Springer Science and Business Media LLC

In this paper we present the results of a study of electronically and mechanically generated transverse magnetic (TM) and transverse electric (TE) dipoles in a lossy environment, so that antenna design guidelines may be established at the system level. At far-zone, the ratio $$|\frac{E}{H}|:= \eta _0$$ is the intrinsic impedance, and they are identical for the TM and its dual TE dipoles. Nonetheless, the ratio in near-zone behaves drastically different between the TM and dual TE. We derived closed form expressions of the antenna Ohmic loss in a spherical lossy shell (SLS) for the first time, yielding precise radiation efficiency $$\eta _r$$ and accurate computations. For electrically small dipole of normalized half dipole-length $$|ka|\ll 1$$ , analytic results show that $$\eta _r$$ is proportional to $$|ka|^3$$ for TM dipole, and |ka| for TE dipole, respectively. Consequently, efficiency $$\eta _r$$ of TE can be better than TM in two to three orders of magnitude for under seawater communication. The time-domain energy flow velocity (EFV) patterns show that the TE dipoles are always radiation-dominating, in either lossless or lossy medium. Numerical results reveal that mechanically spinning dipole is smaller in size and weight but it requires more operation power, compared to its electromagnetic counter-partners. Finally, design, tuning and impedance matching of low-profile TE dipole antenna are outlined.

Theories of interface trap generation in Negative Bias Temperature Instability (NBTI) and Hot Carrier Injection (HCI) mechanisms are unified under the geometric interpretation and computational modeling of Reaction-Diffusion (R-D) theoryframework. Analytical derivations that predict the degradation are shown, simulation methodology is explained and numerical solutions are obtained. Time-exponents and degradation behavior under dynamic bias in agreement with experimental observations are discussed. Implications regarding ultra-scaled surround-gate device structures are presented.

State of the art first-principles calculations of electronic structures aim at finding the ground state electronic density distribution. The performance of such methodologies is determined by the effectiveness of the iterative solution of the nonlinear density functional Kohn-Sham equations. We first outline a solution strategy based on the Newton-Raphson method. A form of the algorithm is then applied to the simplest and earliest density functional model, i.e., the atomic Thomas-Fermi model. For the neutral atom, we demonstrate the effectiveness of a charge conserving Newton-Raphson iterative method for the computation, which is independent of the starting guess; it converges rapidly, even for a randomly selected normalized starting density.

A technique for calculating the characteristic impedance of top metal-covered coplanar waveguide (TCPW) transmission lines using a neural network is presented in this paper. Additionally, the technique is extended to calculate their attenuation constant. Analytical expressions based on conformal mapping techniques are not applicable when the top cover height is < 3 µm. Further, there are no analytical expressions available to calculate their attenuation constant. We used a feed-forward artificial neural network to calculate the characteristic impedance and attenuation constant of TCPWs. The results are compared with those obtained using ANSYS HFSS full-wave simulation software, which shows good agreement. This technique will be useful for equivalent circuit modeling of RF-MEMS.

Oxide thin-film transistors (TFTs) and metal–oxide–semiconductor field-effect transistors (MOSFETs) operate via different conduction mechanisms but exhibit similar device characteristics. In this work, a SPICE level 3 model originally defined for MOSFETs is successfully adapted to provide a behavioral model for oxide TFTs. This adapted compact model is applicable to all kinds of oxide TFTs, irrespective of the channel and dielectric material used. To capture the TFT behavior efficiently, the experimental characteristic of an oxide TFT is used to set various SPICE level 3 parameters.

Thermoelectrics are a promising class of materials for renewable energy owing to their capability to generate electricity from waste heat, with their performance being governed by a competition between charge and thermal transport. A detailed understanding of energy transport at the nanoscale is thus of paramount importance for developing efficient thermoelectrics. Here, we provide a comprehensive overview of the methodologies adopted for the computational design and optimization of thermoelectric materials from first-principles calculations. First, we introduce density-functional theory, the fundamental tool to describe the electronic and vibrational properties of solids. Next, we review charge and thermal transport in the semiclassical framework of the Boltzmann transport equation, with a particular emphasis on the various scattering mechanisms between phonons, electrons, and impurities. Finally, we illustrate how these approaches can be deployed in determining the figure of merit of tin and germanium selenides, an emerging family of layered thermoelectrics that exhibits a promising figure of merit. Overall, this review article offers practical guidelines to achieve an accurate assessment of the thermoelectric properties of materials by means of computer simulations.

A fully quantum mechanical approach must be utilized to investigate the characteristics of nanoscale semiconductor devices and capture the essential physics with high accuracy. In this work a very efficient quantum mechanical transport simulator based on Contact Block Reduction (CBR) method is used to analyze the behavior of 10 nm FinFET device in the quasi-ballistic regime of operation. Simulation results depict the transformation of multiple channels into a single merged channel across the fin as the fin width is reduced gradually. Also we observe that short channel effects can be minimized by reducing the fin thickness, which is evident from the device transfer characteristics for different fin thickness presented in this paper. A comparison of simulation results with the available experimental data is presented. An optimized 10 nm gate length FinFET structure is suggested.

A drain current model for an AlGaN/GaN high-electron-mobility transistor (HEMT) with variable thermal resistance is developed. For the first time, a variable thermal resistance in terms of the substrate thickness $$(t_{\text{SiC}} )$$ is included rather than a constant thermal resistance. One of the distinguishing features of this model is that it is scalable with substrate thickness. The compact drain current model is compared with simulated characteristics for different substrate thicknesses (tSiC = 100 μm, tSiC = 200 μm, and tSiC = 300 μm). The proposed model clearly captures the self-heating effect well in the saturation region of the drain current at an ambient temperature of 300 K. The transfer and transconductance characteristics of the model show good correlations with both experimental and simulation data under a wide range of bias conditions. Furthermore, the smoothness of the model is confirmed by Gummel symmetry and continuity tests. Hence, the proposed model is compact and considered to be a promising candidate for GaN-HEMT circuit simulation.