying GNs with silane coupling agents via Sc-CO₂ process.     

The role of cobalt doping in tuning the band gap,surface morphology and third-order optical nonlinearities of ZnO nanostructures for NLO device applications

The work presented here reported the effect of doping cobalt (Co) in ZnO thin films. The thin films were prepared using the spray pyrolysis technique with 0, 1, 5 and 10 wt% cobalt doping concentrations to study the morphological, optical and third-order nonlinear optical (NLO) properties. X-ray diffraction revealed the crystalline nature of the prepared thin films, and the crystallite size was found to increase with the concentration of doped Co. The morphology and surface topography of the films were largely influenced by doping, as indicated by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). With an increase in Co-doping concentration, the direct optical energy band-gap value increased from 3.21 eV to 3.45 eV for pure to 10 at% of Co concentrations respectively. To study the NLO properties of the prepared thin films, the Z-scan technique was adopted; it was observed that with an increase in the doping concentration from 0 to 10 wt%, the nonlinear absorption coefficient (β) was enhanced from 4.68 × 10⁻³ to 9.92 × 10⁻³ (cm W⁻¹), the nonlinear refractive index (n₂) increased from 1.37 × 10⁻⁸ to 2.90 × 10⁻⁸ (cm² W⁻¹), and the third-order NLO susceptibility (χ⁽³⁾) values also increased from 0.79 × 10⁻⁶ to 1.88 × 10⁻⁶ (esu). At the experimental wavelength, the optical limiting (OL) features of the prepared films were explored, and the limiting thresholds were calculated. The encouraging results of the NLO studies suggest that the Co : ZnO thin film is a capable and promising material for nonlinear optical devices and optical power limiting applications.

The work presented here reported the effect of doping cobalt (Co) in ZnO thin films.     

Annealing temperature effects on photoelectrochemical performance of bismuth vanadate thin film photoelectrodes

The effects of annealing treatment between 400 °C and 540 °C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO₄) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO₄ thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO₄ thin film prepared at a higher annealing temperature (500–540 °C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm⁻² to 1.27 mA cm⁻² and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm⁻² for the samples prepared from 400 °C to 540 °C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO₄ samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO₄ samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (C_dl). C_dl was 0.0074 mF cm⁻² at 400 °C and it decreased to 0.0006 mF cm⁻² at 540 °C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk (η_bulk) and on the surface (η_surface) of the BiVO₄ thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.

The effects of annealing treatment on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO₄) thin films are investigated in this work.     

Hybrid films with excellent oxygen and water vapor barrier properties as efficient anticorrosive coatings

Gas and moisture barrier materials are of crucial importance in various application fields, including food/drug packaging and encapsulation of electronic devices. Herein, a dual-barrier film to gas and water vapor was fabricated by a facile and cost-effective spin-coating of amphiphilic surfactant (Tween 80) modified LDH nanoplatelets (denoted as LDH-80) and polydimethylsiloxane (PDMS). The resultant (LDH-80/PDMS)₁₅ film exhibits low O₂ and H₂O transmission rates with ∼0.701 and ∼0.049 cm³ m⁻² d⁻¹ atm⁻¹, respectively, smaller than those for most of the reported barrier materials. The remarkable barrier properties are ascribed to the prolonged diffusion length for gas permeation and improved inorganic–organic interfacial compatibility between LDH-80 and PDMS. Taking advantage of this unique dual-barrier property, an aluminum foil substrate coated with (LDH-80/PDMS)_n film displays an excellent anti-corrosion effect due to the inhibition of oxygen-consuming corrosion, which enables the (LDH-80/PDMS)_n films to be promising candidates in metal surface protection.

A hydrophobic film is fabricated by spin-coating of Tween 80 modified layered double hydroxide and polydimethylsiloxane alternately, which displays enhanced oxygen/water vapor barrier properties and anti-corrosion behavior toward metal substrates.     

The growth of methylammonium lead iodide perovskites by close space vapor transport

Vapor deposition processes have shown promise for high-quality perovskite solar cells with potential pathways for scale-up to large area manufacturing. Here, we present a sequential close space vapor transport process to deposit CH₃NH₃PbI₃ (MAPI) perovskite thin films by depositing a layer of PbI₂ then reacting it with CH₃NH₃I (MAI) vapor. We find that, at T = 100 °C and pressure = 9 torr, a ∼225 nm-thick PbI₂ film requires ≥125 minutes in MAI vapor to form a fully-reacted MAPI film. Raising the temperature to 160 °C increases the rate of reaction, such that MAPI forms within 15 minutes, but with reduced surface coverage. The reaction kinetics can be approximated as roughly first-order with respect to PbI₂, though there is evidence for a more complicated functional relation. Perovskite films reacted at 100 °C for 150 minutes were fabricated into solar cells with an SLG/ITO/CdS/MAPI/Spiro-OMeTAD/Au structure, and a device efficiency of 12.1% was achieved. These results validate the close space vapor transport process and serve as an advance toward scaled-up, vapor-phase perovskite manufacturing through continuous vapor transport deposition.

This is the first demonstration of an all-vapor close space vapor transport process to deposit methylammonium lead iodide perovskites.     

Anomalous kinetic roughening in growth of MoS2 films under pulsed laser deposition

Growth dynamics of thin films expressed by scaling theory is a useful tool to quantify the statistical properties of the surface morphology of the thin films. To date, the growth mechanism for 2D van der Waals materials has been rarely investigated. In this work, an experimental investigation was carried out to identify the scaling behavior as well as the growth mechanism of 2D MoS₂ thin films, grown on glass substrates by pulsed laser deposition for different deposition time durations, using atomic force microscopy images. The growth of MoS₂ films evolved from layer-by-layer to layer plus island with the increase in deposition time from 20 s to 15 min. The film surface exhibited anisotropic growth dynamics in the vertical and lateral directions where RMS roughness varied with deposition time as w ∼ t^β with the growth exponent β = 0.85 ± 0.11, while the lateral correlation length ξ was ξ = t^1/z with 1/z = 0.49 ± 0.09. The films showed a local roughness exponent α_loc = 0.89 ± 0.01, global roughness exponent α = 1.72 ± 0.14 and spectral roughness exponent α_s = 0.85 ± 0.03, suggesting that the growth of MoS₂ thin films followed intrinsic anomalous scaling behavior (α_s < 1, α_loc = α_s ≠ α). Shadowing owing to conical incoming particle flux distribution towards the substrate during deposition has been attributed to the anomalous growth mode. The optical properties of the films, extracted from ellipsometric analysis, were also correlated with RMS roughness and cluster size variation which unveiled the important role played by surface roughness and film density.

MoS₂ films grown on glass by pulsed laser deposition technique evolve from bilayer to bulk-like structure with time following intrinsic anomalous scaling behaviour caused by shadowing effect during deposition.     

Difference in structural and chemical properties of sol–gel spin coated Al doped TiO2, Y doped TiO2 and Gd doped TiO2 based on trivalent dopants

In this research, pure titanium dioxide (TiO₂) and doped TiO₂ thin film layers were prepared using the spin coating method of titanium(iv) butoxide on a glass substrate from the sol–gel method and annealed at 500 °C. The effects on the structural and chemical properties of these thin films were then investigated. The metal doped TiO₂ thin film which exists as trivalent electrons consists of aluminium (Al), yttrium (Y) and gadolinium (Gd). The anatase phase of the thin films was observed and it was found that the crystal size became smaller when the concentration of thin film increased. The grain size was found to be 0.487 to 13.925 nm. The types of surface morphologies of the thin films were nanoporous, with a little agglomeration and smaller nanoparticles corresponding to Al doped TiO₂, Y doped TiO₂ and Gd doped TiO₂, respectively. The trivalent doping concentration of the thin films increased with a rising of thickness of the thin film. This can contribute to the defects that give advantages to the thin film when the mobility of the hole carriers is high and the electrons of Ti can move easily. Thus, Ti³⁺ existed as a defect state in the metal doped TiO₂ thin film based on lattice distortion with a faster growth thin film that encouraged the formation of a higher level of oxygen vacancy defects.

Ti³⁺ state in metal doped TiO₂ based on lattice distortion that encouraged the formation of oxygen vacancy defects.     

Potential solution-induced HfAlO dielectrics and their applications in low-voltage-operating transistors and high-gain inverters

Recently, much attention has been paid to the investigation of solution-driven oxides for application in thin film transistors (TFTs). In current study, a fully solution-based method, using 2-methoxyethanol as solvent, has been adopted to prepare InZnO thin films and HfAlO_x gate dielectrics. Amorphous HfAlO_x thin films annealed at 600 °C have shown a high transparency (>85%), low leakage current density (6.9 × 10⁻⁹ A cm⁻² at 2 MV cm⁻¹), and smooth surface. To verify the potential applications of HfAlO_x gate dielectrics in oxide-based TFTs, fully solution-induced InZnO/HfAlO_x TFTs have been integrated. Excellent electrical performance for InZnO/HfAlO_x TFTs annealed at 450 °C has been observed, including a low operating voltage of 3 V, a saturated mobility of 5.17 cm² V⁻¹ s⁻¹, a high I_on/I_off of ∼10⁶, a small subthreshold swing of 87 mV per decade, and a threshold voltage shift of 0.52 V under positive bias stress (PBS) for 7200 s, respectively. In addition, time dependent threshold voltage shift under PBS could be described by a stretched-exponential model, which can be due to charge trapping in the semiconductor/dielectric interface. Finally, to explore the possible application in logic operation, a resistor-loaded inverter based on InZnO/HfAlO_x TFTs has been built and excellent swing characteristic and well dynamic behavior have been obtained. Therefore, it can be concluded that fully solution-driven InZnO/HfAlO_x TFTs have demonstrated potential application in nontoxic, eco-friendly and low-power consumption oxide-based flexible electronics.

Recently, much attention has been paid to the investigation of solution-driven oxides for application in thin film transistors (TFTs).     

Roll-to-roll processed,highly conductive,and flexible aluminum (Al) electrodes based on Al precursor inks

In this study, a roll-to-roll (R2R) process for the large-scale fabrication of aluminum thin films on flexible polyimide (PI) films is proposed. The R2R machine for Al-film coating assembled in the current work uses a previously reported Al etherate-based precursor ink as the source. After the PI substrate is exposed to a diluted catalyst, the Al precursor ink is coated directly on to the substrate by a slit-die coating method. To optimize the injection of the Al precursor ink, a low-flow limit was established. At a film speed of 5 cm s⁻¹, the width of the fabricated Al film was 130 mm. Such Al-coated films exhibit many advantageous features, including 5.87 × 10⁶ S m⁻¹ of high electrical conductivity at 60.9 nm film thickness and high durability with good adhesion. There was only a minor change in the resistance of the film when it was heated at 100 °C in an oven for 10 days or when it was exposed to H₂O or ethyl alcohol. Flexibility and tape testing was also conducted and the film showed robustness in both cases. Touch panels (7 cm × 9 cm) were fabricated using the fabricated Al-coated film as one side of the panel; the panel showed enough sensitivity to write recognizable letters on the computer. This indicates that the fabricated Al films can be applied in actual electronic devices without further complicated processing.

R2R machine is designed for the Al thin film coating to the flexible substrate, and the substrate can be applied to the flexible electronics.     

Ethylene-bridged polysilsesquioxane/hollow silica particle hybrid film for thermal insulation material

Ethylene-bridged polysilsesquioxane (EBPSQ) was prepared by the sol–gel reaction of bis(triethoxysilyl)ethane. The whitish slurry was prepared by mixing EBPSQ and hollow silica particles (HSPs) with a median diameter of 18–65 μm at 80 °C, and it formed a hybrid film by heating at 80 and 120 °C for 1 h at each temperature, then at 200 °C for 20 min. The surface temperatures of EBPSQ films containing 10 wt% and 20 wt% of HSPs (90.2 °C–90.5 °C) were lower than those of EBPSQ films (93.6 °C), when the films on the duralumin plate were heated at 100 °C for 10 min from the bottom of the duralumin plate. The thermal conductivity/heat flux (k/q) obtained from the temperature difference between the surface temperature and bottom temperature of the films and the film thickness also decreased with adding the HSPs. EBPSQ film without HSPs exhibited T⁵_d of 258 °C and T¹⁰_d of 275 °C. However, EBPSQ film containing 20 wt% of HSPs exhibited high thermal stability, and T⁵_d and T¹⁰_d were 299 °C and 315 °C, respectively. Interestingly, T⁵_d and T¹⁰_d of the hybrid films increased with an increase in the number of HSPs. Overall, it was shown that HSPs could improve the thermal insulation properties and thermal stability.

Ethylene-bridged polysilsesquioxane/hollow silica particle hybrid films were prepared by the sol–gel reaction. The hybrid film containing hollow silica particles exhibited good thermal insulation properties and thermal stability.