Search

A novel MOS-controlled silicon carbide (SIC) thyristor device, the SiC emitter turn-off thyristor (ETO), as a promising technology for future high-voltage and high-frequency switching applications has been developed. The world's first 4.5-kV SiC p-type ETO prototype based on a 0.36 [cm.sup.2] SiC p-type gate turn-off (GTO) shows a forward voltage drop of 4.6 V at a current density of 25 A/[cm.sup.2] and a turn-off energy loss of 9.88 mJ. The low loss shows that the SiC ETO could operate at a 4-kHz frequency with a conventional thermal management system. This frequency capability is about four times higher than the 4.5-kV-class silicon power devices. The numerical simulations and theoretical analysis have been carried out to show the potentially improved performance of the high-voltage SiC ETOs. The results show that the high-voltage (10-kV) SiC n-type ETO has much better tradeoff performance than that of the p-type ETO due to a smaller current gain of the lower bipolar transistor in the SiC n-type GTO. Further improvement of the 10-kV SiC n-type ETO can be made with the optimum design of the drift layer carrier lifetime and buffer layer doping concentration of the 10-kV SiC GTO. The theoretical analysis and numerical simulation shows the SiC ETO also has the excellent reverse bias safe operating area. The experimental and theoretical studies show that the SiC ETO is a promising candidate for high-voltage (> 5 kV) power conversion applications. Index Terms--Buffer, emitter turn-off thyristor (ETO), high voltage, lifetime, loss, reverse bias safe operating area (RBSOA), silicon carbide (SIC).

The scattering of stellar orbits by galactic molecular clouds is studied in hope of explaining isotopic peculiarities of presolar grains from Asymptotic Giant Branch (AGB) stars. Silicon isotopic anomalies found in the mainstream Silicon Carbide (SiC) grains are observed to have heavy isotopes enriched. To explain the isotopic heaviness I propose that AGB stars that formed in the interior region of the galaxy, with metallicity higher than solar, change their orbits during close encounters with molecular clouds. The AGB stars give up their SiC grains in winds deposited in the solar neighborhood prior to the birth of the Sun. I model the dynamics by superposing on a standard axisymmetric galactic potential the discrete potentials of thousands of molecular clouds moving in constant circular orbits. Gravity assist occurs when a star scattered into a crossing orbit by one cloud experiences forward scattering from a second cloud. Key words: Silicon carbide, AGB stars, gravity assist, INTRODUCTION Many studies (e.g., 5 and 14) have shown that the mainstream presolar Silicon Carbide (SiC) grains extracted from meteorites formed in asymptotic giant branch stars. Ion probe studies show [...]

In this paper, inductive-load switching of a high-voltage lateral JFET (HV-LJFET) on 4H-SiC is investigated with a monolithically integrated driver and with an external driver for high-frequency, high-temperature applications. A new 'capacitor-coupled' gate driver circuitry is proposed and optimized to utilize a standard MOS driver and enable fast switching speed without the need for a negative power supply. Switching times and losses of the silicon carbide (SIC) HV-LJFET are characterized under various driver conditions and device temperatures. The results reveal that the temperature-independent, high switching speed of the SiC LJFET makes it possible to hard-switch at 3 MHz, 200 V, 1.2 A, and 250[degrees]C with good efficiency, significantly higher than silicon devices with similar voltage ratings. Index Terms--High frequency, JFET, power ICs, silicon carbide (SIC).

Distributed energy resources (DERs) are becoming integral components of electric power distribution systems. In most cases, an isolated dc-dc converter forms part of the interface required to connect the DER output to the distribution system. Operation of the converter at high switching frequencies results in size reduction of passive components at the expense of increased switching losses. However, silicon carbide (SiC) power devices have the potential of operating at high switching frequencies without significant loss penalty because of their fast switching times and ability to work at high temperatures when compared to similar Si devices. SiC diodes have already displayed the ability to offer more ideal diode behavior than Si diodes. Engineering samples of SiC MOSFETs are depicting lower switching losses and conduction losses over Si MOSFETs. This display is making SiC devices attractive for dc-dc converters used to connect DERs to the distribution system. This paper particularly deals with the design of a 300-W 100-kHz dc-dc full-bridge converter using zero-voltage zero-current switching for comparison of SiC MOSFETs and diodes against Si MOSFETs and diodes. Index Terms--DC-DC converters, distributed energy resources (DERs), full bridge, silicon carbide (SIC) MOSFET, zero-current zero-voltage switching.

An empirical large-signal model for high-power microwave silicon-carbide MESFETs capable of predicting self-heating thermal behavior is presented. A generalized drain-current equation based on pulsed-gate IV characteristics measuring up to 2 A and 58 V is presented along with its dependence on temperature. A thermal subcircuit with a nonlinear thermal resistance characterized by a dc method is used to model the temperature behavior of the device. The effect of substrate trapping is modeled as a gate--source voltage correction. The complete drain-current model accurately predicts pulsed-gate and pulsed-gate-and-drain IV characteristics for various quiescent biases, as well as static IV characteristics. The complete large-signal model is shown to accurately predict S-parameters, large-signal output, and input reflected power across biases and frequencies, and third-order intermodulation products. Index Terms--MESFET, model, nonlinear, self-heating, silicon-carbide (SIC), thermal.

A 720 mm diameter 12-segment-bonded carbon-fiber-reinforced silicon carbide (C/SiC) composite mirror has been fabricated and tested at cryogenic temperatures. Interferometric measurements show significant cryogenic deformation of the C/SiC composite mirror, which is well reproduced by a model analysis with measured properties of the bonded segments. It is concluded that the deformation is due mostly to variation in coefficients of thermal expansion among segments. In parallel, a 4-degree-of-freedom ball-bearing support mechanism has been developed for cryogenic applications. The C/SiC composite mirror was mounted on an aluminum base plate with the support mechanism and tested again. Cryogenic deformation of the mirror attributed to thermal contraction of the aluminum base plate via the support mechanism is highly reduced by the support, confirming that the newly developed support mechanism is promising for its future application to large-aperture cooled space telescopes. OCIS codes: 120.6650, 220.4840, 230.4040, 350.1260.

The ON-state characteristics of a 6-H silicon carbide (SIC) photoconductive switch with vertical geometry, transverse illumination, and linear-mode operation are presented. The switch is triggered by an optical source with a photon energy that is less than the bandgap energy of SiC. Following low-power matching characteristics, the analysis of a design incorporating [n.sup.+] and [p.sup.+] layers next to the cathode shows higher hold-off voltage with an improved ON-state response mechanism. The p-layered photoconductive semiconductor switch (PCSS) can be operated at a maximum field of 875 kV/cm, whereas the n-layered PCSS, which is operating at a slightly lower field, shows higher current carrying capabilities. Higher current for the n-layer PCSS can be attributed to the nature of the region adjacent to the cathode. In the p-layered PCSS, this region inhibits an initial hole collection, thus decreasing the collected charge. In addition, a kink during the initial collection for the p-layered PCSS could influence the rise time when operating beyond 35-kV bias. Index Terms--High-power microwaves, photoconductive semiconductor switches (PCSSs), silicon carbide (SIC).

Pixel radiation detectors made on epitaxial silicon carbide are presented. Two small-format prototypes have been fabricated: a 4 x 4 matrix with pixels of 400 x 400 [micro][m.sup.2] and 6 x 6 matrix with 200 x 200 [micro][m.sup.2] pixels. Typical leakage currents between 3 fA and 10 fA for the larger pixel size, and between 0.1 fA and 4 fA for the small pixels have been measured at 27[degrees]C, corresponding to current densities between 0.25 and 10 pA/[cm.sup.2]. In terms of equivalent noise charge, the contribution of most of the pixels is lower than 1 electron root mean square (rms) up to peaking times of tens of [micro]s of pulse shaping. These pixel detectors are ready for applications in ultimate-resolution X-ray spectroscopic imaging at room temperature when a suitable ultra low noise front-end electronics, presently not available, will be developed. An analysis of the experimental data on these detectors coupled to front-end transistors of commercial CMOS teclmologies is presented, indicating that a noise level of around 4-electrons rms can be achieved at room temperature, limited by the front-end 1/f noise. The conditions to fully exploit the SiC pixel capabilities are quantitatively analysed by considering CMOS technologies for front-end and preamplifier design and the continuous progress in the SiC growing processes. Index Terms--Schottky junctions, semiconductor detectors, silicon carbide, X-ray detectors.

The type of final chip passivation layer used to fabricate linear bipolar circuits can have a major impact on the total dose hardness of some circuits. It is demonstrated that National Semiconductor Corporation linear bipolar devices fabricated with only an amorphous silicon carbide passivation layer do not exhibit enhanced low-dose-rate sensitivity (ELDRS), while devices from the same production lot fabricated with other types of passivation layers are ELDRS sensitive. SiC passivation possesses mechanical, electrical and chemical properties that make it compatible with linear device fabrication processes. These properties of SiC passivation layers, combined with the excellent radiation response of devices passivated with SiC, make SiC passivation layers a very attractive choice for devices packaged in either ceramic or plastic-encapsulated packages for use in space environments. Index Terms--Enhanced low-dose-rate sensitivity (ELDRS), hardness assurance testing, integrated circuit reliability, integrated circuit testing, linear bipolar integrated circuits, mechanical stress, passivation layers, pre-irradiation elevated temperature stress, radiation effects, radiation hardening (electronics), radiation response, reliability screens, silicon carbide, thermal cycling, thermal stress effects.

The reactions of screw superdislocations or micropipes in silicon carbide single crystals are examined by using synchrotron radiation phase sensitive radiography. The simulation demonstrates that the coalescence of micropipes with opposite-sign Burgers vectors may be realized by their straightforward movement towards each other or their revolution about one another.

Logic circuits capable of operating at high temperatures can alleviate expensive heat-sinking and thermal-management requirements of modern electronics and are enabling for advanced propulsion systems. Replacing existing complementary metal-oxide semiconductor field-effect transistors with silicon carbide (SiC) nanoelectromechanical, system (NEMS) switches is a promising approach for low-power, high-performance logic operation at temperatures higher than 300[degrees]C, beyond the capability of conventional silicon technology. These switches are capable of achieving virtually zero off-state current, microwave operating frequencies, radiation hardness, and nanoscale dimensions. Here, we report a microfabricated electromechanical inverter with SiC complementary NEMS switches capable of operating at 500[degrees]C with ultralow leakage current. 10.1126/science.1192511

A simple and efficient route to produce C filled SiC nanotubes on a bulk scale without the need for oxide-assisted growth is described. The SiC nanotubes are carbon filled and open ended with both their mean diameter and diameter distribution being small.

Byline: Robert F. Davis The extreme thermal and electronic properties of diamond and of silicon carbide provide multiplicative combinations of attributes which lead to the highest figures of merit for any semiconductor materials for possible use in high-power, high-speed, high- temperature and high-frequency applications. The deposition of monocrystalline diamond. at or below 1 atm total pressure and at a temperature T < 1273 K has been achieved on diamond substrates; the deposited film has been polycrystalline on all other substrates but the achievement is no less significant. For electronic applications, heteroepitaxy of single-crystal films of diamond, an understanding of mechanisms of nucleation and growth methods of impurity introduction and activation, and further device development must be achieved. By contrast, all of these problems have already been solved for silicon carbide, including the operation of a MOSFET at 923 K - the highest operating temperature ever reported for a field-effect device. However, considerable research remains to be done regarding the development of large silicon carbide substrates of ohmic and rectifying contacts, of new types of devices, and of low temperature techniques for the deposition of insulating layers. Fugitive donor and acceptor species in unintentionally doped samples must also be identified and controlled.

Byline: Amar Patnaik, Alok Satapathy, S.S. Mahapatra, R.R. Dash Polymer composites with SiC reinforcement have received increased attention for applications in erosive environment because of their light weight and unique properties. Thus, it has become extremely important to investigate their erosion characteristics extensively. This paper describes the development of a theoretical model to estimate wear rate on solid particle erosion of a multi-component composite system consisting of a polyester resin reinforced with glass fibre and particles. Taguchi's orthogonal arrays are used for analysis of experiential results. It identifies significant control factors influencing the erosion wear and also outlines significant interaction effects.

Large-scale molecular dynamics simulation is used for studying the shock-wave propagation in pristine amorphous silicon carbide and carbon-nanotube-reinforced amorphous silicon carbide matrix composites. The studies have shown that the presence of aligned nanotubes in amorphous silicon carbide matrix has led to a reduction of shock-wave velocity and has modified the shock-wave front structure in a wide range of impact velocities.

Spheroidal inclusions in 4H-SiC homoepitaxial layers deposited by silane-based chemical vapor deposition (CVD) process are examined by KOH etching, optical microscopy and transmission electron microscopy. The inclusions consist of polycrystalline 3C silicon carbide and their origin is interpreted as due to SiC particles deposited on the wafer surface at the initial stages of the CVD process.

The article explains the impact of different growth conditions on the structural and morphological properties of the GaN buffer layers that are grown on SiC substrates by using the ammonia molecular beam epitaxy technique. An increase in the thickness of the buffer is shown to lead to a decrease in the dislocation density, as well as the compressive stress of the system.

The electrical properties of heavily Al doped single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multienergy, high-fluence Al implantation and subsequent furnace annealing, are examined by sheet resistance and Hall effect measurements. In single crystalline material efficient impurity band conduction due to strongly interacting acceptors can be achieved in the range of supersaturation and for lower doping levels impurity band conduction is more effective in nanocrystalline SiC.

Synchrotron-radiation photoemission and low electron energy diffraction are used to study the formation of silicon carbide upon deposition of [C.sub.60] onto Si(001) at an elevated temperature of 800 degree Celsius. The results have shown that the [C.sub.60] molecules are totally dissociated on a hot Si surface, where the freed carbon atoms form silicon carbide with the silicon substrate, and the spectral area ratio of both components has shown that the adlayer atoms cover half of the surface, which agrees with the missing-row structure model.

The preparation of highly ordered mesoporous SiC materials by using two types of nanoporous silica as templates and a low viscosity liquid polymer allylhydridopolycarbosilane as a stoichiometric SiC precursor is reported. The results have shown that the ordered structures of mesoporous SiC are exact inverse of their respective silica templates, as characterized by small angle X-ray diffraction (XRD), transmission electron microscope (TEM) images, and the adsorption-desorption isotherm of nitrogen.

The analysis of a 6H silicon carbide (SiC) photoconductive switch, designed and packaged for high-power, linear-mode operations, is presented. The analysis shows that improved performance at high power is possible through passivation using high-permittivity dielectric near the contact-semiconductor interface and by placing a p(super +) layer next to the cathode.

The influence of the operating parameters on 1-D SiC formation yield was studied. The study enlarged the family of nanofibers and nanotubes available and offered a possible, new general route to 1-D crystalline materials.

Interface trap passivation at the SiO2/carbon-terminated (0001) face of 4H-SiC utilizing nitridation and hydrogenation is evaluated. The results indicate that the as-oxidized C face contains a considerably higher trap density than the Si face near the conduction band, but nitric oxide and hydrogen processing results in comparable and low defect densities for all crystal faces.

The shock response of a silicon carbide is investigated using the methods of plate impact, and monitored using manganin stress gauges mounted to be responsive to lateral stress. A two-step stress response is observed, indicating the presence of delayed failure at the impact face.

A study is carried out on the nickel-based contacts deposited on 4H-SiC C-face substrates that were annealed at temperatures ranging from 800 to 1040 degree Celsius. Raman spectroscopy confirms the presence of a 40 nm thick nanocrystalline graphite film at the Ni(sub 2)Si-SiC interface, at the highest annealing temperature of 1040 degree Celsius.

A study develops a model for particulate composites, which includes phase transformations in one or all of the constituents. Representative simulations for a single-phase, brittle particulate (SiC) embedded in a ductile material (Ti), which undergoes a solid-solid phase transformation, are provided.

The model predictions were compared with the device measurements from room temperature to 200 degree C. The model agrees well with experiment and should be of use in designing silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) and related devices.

The self-diffusion in silicon carbide (SiC) utilizing isotopically enriched 4H(super 28)Si(super 12)C/(super nat)SiC heterostructures is examined. The interrelation between self- and B-diffusion is discussed.

The effects of radiation damage and impurity concentration on solid phase epitaxial growth of amorphous silicon carbide (SiC) are investigated. The retardation of recrystallization occurring in high dose sample is attributed to different amorphous structures between high and low dose samples.

Electron microscopy (SEM) and atomic force microscopy (AFM) was scanned to study micropipes in 6H, 4H, and 15R-SiC semiconductor wafers. The bases of the craters were examined by SEM and AFM to determine whether hollow dislocation cores (micropipes) were present.

High-dose phosphorous-ion (P super +) implantation into 4H-SiC (0001) followed by high-temperature annealing with a graphite cap was investigated. The sheet however showed weak temperature dependence.

The mean projected range Rp of 133 implantations into silicon carbide (SiC) with ion energies ranging from 0.2KeV to 4MeV was investigated. The low-velocity electronic stopping cross sections for ions with atomic numbers 1 less than or equal to Z1 less than or equal to 15 in SiC was determined.

Reduction of annealing temperature to prepare low resistance ohmic contact materials for p-type 4H-SiC was achieved by adding Ge to the conventional TiAl contacts. The GeTiA1 ohimic contacts were thermally stable during isothermal annealing at 400 degrees Celsius after preparing the ohmic contacts by annealing at 600 degrees Celsius that is also required by the device packaging process.

A nanosecond pulsed laser direct-write and doping (LDWD) technique is used for the fabrication of carbon-rich silicon carbide nanoribbons heterostructure in a single crystal 4H-SiC wafer. The LDWD technique permits synthesis of heterostructured nanoribbons in a single step without additional material or catalyst, and effectively eliminates the need for nanostructure handling and transferring processes.

4H-SiC wafers of orientation (0001) and (1120) arithmetic means were implanted with 60 keV Al(super -) in different major axial, planar, and low symmetry ('random') directions to ascertain the degree of channeling and to determine the optimum tilt conditions for ion implantation. The results can be used as a guide in the choice of implantation direction in order to minimize channeling, as standards to be used in the development of ion implantation simulators.

A full band Monte Carlo study of the electron transport in 3C-SiC is presented based on an ab initio band structure calculation using the local density approximation to the density functional theory. The scattering rates and impact ionization transition rates are calculated, and electron initiated impact ionization coefficients are found to be 2-10 times stronger than the reported values for the hole initiated impact ionization.

N-type SiC epitaxial growth was carried out in a water-cooled cold wall horizontal chemical vapor deposition (CVD) system using phosphine flow, temperature and C/Si ratio was studied. Variable temperature Hall measurements were used to characterize the doped layers.

An experiment was conducted to evaluate the shallow interface trap density near the conduction band in silicon carbide (SiC) metal-oxide-semiconductor (MOS) structure. The result reveals the close correlation between the channel mobility and the shallow interface trap density for the 4H- and 6H-SiC metal-oxide-semiconductor field-effect transistors (MOSEFTs) prepared with various gate-oxidation procedures.

A study was conducted to investigate the microscopic mapping of specific contact resistances on n-type 4H-SiC using sputtered TiW. The result shows how sample preparation influences differentially prepared samples on the same wafer using linear transmission line method (LTLM) measurements.

An experiment was conducted, by using standard phase modulated spectroscopic elipsometry (PMSE), to measure the ordinary dielectric function of common SiC poly-types 15R, 21R, 6H, and 4H. The result reveals that the effective oscillator strength of the dielectric difference function varies as a cubic polynomial with a turning point at the degree of hexagonality of 50 percent.