Silicon carbide (SiC) power devices have become the best choice for high-power and high-voltage power applications because of better efficiency over silicon devices. This article will show you the development of SiC MOSFET devices and solutions launched by onsemi.
SiC technology in rapid development
SiC, as a rapidly developing semiconductor technology, has been in the early stage of mass production in fast changeover, high temperature and high voltage applications. The first device available was a Schottky diode, followed by junction gate field effect transistor and high-speed switching power MOSFET. At present, a bipolar junction transistor and thyristor are under development.
Compared with silicon material, the higher thermal conductivity of SiC material gives it higher current density, and the higher band gap increases the breakdown field strength and operating temperature of SiC devices. Especially in the development and application of SiC MOSFET, compared with silicon-based MOSFET of the same power level, SiC MOSFET is suitable for higher operating frequency due to the significant reduction of turn-on resistance and switching loss. In addition, its high-temperature operating characteristics greatly improve stability under high temperatures. However, the high price of SiC MOSFET limits its wide application.
In terms of physical characteristics, SiC’s highly stable crystal structure allows it to have an energy bandwidth ranging from 2.2eV to 3.3eV, almost twice as wide as silicon. As a result, SiC can withstand higher temperatures, and the maximum operating temperature of SiC devices can reach 600°C, in general. Furthermore, the breakdown field strength of SiC is more than ten times higher than silicon, making the blocking voltage of SiC devices much higher than silicon devices.
Generally speaking, the conduction loss of semiconductor devices is inversely proportional to the breakdown field strength, which leads to the conduction loss of SiC devices is far less than that of silicon devices at similar power levels. The conduction loss of SiC devices has little dependence on temperature and little change with temperature, which is quite different from traditional silicon devices. The thermal conductivity coefficient of SiC is nearly 2.5 times that of silicon, and the saturated electron drift rate is twice that of silicon, allowing SiC devices to operate at higher frequencies. Based on the above advantages, it is found that, under the same power level, the number of power devices in the equipment, the volume of the radiator and the volume of the filter element can be greatly reduced, and all these make the efficiency greatly improved.
SiC power devices can reduce conduction loss
The FET of SiC architecture is MOSFET, just as the previous silicon-based MOSFET. In a broad sense, both have similar internal physical structure and are three-terminal devices composed of source, drain and gate connections. The difference between the two is that the FET of SiC architecture uses SiC as the base material instead of pure silicon material, and is often widely referred to as the SiC power device in the industry, with MOSFET part omitted.
However, the gate drive circuit of a SiC power device differs from that of a silicon-based semiconductor in that the gate drive circuit voltage is asymmetric (e.g., +20 V and −5 V). In terms of packaging, the higher power density of SiC bare die compared to silicon semiconductors allows the temperature to exceed the upper limit of silicon by 150°C, requiring the use of new die attachment technologies (e.g., sintering) in order to efficiently remove heat from the device, ensuring a reliable interconnection structure.
Because there is no need for bipolar device structure like IGBT in SiC MOSFET (low turn-on resistance and slow switching), low turn-on resistance, high voltage resistance and high-speed switching can be balanced. SiC MOSFET, like IGBT, has no initial voltage and can achieve low conduction loss over a wide range from small current to large.
Larger chip at a lower thermal resistance
onsemi has also launched a variety of SiC MOSFET products to meet the different needs of customers. The NXH006P120MNF2 is a half-bridge 2-pack SiC module with two 1200 V and 6 mΩ SiC MOSFET switches and a thermistor, as well as F2 package and industry-standard pins. The SiC MOSFET switch uses robust M1 planar technology and is driven by an 18V-20V gate driver, featuring a larger chip but lower thermal resistance than Trench MOSFET, making it more suitable for negative gate voltage drive.
The NXH006P120MNF2's planar technology and lower chip thermal resistance improve reliability and operate at 20V to reduce losses, with support for 18V for compatibility with other modules. Options with/without pre-applied thermal interface material (TIM) and options with solderable pins and press-fit pins make it fit well with the standard NCD5700x driver solutions of onsemi. These devices, Pb-free, Halide-free and RoHS compliant, can be used in a variety of DC-AC conversions, DC-DC conversions, and AC-DC conversions. Common end products include uninterruptible power supplies (UPS), energy storage systems, electric vehicle charging stations, solar inverters, industrial power supplies, etc.
Improvement of RDS(ON) is possible at higher voltage
The NXH010P120MNF1 SiC module introduced by onsemi uses a two-pack half-bridge topology, and is composed of a 1200 V and 10 mΩ SiC MOSFET half bridge and a NTC thermistor, with recommended gate voltage of 18V – 20V, low thermal resistance, with/without TIM options and press-fit pins.
The NXH010P120MNF1 can improve the RDS(ON) at higher voltage, allowing it to increase efficiency or power density, making it a flexible solution with a highly reliable thermal interface. It can also be used in a variety of AC/DC conversion applications, as well as electric vehicle chargers, energy storage systems, three-phase solar inverters and uninterruptible power supplies, industrial power supplies and other products.
Conclusion
The company's unique design of SiC MOSFET modules simplifies the development process, and its continued investment in enhanced packaging technology and accurate thermal modeling reduces cooling effort and extends service life. Its optimized bare die size and pre-applied TIM enable it to enhance stability in harsh environments. Patented termination structures, full value chain integration, whole process from base material to end product, and off-the-shelf and tailored solutions enable the company to help customers reduce time to market, ensure quality, reliability and scalability, making it one of the best choices for relevant power applications.