Spread Spectrum System Using Noise Band Shift Keying

A new spread spectrum technique using band-limited Gaussian noise for transmission and incoherent detection at the receiver has been discussed. The proposed system called noise band shift keying (NBSK) may be considered as a modified form of the frequency-shift keying (FSK) system. In the NBSK system nonoverlapping bandlimited noise is transmitted instead of pure tones as in the FSK system and the center frequency of the noise is chosen on the basis of the binary data signal. For this system, an expression for the probability of error has been derived and it has been shown that its performance under nonfading channel conditions is identical to that of the FSK system with frequency diversity under Rayleigh fading conditions. Compared to the conventional spread spectrum systems, the proposed method is considerably more simple to implement and is attractive where adequate bandwidth is available.     

Forward I-V characteristics of Pt/n-GaAs Schottky barrier contacts

The forward I-V characteristics of Pt/n-GaAs planar Schottky diodes and the effect of high temperature annealing on these characteristics have been investigated. Near-ideal (thermionic emission theory) I-V characteristics with an ideality factor n ≈ 1·00–1·09 and a barrier height φ_B ≈ 0·90–0·95 V are obtained for diodes made on as-received GaAs. On annealing at 350°C in vacuum, n remains practically unchanged although φ_B increases by ≈ 5–6 per cent and rather large currents are detected at voltages <0·3 V, which are attributed to the recombination centers created during alloying.For diodes made on GaAs which was preannealed in air at 350°C, non-ideal behavior is observed with φ_B ≈ 0·79–0·80 V and n ≈ 1·29. After annealing at 350°C in vacuum, n gradually decreases to 1·07 whereas φ_B increases to 0·96 V. Recombination currents are now observed at lower voltages. After further annealing at 350°C in air, n increases, φ_B decreases and recombination currents at lower voltages are no longer observed. A mechanism is proposed to explain the observed forward I-V characteristic behavior.     

Study on electrical characteristics of fluorinated polyimide film

The electrical characteristics (I–V and I–t) of fluorinated polyimide dielectric films were measured as function of time, electric field and sample temperature and the results were discussed in view of existing conduction and charge-transport mechanisms. Experiments and analysis to elucidate conduction mechanisms at low and high electric fields were carried out. The results are presented and discussed. It is concluded that the bulk-limited Pool–Frenkel conduction mechanism is likely to dominate for the steady state current at high electric field above 1 MV cm-1, and in the range of low electric field below 1 MV cm-1, the Ohmic conduction is the main conduction mechanism. © 1998 Kluwer Academic Publishers     

High-temperature stability of Au Pt/n-GaAs Schottky barrier diodes

The operating surface temperature for the Au/Pt/n-GaAs Schottky barrier microwave devices is in the temperature range of 200–250°C. In order to determine operating lifetimes for these devices accelerated aging studies were performed. In this study the reverse bias voltage at currents of 10 μA, 100 μA and 1 mA were determined as a function of annealing time at 350°C for diodes metallized with AuPt and with Pt alone. Two distinct degradation mechanisms were observed. (a) Penetration of Au by diffusion through thin Pt films or by surface migration along edges or cracks in the Pt films resulted in rapid degradation of the devices. (b) The second degradation mechanism was observed in absence of Au and was found to be related to annealing ambient and the metallurgical interaction between Pt and GaAs. A decrease in the reverse bias voltage was observed due to the diffusion of oxygen from the interfacial oxide and from the ambient. Oxygen from the ambient diffused throug platinum into GaAs and was the cause of the final degradation of devices annealed in air. An increase in the reverse bias voltage occurred immediately after the initial decrease due to the interfacial oxide. This recovery has been attributed to the metallurgical interaction between Pt and GaAs which led to the formation of PtAs₂ at the interface and GaPt phases away from the interface.     

Integration of copper multilevel interconnects with oxide and polymer interlevel dielectrics

Copper interconnect structures are being evaluated for 0.25 μm minimum feature size technology and below. This work focuses on fabrication of one- and two-level test structures with copper metallization and both oxide and polymer interlevel dielectrics to demonstrate the compatibility of unit processes being developed for future copper-based interconnects. Emphasis is placed on dual Damascene patterning and material and process compatibility with such patterning and the required barriers and passivation techniques required with copper. Future directions of this work are described in this invited review paper.     

Filter objects for Java

Filtering is an emerging abstraction in object‐oriented systems. Filtering can be characterized by an ability to filter messages in transit and perform intermediate actions. Filters can be used for carrying out intermediate tasks such as encryption, load balancing, caching, security checks and add‐on computations. A few filtering approaches have been proposed earlier and some commercial implementations with specialized filtering capabilities are available. This paper discusses a model for transparent and dynamically pluggable first class filter objects for object‐oriented systems based on the Java programming language. The filter object model is based on an interclass filter relationship. The model is realized through extensions to the Java programming language. Filter objects can be injected into message paths during execution time and they are transparent to both clients and servers. The properties of filter objects enable them to be employed as a mechanism for evolution promoting reuse of existing code. A method of evolution through filter objects is discussed. A translator for Java filters (TJF) has been designed and implemented. TJF translates an extended Java program involving filter constructs into an equivalent Java code. The translation scheme is presented and the performance of the translated code is analyzed. A brief survey of existing approaches related to filtering in object‐oriented systems has also been presented. Copyright © 2003 John Wiley & Sons, Ltd.     

R.F. diode sputtered platinum films

Platinum films have been deposited using the technique of r.f. sputtering. The properties of the sputtered films were studied as a function of experimental sputtering power, ambient gas pressure, substrate temperature and bias. As a result of these studies it was possible to deposit platinum films of resistivity as low as approximately 13 μΩcm. It was found that the stress in these films can be varied from about 5x10⁹ dyn/cm² compressive to about 5x10⁹ dyn/cm² tensile depending upon the deposition conditions.     

Transition-metal-free oxidative coupling reactions for the formation of C-C and C-N bonds mediated by TEMPO and its derivatives

The application of nitroxides for the development of new synthetic methods and their implementation in polymer chemistry, material science and beyond is one of the major research topics in our laboratory in the institute of organic chemistry at the WWU Münster. This short review focuses on our recent progress towards nitroxide-based transition-metal-free oxidative coupling reactions. The demand for organic surrogates for transition metals in such transformations is in our eyes unquestionable, since environmental and economic issues have become progressively more important in recent years. For this purpose, the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) is shown to be a highly efficient oxidant for the homo- and cross-coupling of Grignard reagents. This powerful C-C bond forming strategy allows the generation of conjugated polymers from bifunctional Grignard reagents. Moreover, cross-coupling of alkynyl Grignard compounds and nitrones can be accomplished under aerobic atmosphere with catalytic amounts of TEMPO. It is also shown that TEMPO-derived N-oxoammonium salts can act as suitable oxidants for formation of C-N bonds between non-preactivated benzoxazoles and secondary amines under metal-free conditions.     

Heats of formation of transition-metal silicides

Heats of formation per metal atom of the transition-metal silicides are found to increase with the increasing silicon content in the intermetallics. The relationship, which is found to hold without exception, explains the observed higher stability of the silicon-rich silicides.