Electrical properties of sol-gel processed barium titanate films

The sol-gel technique has been used to prepare ferroelectric barium titanate (BaTiO₃) films. The electrical properties of the films have been investigated systematically. The room temperature dielectric constant (ε) and loss tangent (tanδ) at 1 kHz were respectively found to be 370 and 0.012. Both ε and tanδ showed anomaly peaks at 125°C. The room temperature remanant polarization (P_r) and coercive field (E_c) were found to be 3.2 μC/cm² and 30 kV/cm, respectively. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics also showed hysteresis effect. The temperature variation of C–V and G–V characteristics also confirms the ferroelectric to paraelectric phase transition at 125°C.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

MBE growth and characterization of buried silicon oxide films on Si(100)

Silicon molecular beam epitaxy (Si-MBE) has been used to produce silicon oxide (SiO_x) films by evaporating Si on a heated Si(100) substrate in an ultra high vacuum system with an O₂ pressure of 10⁻⁶ to 10⁻⁴ mbar. Then the SiO_x films were overgrown with pure Si. The influence of the substrate temperature, the O₂ pressure and the Si deposition rate on the oxygen content in the SiO_x films and on the crystalline quality of the Si top-layer was investigated by Rutherford backscattering spectrometry and ion channeling. Epitaxial growth of the Si top-layer was observed up to a maximum concentration of ≈20 at.% oxygen content in the SiO_x film. Cross-sectional transmission electron microscopy shows that the structure of the SiO_x film changes duringa subsequent annealing procedure. Electron energy loss spectrometry proves that amorphous SiO₂ is formed and the development of holes indicates that the density of the as-grown SiO_x film is much lower than that of SiO₂. The specific for the as-grown SiO_x films was determined by I–V measurements.     

Field-lowering carrier excitation in cadmium arsenide thin films

Cadmium arsenide is a II–V semiconductor which exhibits n-type intrinsic conductivity with high mobility up to μ_n=1.0–1.5 m²/V s. Potential applications include magnetoresistors and both thermal and photodetectors, which require electrical characterization over a wide range of deposition and measurement conditions. The films were prepared by vacuum evaporation with deposition rates in the range 0.5–6.0 nm/s and substrate temperatures maintained at constant values of 20–120°C. Sandwich-type samples were deposited with film thicknesses of 0.1–1.1 μm using evaporated electrodes of Ag and occasionally Au or Al. Above a typical electric field F_b of up to 5×10⁷ V/m all samples showed instabilities characteristic of dielectric breakdown or electroforming. Below this field they showed a high-field conduction process with logJ∝V^1/2, where J is the current density and V the applied voltage. This type of dependence is indicative of carrier excitation over a potential barrier whose effective barrier height has been lowered by the high electric field. The field-lowering coefficient β had a value of (1.2–5.3)×10⁻⁵ eV m^1/2/V^1/2 which is reasonably consistent with the theoretical value of β_PF=2.19×10⁻⁵ eV m^1/2/V^1/2 expected when the field-lowering occurs at donor-like centres in the semiconductor (Poole–Frenkel effect). For thinner films Schottky emission was more probable. The effects of the film thickness, electrode materials, deposition rate, and substrate temperature on the conductivity behaviour are discussed.     

The formation of a SiOx interfacial layer on low-k SiOCH materials fabricated in ULSI application

The characterizations of SiOCH films using oxygen plasma treatment depends linearly on the O₂/CO flow rate ratio. According to the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, it was found that the carbon composition decreases with increasing O₂/CO flow rate ratio, because more carbon in the Si–O–C and Si–CH₃ bonds on the film surface would be converted by oxygen radicals. It was believed that the oxygen plasma could oxidize the SiOCH films and form a SiO_x interfacial capping layer without much porosity. Moreover, the result of FTIR analysis revealed that there was no water absorbed on the film. A SiO₂-like capping layer formed at the SiOCH film by the O₂/CO flow rate ratio of 0.75 had nearly the same dielectric properties from the result of capacitance–voltage (C–V) measurement in our research.     

Nitrogen dilution effects on structural and electrical properties of hot-wire-deposited a-SiN:H films for deep-sub-micron CMOS technologies

Hot-wire chemical vapor-deposited silicon nitride is a potential dielectric material compared to glow-discharge-deposited material due to its lower hydrogen content. In several earlier publications we have demonstrated these aspects of the HWCVD nitride. However, to replace SiO₂ with a-SiN:H as the gate dielectric, this material needs further improvement. In this paper we report the results of our efforts to achieve this through nitrogen dilution of the SiH₄+NH₃ gas mixture used for deposition. To understand the electrical behavior of these nitride films, we characterized the films by high-frequency capacitance–voltage (HFCV) and DC J–E measurements. We attempted to evolve a correlation between the breakdown strength, as determined from the J–E curves, and aspects such as the bond density, etching rate, deposition rate and refractive index. From these correlations, we infer that nitrogen dilution of the source gas mixture has a beneficial effect on the physical and electrical properties of the hot-wire a-SiN:H films. For the highest dilution, we obtained a breakdown voltage of 12 MV cm⁻¹.     

Characterization of Cat-CVD grown Si–C and Si–C–O dielectric films for ULSI applications

Si–C films with the Si compositions ranging from 40 to 70% have been grown by Cat-CVD using dimethylsilane [DMSi, Si(CH₃)₂H₂] compounds. Tetraethoxysilane [TEOS, Si(OC₂H₅)₄] and dimethyldimethoxysilane [DMDMOS, Si(CH₃)₂(OCH₃)₂] gas source gave us Si–C–O (C-doped SiO_x) films with wide ternary alloy compositions. The dielectric constant of a Si–C film has been evaluated by C–V measurements (at 1 MHz) using Al/Si–C/n-Si(001)/Cu MIS structure. The relative dielectric constant value of a Si–C film was estimated to be 3.0. The resistivity of the Si–C layer with 1 mm diameter and 0.24 μm thickness was estimated to be more than 24.5 Gohm·cm. These results gave us promising characteristics of Si–C and Si–C–O films grown by alkylsilane- and alcoxysilane-based Cat-CVD.     

Dark and photoelectric conversion properties of p-MgPc/n-Si (Organic/Inorganic) heterojunction cells.

Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si100 single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open–circuit voltage of 0.35 V, a short–circuit current of 3.57 mA and a power conversion efficiency of 1.05%. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm². The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2 kΩ have been evaluated from the measurements of the dark I–V characteristics. A free–carrier concentration of 2.2×10¹⁶ cm⁻³ and a barrier width of 75 nm have been estimated from C–V measurements. The temperature dependence of photocurrent, at constant illumination, has been also investigated.     

A comparative study of low dielectric constant barrier layer, etch stop and hardmask films of hydrogenated amorphous Si-(C, O, N)

New barrier layer, etch stop and hardmask films, including hydrogenated amorphous a-SiC_x:H (SiC), a-SiC_xO_y:H (SiCO), and a-SiC_xN_y:H (SiCN) films with a dielectric constant (k) approximately 4.3, are produced using the plasma-enhanced chemical vapor deposition technique. The chemical and structural nature, and mechanical properties of these films are characterized using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and nano-indentation. The leakage current density and breakdown electric field are investigated by a mercury probe on a metal-insulator-semiconductor structure. The properties of the studied films indicate that they are potential candidates as barrier layer, etch stop and hardmask films for the advanced interconnect technology. The SiC film shows a high leakage current density (1.3×10⁻⁷ A/cm² at 1.0 MV/cm) and low breakdown field (1.2 MV/cm at 1.0×10⁻⁶ A/cm²). Considering the mechanical and electrical properties requirements of the interconnect process, SiCN might be a good choice, but the N content may result in via poison problem. The low leakage current (1.2×10⁻⁹ A/cm² at 1.0 MV/cm), high breakdown field (3.1 MV/cm at 1.0×10⁻⁶ A/cm²), and relative high hardness (5.7 GPa) of the SiCO film indicates a good candidate as a barrier layer, etch stop, or hardmask.     

Doping and electrical characteristics of in-situ heavily B-doped Si1−x−yGexCy films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in-situ heavily B-doped Si_1−x−yGe_xC_y (0.22<x<0.6, 0<y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH₄–GeH₄–CH₃SiH₃–B₂H₆–H₂ gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH₄ partial pressure, and only at high GeH₄ partial pressure did it decrease with increasing B₂H₆ as well as CH₃SiH₃ partial pressures. With the B₂H₆ addition, the Ge and C fractions scarcely changed and the B concentration (C_B) increased proportionally. The C fraction increased proportionally with increasing CH₃SiH₃ partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si_1−x−yGe_xC_y with y=0.0054 or below, the carrier concentration was nearly equal to C_B up to approximately 2×10²⁰ cm⁻³ and was saturated at approximately 5×10²⁰ cm⁻³, regardless of the Ge fraction. The B-doped Si_1−x−yGe_xC_y with high Ge and C fractions contained some electrically inactive B even at the lower C_B region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially.     

Computational simulations of the dynamic compaction of porous media

The goal of this study was to apply and compare different computational compaction models to the dynamic compaction of porous silicon dioxide (SiO₂) powder. Three initial specific volumes were investigated in this study, V₀₀=1.3, 4 and 10 cm³/g, where the solid material specific volume is V₀=0.4545 cm³/g. Two hydrodynamic codes, KO and CTH, were used to simulate the experimental results. Two compaction models, P– and P–λ were implemented within CTH in conjunction with the Mie–Grüneisen (MG) equation of state. The snowplow (SP) compaction model was implemented within KO. In addition, the MG equation of state based on the experimentally measured Hugoniot was implemented within CTH and was compared to the data as well. One-dimensional flyer plate experiments were conducted with impact velocities ranging from 0.25 to 1.0 km/s, which corresponded to a shock incident pressure range of 0.77–2.25 GPa. The computational simulations were compared to the temporal lateral stress signatures measured with manganin gauges, placed before and after the silica powder. It was found that the MG equation of state (EOS) most accurately reproduce all of the experimental data whereas none of the compaction models accurately reproduced all of the experimental data. However, of the compaction models investigated that the P– model tended to outperform the other considered.     

Microstructure, crystallinity, and properties of low-pressure MOCVD-grown europium oxide films

A study of growth, structure, and properties of Eu₂O₃ thin films were carried out. Films were grown at 500–600 °C temperature range on Si(1 0 0) and fused quartz from the complex of Eu(acac)₃·Phen by low pressure metalorganic chemical vapor deposition technique which has been rarely used for Eu₂O₃ deposition. These films were polycrystalline. Depending on growth conditions and substrates employed, these films had also possessed a parasitic phase. This phase can be removed by post-deposition annealing in oxidizing ambient. Morphology of the films was characterized by well-packed spherical mounds. Optical measurements exhibited that the bandgap of pure Eu₂O₃ phase was 4.4 eV. High frequency 1 MHz capacitance–voltage (C–V) measurements showed that the dielectric constant of pure Eu₂O₃ film was about 12. Possible effects of cation and oxygen deficiency and parasitic phase on the optical and electrical properties of Eu₂O₃ films have been briefly discussed.     

Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode

We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq₃) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq₃ layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF = − 1.9 (Cs) to − 2.9 (Ca), − 3.8 (Mg), − 4.4 (Al), − 4.6 (Ag), and − 5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq₃ interfaces influence their current density–voltage (J–V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J–V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J–V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq₃ interface.     

A novel transparent pn junction based on indium tin oxides

p-Type indium-doped SnO₂ thin films were successfully fabricated on degenerate n⁺ indium tin oxide glass and quartz glass by sol gel dip-coating method. It was found from the X-ray diffraction results that indium-doped SnO₂ thin films were in the same rutile structure as that of undoped SnO₂. Hall effect measurement results showed that for In/Sn ratio≤0.33 and process temperature approximately 525 °C, the indium-doped tin oxide were p-type. The I–V curve measurement of a prototype transparent pn⁺ junction consisting of a layer of p-type indium-doped SnO₂ and a layer of degenerate n⁺ tin-doped indium oxide showed typical rectifying characteristics.     

Analysis of interface states and series resistance at MIS structure irradiated under Co γ-rays

In this research, we investigated the effect of ⁶⁰Co γ-ray exposure on the electrical properties of Au/SnO₂/n-Si (MIS) structures using current–voltage (I–V) measurements. The fabricated devices were exposed to γ-ray doses ranging from 0 to 300 kGy at a dose rate of 2.12 kGy h⁻¹ in water at room temperature. The density of interface states N_ss as a function of E_c–E_ss is deduced from the forward bias I–V data for each dose by taking into account the bias dependence effective barrier height and series resistance of device at room temperature. Experimental results show that the γ-irradiation gives rise to an increase in the zero bias barrier height Φ_BO, as the ideality factor n and N_ss decrease with increasing radiation dose. In addition, the values of series resistance were determined using Cheung's method. The R_s increases with increasing radiation dose. The results show that the main effect of the radiation is the generation of interface states with energy level within the forbidden band gap at the insulator/semiconductor interface.     

Formation of low-resistivity poly-Si and SiNx films by Cat-CVD for ULSI application

In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiN_x films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O₂ oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiN_x prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiN_x films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm⁻¹ of OFF leakage current and ON/OFF ratio of 10⁷–10⁸ are realized, i.e. the devices can operate similarly to conventional thermal CVD process.     

Highly conducting doped poly-Si deposited by hot wire CVD and its applicability as gate material for CMOS devices

Highly conducting p- and n-type poly-Si:H films were deposited by hot wire chemical vapor deposition (HWCVD) using SiH₄+H₂+B₂H₆ and SiH₄+H₂+PH₃ gas mixtures, respectively. Conductivity of 1.2×10² (Ω cm)⁻¹ for the p-type films and 2.25×10² (Ω cm)⁻¹ for the n-type films was obtained. These are the highest values obtained so far by this technique. The increase in conductivity with substrate temperature (T_s) is attributed to the increase in grain size as reflected in the atomic force microscopy results. Interestingly conductivity of n-type films is higher than the p-type films deposited at the same T_s. To test the applicability of these films as gate contact Al/poly-Si/SiO₂/Si capacitor structures with oxide thickness of 4 nm were fabricated on n-type c-Si wafers. Sputter etching of the poly-Si was optimized in order to fabricate the devices. The performance of the HWCVD poly-Si as gate material was monitored using C–V measurements on a MOS test device at different frequencies. The results reveal that as deposited poly-Si without annealing shows low series resistance.     

Microwave dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low-temperatures

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics sintered at low temperatures with 2–3 wt.% NaF additives were investigated. BMT ceramics sintered at 1340 °C for 3–12 h showed dielectric constants (_r) of 25.5–25.7, Qf values of 41 500–50 400 GHz and temperature coefficients of the resonator frequency (τ_f) of 10.9–21.4 ppm °C⁻¹. The variation of sintering time almost had no effect on the dielectric constant. The Qf value increased and the τ_f decreased with increasing sintering time. The ordering degree of Mg²⁺ and Ta⁵⁺ at B-sites increased with increasing sintering time.     

The evolution of a-GaAs1−xNx/c-GaAs interface states as a function of Ar-NH3 plasma

This work concerns investigations on electrical properties of amorphous GaAs_1−xN_x thin films grown on GaAs substrates. Film deposition was carried out by RF sputtering of a GaAs target by adding a nitrogen carrier gas (NH₃) to an Ar plasma. Chemical etching of substrates followed by different plasma treatments (like reverse bias and/or NH₃ glow discharge) prior to film deposition have been studied. The effects of substrate and growth temperature and of total pressure in the reactor have been analysed. Electrical characteristics (C–V and C–V(T)) have enabled us to put in evidence the evolution of interface states of the a-GaAs_1−xN_x/c-GaAs junctions. The amorphous GaAs_1−xN_x thin films are potentially interesting to be considered for GaAs-based MIS structures, due to their relatively high resistivity values, or as passivating layers on GaAs devices.     

Structure and electrical properties of boron-added (Ba,Sr)TiO3 thin films fabricated by the sol-gel method

Thin films of Ba_xSr_1−xTiO₃ (BST, with x=0.5) were fabricated on a RuO₂/Ru/SiO₂/Si substrate by the spin coating of the multicomponent sol prepared using metal alkoxides. Boron alkoxide was intentionally introduced to establish a better microstructure and to reduce the leakage current. AFM indicated that a crack-free uniform microstructure having a smooth surface was gradually developed with increasing boron content. The relative dielectric permittivity of the 250-nm thick BST thin films fired at 700°C decreased with increasing content of boron, from 420 for the undoped film to 190 for the 10 mol% boron-added film at 1 MHz. This observation was interpreted in terms of a serial capacitance composed of the perovskite BST grain and the interfacial B₂O₃ glassy phase having a low dielectric permittivity. The leakage current density (J) also decreased with the amount of boron added. The leakage current for the applied voltage greater than 1 V showed a linear variation of logJ with E^1/2 at room temperature, suggesting that the interface-controlled Schottky emission was the dominant conduction process for the BST thin films fabricated on the RuO₂ electrode.