Effect of leakage current and dielectric constant on single and double layer oxides in MOS structure

MOS structure of Al/Al₂O₃/n-Si, Al/TiO₂/n-Si and Al/Al₂O₃/TiO₂/n-Si was obtained by deposition of Al₂O₃ and TiO₂ on silicon substrate by RF Magnetron Sputtering system. The total thickness of the oxide layer ~ 40 ± 5 nm in the MOS structure was kept constant. Samples were characterized by X-Ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Impedance analyzer and Current-voltage (J-V) characteristics. The variations in the dielectric constant and tan δ of the MOS capacitor in the frequency range of 1000Hz-1MHz were measured by impedance analyzer. The variation in dielectric constant of the Al/Al₂O₃/TiO₂/n-Si multilayer compared to single layer of Al/Al₂O₃/n-Si and Al/TiO₂/n-Si is due to high probability of defects, lattice mismatch and interface interactions. The steep rise of Tan δ values in the Al/Al₂O₃/TiO₂/n-Si structure is due to the resonance effect of both Al₂O₃ and TiO₂ layers. The leakage current mechanisms of MOS structures were extracted from Schottky coefficient and Poole-Frenkel coefficient. Theoretical values of Schottky coefficients (β_SC) and Poole-Frenkel coefficients (β_PF) for each sample were estimated using the real part of the dielectric constant. The experimental values were calculated from J-V characteristics and compared with theoretical values. The appropriate model has been proposed. It was found that Schottky and Poole-Frenkel mechanisms are applicable at low and high field respectively for all MOS structures. The combination of Al/Al₂O₃/TiO₂/n-Si is found to be a promising structure with high dielectric constant and low leakage current suitable for MOS devices.     

The influence of porous silica substrate on the properties of alumina films studied by X-ray reflection spectroscopy

The structure of alumina (Al₂O₃) films of various thicknesses grown by the atomic layer deposition method on porous silica (por-SiO₂) substrates has been studied using soft X-ray reflection spectroscopy. It is established that the synthesized films are amorphous and that the ratio of Al atoms with tetrahedral and octahedral coordinations in a film depends on its thickness. It can be suggested that thicker Al₂O₃ films contain a greater proportion of Al atoms with tetrahedral coordination.     

Self-assembly of ultrathin composite TiO2/polymer films

A wet layer-by-layer self-assembly of composite TiO₂/polymer films on Si and Al₂O₃/Al, substrates has been studied by AFM, STM, and ellipsometry techniques. The quality of the first adsorbed TiO₂ layer has been found to be the governing factor in multilayer film growth. The first layer consists of single particles and particle agglomerates 30–120 nm wide The surface coverage in the layer is determined by the chemical composition of the substrate surface and water pH in post-adsorption rinsing procedure. Well-packed TiO₂/polymer film completely covering the surface has been prepared in five adsorption cycle on Al₂O₃/Al substrate. The film remained crack-free after heat treatment at 300°C. I–V curves measurement reveals high resistivity (R∼10¹⁰ O in the voltage range from −2 to +3 V) of TiO₂/polymer films prepared in ten adsorption cycles.     

Ni(Al,Fe)2O4-TiO2 ceramic humidity sensors

In this study, the electrical resistance relative to the water absorption of humidity sensors made from Ni(Al, Fe)₂O₄-TiO₂ ceramic is investigated. This ceramic body forms a spinel structure after sintering and exhibits a porous structure. Porous ceramics easily absorb and desorb water vapour through the pores, and the electrical conductivity is enhanced by water absorption. In this ceramic system the conduction mechanism is ionic. The Ni(Al, Fe)₂O₄-TiO₂ porous ceramic has a high humidity activity, short response time for humidity detection (less than 40 s), and high stability. The highest sensitivity among the specimens studied is found in Ni(Al_0.875Fe_0.125)₂O₄–5 mol% TiO₂.     

Atomic-layer-deposited (ALD) Al_2O_3passivation dependent interface chemistry,band alignment and electrical properties of HfYO/Si gate stacks

In this work, the effects of atomic-layer-deposited(ALD) Al_2O_3 passivation layers with different thicknesses on the interface chemistry and electrical properties of sputtering-derived HfYO gate dielectrics on Si substrates have been investigated. The results of electrical measurements and X-ray photoelectron sepectroscopy(XPS) showed that 1-nm-thick Al_2O_3 passivation layer is optimized to obtain excellent electrical and interfacial properties for HfYO/Si gate stack. Then, the metal-oxide-semiconductor capacitors with HfYO/1-nm Al_2O_3/Si/Al gate stack were fabricated and annealed at different temperatures in forming gas(95% N_2+5% H_2). Capacitance-voltage(C-V) and current density-voltage(J-V) characteristics showed that the 250℃-annealed HYO high-k gate dielectric thin film demonstrated the lowest border trapped oxide charge density(-3.3 × 10~(10) cm~(-2)), smallest gate-leakage current(2.45 × 10~(-6) A/cm~2 at 2 V)compared with other samples. Moreover, the annealing temperature dependent leakage current conduction mechanism for Al/HfYO/Al_2O_3/Si/Al MOS capacitor has been investigated systematically. Detailed electrical measurements reveal that Poole-Frenkle emission is the main dominant emission in the region of low and medium electric fields while direct tunneling is dominant conduction mechanism at high electric fields.     

Metal/nonpolar <Emphasis Type="Italic">m</Emphasis>-plane ZnO contacts with and without thin Al<Subscript>2</Subscript>O<Subscript>3</Subscript> interlayer deposited by atomic layer deposition

Using the temperature dependent current–voltage (I–V) measurements, the electrical properties of Au/nonpolar m-plane ZnO Schottky diodes with an Al₂O₃ interlayer prepared by atomic layer deposition (ALD) was investigated. With an Al₂O₃ interlayer, it was found to have higher barrier heights and higher rectifying ratio. Modified Richardson plots produced effective Richardson constants of 30.0 and 37.6 Acm^?2K^?2 for the samples with and without Al₂O₃ interlayer, respectively, which are similar to the theoretical value of 32.0 Acm^??2K^??2 for n-ZnO. Scanning transmission electron microscope (STEM) results showed that the oxygen-contained layer on ZnO surface degraded the film quality of subsequently deposited Al₂O₃ layer. In addition, the inter-diffusion of Au and Al atoms into ZnO subsurface region also modulated the electrical properties of Au/ZnO contacts.     

Structural and electrical properties of thin Ho2O3 gate dielectrics

This paper describes the structural properties and electrical characteristics of thin Ho₂O₃ gate dielectrics deposited on silicon substrates by means of reactive sputtering. The structural and morphological features of these films after postdeposition annealing were studied by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. It is found that Ho₂O₃ dielectrics annealed at 700 °C exhibit a thinner capacitance equivalent thickness and excellent electrical properties, including the interface trap density and the hysteresis in the capacitance-voltage curves. Under constant current stress, the Weibull slope of the charge-to-breakdown of the 700 °C-annealed films is about 1.7. These results are attributed to the formation of well-crystallized Ho₂O₃ structure and the reduction of the interfacial SiO₂ layer.     

Effect of postdeposition annealing on the structural and electrical properties of thin Dy2TiO5 dielectrics

This paper describes the effect of postdeposition annealing on the structural and electrical characteristics of high-k Dy₂TiO₅ dielectric films deposited on Si (100) through reactive cosputtering. We used X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy to investigate the structural and morphological features of these films after they had been subjected to annealing at different temperatures. The Dy₂TiO₅ dielectrics annealed at 800 °C exhibited excellent electrical properties such as high capacitance value, small density of interface state, almost no hysteresis voltage, and low leakage current. This phenomenon is attributed to a rather well-crystallized Dy₂TiO₅ structure and the reduction of the interfacial layer at oxide/Si interface. This film also shows almost negligible charge trapping under high constant voltage stress.     

Synthesis,Characterization and Photocatalytic Activity of TiO_2 Film/Bi_2O_3 Microgrid Heterojunction

TiO2 film modified by Bi2O3 microgrid array was successfully fabricated by using a microsphere lithography method.The structure and morphology of TiO2 film,Bi2O3 film and TiO2 film/Bi2O3 microgrid heterojunction were characterized through X-ray diffraction,atomic force microscopy and scanning electron microscopy.The optical transmittance spectra and the photocatalytic degradation capacity of these samples to rhodamine B were determined via ultraviolet-visible spectroscopy.The results indicated that the coupled system showed higher photocatalytic activity than pure TiO2 and Bi2O3 films under xenon lamp irradiation.The enhancement of the photocatalytic activity was ascribed to the special structure,which could improve the separation of photo-generated electrons and holes,enlarge the surface area and extend the response range of TiO2 film from ultraviolet to visible region.     

Surface roughness and interface engineering for gate dielectrics on strained layers

The change in the morphology of various gate dielectrics (including deposited ZrO₂ and TiO₂) on strained-Si on relaxed SiGe/Si and strained-SiGe layers is studied using an atomic force microscope (AFM). The AFM observation was carried out before and after oxidation. It has been found that the oxidation rate of strained-Si was affected by the existence of the cross-hatch related surface morphology. As a result, the surface roughness increases after oxidation. The roughness increase is more pronounced in a 26% Ge-content samples than in a 9% Ge-content sample. Transmission electron microscopy (TEM) has been used to identify the structure of the deposited layers and their interface with the strained-Si or SiGe substrates. Structural and electrical characterization results for deposited high-k gate dielectrics on strained-Si using Al/ZrO₂/n-Si and Al/TiO₂/n-Si metal-insulator-semiconductor (MIS) structures with equivalent oxide thickness (EOT) of 2.5 nm are presented. Effects of nitrogen incorporation on the electrical, interfacial, charge trapping and reliability properties of ultrathin oxide/oxynitride films grown using rapid thermal oxidation on strained-SiGe substrates are also discussed.     

Resistive switching characteristics of multilayered (HfO2/Al2O3)n n = 19 thin film

A transparent resistive random access memory used as Indium Tin Oxide (ITO) electrode, ITO/HfO₂/Al₂O₃/…/HfO₂/Al₂O₃/ITO capacitor structure is fabricated on glass substrate by atomic layer deposition. The unipolar resistive switching characteristics can be performed by applying the positive- or negative-bias through top electrode, however, the differences of switching and stability in the two different operations can be observed. The diversities of electrical property are attributed to different oxide/ITO interface materials, which influence the current flow of the injected electrons.     

Influence of Coating Parameter and Sintering Atmosphere on the Corrosion Resistance Behavior of Electrophoretically Deposited Composite Coatings

The purpose of this study is to synthesize and characterize nanosized titania (TiO₂), zinc oxide (ZnO), and its composite coating on Ti–6Al–4V to enhance its corrosion protection behavior in Ringer's solution. Nanosized powders of TiO₂ and ZnO was characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy - energy dispersive atomic spectroscopy (SEM-EDAX) analysis. As a result of antibacterial activity, both ZnO and TiO₂/ZnO have produce remarkable inhibition zone on Escherichia coli. The antibacterial activity of composites are due to the combined effect of ZnO on TiO₂. The adherence and surface uniformity of TiO₂/ZnO composite film on titanium implant was examined by optical microscopy and Vickers microhardness test. Corrosion resistant behavior of the coating on titanium implant was investigated by tafel polarization and impedance analysis. The composite coatings on Ti–6Al–4V have produced improved corrosion resistance with a pronounced shift in the anodic corrosion potential (E_corr) with a corresponding less corrosion current density (I_corr) compared to monophase coating. Similar results have been obtained for impedance analysis which indicated a reduction in double layer capacitance (C_dl) and with enhancement in charge transfer resistance (R_ct). These observations suggest improved corrosion resistance property of TiO₂/ZnO composite coating on Ti–6Al–4V.     

Surface Modification of Fe7S8/C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO₂ layer is constructed on the surface of a metal–organic framework derived porous Fe₇S₈/C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe₇S₈/C, the electroactive TiO₂ layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO₂‐modified Fe₇S₈/C anode exhibits significant performance improvement for sodium‐ion batteries. The optimal TiO₂‐modified Fe₇S₈/C electrode delivers reversible capacity of 423.3 mA h g^?1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO₂ coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high‐performance metal sulfide‐based anode materials for sodium‐ion batteries.     

Investigation of Ti-doped Gd2O3 charge trapping layer with HfO2 blocking oxide for memory application

In this study, Ti-doped gadolinium oxide (Gd₂TiO₅) is investigated by X-ray diffraction, atomic force microscopy, and capacitance voltage curves (C-V) as the charge trapping layer in metal-oxide-high-k material-oxide-silicon structure memories. It was found that the Gd₂TiO₅ charge-trapping layer with an HfO₂ blocking layer annealed at 900 °C had a larger window of 4.8 V in the C-V hysteresis loop, a faster program/erase speed and good retention without significant drift up to 10⁴ cycles. This excellent performance was attributed to the well-crystallized Gd₂TiO₅ structure and the higher probability of charges being trapped in the deep trap energy level of the Gd₂TiO_5. This Gd₂TiO₅ memory device with post-annealing shows considerable promise for use in future flash memory applications.     

Conducting and topographic AFM analysis of Hf-doped and Al-doped Ta2O5 films

A conductive atomic force microscopy (C-AFM) has been used to study conductivity and electrical degradation of ultrathin (4 nm) Hf- and Al-doped Ta₂O₅ at the nanometer scale. The hardness testing has been also performed using the force measuring ability of the AFM. Since the size of the analyzed area is very small, features which are not visible by macroscopic tests are observed: extremely low leakage current (~ pA) up to significantly higher than the fields during standard current-voltage measurements; charge trapping/detrapping processes manifesting as current peaks at pre-breakdown voltages. Hf and Al addition improves the local conductivity of Ta₂O₅, provokes modification of the leakage current mechanism, and is effective in extending the potential of pure Ta₂O₅ as a high-k material at the nanoscale. The results point to a decisive role of the type of the dopant on the electrical and mechanical properties of the films and their local response to short term microwave irradiation. Hf-doped Ta₂O₅ exhibits excellent electrical stability and high hardness. Al doping provides more plastic films with large electrical inhomogeneities; the microwave treatment at room temperature is a way to improve these parameters to a level comparable to those of Hf-doped films.     

Study of electrical and micro-structural properties of high-κ gate dielectric stacks deposited using pulse laser deposition for MOS capacitor applications

The electrical properties of hafnium oxide (HfO₂) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO₂–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (V_fb) and oxide-charge density (Q_ox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La₂O₃ into HfO₂ to fabricate HfO₂/La₂O₃ dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO₂–La₂O₃–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO₂ based MOS capacitors using the PLD deposition technique.     

Enhanced performance in organic light-emitting diodes by sputtering TiO2 ultra-thin film as the hole buffer layer

Organic light-emitting diodes were prepared using titanium oxide (TiO₂) ultra-thin film by RF magnetron sputtering as the hole buffer layer. The device configuration is ITO/TiO₂/N-N′-diphenyl-N-N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/tris(8-quinolinolato)-aluminum/LiF/Al. The maximum luminous efficiency for the 1.2 nm TiO₂ device is increased by approximately 46% (6.0 cd/A), in comparison with that of the control device (4.1 cd/A). The atomic force microscopy shows that with the insertion of TiO₂ buffer layer, the roughness of ITO surface decreases, which is favorable to improve the device luminance and increase the device lifetime. The mechanism behind the enhanced performance is that the TiO₂ layer enhances most of the holes injected from the anode and improves the balance of the hole and electron injections.     

Electronic surface state of TiO2 electrode doped with transition metals, studied with cluster model and DV-Xα method

The surface electronic structure of rutile TiO₂ used for a photo-catalyst and an electrode of the dye-sensitized solar cell, was calculated by the DV-Xα method. The electrical properties of mesoporous TiO₂ electrode are dependent on the surface levels introduced by a high surface area. In this study, the electronic state of bulk TiO₂ structure was calculated using the (Ti₁₅O₅₆)⁵²⁻ model and the surface state of (1 1 0) plane was calculated using the (Ti₁₁O₃₄)²⁴⁻–O^* (O^*=surface oxygen) model, respectively. In addition to the surface state of pure TiO₂, the surface dopant levels introduced by the doping of transition metals in Ti⁴⁺ ion site were also calculated using the MTi₁₁O₃₄–O^* (M=transition metal) model. With calculated results, the variation of surface levels including dopant levels was discussed in association with electrode properties.     

Formation process of Al2O3 thin film by reactive sputtering

Al and Al₂O₃ films were deposited by RF magnetron sputtering using a mixed gas of Ar and O₂. The surface of the Al target was changed from the metallic mode to the oxide mode at a critical O₂ flow ratio of 8%. The atomic ratio of sputtered Al atoms to supplied oxygen atoms was found to be approximately 2:3 at the critical O₂ flow ratio. The oxide layer thickness formed on the Al target was estimated to be 5-7 nm at an O₂ flow ratio of 100% by ellipsometry.     

Structural and electrical properties of Ta<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>O<Subscript><Emphasis Type="Bold">5</Emphasis></Subscript> thin films prepared by photo-induced CVD

Tantalum oxide (Ta ₂ O ₅ ) films and Al/Ta ₂ O ₅ /Si MOS capacitors were prepared at various powers by ultraviolet photo-inducing hot filament chemical vapour deposition (HFCVD). Effects of ultraviolet light powers on the structure and electrical properties of Ta ₂ O ₅ thin films were studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The dielectric constant, leakage current density and breakdown electric field of the samples were studied by the capacitance–voltage (C–V) and current–voltage (I–V) measurements of the Al/Ta ₂ O ₅ /Si MOS capacitors. Results show that the Ta ₂ O ₅ thin films grown without inducement of UV light belong to amorphous phase, whereas the samples grown with inducement of UV-light belong to δ-Ta ₂ O ₅ phase. The dielectric constant and leakage current density of the Ta ₂ O ₅ thin films increase with increasing powers of the UV- lamps. Effects of UV- lamp powers on the structural and electrical properties were discussed.