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We report the development of a process/device simulation platform to model superconductor electronics. The process simulator leverages the back-end modeling capabilities of Florida object-oriented process/device/reliability simulator (FLOOXS) and builds on the existing models to simulate processes specific to Josephson junction (JJ) fabrication. The device simulator uses the process generated models and computes the normal-state electrical properties of a Nb/Al-AlO/Nb JJ. It is used to predict key operational figures of merit and how they vary with changes in process models. By integrating the process and device simulation tools, this research aims to offer an environment for the simulation of JJ circuits.

By modeling the propagation of a seed layer with various crystal orientations, this study explores the influence of process variations on grain formation with the help of a physics-based process simulator. Grain boundaries allow easy diffusion of foreign atoms through the lattice, which causes Al to move inside the Nb bottom electrode layer and more interestingly, O to penetrate through the Al layer during oxidation and create a barrier with non-uniform thickness. In addition to thickness variations, the grain structure exhibited by Nb and Al can cause significant suppression of supercurrent at the boundaries depending on the degree of lattice mismatch, impurity deposition, etc. This work details the process simulation of grain boundary formation and aims to provide geometrical models that may be used in the simulation of device performance to account for process-induced variations.

Some packaging technologies of electronic devices introduce compressive biaxial stress and variable vertical stress. In unipolar MOS devices, stress variations typically only linearly affect drain current via carrier mobility. Collector currents of bipolar devices are additionally affected by variations in intrinsic carrier concentration. This leads to increased variability of key device parameters in the compressive stress regime. Reducing package-induced compressive stress, or inducing tensile stress, should improve device variability due to local stress variations.

TCAD has been a useful tool for device design for decades. Radiation damage of devices requires accurate simulation of how charges move and are trapped, and the trap populations. This paper describes a simulation capability for these classes of problems and provides examples demonstrating its usefulness for investigation of device failure.

A flipped-classroom approach was implemented in a Circuits I class for electrical and computer engineering majors to lower its high attrition and failure rate. Students were asked to watch online lectures and then come to class prepared to work problems in small groups of four. The attitude, retention, and performance of students in the flipped group in Spring 2013 were compared to those for the traditionally taught group in Fall 2012. The Fall 2012 lectures were recorded, so that each group saw the same lectures. Student retention and test performance was significantly higher in the flipped course. In Fall 2012, 56% of the initially enrolled students received a C or better. In Spring 2013, this improved to 83%. The first exam scores were significantly better in Spring 2013, and this helped with student success. The authors believe that it was the alignment of online lectures, face-to-face student/teacher and peer/peer interactions, combined with the active learning component of the flipped classroom that led to these improvements .

A combination of TRIM and FLOODS models the effect of radiation damage on AlGaN/GaN HEMTs. While excellent fits are obtained for threshold voltage shift, the models do not fully explain the increased reliability observed experimentally. In short, the addition of negatively-charged traps in the GaN buffer layer does not significantly change the electric field at the gate edges at radiation fluence levels seen in this study. We propose that negative trapped charge at the nitride/AlGaN interface actually produces the virtual-gate effect that results in decreasing the magnitude of the electric field at the gate edges and thus the increase in critical voltage. Simulation results including nitride interface charge show significant changes in electric field profiles while the I-V device characteristics do not change.

A model for radiation-induced interface-trap buildup distinguishes among the contributions of hydrogen dimerization, electron recombination, and electric field mechanisms, quantitatively explaining time-dependent and true dose rate effects in irradiated bipolar isolation oxides. Hydrogen dimerization is the dominant ELDRS mechanism for devices exposed to medium H2 concentrations (1% per volume), whereas H2 cracking dominates as H2 concentration is increased further. Electron recombination mechanisms contribute at high dose rates ( >; 100 rad(SiO2)/s), but are not the dominant ELDRS mechanism at dose rates lower than 100 rad(SiO2)/s).

Interface-trap buildup and annealing are examined as a function of temperature, dose rate, and H2 concentration using a physics-based model. The roles of a number of common oxide defects in radiation-induced interface-trap buildup are evaluated under various conditions. Defects near the interface play a significant role in determining interface-trap buildup by trapping protons as proton concentration and temperature increase.

Electronic structure calculations and irradiation measurements are used to obtain insight into oxide trapped charge mechanisms in varying hydrogen ambients. Quantitative agreement between measured and simulated oxide and interface-trap charge densities is obtained over a wide range of H $_{2}$ concentrations by implementing first-principles calculations of the energetics, and dynamics of charge transport and trapping, into TCAD simulations of irradiated MOS structures. Hole trapping dominates for typical H $_{2}$ densities, but protons can dominate at high H $_{2}$ densities. The rate of the interface trap reaction, in which protons that are liberated from charged oxygen vacancies by molecular hydrogen form dangling bonds on the interface, is found to play a key role in determining the relative concentrations of oxide and interface-trap charge densities.

A physics-based TCAD model for enhanced low-dose-rate sensitivity in linear bipolar devices is developed. Quantitative agreement is found with measured data over a wide range of dose rates and H2 concentrations. Analysis of the degradation effects of individual defect types, the implementation of which has been informed by first principles calculations, provides insights into the mechanisms behind enhanced low-dose-rate effects in different hydrogen environments. The effects of initial defect concentration and location and the energetics of the defect-related reactions are explored. Conclusions are drawn about the roles of molecular hydrogen and hydrogenated defects in the radiation response of these devices.

In this brief, a 60-GHz frequency synthesizer for wireless personal area networks is designed using 0.13- μm CMOS technology. The synthesizer operates at 60 GHz with phase noises of -98, -117, and -128 dBc/Hz at 1-, 10-, and 40-MHz frequency offsets, respectively. The 60-GHz clock is generated by combining a phase-locked loop (PLL) and an injection-locked oscillator. The PLL provides frequency tuning of the 60-GHz voltage-controlled oscillator (VCO) using replica tuning. A pulse train is generated using a novel passive delay-locked loop and a CMOS pulse generator. This pulse train is then used for filtering the phase noise of 60-GHz VCO up to a high offset frequency. The total power consumption of the frequency synthesizer is 57 mW with a 1.2-V power supply.

The results of semiconductor device simulations are highly dependent on the electron and hole mobility models. The manner in which mobility is modeled at high-injection levels is especially important for single-event upset simulations due to the large number of electron-hole pairs generated along a particle strike path. This paper presents an approach to modeling mobility that describes majority and minority carrier mobility, carrier-carrier scattering, and temperature dependence in a computationally efficient form relevant for radiation effects simulations in silicon.

Laser-induced current transients are measured on uniaxially stressed silicon (Si) N+/P diodes using a high speed measurement system. Controlled external mechanical stress along the (110) direction is applied via a four-point bending jig while the samples are irradiated using a cavity-dumped dye laser with a wavelength of 590 nm. A decrease in the peak current is observed for increasing tensile stress applied to the diode. Unlike tensile stress, compressive stress increases the peak current. Charge collection is observed to decrease with tensile and increase with compressive stress. These results suggest that uniaxial mechanical stress alters the current transients due to strain-induced changes in electron mobility along the (001) direction. The average effective electron mass along the (001) direction increases with tensile and decreases with compressive stress resulting from the splitting of degenerate conduction band valleys and the repopulation of electrons from higher to lower valleys. The Florida object oriented device simulator (FLOODS) is used to explain the mechanism of current transients in unstressed and stressed diodes. FLOODS is also used to predict results for values of applied stress ( ~ 1 GPa) beyond those that can be obtained using the bending jig (~ 240 MPa).

Reactions of H2 in lateral PNP BJTs are investigated through experiments and simulations. Pre-irradiation hydrogen exposure makes the devices more sensitive to ionizing radiation, which is explained through first-principles calculations and numerical simulations. Mechanisms for the cracking of hydrogen molecules and proton generation are proposed. We also suggest a mechanism of formation of border traps. When protons are trapped by oxygen vacancies right at or very near the interface, they form electrically active defects near the middle of the band gap. Activation energies of the reaction are used to construct rate equations. The rate equations are solved numerically to determine the spatial and temporal concentrations of hydrogen, holes, and protons. The calculated concentrations of interface and border traps agree well with the experimental results and help to explain the role of hydrogen in determining the total-dose response of BJTs.

This brief presents a new quadrature phase-shift keying (QPSK) modulator for Bluetooth applications with an optimal transaction bandwidth control. The modulator reduces the bandwidth of the modulated carrier by minimizing their transition sharpness. CMOS active transformers are developed and utilized in quadrature oscillator and multiplexer of the modulator to provide comparable phase noise performance without using spiral inductors and transformers. The performance of the modulator is assessed using a 1.6-GHz QPSK base-band modulator implemented in TSMC 0.18-mum 1.8-V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3v3 device models. The total transistor area and power consumption of the modulator are 2840 mum2 and 30 mW, respectively. The phase noise of the quadrature oscillator is 110 dBc/Hz at 500-kHz frequency offset.

The Moderate Resolution Spectroradiometer (MODIS) sensor has provided near real-time estimates of gross primary production (GPP) since March 2000. We compare four years (2000 to 2003) of satellite-based calculations of GPP with tower eddy CO2 flux-based estimates across diverse land cover types and climate regimes. We examine the potential error contributions from meteorology, leaf area index (LAI)/fPAR, and land cover. The error between annual GPP computed from NASA's Data Assimilation Office's (DAO) and tower-based meteorology is 28%, indicating that NASA's DAO global meteorology plays an important role in the accuracy of the GPP algorithm. Approximately 62% of MOD15-based estimates of LAI were within the estimates based on field optical measurements, although remaining values overestimated site values. Land cover presented the fewest errors, with most errors within the forest classes, reducing potential error. Tower-based and MODIS estimates of annual GPP compare favorably for most biomes, although MODIS GPP overestimates tower-based calculations by 20%-30%. Seasonally, summer estimates of MODIS GPP are closest to tower data, and spring estimates are the worst, most likely the result of the relatively rapid onset of leaf-out. The results of this study indicate, however, that the current MODIS GPP algorithm shows reasonable spatial patterns and temporal variability across a diverse range of biomes and climate regimes. So, while continued efforts are needed to isolate particular problems in specific biomes, we are optimistic about the general quality of these data, and continuation of the MOD17 GPP product will likely provide a key component of global terrestrial ecosystem analysis, providing continuous weekly measurements of global vegetation production

The simulation of generation-recombination (GR) noise under periodic large-signal conditions in a partial differential equation-based silicon device simulator is presented. Using the impedance-field method with cyclostationary noise sources, it is possible to simulate the self- and cross-spectral densities between sidebands of a periodic large-signal stimulus. Such information is needed to develop noise correlation matrices for use with a circuit simulator. Examples are provided which demonstrate known results for shot noise in bipolar junction transistors. Additional results demonstrate the upconversion of low-frequency GR noise for microscopically cyclostationary noise sources and provide evidence for applying the modulated stationary noise model for low-frequency noise when there is a nearly quadratic current dependence.

Carrier trapping via tunneling into the gate oxide was implemented into a partial differential equation-based semiconductor device simulator to analyze the 1/f-like noise in silicon MOSFETs. Local noise sources are calculated using the carrier tunneling rates between trap centers in the oxide and those at the interface. Using the Green's transfer function approach, noise contributions from each node in the oxide mesh to the overall noise at the specified contact terminals are simulated. Unlike traditional 1/f noise analyses in MOSFETs, the simulator is capable of simulating noise for a wide range of bias voltages and device structures. The simulation results show that for an uniformly doped channel, the region in the oxide above the pinch-off point in saturation is most critical for low frequency noise generation while for a graded channel device the source side of the gate oxide region becomes important. By comparing the simulation results with the measured noise data, the oxide defect density in the noise producing regions can be profiled.

Integrating the entire system on a chip (SoC) is one of the main challenges for many researchers all over the world. One of the major breakthroughs toward achieving this goal has been the ability to manufacture multiple gate oxides for different requirements on the same chip. The most attractive of the techniques currently in the literature is the implantation of nitrogen in silicon, which can be used to achieve the goal of multiple gate oxide thickness. The rate of oxidation depends on the amount of nitrogen incorporated at the silicon/silicon oxide interface. By modulating the amount of nitrogen incorporated at the interface, the rate of oxidation and hence the oxide thickness can be moderated. This paper reviews the diffusion, oxidation, and device issues pertaining to the use of nitrogen implants in silicon and also compares it to other implant-based techniques related to the achievement of multiple oxide thickness across the chip for SoC integration.

Nonmelt laser annealing has been investigated for the formation of ultrashallow, heavily doped regions. With the correct lasing and implant conditions, the process can be used to form ultrashallow, heavily doped junctions in boron-implanted silicon. Laser energy in the nonmelt regime has been supplied to the silicon surface at a ramp rate greater than 10/sup 10//spl deg/C/s. This rapid ramp rate will help decrease dopant diffusion while supplying enough energy to the surface to produce dopant activation. High-dose, nonamorphizing boron implants at a dose of 10/sup 15/ ions/cm/sup 2/ and energies of 5 KeV and 1 KeV are annealed with a 308-nm excimer laser. Subsequent rapid thermal anneals are used to study the effect of laser annealing as a pretreatment. SIMS, sheet resistance and mobility data have been measured for all annealing and implant conditions. For the 5-KeV implants, the 308-nm nonmelt laser preanneal results in increased diffusion. However, for the 1-KeV implant processed with ten laser pulses, the SIMS profile shows that no measurable diffusion has occurred, yet a sheet resistance of 420 /spl Omega//sq was produced.

Full-thermodynamic device simulation solves drift-diffusion (DD), energy balance, and lattice self-heating equations simultaneously and the solution time is extensive. An algorithm to reduce the solution time is presented. The method uses a single lattice temperature to describe the self-heating in the whole semiconductor device. It is shown that the solution time is reduced by 20% and little error is induced compared with the full-thermodynamic simulations. This approach appears useful for submicron device structures.

During simulation of silicidation and oxidation, some layers are consumed (poly, silicon) and other layers grow (oxide, silicide). During these growth processes, grid must be added behind the advancing interface and removed in front of it. In a full integrated circuit process simulator, this has to be performed simultaneously with the transient solution of the diffusion equations for silicon dopants. This paper describes an approach of local adaption that leaves unchanged most of the grid. Robust algorithms are described for handling adaption in two-dimensional process simulation. Examples for etching, deposition, and oxidation are described. >

C++ and object-oriented programming techniques are becoming popular for their modularity, ease of use, and simplicity to maintain and enhance. This paper describes an approach used for device simulation. The object library and organization are described. Specific areas of modularity and enhancement are illustrated in both the areas of physical models and mathematics. Comparisons of both performance and ease of enhancement are made to PISCES-II. >

As device technologies improve, the traditional drift-diffusion transport model becomes inadequate to predict the performance of state-of-the-art semiconductor devices. The reasons are believed to be the larger field and field gradient inside advanced devices which cause lattice heating and hot carrier nonlocal transport phenomena. For more accurate prediction on device performance, a new device simulator capable of full thermodynamic simulation was developed. The carrier and carrier energy transport equations are directly derived from the Boltzmann transport equation, and the energy transfer among electrons, holes and crystal lattice takes into account most of the possible mechanisms. This simulator was used to simulate the DC behavior of a BJT and a half-micron NMOS. The simulation results show that for advanced devices, not only the drift-diffusion model becomes inadequate, but including only one of the two thermal effects results in error in simulated device characteristics. >

Generation-recombination noise associated with bulk defect levels in silicon is modeled in a partial differential equation-based device simulator to study the maximum allowable defect density that guarantees generation-recombination (g-r) noise-free operation in the presence of hot-carrier effects and space-charge injection.

The authors point out that modern numerical process simulators are becoming increasingly complicated in both physical models and domain shape. Grid generation is difficult for these simulators because of the inherently transient nature of the problems being solved. Here, adaptive grid refinement is considered for use in solving diffusion problems. Higher order approximations to the discretized diffusion flux are also studied. Several methods of both adaptive grid refinement and discretization are investigated and compared in terms of CPU time and final discretization error. All the methods are directly applied to the one-dimensional version of SUPREM-IV. >

An adaptive grid scheme for single-event upset device simulations is presented. Single-event transient simulations for a reverse-biased N + /P diode and nMOSFET were performed using the adaptive grid scheme, a customized grid scheme and a uniform grid scheme. Results show that adaptive gridding can offer significant simulation time savings while preserving accuracy.

Point-defect kinetics is important for understanding and modeling dopant diffusion in silicon. The author describes models for point-defect transport and recombination used in SUPREM-IV, and does extensive fitting for the model parameters. The experimental data used are from experiments on oxidation-enhanced diffusion. Interstitial traps are shown to be critical for consistent agreement with experiment data. Point-defect parameters in lightly doped regions are extracted and fit to Arrhenius expressions. >

A model for damage enhancement that is suitable for two-dimensional simulation is proposed. The formation of arsenic and phosphorus junctions is an important process step in modern device fabrication. The accurate prediction of the vertical and lateral profile is crucial for optimization of the device behavior and reliability. Experimental data show that the damage from implantation of the dopant species has an important and controlling effect on the final profile during low-temperature annealing. Modeling of the dopant and point defect interaction during this anneal indicates that the junction is determined by the number of point defects created during the implantation. Calibration is performed by using one-dimensional experimental work on both boron and arsenic/phosphorus junctions. Two-dimensional calculations are performed and compared to experimental device data. >

The implementation of an improved small-signal AC simulation capability in the general-purpose device simulator PISCES-IIB is described. The preconditioned generalized conjugate residual (GCR) algorithm has been implemented, which allows AC simulations to be performed up to any frequency without convergence problems, although at great computational expense. The current implementation of PISCES-IIB uses the block successive overrelaxation algorithm for AC simulations. This algorithm fails at high frequencies, thus making it impossible to determine accurately the cutoff frequency and switching speed of high-frequency devices. The preconditioned GCR algorithm has been implemented using two different preconditioners. A comparison of the three methods shows that they are most efficient at different frequency ranges, allowing programming of an automatic switching algorithm that chooses the most efficient simulation method. >

A self-consistent approach is proposed for extracting the minority-carrier mobility from fits to experimental data for lifetime and diffusion length and then comparing the extracted mobility to experimental mobility data. A value for electron and hole lifetime is extracted using a doping-dependent Shockley-Read-Hall mechanism with an Auger process. The hole lifetime is used to extract a minority carrier hole mobility that is consistent with the reported measurements of the hole diffusion length. The good agreement between extracted and experimental mobilities justifies incorporating the results into numerical device and circuit CAD tools. >

Germanium doping in silicon tends to suppress any enhancement in dopant diffusion due to excess point defects. By performing a dual implantation of germanium and the normal source-drain dopant, lateral diffusion of the source-drain profile can be controlled, thus resulting in improved short-channel device behavior. >

Two-dimensional process modeling has been complicated by the increasing complexity of the physical models needed to characterize modern processes. Present physical models for diffusion favor modeling of both the vacancies and interstitials as well as the dopant impurities. these vacancies and interstitials are important in two dimensions since the lateral characteristic lengths are on the order of a few microns, which is comparable to device dimensions. Hence, full two-dimensional solutions of the point defect equations are required to accurately model two-dimensional diffusion. Since the defects diffuse many order of magnitude faster than the impurities, the problem of solving the coupled equations is numerically stiff and the numerical techniques become critical. The numerical methods in SUPREM-IV are described. Since the numerical solutions are time consuming, suitable analytic solutions are considered as an alternative. These analytic solutions are compared to the numerical results to test the limits of the assumptions used in the analytic formulation. The comparison forces the conclusion that analytic solutions are of limited use in prediction of point defect profilesin two dimensions. >