International Journal of High Speed Electronics and Systems

As novel theories and uses of carbon nanotubes (CNT) advance, it becomes increasingly important to characterize the methods of production. One such method of CNT production uses a liquid phase precursor (hydrocarbon with nanoparticle catalyst mix) that is injected into a tube furnace with a flowing carrier gas. The CNTs are grown in high purity and are collected on the surface of the quartz tube. The system allows for a number of variables to be tested such as growth temperatures, flow rate of the carrier gas, precursor injection rates and variations of precursor mix however, here only thermal effects are considered. Under thermal conditions ranging from 500 to 850°C, multi-walled carbon nanotubes (MWCNTs) are synthesized and characterized to determine inner and outer diameter as well as tube thickness.

The present contribution provides a strategy to enhance the dielectric constant of polyethylene by chemical modification while not overly compromising its large band gap. Isolated polyethylene chains are considered and the CH2 motifs in the backbone are allowed to be substituted by a number of Group 14 motifs, including SiF₂, SiCl₂, GeF₂, GeCl₂, SnF₂, and SnCl₂, in a systematic, progressive, and exhaustive combinatorial manner. Our results indicate that consecutive SnF₂ or GeF₂ motifs in the polyethylene backbone are most desirable, which can lead to systems with dielectric constant as high as 47.

Germanium nucleation on a silicon surface typically proceeds via spontaneous formation of nanoscopic islands, or quantum dots (QDs), at random locations. However, potential applications of epitaxial QDs, such as quantum cellular automata, require precise control of Ge island positions on Si in clusters with the individual islands' separation of tens of nanometers or less. Controlled Ge island placement with an inter-island separation down to 100 nm can be reliably obtained by depositing Ge onto a Si(001) surface modified with a low dose focused ion beam (FIB) pattern to create preferred nucleation sites for individual islands. Here we investigate QD self-assembly of multiple islands on single topographical features intended to obtain clusters of QDs with smaller separations. We observe formation of 50 nm clusters on a single location defined by the FIB patterning of a larger and shallower feature, where cluster formation is promoted by reduced surface diffusion. We also discuss cluster formation on single sites defined by residual trenches on a footprint of a larger island that has been desorbed. We propose that controlled placement of islands during the first deposition may result in greater control over subsequent cluster size and placement fidelity due to improved uniformity of target features.

A diode with a quantum dot superlattice on silicon has been reported. Step-wise features are shown in the diode output characteristic, which can be explained by the presence of mini-energy bands in the structure. The theory regarding quantum dot superlattice is also presented.

Metamorphic semiconductor devices are commonly fabricated with linearly-graded buffer layers, but equilibrium modeling studies suggest that S-graded buffers, following a normal cumulative distribution function, may enable lower threading defect densities. The present work involves a study of threading dislocation density behavior in S-graded ZnS_xSe_1-x buffer layers for metamorphic devices on mismatched GaAs (001) substrates using a kinetic model for lattice relaxation and misfit-threading dislocation interactions. The results indicate that optimization of an S-graded buffer layer to minimize the surface threading dislocation density requires adjustment of the standard deviation parameter and cannot be achieved by varying the buffer thickness alone. Furthermore, it is possible to tailor the design of the S-graded buffer layer in such a way that the density of mobile threading dislocations at the surface vanishes. Nonetheless, the threading dislocation behavior in these heterostructures is quite complex, and a full understanding of their behavior will require further experimental and modeling studies.

Surface Acoustic Wave (SAW) propagation on the surface of a piezoelectric crystal is used as a carrier of information. SAW Sensors are micro-electromechanical systems (MEMS) in which high frequency acoustic waves travel close to the surface of a piezoelectric substrate. Because of confined acoustic energy near the surface within the range of one acoustic wavelength, SAW devices are highly sensitive for surface perturbation such as molecular absorption or adsorption and change of viscoelastic properties. Surface acoustic wave (SAW) devices are very promising in providing a high-performance sensing platform with wireless and remote operational capabilities. Research focus is on studying methods to characterize conductance, susceptance, viscosity, and other properties of protein samples, like albumin using SAW related resonator devices quickly and inexpensively using quantities of less than one Nano-liter. Applied pressure or bending of the quartz sets up a condition where a separation of charge occurs (due to change in dipole moment density). The potential difference is proportional to the magnitude of stress. When a mass is deposited on the electrode the resultant decrease in resonant frequency can detect mass changes at nanogram level. We propose to advance the sensitivity of the characterization by use of quartz SAW resonators since they can operate at much higher frequency than bulk wave oscillators.

Crystalline lattice point defects in integrated circuit can lay hidden below the silicon surface exist in the atomic lattice point structure or as interstitials. Initially they may not necessary represent an electrical failure but can act as seeds for electrical degradation in a time period. This paper study one category of Silicon defect “Dislocation loops” that initially were dormant then propagated under the silicon surface in the crystal lattice structure causing catastrophic EOS damage. This is particularly true if the crystalline defect exists near or at the boundary of PN junctions. This paper present evidence of dormant crystalline lattice defects in the form of crystalline dislocation loops degrading to EOS. Over a period of time under normal operation life of the part these dislocation loops can trigger EOS/ESD events.

The electronics industry uses high volumes of heavy metals in its production processes. Many of these heavy metals can end up in water and can be very difficult to remove due to the different forms that the heavy metal can exist in. Special design characteristics should be used to produce filters to remove heavy metals. In this study, we identify the different species of heavy metals and describe a method that has been tested for removing all types of species for heavy metals from water. This filtration technique utilizes multiple layers to ensure the removal of soluble, insoluble and complex species of heavy metals in water. The testing was done with a complex solution of lead according to NSF/American National Standards Institute (ANSI) standard 53 for the removal of lead at pH 8.5, using a combination of soluble, particulate and semi-insoluble lead. Filters were compared to standard, commercially available, gravity pitcher filters. The testing showed that the newly designed filter removed over 80 gallons of lead below the drinking water limit, compared to a standard filter which failed immediately. When trying to remove heavy metals from water, special care needs to be used in the design of the system to ensure the removal of all species of heavy metals.

Integrated optics is a promising optical platform both for its enabling role in optical interconnects and applications in on-chip optical signal processing. In this paper, we discuss the use of group III-nitride (GaN, AlN) as a new material system for integrated photonics compatible with silicon substrates. Exploiting their inherent second-order nonlinearity we demonstrate and second, third harmonic generation in GaN nanophotonic circuits and high-speed electro-optic modulation in AlN nanophotonic circuits.

In this paper, we are presenting fast digital to analog convertor designs using Spatial Waveform Switched FETs (SWSFET). SWSFET was introduced by Jain et.al. These FETs have multiple channels stacked vertically. The Carrier wavefunction switches from one channel to another with the application of different gate voltages. Designs of multi-bit SRAM, logic and sequential cells using SWSFETs have been demonstrated. Here we are introducing the use of SWSFET in mixed signal architectures. Single cycle architectures for two-bit, four-bit and eight-bit analog to digital converters are presented. Four bit architecture has been simulated and results are discussed. SWSFET presents the opportunity with its multiple stacked channel features to extend the Moors law using next generation of devices.

Conventional epitaxial techniques requires single crystalline substrates to form semiconductor material of desired material quality for device applications. The use of amorphous substrates, in many applications, provides an opportunity to consider new materials and designs, which can fundamentally alter the performance, functionality and/or cost limitations of many optoelectronic devices. Here, a growth process is described to achieve single crystalline GaN material on amorphous SiO₂. The evolutionary selection principle in crystal growth is the basis of this technique, and the mechanism is described and analyzed in detail. It is expected that this process can be extended to other semiconductor and substrate combinations, allowing heterogenous integration with functional substrates to produce new classes of semiconductor devices.

Phase change memory is a non-volatile memory technology that utilizes the electrical resistivity contrast between resistive amorphous and conductive crystalline phases of phase change materials. These devices operate at high current densities and high temperature gradients which lead to significant thermoelectric effects. We have performed numerical modeling of electrothermal effects in p-type Ge₂Sb₂Te₅ phase change memory structures suspended on TiN contact pads using COMSOL Multiphysics. Temperature dependent material parameters are used in the model. Strong asymmetry is observed in temperature profiles in all cases: the hottest spot appears closer to the higher potential end suggesting that the thermal profile can be significantly altered by the thermoelectric effects during device operation. Hence, thermoelectric effects need to be considered for device designs for lower power and higher reliability devices.

In this paper, we propose a new architecture for analog-to-digital converters (ADCs) using multistate spatial wavefunction-switched field-effect transistors (SWSFETs). SWSFETs are multiple quantum coupled well devices, where the wells are stacked vertically and the electron wavefunction switches from one well to another with the change in gate voltage. Quantum mechanical simulations of 3-well InGaAs-AlInAs SWSFET structures are presented. The designs and simulations of 2-bit and 3-bit ADCs using SWSFETs result in low power consumption and reduced device count which improves the speed of the data conversion.

Vertically aligned carbon nanofibers (VACNFs) have recently become an important tool for biosensor design. Carbon nanofibers (CNF) have excellent conductive and structural properties with many irregularities and defect sites in addition to exposed carboxyl groups throughout their surfaces. These properties allow a better immobilization matrix compared to carbon nanotubes and offer better resolution when compared with the FET-based biosensors. VACNFs can be deterministically grown on silicon substrates allowing optimization of the structures for various biosensor applications. Two VACNF electrode architectures have been employed in this study and a comparison of their performances has been made in terms of sensitivity, sensing limitations, dynamic range, and response time. The usage of VACNF platform as a glucose sensor has been verified in this study by selecting an optimum architecture based on the VACNF forest density.

Spatial wave-function switched field effect transistor (SWSFET) switches the current flow between different channels inside the FET based on the applied voltage in its gate terminal. SWSFET can be used to implement multi-valued logic circuit with less number of circuit elements. Recently we presented unipolar inverter circuit using SWSFET. In this paper we develop a circuit model of SWSFET based on BSIM 3.2.0 and BSIM 3.2.4 and implement membership function using that circuit model of SWSFET.

The spatial wave-function switched field effect transistor (SWSFET) has two or three low band-gap quantum well channels inside the substrate of the semiconductor. Applied voltage at the gate region of the SWSFET, switches the charge carrier concentration in different channels from source to drain region. A circuit model of SWSFET is developed in BSIM 3.2.0. Membership function is implemented using the circuit model of the SWSFET. Membership function implementation using less number of SWSFET will reduce the device count in future analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuits.

Magnetotactic bacteria (MTB), discovered in early 1970s contain single-domain crystals of magnetite (Fe₃O₄) called magnetosomes that tend to form a chain like structure from the proximal to the distal pole along the long axis of the cell. The ability of these bacteria to sense the magnetic field for displacement, also called magnetotaxis, arises from the magnetic dipole moment of this chain of magnetosomes. In aquatic habitats, these organisms sense the geomagnetic field and traverse the oxic-anoxic interface for optimal oxygen concentration along the field lines. Here we report an elegant use of MTB where magnetotaxis of Magnetospirillum magneticum (classified as AMB-1) could be utilized for controlled navigation over a semiconductor substrate for selective deposition. We examined 50mm long coils made out of 18AWG and 20AWG copper conductors having diameters of 5mm, 10mm and 20mm for magnetic field intensity and heat generation. Based on the COMSOL simulations and experimental data, it is recognized that a compound semiconductor manufacturing technology involving bacterial carriers and carbon-based materials such as graphene and carbon nanotubes would be a desirable choice in the future.

This work presents a computational approach for the determination of equilibrium strain and dislocation density in nitride-based heterostructures. Verification of this approach is demonstrated in the calculation of critical layer thickness for In_xGa_1-xN/GaN (0001) as compared to other work. The present modeling approach can also be applied to heterostructures of varying compositional profiles and structure. To demonstrate this, we studied the equilibrium strain and misfit dislocation density profiles for metamorphic In_xGa_1-xN/GaN (0001) heterostructures containing uniform layers on top of linearly-graded buffers. These structures were also compared to similar arsenide-based heterostructures involving In_xGa_1-xAs/GaAs (001) with the zinc blende crystal structure. The generalized energy minimization modeling tool presented here can be readily extended to arbitrarily graded nitride heterostructures with polar, semi-polar, or non-polar orientations.

The design and fabrication of miniaturized, implantable, low-power wireless systems for continuous glucose monitoring hold great promise for diabetes mellitus inflicted patients. This involves addressing a variety of issues including extreme circuit miniaturization, robust electrochemical sensors as well as counteracting negative tissue response and biofouling following sensor implantation. In this contribution, we present a highly miniaturized microelectronic sensor platform that fits through a hypodermic needle and holistically addresses all aforementioned tribulations. For this, a custom designed complementary metal-oxide-semiconductor electronic device employing the 0.35 µm design rule has been integrated with a high performance amperometric electrochemical glucose sensor. The fabricated electrochemical sensor utilizes the stratification of five functional layers resulting in linear amperometric response within the physiological glucose range (2 – 22mM). The sensor is encased with a thick polyvinyl alcohol (PVA) hydrogel containing poly (lactic-co-glycolic acid) (PLGA) microspheres which provides continuous, localized delivery of dexamethasone utilized to combat inflammation and fibrosis subsequent to implantation. In vivo evaluation in a rat has shown that this system accurately tracks glycemic events. Such miniature size and low power operation (0.665 mm2 and 140 µW, respectively) of the electronic system render it an ideal platform for continuous glucose monitoring and other metabolic sensing applications.

Virtual reality technology is an attractive means for medical simulations and treatment, especially for patients with cancer. The overall goal of this research is to introduce a conceptual virtual environment with real-world dynamic contents to develop an effective breathing exercise tool that will aid in regulating breathing movements and eventually increase the oxygen intake of users/patients.

This study focuses on an essential component of the virtual reality therapy framework. The work introduces a novel automated approach towards computing the lung capacity. The overall objective is to aid lung cancer patients, or those with breathing disorders regulate their breath through real-time analysis of respiration movements using a smart-phone.

Traditionally, lung cancer patients and those with certain breathing disorders use a spirometer device to measure their lung capacity. However, accurate measurements using the spirometer requires some sort of training and adjustment, which may be difficult for certain groups of patients, especially the elderly.

In this paper, a methodology is proposed to process the recorded acoustic signal of respiration using a microphone, and a model is introduced to estimate the lung size with a high degree of accuracy. To estimate the lung capacity, Voice-Activity-Detection (VAD) is fine-tuned and applied to the acoustic signal of respiration to split the signal into voice and silence phases. The average time duration and energy of the breathing phases (inhale and exhale voice phases) are computed to derive the lung capacity. The signal processing relies on accurate signal segmentation and signal energy computation of the breathing cycles. This model of using a microphone and the acoustic signal of respiration to estimate lung capacity yields a high degree of accuracy, exceeding 85%.

In the framework, lung capacity is computed simultaneously as the patient is breathing in real time. Consequently, the patient will be motivated to take the next coming breath deeply if the previous one was not sufficient, thus, virtually regulating his/her own breath.

The results indicate that the proposed model is highly accurate and effective for estimating lung capacity. The potential outcome of this research is that the intended virtual reality framework, if fully implemented and integrated with a high quality animated application on a smart-phone, would directly aid individuals, especially lung cancer patients, regulate their breath by having a daily basis estimate of their lung size using a hand-held device at home.

This paper presents the design of an underwater energy harvesting system, which would provide persistent and sustainable power supply for remote underwater sensing and surveillance devices. The system consists of Distributed Benthic Microbial Fuel Cell (DBMFC) and the associated power management integrated circuit. The DBMFC exploits bacterial metabolic activities associated with the redox reaction to generate electrical energy directly from biodegradable substrates. The power management circuit collects the energy harvested by the DBMFC and boosts the output voltage to a sufficient and stable level for loads such as sensor devices. Simulation results of the power management system in a 90nm CMOS process demonstrate the expected functions and the significant improvement in energy conversion efficiency.

InGaAs high mobility transistors presently provide the fastest speeds. As InGaAs nonvolatile memory field effect transistors (NVMFETs) are scaled down past 22 nm gate width, threshold voltage variation becomes a limiting factor. Replacing the amorphous SiO₂ or HfO₂ with a heteroepitaxial barrier stack the threshold voltage can be stabilized by minimizing the interface charge at the barrier-channel interface. The floating gate is comprised of individually germanium-oxide cladded germanium quantum dots. The tunneling layer is comprised of a quantum well stack of ZnSe/ZnS/ZnMgSeTe/ZnS/ZnSe. The magnesium incorporation increases the the energy barrier but introduces dislocation that can leak charge. The ZnS and ZnSe layers have a lower bandgap but a lower dislocation density to assist with gate leakage prevention. We present simulation and experimental C-V data on InGaAs FET and II-VI tunneling layer on an InGaAs substrate respectively.