An improved technique and experimental results for the extractionof electron and hole mobilities in MOS accumulation layers

For the first time, experimental results are presented for electron and hole mobilities in the electron and hole accumulation layers of a MOSFET for a wide range of doping concentrations. Also presented is an improved methodology that has been developed in order to enable more accurate extraction of the accumulation layer mobility. The measured accumulation layer mobility for both electrons and holes is observed to follow a universal behavior at high transverse electric fields, similar to that observed for minority carriers in MOS inversion layers. At low to moderate transverse fields, the effective carrier mobility values are greater than the bulk mobility values for the highest doping levels. This is due to screening by accumulated carriers of the ionized impurity scattering by accumulated carriers, which dominates at higher doping concentrations. For lower doping levels, surface phonon scattering is dominant at low to moderate transverse fields so that the carrier mobility is below the bulk mobility value     

Enhanced output power of near-ultraviolet InGaN-GaN LEDs grown on patterned sapphire substrates

Near-ultraviolet nitride-based light-emitting diodes (LEDs) with peak emission wavelengths around 410 nm were fabricated onto c-face patterned sapphire substrates (PSS). It was found that the electroluminescence intensity of the PSS LED shown 63% larger than that of the conventional LED. For a typical lamp-form PSS LED operating at a forward current of 20 mA, the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The improvement in the light intensity could be attributed to the decrease of threading dislocations and the increase of light extraction efficiency in the horizontal direction using a PSS.     

Complete methodology for electrical modeling of RFIC packages

A complete methodology based on broadband S-parameter measurement is proposed to establish the electrical models for radio-frequency integrated circuit (RFIC) packages. The research is focused on calibration of the test-fixture parasitics to obtain the intrinsic S-parameters from which an equivalent coupled lumped model can be extracted for any pair of package leads under test. Then a step-by-step optimization scheme is employed to construct an equivalent circuit for the whole package. A real example on modeling a 16-lead Thin Shrink Small Outline Package (TSSOP) has been demonstrated. The established model can account for various package effects at radio frequencies     

ZBP: A Zone-Based Broadcasting Protocol for Wireless Sensor Networks

Wireless Sensor Networks (WSNs) have been widely used in motoring and collecting interests of environment information. Packet flooding or broadcasting is an essential function for establishing a communication path from sink node to a region of sensor nodes. However, flooding operation consumes power and bandwidth resources and raises the packet collision and contention problems, which reduce the success rate of packet transmissions and consume energy. This article proposes an efficient broadcasting protocol to reduce the number of sensor nodes that forward the query request, hence improves the packet delivery rate and saves bandwidth and power consumptions. Sensor node that received the query request will dynamically transfers the coordinate system according to the zone-ID of source node and determines whether it would forward the request or not in a distributed manner. Compared with the CBM and traditional flooding operation, experimental results show that the proposed zone-based broadcasting protocol decreases the bandwidth and power consumptions, reduces the packet collisions, and achieves high success rate of packet broadcasting.Chih-Yung Chang received the Ph.D. degree in Computer Science and Information Engineering from National Central University, Taiwan, in 1995. He joined the faculty of the Department of Computer and Information Science at Aletheia University, Taiwan, as an Assistant Professor in 1997. He was the Chair of the Department of Computer and Information Science, Aletheia University, from August 2000 to July 2002. He is currently an Associate Professor of Department of Computer Science and Information Engineering at Tamkang University, Taiwan. Dr. Chang served as an Associate Guest Editor of Journal of Internet Technology (JIT), Special Issue on “Wireless Ad Hoc and Sensor Networks” (2004) and a member of Editorial Board of Tamsui Oxford Journal of Mathematical Sciences (2001–2005). He was an Area Chair of IEEE AINA′2005, Vice Chair of IEEE WisCom2005, Track Chair (Learning Technology in Education Track) of IEEE ITRE′2005, Program Co-Chair of MNSA′2005, Workshop Co-Chair of INA′2005, MSEAT′2003, MSEAT′2004, Publication Chair of MSEAT′2005, and the Program Committee Member of ICPP′2004, USW′2005, WASN′2005, and the 11th Mobile Computing Workshop. Dr. Chang is a member of the IEEE Computer Society and IEICE society. His current research interests include wireless sensor networks, mobile learning, Bluetooth radio systems, Ad Hoc wireless networks, and mobile computing.Kuei-Ping Shih received the B.S. degree in Mathematics from Fu-Jen Catholic University, Taiwan, Republic of China, in June 1991 and the Ph.D. degree in Computer Science and Information Engineering from National Central University, Taiwan, Republic of China, in June 1998. After two years of military obligation, he joined the faculty of the Department of Computer Science and Information Engineering, Tamkang University, Taiwan, Republic of China, as an assistant professor in 2000. Dr. Shih served as a Program Area Chair in the IEEE International Conference on Advanced Information Networking and Applications (AINA), 2005, and as a Technical Track Chair in the IEEE International Conference on Information Technology: Research and Education (ITRE), 2005. Dr. Shih’s current research interests include wireless networks, sensor networks, mobile computing, and network protocols design.Dr. Shih is a member of the IEEE Computer and Communication Societies and Phi Tau Phi Scholastic Honor Society.Shih-Chieh Lee received the B.S. degree in Computer Science and Information Engineering from Tamkang University, Taiwan, in 1997. Since 2003 he has been a Ph.D. Students in Department of Computer Science and Information Engineering, Tamkang University. His research interests are wireless sensor networks, Ad Hoc wireless networks, and mobile/wireless computing.     

Cooperative detection and protection for Interest flooding attacks in named data networking

Named data networking (NDN) is a new emerging architecture for future network, which may be a substitute of the current TCP/IP‐based network, for the content‐oriented data request mode becoming the future trend of development. The security of NDN has attracted much attention, as an implementation of next‐generation Internet architecture. Although NDN is immune to most current attack, it cannot resist the distributed denial of service like attack – Interest flooding attack (IFA) – effectively. IFA takes advantages of the forwarding mechanism of NDN, flooding a large number of malicious Interest packets at quite a high rate, and exploits the network resources, which may cause the paralysis of the network. Taking into account the severity of the destruction, we propose an algorithm to counter such new type of attack. We analyze three properties of IFA, and use them to judge and filter Interest packets. Vector space model and Markov model are used in our method to realize a cooperative detection. Meanwhile, we present the retransmission forwarding mechanism to ensure legitimate user request. The ndnSIM module of ns3 is used for the corresponding simulation, and results of the simulation will be given to show the effectiveness of our algorithm. Copyright © 2014 John Wiley & Sons, Ltd.     

Si-H bond breaking induced retention degradation during packaging process of 256 mbit DRAMs with negative wordline bias

Data retention degradation of a 256-Mbit DRAM during the packaging process is investigated in this paper. Electrical measurement and device simulation show that a trap-assisted leakage degrades the retention time even in packaging process at about 250/spl deg/C. Retention time of the degraded chip is strongly dependent on the negative wordline voltage and operation temperature, but less sensitive to the substrate bias. Trap-assisted gate induced drain leakage is proposed as the mechanism of retention loss in the degraded chip. The degraded chips usually can be repaired by another thermal baking process. We propose Si-H bond breaking and the subsequent trap generation at the gate and drain overlap region as the root cause of retention degradation according to the fact that the Si-H bond density of backend passivation oxide and nitride layers correlate well with the retention performance of DRAM chips with negative wordline bias. Moreover, the packaged chip shows variable retention behavior during a thermal baking of 250/spl deg/C. Theoretical calculation indicates that the trap generation or movement to the high electrical field region beneath the gate can increase the trap-assisted gate induced drain leakage by about an order of magnitude.     

Majority and minority carrier traps in monocrystalline CulnSe2

Electron and hole traps in Bridgman-grown monocrystalline CuInSe₂ were investigated by carrying out deep level transient spectroscopy measurements on homojunctions, Al-CuInSe₂ (p-type), and Au-CuInSe₂ (n-type) Schottky junctions. Three hole trap levels and two electron trap levels were observed on these devices. Effects of oxygen and etching on the electron trap level at 182 ±15 meV from the conduction band edge were specifically studied. It was found that the election trap densities in the homojunctions prepared using the CuInSe₂ samples treated in NH₂NH₂ solution, which absorbes oxygen atoms in the samples, were larger than the electron trap densities in the homojunctions prepared using untreated samples. Moreover, the electron trap densities in the homojunctions after prolonged heat treatment in O₂ were less than that without prolonged heat treatment. The results thus suggested that oxygen atoms in CuInSe₂ can reduce the electron trap density of p-type CuInSe₂. The effects of chemical etching on these electron traps were also studied. The excess indium atoms in the CuInSe₂ were considered to affect the electron traps.     

Stochastic geometry based models for modeling cellular networks in urban areas

Recently a new approach to modeling cellular networks has been proposed based on the Poisson point process (PPP). Unlike the traditional, popular hexagonal grid model for the locations of base stations, the PPP model is tractable. It has been shown by Andrews et al. (in IEEE Trans Commun 59(11):3122–3134, 2011) that the hexagonal grid model provides upper bounds of the coverage probability while the PPP model gives lower bounds. In this paper, we perform a comprehensive comparison of the PPP and the hexagonal grid models with real base station deployments in urban areas worldwide provided by the open source project OpenCellID. Our simulations show that the PPP model gives upper bounds of the coverage probabilities for urban areas and is more accurate than the hexagonal grid model. In addition, we show that the Poisson cluster process is able to accurately model the base station location distribution.     

Thermally induced variation in barrier height and ideality factor of Ni/Au contacts to p-GaN

In this paper, we describe the change in barrier heights (ϕ_B) and ideality factors (n) of Ni/Au contacts to p-GaN determined from current-voltage measurements as a result of (a) rapid thermal annealing between 400–700°C under flowing nitrogen, and (b) testing at temperatures of 20–300°C. The lowest barrier height and ideality factor values were obtained from samples annealed at 500–600°C. These results provide supporting evidence that thermal processing helps to remove contaminants at the contact-GaN interface, thus decreasing effective barrier height and consequently, contact resistance.     

Wetting interaction between Sn-Zn-Ag solders and Cu

The wetting interaction of Sn-(7.1–9)Zn-(0–3)Ag solders with Cu was investigated from 230°C to 300°C. The wetting time, wetting forces, and activation energy of the wetting reaction were studied. The wetting time decreases with increasing temperature and increases with Ag content. The wetting force exhibits a disproportional correlation to temperature rise, while no trend was observed with respect to Ag content. The wetting behavior was ascribed to the interaction between Cu and Zn. The AgZn₃ compound was formed at the interface when the solder contains 0.3% Ag and above, while it was formed within the bulk solder at 2% Ag and above.