Papers by Keyword: Avalanche Breakdown

Abstract: A p-n junction diode with mesa structure by silicon carbide (SiC) has been developed to utilize the avalanche breakdown in an excessed reverse bias condition to clamp the surge voltage in switch-mode power supplies. Static voltage-current correlation by pulsed reverse voltage has been measured. The increase of the breakdown voltage was measured to be 32 volts with increased current density up to 3900 A/cm². The operational performance in suppressing the surge voltage in a step-down DC/DC converter has been evaluated. A superior performance in suppressing the surge voltage by the SiC p-n junction diode has been confirmed. It was also found that a resonant oscillation induced during clamping period limits the performance. By a circuit analysis with an equivalent circuit model, it was found that a parasitic wiring inductance between the diode and switching element induces the resonance. It was also found that a promising way to mitigate the disturbing effect is to minimize the inductance.

Abstract: The reliability of SiC devices remains to be a field of hectic activity because it is one of the obstacles for the ubiquitous application of SiC devices. Without decades of field experience, reliability testing, especially accelerated testing, is the only way to obtain information on reliability during the projected lifespan of the devices. For silicon devices, such tests exist and they are canonized in internationally recognized test standards. For SiC devices, these standards have to be revised and/or supplemented with tests to capture SiC specific degradation mechanisms. On the one hand, this requires a detailed knowledge about the mechanisms but on the other hand, this also requires the mission profile of the devices. In fact, it is not the mission profile of the device that determines its reliability but the mission profile of the chip. This contribution reviews the standard silicon tests useful for SiC devices and looks into additional, SiC specific tests that have been proposed but not yet been recognized as standards.

Abstract: Wide-bandgap power semiconductor devices offer enormous energy efficiency gains in a wide range of potential applications. As silicon-based semiconductors are fast approaching their performance limits for high power requirements, wide-bandgap semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) with their superior electrical properties are likely candidates to replace silicon in the near future. Along with higher blocking voltages wide-bandgap semiconductors offer breakthrough relative circuit performance enabling low losses, high switching frequencies, and high temperature operation. ARPA-E’s SWITCHES program, started in 2014, set out to catalyze the development of vertical GaN devices using innovations in materials and device architectures to achieve three key aggressive targets: 1200V breakdown voltage (BV), 100A single-die diode and transistor current, and a packaged device cost of no more than ȼ10/A. The program is drawing to a close by the end of 2017 and while no individual project has yet to achieve all the targets of the program, they have made tremendous advances and technical breakthroughs in vertical device architecture and materials development. GaN crystals have been grown by the ammonothermal technique and 2-inch GaN wafers have been fabricated from them. Near theoretical, high-voltage (1700-4000V) and high current (up to 400A pulsed) vertical GaN diodes have been demonstrated along with innovative vertical GaN transistor structures capable of high voltage (800-1500V) and low R_ON (0.36-2.6 mΩ-cm2). The challenge of selective area doping, needed in order to move to higher voltage transistor devices has been identified. Furthermore, a roadmap has been developed that will allow high voltage/current vertical GaN devices to reach ȼ5/A to ȼ7/A, realizing functional cost parity with high voltage silicon power transistors.

Abstract: Silicon carbide Schottky-barrier diode (SBD) rectifiers have been manufactured with low on-state voltages, high surge currents and high avalanche ruggedness. Non-destructive unclamped inductive switching currents of 188 A (mean) are achieved for the 1200 V 15 A rectifier. Very tight distribution of maximum sustained UIS current is confirmed. We relate improved avalanche ruggedness to bulk avalanche breakdown and show the breakdown pattern of the new Schottky rectifier being the same type as that for the p-n diode.

Abstract: A two-dimensional position sensitive detecting sensor (PSD) based on avalanche breakdown is introduced in this paper. The structure of the sensor is designed under the assumption that the breakdown of the PN junction in the sensor occurs at the bottom of the PN junction. The breakdown structure and characteristics of the sensor are simulated by Medici software and the doping structure and process conditions are calculated by Tsuprem4 software. By using COMSOL Multiphysics, we obtained current allocation of the straight and right angle type electrodes, which is corresponding to the optimal structure. In simulation, the root mean square error of the rectangular-shaped electrode and the straight line-shaped electrode are 0.198, 0.145 respectively. Experiment results show that in the 50% photosensitive area with the center as the origin, the rectangular-shaped electrode error is much smaller than a straight line-shaped electrode and fits in to linear relationship better. But the error of the angle the boundary of the electrode is significantly worse than the line-shaped electrode.

Abstract: A breakdown of a conventional trench SiC-MOSFET is caused by oxide breakdown at the bottom of the trench. We have fabricated a novel trench SiC-MOSFET with buried p+ regions and demonstrated the high breakdown voltage of 1700 V and the specific on-resistance of 3.5 mΩcm².

Abstract: Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (M_p) and electrons (M_n), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

Abstract: The energy dissipation capabilities of a 1200 V, 0.1 cm2 JFET operating in blocking mode were investigated. These devices, which are used in bidirectional circuit breaker applications, can conduct a current of 13 A in forward-conduction mode, and typically block a voltage up to 1200 V in blocking mode. In this document, the blocking limits of the device were pushed slightly to the point where avalanche breakdown occurs. A high voltage pulse generator was designed and constructed to drive the JFET into this state and to monitor the dissipated energy. The devices were able to handle up to 18.14 mJ.

Abstract: PN junction is one of the most important parts of solar cells. Its quality affects lifetime and efficiency of solar cells. Local defects which appear in PN junctions during the manufacture process are very important from this point of view. These are caused by localized areas with high donor or acceptor doping agents, impurities, dislocations or other mechanisms which effect in lower breakdown voltage of PN junction in reverse bias. Several base methods can be used for solar cells nondestructive diagnostics. Measuring methods of low-band noise current effective value with reverse bias junction were used in this paper. This method allows detection of local defects and volume degradation in PN junctions of solar cells and it can be used for detection of microplasma noise. This noise is an impulse noise and it is caused by local avalanche breakdowns in small area of the junction. It can be recognized by two or more level random square current pulses with constant height, random appearance time and random pulse length. Information about these effects can be used in noise diagnostics of structural defects of PN junctions and then it can be used for quality and lifetime estimation of samples with these parameters.

Abstract: In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.