Rigorous Electromagnetic Simulation Research Articles

Alternative A-gate structures for the realization of semiconductor quantum computers

Two new A-gate structures for the realization of the qubit for the semiconductor quantum computer are proposed and investigated rigorously by a numerical simulation method. The coplanar A-gate structure has the advantage of easy fabrication, but it offers only a relatively weak voltage control over the nuclear magnetic resonance (NMR) frequency of the donor atom. However, this short-coming can be overcome by doping the donor closer to the substrate interface. The split-ground A-gate structure, on the other hand, produces a similar potential distribution as that of the original Kane's A-gate structure and provides a relatively stronger control over the NMR frequency of the donor atom. Both structures have the advantage of allowing device integration or heterostructure fabrication from below the silicon substrate. All simulations in this study are carried out by a rigorous electromagnetic simulation tool plus a quantum mechanical perturbation theory.

Perturbation Theory in the Design of Degenerate Spherical Dielectric Resonators

The design of resonators with degenerate magnetic and electric modes for negative-index metamaterial applications usually requires the ability to perturb one or both types of modes in order to induce alignment of the negative magnetic and electric properties. The incentive behind the resonator designs presented in this paper is to minimize both the losses and the size of the unit cell, particularly in the case of high frequencies such as the infrared or visible. Thus, the designs discussed in this paper are based on degenerate-mode (the fundamental magnetic and electric modes are aligned in frequency) spherical dielectric resonators which rely on only a single-particle resonator and thereby do not require physical or electrical extensions of the unit cell, as might be seen with other negative-index unit cell designs. Cavity-perturbation techniques are used to arrive at the types of inclusions (in terms of material, polarization, and placement) that are necessary to realize a degenerate spherical dielectric resonator, as well as to derive simple formulas which can be used for the design of these types of resonators. Rigorous electromagnetic simulations of the degenerate resonators are also provided for comparison to the theoretical derivations.

Simple Composite Dipole Model for the Optical Modes of Strongly-Coupled Plasmonic Nanoparticle Aggregates

Self-assembled strongly coupled plasmonic aggregates exhibit optical spectra which show complex plasmonic resonances. To understand the optics of such systems, we introduce an effective composite dipole model extending previous effective models of aggregates into the plasmonic domain. The ingredients in this model are found by comparing the time-resolved extinction of self-assembling growing aggregates of gold nanoparticles spaced by rigid sub-nm gaps to recent rigorous electromagnetic simulations of this geometry. The highly reproducible spectral signatures from experiments match our simulations, confirming that the electromagnetic response of such fractal plasmonic clusters can be well-understood in terms of embedded straight chains of plasmonically coupled nanoparticles surrounded by an optically decoupled halo of dimers. We show how to derive simple analytical formulas that lead to rapid extraction of key parameters from such experimental spectra and which properly account for the long-wavelength lineshapes. In particular, we find these effective parameters describe the extent of plasmon delocalization along such chains, the eccentricity of these optically dominant cores, and the fraction of nanoparticles active within them. This underpins applications which depend on spectral selectivity and field enhancements in such tightly coupled plasmonic systems.

Rigorous electromagnetic field simulation of the impact of photomask line-edge and line-width roughness on lithographic processes

The impact of edge profile roughness of the absorber lines on an optical photomask has been studied by means of rigorous electro-magnetic field (EMF) simulation for the mask diffraction spectrum and subsequent imaging. Roughness has been modeled using two different approaches, a sinusoidal description and an algorithm known from literature-based on Fourier transformation. The latter can arbitrarily create rough profiles and surfaces based on the three morphological parameters standard deviation σ, roughness exponent α, and correlation length ξ. In this study, the standard deviation has been kept fixed while varying the remaining two morphological parameters, still showing impact on the lithographic process. A software interface for use of the generated profiles with the Waveguide EMF solver of the Dr.LiTHO lithography simulation suite has been implemented. It was shown by means of image analysis and study of the resulting process windows that mask roughness is partially transferred to the aerial image. Isolated and dense features behave differently, leading inter alia to an iso-dense bias different to that of ideal lines. Due to the roughness, process windows now depend on the position along the line. Determing process windows at multiple positions for statistical analysis implies a reduction of the effective process window. Correlation length ξ has shown to be an important parameter and, thus, morphology should not be ignored in the modeling of rough lines. Tapered sidewalls can add to the shift of the process windows in the same order of magnitude.

Scanning effects in coherent fourier scatterometry

Incoherent Fourier Scatterometry (IFS) is a successful tool for high accuracy nano-metrology. As this method uses only far field measurements, it is very convenient from the point of view of industrial applications. A recent development is Coherent Fourier Scatterometry (CFS) in which incoherent illumination is replaced by a coherent one. Through sensitivity analyses using rigorous electromagnetic simulations, we show that the use of coherence and multiple scanning makes Coherent Fourier Scatterometry (CFS) more sensitive than Incoherent Fourier Scatterometry (IFS). We also report that in Coherent Fourier Scatterometry it is possible to determine the position of the sample with respect to the optical axis of the system to a precision dependent only on the experimental noise.

Toward building full-system EMI verification and early design flows through full-wave electromagnetic simulation

Package and PCB-system aware IC co-design and verification entail early awareness of the impact of signal integrity, power integrity, timing, and electromagnetic interference (EMI) impact on functionality and performance. Higher frequencies, along with stringent EMC regulations, are driving the need for developing EMI-aware design methodologies in early and sign-off phases of design cycles. This article discusses the significant challenges of scale, connectivity, turnaround time, and accuracy needed in developing such a flow. In particular, the numerical effect of violating established EMI guidelines is quantified in the flow, enabling cutting-edge designs that are less conservative and still satisfy EMI constraints. The role of rigorous large-scale 3D full-wave electromagnetic simulation in developing such a full-system EMI prediction and early design flow is discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Insulator—insulator—metal plasmonic waveguide for parasitic scattering suppression in plasmonic optics

We have shown using rigorous electromagnetic simulations that a planar structure consisting of two isotropic dielectric layers can be used to reduce parasitic scattering in plasmonic elements by an order-of-magnitude (to 1–3%). The proposed approach can be used for designing various plasmonic elements such as lenses, Bragg reflectors and plasmonic crystals.

Scattering suppression in plasmonic optics using a simple two-layer dielectric structure

We demonstrate that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering in plasmonic elements. It is shown using rigorous electromagnetic simulations that the utilization of the proposed structure allows reducing the scattering losses by an order-of-magnitude (1%–2%). The proposed approach can be used for the design of various plasmonic elements such as lenses, reflectors, and plasmonic crystals.

Wideband model of on-chip CMOS interconnects using space-mapping technique

A new wideband model for on-chip complementary metal–oxide–semiconductor (CMOS) interconnects is developed by virtue of a space-mapping neural network (SMNN) technique. In this approach, two subneural networks are used for improving the reliability and generalization ability of the model. This approach also presents a new methodology for data generation and training of the two neural networks. Two different structures are used for the two subneural networks to address different physical effects. Instead of the S parameters, the admittances of sub-block neural networks are used as optimization targets for training so that different physical effects can be addressed individually. This model is capable of featuring frequency-variant characteristics of radio-frequency interconnects in terms of frequency-independent circuit components with two subneural networks. In comparison with results from rigorous electromagnetic (EM) simulations, this SMNN model can achieve good accuracy with an average error less than 2% up to 40 GHz. Moreover, it has much enhanced learning and generalization capabilities and as fast as equivalent circuit while preserves the accuracy of detailed EM simulations. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.

Rigorous Three-dimension Electromagnetic Simulations and Optimization for CMOS Image Sensor pixels

The size of pixels in complementary metal-oxide-semiconductor image sensor has steadily decreased during the last decade, which leads to a challenge on maintaining the pixels' optical performance. The diffraction effects result in increased spatial crosstalk and decreased optical efficiency, so rigorous simulation and optimization are important. FDTD method is used to simulate the optical performance and a diffuse-like source is used to reproduce real conditions. A commercial tool from Lumerical Solutions is used to do three-dimension FDTD simulation. The diffuse-like sources are simulated by the uniform sum of several focused beams characterized by a given f-number of the objective len. The typical 1.75μm, 1.45μm and 1.1μm pixels are simulated and analyzed. The results show that the optical efficiency of the pixels decreases dramatically when the pixels size scaling down. Several approaches to produce better device performance for sub-2um pixels are analyzed. Micro-lens optimization, dielectric stack height reduction can decrease the optical power loss and optical confinement realized by an air-gap can reduce the spatial crosstalk. The results show that the optical performances of the optimized 1.1μm pixel are comparable to those of conventional 1.75μm pixel.

NEGATIVE REFRACTIVE INDEX BEHAVIOR THROUGH MAGNETO-ELECTRIC COUPLING IN SPLIT RING RESONATORS

An investigation on the possibility of obtaining a negative refractive index behavior in split ring resonators (SRRs) through magneto-electric coupling is presented. We have performed rigorous electromagnetic simulations using a full-wave 3D simulator, and the obtained results have been verifled by our experimental realizations and measurements. The results conflrm that the increase of magneto- electric gyrotropic activity inside a bi-anistropic medium can lead to the establishment of backward-wave propagation.

Diffractive arrays of gold nanoparticles near an interface: Critical role of the substrate

The optical properties of periodic arrays of plasmonic nanoantennas are strongly affected by coherent multiple scattering in the plane of the array, which leads to sharp spectral resonances in both transmission and reflection when the wavelength is commensurate with the period. We demonstrate that the presence of a substrate (i.e., an asymmetric refractive-index environment) can inhibit long-range coupling between the particles and suppress lattice resonances, in agreement with recent experimental results. We find the substrate-to-superstrate index contrast and the distance between the array and the interface to be critical parameters determining the strength of diffractive coupling. Our rigorous electromagnetic simulations are well reproduced by a simple analytical model. These findings are important in the design of periodic structures and in the assessment of their optical resonances for potential use in sensing and other photonic technologies.

Mask-topography-induced phase effects and wave aberrations in optical and extreme ultraviolet lithography

Rigorous electromagnetic field simulations are applied to investigate phase effects in the light diffraction from masks for advanced optical and extreme ultraviolet lithography. Analogies of these phase effects with wave aberrations of the projection lens and their impact on the lithographic process performance are discussed.

Broadband infrared mirror using guided-mode resonance in a subwavelength germanium grating

We demonstrate a broadband mirror for the IR wavelength region comprising a subwavelength grating made of germanium. We design and optimize the guided-mode resonances in the structure for TM-polarized incident light by rigorous electromagnetic simulations. The grating structure is realized by nanoimprint lithography and dry etching. The reflectivity of the mirror is over 95% for the wavelength range between 2245 and 3080nm.

High-Pass Filtering Characteristics of Transmission-Line Combs

The filtering characteristics of a transmission line loaded at regular intervals with closely spaced shorted stubs are investigated theoretically, experimentally, and by means of rigorous electromagnetic simulations. It is shown that this periodic structure exhibits waveguide-like behavior with a first passband whose width is a function of the characteristic impedance and pitch of the stubs. It is also shown that when the stub pitch vanishes, the structure degenerates into a waveguide whose mode-cutoff frequencies correspond to a shorted-stub length that is an odd multiple of the wavelength. These features enable the design of compact high-pass filters, and make possible cutoff-frequency hopping and tuning. Implementations in microstrip are shown that demonstrate desirable characteristics such as wide bandwidth, low insertion loss, reduced size, easy integration with planar circuits, as well as common and differential-mode filtering, making such structures attractive for use in low-cost microwave and millimeter-wave applications.

Extraordinary optical transmission through multi-layered systems of corrugated metallic thin films

Optical transmission through multi-layered systems of corrugated metallic thin films is investigated by rigorous electromagnetic simulations based on an exact Green tensor method. Compared to a single metal slab of equivalent thickness and volume, it was found that the multi-layered system can significantly impede the field decay, often leading to transmission greater than that expected from the Fabry-Perot resonance-like behavior exhibited by subwavelength slits in a single slab. Extraordinary optical transmission is also observable for systems of layers whose combined thicknesses are much greater than the skin depth of the metal. Structures consisting of up to five layers with a net thickness of 500 nm for the metal films were considered in our study. These findings demonstrate that an appreciable fraction of the optical power that is incident on the thin metal films can be transmitted over distances greater than their skin depth using plasmonic resonances.

A Double-Angular Propagation Model With Cluster Scattering

A statistical multipath propagation model is developed in the double-angular domain to include effects of both angle of departure and angle of arrival. The model is characterized by a discrete stochastic double-angular spectrum of the Green's function between two volumes that communicate with each other in the presence of cluster scattering. The whole modeling process is a combination of theories, assumptions, and numerical verification by rigorous full wave electromagnetic simulations. Notably, an uncorrelated scattering assumption for received fields is extended to the double-angular domain, and the transport theory plays a key role defining the statistical properties of the spectrum of the Green's function. The spectrum is eventually modeled as a random matrix whose entries are uncorrelated zero-mean complex Laplacian random variables. The real and imaginary parts of the matrix entries are independent and identically distributed, and the variance profile follows the reduced incident intensity of the waves through random media. The parameters of the model are completely obtained from bulk statistical knowledge of the scattering environments, and the resulting model demonstrates good performance on EM DOF and MIMO capacity estimation.

Plasmon-enhanced optical transmission of nanostructured metallic multilayers

Surface plasmons (SPs) – charge oscillations on metallo-dielectric interfaces – offer the possibility of controlling light at a scale much smaller than its wavelength, even down to the nanometre scale for visible wavelengths. Experiments have been performed to study the influence of SPs on the optical transmission of metallic multilayers in which one of the layers has been patterned at the nanometre scale to excite localised and extended SP modes. Films with linear gratings or two-dimensional hole arrays have been studied, and exceptionally-high transmission levels (up to 39%) are measured for these otherwise-opaque systems. The transmission resonances can be designed to be much narrower than for an equivalent Fabry-Perot filter, and can be tuned with geometrical parameters (film thicknesses and/or grating dimensions) or illuminations conditions (angle of incidence or polarisation). The measured dispersion of the transmission maxima agrees with the theoretical dispersion of extended surface plasmon polariton (SPP) modes on a planar metal film, which strongly suggests that the excitation of these SPP modes is responsible for the transmission features. This is further supported by rigorous electromagnetic simulations.

Optical focusing of plasmonic Fresnel zone plate-based metallic structure covered with a dielectric layer

By modulating the zone width of a plasmonic Fresnel zone plate, consisting of metallic nanostructures covered with a dielectric layer, the authors demonstrated numerically that a focused beam can be achieved with higher intensity and smaller spot size than the diffraction-limited conventional Fresnel zone plate. Rigorous electromagnetic simulation predicts a full width at half maximum of 162nm (equivalent to an effective numerical aperture of 1.30) at 0.5μm focal length, using 405nm wavelength illumination. This sub-diffraction-limit focusing has potential in applications such as maskless nanolithography, high resolution scanning optical microscopy, optical data storage, and optical antenna. This focusing capability is related to extraordinary optical transmission, which is explained by the complex propagation constant in the zones afforded by higher refractive index dielectric layer and surface plasmons.

Fabrication and characterization of optimized corner-cut square microresonators

In this paper we report the fabrication and characterization of waveguide coupled square resonators with modified corners, in particular the corner-cut square resonator. We employ rigorous FDTD analysis to identify an optimal corner-cut length and compare this with our experimental findings. Two- and three dimensional FDTD analysis is also used to optimize the coupling gap and the width of the coupling waveguide. Fabrication of the square microresonators on silicon-on-insulators by conventional E-beam lithography and dry etching techniques will be discussed in detail. The characterization of these corner-cut square microresonators shows good performance and excellent agreement with the rigorous electromagnetic simulations.