Papers by Author: Andrew A. Woodworth

Abstract: We compare the failure mechanism and performance of a silicon carbide (SiC) semi-superjunction (semi-SJ) power DMOSFET against pure SJ and conventional DMOSFET when struck by a single heavy ion. The Single-Event Burnout (SEB) failure mechanism was identified as the thermal runaway from second breakdown resulting in mesoplasma formation. The semi-SJ design shifts the mesoplasma location from the drift/substrate interface seen in the control device structures to a location along the center of the P-pillar and closer towards the DMOSFET surface, thus significantly improving the SEB threshold voltage (V_SEB). The V_SEB varies with pillar width and ratio of pillar thickness to drift layer thickness. A maximum value of V_SEB is reached when the pillar to drift layer ratio is 0.9 and the pillar width is 2.4 μm. The semi-SJ SEB/breakdown voltage ratio is 100% and 13% higher than the pure SJ and conventional DMOSFET, respectively. Using a new Figure of Merit (FoM), which accounts for the tradeoff between V_SEB and on-state performance, we find that the SiC semi-SJ DMOSFET achieves a FoM that is 1.8 and 8 times higher than SJ and conventional DMOSFET, respectively, making the semi-SJ a competitive candidate for radiation hardened applications.

Abstract: This paper describes the mechanisms behind the failure of silicon carbide (SiC) Power MOSFETs (metal oxide semiconductor field effect transistors) when struck by a heavy ion. The modeled device is designed to simulate a commercially available 1200 V power MOSFET under the strike of a silver ion with a Linear Energy Transfer (LET) of 46 MeV-cm²/mg commonly used in single event effect (SEE) testing. The device is shown in simulation to fail near 500 V, which is in close agreement to experiments. The failure occurs near the interface between the epitaxial layer and the substrate layer due to the rapid increase of the electric field in that region and destruction of the device from impact ionization. Two improved designs were proposed and investigated that would help to mitigate the electric field in these regions and improve the device’s tolerance to single-event burnout (SEB). The new designs increased the voltage at which SEB occurs from 500 V to over 900 V and increased the specific on-resistance (R_on,sp) by only 5%.

Abstract: In an effort to grow single crystal SiC fibers for seed crystals the following two growth methods have been coupled in this work: traveling solvent and laser heated floating zone to create the solvent-laser heated floating zone (Solvent-LHFZ) crystal growth method. This paper discusses the results of these initial experiments, which includes, source material, laser heating, and analysis of the first ever SiC crystals (confirmed by synchrotron white beam x-ray topography)

Abstract: Lateral expansion of small mixed polytype 4H/6H-SiC and 6H-SiC slivers were realized by hot wall chemical vapor deposition (HWCVD). Small slivers cut from m-oriented (11 ̅00) SiC boule slices containing regions of 4H and 6H-SiC or just single polytype 6H-SiC were exposed to HWCVD conditions using standard silane/propane chemistry for a period of up to eight hours. The slivers exhibited approximately 1500 μm (1.5 mm) of total lateral expansion. Initial analysis by synchrotron white beam x-ray topography (SWBXT) confirms, that the lateral growth was homoepitaxial, matching the polytype of the respective underlying region of the seed sliver.