With the emergence of new semiconductor materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN), semiconductor chips using silicon as the main material in the past have undergone different market and application changes. This article will introduce you to the application development of Wide Bandgap (WBG) SiC MOSFET and the solutions introduced by onsemi.
Compound semiconductors gradually replace silicon's dominant position
In the past few decades, silicon has dominated the transistor world, but this phenomenon has begun to change gradually. Some compound semiconductors made of two or three materials have been developed, which have unique advantages and superior characteristics. For example, compound semiconductors provide us with light-emitting diodes (LED), one of which is composed of Gallium Arsenide (GaAs) and a mixture of Gallium Arsenide and Phosphorus (GaAsP), and some others use Indium and Phosphorus.
The problem with compound semiconductors is that they are more difficult to manufacture and more expensive. However, because they have obvious advantages over silicon, compound semiconductors can better meet the strict demanding specification requirements of new applications such as automotive electrical systems and Electric Vehicles (EVs).
At present, the most popular compound semiconductors are GaN and SiC power transistors. These devices can compete with long-lived silicon power LDMOS MOSFETs and super junction MOSFETs. The characteristics of GaN and SiC devices are similar in some respects, but there are also significant differences.
WBG devices can withstand higher breakdown voltage
Compound semiconductors are also known as WBG devices. In case of not discussing the crystal lattice structures, energy levels, and other mind-numbing semiconductor physics, WBG can be defined as a model that attempts to describe how current (electrons) flows in compound semiconductors.
WBG compound semiconductors have higher electron mobility and higher bandgap energy, which can be transformed into characteristics superior to silicon. Transistors made of WBG compound semiconductors have higher breakdown voltage and higher high-temperature tolerance, and these devices are superior to silicon in high-voltage and high-power applications.
SiC and GaN have a wider bandgap energy, which means that it takes about 3 times the energy to move electrons from the valence band to the conduction band. This makes the material behave more like an insulator than a conductor. This allows WBG semiconductors to withstand a higher breakdown voltage, the breakdown field of which is 10 times more robust than silicon. For a given voltage rating, a higher breakdown field can reduce the thickness of the device, thereby reducing the on-resistance and current capability.
WBG devices are suitable for demanding automotive applications
WBG transistors also have faster switching speeds and can operate at higher frequencies than silicon. Lower on-resistance means they consume less power, which improves efficiency. This unique combination of features makes these devices attractive to some of the most demanding circuits in automotive applications, especially hybrid and electric vehicles.
GaN and SiC transistors are becoming easier and easier to solve the challenges of automotive electrical equipment. GaN and SiC devices have high voltage functions of 650, 900, and 1200 V devices, have faster switching speeds, and higher operating temperatures, and have lower conduction resistance, minimum power dissipation, and higher efficiency.
The mobility parameters of SiC and GaN are of the same order of magnitude as those of silicon, and both materials are very suitable for high-frequency switching applications. However, the most different parameter of SiC is that its thermal conductivity is more than three times that of silicon and GaN. For given power consumption, a higher thermal conductivity can reduce the rate of temperature rise.
The guaranteed maximum operating temperature of commercially available SiC MOSFETs is 150°C <TJ <200°C. In contrast, SiC junction temperature can reach 600°C, but it is still mainly limited by bonding and packaging technology. This makes SiC an excellent WBG semiconductor material for high-voltage, high-speed, high-current, high-temperature, switching power applications.
SiC MOSFET meets high-voltage switching power supply application requirements
SiC is one of the WBG series semiconductor materials used to manufacture discrete power semiconductors. For high-voltage switching power applications, compared with traditional silicon MOSFETs and IGBTs, SiC MOSFETs have obvious advantages. They can switch high-voltage power rails over 1,000 V and operate at an extraordinary frequency of hundreds of kHz, which is that the best super junction silicon MOSFET cannot provide. IGBTs are also commonly used in this field but are restricted to lower operating frequencies due to their "tailing current" and slow turn-off. As a result, for lower voltage and high-frequency operation, silicon MOSFET is the first choice; while for higher voltage, high current, and low-frequency applications, IGBT is more suitable; however, SiC MOSFET provides the best combination of advantages in high voltage, high frequency, and switching performance. They are voltage-controlled field-effect devices that can switch at the same high voltage as the IGBT, or have a higher switching frequency than lower voltage silicon MOSFETs.
Compared to silicon, SiC MOSFET provides superior switching performance and higher reliability. In addition, low on-resistance and compact chip size ensure low capacitance and gate charge. Therefore, the overall benefits for the system include the highest efficiency, faster-operating frequency, increased power density, reduced EMI, and reduced system size.
SiC MOSFETs are usually available in the range of 650 V <BVDSS <1.7 kV, with the main focus on 1.2 kV and above. In the lower 650 V range, traditional silicon MOSFETs and GaN are superior to SiC. However, one of the reasons for considering the use of low-voltage SiC MOSFET may be to take advantage of its superior thermal characteristics. Although the dynamic switching behavior of a SiC MOSFET is very similar to that of a standard silicon MOSFET, the unique gate drive requirements determined by its device characteristics still need to be considered.
Diversified product specifications meets different application requirements
onsemi’s SiC MOSFET product portfolio is designed to achieve fast and robust designs. The dielectric breakdown field strength of SiC MOSFET is 10 times higher, the electron saturation speed is 2 times higher, the energy band gap is 3 times higher, and the thermal conductivity is 3 times higher. All of onsemi’s SiC MOSFETs include options that have passed AEC-Q101 Qualified and PPAP Capable. These options are specifically designed and qualified for automotive and industrial applications. The systematic advantages of these SiC MOSFETs include the ability to increase efficiency by reducing power loss, increasing power density, increasing operating frequency, increasing temperature operating efficiency, reducing EMI, and most importantly, reducing system size and cost.
onsemi’s SiC MOSFET product lines are mainly divided into various types of supporting 900 V and 1200 V. The 900 V product series can provide RDS(ON) supporting 20 mΩ and 60 mΩ devices, as well as package combinations of TO247-3L and D2PAK-7L. The 1200 V product series can provide RDS(ON) supporting 20 mΩ, 40 mΩ, 80 mΩ, and 160 mΩ devices, as well as package combinations of TO247-3L, TO247-4L, D2PAK-7L, and Bare Die. The product specifications are quite diverse, which can meet the different needs of customers.
Conclusion
WBG SiC MOSFET has an excellent performance in high voltage, high frequency, and switching performance. It is an ideal choice for automotive and industrial applications. As the technology matures, the product prices are more competitive than ever. The 900 V and 1200 V SiC MOSFETs launched by onsemi have diversified specifications to meet the various needs of customers, and have excellent performance and stable quality to meet stringent application specifications.