Gate etch induced diode leakage prevention with 7-nm CVD stackedgate dielectric

Using a CVD stacked oxide, containing a thermally grown layer and a deposited CVD film, as the gate dielectric for MOS devices provides significant advantages over a single thermally grown oxide, due to mismatch of weak spots in the two layers, reduced substrate consumption and stress compensation between component layers. This paper discusses how a 7-nm stacked gate oxide reduced process-induced diode leakage by ~10², an advantage not reported previously. Micropore misalignment in the two component layers of the stacked gate oxide preventing the reactive etchant ions from reaching the substrate could explain the enhanced “etch stop” provided by the stacked oxide     

A centroid-based PWM switching technique for full-bridge inverterapplications

A novel centroid-based pulse-width-modulation (PWM) switching strategy is proposed which is suitable for full-bridge inverter applications. This method is evaluated, and its performance is compared with existing PWM switching strategies. The performance evaluation and comparison are based on the total harmonic distortion (THD) and number of pulses per cycle of the inverter output waveform. The objective of the new switching strategy is to minimize both the THD and low-order harmonics. Simulation results show that this technique yields a significant improvement in performance. In addition, a hybrid switching sequence is developed for the proposed scheme, which can lead to further reduction in switching losses     

Effect of pigmentation on organic coating characteristics

The paper reviews the effects of pigmentation, i.e. type of pigment and pigment volume concentration, on organic coating characteristics, such as curing and film formation, mechanical properties, thermal expansion coefficient, glass transition temperature, stress development, physical ageing and water transport. The main families of pigments used in the fabrication of organic coatings and the effect of nanopigments incorporation in binders are also discussed.     

Osmolality and buffering agents in soft contact lens packaging solutions.

AIM: The study determined the effects of packaging solution osmolality and buffering agent on soft contact lens parameters. METHODS: One lens type from each FDA contact lens material category was equilibrated to phosphate buffered saline (PBS) or borate buffered saline (BBS), at three osmolality concentrations: 270, 310 and 414 mOsmol/kg. Lens diameter (LD), base curve (BOZR) and back vertex power (BVP) were measured and compared to nominal packaging label values. RESULTS: Statistically significant differences were found in all three parameters across all osmolality levels for both buffering agents. Etafilcon A showed the largest amount of parameter change, followed by alphafilcon A and balafilcon A. Lotrafilcon A was the least affected. LD of alphafilcon A lenses (greater than +/- 0.2 mm) and BVP of lotrafilcon A and etafilcon A lenses (greater than +/- 0.25 D) measured outside the International Standards Organization (ISO) tolerance from their packaging labels when measured in solutions that mimicked their packaging solutions. CONCLUSION: Osmolality and buffering agents influence lens parameters. Packaging solutions can vary the parameters of some lens types from their nominal value to outside the tolerance range set by ISO.     

Network characteristics of homopolymer and some copolymers of poly(2-hydroxyethyl methacrylate)

Soluble poly(2-hydroxyethyl methacrylate) and copolymers of 2-hydroxyethyl methacrylate with n-butyl acrylate and 2-hydroxypropyl acrylate of varying compositions were synthesised by solution polymerisation. The polymers were characterised by dilute solution viscometry and shear viscosity. Crosslinked membranes were prepared from these polymers by introducing crosslinks in solution state through the reaction with 1,6-hexamethylene diisocyanate at a number of different crosslinker concentrations. The membranes swollen in dimethylformamide and water were characterised by performing equilibirium swelling measurements and calculating polymer volume fraction, the molecular mass between crosslinks (M?^c) and equilibrium water content (EWC) at 25°C. The calculation of M?^c used an expression developed by Peppas & Lucht for equilibrium swelling. This is a modified equation of the original Flory–Rehner expression, that allows non-Gaussian distribution of chain lengths. The variation of M?^c with crosslinker concentration and copolymer composition is discussed in terms of structural and molecular characteristics of these highly crosslinked networks.     

Synthesis and rheological properties of soluble poly(hydroxyethyl methacrylate) and some copolymers

Methods to synthesise soluble poly(2-hydroxyethyl methacrylate) (PHEMA) with varying molar mass were developed. Conversions over 90% were achieved without losing solubility. Steady state tests (range 0.01–590 Pa) and oscillatory tests (range 0.001–40 Hz) were carried out on 40% solutions in dimethyl formamide using a Carri-Med rheometer. Only PHEMA having molar mass over 500000 showed significant shear thinning and viscoelastic properties. The copolymers of 2-hydroxyethyl methacrylate (HEMA) with n-butyl acrylate (BA) and 2-hydroxypropyl acrylate (HPA) showed higher viscosities and viscoelastic properties compared with PHEMA homopolymer prepared under identical conditions. Also, viscosity and viscoelasticity increased with increase in acrylate content in the initial mixture. This was attributed to the higher molar mass of copolymers, which resulted from faster polymerisation rates owing to the inclusion of relatively highly reactive acrylates. However, in the case of HEMA : BA copolymers, first, the viscosity and viscoelasticity increased with increasing BA content and then dropped again, giving a maximum around HEMA : BA 75 : 25. This anomaly was explained by taking the effects of changes in inter-and intra-molecular hydrogen bonding as well as conformational differences caused by inclusion of BA in the PHEMA chain into account.     

A computer program for the geographic distribution of fluvial mollusks of medical interest in Cuba

The need to know the distribution of mollusks considered to play an important medical role in Cuba through a geographic representation motivated us to develop a software capable of acting as a system for the retrieval of geographic information in which the requested data would be presented in maps. The system has been called DMIM and it is a useful tool for malacological studies, and assessment and planning of programs for the control of intermediate host mollusks, as well as for teaching purposes.     

Dopant Migration-Induced Interface Dipole Effect in n-Doped GaAs/AlGaAs Terahertz Detectors

A heterojunction interfacial workfunction internal photoemission (HEIWIP) terahertz detector with ~1times10¹⁸cm^-3 n-type doped GaAs emitters in a multilayer GaAs/Al_0.13Ga_0.87 As heterostructure is presented. The detection mechanism is based on free carrier absorption with a broad response extending to ~ 5.26 THz (57 mum), corresponding to an effective workfunction of ~ 21.8 meV, which is much smaller than the offset expected for an Al fraction of x = 0.13 at a 1times10¹⁸ cm^-3 doping. This is attributed to a reduction of the conduction band offset by interface dipole formation between the accumulated negative charges at the interface states and migrated positively charged donors in the barrier. The device has a peak responsivity of 0.32 A/W at ~ 26 mum at 5 K. It is demonstrated that the dopant migration-induced interface dipole effect can be used to extend the zero response threshold frequency (f ₀) of n-type HEIWIP detectors.     

CO<Subscript>2</Subscript> gas sensitivity of sputtered zinc oxide thin films

For the first time, sputtered zinc oxide (ZnO) thin films have been used as a CO₂ gas sensor. Zinc oxide thin films have been synthesized using reactive d.c. sputtering method for gas sensor applications, in the deposition temperature range from 130–153°C at a chamber pressure of 8·5 mbar for 18 h. Argon and oxygen gases were used as sputtering and reactive gases, respectively. ZnO phase could be crystallized using a pure metal target of zinc. The structure of the films determined by means of X-ray diffraction method indicates that the zinc oxide single phase can be fabricated in this substrate temperature range. The sensitivity of the film synthesized at substrate temperature of 130°C is 2·17 in the presence of CO₂ gas at a measuring temperature of 100°C.