We report on the first encapsulated rotary ball bearing mechanism using silicon microfabrication and stainless steel balls. The method of capturing stainless steel balls within a silicon race to support a silicon rotor both axially and radially is developed for rotary micro machines and MEMS ball bearing tribology studies. Initial demonstrations show speeds up to 6.8 krpm without lubrication, while speeds up to 15.6 krpm with lubrication are possible. Qualitative analysis is used to explain start-up behavior and investigate the wear of the stainless steel ball and silicon race.

This paper presents the development of 1000 V, 30 A bipolar junction transistor (BJT) with high dc current gain in 4H-SiC. BJT devices with an active area of 3 3 mm 2 showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm 2 , at a forward voltage drop of 2 V. A common-emitter current gain of 40, along with a low specific on-resistance of 6.0 m cm 2 was observed at room temperature. These results show significant improvement over state-of-the-art. High temperature current-voltage characteristics were also performed on the large-area bipolar junction transistor device. A collector current of 10 A is observed at CE = 2 V and = 600 mA at 225 C. The on-resistance increases to 22.5 m cm 2 at higher temperatures, while the dc current gain decreases to 30 at 275 C. A sharp avalanche behavior was observed at a collector voltage of 1000 V. Inductive switching measurements at room temperature with a power supply voltage of 500 V show fast switching with a turn-off time of about 60 ns and a turn-on time of 32 ns, which is a result of the low resistance in the base.Index Terms-4H-SiC, current gain, high-speed switching, power BJT.

In this paper, we review the performance, reliability, and robustness of the current 4H-SiC power DMOSFETs. Due to advances in device and materials technology, high power, large area 4H-SiC power DMOSFETs (1200 V, 67 A and 3000 V, 30 A) can be fabricated with reasonable yields. The availability of large area devices has enabled the demonstration of the first MW class, all SiC power modules. Evaluations of 1200 V 4H-SiC DMOSFETs showed that the devices offer avalanche power exceeding those of commercially available silicon power MOSFETs, and have the sufficient short circuit robustness required in most motor drive applications. A recent TDDB study showed that the gate oxides in 4H-SiC MOSFETs have good reliability, with a 100-year lifetime at 375oC if Eox is limited to 3.9 MV/cm. Future work on MOS reliability should be focused on Vth shifts, instead of catastrophic failures of gate oxides.

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