Jet Vapor Research Articles

Interaction of a mesoscale low and diffused tropical depression during south Asian summer monsoon

This paper presents the results of a diagnostic study of a typical case in south Asian summer monsoon when a meso-scale low in a desert climate interacted with a diffused tropical depression originated over the Bay of Bengal. Surface and NCEP reanalysis data supported by satellite and radar images were incorporated in diagnosis. The relationship between heavy precipitation process and large-scale circulations such as westerly jet, low level jet, convergence, vorticity and water vapor transport were investigated to further understand the mechanism of this peculiar interaction. It has been found that the meso-scale low developed as a result of cold air advection aloft from northern latitudes and strong convection over the region of humidity convergence, i.e., Rajasthan (India) on 24th July 2003. On the same day, a low formed on the Bay of Bengal which further developed into monsoon depression. It moved westward from the Bay towards the meso-scale low over southwest India. Meso-scale low remained more or less stationery for two days gaining intensity and then moved relatively with slower speed in southwestward direction. Both the systems yielded moderate to heavy rain in areas under their influence. Interaction resulted into huge accentuation with an abrupt increase in intensity.

Two-phase structure above hot surfaces in jet impingement boiling

Jet impingement boiling is very efficient in cooling of hot surfaces as a part of the impinging liquid evaporates. Several studies have been carried out to measure and correlate the heat transfer to impinging jets as a function of global parameters such as jet subcooling, jet velocity, nozzle size and distance to the surface, etc. If physically based mechanistic models are to be developed, studies on the fundamentals of two-phase dynamics near the hot surface are required. In the present study the vapor–liquid structures underneath a subcooled (20 K) planar (1 mm × 9 mm) water jet, impinging the heated plate vertically with a velocity of 0.4 m/s, were analyzed by means of a miniaturized optical probe. It has a tip diameter of app. 1.5 μm and is moved toward the plate by a micrometer device. The temperature controlled experimental technique enabled steady-state experiments in all boiling regimes. The optical probe data provides information about the void fraction, the contact frequencies and the distribution of the vapor and liquid contact times as a function of the distance to the surface. The measured contact frequencies range from 40 Hz at the onset of nucleate boiling to nearly 20,000 Hz at the end of the transition boiling regime. Due to condensation in the subcooled jet vapor disappears at a distance to the surface of app. 1.2 mm in nucleate boiling. This vapor layer becomes smaller with increasing wall superheat. In film boiling a vapor film thickness of 8 ± 2 μm was found.

A diagnostic study of heavy rainfall in karachi due to merging of a mesoscale low and a diffused tropical depression during South Asian summer monsoon

This paper presents the results of a diagnostic study of a typical case of very heavy rainfall during the South Asian summer monsoon when a mesoscale low in a desert climate merged with a diffused tropical depression. The former low was located over Pakistan’s desert region and the latter depression originated over the Bay of Bengal. Surface and NCEP reanalysis data supported by satellite and radar images were incorporated in the diagnosis. The relationship between the heavy precipitation process and large-scale circulations such as monsoon trough, subtropical high, westerly jet, low level jet and water vapor transport were investigated to further understand the mechanism of this peculiar interaction. It was found that: (1) the mesoscale low developed as a result of cold air advection aloft from northern latitudes and strong convection over the region of humidity convergence on 24 July 2003 over the Indian Rajistan area. (2) On the same day, a low that formed over the Bay of Bengal was transformed into a monsoon depression and moved westward to the mesoscale low which existed over southwest India and the adjoining southeastern parts of Pakistan. (3) Initially, the mesoscale low received moisture supply from both the Bay of Bengal as well as the Arabian Sea, whereas the Bay of Bengal maintained the continuous supply of moisture to the monsoon depression. (4) After the depression crossed central India, the Bay’s moisture supply was cut off and the Arabian Sea became the only source of moisture to both the closely located systems. On 27 July, both of the systems merged together and the merger resulted in a heavy downpour in the Karachi metropolitan and in its surroundings. (5) With the intensification as well as the southeastward extension of the subtropical high and the shift of the monsoon trough axis from southwest-west to northeast-east, the monsoon depression moved southwestward. In this situation, there existed a very favourable condition for a merger of the two systems in the presence of cross-latitude influence. (6) A number of convective cloud clusters were developed and organized in the mesoscale low. Probably, interactions existed among the multi-scale systems.

High-temperature phase stability of hafnium aluminate films for alternative gate dielectrics

Hafnium aluminate films with different compositions were deposited at room temperature by jet vapor deposition. The as-deposited films were amorphous. After annealing at 1100 °C, the microstructure of the films was analyzed by high-resolution transmission electron microscopy, electron diffraction and electron energy loss spectroscopy (EELS). The crystalline phase in pure HfO2 films was monoclinic. With an increase in the Al content in the films, the amount of metastable HfO2 with a tetragonal distorted fluorite structure increased. In addition, the grain sizes decreased, making the detection of crystallization by x-ray diffraction difficult. No crystalline Al2O3 phase could be unambiguously detected in electron diffraction patterns in films with up to 30 mol % Al2O3. However, an Al-rich intergranular phase was identified by EELS. Films with ∼64 mol % Al2O3 crystallized as tetragonal HfO2 and metastable cubic Al2O3 with the spinel structure. The complex microstructures of the films should be considered in the interpretation of their dielectric and electrical properties after high temperature anneals.

Stress Voltage Polarity Dependence of JVD-<tex>$hboxSi_3 hboxN_4$</tex>MNSFET Degradation

In this paper, we study the stress voltage polarity-dependent reliability of n-channel metal-nitride-silicon field-effect transistors (MNSFETs) with ultrathin jet vapor deposited (JVD) silicon nitride dielectric. Under constant voltage stress, device parameters such as threshold voltage and transconductance degrade. Charge trapping due to interface and bulk traps is observed. Our study shows that the degradation is polarity dependent. MNSFETs show lower degradation under positive stress fields. We have also compared the performance of MNSFETs with conventional MOSFETs under identical stress conditions. Under positive stressing, MNSFETs clearly outperform MOSFETs, but under negative stressing, MNSFETs show more degradation.

Analysis of simulated heavy rain over the Yangtze River valley during 11–30 June 1998 using RIEMS

RIEMS’ ability to simulate extreme monsoon rainfall is examined using the 18-month (April 1997 September 1998) integrated results. Model-simulated heavy precipitation over the Yangtze River valley during 11–30 June 1998 is compared with the observation, and the relationships between this heavy rainfall process and the large-scale circulations, such as the westerly jet, low-level jet, and water vapor transport, are analyzed to further understand the mechanisms for simulating heavy monsoon rainfall. The analysis results show that (1) RIEMS can reproduce the pattern of heavy precipitation over the Yangtze River valley during 11–30 June 1998, but it is shifted northwestwards. (2) The simulated West Pacific Subtropical High (WPSH) that controls the East Asia Monsoon evolution is stronger than the observation and is extended westwards, which possibly leads to the north westward shift of the heavy rain belt. (3) The Westerly jet at 200 hPa and the Low-level jet at 850 hPa, both of which are related to the heavy monsoon rainfall, are reasonably reproduced by RIEMS during 11–30 June 1998, although the intensities of the simulated Westerly/Low-level jets are strong and the location of the Westerly jet leans to the southeast, which may be the causes of RIEMS producing too much heavy rainfall in the north of the Yangtze River valley.

Gate dielectrics for Si, SiC, and GaN as synthesized by jet vapor deposition

The principle of the Jet-Vapor Deposition (JVD) technique for thin dielectric deposition will be introduced, the properties of JVD silicon nitride (SiN), silicon oxide, and oxide/nitride/oxide (ONO) stacks as MOS gate dielectrics for Si, SiC, and GaN will be presented.

A new method to characterize border traps in submicron transistors using hysteresis in the drain current

In this paper, a new method for measuring border trap density (n/sub BT/) in submicron transistors using hysteresis in the drain current is proposed. This method is used to measure energy and spatial distribution of border traps in jet vapor deposited (JVD) metal-silicon nitride-semiconductor field effect transistors (MNSFETs). The drain current transient varies linearly with logarithmic time suggesting that tunneling to and from the spatially uniform border traps is the dominant charge exchange mechanism. Using a feedback mechanism gate voltage transients are obtained from which n/sub BT/ is calculated. The prestress energy distribution in JVD MNSFETs is found to be uniform whereas the post-stress energy distribution shows a peak near the midgap.

Evolution of carbon from atomic clusters to fullerenes in an arc discharge

The formation of fullerenes from an arc-produced turbulent jet of carbon vapor is described. Both direct and backward mono-and bimolecular reactions are analyzed. Initial characteristics of the jet are used as the input parameters of the problem. The analytical dependences of the fullerene yield on the initial velocity of the jet and carbon vapor concentration explain experimental relationships between the fullerene yield, current, pressure, and buffer gas sort.

JVD silicon nitride as tunnel dielectric in p-channel flash memory

High-quality jet vapor deposition nitride is investigated as a tunnel dielectric for flash memory device application. Compared to control devices with SiO/sub 2/ tunnel dielectric, faster programming speed as well as better retention time are achieved with low programming voltage. The p-channel devices can be programmed by hot electrons and erased by hot holes, or vice versa. Multilevel programming capability is shown.

Polarity Dependence of Degradation in Ultra Thin Oxide and JVD Nitride Gate Dielectrics

AbstractWe have studied high field degradation of Jet Vapor Deposited (JVD) silicon nitride MNSFETs with DC stress fields and compared their degradation with conventional silicon dioxide MOSFETs under identical stress conditions. We have observed that in both oxide and nitride devices, the interface degradation is higher for negative gate field. Further, the relative degradation of nitrides is always lower compared to that of oxides for both positive and negative stress conditions. AC stress experiments were performed on these ultra thin oxide transistors to understand possible degradation processes. The frequency, the peak-to-peak and offset voltage of the applied AC signal are some of the parameters that have been varied. Detailed characterization results and an analysis of the degradation mechanisms are presented in this paper. We conclude that many of the degradation results can be explained using the trapped hole recombination model.

Performance and hot-carrier reliability of 100 nm channel length jet vapor deposited Si/sub 3/N/sub 4/ MNSFETs

Metal-nitride-semiconductor FETs (MNSFETs) having channel lengths down to 100 mm and a novel jet vapor deposited (JVD) Si/sub 3/N/sub 4/ gate dielectric have been fabricated and characterized. When compared with MOSFETs having a thermal SiO/sub 2/ gate insulator, the MNSFETs show a comparable drain current drive, transconductance, subthreshold slope and pre-stress interface quality. A novel charge pumping technique is employed to characterize the hot-carrier induced interface-trap generation in MNSFETs and MOSFETs. Under identical substrate current during stress, MNSFETs show less interface-state generation and drain current degradation, for various channel lengths, stress times and supply voltages, despite the fact that the Si-Si/sub 3/N/sub 4/ barrier (2.1 eV) is lower than the Si-SiO/sub 2/ barrier (3.1 eV). The time and voltage dependence of hot-carrier degradation has been found to be distinctly different for MNSFETs compared to SiO/sub 2/ MOSFETs.

High-quality oxide/nitride/oxide gate insulator for GaN MIS structures

We report on a SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ (ONO) gate insulator stack deposited on GaN by jet vapor deposition (JVD) technique. Capacitors fabricated using the JVD-ONO on GaN are characterized from room temperature to 450/spl deg/C using capacitance-voltage (C-V), current-voltage (I-V), AC conductance, and constant-current stress measurements. We find excellent operating characteristics over the measured range, most notably: (1) very low leakage current, (2) extremely high hard-breakdown strength, (3) low interface-trap density, and (4) low net dielectric-charge density. Moreover these performance figures remain well within acceptable limits even for operating temperatures as high as 150/spl deg/C. In addition, we measure both the capture cross-section of the interface traps and the surface-potential fluctuation at the GaN/ONO interface. All results suggest that JVD-ONO is an excellent choice for a gate dielectric in GaN-based MISFETs.

Hot-carrier reliability comparison for pMOSFETs with ultrathin silicon-nitride and silicon-oxide gate dielectrics

The degradation of 100-nm effective channel length pMOS transistors with 14 /spl Aring/ equivalent oxide thickness Jet Vapor Deposition (JVD) Si/sub 3/N/sub 4/ gate dielectric under hot-carrier stress is studied. Interface-state generation is identified as the dominant degradation mechanism. Hot-carrier-induced gate leakage may become a new reliability concern. Hot-carrier reliability of 14 /spl Aring/ Si/sub 3/N/sub 4/ transistors is compared to reliability of 16 /spl Aring/ SiO/sub 2/ transistors.

Transmission electron microscope investigation of SrBi2Ta2O9 memory capacitors on Si with silicon dioxide and silicon nitride as buffers

Ferroelectric memory capacitors were made by deposition of SrBi2Ta2O9 (SBT) on Si with thin (∼40–90 Å) buffer layers of jet vapor deposition (JVD) silicon nitride and oxide. Transmission electron microscope analysis was carried out to compare the microscopic integrity of both films after subsequent processing steps. It was found that the thin SiO2 buffer layer failed to prevent further oxidation of the Si substrate and furthermore allowed the diffusion of the SBT towards the SiO2/Si interface. In contrast the silicon nitride layer deposited by the JVD process acted as a good barrier for the diffusion of SBT. It also stopped further oxidation of the Si substrate during subsequent annealing in oxygen. Electrical tests show that the capacitors have large memory windows and that the windows present only slight degradation after 1011 switching cycles. The use of JVD nitride as a buffer is encouraging for the further development of ferroelectric memory transistors.

Highly robust ultrathin silicon nitride films grown at low-temperature by microwave-excitation high-density plasma for giga scale integration

This paper focuses attention on electrical properties of ultra-thin silicon nitride films grown by radial line slot antenna high-density plasma system at a temperature of 400/spl deg/C as an advanced gate dielectric film. The results show low density of interface trap and bulk charge, lower leakage current than jet vapor deposition silicon nitride and thermally grown silicon oxide with same equivalent oxide thickness. Furthermore, they represent high breakdown field intensity, almost no stress-induced leakage current, very little trap generation even in high-field stress, and excellent resistance to boron penetration and oxidation.

“Jet Vapor Deposition”, a novel vacuum coating technique with superior properties

Dry coating technologies offer the steel industry a wide range of new possibilities. In this context, CRM develops a new process for evaporation under vacuum : the JVD (Jet Vapor Deposition).

Jet vapor deposition nitride processing and application to advanced CMOS devices for reduction of gate leakage current and boron penetration

The increase in gate leakage current and boron penetration are major problems for scaled gate dielectrics in advanced device technology. We have demonstrated, for the first time, reduction in gate leakage current and strong resistance to boron penetration when jet vapor deposition (JVD) nitride is used as a gate dielectric in an advanced CMOS process. JVD nitride provides a robust interface in addition to well behaved bulk properties, MOSFET characteristics and ring oscillator performance. Process optimization is discussed. Manufacturing issues remain to be addressed.

High-temperature characteristics of high-quality SiC MIS capacitors with O/N/O gate dielectric

This paper reports the high temperature (up to 450/spl deg/C) characteristics of 6H-SiC MIS capacitors made with SiO/sub 2//SiN/SiO/sub 2/ (ONO) stack gate dielectric deposited by the jet vapor deposition (JVD) process. This ONO stack gate dielectric provides: (1) high immunity to instability caused by mobile ions, (2) orders of magnitude lower gate leakage current than its thermal oxide counterpart, (3) the highest dielectric breakdown strength ever reported for SiC MIS structures at elevated temperatures (i.e., greater than 12 MV/cm at 450/spl deg/C), (4) relatively symmetric p-and n-type C-V and current-voltage (I-V) characteristics, due to low densities of dielectric charge as well as interface traps in both types of samples, and (5) over ten years of projected lifetime for both types operating at an electric field of 3 MV/cm at 350/spl deg/C. The key factors contributing to such success are briefly discussed.

Electrical and Physical Characterization of Ultrathin Silicon Oxynitride Gate Dielectric Films Formed by the Jet Vapor Deposition Technique

ABSTRACTThis paper describes the electrical and physical characteristics of ultrathin Jet Vapor Deposited (JVD) Silicon Oxynitride films. Capacitance-Voltage measurements indicate an equivalent oxide thickness (EOT) of less than 2 nm, taking into account the quantum-mechanical correction. These films have leakage currents almost two orders of magnitude lower than thermal oxide of the same equivalent thickness. Measurements on NMOSFETs with 0.15 μm of channel length demonstrate excellent electrical properties, including high drive currents (∼0.5 mA/μm @ Vd=Vg–Vt=l.5 V), low sub-threshold swings (∼72 mV/decade), and high transconductance (∼0.36 mS/μm @ Vd=1.5 V). These films were also analyzed using a variety of physicochemical methods, including Total X-ray Fluorescence (TXRF), Atomic Force Microscopy (AFM), Nuclear Reaction Analysis (NRA), Low Energy (500 eV) Secondary Ion Mass Spectrometry (SIMS), and Transmission Electron Microscopy (TEM). Surface metal concentrations of less than 1011 atoms/cm2 were measured from the TXRF analysis. The microroughness values for these films varied between 0.15 – 0.17 nm as measured by AFM. Low energy (500 eV) SIMS and NRA indicate high [N] near the top as well as throughout the bulk of the film, and a significant amount of [O] near the top of the film. High Resolution TEM pictures show a very uniform film with a physical thickness of 2.8 ± 0.1 nM, which yields an effective dielectric constant of 5.5, consistent with these types of oxynitride films.