Challenges for High Temperature Silicon Carbide Electronics
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Challenges for High Temperature Silicon Carbide Electronics C.-M. Zetterling, S.-M. Koo, E. Danielsson, W. Liu, S.-K. Lee, M. Domeij, H.-S. Lee, and M. Ostling Department of Microelectronics and Information Technology, KTH, Royal Institute of Technology, Electrum 229, S-164 40 Stockholm-Kista, SWEDEN ABSTRACT Silicon carbide has been proposed as an excellent material for high-frequency, high-power and high-temperature electronics. High power and high frequency applications have been pursued for quite some time in SiC with a great deal of success in terms of demonstrated devices. However, self-heating problems due to the much higher power densities that result when ten times higher electrical fields are used inside the devices needs to be addressed. High-temperature electronics has not yet experienced as much attention and success, possibly because there is no immediate market. This paper will review some of the advances that have been made in hightemperature electronics using silicon carbide, starting from process technology, continuing with device design, and finishing with circuit examples. For process technology, one of the biggest obstacles is long-term stable contacts. Several device structures have been electrically characterized at high temperature (BJTs and FETs) and will be compared to surface temperature measurements and physical device simulation. Finally some proposed circuit topologies as well as novel solutions will be presented.
INTRODUCTION It is well known that SiC devices are promising for high voltage and high power applications because of its wide energy bandgap, high breakdown field, and high saturation drift velocity[1]. On the other hand, there are relatively few published papers on high-temperature properties of SiC devices [2, 3, 4, 5] The intrinsic carrier concentration ni of SiC is very low due to its wide energy bandgap. As ni is exponentially dependent on the temperature and the energy bandgap, SiC devices can operate at higher temperatures than other conventional materials with smaller bandgap (see Fig. 1). The horizontal line in Fig. 1 shows the temperature where devices may stop working as ni exceeds the background doping concentration (typically 1014 cm-3 for the low-doped region of power devices). Unlike e.g. silicon, the intrinsic concentration is not the limitation to high temperature operation of SiC devices. Considering the higher critical field of SiC (almost ten times that of Si), ten times smaller devices can be made and ten times higher power density is expected. However, SiC has only 2-3 times higher thermal conductivity λ (3.5 - 5 W/cmK) than silicon, hence 2-3 times higher junction temperature will result. These self-heating issues should be distinguished from the operation of sensors and circuits at elevated temperatures or perhaps in harsh environments. This paper considers some challenges for high-T electronics in terms of both self-heating and high temperature operation. The issues are divided into sections on process technology, device characteristics and ci
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