High-field stressing of LPCVD gate oxides

We have investigated gate oxide degradation as a function of high-field constant current stress for two types of oxides, viz. standard dry and LPCVD oxides. Charge injection was done from both electrodes, the gate and the substrate. Our results indicate that compared to dry oxides, LPCVD oxides show reduced charge trapping and interface state generation for inversion stress. The degradation in LPCVD oxides with constant current stress has been explained by the hydrogen model     

Thermal distribution calculations for block level placement in embedded systems

Reliability is a very important concern for the embedded systems. Thermal distribution has become an important reliability concern for today’s integrated circuits and these circuits are being used increasingly in embedded systems. In traditional design flows, the temperature of the chip is assumed to be uniform across the substrate. However, non-uniform thermal distribution can be a major source of inaccuracy in delay and clock skew computations, and can have an impact on elctromigration reliability and self-heating effects for today’s very deep submicron technology. Hence, it has become necessary to obtain design with uniform temperature distribution to ensure minimum temperature gradient and avoid hot spots across the chip area. This will minimise reliability problems during the operation of the chip. The uniform temperature distribution can be achieved by appropriate placement of circuit blocks during the physical design. In this paper, thermal distribution of single chip embedded system on silicon is discussed. The thermal distribution calculations require evaluation of switching activity factor of circuit blocks. This factor is determined by computing activities of the blocks based on the application software of embedded system.     

Fabrication and characterization of zinc oxide piezoelectric MEMS resonator

Microsystem Technologies - Micro electromechanical system resonators (MEMS) are being explored to fulfil the demands of speedy wireless communication circuits, which may be utilized as oscillators...     

Influence of Pendant Group on Mobility of Organic Thin Film Transistor in Correlation with Reorganization Energy of Molecules

Charge transport properties of common donor copolymers in organic photovoltaics, poly({4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl}{3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl}) (PTB7) and poly([2,6′‐4,8‐di(5‐ethylhexylthienyl)benzo[1,2‐b;3,3‐b]dithiophene]{3‐fluoro‐2[(2‐ethylhexyl) carbonyl]thieno[3,4‐b]thiophenediyl}) (PTB7‐Th), with molecular structures differing only in the pendant group, are studied. This is the first report of field‐effect transistor mobility (µ_FET) of PTB7‐Th (0.14 cm² V^?1 s^?1) and the highest µ_FET for PTB7 (0.01 cm² V^?1 s^?1). µ_FET of PTB7‐Th is found to be almost one order of magnitude higher than PTB7. To understand the influence of molecular structure on charge transport, hole reorganization energy (λ_h) is calculated from first‐principles. λ_h of PTB7‐Th (≈150 meV) is found to be lower than PTB7 (≈346 meV). Further, the ratio of hopping rate versus square of charge transfer integral calculated from Marcus theory using λ_h for these systems is found to indicate a higher rate of hole transfer across dimers or homojunction interface for PTB7‐Th. These results are supplemented by experimentally determined λ using bulk‐heterojunction organic solar cells, where λ_PTB7‐Th≈200 meV and λ_PTB7≈310 meV follow a similar trend. The effective hole‐mobility estimation from BHJ devices correlates well with these λ values. This study provides understanding of charge transport properties via reorganization energy, as a function of pendant group without altering the backbone of the chains.     

Investigation of surface roughness effects on fluid flow in passive micromixer

Surface roughness effects are dominant at microscale. In this study, microchannels are fabricated on Silicon substrate. The roughness morphology is modeled for the fabricated structure using Weierstrass-Mandelbrot function for self-similar fractals. A two dimensional model of hexagonal passive micromixer is analyzed with surface roughness present on inner walls of channels using parallel Lattice Boltzmann method, implemented on sixteen node cluster. The results are compared by simulating this micromixer structure using Navier–Stokes equations. The experimental results on the fabricated micromixers are also presented. The effects of relative roughness, fractal dimension and Reynolds number are discussed on laminar flow in hexagonal passive micromixers. The study concludes the importance of modeling surface roughness effect for better mixing efficiency.     

Field acceleration factor for dielectric breakdown of MOS devices

In this paper a model is presented for estimating the field acceleration factor for dielectric breakdown of SiO₂. Using the observation that the total charge through the oxide is invariant (for MOS capacitors fabricated by identical process steps) and assuming that the I-V characteristic is dominated by Fowler Nordheim tunneling prior to breakdown, a simple expression for the acceleration factor can be obtained. The expression gives a good fit to experimentally obtained acceleration factors in the literature. It also indicates that the acceleration factor is field dependent such that the logarithm of acceleration factor vs field is not a straight line and care is required while extrapolating the results of accelerated testing.     

Control of dynamic systems using fuzzy logic and neural networks

The use of artificial neural network is proposed for high-speed processing of rules in fuzzy logic controller (FLC). the logic element of an FLC is replaced by a single hidden layer feedforward network. the input and output fuzzy subsets are expressed it of numerical patterns. the network is trained using the back-propagation algori to establish fuzzy associations between the input and output fuzzy subsets. the inference mechanism of the network is compared with that of compositional law of inference. In the proposed implementation of FLC, all the rules are processed in paralle. This implementation has potential for high-speed processing of rules if the network is realized in hardware. the use of neural networks in fuzzy logic self-organizing is also ivestigated. © 1993 John Wiley & Sons, Inc.     

New method for assessing dielectrjc integrity of MOS oxides

Evaluation of dielectric integrity of MOS oxides is essential because the performance, especially relative long term performance, of modern MOS integrated circuits depends upon the functional stability of thin oxides. Since mechanisms of high field degradation are not yet clear, critical assessment of dielectric qualities of oxides based on microscopic models of wearout can not be done. However experimental observations, such as positive charge generation with high field stressing are common. Also microscopic defects generation because of high field stressing seems to be the cause of degradation. We have shown that defect generation shows same behavior over a large range of stress conditions. Our experiments show that there is a monotonic flat band voltage shift with stressing because of this. This flatband shift acts as a signature of wearout. On the basis of these observations a new method is suggested for assessing dielectric reliability and has the advantage of being close to the physical mechanisms of high field degradation of oxides.     

Net positive-charge buildup in various MOS insulators due tohigh-field stressing

The buildup of net positive charge with field stressing has been observed in all thermally grown oxides, viz. dry, pyrogenic, reoxidized nitrided oxides (RNO), and reoxidized nitrided pyrogenic oxides (RNPO). The authors observed a faster rate of growth of net positive charge for dry oxides given a postmetalization anneal (PMA) in hydrogen than for those given a PMA in nitrogen; the fastest growth of net positive charge, however, was observed in pyrogenic oxides. It has been observed that in dry and pyrogenic oxides the positive-charge growth as a function of time obeys a power law with time under the stress of constant current or voltage. On the other hand, growth of positive charge in RNO and RNPO shows a two-piece linear growth of positive charge. These results suggest that positive-charge growth at high fields is related to both the hydrogen concentration and its drift in the oxide