SBIR-STTR Award

The rapid development of the technology for producing high quality single crystal SiC wafers and thin films presents the opportunity to fabricate solid-state devices with power-temperature capability far greater than devices currently available. While conventional silicon power devices are already being used near their limits of operating temperature and power, the potential of SiC is just beginning to be demonstrated. Vertical power MOSFET structures fabricated in 4H-SiC with 150 V capability have already shown current densities of 100 A/cm2 with a voltage drop of 3.3 V (specific on-resistance of 33 m -cm2. These devices showed good characteristics at temperatures up to 300 C. 4H-SiC thyristors have been demonstrated up to 500 C that block 200 V and have current densities of 500 A/cm2 at 3.8 V. While these are promising results, these devices have been far from reaching their theoretical voltages based on the doping levels used. One of the reasons for the relatively low voltages is the lack of good junction termination techniques for SiC. Therefore it is proposed that different junction termination designs and processes be explored and evaluated. The Phase I effort will focus on the application of these terminations to relative simple pn junction rectifiers. The methods to be evaluated will be improved passivation of mesa sidewalls and the use of non-mesa terminations such as floating field rings or field plates. A batch of identical pn junction structures will be grown on which these different methods will be used so that they can be systematically compared. The surface breakdown of SiC will also be characterized because of its importance in achieving higher power Sic microwave MESFETs, which are becoming vital for next generation phased array radar systems. The termination techniques for the rectifiers and the surface breakdown information can then be applied to more complex SiC devices currently being developed such as power MOSFETs, thyristors, and microwave MESFETS. High power silicon carbide devices which operate at high temperatures are required for a variety of power conditioning applications on radar systems, all-electric airplanes, turbine engine actuators, and space-based power systems. T

Keywords:
4h-Sic Junction Termination High Voltage Surface Breakdown Floating Field Ring Mesa Termination

4H silicon carbide bipolar power devices are expected to have 3x higher current densities and 10x higher switching speed as compared to silicon bipolar power devices (like MCTs), while still operating up to 350°C. this is because of an order of magnitude higher breakdown electric field and a 2-3x higher thermal conductivity of 4H-SiC as compared to Si. Such characteristics are ideally suited for the "more electric" initiative for propulsion, electro-mechanical actuation and high power weapons systems on ships, submarines and aircraft as outlined in the Navy's PEBBs program. Recent advances in 4H-SiC crystal quality, low doped epitaxial uniformity, reactive ion etching, high voltage edge termination and dopant ion implement at Cree presents tremendous opportunity to fabricate high power 4H-SiC bipolar power devices. In the Phase I research, 350 V, 1 Amp field controlled thyristors capable of operating up to 350°C were demonstrated. These capabilities exceed the proposed 200V, 1 Amp on this device by using a novel technique of epitaxial regrowth over implanted regions. In this Phase II effort, development of 4H-SiC FCTs capable of 1000 V, 5 A is proposed. In addition, fabrication and characterization of optimized 1000V, 5 A 4H-SiC Insulated gate bipolar transistors (IGBTs) is also proposed.

Keywords:
Silicon Carbide Power Electronics Bipolar 4h-Sic High Temperature Fct Igbt