Probing stress effects in HfO2 gate stacks with time dependent measurements

Effects of constant voltage stress (CVS) on gate stacks consisting of an ALD HfO₂ dielectric with various interfacial layers were studied with time dependent sensing measurements: DC I–V, pulse I–V, and charge pumping (CP) at different frequencies. The process of injected electron trapping/de-trapping on pre-existing defects in the bulk of the high-κ film was found to constitute the major contribution to the time dependence of the threshold voltage (V_t) shift during stress. The trap generation observed with the low frequency CP measurements is suggested to occur within the interfacial oxide layer or the interfacial layer/high-κ interface, with only a minor effect on V_t.     

High‐Mobility ZnO Thin Film Transistors Based on Solution‐processed Hafnium Oxide Gate Dielectrics

The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO₂). Despite their attractive properties, these high‐k dielectrics are usually manufactured using costly vacuum‐based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution‐processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high‐quality hafnium oxide (HfO₂) gate dielectrics and their implementation in thin film transistors employing spray‐coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X‐ray diffraction, UV–Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field‐effect measurements. Analyses reveal polycrystalline HfO₂ layers of monoclinic structure that exhibit wide band gap (≈5.7 eV), low roughness (≈0.8 nm), high dielectric constant (k ≈ 18.8), and high breakdown voltage (≈2.7 MV/cm). Thin film transistors based on HfO₂/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (≈6 V), high on/off current modulation ratio (～10⁷) and electron mobility in excess of 40 cm² V^?1 s^?1.     

Condition assessment of EPDM composite insulators using FTIRspectroscopy

Two new sampling and analysis techniques for assessing the condition of EPDM (ethylene-propylene diene monomer) composite insulators are presented. Polymer oxidation is assessed by removing small amounts of surface polymer by swabbing with xylene and analyzing this material by FTIR (Fourier transform infrared) emission spectroscopy. A measure of the amount of surface chalking is obtained by scraping a small amount of degraded surface material with a blade and analyzing by FTIR absorption spectroscopy. Numerical indices quantifying the amount of oxidation and surface chalking are obtained by calculating the ratios of absorption or emission peak heights in the infrared spectra. These indices are named the oxidation index and the chalking index. Three types of field-aged 275 kV EPDM composite insulators are investigated and the results from the new techniques compared with analyzes by XPS (X-ray photoelectron spectroscopy) with good agreement. It is found that for two types of insulator that the oxidation index is increased in regions near the HV conductor     

Rational approximation via selective modal analysis

We describe a recently developed framework for exploring the structure of linear time-invariant models of large systems, and for constructing interpretable or physically-based, reduced-order models that reproduce selected modes of the original systems to a desired accuracy. Application of this framework to constructing lumped approximations for interconnections of lumped and distributed systems is briefly explored.Support for this work has come partially from the Electric Power Research Institute, Palo Alto, California, under Contract RP 1764-8 monitored by Dr. Neal Balu, and for the second author from the I.T.P. Foundation, Madrid, Spain.     

Multiprocessor Architecture for Rapid EEG Frequency Analysis

A multicomputer array is described that speeds up the processing of spectral representation for the EEG.     

A MECHANISTICALLY BASED MATHEMATICAL MODEL OF SULFUR DIOXIDE ABSORPTION INTO A CALCIUM HYDROXIDE SLURRY IN A SPRAY DRYER

A mathematical model has been developed to predict So₂ absorption and removal during the constant rate drying period of a spray dryer. The model, based on film theory, treats the atomized slurry droplets as spheres containing discrete sorbent particles of slaked lime with the fluid uniformly distributed around the individual particles. The model includes gas and liquid phase mass transfer coefficients as well as resistance to Ca(OH)₂ dissolution. A sensitivity analysis has been conducted and a comparison was made between pilot-scale experimental data and model-predicted values of S0₂ removal efficiency.     

Theory of Drying

This review examines the stages of drying, with the emphasis on the constant rate period (CRP), when the pores are full of liquid. It is during the CRP that most of the shrinkage occurs and the drying stresses rise to a maximum. We examine the forces that produce shrinkage and the mechanisms responsible for transport of liquid. By analyzing the interplay of fluid flow and shrinkage of the solid network, it is possible to calculate the pressure distribution in the liquid in the pores. The tension in the liquid is found to be greatest near the drying surface, resulting in greater compressive stresses on the network in that region. This produces differential shrinkage of the solid, which is the cause of cracking during drying. The probability of fracture is related to the size of the body, the rate of evaporation, and the strength of the network. A variety of strategies for avoiding fracture during drying are discussed.     

Thermodynamic Theory of Single-Crystal Lead Titanate with Consideration of Elastic Boundary Conditions

A phenomenological free-energy function including the effects of elastic boundary conditions was presented and used to investigate the single-domain, single-crystal properties of the ferroelectric perovskite, PbTiO₃. In particular, the effects of tensile and compressive hydrostatic stress on the spontaneous polarization, Curie point, dielectric susceptibility, and piezoelectric property coefficients were examined. The calculated shift of the Curie point with hydrostatic stress, along with the entropy and enthalpy of the ferroelectric-paraelectric phase transition, was found to be in good agreement with experimental measurements. The isothermal variation of the relative dielectric susceptibility and piezoelectric coefficients with hydrostatic stress exhibited the expected behavior near the ferroelectric-paraelectric phase transition.     

Molecular weight viscosity relationships for PVC

The inherent viscosity of PVC resin in compounds containing fillers and additives can be calculated accurately and conveniently from the weight average molecular weight or the peak molecular weight as measured by High Performance-Size Exclusion Chromatography (HP-SEC). Molecular weight/inherent viscosity relationships are shown for typical production PVC resins. The utility of HP-SEC instrumentation for the determination of IV for samples of commercial interest is demonstrated. Mark-Houwink coefficients from the literature were used to calculate a convenient conversion factor of 0.612, which can be used to convert the molecular weight measured relative to polystyrene by HP-SEC to the actual molecular weight for PVC.