Gate Delay Time Research Articles

Emission Characteristics of Laser-Induced Plasma Using Collinear Long and Short Dual-Pulse Laser-Induced Breakdown Spectroscopy (LIBS).

Collinear long and short dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) was employed to clarify the emission characteristics from laser-induced plasma. The plasma was sustained and became stable by the long pulse-width laser with the pulse width of 60 μs under free running (FR) conditions as an external energy source. Comparing the measurement results of stainless steel in air using single-pulse LIBS (SP-LIBS) and DP-LIBS, the emission intensity was markedly enhanced using DP-LIBS. The temperature of plasma induced by DP-LIBS was maintained at a higher temperature under different gate delay time and short pulse-width laser power conditions compared with those measured using short SP-LIBS. Moreover, the variation rates of plasma temperatures measured using DP-LIBS were also lower. The superior detection ability was verified by the measurement of aluminum sample in water. The spectra were clearly detected using DP-LIBS, whereas it cannot be identified using SP-LIBS of short and long pulse widths. The effects of gate delay time and short pulse-width laser power were also discussed. These results demonstrate the feasibility and enhanced detection ability of the proposed collinear long and short DP-LIBS method.

Evaluation of Optical Depths and Self-Absorption of Strontium and Aluminum Emission Lines in Laser-Induced Breakdown Spectroscopy (LIBS).

Laser-induced breakdown spectroscopy (LIBS) is a widely used laser spectroscopic technique in various fields, such as material science, forensic science, biological science, and the chemical and pharmaceutical industries. In most LIBS work, the analysis is performed using radiative transitions from atomic emissions. In this study, the plasma temperature and the product [Formula: see text] (the number density N and the absorption path length [Formula: see text]) were determined to evaluate the optical depths and the self-absorption of Sr and Al lines. A binary mixture of strontium nitrate and aluminum oxide was used as a sample, consisting of variety of different concentrations in powder form. Laser-induced breakdown spectroscopy spectra were collected by varying various parameters, such as laser energy, gate delay time, and gate width time to optimize the LIBS signals. Atomic emission from Sr and Al lines, as observed in the LIBS spectra of different sample compositions, was used to characterize the laser induced plasma and evaluate the optical depths and self-absorption of LIBS.

Laser-induced breakdown spectroscopy of liquid solutions: a comparative study on the forms of liquid surface and liquid aerosol.

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869 μg/mL, which were close to those of liquid aerosol, 2.847 μg/mL of Cr and 97.635 μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R2 of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Optimization of liquid jet system for laser-induced breakdown spectroscopy analysis

A complex optimization of geometrical and temporal parameters of a jet system (developed in Laser-induced breakdown spectroscopy (LIBS) laboratory of Brno University of Technology) for direct elemental analysis of samples in a liquid state of matter using LIBS was carried out. First, the peristaltic pump was synchronized with the flashlamp of the ablation laser, which reduced variation of the ablated sample amount. Also, the fluctuation of the laser ray angle incident on the jet surface was diminished. Such synchronization reduced signal standard deviations and thus increased repeatability of the measurements. Then, laser energy and distance of the focusing lens from the sample were optimized. The gate delay time and the gate width were optimized for single pulse (SP) experiments; the gate delay time and the inter-pulse delay were optimized for the use of double pulse (DP) variant. Results were assessed according to the highest signal to noise ratios and the lowest relative standard deviations of the signal. The sensitivity of the single pulse and the double pulse LIBS for the detection of heavy metals traces, copper (Cu i at 324.754 nm) and lead (Pb i at 405.781 nm), in aqueous solution of copper (ii) sulfate and lead (ii) acetate, was estimated in terms of limits of detection (LODs). As a result, sensitivity improvement of DP LIBS system was observed, the LOD of Cu obtained with DP was calculated 40% lower than LOD gained from SP technique.

The Influence of Acquisition Delay for Calibration-Free Laser-Induced Breakdown Spectroscopy.

Time-resolved spectra of neutral and ionized atomic emissions from slag sample are measured by laser-induced breakdown spectroscopy (LIBS). Various factors affecting the calibration-free CF-LIBS method are carefully analyzed, and subsequently these factors are either avoided or corrected. Plasma temperature and electron density are calculated by Saha-Boltzmann plot and Stark broadening of Ca, respectively. At the same time, self-absorption and local thermodynamic equilibrium have been carefully studied. An automatic spectral lines elimination algorithm is applied to calculate plasma temperature and element concentration. The calculated element concentrations show marked changes with acquisition time increasing. Due to the influence of continuous spectrum at early times and self-absorption at late times, the large absolute errors sum is obtained in these two periods. The smallest absolute errors sum corresponds to the gate delay time 1.5 μs < td < 2 μs for our experimental setup.

Scaling Effects on Static Metrics and Switching Attributes of Graphene Nanoribbon FET for Emerging Technology

In this paper, we have investigated the static metrics and switching attributes of graphene nanoribbon field-effect transistors (GNR FETs) for scaling the channel length from 15 nm down to 2.5 nm and GNR width by approaching the ultimate vertical scaling of oxide thickness. We have simulated the double-gate GNR FET by solving a numerical quantum transport model based on selfconsistent solution of the 3D Poisson equation and 1D Schrödinger equation within the non-equilibrium Green's function formulism. The narrow armchair GNR, e.g. (7,0), improved the device robustness to shortchannel effects, leading to better OFF-state performance considering OFF-current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio, subthreshold swing, and drain-induced barrier-lowering. The wider armchair GNRs allow the scaling of channel length and supply voltage, resulting in better ON-state performance, such as the larger intrinsic cut-off frequency for the channel length below 7.5 nm at smaller gate voltage as well as smaller intrinsic gate-delay time with the constant slope for scaling the channel length and supply voltage. The wider armchair GNRs, e.g. (13,0), have smaller power-delay product for scaling the channel length and supply voltage, reaching to ~0.18 (fJ/μm).

Laser-induced breakdown spectroscopy and inductively coupled plasma-mass spectrometry for determination of Cr in soils from Brits District, South Africa

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical technique, which can be used to perform elemental analysis of any material, irrespective of its physical state. In this study, the LIBS technique has been applied for quantification of total Cr in soil samples collected from polluted areas of Brits, North West Province, South Africa. A Q-switched neodymium-yttrium aluminium garnet (Nd-YAG) laser (10 Hz, λ = 1064 nm) was employed for generation of a laser-induced plasma on the surface of the soil sample. The atomic emission lines were recorded using an Andor Shamrock SR-303i spectrometer, fitted with an intensified charge-coupled device (ICCD) camera. Detailed investigation of experimental parameters such as gate delay time, gate width and laser pulse energy was conducted. Soil samples were dried, finely ground, sieved and thereafter pelletized before LIBS analysis. Calibration curve for the quantification of Cr was constructed using certified reference materials of soils and sediments. The concentrations of Cr in soil samples varied from 111 to 3180 mg/kg. In order to test the validity of the LIBS results, inductively coupled plasma-mass spectrometry (ICP-MS) was also employed for determination of Cr. The results obtained using LIBS were found to be in good agreement with those of ICP-MS. KEY WORDS : Chromium, Direct determination, Soil, LIBS, ICP-MS Bull. Chem. Soc. Ethiop. 2015 , 29(3), 357-366. DOI: http://dx.doi.org/10.4314/bcse.v29i3.3

Effect of parameters on Si plasma emission in collinear double-pulse laser-induced breakdown spectroscopy

Collinear dual-pulse laser-induced breakdown spectroscopy was carried out on Si crystal by using a pair of nanosecond Nd:YAG laser sources emitting at 1064 nm. The spectral intensities and signalto- noise ratios of selected Si atomic and ionic lines were used to evaluate the optical emission. The optical emission intensity was recorded while varying the interpulse delay time and energy ratio of the two pulsed lasers. The effects of the data acquisition delay time on the line intensity and signal-to-noise ratio have been investigated as well. Based on the results, the optimal interpulse delay time, energy ratio of the two pulsed lasers, and data acquisition delay time for achieving the maximum atomic and ionic line intensities were found for generation of Si plasma with the collinear dual-pulse laser approach. The dominant mechanism for the observed line intensity variation was also discussed. In addition, the plasma temperature and electron number density at different gate delay times and different interpulse delay times were derived. A significant influence of plasma shielding on the electron temperature and electron number density at shorter interpulse delay times was observed.

An Inverter Gate Design Based on Nanoscale S-FED as a Function of Reservoir Thickness

In this paper, an inverter logic gate has been successfully designed based on the previously proposed side-contacted field-effect diodes (S-FEDs). Effect of the reservoir thickness on the S-FED performance is investigated, and then the output characteristics of the S-FED-based inverter are studied and compared with those of the existing CMOS technology. The S-FED performance evaluation is performed in terms of important figures of merit for logic application in various reservoir thicknesses, including transconductance, intrinsic gate delay time, energy delay product, and subthreshold slope. The numerical results demonstrate that the optimum reservoir thickness is 7 nm, and the threshold voltage can be controlled by reservoir thickness. Mixed-mode simulations also indicate that, in the design of an inverter utilizing S-FEDs, the delay and the power dissipation of the logic gate are reduced. These results indicate that the S-FED can be an interesting candidate for designing low-power and high-speed logic gates.

Effect of laser wavelength on the correlation between plasma temperature and surface hardness of Fe–V–C metallic alloys

We investigated the effect of the excitation laser wavelength in laser induced breakdown spectroscopy (LIBS) on the correlation between the generated plasma temperature and the mechanical surface hardness of Fe–V18%–C1% alloys. The dependence of the choice of gate width and delay time in the LIBS measurements on the excitation wavelength was discussed. We demonstrated the feasibility of hardness monitoring using the linear relationship between the plasma temperature and Vickers test at three laser wavelengths 1064, 532 and 355nm. The sensitivity of this approach has been discussed for all cases. The experimental results show that the first harmonic is more appropriate for such application. The crater depth was significantly higher in case of using UV laser compared with the IR, as has been seen using the profilometer. This revealed that surface hardness measurement using LIBS is more efficient (less destructive) by adopting the IR wavelength than the UV for the excitation laser.

Impact of T-gate stem height on parasitic gate delay time in InGaAs-HEMTs

The impact of the stem height of T-gate electrodes on the parasitic gate delay time in InGaAs high electron mobility transistors (HEMTs) is studied. Since T-gates with higher stem height make the parasitic gate capacitance smaller, the higher stem height is expected to minimize the parasitic gate delay. However, a systematic study using the devices with different stem height of T-gates reveals that the parasitic gate delay time decreases with the parasitic gate capacitance only at a drain voltage around the knee voltage and it becomes less sensitive to the parasitic capacitance by the T-gate when the device is operated in the deep saturation region at high drain bias voltage. This result suggests a design strategy for T-gate electrodes so that the tradeoff between the gate resistance and gate capacitance must be considered seriously in the devices for low-voltage applications, while one has more flexibility to use the T-gate electrode with a large head in the devices for high-voltage applications.

SILICON ON RAISED INSULATOR FIELD EFFECT DIODE (SORI-FED) FOR ALLEVIATING SCALING PROBLEM IN FED

One of the main shortcomings in a field effect diode (FED) is its scaling. Use of an oxide layer in the channel is proposed to enhance the control of the gate on the channel carriers. This is the so-called silicon on raised insulator FED (SORI-FFD) structure. The Shockley–Read–Hall (SRH) mechanism is one of the main components of leakage current in FED devices. The potential induced by the gates in the OFF-state of a SORI-FFD, is larger than that induced by the gates of a regular FED. This reduces, SRH recombination rate. Hence, OFF-state characteristics of the SORI-FED device improves. We evaluate the impact of band-to-band tunneling (BTBT) on the electrical characteristics of Modified FED (M-FED).We show that for channel lengths of 35 nm and lower this device does not turn off. While, the proposed structure makes device channel length scaling possible down to 15 nm. We will also compare electrical characteristics of SORI-FED and M-FED using three metrics: gate delay time versus channel length, gate delay time versus I ON /I OFF ratio and energy-delay product versus channel length. Benchmarking results show the proposed FED structure provides improvement in I ON /I OFF ratio and holds promise for future logic transistor applications.

Effects of the Spacer Length on the High-Frequency Nanoscale Field Effect Diode performance

The performance of nanoscale Field Effect Diodes as a function of the spacer length between two gates is investigated. Our numerical results show that the Ion/Ioff ratio which is a significant parameter in digital application can be varied from 101 to 104 for S-FED as the spacer length between two gates increases whereas this ratio is approximately constant for M-FED. The high-frequency performance of FEDs is investigated and the cut-off frequency of the intrinsic transistor without parasitic capacitance is calculated. The figures of merit including intrinsic gate delay time and energy-delay product have been studied for the field effect diodes which are interesting candidates for future logic applications.

(Invited) The Materials Integration of Ge and InxGa1-X As on Si Template for Next Generation CMOS Applications

Lately, the semiconductor industry has paid a lot of attentions to the III-V compound semiconductor materials such as InSb, InxGa1-xAs for next generation CMOS applications, because these materials have significantly higher carrier mobility than silicon. For example, the electron mobility of InAs could reach 20000 cm2V-1s-1. High-speed devices such as quantum-well field-effect transistors (QWFETs) made from these III-V materials have demonstrated very low gate delay time. However, hole mobility for III-V materials are very low in general, some are even lower than the hole mobility of Si. So, it is important to look for a proper material with high hole mobility as p-channel FETs for future complementary CMOS architecture. Since Ge has a much higher bulk hole mobility (mh =1900 cm2/Vs) as compared to GaAs (mh = 400 cm2/Vs), Ge is suitable as p type channel material. Due to the small lattice mismatch (~0.08%) between GaAs and Ge, the integration of Ge with GaAs is comparable easy as compared to grow on Si , therefore thick Ge film can be grown as channel on GaAs substrates with very low defect density and integrate with InxGa1-xAs devices as a CMOS structure. In this talk, the growth of high quality Ge film on GaAs substrate by ultra high vacuum chemical vapor deposition (UHVCVD) and high quality InAs material on Ge/SiGe/Si template grown by molecular beam epitaxy (MBE) will be particularly reported. By the observation of XRD and AFM, both Ge film grown on GaAs material and InAs grown on Si substrates demonstrate high crystallinity and good surface morphology. The developed epitaxial materials systems including Ge on GaAs and InAs on Si are useful for future III-V/Ge/Si integration for next generation high speed low power CMOS application as well as for RF/digital mixed signal circuit application in the future.

Gate capacitance modeling and width-dependent performance of graphene nanoribbon transistors

The width-dependent performance of armchair GNRs-FETs is investigated by developing a fully analytical gate capacitance model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor interaction as well as thermal broadening. To calculate the performance metrics of GNR-FETs, analytical expressions are used for the charge density, quantum capacitance as well as drain current as functions of both gate and drain voltages. Intrinsic gate delay time, cutoff frequency and Ion/Ioff ratio are also calculated for different GNR widths. Numerical results for a double-gate AGNR-FET operating close to quantum capacitance limit show that nanoribbon widths of about 3–4nm at most are required in order to obtain optimum on/off performance.

Temporal filtering with fast ICCD cameras in Raman studies

A common problem when applying Raman scattering in applied research is spectral interference from laser‐induced fluorescence. Extensive work has been invested in developing spectral and polarization filters as well as modulation schemes to refine spontaneous Raman signals. This current work, however, focuses on utilizing the temporal domain using a picosecond laser system and ICCD cameras with relatively short decay of the camera gate to prevent the fluorescence tail from being captured in Raman experiments. Further, the approach of using an ICCD camera to perform temporal filtering is compared to earlier proposed detection schemes using streak cameras or Kerr gates. The temporal‐filtering scheme is evaluated in a spectroscopic investigation where a background subtraction algorithm is presented. The temporal‐filtering scheme was also evaluated for Raman imaging of a levitated water droplet surrounded by fluorescing toluene vapor. Furthermore, the temporal‐filter detection scheme was simulated in order to provide straight forward evaluation tools to estimate the potential of performing temporal filtering with a laser/camera system considering: laser‐pulse duration, time jitter, camera‐gate characteristics, gate delay times, fluorescence lifetimes, and relative signal strength between the Raman and fluorescence signal. The fluorescence signal was modeled with a closed two‐level system, and the simulated results were compared to results from an investigation of the rising slope of toluene fluorescence. These evaluation tools and experimental investigations may serve as guidelines for planning and performing Raman measurements in situations where traditional filter‐rejection schemes are insufficient. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Controllable Electrical Properties of Metal-Doped In2O3 Nanowires for High-Performance Enhancement-Mode Transistors

In recent years, In(2)O(3) nanowires (NWs) have been widely explored in many technological areas due to their excellent electrical and optical properties; however, most of these devices are based on In(2)O(3) NW field-effect transistors (FETs) operating in the depletion mode, which induces relatively higher power consumption and fancier circuit integration design. Here, n-type enhancement-mode In(2)O(3) NW FETs are successfully fabricated by doping different metal elements (Mg, Al, and Ga) in the NW channels. Importantly, the resulting threshold voltage can be effectively modulated through varying the metal (Mg, Ga, and Al) content in the NWs. A series of scaling effects in the mobility, transconductance, threshold voltage, and source-drain current with respect to the device channel length are also observed. Specifically, a small gate delay time (0.01 ns) and high on-current density (0.9 mA/μm) are obtained at 300 nm channel length. Furthermore, Mg-doped In(2)O(3) NWs are then employed to fabricate NW parallel array FETs with a high saturation current (0.5 mA), on/off ratio (>10(9)), and field-effect mobility (110 cm(2)/V·s), while the subthreshold slope and threshold voltage do not show any significant changes. All of these results indicate the great potency for metal-doped In(2)O(3) NWs used in the low-power, high-performance thin-film transistors.

Spectroscopic studies of UV lead plasmas produced by single and double-pulse laser excitation

A spectroscopic study to compare single- and double-pulse laser-induced breakdown spectroscopy (LIBS) using two Q-switched Nd:YAG lasers emitting at 532 nm is reported. The two laser beams were combined in the same direction (collinear beam geometry) to focus on the Pb targets in the open air. Various parameters, such as incident laser irradiance, placement of the laser beam focus position relative to the illuminated surface and gate delay times (delay between the incident laser pulse and the ICCD camera), were used as variables to enhance the sensitivity of LIBS signals. Several atomic and ionic emission lines of Pb were registered in the 200–290 nm UV spectral domains. In order to study the temporal evolution of plasma parameters for single- and double-pulse laser (SP and DP) configurations, the observed profiles of neutral lead lines were used to extract the plasma temperature (Te) using Boltzmann plots, whereas electron number density (ne) was determined from the profile of the Stark-broadened line. In the case of the DP configuration, the intensity of the atomic Pb I signal at 280.2 nm was enhanced eightfold. The intensity enhancement could help the analytical performance of the LIBS technique in terms of improvement of sensitivity and reduction of the self-absorption effect. This study contributes to a better understanding of the LIBS plasma dynamics by observing the temporal evolution of various emission lines of Pb. The results demonstrate a faster decay of the continuum relative to the spectral lines and a slightly longer plasma life-time for the DP configuration as compared with the SP configuration. In order to avoid inhomogeneous effects in the plasma, sufficiently high laser intensity and short delay time are required. Special attention was paid to possible self-absorption of different transitions. The micro-craters generated by SP and DP laser ablation were also compared using an optical microscope.

A comparative spectroscopic study of single and dual pulse laser produced UV tin plasmas

A comparative study of single-pulse (SP) and dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) using two Q-switched Nd:YAG lasers emitting at 532nm is presented. Both lasers were combined in the same direction (collinear beam scheme) to focus on planar Sn targets at ambient pressure. The effect of the delay times between the incident laser pulse and the ICCD gate, placement of the laser beam focal position with respect to the illuminated surface, incident laser irradiance, and ambient argon pressure on the signal intensity enhancement for the dual pulse scheme have been studied. Atomic and ionic emission lines of Sn were recorded in the 272–296nm UV spectral region. By using the DP-LIBS excitation technique, the intensity of Sn lines was enhanced by nearly seven times as compared to the single pulse signal that could help the analytical performance of the LIBS technique in terms of increasing sensitivity and reducing self-absorption effects for Sn targets. In the case of the DP-LIBS scheme, the intensities of the atomic Sn I at 283.9nm were recorded at different optimal angles of 45° and 90° and were compared. This comparison was done at different positions of the laser beam focus with respect to the illuminated surface (at 2.45mm in front of the surface, on the surface, at 1.7mm and 4.7mm behind the surface). Furthermore, in the DP-LIBS scheme, an intensity enhancement of the atomic Sn I line at 283.9nm occurs when the signal was recorded at an angle of 90° to the plasma expansion along the direction of the incident laser beam and the detector set at short delay times. The investigation proved that an optimized value of short delay times between the incident laser pulse and the ICCD gate is required. Variations in the electron temperature (Te) and electron number density (Ne) as a function of gate delay time and laser irradiance have been studied by using the emission lines of neutral tin. Special attention was paid to possible self-absorption of the different transitions. The micro-craters created by SP and DP laser ablation were compared using a reflection optical microscopy (ROM).

Random Interface-Traps-Induced Electrical Characteristic Fluctuation in 16-nm-Gate High-κ/Metal Gate Complementary Metal–Oxide–Semiconductor Device and Inverter Circuit

This work estimates electrical and transfer-characteristic fluctuations in 16-nm-gate high-κ/metal gate (HKMG) metal–oxide–semiconductor field effect transistor (MOSFET) devices and inverter circuit induced by random interface traps (ITs) at high-κ/silicon interface. Randomly generated devices with two-dimensional (2D) ITs at HfO2/Si interface are incorporated into quantum-mechanically corrected 3D device simulation. Device characteristics, as influenced by different degrees of fluctuation, are discussed in relation to random ITs near source and drain ends. Owing to a decreasing penetration of electric field from drain to source, the drain induced barrier lowering (DIBL) of the edvice decreases when the number of ITs increases. In contrast to random-dopant fluctuation, the screening effect of device's inversion layer cannot effectively screen potential's variation; thus, devices still have noticeable fluctuation of gate capacitance (CG) under high gate bias. The cutoff frequency decreases as increasing the number of ITs owing to the decreasing transconductance and increasing CG. Decreasing on-state current and increasing CG further result in increasing intrinsic gate delay time (τ) when the number of ITs increases. The fluctuation magnitude of DIBL, cutoff frequency, and τ above is increased as the number of ITs increases. Even for cases with the same number of random ITs, noise margins (NMs) of the 16-nm-gate complementary metal–oxide–semiconductor inverter circuit are still quite different due to the different distribution of random ITs. The NMs of inverter circuit increase as the number of random ITs increases; however, the NMs' fluctuations are increased due to the more sources of fluctuation at HfO2/Si interface of HKMG devices.