Wave-mechanical study of gate tunneling leakage reduction in ultra-thin (<2 nm) dielectric MOS and H-MOS devices

The downsizing of the metal oxide semiconductor field effect transistor (MOSFET) to dimensions <0.1 μm in the next years requires the adoption of <2 nm thick gate oxides, which unfortunately give rise to a significant direct tunneling current. We apply in this paper a self-consistent one-dimensional Schrödinger–Poisson model to study MOSFET channel architectures likely to reduce this leakage. They consist in either increasing the insulator thickness using a larger permittivity nitride/oxide stack or burying the channel thanks to a tensile strained IV–IV heterostructure. It is shown that both solutions yield separately a reduction, and that the combination of these two strategies offers promising opportunities to fulfill ultimate complementary metal oxide semiconductor technology (0.1 μm) requirements regarding gate oxide downsizing.     

Non-equilibrium gate tunneling current in ultra-thin (<2 nm) oxide MOS devices

The modeling of the electrical properties of ultra-thin (<2 nm thick) oxide metal–oxide–semiconductor (MOS) structures requires the self-consistent solution of the Schrödinger and the Poisson equations. To calculate the change density profile required by the Poisson equation, the occupancy of the quantum electronic states solution of the Schrödinger equation is a key issue. The most widely used approximation consists in assuming that the states that impinge from cathode and anode are occupied according to the Fermi–Dirac distribution with a quasi-Fermi (imref) level equal to that of the corresponding reservoir. The cathode and anode quasi-Fermi levels differ in the applied bias. In this work, we study the failure of this quasi-equilibrium approximation in the case of a MOS structure biased in accumulation. Our approach consists in considering the balance between inelastic scattering of electrons in the accumulation layer and the tunneling through the oxide. Using this procedure, we estimate that this quasi-equilibrium approximation fails for oxide thickness between 1 and 2 nm. Finally, we argued that kinetic treatments of transport are required for thinner oxides.     

1.5–2.5 nm RTP gate oxides: process feasibility, properties and limitations

To support the international roadmaps' requirements, semiconductor manufacturers must develop new processing technologies, both to shrink the dimensions and to improve the performances of devices. As a consequence, gate oxidation must advance to the 1.5–2.5 nm range over the coming years, to support the sub-0.18 μm technologies. We present here an overview of the more critical concern regarding this gate oxide downscaling. The limitations of rapid thermal processed (RTP) gate dielectric for oxide thickness <2 nm are discussed in terms of process feasibility, oxide thickness determination and maximum gate leakage current. As a result, we show that oxides as thin as 1.2 nm can be processed with control of the film uniformity (range within 0.06 nm). However, we also demonstrate that the exponential increase of the gate leakage current for oxides <2 nm does not allow integrating such thin dielectric layers in present metal oxide semiconductor (MOS) devices (oxide thickness limit around 2.3 nm).     

Dependence of Electrical Conductivity (σ) and Activation Energy of Lithium Ferrite on Sintering Temperature and Porosity

The electrical conductivity (σ) of lithium ferrite sintered at 950, 1000, 1050 and 1100 °C was investigated in the temperature range of 300 to 1000 K. Three distinct regions have been observed in log (σT) vs 10³/T curves for four samples of lithium ferrite sintered at different temperatures. The conduction in the first region is due to impurities. In the second and third region is due to ordered and disordered state of the material. The transition from the first region to the second region is due to lowering of symmetry. The transition from second to third region is due to magnetic transition, i.e. ferrimagnetic to paramagnetic state. The transition temperatures are nearly equal to the Curie temperatures of the materials. The porosity and activation energy were calculated. It was found that the electrical conductivity is progressively increasing with increase of sintering temperature while the porosity and activation energy decrease continuously. The Seebeck coefficient (Q), carrier concentration (n) and mobility (μ) of charge carriers have been discussed as a function of sintering temperature and temperature.     

N‐H⋅⋅⋅O,O‐H⋅⋅⋅O hydrogen bonded supramolecular formation in the cocrystal of salicylic acid with N‐containing bases

Cocrystals of salicylic acid (derived from reaction between aspirin and coformers) with 4,4′dipyridyl, nicotinamide, isonicotinamide, N,N′‐diacetylpiperazine and piperazine have been examined with intent to improve physicochemical properties of antipyretic agent. All of the resulting cocrystals, salicylic acid/4,4′dipyridyl (2:1), salicylic acid/nicotinamide (1:1), salicylic acid/isonicotinamide (1:1), salicylic acid/piperazine (1:0.5) and salicylic acid/ N,N′‐diacetylpiperazine (2:1) (derived from reaction between aspirin and piperazine) are obtained solution cooling/evaporation experiments. The structural analysis has shown that the well‐known COOH ⋅⋅⋅ N heterosynthon was considered the key element in the cocrystals design strategy. The carboxylic acid ⋅⋅⋅ pyridine hydrogen bond is an often used supramolecular synthon. The results from X‐ray Powder Diffraction, DSC, Raman and single‐crystal X‐ray analysis revealed the formation of cocrystal of salicylic acid with several coformers.     

Crystal structure of 4-(2-hydroxyethyl)-4-aza-5α-androstan-17β-ol “HS-478”

The crystal structure of HS-478 (aqueous solvate) has been determined by direct method and refined by block diagonal least squares to R₀ = 0.043. The intensity was measured in a four-circle diffractometer in the ω/2θ scanning mode, CuKα radiation. The crystals are triclinic P1, a = 6.721(3), b = 66.532(3), c = 12.188(5) Å, α = 96.86(2)°, β = 82.82(2)°, and γ = 114.68(2)°. Rings A, B, C are chair whereas ring D is envelope. Rings A/B and B/C are trans fused, whereas rings C/D are quasi trans. The hydroxyethyl side chain connected to N(4) has conformation of (−t, t).     

Magnetic field dependence of the relative critical current density in γ‐irradiated polycrystalline YBa2Cu3O7

The effect of different doses of γ‐rays on the behavior of the critical current density, J_c in an YBa₂Cu₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ‐ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical properties of multilayer X-ray mirrors for long wave part (3.1–4.4 nm) of “water window”

Structure and optical properties (at λ - 0.154 nm and λ - 3.16 nm) of W Ti, W TiN, W Sc, and Cr Sc multilayer X-ray mirrors for long wave part of “water window”' wavelength range (3.1–4.4 nm) were studied by methods of X-ray diffractometry and cross-sectional electron microscopy. The reflectivities at λ - 0.154 nm are increased going from W TiN, Cr Sc, W Ti to W Sc multilayers. Cr Sc mirrors have highest reflectivity and resolution at λ - 3.16 nm. Influence of the ambient atmosphere on optical properties of multilayer mirrors is shown.     

Structure and morphological stability of (Lu1–xEux)2O3 thin films

(Lu_1–xEu_x)₂O₃ smooth, crack‐free, transparent films were prepared by the Pechini sol–gel method and a spin‐coating technique. Thermogravimetric analysis, differential thermal analysis and FITR spectroscopy were used to study the chemical processes during annealing of the films. Film structure, morphology and optical properties were investigated. X‐ray diffraction (XRD) analysis reveals the cubic phase of (Lu_1–xEu_x)₂O₃ films annealed in the 600–1000 °C temperature range. Smooth and crack‐free films with thicknesses of 250–1000 nm were obtained in the 600–800 °C temperature range. The thickness upper limit (1000 nm) of morphological stability of films (Lu_1–xEu_x)₂O₃ on sapphire substrates has been studied.     

Effect of γ-radiation on mechanically processed MgO powder (compressive and shear stress)

In mechanically processed MgO samples, γ-irradiation results in the formation of F⁺ and V⁻ centres. The higher the mechanically induced degree of distortion of the samples, the higher the concentration of F⁺ centres obtained by the irradiation. Our experiments suggest that the irradiation can be used as a probe in determining the concentration of the mechanically induced vacant anion and cation sites.     

Crystal and molecular structure of (21R)-3β-acetoxy-14,21-epoxy-5β,14β-card-20(22)-enolide

The title compound (21R)-3β-acetoxy-14,21-epoxy-5β,14β-card-20(22)-enolide crystallizes in the monoclinic space group P2₁ with 2 formular units C₂₅H₃₄O₅ in the unit cell. The lattice parameters are a = 13.471, b = 7.959, c = 10.514 Å and β = 102.73°. The crystal structure was determined by direct methods and refined by least-squares procedures to the discrepancy factor R = 0.045. Bond length, bond angles, ring conformations and the configuration at C(21) were determined. Intermolecular interactions are only of van der Waals type.     

Crystal Structure Analysis of 3'5' (dichloro phenyl)‐3‐ethyl‐5‐phenyl thio indalo [1,2‐e] imidazolidine

The title compound crystallizes in monoclinic system with space group P2₁ /n. The cell parameters are a = 12.3824(3) Å, b = 8.9255(1) Å, c = 19.9188(4) Å, V = 2181.75(7) ų , α = γ = 90.0° and β = 97.663(1)°. The structure has an indole moiety and an imidazolidine ring connected together. The phenyl sulfonyl group is attached to the indole moiety and the dichlorophenyl ring to the imidazolidine ring. The structure has a C‐H … Cl intra molecular hydrogen bond and C‐H … π type intermolecular interactions.     

Crystal and molecular structure of 3β-hydroxy-5β-estr-8(14)-en-17-one

The title compound crystallizes in the orthorhombic space group P2₁2₁2₁ with 4 formula units C₁₈H₂₆O₂ in the unit cell. The lattice constants are a = 10.356(2) Å, b = 19.743(3) Å, and c = 7.487(1) Å. The structure was solved by direct methods of phases determination and refined by least-squares calculations to the conventional R = 0.054. The configuration and conformation of the molecule were determined and compared with those of Δ-8,14-anhydrodigitoxigenin.     

Extraction of the oxide thickness using a MOS structure quantum model for SiO2 oxide <5 nm thick films

In this paper, we present a full quantum model of metal oxide semiconductor capacitance based on a self-consistent resolution of Schrödinger and Poisson equations. The model is used in accumulation to extract the oxide thickness of N⁺ polycrystalline silicon–SiO₂–P silicon capacitors in the range 2–5 nm. The extraction results are in agreement with reference ellipsometric measurements to <±4%. We also show the necessity of a quantum computation of the gate capacitance for high substrate doping and low oxide thickness. The influence of the tunneling current is also discussed.     

Three‐Dimensional Structure Constructed via Hydrogen Bonds and π‐π Stacking Interaction. Crystal Structure of [Cu(AFO)2(H2O)2](ClO4)2.2(AFO).2H2O (AFO = 4,5‐Diazafluoren‐9‐one)

The structure of the title complexes [Cu(AFO)₂(H₂O)₂](ClO₄)₂.2(AFO).2H₂O (AFO = 4,5‐Diazafluoren‐9‐one)has been established by single‐crystal X‐ray diffraction. The complex crystallizes in the triclinic space group P‐1 with cell constants a = 7.659(3) Å, b = 11.066(3) Å, c = 14.203(5) Å, alpha = 75.16(3)°, β = 79.87(3)°, gamma = 85.71(3)°, Z = 1. The structure was solved by direct methods and refined to R₁ = 0.0595 (wR₂ = 0.1164). The X‐ray analysis reveals that a pair of AFO ligands chelate to a Cu(II) atom in an asymmetric fashion with one Cu‐N bond being much longer than the other, the Cu(II) atom is further coordinated by a pair of aqua ligands to form an elongated octahedral geometry. In the crystal of the complex, the mononuclear complex cations [Cu(AFO)₂(H₂O)₂]²⁺, uncoordinated AFO molecules, lattice water molecules and perchlorate anions are assembled into 3‐D structure via hydrogen bonds and π‐π stacking interaction.     

Confrontation of the BCF theory and computer simulation experiments with measured (R, σ) curves

A brief summary of crystal growth models – the surface diffusion model of Burton, Cabrera and Frank and computer simulation models – is given and these models are confronted with measured (R, σ) curves. It was found that the most (R, σ) curves measured so far can be fitted by BCF curves with 10⁻² ≲ σ₁ ≲ 10⁻¹ and C having an order of magnitude of 10⁻⁴ cm ≲ s⁻¹. ΔG turns out to be 12 ± 5 kcal ≲ mol⁻¹. – Some of the (R, σ) curves can be described better by a nucleus above nucleus formalism. The order of magnitude of A is 10⁻⁴ cm · s⁻¹ and 10⁻² ≲ B ≲ 10⁻¹. – It is concluded what kind of work should be done in future to check theoretical models.     

Temperature dependence of optical absorption in In1‐xGaxAs solid solutions

Absorption spectra near the fundamental absoption edge of n‐type of In_1‐xGa_xAs are studied. The temperature coefficient of the In_1‐xGa_xAs energy gap, dE_g/dT, has been obtained and compared with calculated data. An exponential dependence of the absorption coefficient on photon energy has been found. The slope of the exponential absorption curve is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substitution effects on ferroelectric,leakage current and anti‐fatigue characteristic of Bi4‐xSbxTi3O12 thin films

Bi_4‐xSb_xTi₃O₁₂ (BSTO) (x = 0, 0.03, 0.04, 0.05, 0.06 and 0.07) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by sol‐gel method. The effects of various Sb³⁺ content on microstructure and ferroelectric properties of systems are investigated. XRD show that Bi_4‐xSb_xTi₃O₁₂ (x≠0) thin films prefer (117) orientation. The substitution Sb³⁺ for Bi³⁺ reduces the grain size of the film surface. Compared to the BTO (x = 0) film, Bi_4‐xSb_xTi₃O₁₂ films display exciting electric properties. Especially when x = 0.04, the film Bi_3.96Sb_0.04Ti₃O₁₂ has achieved the max 2Pr value of 87μC/cm². This film also has a better anti‐fatigue characteristic, which can be up to 10¹⁰ switching cycles without fatigue. The leakage current density improved with J = 8×10⁻⁸ A/cm².     

Characterization of different ice habits according to nucleation processes in the electrolyte LiCl · RH2O (6 < R < 9)

The ability to observe different ice nucleation processes in LiCl · RH₂O electrolytes is demonstrated by light scattering experiments. The homogeneous ice nucleation mechanism is analyzed on the basis of Turnbull's theory. This nucleation operates in supercooled water, as deduced from the volumic dependence of the samples on R(5 < R < 9), and is compatible with the definition of the electrolyte as a heterogeneous submicroscopic LiCl·6H₂O medium composed of H₂O and LiCl·6H₂O.