Design of an X-band transformer-coupled amplifier withimproved stability and layout

The authors present a push-pull transformer-coupled amplifier for monolithic microwave applications, and discuss how its stability and layout have been improved with respect to conventional approaches by means of opposite-phase feedback and fully symmetrical layout. The circuit provides state-of-the-art performance (10-dB gain and 18-dBm saturated power in the 4-8-GHz band) with only 165-mW DC power consumption     

Program schemes for multilevel flash memories

This paper presents a synthetic overview of multilevel (ML) flash memory program methods. The problem of increasing program time with the number of bits stored in each cell is discussed and methods based on both channel hot electrons (CHE) and Fowler-Nordheim tunneling (FNT) are discussed. In the case of CHE, the use of an increasing voltage rather than a constant one on the control gate (CG) leads to narrower threshold voltage distributions and smaller current absorption, with positive effects on the degree of parallelism and program throughput. As for FNT, much faster programming than that commonly used today can be done using high CG voltages without producing intolerable degradation of cell reliability.     

SILC dynamics in MOS structures subject to periodic stress

This work investigates stress-induced leakage current (SILC) in thin-oxide MOS capacitors subject to (quasiperiodic) ac voltage stress, under the condition of fixed charge fluence through the oxide. It shows that both trap creation and spontaneous trap annealing play a significant role when the duration of, and the time between, high-voltage pulses are comparable with characteristic times of trap dynamics. A phenomenological model is introduced that is able to accurately represent the main physical phenomena due to pulsed voltage stress under conditions of interest for unconventional programming schemes for fast programming nonvolatile memories (NVMs) with acceptable oxide degradation.     

Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces

We demonstrate a technique to recirculate liquids in a microfluidic channel by alternating predominance of centrifugal and capillary forces to rapidly bring the entire volume of a liquid sample to within one diffusion length, δ, of the surface, even for sample volumes hundreds of times the product of δ and the geometric device area. This is accomplished by repetitive, random sampling of an on-disc sample reservoir to form a thin fluid layer of thickness δ in a microchannel, maintaining contact for the diffusion time, then rapidly exchanging the fluid layer for a fresh aliquot by disc rotation and stoppage. With this technique, liquid volumes of microlitres to millilitres can be handled in many sizes of microfluidic channels, provided the channel wall with greatest surface area is hydrophilic. We present a theoretical model describing the balance of centrifugal and capillary forces in the device and validate the model experimentally.     

Conferring selectivity to chemical sensors via polymer side-chain selection: thermodynamics of vapor sorption by a set of polysiloxanes on thickness-shear mode resonators

Entropy of mixing is shown to be the driving interaction for the endothermic physisorption process of organic vapor partitioning into seven systematically side-chain-modified (polar, acidic, basic, polarizable side groups and groups interacting via H-bridges) polysiloxanes on thickness-shear mode resonators. Each sensor was exposed to seven analytes, selected for their diversity of functional groups. This systematic investigation of sorption yields benchmarking data on physisorption selectivity: response data and modeling reveal a direct correlation of partition coefficients with interactions between specific polymer side chains and analyte functional groups. Partition coefficients were determined for every polymer/analyte pairing over the 273-343 K range at 10 K intervals; from partition coefficient temperature dependence, overall absorption enthalpies and entropies were calculated. By subtracting the enthalpy and entropy of condensation for a given pure analyte, its mixing entropy (primarily combinatorial) and mixing enthalpy (associated with intermolecular interactions) with each polymer matrix were determined. These two crucial thermodynamic parameters determine the chemical selectivity patterns of the polymers for the analytes. Simple molecular modeling based on the polymer contact surface share of the modified side group or the introduced functional group reveals a direct correlation between the partition coefficients and the side-group variation.     

Characteristics of acoustic plate modes on rotated Y-cuts of quartz utilized for biosensing applications

Acoustic plate modes (APM) on various quartz substrates have been investigated in order to determine their usefulness for liquid-sensing applications. The modes have been characterized in terms of their mass sensitivity, mode separation, temperature sensitivity, and reproducibility of the experimental results. Promising characteristics are found for rotated Y-cuts of quartz with the direction of acoustic mode propagation being perpendicular to the X-axis of the quartz crystal. Experiments on the detection of immunochemical reactions are performed using different quartz APM sensors, and the results are compared to similar experiments utilizing APM devices on ZX-LiNbO3.     

Simple and efficient modeling of EPROM writing

A simple and efficient model for first-order simulation of the writing of n-channel erasable programmable ROM (EPROM) cells is presented. It allows the current injected into the gate insulator of the cell transistor to be calculated, accounting (at first order) both for the nonMaxwellian form of the electron energy distribution and for the nonlocal nature of carrier heating. The model is implemented as a postprocessor of a two-dimensional device simulator, and it is validated by means of a comparison with experimental data obtained with devices with effective channel lengths ranging from 1.4 to 0.5 μm     

Toxicity assessment of common xenobiotic compounds on municipal activated sludge: comparison between respirometry and Microtox

The toxicity of four xenobiotic compounds 3,5-dichlorophenol, formaldehyde, 4-nitrophenol and dichloromethane, representative of industrial wastewater contaminants was evaluated by a simple respirometric procedure set up on the basis of OECD Method 209 and by the Microtox bioassay. Very good reproducibility was observed for both methods, the variation coefficients being in the range of 2-10% for the respirometric procedure and 6-15% for Microtox, values that can be considered very good for a biological method. Comparison of EC(50) data obtained with the two methods shows that in both cases 3,5-dichlorophenol is more toxic than other compounds investigated and dichloromethane has a very low toxicity value. Intermediate EC(50) values were found for the two other chemicals, formaldehyde and 4-nitrophenol. Moreover, the Microtox EC(50) values are generally lower (except for dichloromethane) than the respirometric ones: these differences could be explained by the fact that the Microtox method uses a pure culture of marine species and, therefore, should not necessarily be expected to behave like a community of activated sludge bacteria. In conclusion, both methods can be usefully applied for toxicity detection in wastewater treatment plants but it is advisable to take into account that Microtox is more sensitive than respirometry in estimating the acute toxicity effect on the biomass operating in the plant.