The World's First Low-Resistance Single-Chip 300A SiC Trench MOSFET

ROHM Co., Ltd., in collaboration with Professor Tsunenobu Kimoto of the Kyoto University Graduate School of Engineering, has successfully achieved dramatic current increases from a large surface area trench gate vertical-type MOSFET composed of SiC (Silicon Carbide). More than 300A can be driven from a single chip, paving the way for large SiC power and current conversion modules – devices that, until now, could only be realized using Si technology due to the crystal defects in SiC which limit current capacity.

The inherent loss incurred by silicon semiconductor devices during power conversion has become increasingly problematic, leading designers to search for an alternative semiconductor material. Silicon carbide has emerged as the ideal successor due to its superior material properties. It is believed that utilizing SiC in place of Si will significantly reduce size while increasing the efficiency of power conversion modules.
Previous efforts at ROHM have resulted in the development of low ON-resistance SiC trench MOSFETs capable of driving 100A from an area 3mm×3mm. However, power conversion modules for electric vehicles, power transmission and railroads, require a minimum current capacity of approximately 600A, which is currently only obtainable through the parallel connection of several large-area Si chips exceeding 1cm×1cm capable of outputting 200A to 300A.

To increase current it is necessary to reduce ON resistance while increasing the surface area of the chip. However, although SiC features excellent ON resistance characteristics, increasing area introduces a greater number of crystal defects, leading to device failure. Therefore, it was previously necessary to connect multiple chips in parallel in order to achieve a current of a few hundred amps - impractical from a wiring standpoint.
In response to this ROHM has refined its epitaxial process technology in order to successfully reduce the effects of crystal defects, making it possible to expand chip area by 2.5 times, from 3mm×3mm to 4.8mm×4.8mm. In addition, ON resistance is reduced by 20% through an improved voltage resistance structure. As a result, current capacity is increased to 300A.

This technology is expected to significantly increase efficiency in large current applications such as hybrid/electric vehicles, power transmission and railroads, resulting in lower loss, less environmental impact, and reduced energy dependence.

Samples will be available by next spring. ROHM will continue to improve reliability and manufacturing capability by further reducing ON voltage and voltage resistance based on customer feedback (target: 1mΩ･cm², 1200V).

ROHM would like to acknowledge the valuable contributions provided by the Kyoto Environmental Nanotechnology Cluster of the Knowledge Cluster Initiative of the Ministry of Education, Culture, Sports, Science and Technology (Central organization: Advanced Scientific Technology and Management Research Institute of Kyoto).

■ON Characteristics and Chip Photo

■L Load Switching Waveforms and Measurement Circuit

■Terminology

• SiC（Silicon Carbide）
  A compound semiconductor possessing excellent solid state values with approximately 3 times the band gap, 10 times the dielectric breakdown field, and 3 times the thermal coefficient of silicon, making it well-suited for use in power device applications and for high-temperature operation.
• MOSFET（Metal Oxide Semiconductor Field Effect Transistor)
  This type is the most commonly used FET structure, often as a switching element.
• Power Electronics
  Devices in this field convert power into a convenient form using semiconductor devices for flexible control. Products range from household electrical appliances to industrial, railroad and power systems.
  *Power Electronics by Eisuke Masada and Kazuyuki Kusumoto, published by Ohmsha
• Hybrid Vehicle
  A vehicle that utilizes a combination of power sources – normally from an internal combustion engine and an electric motor. Both sources are used separately or in combination, depending on driving conditions. The total efficiency of a hybrid vehicle is comparable to that of an electric or fuel cell vehicle.
• Electric Vehicle
  A vehicle powered solely by electricity. Electric vehicles use a secondary battery (or a primary battery in rare cases) as a power source and obtain power for driving either by recharging from an external source or replacing the battery.
• ON Resistance
  The resistance value of a power element during operation. This is the most important parameter that influences the performance of a power MOSFET. The lower the value the better the performance.
• SBD(Schottky Barrier Diode)
  A diode possessing rectifying properties (diode characteristics) due to the Schottky junction formed by contact between a metal and a semiconductor. The absence of the minority carrier storage effect gives the diode excellent high-speed performance.
• Trench Structure
  A structure in which channels (trenches) are formed on the chip surface and MOSFET gates are formed on the side walls of the trenches. This structure does not have the JFET resistance inherent with planar-type MOSFETs, and it can be made smaller than the planar structure, resulting in an ON resistance roughly equivalent to that of SiC.
• JFET Resistance(Junction Field Effect Transistor)
  A JFET is a transistor that controls the current based on the expansion of the depletion layer of PNP junctions (or NPN junctions). In a planar structure, the JFET is formed parasitically as a resistance component between adjacent cells.