Papers by Keyword: Heavy Ions

Abstract: Single Event Gate Rupture (SEGR) is one of the catastrophic failures caused by heavy ions in power MOS devices. In this study, n-type SiC MOS capacitors representing the gate structure generally used in SiC power MOSFETs were used to conduct heavy ion irradiation tests to clarify the SEGR mechanism. The Linear Energy Transfer (LET) dependence of the critical electric field (E_cr) for these capacitors was evaluated with two different oxidation processes in accumulation to confirm whether the oxidation process affects SEGR tolerance. We found that the E_cr value and slopes of the LET dependence for SEGR between DRY samples and DRY + POA samples were approximately consistent. We also simulated SEGR and studied its mechanism. The simulation results suggested that SEGR for SiC MOS capacitors is caused by carriers in electron-hole pairs generated by a heavy ion instead of gate electric field fluctuation.

Abstract: We compare the failure mechanism and performance of a silicon carbide (SiC) semi-superjunction (semi-SJ) power DMOSFET against pure SJ and conventional DMOSFET when struck by a single heavy ion. The Single-Event Burnout (SEB) failure mechanism was identified as the thermal runaway from second breakdown resulting in mesoplasma formation. The semi-SJ design shifts the mesoplasma location from the drift/substrate interface seen in the control device structures to a location along the center of the P-pillar and closer towards the DMOSFET surface, thus significantly improving the SEB threshold voltage (V_SEB). The V_SEB varies with pillar width and ratio of pillar thickness to drift layer thickness. A maximum value of V_SEB is reached when the pillar to drift layer ratio is 0.9 and the pillar width is 2.4 μm. The semi-SJ SEB/breakdown voltage ratio is 100% and 13% higher than the pure SJ and conventional DMOSFET, respectively. Using a new Figure of Merit (FoM), which accounts for the tradeoff between V_SEB and on-state performance, we find that the SiC semi-SJ DMOSFET achieves a FoM that is 1.8 and 8 times higher than SJ and conventional DMOSFET, respectively, making the semi-SJ a competitive candidate for radiation hardened applications.

Abstract: This paper describes the mechanisms behind the failure of silicon carbide (SiC) Power MOSFETs (metal oxide semiconductor field effect transistors) when struck by a heavy ion. The modeled device is designed to simulate a commercially available 1200 V power MOSFET under the strike of a silver ion with a Linear Energy Transfer (LET) of 46 MeV-cm²/mg commonly used in single event effect (SEE) testing. The device is shown in simulation to fail near 500 V, which is in close agreement to experiments. The failure occurs near the interface between the epitaxial layer and the substrate layer due to the rapid increase of the electric field in that region and destruction of the device from impact ionization. Two improved designs were proposed and investigated that would help to mitigate the electric field in these regions and improve the device’s tolerance to single-event burnout (SEB). The new designs increased the voltage at which SEB occurs from 500 V to over 900 V and increased the specific on-resistance (R_on,sp) by only 5%.

Abstract: Passage of heavy ions produces radiation-damage trails known as latent tracks in a variety of solid-state nuclear-track detectors (SSNTDs). These tracks are made visible in an optical microscope by a simple process known as chemical etching. It is a well-known fact that latent tracks are radiation damage trails in SSNTDs, which can be annealed by thermal heating. Modgil-Virk formulation of single-activation-energy model of radiation damage annealing was proposed as an empirical approach for explaining the thermal fading of nuclear tracks in SSNTDs. The empirical formulation of this model is based on track annealing data collected from both isothermal and isochronal experiments performed on different types of SSNTDs using a variety of heavy ion beams and fission fragments. The main objective of this empirical model was to resolve some contradictions of variable activation energy derived by using Arrhenius plots to study annealing in mineral SSNTDs. Some equivalent versions of the Modgil-Virk model have been proposed but the concept of single activation energy is vindicated in all empirical formulations. The model always yields a unique value of activation energy independent of the nature of the ion beam used and the degree of annealing. The anisotropy of the mineral SSNTDs is revealed by variation in activation energy along different crystal planes and even with different orientations of the ion beam on the same plane. Some recent experiments are a pointer to the successful exploitation of this model for future cosmic-rays studies using SSNTDs.

Abstract: The energy loss for swift heavy ions, covering Z=3-29(~0.2 - 5.0MeV/n), has been calculated in the elemental absorbers like C, Al and Ti. The present calculations are based on Bohr’s approach applicable in both classical and quantum mechanical regimes. The major input parameter, the effective charge, has been calculated in a different way without any empirical/semi-empirical parameterization. The calculated energy loss values have been compared with the available experimental data which results in a close agreement.

Abstract: Range of heavy ion is one of the important parameters and understanding of this parameter is highly essential in almost all those experiments where heavy ions are used. The present review deals with the range measurements of different heavy ions through solid state nuclear track detectors (SSNTDs) technique. The importance of SSNTD technique as compared to other techniques is highlighted and different methods/models proposed for range measurements are described. An attempt has been made to compile the measured range values for heavy ions from H⁴ to U²³⁸ in different classes of SSNTD materials viz. polymers, glasses and minerals, from the available literature. An inter-comparison between the measured range values of different laboratories and through different range measurement methods has been made. Further, the reliability and validity of most commonly used theoretical and semi-empirical/empirical range formulations, through comparison with the measured range, are highlighted. Furthermore, the isotropic and anisotropic behaviour in polymers and minerals through range measurements has been described.Contents of Paper

Abstract: 4H-SiC ultraviolet photodetectors based on Schottky barriers have been formed on lightly doped n-type epitaxial layers grown by chemical vapor deposition method on industrial substrates. The diode structures were irradiated at 25°C with 167 MeV Xe ions at a fluence of 6x10⁹ cm^-2. Comparative studies of the optical and electrical properties of initial and irradiated structures with Schottky barriers were carried out in temperature range 23-180°C. Swift heavy ion stimulated changes in photosensitivity and electrical characteristics of the initial and irradiated detectors are explained in terms of the fluctuation traps model with the subsequent thermal dissociation.

Abstract: This paper shows a comparison between two different MOSFET structures: a conventional layout (CM) and Diamond (DM - enclosed layout transistor), as tolerance to the Single Event effect - SEE. Both CMOS 0.35μm technology devices types have the same geometric factor (W/L) and during irradiation were monitored continuously to detect and acquire the SEEs applying a new approach with a PXI test system. For this work was used heavy ion beams produced at the São Paulo 8 UD Pelletron accelerator.

Abstract: t is well established that the properties of the materials can be tailored as per specific requirements as a result of swift heavy ion irradiation. This is because of the radiation damage induced changes in the properties of the materials as a result of the energy loss process of the incident ions along their trajectory. In order to correlate such induced changes with the energy loss of the impinging ions, the exact evaluation of energy loss for swift ions in different materials is extremely important. Keeping in mind the polymers as versatile materials, in the present work, we have focused on energy loss calculations for swift heavy ions with Z= 3-29 in different polymeric absorbers, e.g. Polypropylene PP (C₃H₆), Polycarbonate PC (C₁₆H₁₄O₃), Polyethylene terepthalate PET (C₁₀H₈O₄), Polyethylene naphthalate PEN (C₇H₅O₂), Diethylene glycol bis (allyl carbonate) CR-39 (C₁₂H₁₈O₇), Cellulose nitrate LR-115 (C₆H₉O₉N₂) and Polypyromellitimide KAPTON (C₂₂H₁₀O₅N₂) in the energy range 0.5-6.00 MeV/n. The present calculations have been made by employing the proper energy loss formulation applicable both at low as well as high energies, involving a new approach for effective charge parameterization without any empirical/semi-empirical means. A close agreement between these calculated and experimentally measured values has been observed. Such calculations will provide an input towards the modeling or simulation for swift heavy ion induced changes in the properties of materials.

Abstract: The paper presents some results of a complex research of 12Cr18Ni10Ti stainless steel in the initial, deformed and irradiated ( ⁸⁴₃₆K_r⁺¹⁴, E=130MeV, F_max=9x10¹⁵ ions/сm2) states using magnetometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD – analysis). Application of the EBSD method revealed differences between the non-irradiated and irradiated 12Cr18Ni10Ti steel specimens consisting in the fact that in the surface layer of an irradiated sample α-and ε - phases are formed. It was established that the fluence value affects the amount of magnetic α-phase. The study of the martensite α-phase morphology showed that in the deformed steel specimens there is αʹ- martensite of two scale levels.