Krishna Shenai

Bio: Krishna Shenai is an academic researcher from University of Illinois at Chicago. The author has contributed to research in topics: Power semiconductor device & Power MOSFET. The author has an hindex of 30, co-authored 223 publications receiving 3767 citations. Previous affiliations of Krishna Shenai include University of Illinois at Urbana–Champaign & University of Maryland, College Park.

Optimum semiconductors for high-power electronics

Abstract: Elemental and compound semiconductors, including wide-bandgap semiconductors, are critically examined for high-power electronic applications in terms of several parameters. On the basis of an analysis applicable to a wide range of semiconducting materials and by using the available measured physical parameters, it is shown that wide-bandgap semiconductors such as SiC and diamond could offer significant advantages compared to either silicon or group III-V compound semiconductors for these applications. The analysis uses peak electric field strength at avalanche breakdown as a critical material parameter for evaluating the quality of a semiconducting material for high-power electronics. Theoretical calculations show improvement by orders of magnitude in the on-resistance, twentyfold improvement in the maximum frequency of operation, and potential for successful operation at temperatures beyond 600 degrees C for diamond high-power devices. New figures of merit for power-handling capability that emphasize electrical and thermal conductivities of the material are derived and are applied to various semiconducting materials. It is shown that an improvement in power-handling capabilities of semiconductor devices by three orders of magnitude is feasible by replacing silicon with silicon carbide; improvement in power-handling capability by six orders of magnitude is projected for diamond-based devices. >

Performance evaluation of high-power wide band-gap semiconductor rectifiers

Abstract: Applicability of GaN in unipolar and bipolar devices for high-power electronic applications is evaluated with respect to similar devices based on other materials. Specific resistance is used as a measure of unipolar performance. In order to evaluate bipolar performance, 700 and 6000 V p-i-n diodes based on Si, 6H-SiC, and GaN are compared with respect to forward conduction and reverse recovery performance at room temperature and high-temperature conditions. It is shown that GaN is advantageous not only for high voltage unipolar applications, but also for bipolar applications. An empirical closed-form expression is presented to predict the avalanche breakdown voltage of wide band-gap semiconductors. Formulation of the expression is based on an approximation of the impact ionization coefficient in terms of seventh power of the electric field.

Dynamics of power MOSFET switching under unclamped inductive loading conditions

Abstract: The parasitic bipolar transistor inherent in a vertical power DMOSFET structure can have a significant impact on its reliability. Unclamped Inductive Switching (UIS) tests were used to examine the reliability of DMOSFET's in extremely harsh switching conditions. The reliability of a power DMOSFET under UIS conditions is directly related to the amount of avalanche energy the device can survive. A number of DMOSFET structures were critically examined under UIS conditions to determine the impact of bipolar transistor parameters on device reliability. The UIS dynamics were studied based on the results obtained from an advanced mixed device and circuit simulator in which the internal carrier dynamics were evaluated under boundary conditions imposed by the circuit operation. It is shown that premature open base bipolar transistor breakdown can occur when the p-base sheet resistance is high. A device structure with a shallow self-aligned p/sup +/ region is shown to prevent the parasitic bipolar turn-on and avoid premature UIS breakdown without compromising the power-switching efficiency. The simulation results are shown to be in excellent agreement with the measured data under a wide range of inductive loading conditions.

Current transport mechanisms in atomically abrupt metal-semiconductor interfaces

Abstract: A comprehensive model for electron transport mechanisms across a fully formed Schottky-barrier junction is proposed in which the metal-semiconductor interface is approximated as an abrupt quantum mechanical transition. Improved formulations of the barrier-lowering mechanisms and carrier tunneling effects are derived where the dipole barrier lowering is modeled as a single exponential decay of the total surface charge density. Quantum calculations follow a two-band model in which the imaginary component of the electron wave vector in the semiconductor energy gap is obtained by including the effect of both conduction and valence states. The energy band profile effects are included in the calculation of tunneling current, and it is shown that the finite negative charge residing at the metal-semiconductor interface considerably modulates the tunneling transmission probability of carriers. Experimental results obtained from atomically clean Al-n/sup +/GaAs-nGaAs interfaces fabricated by in situ molecular-beam epitaxy (MBE) are shown to be in excellent agreement with the transport calculations. >

Future Prospects of Widebandgap (WBG) Semiconductor Power Switching Devices

Abstract: Electrical power switching devices based on widebandgap (WBG) semiconductors have the potential for transformative impact on a wide range of energy conversion applications. Significantly improved electrical and thermal conductivities of WBG semiconductors compared with the semiconductor silicon have the potential for more efficient, compact, and robust power conversion systems. However, to offset inherently higher manufacturing cost of WBG power devices and obtain system-level benefits, power converters need to be operated at higher semiconductor chip junction temperatures and/or at higher switching frequencies. This paper discusses the future prospects of WBG-based power electronics by considering the current state of the art of WBG chip manufacturing, packaging, and thermal management technologies.

Comparison of 6H-SiC, 3C-SiC, and Si for power devices

Abstract: The drift region properties of 6H- and 3C-SiC-based Schottky rectifiers and power MOSFETs that result in breakdown voltages from 50 to 5000 V are defined. Using these values, the output characteristics of the devices are calculated and compared with those of Si devices. It is found that due to very low drift region resistance, 5000-V SiC Schottky rectifiers and power MOSFETs can deliver on-state current density of 100 A/cm/sup 2/ at room temperature with a forward drop of only 3.85 and 2.95 V, respectively. Both devices are expected to have excellent switching characteristics and ruggedness due to the absence of minority-carrier injection. A thermal analysis shows that 5000-V, 6H-, and 3C-SiC MOSFETs and Schottky rectifiers would be approximately 20 and 18 times smaller than corresponding Si devices, and that operation at higher temperatures and at higher breakdown voltages than conventional Si devices is possible. Also, a significant reduction in the die size is expected. >

HVDC Circuit Breakers: A Review Identifying Future Research Needs

Abstract: The continuously increasing demand for electric power and the economic access to remote renewable energy sources such as off-shore wind power or solar thermal generation in deserts have revived the interest in high-voltage direct current (HVDC) multiterminal systems (networks). A lot of work was done in this area, especially in the 1980s, but only two three-terminal systems were realized. Since then, HVDC technology has advanced considerably and, despite numerous technical challenges, the realization of large-scale HVDC networks is now seriously discussed and considered. For the acceptance and reliability of these networks, the availability of HVDC circuit breakers (CBs) will be critical, making them one of the key enabling technologies. Numerous ideas for HVDC breaker schemes have been published and patented, but no acceptable solution has been found to interrupt HVDC short-circuit currents. This paper aims to summarize the literature, especially that of the last two decades, on technology areas that are relevant to HVDC breakers. By comparing the mainly 20+ years old, state-of-the art HVDC CBs to the new HVDC technology, existing discrepancies become evident. Areas where additional research and development are needed are identified and proposed.

Condition Monitoring for Device Reliability in Power Electronic Converters: A Review

Abstract: Condition monitoring (CM) has already been proven to be a cost effective means of enhancing reliability and improving customer service in power equipment, such as transformers and rotating electrical machinery. CM for power semiconductor devices in power electronic converters is at a more embryonic stage; however, as progress is made in understanding semiconductor device failure modes, appropriate sensor technologies, and signal processing techniques, this situation will rapidly improve. This technical review is carried out with the aim of describing the current state of the art in CM research for power electronics. Reliability models for power electronics, including dominant failure mechanisms of devices are described first. This is followed by a description of recently proposed CM techniques. The benefits and limitations of these techniques are then discussed. It is intended that this review will provide the basis for future developments in power electronics CM.

Power semiconductor device figure of merit for high-frequency applications

Abstract: A figure of merit (the Baliga high-frequency figure of merit) is derived for power semiconductor devices operating in high-frequency circuits. Using this figure of merit, it is predicted that the power losses incurred in the power device will increase as the square root of the operating frequency and approximately in proportion to the output power. By relating the device power dissipation to the intrinsic material parameters, it is shown that the power loss can be reduced by using semiconductors with larger mobility and critical electric field for breakdown. Examination of data in the literature indicates that significant performance improvement can be achieved by replacing silicon with gallium arsenide, silicon carbide, or semiconducting diamond. >

A Literature Review of IGBT Fault Diagnostic and Protection Methods for Power Inverters

Abstract: This paper presents a survey on existing methods for fault diagnosis and protection of insulated gate bipolar transistors with special focus on those used in three-phase power inverters. Twenty-one methods for open-circuit faults and ten methods for short-circuit faults are evaluated and summarized, based on their performance and implementation efforts. The gate-misfiring faults and their diagnostic methods are also briefly discussed. Finally, the promising methods are recommended for future work.