Fabrication of a <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Heterojunction Using Topological Insulator Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>–Si and Its Annealing Response

A junction device has been fabricated by growing p-type Bi₂Te₃ topological insulator (TI) film on an n-type silicon (Si) substrate using a thermal evaporation technique. Annealing using different temperatures and durations was employed to improve the quality of the film, as confirmed by microstructural study using x-ray diffraction (XRD) analysis and atomic force microscopy (AFM). The p–n diode characteristics of the junction devices were studied, and the effect of annealing investigated. An improved diode characteristic with good rectification ratio (RR) was observed for devices annealed for longer duration. Reduction in the leakage or reverse saturation current (\( I_{\rm{R}} \)) was observed with increase in the annealing temperature. The forward-bias current (\( I_{\rm{F}} \)) dropped in devices annealed above 400°C. The best results were observed for the sample device annealed at 450°C for 3 h, showing figure of merit (FOM) of 0.621 with RR ≈ 504 and \( I_{\rm{R}} \) = 0.25 μA. In terms of ideality factor, the sample device annealed at 550°C for 2 h was found to be the best with \( n \) = 6.5, RR ≈ 52.4, \( I_{\rm{R}} \) = 0.61 μA, and FOM = 0.358. The majority-carrier density \( \left( {N_{\rm{A}} } \right) \) in the p-Bi₂Te₃ film of the heterojunction was found to be on the order of 10⁹/cm³ to 10¹¹/cm³, quite close to its intrinsic carrier concentration. These results are significant for fundamental understanding of device applications of TI materials as well as future applications in solar cells.     

MDP-Based Network Selection Scheme by Genetic Algorithm and Simulated Annealing for Vertical-Handover in Heterogeneous Wireless Networks

The hybrid algorithm for real-time vertical handover using different objective functions has been presented to find the optimal network to connect with a good quality of service in accordance with the user’s preferences. Markov processes are widely used in performance modelling of wireless and mobile communication systems. We address the problem of optimal wireless network selection during vertical handover, based on the received information, by embedding the decision problem in a Markov decision process (MDP) with genetic algorithm (GA), we use GA to find a set of optimal decisions that ensures the best trade-off between QoS based on their priority level. Then, we emerge improved genetic algorithm (IGA) with simulated annealing (SA) as leading methods for search and optimization problems in heterogeneous wireless networks. We formulate the vertical handoff decision problem as a MDP, with the objectives of maximizing the expected total reward and minimizing average number of handoffs. A reward function is constructed to assess the QoS during each connection, and the AHP method are applied in an iterative way, by which we can work out a stationary deterministic handoff decision policy. As it is, the characteristics of the current mobile devices recommend using fast and efficient algorithms to provide solutions near to real-time. These constraints have moved us to develop intelligent algorithm that avoid the slow and massive computations. This paper compares the formulation and results of five recent optimization algorithms: artificial bee colony, GA, differential evolution, particle swarm optimization and hybrid of (GA–SA). Simulation results indicated that choosing the SA rules would minimize the cost function, and also that, the IGA–SA algorithm could decrease the number of unnecessary handovers, and thereby prevent the ‘Ping-Pong’ effect.     

Discrete-time chaotic-map truly random number generators: design, implementation, and variability analysis of the zigzag map

In this paper, we introduce a novel discrete chaotic map named zigzag map that demonstrates excellent chaotic behaviors and can be utilized in truly random number generators (TRNGs). We comprehensively investigate the map and explore its critical chaotic characteristics and parameters. We further present two circuit implementations for the zigzag map based on the switched current technique as well as the current-mode affine interpolation of the breakpoints. In practice, implementation variations can deteriorate the quality of the output sequence as a result of variation of the chaotic map parameters. In order to quantify the impact of variations on the map performance, we model the variations using a combination of theoretical analysis and Monte-Carlo simulations on the circuits. We demonstrate that even in the presence of the map variations, a TRNG based on the zigzag map passes all of the NIST 800-22 statistical randomness tests using simple post processing of the output data.     

EMI Shielding Characteristics of Electrically Conductive Polymer Blends of PS/PANI in Microwave and IR Region

Conductive polymeric blends (CPBs) of polystyrene and polyaniline (PS/PANI) were prepared by solution casting method in various compositions. Film thickness of CPBs was achieved?～?250 micron. PS/PANI blend films were analyzed for electromagnetic interference (EMI) shielding characteristics in microwave and near-infrared (NIR) regions. PS/PANI blends showed remarkable features. Most mobile telecommunications use GHz frequency range and shielding effectiveness was observed in 9 GHz to 18 GHz. In 9 GHz to 18 GHz frequency range, 45 dB shielding effectiveness was measured. CPBs were also analyzed in the NIR region and showed transmittance of <1%. Microwaves and NIR radiation are the most abundant in the environment and cause damage to human health. Both types of radiation causes serious damage to electronic devices as well.

     

Low-power CMOS distributed amplifier using new cascade gain cell for high and low gain modes

A CMOS distributed amplifier (DA) with low-power and flat and high power gain (S₂₁) is presented. In order to decrease noise figure (NF) an RL terminating network used for the gate transmission line instead of single resistance. Besides, a flat and high S₂₁ is achieved by using the proposed cascade gain cell consist of a cascode-stage with bandwidth extension capacitor. In the high-gain mode, under operation condition of V _dd  = 1.2 V and the overall current consumption of 7.8 mA, simulation result shown that the DA consumed 9.4 mW and achieved a flat and high S₂₁ of 20.5 ± 0.5 dB with an average NF of 6.5 dB over the 11 GHz band of interest, one of the best reported flat gain performances for a CMOS UWB DA. In the low-gain mode, the DA achieved average S₂₁ of 15.5 ± 0.25 dB and an average NF of 6.6 dB with low power consumption (P_DC) of 3.6 mW, the lowest P_DC ever reported for a CMOS DA or LNA with an average gain better than 10 dB.     

New radix-(2/spl times/2/spl times/2)/(4/spl times/4/spl times/4) and radix-(2/spl times/2/spl times/2)/(8/spl times/8/spl times/8) DIF FFT algorithms for 3-D DFT

In this paper, new three-dimensional (3-D) radix-(2/spl times/2/spl times/2)/(4/spl times/4/spl times/4) and radix-(2/spl times/2/spl times/2)/(8/spl times/8/spl times/8) decimation-in-frequency (DIF) fast Fourier transform (FFT) algorithms are developed and their implementation schemes discussed. The algorithms are developed by introducing the radix-2/4 and radix-2/8 approaches in the computation of the 3-D DFT using the Kronecker product and appropriate index mappings. The butterflies of the proposed algorithms are characterized by simple closed-form expressions facilitating easy software or hardware implementations of the algorithms. Comparisons between the proposed algorithms and the existing 3-D radix-(2/spl times/2/spl times/2) FFT algorithm are carried out showing that significant savings in terms of the number of arithmetic operations, data transfers, and twiddle factor evaluations or accesses to the lookup table can be achieved using the radix-(2/spl times/2/spl times/2)/(4/spl times/4/spl times/4) DIF FFT algorithm over the radix-(2/spl times/2/spl times/2) FFT algorithm. It is also established that further savings can be achieved by using the radix-(2/spl times/2/spl times/2)/(8/spl times/8/spl times/8) DIF FFT algorithm.     

Optimized ITO-free tri-layer electrode for organic solar cells

The optical properties of ZnO/Ag/ZnO (ZAZ) multilayer structures were numerically modeled and calculated by a FDTD method. Such tri-layers were also manufactured using an ion beam sputtering plant. A good agreement is obtained between modelizations and realizations. The impact of the oxide thicknesses on the optical properties of the ZAZ structures were experimentally and numerically investigated, and allow us to adjust the spectral position of the transmission maximum. The transmission of these structures is optimized up to around 74%, on the whole absorption spectral range of the photoactive P3HT:PCBM bulk heterojunction. The best electrode design is glass/ZnO (30 nm)/Ag (14 nm)/ZnO (30 nm), which presents a sheet resistance of 7 Ω/□. The optimized ZAZ structure was successfully integrated in an organic solar cell as anode. A photovoltaic efficiency of 2.58% is obtained and is compared to an organic solar cell integrating a traditional ITO anode with an efficiency of 2.99%. Numerical calculations of the intrinsic absorption inside each layer of the organic solar cells are performed. Alternative ITO-free electrodes for organic solar cells are demonstrated.     

Optimized intrusion detection mechanism using soft computing techniques

Intrusion detection is an important technique in computer and network security. A variety of intrusion detection approaches be present to resolve this severe issue but the main problem is performance. It is important to increase the detection rates and reduce false alarm rates in the area of intrusion detection. Therefore, in this research, an optimized intrusion detection mechanism using soft computing techniques is proposed to overcome performance issues. The KDD-cup dataset is used that is a benchmark for evaluating the security detection mechanisms. The Principal Component Analysis (PCA) is applied to transform the input samples into a new feature space. The selecting of an appropriate number of principal components is a critical problem. So, Genetic Algorithm (GA) is used in the optimum selection of principal components instead of using traditional method. The Support Vector Machine (SVM) is used for classification purpose. The performance of this approach is addresses. Further, a comparative analysis is made with existing approaches. Consequently, this method provides optimal intrusion detection mechanism which is capable to minimize amount of features and maximize the detection rates.     

A design and implementation of fully programmable switched-currentIIR filters

An approach to switched-current filter design based on digital multiply-accumulator and delay blocks is presented. The characteristics of the filter are made fully programmable by simply changing the ratios of the coefficient transistors. To reduce the effect of switch charge injection and channel-length modulation, a high-performance, single-ended differential, switched-current memory cell is developed and used as a basic building block. To reduce the chip area and to maintain the required accuracy of the coefficients, an array consisting of three different sizes of transistors is designed instead of using a unit transistor array as coefficient transistors. An experimental prototype infinite impulse response filter array consisting of six second-order switched-current sections is designed and fabricated with a standard 1.2-μ CMOS process technology. A hard-wiring technique is used to program the filters. The test results show that the characteristics of the filters satisfy the design requirements