Permeation barrier properties of an Al2O3/ZrO2 multilayer deposited by remote plasma atomic layer deposition

We report the permeation barrier properties of Al₂O₃/ZrO₂ multi-layers deposited by remote plasma atomic layer deposition. Electrical Ca degradation tests were performed to derive the water vapor transmission rate (WVTR) of Al₂O₃, ZrO₂ and Al₂O₃/ZrO₂ multi-layers at 50 °C and 50% relative humidity (RH). Al₂O₃/ZrO₂ multi-layers exhibit better barrier properties than Al₂O₃ and ZrO₂ layers, and when more individual layers were deposited in the same total thickness, the WVTR value was reduced further, indicating a better barrier property. The WVTR of the Al₂O₃ and ZrO₂ layers were 9.5 × 10⁻³ and 1.6 × 10⁻² g/m² day, respectively, but when deposited alternatively with 1 cycle of each layer, the WVTR decreased to 9.9 × 10⁻⁴ g/m² day. X-ray diffraction results indicated that ZrO₂ has a monoclinic structure but Al₂O₃ and Al₂O₃/ZrO₂ multi-layers show an amorphous structure. Cross sectional Al₂O₃/ZrO₂ multi-layer structures and the formation of a ZrAl_xO_y phase are observed by transmission electron microscopy (TEM). X-ray photoelectron spectrometry (XPS) results indicate that Al₂O₃ and ZrO₂ contain 33.7% and 37.8%, respectively, Al–OH and Zr–OH bonding. However, the ZrAl_xO_y phase contained 30.5% Al–OH and Zr–OH bonding. The results of transmittance measurement indicate that overall, Al₂O₃, ZrO₂ and Al₂O₃/ZrO₂ multi-layers show high transmittance greater than 80% in the visible region.     

The effect of post-metal annealing on the electrical performance and stability of two-step-annealed solution-processed In2O3 thin film transistors

In this work, solution-processed indium oxide (In₂O₃) thin film transistors (TFTs) were fabricated by a two-step annealing method. The influence of post-metal annealing (PMA) temperatures on the electrical performance and stability is studied. With the increase of PMA temperatures, the on-state current and off-state current (I_on/I_off) ratio is improved and the sub-threshold swing (SS) decreased. Moreover, the stability of In₂O₃ TFTs is also improved. In all, In₂O₃ TFT with post-metal annealing temperature of 350°С exhibits the best performance (a threshold voltage of 4.75 V, a mobility of 13.8 cm²/V, an I_on/I_off ratio of 1.8 × 10⁶, and a SS of 0.76 V/decade). Meanwhile, the stability under temperature stress (TBS) and positive bias stress (PBS) also show a good improvement. It shows that the PMA treatment can effectively suppress the interface trap and bulk trap and result in an obviously improvement of the In₂O₃ TFTs performance.     

Improving the dielectric constant of Al2O3 by cerium substitution for high-k MIM applications

Process compatible high-k dielectric thin films are one of the key solutions to develop high performance metal–insulator–metal (MIM) structures for future microelectronic devices. Engineered cerium–aluminate (Ce_xAl_2–xO₃) thin films were deposited on titanium nitride metal electrodes by electron-beam co-evaporation of ceria and alumina in a molecular beam deposition chamber. X-ray photoelectron spectroscopy clearly reveals that Ce cations can be stabilized in the 3+ valence state in Ce_xAl_2–xO₃ up to x = 0.7 by accommodation in the alumina host matrix. Higher Ce content was observed to result in cerium dioxide segregation in cerium aluminate matrix, probably due to the chemical tendency of Ce cations to exist rather in the 4+ than in the 3+ state. Electrical characterization of the X-ray amorphous Ce_0.7Al_1.3O₃ films reveals a dielectric constant value of about 11 and leakage current lower than 10^?4 A/cm². No parasitic low-k interface formation between the high-k Ce_0.7Al_1.3O₃ film and the TiN metal electrode is detected.     

Forming process of unipolar resistance switching in Ta2O5−x thin films

We investigated the film-thickness and ambient oxygen-pressure dependence of the electric field, E_F, required to initiate unipolar resistance switching (URS) in Ta₂O_5?x thin films. We measured the dependence of E_F by applying a triangular-waveform voltage signal to the film over a wide sweep-rate range (v = 20 mV s^?1 to 5 MV s^?1). Our results showed that the URS-E_F was not influenced by the Ta₂O_5?x film thickness nor ambient oxygen-pressure. This suggested that the URS-forming process in Ta₂O_5?x thin films should be governed by thermally assisted dielectric breakdown in our measurement range.     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

Effect of Ge doping on the electrical properties of amorphous Zn–Sn–O thin films

We report the effect of germanium doping on the active layer of amorphous Zinc–Tin-Oxide (a-ZTO) thin film transistor (TFT). Amorphous thin film samples were prepared by RF magnetron sputtering using single targets composed of Zn₂Ge_0.05Sn_0.95O₄ and Zn₂SnO₄ with variable oxygen contents in the sputtering gases. In comparison with undoped, Ge-doped a-ZTO films exhibited five order of magnitude lower carrier density with a significantly higher Hall-mobility, which might be due to suppressed oxygen vacancies in the a-ZTO lattice since the Ge substituent for the Sn site has relatively higher oxygen affinity. Thus, the bulk and interface trap densities of Ge-doped a-ZTO film were decreased one order of magnitude to 7.047 × 10¹⁸ eV⁻¹cm⁻³ and 3.52 × 10¹¹ eV⁻¹cm⁻², respectively. A bottom-gate TFT with the Ge-doped a-ZTO active layer showed considerably improved performance with a reduced SS, positively shifted V_th, and two orders of magnitude increased I_on/I_off ratio, attributable to the doped Ge ions.     

Mixed conductivity and electrocatalytic performance of SrFeO3-δ–SrAl2O4 composite membranes

Oxygen-ionic and electronic transport in dense (SrFe)_1−x(SrAl₂)_xO_z composites, consisting of strontium-deficient Sr(Fe,Al)O_3-δ and SrAl₂O₄ phases, is determined by the properties of perovskite-like solid solution. Increasing the content of SrAl₂O₄, with a total conductivity as low as 5 × 10^− 7 −  10^− 5 S × cm^− 1 at 973–1273 K in air, results in the gradual decrease of the partial conductivities, but also enables the suppression of thermal expansion. Compared to single-phase SrFe_1−xAl_xO_3-δ, (SrFe)_1−x(SrAl₂)_xO_z composites exhibit enhanced thermomechanical properties, while the oxygen permeability of these materials has similar values. The composite membranes exhibit stable performance under air/(H₂–H₂O–N₂) and air/(CH₄–He) gradients at 973–1173 K. The oxidation of dry methane by oxygen permeating through (SrFe)_0.7(SrAl₂)_0.3O_z results in dominant total oxidation, suggesting the necessity to incorporate a reforming catalyst into the ceramic reactors for natural gas conversion.     

Investigation of the electrical properties and stability of HfInZnO thin-film transistors

In this study, amorphous HfInZnO (a-HIZO) thin films and related thin-film transistors (TFTs) were fabricated using the RF-sputtering method. The effects of the sputtering power (50–200 W) on the structural, surface, electrical, and optical properties of the a-HIZO films and the performance and NBIS stability of the a-HIZO TFTs were investigated. The films’ N_e increased and resistivity decreased as the sputtering power increased. The 100 W deposited a-HIZO film exhibited good optical and electrical properties compared with other sputtering powers. Optimization of the 100 W deposited a-HIZO TFT demonstrated good device performance, including a desirable μ_FE of 19.5 cm²/Vs, low SS of 0.32 V/decade, low V_th of 0.8 V, and high I_on/I_off of 10⁷, respectively. The 100 W deposited a-HIZO TFT with Al₂O₃ PVL also exhibited the best stability, with small V_th shifts of -2.2 V during NBIS testing. These high-performance a-HIZO thin films and TFTs with Al₂O₃ PVL have practical applications in thin-film electronics.     

Extraction of density-of-states in amorphous InGaZnO thin-film transistors from temperature stress studies

The instability of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with different active layer thicknesses under temperature stress has been investigated through using the density-of-states (DOS). Interestingly, the a-IGZO TFT with 22 nm active layer thickness showed a better stability than the others, which was observed from the decrease of interfacial and semiconductor bulk trap densities. The DOS was calculated based on the experimentally-obtained activation energy (E_A), which can explain the experimental observations. We developed the high-performance Al₂O₃ TFT with 22 nm IGZO channel layer (a high mobility of 7.4 cm²/V, a small threshold voltage of 2.8 V, a high I_on/I_off 1.8 × 10⁷, and a small SS of 0.16 V/dec), which can be used as driving devices in the next-generation flat panel displays.     

Microstructure and varistor properties of ZnO–V2O5–MnO2 ceramics with Ta2O5 addition

The effect of Ta₂O₅ addition on microstructure, electrical properties, and dielectric characteristics of the quaternary ZnO–V₂O₅–MnO₂ vaistor ceramics was investigated. Analysis of the microstructure indicated that the quaternary ZnO–V₂O₅–MnO₂–Ta₂O₅ ceramics consisted of mainly ZnO grain and minor secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, TaVO₅, and Ta₂O₅. As the amount of Ta₂O₅ increased, the sintered density increased from 94.8 to 97.2% of the theoretical density (5.78 g/cm³ for ZnO), whereas the average grain size decreased from 7.7 to 6.0 μm. The ceramics added with 0.05 mol% Ta₂O₅ exhibited the highest breakdown field (2715 V/cm) and the highest nonlinear coefficient (20). However, further increase caused α to abruptly decrease. The Ta₂O₅ acted as a donor due to the increase of electron concentration in accordance with the amount of Ta₂O₅. The donor concentration increased from 1.97×10¹⁸ to 3.04×10¹⁸cm^?3 with increasing the amount of Ta₂O₅ and the barrier height exhibited the maximum value (0.95 eV) at 0.05 mol% Ta₂O₅.     

Electrochemical evaluation of Ta2O5 thin film for all-solid-state switchable mirror glass

We investigated the electrochemical property of Ta₂O₅ thin film for all-solid-state switchable mirror glass. The film was deposited by reactive dc magnetron sputtering in a mixture gas of argon and oxygen. The current density of the film covered WO₃/ITO/glass was decreased with decreasing argon/oxygen ratio and working pressure measured by cyclic voltammetry. The film deposited at argon/oxygen ratio of 4.7 and working pressure of 1.0 Pa had better electrochemical property than that of other deposition condition. Its estimated proton conductivity was 2.1 × 10^? 9 S/cm by conventional ac impedance method. However, the device using the film showed poor optical switching property. The transmittance change of the device at a wavelength of 670 nm was only 16% by applying voltage. On the other hand, the device using the film deposited at working pressure of 0.7 Pa was able to switch its optical switching property from reflective of 0.1% to transparent states of 44% within 15 s. These results indicate that the suitable deposition condition of the Ta₂O₅ thin film existed to be used for all-solid-state switchable mirror glass.     

O− emission from 12CaO·7Al2O3 and MSZ composite and its application for silicon oxidation

The solid electrolyte 12CaO·7Al₂O₃ (C12A7) is an interesting material where an atomic oxygen radical anion (O⁻) can be emitted from the C12A7 to vacuum when it is heated to 1000 K under an applied electric field (100 V/cm). However, the mechanical strength of the C12A7 is not enough for an application study. In order to enhance the mechanical strength of the C12A7, a magnesia-stabilized zirconia (MSZ) support C12A7 film composite was developed, and ion emission from the MSZ/C12A7 composite was investigated. The MSZ/C12A7 composite showed O⁻ emission and also electron emission. The generated O⁻ was applied to a silicon sample to confirm its oxidation ability. Even though the surface temperature is less than 383 K, SiO₂ film formation was achieved.This O⁻ oxidation method is applicable for low-temperature and low-damage silicon oxidation processes.     

Electrical transport and crystallization in Cu+ ion substituted AgI–Ag2O–V2O5 glassy superionic system

A new glassy solid electrolyte system Cu_xAg_1 − xI–Ag₂O–V₂O₅ has been synthesized. The structural, thermal and electrical properties of the samples have been investigated. The glassy nature of the samples is confirmed by X-Ray diffraction and Differential Scanning Calorimetry studies. The electrical conductivity of these samples increases with CuI content and approaches a maximum value of ∼ 10⁻² Ω^− 1 cm^− 1 for x = 0.35 at room temperature. Ionic mobility measurements suggest that enhancement in the conductivity with Cu⁺ ion substitution may be attributed to increase in the mobility of Ag⁺ ions. The electrical conductivity versus temperature cycles carried out at well-controlled heating rate above T_g and T_c reveal interesting thermal properties. For lower CuI content samples conductivity exhibits anomalous rise above T_g and subsequent fall at T_c. It is also found that CuI addition into AgI–Ag₂O–V₂O₅ matrix reduces the extent of crystallization.     

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li6CaLa2Ta2O12 and Li6BaLa2Ta2O12

High-purity specimens of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li₆CaLa₂Ta₂O₁₂ and a = 13.001(4) Å for Li₆BaLa₂Ta₂O₁₂. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li⁺ ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ samples exhibit the conductivity σ = 2.2 × 10^? 6 S cm^? 1 at 27 °C (E_a = 0.50 eV) and σ = 1.3 × 10^? 5 S cm^? 1 at 25 °C (E_a = 0.44 eV), respectively.     

Chemical diffusion of water in the double perovskites Ba4Ca2Nb2O11 and Sr6Ta2O11

The mechanism and kinetics of water incorporation in the double perovskites Ва₄Ca₂Nb₂O₁₁ and Sr₆Ta₂O₁₁ has been investigated (T = 300÷500 °C and aH₂O = 1 · 10^− 3÷2.2 · 10^− 2). The formation of hydration products Ba₄Ca₂Nb₂O₁₁·xH₂O and Sr₆Ta₂O₁₁·xH₂O (0.2 < x < 0.50) was limited by the diffusion of H₂O. It has been found that the concentration dependences of D˜_H2O are the same for both samples: small increasing of D˜_H2O with increasing x. The temperature dependences of the chemical diffusion coefficients of water for compositions of Ba₄Ca₂Nb₂O₁₁·0.35H₂O and Sr₆Ta₂O₁₁·0.35H₂O could be described with close activation energies of E_a = 0.38 ± 0.03 eV and E_a = 0.49 ± 0.03 eV, respectively. The chemical diffusion coefficients of water are nearly one order of magnitude smaller for tantalate Sr₆Ta₂O₁₁. This result correlates with lower oxygen and proton conductivities in Sr₆Ta₂O₁₁ as the consequence of lower mobilities.     

Thickness-dependence of optical constants for Ta2O5 ultrathin films

An effective method for determining the optical constants of Ta₂O₅ thin films deposited on crystal silicon (c-Si) using spectroscopic ellipsometry (SE) measurement with a two-film model (ambient–oxide–interlayer–substrate) was presented. Ta₂O₅ thin films with thickness range of 1–400 nm have been prepared by the electron beam evaporation (EBE) method. We find that the refractive indices of Ta₂O₅ ultrathin films less than 40 nm drop with the decreasing thickness, while the other ones are close to those of bulk Ta₂O₅. This phenomenon was due to the existence of an interfacial oxide region and the surface roughness of the film, which was confirmed by the measurement of atomic force microscopy (AFM). Optical properties of ultrathin film varying with the thickness are useful for the design and manufacture of nano-scaled thin-film devices.     

Extraordinary fast oxide ion conductivity in La1.61GeO5−δ thin film consisting of nano-size grain

Thin films of La_1.61GeO_5−δ, a new oxide ionic conductor, were fabricated on dense polycrystalline Al₂O₃ substrates by a pulsed laser deposition (PLD) method and the effect of the film thickness on the oxide ionic conductivity was investigated on the nanoscale. The deposition parameters were optimized to obtain La_1.61GeO_5−δ thin films with stoichiometric composition. Annealing was found necessary to get crystalline La_1.61GeO_5−δ thin films. It was also found that the annealed La_1.61GeO_5−δ film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La_1.61GeO_5−δ thin films increased with the decreasing thickness as compared to that in bulk La_1.61GeO_5−δ. In particular, the improvement in conductivity of the film at low temperature was significant .The electrical conductivity of the La_1.61GeO_5−δ film with a thickness of 373 nm is as high as 0.05 S cm^− 1 (log(σ/S cm^− 1) = − 1.3) at 573 K.     

SiOx interlayer to enhance the performance of InGaZnO-TFT with AlOx gate insulator

We have fabricated indium–gallium–zinc (IGZO) thin film transistor (TFT) using SiO_x interlayer modified aluminum oxide (AlO_x) film as the gate insulator and investigated their electrical characteristics and bias voltage stress. Compared with IGZO-TFT with AlO_x insulator, IGZO-TFT with AlO_x/SiO_x insulator shows superior performance and better bias stability. The saturation mobility increases from 5.6 cm²/V s to 7.8 cm²/V s, the threshold voltage downshifts from 9.5 V to 3.3 V, and the contact resistance reduces from 132 Ωcm to 91 Ωcm. The performance improvement is attributed to the following reasons: (1) the introduction of SiO_x interlayer improves the insulator surface properties and leads to the high quality IGZO film and low trap density of IGZO/insulator interface. (2) The better interface between the channel and S/D electrodes is favorable to reduce the contact resistance of IGZO-TFT.     

Improvement of sonocatalytic activity of TiO2 by using Yb,N and F-doped Er3+:Y3Al5O12 for degradation of organic dyes

In this study, several up-conversion luminescence agents (Er³⁺:Y₃Al₅O₁₂, Er³⁺:Yb_0.2Y_2.79Al₅O₁₂, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01O_11.99, Er³⁺:Yb_0.2Y_2.79Al₅F_0.01O_11.99 and Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98) were synthesized using sol–gel method. And then, the corresponding sonocatalyst (Er³⁺:Y₃Al₅O₁₂/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅O₁₂/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01O_11.99/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅F_0.01O_11.99/TiO₂ and Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites) were prepared by sol–gel coating process. The synthesized up-conversion luminescence agents and their coated composites were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). And that, the sonocatalytic activities were detected through the degradation of Azo Fuchsine (AF) dye in aqueous solution by UV–vis spectroscopy. Some key influences such as heat-treated temperature and heat-treated time on the sonocatalytic activity of Er³⁺:Yb_aY_2.99−aN_xF_yAl₅O_12−x−y/TiO₂ coated composite, as well as ultrasonic irradiation time and initial dye concentration on the sonocatalytic degradation were studied. The results showed that the doping of Yb, N and F into Er³⁺:Y₃Al₅O₁₂/TiO₂ significantly enhanced the sonocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂ coated composite in the degradation of organic dyes. Particularly, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites with 3:7 M ratio heat-treated at 550 °C for 60 min showed the highest sonocatalytic activity. At last, the experiments also indicated that the Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites has a good sonocatalytic activity to degrade other organic dyes under ultrasonic irradiation.     

Development of a 2D dosimetry system based on the optically stimulated luminescence of Al2O3

A laser-scanning 2D dosimetry system based on the Optically Stimulated Luminescence (OSL) signal from Al₂O₃ films was built and demonstrated. The main challenge of using the OSL from Al₂O₃ for 2D dosimetry by laser scanning is the long lifetime (∼35 ms) of the main luminescence centers in this material (F-centers). In this work, we demonstrated the possibility of performing 2D dosimetry by laser scanning using a combination of the fast UV emission of F⁺-centers (lifetime <7 ns) and the slow F-center emission of Al₂O₃:C, and an algorithm to correct for the slow F-center luminescence lifetime. We also investigated the possibility of using Al₂O₃:C,Mg, to take advantage of its greater F⁺-center emission compared to Al₂O₃:C. Results from 6 MV photon beam irradiations from a clinical linear accelerator were compared to radiographic and radiochromic film profiles showing a good qualitative agreement.