Srikanth Kulkarni

Bio: Srikanth Kulkarni is an academic researcher from University of Idaho. The author has contributed to research in topics: Inverter & Power module. The author has an hindex of 3, co-authored 6 publications receiving 173 citations. Previous affiliations of Srikanth Kulkarni include Micron Technology & Maxim Integrated.

Development of a SiC JFET-Based Six-Pack Power Module for a Fully Integrated Inverter

Abstract: In this paper, a fully integrated silicon carbide (SiC)-based six-pack power module is designed and developed. With 1200-V, 100-A module rating, each switching element is composed of four paralleled SiC junction gate field-effect transistors (JFETs) with two antiparallel SiC Schottky barrier diodes. The stability of the module assembly processes is confirmed with 1000 cycles of -40°C to +200°C thermal shock tests with 1.3°C/s temperature change. The static characteristics of the module are evaluated and the results show 55 mΩ on-state resistance of the phase leg at 200°C junction temperature. For switching performances, the experiments demonstrate that while utilizing a 650-V voltage and 60-A current, the module switching loss decreases as the junction temperature increases up to 150°C. The test setup over a large temperature range is also described. Meanwhile, the shoot-through influenced by the SiC JFET internal capacitance as well as package parasitic inductances are discussed. Additionally, a liquid cooled three-phase inverter with 22.9 cm × 22.4 cm × 7.1 cm volume and 3.53-kg weight, based on this power module, is designed and developed for electric vehicle and hybrid electric vehicle applications. A conversion efficiency of 98.5% is achieved at 10 kHz switching frequency at 5 kW output power. The inverter is evaluated with coolant temperature up to 95°C successfully.

High density 50 kW SiC inverter systems using a JFET based six-pack power module

Abstract: Recent progress on Silicon Carbide (SiC) power devices has shown their better power conversion efficiency compared to Silicon power devices due to the significant reduction in both conduction and switching losses. Combined with their high operating junction temperature capability, six-pack SiC power modules have been developed for high reliable and compact power systems. This paper focuses on the development of a high efficiency and high temperature inverter based on fully integrated SiC power modules. The main topic includes the SiC power module design targeting on high temperature operation (Tj>200 °C), full three phase inverter design and prototype development, and the inverter evaluation. A liquid cooled SiC inverter prototype with a peak power rating of 50 kW has been developed and demonstrated. When tested at moderate load levels compared to the inverter rating, an efficiency of 98.5% is achieved by the initial prototype, which is higher than most Si inverters.

Implementation of a fully integrated 50 kW inverter using a SiC JFET based six-pack power module

Abstract: A fully integrated Silicon Carbide (SiC) JFET/SBD based six-pack power module is designed and developed. The stability of the module assembly processes are confirmed with thermal shock test of −40 to +200 °C temperature cycling. A three phase inverter with the SiC power module is designed and developed for the EV/HEV applications. The liquid cooled inverter is 22.9 × 22.4 × 7.1 cubic centimeters in volume (∼8.35kW/L) and 3.53 kilograms in weight (∼8.5kW/kg). A conversion efficiency of 98.5% is achieved at 10 kHz switching frequency and 10 kW. The inverter is evaluated with coolant temperature up to 95 °C successfully.

Techniques for adhesive control between a substrate and a die

Abstract: Semiconductor devices are described that employ techniques configured to control adhesive application between a substrate and a die. In an implementation, a sacrificial layer is provided on a top surface of the die to protect the surface, and bonds pads thereon, from spill-over of the adhesive. The sacrificial layer and spill-over adhesive are subsequently removed from the die and/or chip carrier. In an implementation, the die includes a die attach film (DAF) on a bottom surface of the die for adhering the die to the cavity of the substrate. The die is applied to the cavity with heat and pressure to cause a portion of the die attach film (DAF) to flow from the bottom surface of the die to a sloped surface of the substrate cavity.

Evaluation of Direct Bond Aluminum Substrates for Power Electronic Applications in Extreme Environments

Abstract: Power packages that require large current capacities typically employ some form of thick conductive traces attached to a thermally conductive ceramic material to create a suitable package substrate. The most common substrate currently used in high power applications is Direct Bonded Copper (DBC). Though this is a well established, reliable, and commonly used substrate, DBC suffers from poor long term mechanical reliability when exposed to extreme temperature excursions. In an attempt to improve on this technology, substrate materials such as Active Metal Bond / Braze (AMB) and Direct Bonded Aluminum (DBA) are being investigated. Previous work has shown that the accelerated aging / thermal shock lifetimes of DBC and AMB are significantly shorter than that of DBA substrates. Though DBA substrates last longer, they still have some issues that require attention before it can be accepted as an improved alternative to DBC substrates in these types of applications. The main issues that have been observed are DBA...

An Experimental Investigation of the Tradeoff between Switching Losses and EMI Generation With Hard-Switched All-Si, Si-SiC, and All-SiC Device Combinations

Abstract: Silicon carbide (SiC) switching power devices (MOSFETs, JFETs) of 1200 V rating are now commercially available, and in conjunction with SiC diodes, they offer substantially reduced switching losses relative to silicon (Si) insulated gate bipolar transistors (IGBTs) paired with fast-recovery diodes. Low-voltage industrial variable-speed drives are a key application for 1200 V devices, and there is great interest in the replacement of the Si IGBTs and diodes that presently dominate in this application with SiC-based devices. However, much of the performance benefit of SiC-based devices is due to their increased switching speeds ( di/dt, dv/ dt), which raises the issues of increased electromagnetic interference (EMI) generation and detrimental effects on the reliability of inverter-fed electrical machines. In this paper, the tradeoff between switching losses and the high-frequency spectral amplitude of the device switching waveforms is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. While exploiting the full switching-speed capability of SiC-based devices results in significantly increased EMI generation, the all-SiC combination provides a 70% reduction in switching losses relative to all-Si when operated at comparable dv/dt. It is also shown that the loss-EMI tradeoff obtained with the Si-SiC device combination can be significantly improved by driving the IGBT with a modified gate voltage profile.

A 1200-V, 60-A SiC MOSFET Multichip Phase-Leg Module for High-Temperature, High-Frequency Applications

Abstract: In this paper, a high-temperature, high-frequency, wire-bond-based multichip phase-leg module was designed, fabricated, and fully tested. Using paralleled Silicon Carbide (SiC) MOSFETs, the module was rated at 1200 V and 60 A, and was designed for a 25-kW three-phase inverter operating at a switching frequency of 70 kHz, and in a harsh environment up to 200 °C, for aircraft applications. To this end, the temperature-dependent characteristics of the SiC MOSFET were first evaluated. The results demonstrated the superiority of the SiC MOSFET in both static and switching performances compared to Si devices, but meanwhile did reveal the design tradeoff in terms of the device's gate oxide stability. Various high-temperature packaging materials were then extensively surveyed and carefully selected for the module to sustain the harsh environment. The electrical layout of the module was also optimized using a modeling and simulation approach, in order to minimize the device parasitic ringing during high-speed switching. Finally, the static and switching performances of the fabricated module were tested, and the 200 °C continuous operation of the SiC MOSFETs was verified.

Active Gate Driver for Crosstalk Suppression of SiC Devices in a Phase-Leg Configuration

Abstract: In a phase-leg configuration, the high-switching-speed performance of silicon carbide (SiC) devices is limited by the interaction between the upper and lower devices during the switching transient (crosstalk), leading to additional switching losses and overstress of the power devices. To utilize the full potential of fast SiC devices, this paper proposes two gate assist circuits to actively suppress crosstalk on the basis of the intrinsic properties of SiC power devices. One gate assist circuit employs an auxiliary transistor in series with a capacitor to mitigate crosstalk by gate loop impedance reduction. The other gate assist circuit consists of two auxiliary transistors with a diode to actively control the gate voltage for crosstalk elimination. Based on CREE CMF20120D SiC MOSFETs, the experimental results show that both active gate drivers are effective to suppress crosstalk, enabling turn-on switching losses reduction by up to 17%, and negative spurious gate voltage minimization without the penalty of decreasing the switching speed. Furthermore, both gate assist circuits, even without a negative isolated power supply, are more effective in improving the switching behavior of SiC devices in comparison to the conventional gate driver with a -2 V turn-off gate voltage. Accordingly, the proposed active gate assist circuits are simple, efficient, and cost-effective solutions for crosstalk suppression.

Improving SiC JFET Switching Behavior Under Influence of Circuit Parasitics

Abstract: This paper investigates the switching behavior of normally OFF silicon carbide (SiC) JFETs in an inverter for a motor drive. The parasitic ringing caused by different parasitic effects is analyzed. Two different methods, the use of an RC snubber and the use of suppression ferrite component, are investigated for dampening the parasitic oscillations. It is found that applying a ferrite bead not only dampens the parasitic oscillations, but also results in significantly lower switching losses. Furthermore, it is shown that the capacitive coupling between SiC devices in the bridge leg and heat sinks significantly deteriorates the JFETs' switching performance. The effect of two substrates, an insulated metal substrate and a printed circuit board, on the capacitive coupling is investigated. A method in which the use of two separate heat spreaders minimizes the capacitive coupling, thus, exploiting the full potential of fast SiC JFETs is proposed.

Datasheet Driven Silicon Carbide Power MOSFET Model

Abstract: A compact model for SiC Power MOSFETs is presented. The model features a physical description of the channel current and internal capacitances and has been validated for dc, CV, and switching characteristics with measured data from a 1200-V, 20-A SiC power MOSFET in a temperature range of 25°C to 225°C. The peculiar variation of on-state resistance with temperature for SiC power MOSFETs has also been demonstrated through measurements and accounted for in the developed model. In order to improve the user experience with the model, a new datasheet driven parameter extraction strategy has been presented which requires only data available in device datasheets, to enable quick parameter extraction for off-the-shelf devices. Excellent agreement is shown between measurement and simulation using the presented model over the entire temperature range.