Silicon Carbide Power Devices and Processing
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Silicon Carbide Power Devices and Processing J.B. Casady, J.R. Bonds, W.A. Draper, J.N. Merrett, I. Sankin, D. Seale1 and M.S. Mazzola1 SiC Devices Group, SemiSouth Laboratories, Inc., One Research Blvd., Starkville, MS 39759, U.S.A. 1 ECE Department, Mississippi State University Mississippi State, MS 39762, U.S.A. ABSTRACT An overview of silicon carbide (SiC) power device technology is given with an emphasis on processing issues and commercial applications. Schottky Barrier Diodes (SBDs) were the first to be made commercially available in 2001, with power switch and RF amplifiers soon to follow. This paper discusses the performance of current available rectifiers and published power switch development and identifies key issues in processing and device structures which have influenced past and will impact future SiC product development. INTRODUCTION Silicon carbide (SiC) power devices have advanced considerably in recent years, with the release of commercial 600 V, 1-10 A Schottky Barrier Diodes (SBD’s) in 2001 from corporations such as Cree, Infineon, and SemiSouth. These rectifiers are available commercially in packaged form from other suppliers such as IXYS, Microsemi, and SiCED. Higher rated rectifiers (in both voltage and current) are being developed and released, in addition to SiC power switch development. An example of a higher rated rectifier is shown in Figure 1, where a 1.6 kV SiC SBD’s blocking characteristics are illustrated on a curve tracer. These diodes, fabricated in early 2003 at SemiSouth, had a 10 µm thick drift region, doped n-type at 5x1015 cm-3. Diode diameter for 1.6 kV SBD was 200 µm, while 1 mm diameter diodes on the same wafer (2 A forward current at 2 V drop) were typically blocking 1.0-1.4 kV.
Figure 1: Reverse blocking characteristics of a 1.6 kV 4H-SiC SBD (left), and a die-level view of probed SBD’s (right) fabricated in early 2003 at SemiSouth. Blocking layer epitaxy was 10 µm thick, doped n-type at 5x1015 cm-3. Diode area for 1.6 kV SBD was 3.14x10-2mm2, while 1 mm2 on the same wafer were typically blocking 1.0-1.4 kV.
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In switch development, although Gate Turn-Off thyristors (GTO’s) and Insulated Gate Bipolar Transistors (IGBT’s) have been reported, most of the near-term switch development appears to be focused on basic MOSFET, VJFET, and BJT configurations [1-8]. From a processing and applications point of view, each device type has strengths and weaknesses. The MOSFET is a normally-off, voltage driven switch, ideal for many applications. However, it suffers from poor inversion layer mobility and suspect high-temperature, high-field reliability because of the relatively low barrier to Fowler-Nordheim tunneling on wide bandgap (3.2 eV) SiC. The JFET is also a voltage-driven switch, and is more robust for high-temperature, highfield, and even high-radiation environments because of the absence of the MOS system. It has high input impedance, but is difficult to make normally-off without modification for high-current devices. Finally, the BJT has demonstrated good vol
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