Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

In recent years, silicon carbide has received increased attention because of its potential for high-power devices. The unique material properties of SiC, high electric breakdown field, high saturated electron drift velocity, and high thermal conductivity are what give this material its tremendous potential in the power device arena. 4H-SiC Schottky barrier diodes (1400 V) with forward current densities over 700 A/cm/sup 2/ at 2 V have been demonstrated. Packaged SITs have produced 57 W of output power at 500 MHz, SiC UMOSFETs (1200 V) are projected to have 15 times the current density of Si IGBTs (1200 V). Submicron gate length 4H-SiC MESFETs have achieved f/sub max/=32 GHz, f/sub T/=14.0 GHz, and power density=2.8 W/mm @ 1.8 GHz. The performances of a wide variety of SiC devices are compared to that of similar Si and GaAs devices and to theoretically expected results.

Silicon carbide high-power devices

Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.

Ionization rates and critical fields in 4H silicon carbide

High-power device technology is a key technological factor for wireless communication, which is one of the information network infrastructures in the 21st century, as well as power electronics innovation, which contributes considerably to solving the energy saving problem in the future energy network. Widegap semiconductors, such as SiC and GaN, are strongly expected as high-power high-frequency devices and high-power switching devices owing to their material properties. In this paper, the present status and future prospect of these widegap semiconductor high-power devices are reviewed, in the context of applications in wireless communication and power electronics.

/pdf/present-status-and-future-prospect-of-widegap-semiconductor-331khupory.pdf

Present Status and Future Prospect of Widegap Semiconductor High-Power Devices

The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described. A synopsis of recent complementary technological developments in passives, integrated driver, and protection circuitry and electronic packaging are described, followed by an outline of the applications that stand to be impacted. A glimpse into the future based on the current technological trends is offered.

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

MESFET's were fabricated using 4H-SiC substrates and epitaxy The DC, S-parameter, and output power characteristics of the 07 /spl mu/m gate length, 332 /spl mu/m gate width MESFET's were measured At /spl nu//sub ds/=25 V the current density was about 300 mA/mm and the maximum transconductance was in the range of 38-42 mS/mm The device had 93 dB gain at 5 GHz and f/sub max/=129 GHz At V/sub ds/=54 V the power density was 28 W/mm with a power added efficiency=127% >

4H-SiC MESFET with 2.8 W/mm power density at 1.8 GHz

4H-SiC MESFET's on conducting substrates were fabricated and characterized for large-signal performance over a wide range of gate and drain biases. At V/sub ds/=25 V the current density was 225 mA/mm and the peak f/sub max/ for these devices was 16 GHz. At V/sub ds/=50 V and I/sub dq/=50% I/sub dss/, the power density was 3.3 W/mm at 850 MHz. At V/sub ds/=40 V and I/sub dq/=5% I/sub dss/, the power added efficiency was 65.7%, which is the highest ever reported for a SiC MESFET. This is the first Class B data presented for a SiC MESFET.

4H-SiC MESFET with 65.7% power added efficiency at 850 MHz

Silicon carbide MESFET's with 0.7 /spl mu/m/spl times/332 /spl mu/m gates under class B bias at 1.8 GHz had P/sub 1dB/=28.3 dBm (2 W/mm CW) and 50.4% PAE. At the same power density, these FET's had 66% PAE at 0.85 GHz. This high power density combined with the extremely high thermal conductivity of SiC makes it a promising technology for high power microwave applications.

Silicon carbide MESFET's with 2 W/mm and 50% P.A.E. at 1.8 GHz

MESFET's fabricated on high resistivity 4H-SiC substrates have attained an f/sub max/ of 30.5 GHz and an f/sub /spl tau// of 14.0 GHz. Both of these figures of merit are the highest ever reported for a SiC MESFET, and this is the first report of high resistivity 4H-SiC substrates. With the continued advances in bulk crystal growth, including the availability of high resistivity material, the development of two-inch substrates and the reduction of micropipe defect densities to <30 cm/sup -2/, SiC is rapidly emerging as a viable technology for high power microwave applications.

4H-SiC MESFET's on high resistivity substrates with 30 GHz f/sub max/

Silicon carbide has tremendous potential for high power microwave devices because of its high breakdown electric field (4x106 V/cm), high thermal conductivity (4.9 W/cm-K), high saturated electron drift velocity ( 2 . 0 ~ 107 cm/sec) and low dielectric constant (10.0). The high velocity allows the devices to operate at relatively high frequencies despite the low mobility of S i c . The high breakdown field allows about ten times higher voltages to be applied for a given channel doping, which should allow a much higher output power density to be achieved than with Si or GaAsl . Submicron MESFETs have been previously fabricated in 6H-Sic and have shown desirable microwave performance with RF output powers of about 1 W/mm at 1-2 G H Z ~ ~ ~ . However, another polytype, 4H-SiC, shows even more potential for high power, high frequency operation, because its electron mobility (>550 cm2/V-sec) is about twice that of 6H-Sic. Thus we report the first DC, S-parameter, and output power results obtained with 4H-Sic MESFETs.

4H-silicon carbide mesfet with 2.8 W/mm rf power density

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