Device Research

Silicon carbide has several unique properties that can lead to enhanced performance in devices, as discussed below. These properties include higher breakdown field, wider bandgap, lower thermal generation rate, and lower intrinsic carrier concentration.

Power MOSFETs: The breakdown electric field of SiC is approximately 8x higher than silicon. This makes it possible to design power switching devices having correspondingly higher blocking voltages than their silicon counterparts. More importantly, the specific on-resistance (i.e. resistance-area product) of a power device scales inversely as the cube of the breakdown field, so the on-resistance of SiC power MOSFETs are 100-200x lower than comparable devices in silicon.

Lateral Power MOSFETs: The maximum blocking voltage of vertical power devices in SiC is presently limited by the thickness of commercially available epilayers. We have developed the first lateral power MOSFETs in SiC. These devices exhibit blocking voltages of 2.6 kV, a new record.

Schottky Barrier Diodes: Schottky barrier diodes (SBD's) are attractive as power rectifiers because they do not store minority carriers in the on-state, and therefore can be switched off quickly with negligible reverse current. It is widely felt that SBD's will be the first SiC power devices to go into commercial production. We have fabricated SBD's on 4H-SiC that exhibit blocking voltages of 1720 V, equal to the current world record.

Microwave Devices: The high saturated drift velocity, high breakdown field, and high thermal conductivity of SiC make it an ideal material for high-power microwave amplifiers in the 1 - 10 GHz regime. Two types of devices are under development: a vertical device known as a static induction transistor (SIT) and a lateral MESFET with sub-micron gate.

IMPATT Diode Microwave Oscillators: IMPATT diodes are two-terminal semiconductor devices that generate RF power by introducing a 180° phase shift between current and voltage waveforms at microwave frequencies. We have fabricated the first IMPATT diodes in 4H-SiC. These devices exhibit microwave oscillations at around 8 GHz when operated in an X-band waveguide cavity under pulsed bias.

CMOS Integrated Circuits: We completed our first 6H-SiC CMOS digital integrated circuits in September 1996. A second generation was completed in March 1997. These are the first SiC CMOS circuits fabricated with an implanted P-well process, and the first to operate on a single 5 V power supply.

Nonvolatile Memories: The thermal generation rate in semiconductors is proportional to the intrinsic carrier concentration n_i, and n_i decreases exponentially with band gap energy. Wide band gap semiconductors have dramatically lower thermal generation, with the thermal generation rate of 6H-SiC being about 16 orders-of-magnitude lower than silicon. This makes it possible to construct one-transistor memory cells in SiC which retain information for many years without power.

Charge Coupled Devices: CCDs are unique MOS devices in which charge packets are shifted laterally along the semiconductor surface by appropriate clocking applied to surface electrodes. CCDs are widely used as imagers in video cameras and digital still cameras. We have developed the first CCDs in SiC, where the wider bandgap makes it possible to image scenery in the UV portion of the spectrum without being overwhelmed by visible light.

NMOS Integrated Circuits: The low thermal generation rate in SiC makes it possible to operate integrated circuits at much higher temperatures than silicon. Our group developed the first digital integrated circuits in SiC in late 1993. These early circuits were implemented in enhancement mode NMOS.

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