Materials Science Forum Vols. 778-780

Abstract: The bidirectional wireless power transfer system will have many advantages to charge the batteries of the electric vehicles. In their power supply circuit, the efficiency of the inverter and rectifier is important for total system efficiency. The inverter-rectifier, which is a type of power supply circuit in this system, performs inverter operation and rectifier operation. To reduce the loss of operation modes of both, we decided to use SiC power devices that are able to reduce switching loss. However, there is a problem of high conduction loss caused by the use of SiC power devices in rectifier operation. We propose the method of parallelizing SiC-MOSFET and diode of low forward voltage, and achieved a higher efficiency.

Abstract: Comparable to silicon the main way to improve the cost performance of SiC power devices is to go up with current density since the main selling point of a power device is its current handling capability. To follow this path successfully a couple of application and system relevant aspects should be taken into account beside the pure focus on reducing nominal or absolute losses at chip level. This paper will address some of those topics in combination with discussing state of the art device technologies on SiC. Also some considerations regarding the operation of SiC devices at elevated temperatures will be given, mainly targeting for increased power density and reduced losses in power electronic systems.

Abstract: High temperature SiC devices require the materials for packaging also capable of working at higher temperature than those for Si devices. SiC devices are expected to help hybrid vehicle power control units (PCUs) produce higher power in a more compact size as SiC can withstand higher voltages and temperatures (above 300°C) than silicon with less power loss. The improvement of interconnection technologies is increasingly becoming a top priority, particularly for the operation of SiC devices at relatively high temperatures. We propose a new interconnection method using nickel electroplating to replace Al wire bonding or die-bonding using solder materials. During the evaluation of the reliability of interconnections annealed at up to 500°C, we observed no significant changes in mechanical or electrical properties. We found that micro-plating connections can be used successfully for high-temperature-resistant packaging for SiC devices.

Abstract: In order to take full advantage of the high power density available by the packaging of SiC devices, this group has been exploring die attachment methods based on the sintering of silver particles between the device and Silver-plated Cu substrates with void free results. We have also extended this capability from not only attaching single chips assembled in TO-247 packages but also to multiple chips attached at once on a copper substrate. This multi-chip processing capability will aid in further development of SiC power modules.

Abstract: Thermal contact resistances have been measured in an experiment emulating heat transfer from a SiC die to a cooled heat sink through a heat spreader and a DBC structure. The major surface-dependent parameters are the surface roughness, surface hardness, and planarity. The measured thermal contact resistances are in agreement with theoretical values. When investigating DBC copper surfaces a second interface between the bonded Cu to AlN has to be taken into account.

Abstract: The aim of this study consists in comparing the effects of temperature on various SiC power devices. Electrical characteristics have been measured for temperatures from 100K to 525K. All devices are suitable for high temperature. However, SiC MOSFETs are not a good choice for cryogenic temperature, while SiC BJTs are less affected by temperature than other components, especially for cryogenic temperature.

Abstract: Low power Silicon Carbide (SiC) devices and Integrated Circuits (ICs) in conjunction with SiC or Aluminum Nitride (AlN) sensing elements will enable sensing functions in high temperature environments up to 600 °C where no silicon based devices or circuits have been able to survive in that temperature range. In power electronics applications, existence of low power SiC devices and IC technologies will significantly aid the development of high power density power modules in which total weights and cooling systems sizes are reduced. This paper will be evaluating the performances of the fabricated low power SiC device candidates (JFET and BJT) for SiC-based analog ICs design for high temperature and power electronics applications.

Abstract: Due to our demonstrated stable Tungsten-Schottky barrier at elevated temperatures, and also thanks to our technological process maturity regarding SiC-Schottky contact fabrication, we have implemented the digital logic gates library adopting a normally-on MESFET topology. In this paper we present new experimental results showing the thermal behavior up to 300oC of 4H-SiC logic gates library, monolithically integrating normally-on MESFETs and epitaxial resistors. The implemented SiC devices are based on important CMOS features and are specially designed for large ICs device integration density.

Abstract: Silicon carbide (SiC) is a well-known material for UV detection however the effect of UV illumination on the electron donation between the substrate, interfacial (or buffer layer) and graphene is not well understood. The effect of ultraviolet (UV) illumination on the carrier concentration of an epitaxial graphene hall bar device is investigated by scanning Kelvin probe microscopy (SKPM) and transport measurements in ambient and vacuum conditions. Modulation of the carrier concentration is demonstrated and shown to be due to both substrate and environmental effects.

Abstract: Epitaxial graphene fabricated by thermal decomposition of the Si-face of silicon carbide (SiC) forms a defined interface to the SiC substrate. As-grown monolayer graphene with buffer layer establishes an ohmic interface even to low-doped (e. g. [N] ≈ 10¹⁵ cm^-3) SiC, and a specific contact resistance as low as ρ_C = 5.9×10^-6 Ωcm² can be achieved on highly n-doped SiC layers. After hydrogen intercalation of monolayer graphene, the so-called quasi-freestanding graphene forms a Schottky contact to n-type SiC with a Schottky barrier height of 1.5 eV as determined from C-V analysis and core level photoelectron spectroscopy (XPS). This value, however, strongly deviates from the respective value of less than 1 eV determined from I-V measurements. It was found from conductive atomic force microscopy (C-AFM) that the Schottky barrier is locally lowered on other crystal facets located at substrate step edges. For very small Schottky contacts, the barrier height extracted from I-V curves approaches the value of 1.5 eV from C-V and XPS.