The application of polyimide/silicon nitride dual passivation to AlxGa1−xN/GaN high electron mobility transistors

PECVD silicon nitride passivation is quite frequently done at the end of AlGaN/GaN HEMT fabrication before substrate back-side lapping. However, the PECVD silicon nitride process is likely to produce pinholes in the passivation film. A very thick PECVD silicon nitride film may produce mechanical stress on the underlying device. Polyimide passivation has also been known to be effective for AlGaN/GaN HEMT and it can also serve as a stress buffer. However, polyimide can take up water while PECVD silicon nitride is a good diffusion barrier for water, etc. Thus it is expected that a dual PECVD silicon nitride/polyimide passivation will be a better choice than just a single layer of PECVD silicon nitride or polyimide. In this paper, we will demonstrate the application of a dual PECVD silicon nitride/polyimide passivation to AlGaN/GaN HEMT process.     

Spectral envelope sensitivity of musical instrument sounds

It is well known that the spectral envelope is a perceptually salient attribute in musical instrument timbre perception. While a number of studies have explored discrimination thresholds for changes to the spectral envelope, the question of how sensitivity varies as a function of center frequency and bandwidth for musical instruments has yet to be addressed. In this paper a two-alternative forced-choice experiment was conducted to observe perceptual sensitivity to modifications made on trumpet, clarinet and viola sounds. The experiment involved attenuating 14 frequency bands for each instrument in order to determine discrimination thresholds as a function of center frequency and bandwidth. The results indicate that perceptual sensitivity is governed by the first few harmonics and sensitivity does not improve when extending the bandwidth any higher. However, sensitivity was found to decrease if changes were made only to the higher frequencies and continued to decrease as the distorted bandwidth was widened. The results are analyzed and discussed with respect to two other spectral envelope discrimination studies in the literature as well as what is predicted from a psychoacoustic model.     

Anomalous giant piezoresistance in AlAs 2D electron systems with antidot lattices

An AlAs two-dimensional electron system patterned with an antidot lattice exhibits a giant piezoresistance effect at low temperatures, with a sign opposite to the piezoresistance observed in the unpatterned region. We suggest that the origin of this anomalous giant piezoresistance is the nonuniform strain in the antidot lattice and the exclusion of electrons occupying the two conduction-band valleys from different regions of the sample. This is analogous to the well-known giant magnetoresistance effect, with valley playing the role of spin and strain the role of magnetic field.     

High performance wire‐array silicon solar cells

Nano/micro‐wire silicon solar cells, consisting of wire‐arrays of radial p–n junction structures, are expected to offer performance enhancement at lower costs, using smaller volumes of low carrier lifetime, cheaper silicon. Using inexpensive microsphere‐lithography‐based fabrication that is scalable to large areas, we have demonstrated wire‐array solar cells that outperform the control cell. Key to the design of these cells is the impact of various parameters, such as wire diameter and junction depth, that influences the competing effects of light trapping ability of the wire‐array, quantum efficiency, and series resistance of the resulting device. Using capacitance measurements we can identify two possible types of junction structure in a wire‐array solar cell: radial and planar. We show that the former is the prerequisite for performance‐enhancing wire‐array solar cells. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance of DS/CDMA-based equatorial LEO satellite system usingturbo-codes

Improving the bit error rate (BER) performance at low elevation angles is a crucial determining factor for the capacity of any low earth orbit (LEO) satellite system. In previous work, it has been demonstrated that the BER performance of a DS/CDMA-based equatorial LEO satellite system on a downlink can be improved significantly by using satellite diversity. The authors address the issue of improving BER at low elevation angles by using turbo codes     

Performance study of close-loop power control algorithms for acellular CDMA system

Performance of a reverse link code-division multiple-access (CDMA) system with fast close-loop power control algorithms is studied. It is found that if the fast close-loop power control algorithm functions effectively, the speed of the mobile unit is in the range such that its Doppler frequency is less than one tenth of the power control updating rate. This paper also proposes a new predictive power control algorithm with better performance in terms of system capacity than the conventional and adaptive step size algorithms. An increase in system capacity as high as 22% compared with the conventional algorithm can be achieved depending on the mobile velocity     

Electrodeposited Cu2ZnSnSe4 thin film solar cell with 7% power conversion efficiency

High performance Cu₂ZnSnSe₄ (CZTSe) photovoltaic materials were synthesized by electrodeposition of metal stack precursors followed by selenization. A champion solar cell with 7.0% efficiency is demonstrated. This is the highest efficiency among all of the CZTSe solar cells prepared from electrodeposited metallic precursors reported to‐date. Device parameters are discussed from the perspective of material microstructure and composition in order to improve performance. In addition, a high performance electrodeposited CZTS (S only) solar cell was demonstrated and its device characteristics were compared against the CZTSe (Se only) cell. Using secondary ion mass spectrometry for the analysis of the chemical composition of the absorber layer, a higher concentration of oxygen in the electrodeposited absorber is thought to be the root cause of the lower performance of the electrodeposited CZTS or CZTSe solar cells with respect to a solar cell fabricated by evaporation. The grain boundary areas of Sn‐rich composition are thought to be responsible for the lower shunt resistance commonly observed in CZTSe devices. We measured the longest minority carrier lifetime of 18 ns among all reported kesterite devices. This work builds a good baseline for obtaining higher efficiency earth‐abundant solar cells, while it highlights electrodepositon as a low cost and feasible method for earth‐abundant thin film solar cell fabrication. Copyright © 2013 John Wiley & Sons, Ltd.     

WEAK TYPE INEQUALITIES FOR FRACTIONAL INTEGRAL OPERATORS ON GENERALIZED NON-HOMOGENEOUS MORREY SPACES

We obtain weak type (1,q) inequalities for fractional integral operators on generalized non-homogeneous Morrey spaces.The proofs use some properties of maximal operators.Our results are closely related to the strong type inequalities in [13,14,15].     

Densitometric Determination of Taurine and l-Lysine Hydrochloride in an Energy Drink and in Multi-Vitamin Syrup,and Validation of the Method

JPC – Journal of Planar Chromatography – Modern TLC - A simple and rapid densitometric method has been developed for determination of taurine and lysine in ‘energy drinks’...     

Simplified Iterative MMSE Multiuser Detector Using Polynomial-Expansion Approximation

We propose to simplify the inverse matrix computation of the iterative MMSE multiuser detector by using a low-complexity polynomial-expansion matrix approximation. This approximation is an application of the polynomial-expansion multiuser detector. The number of stages is set to the number of users to obtain a linear complexity. Simulations under AWGN and asynchronous multipath channels show that the approximation performs as well as the exact inverse implementation for iterative MMSE multiuser detector.