Partial soi power LDMOS with a variable low-kappa; Dielectric buried layer and a buried P layer

A power LDMOS on partial silicon on insulator (PSOI) with a variable low-κ dielectric (VLKD) buried layer and a buried p (BP) layer is proposed (VLKD BPSOI). At a low κ value, the electric field strength in the buried dielectric (EI) is enhanced, and a Si window makes the substrate share the vertical voltage drop, leading to a high vertical breakdown voltage (BV). Moreover, three interface field peaks are introduced by the BP, the Si window, and the VLKD, which modulate the fields in the SOI layer, the VLKD layer, and the substrate; consequently, a high BV is obtained. Furthermore, the BP reduces the specific on-resistance (Ron), and the Si window alleviates the self-heating effect (SHE). The BV for VLKD BPSOI is enhanced by 34.5%, and Ron is decreased by 26.6%, compared with those for the conventional PSOI, and VLKD BPSOI also maintains a low SHE. © 2006 IEEE.

Fixed-lag blind equalization and sequence estimation in digital communications systems using sequential importance sampling

We present methods for fixed-lag smoothing using Sequential Importance sampling (SIS) on a discrete non-linear, non-Gaussian state space system with unknown parameters. Our particular application is in the field of digital communication systems. Each input data point is taken from a finite set of symbols. We represent transmission media as a fixed filter with a finite impulse response (FIR), hence a discrete state-space system is formed. Conventional Markov chain Monte Carlo (MCMC) techniques such as the Gibbs sampler are unsuitable for this task because they can only perform processing on a batch of data. Data arrives sequentially, so it would seem sensible to process it in this way. In addition, many communication systems are interactive, so there is a maximum level of latency that can be tolerated before a symbol is decoded. We will demonstrate this method by simulation and compare its performance to existing techniques.

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesized using a high plasma density electron cyclotron wave resonance (ECWR) technique using N2 and C2H2 as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N2/C2H2 gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp3-bonded carbon fraction decrease from 1.7 to 1.1 eV and approximately 65 to 40%, respectively. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (109 Ω cm) and moderate sp3-bonded carbon fraction (40%), they should be classed as polymeric in nature.

Chemical sputtering of ta-C: Implications for the deposition of carbon nitride

The majority of attempts to synthesize the theoretically predicted superhard phase β-C3N4 have been driven towards the use of techniques which maximize both the carbon sp3 levels and the amount of nitrogen incorporated within the film. However, as yet no attempt has been made to understand the mechanism behind the resultant chemical sputter process and its obvious effect upon film growth. In this work, however, the chemical sputtering process has been investigated through the use of an as-deposited tetrahedrally bonded amorphous carbon film with a high density nitrogen plasma produced using an rf-based electron cyclotron wave resonance source. The results obtained suggested the presence of two distinct ion energy dependent regimes. The first, below 100 eV, involves the chemical sputtering of carbon from the surface, whereas the second at ion energies in excess of 100 eV exhibits a drop in sputter rate associated with the subplantation of nitrogen within the carbon matrix. Furthermore, as the sample temperature is increased there is a concomitant decrease in sputter rate suggesting that the rate is controlled by the adsorption and desorption of additional precursor species rather than the thermal desorption of CN. A simple empirical model has been developed in order to elucidate some of the primary reactions involved in the sputter process. Through the incorporation of various previously determined experimental parameters including electron temperature, ion current density, and nitrogen partial pressure the results indicated that molecular nitrogen physisorbed at the ta-C surface was the dominant precursor involved in the chemical sputter process. However, as the physisorption enthalpy of molecular nitrogen is low this suggests that activation of this molecular species takes place only through ion impact at the surface. The obtained results therefore provide important information for the modeling and growth of high density carbon nitride. © 2001 American Institute of Physics.

Analysis of the ellipsometric spectra of amorphous carbon thin films for evaluation of the sp3-bonded carbon content

Using spcctroscopic ellipsometry (SE), we have measured the optical properties and optical gaps of a series of amorphous carbon (a-C) films ∼ 100-300 Å thick, prepared using a filtered beam of C+ ions from a cathodic arc. Such films exhibit a wide range of sp3-bonded carbon contents from 20 to 76 at.%, as measured by electron energy loss spectroscopy (EELS). The Taue optical gaps of the a-C films increase monotonically from 0.65 eV for 20 at.% sp3 C to 2.25 eV for 76 at.% sp3 C. Spectra in the ellipsometric angles (1.5-5 eV) have been analyzed using different effective medium theories (EMTs) applying a simplified optical model for the dielectric function of a-C, assuming a composite material with sp2 C and sp3 C components. The most widely used EMT, namely that of Bruggeman (with three-dimensionally isotropic screening), yields atomic fractions of sp3 C that correlate monotonically with those obtained from EELS. The results of the SE analysis, however, range from 10 to 25 at.% higher than those from EELS. In fact, we have found that the volume percent sp3 C from SE using the Bruggeman EMT shows good numerical agreement with the atomic percent sp3 C from EELS. The SE-EELS discrepancy has been reduced by using an optical model in which the dielectric function of the a-C is determined as a volume-fraction-weighted average of the dielectric functions of the sp2 C and sp3 C components. © 1998 Elsevier Science S.A.

Perturbation of the stability of amyloid fibrils through alteration of electrostatic interactions.

The self-assembly of proteins and peptides into polymeric amyloid fibrils is a process that has important implications ranging from the understanding of protein misfolding disorders to the discovery of novel nanobiomaterials. In this study, we probe the stability of fibrils prepared at pH 2.0 and composed of the protein insulin by manipulating electrostatic interactions within the fibril architecture. We demonstrate that strong electrostatic repulsion is sufficient to disrupt the hydrogen-bonded, cross-β network that links insulin molecules and ultimately results in fibril dissociation. The extent of this dissociation correlates well with predictions for colloidal models considering the net global charge of the polypeptide chain, although the kinetics of the process is regulated by the charge state of a single amino acid. We found the fibrils to be maximally stable under their formation conditions. Partial disruption of the cross-β network under conditions where the fibrils remain intact leads to a reduction in their stability. Together, these results support the contention that a major determinant of amyloid stability stems from the interactions in the structured core, and show how the control of electrostatic interactions can be used to characterize the factors that modulate fibril stability.