The surface science of titanium dioxide

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

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High-κ gate dielectrics: Current status and materials properties considerations

The major strategies for designing surfaces that prevent fouling due to proteins, bacteria, and marine organisms are reviewed. Biofouling is of great concern in numerous applications ranging from biosensors to biomedical implants and devices, and from food packaging to industrial and marine equipment. The two major approaches to combat surface fouling are based on either preventing biofoulants from attaching or degrading them. One of the key strategies for imparting adhesion resistance involves the functionalization of surfaces with poly(ethylene glycol) (PEG) or oligo(ethylene glycol). Several alternatives to PEG-based coatings have also been designed over the past decade. While protein-resistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection it is highly desirable to design coatings that are bactericidal. Traditional techniques involve the design of coatings that release biocidal agents, including antibiotics, quaternary ammonium salts (QAS), and silver, into the surrounding aqueous environment. However, the emergence of antibiotic- and silver-resistant pathogenic strains has necessitated the development of alternative strategies. Therefore, other techniques based on the use of polycations, enzymes, nanomaterials, and photoactive agents are being investigated. With regard to marine antifouling coatings, restrictions on the use of biocide-releasing coatings have made the generation of nontoxic antifouling surfaces more important. While considerable progress has been made in the design of antifouling coatings, ongoing research in this area should result in the development of even better antifouling materials in the future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201001215

Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms.

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter- or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C(6)F(5))(2) components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H(+)/H(-) pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal-free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three-component reactions, offering new strategies for synthetic chemistry.

Frustrated Lewis pairs: metal-free hydrogen activation and more.

Layers of polycrystalline anatase TiO/sub 2/ have been deposited through the thermal decomposition of titanium tetrakisisopropoxide (TTIP). 500 /spl Aring/ films deposited and annealed in oxygen at 750/spl deg/C had average roughnesses (R/sub a/) of about 30 /spl Aring/. Capacitors made from 190 /spl Aring/ layers of TiO/sub 2/ displayed a voltage dependent accumulation capacitance. This was postulated to be caused by finite width effects in the accumulation layer which we have dubbed the quantum capacitance effect. N-channel transistors made with these films showed near ideal behavior, but mobilities were significantly lower than those of thermal oxide MOSFETs. This mobility reduction was believed to be caused by interface states, which fell below 10/sup 11/ cm/sup -2/ eV/sup -1/ at midgap, but rose sharply on either side, unlike the "U" shaped behavior in thermal oxide MOSFET's.

MOSFET transistors fabricated with high permitivity TiO/sub 2/ dielectrics

Titanium dioxide has been deposited on silicon for use as a high-permittivity gate insulator in an effort to produce low-leakage films with oxide equivalent thicknesses below 2.0 nm. Excellent electrical characteristics can be achieved, but TEM and electrical measurements have shown the presence of a low-resistivity interfacial layer that we take to be SiO2. The leakage current follows several mechanisms depending on the bias voltage. Reasonably good agreement has been seen between current-voltage measurements and a 1D quantum transport model.

Titanium dioxide (TiO 2 )-based gate insulators

A brief survey of the precursors used for the chemical vapour deposition of the dioxides of titanium, zirconium and hafnium is presented. The review covers precursors used for the closely related process known as atomic layer chemical vapour deposition (ALCVD or ALD). Precursors delivered by standard carrier gas transport and by direct liquid injection (DLI) methods are included. The complexes fall into four classes based upon the ligands: halides, alkoxides, acetylacetonates (acac) and nitrates. Compounds bearing a mixture of ligand types have also found application in this area. The impact of the ligand on the microstructure of the metal oxide film is greatest at lower temperatures where the deposition rate is limited by the surface reactivity. The first use of anhydrous hafnium nitrate, Hf(NO3)4, to deposit films of hafnium oxide on silicon is reported. The films are characterized by Rutherford backscattering and X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. Copyright © 2000 John Wiley & Sons, Ltd.

Chemical vapour deposition of the oxides of titanium, zirconium and hafnium for use as high-k materials in microelectronic devices. A carbon-free precursor for the synthesis of hafnium dioxide

A quantitative method, using temperature-controlled friction force microscopy (FFM), has been developed to determine the frictional (dissipative) character of thin polymer films. With this method variations in friction are sampled over micrometer-scale regions and are reduced to "friction histograms," yielding the distribution of frictional forces on the surface. The temperature dependence of the mean value of the frictional distribution is correlated to the known glass-to-rubber transition (Tg) and/or secondary relaxation mechanisms in films of poly(methyl methacrylate) (PMMA), poly(ethylene tereph- thalate) (PET), and polystyrene (PS). The dominant contribution to friction, on polymer films, was attributed to viscoelastic mechanical loss. Using equivalent time scales, measured Tg's were lower than bulk polymer values. The frictional response of PMMA displayed time-temperature equivalence upon variation of scan-velocity and temperature. The rate dependence of the hindered rotation of the -COOCH3 group (‚ relaxation) in PMMA was consistent with Arrhenius type behavior, allowing calculation of an activation energy. The activation energy of the thin film was found to be lower than measured bulk energies.

Wayne L. Gladfelter

Papers

MOSFET transistors fabricated with high permitivity TiO/sub 2/ dielectrics

Titanium dioxide (TiO 2 )-based gate insulators

Chemical vapour deposition of the oxides of titanium, zirconium and hafnium for use as high-k materials in microelectronic devices. A carbon-free precursor for the synthesis of hafnium dioxide

Probing Polymer Viscoelastic Relaxations with Temperature-Controlled Friction Force Microscopy

Trimethylamine Complexes of Alane as Precursors for the Low-Pressure Chemical Vapor Deposition of Aluminum