To curb the emissions of CO₂, which is a cause of global warming, effective measures include utilizing renewable energy represented by photovoltaic and wind power generation, improving energy conversion efficiency and introducing electrically driven vehicles, such as hybrid electric vehicles (HEVs) and electric vehicles (EVs). One key to those measures is power electronics technology, which controls electric energy. Fuji Electric has developed and commercialized power semiconductors, which contribute to overwhelming downsizing and efficiency improvement of power electronics equipment.
This special issue presents the latest technologies and products relating to Fuji Electric's power semiconductors.

Against the background of global needs for energy saving, efficiency improvement and reduction of CO₂ emissions, great expectations are placed on power electronics technology, which can meet those needs. The size of the market for power semiconductors, which are key devices of the technology, is expected to increase. Among industrial equipment applications, growth is estimated in the fields of new energy, including photovoltaic and wind power generation, and of uninterruptible power systems for data centers. Regarding automotive applications, as the use of electric and electronic equipment further advances, which equipment includes DC-to-DC converters, sensors, electronic switches, and inverters for HEVs and EVs, the number of power semiconductors used is expected to increase.
This paper presents the technical trends of power semiconductors and describes the status of technology development carried out by Fuji Electric.

Fuji Electric has developed and released SiC planar gate MOSFETs. Excessive shrinkage of the cell pitch of planar MOSFETs leads to a high JFET resistance, which prevents them from achieving a low on-resistance close to the theoretical limit. To the contrary, the cell pitch of trench-gate MOSFETs can be shrunk without the increase of the JFET resistance. We have therefore developed a 1.2-kV SiC trench gate MOSFET. We have optimized the structures of the MOS channel and the JFET region, as well as reduced the cell pitch. Our trenchgate MOSFETs realize low switching loss, the increase of the threshold voltage 2.4 times, and the reduction of the on-state resistance by 48% compared with the conventional planar MOSFETs.

Fuji Electric has developed an All-SiC 2-in-1 module utilizing a SiC device that has been adopted in the development of a high-performance compact IP65-rated inverter characterized by its dustproof and waterproof features. In order to make use of the much lower switching loss of SiC devices compared with Si devices, it is necessary to create a highly reliable packaging technology that ensures high-temperature operation while also reducing wiring inductance inside the module. Fuji Electric has developed a package with a new structure to meet these requirements. As a result, the IP65-rated inverter reduces loss in the main circuit by 44% when compared with conventional inverters that use Si devices.

In recent years, SiC devices have been widespread mainly in fields that require a breakdown voltage of approximately 1 kV. They are expected to be used in the high voltage fields that require a breakdown voltage from 3 to 10 kV such as railways, as well as the automotive field that require high reliability such as hybrid vehicles and electric vehicles. Fuji Electric has developed a newly structured package featuring copper pin connections and resin molding to achieve SiC modules with high breakdown voltage. Based on the results of electric field simulations and thermal analysis, the electric field strength relaxation and high heat radiation are achieved by the optimization of the positioning and thickness of electrodes on the insulation substrate.

SiC devices are capable of operating at high temperatures of 200 ℃ or higher, while conventional Si devices at 175 ℃, and the molding resin that molds the power devices requires an even higher thermal resistance to spread in the market. Our All-SiC module maximizes the performance of SiC devices, and we have confi rmed that the module can operate continuously at temperatures of 200 ℃ or higher through the use of a high thermal-resistant molding resin that is characterized by a longer thermal-resistant service life and improved tracking resistance.

Power conversion equipment has been increasingly required to exhibit compactness, low loss and high reliability, and it is against this backdrop that Fuji Electric developed the 7th-generation “X Series” IGBT module “Dual XT” (X Series Dual XT) as a module that expands rated current. The X Series Dual XT has reduced power loss through semiconductor chip characteristic enhancement, while also improving the package current-carrying capability through package structure enhancement. In addition, by improving the ΔT _j power cycle capability and the heat resistance of the insulation-use silicone gel, the module achieves a junction temperature of T _jop=175 ℃ under continuous operation. It is also the industry's first module in this package size that has a 1,200-V/800-A rating.

In recent years, IGBT modules have been increasingly required to be smaller in size while exhibiting lower loss and higher reliability. To meet the requirements, Fuji Electric has developed an industrial-use reverse conducting IGBT (RC-IGBT) module by using an RC-IGBT that integrates an IGBT and a free wheeling diode (FWD) on a single chip. Furthermore, the module greatly reduces loss and thermal resistance and enhances reliability through optimization based on our 7th-generation “X Series” technology. These technology innovations have achieved enhancements such as expansion of rated current, increased power density and miniaturization, all of which were impossible through the combination of conventional IGBT and FWD.

Fuji Electric has recently added products with current ratings of 20 and 30 A to our 2nd-generation small IPM series to meet the needs of motor drive devices. Applying the 7th-generation IGBT chip technology as a base and optimizing the lifetime control and drift layer thickness of the FWD, we have significantly reduces the temperature rise while lowering noise and loss. We ran a temperature rise simulation of a package air conditioner that has a standard cooling capacity of 14 kW at the maximum load, which are expected to be actual conditions. It showed 11 ℃ lower temperatures than the 1st-generation small IPM. It can therefore expand the allowable output current of the devices.

Fuji Electric has employed a thin reverse-conducting IGBT (RC-IGBT) in the development of a 3rd-generation direct liquid cooling module for automotive applications that is characterized by its high-speed packaging structure. By utilizing an RC-IGBT that integrates an IGBT and FWD on a single chip, the module achieves faster switching at turn-on and turn-off . In addition, parasitic inductance has been decreased by 50% compared with conventional packages through use of the RC-IGBT and internal layout optimization. Furthermore, superimposed surge voltage has been reduced by adopting a packaging structure that equips all 3 phases with a PN terminal pair. These technologies have enabled the 3rd-generation module to reduce switching loss by 30% compared with 2nd-generation modules.

Fuji Electric has developed a 3rd-generation direct liquid cooling power module for automotive applications such as hybrid and electric vehicles. Power modules for automotive applications are required to be compact and exhibit low power loss. We have improved heat dissipation performance of the module by using an aluminum water jacket that combines the liquid cooling fins with cover as well as refrigerant inlet and outlet ports with a fl ange structure. In addition, employing a reverse conducting IGBT (RC-IGBT) that integrates an insulated gate bipolar transistor (IGBT) with free wheeling diode (FWD) enables the power module with the same active area to reduce power loss by 20%. As a result, the power module has achieved a lower loss and a smaller size.

In recent years, electronic control has been advancing in automotive electrical systems based on the keywords of safety, environment, and energy savings. In addition to these keywords, semiconductor products are also required to be compact and highly reliable. Fuji Electric has developed the high-side 2-in-1 intelligent power switch (IPS) “F5114H” for automotive applications to achieve even greater device miniaturization. Fuji Electric has equipped the SSOP-12 package, which has the same external dimensions as the SOP-8 package, with 2 chips that have the same functionality as previous products, allowing for two channels on the same mounting area as the previous one channel products. It also utilizes a highly reliable wire that can be used in high temperature environments. These enhancements have made it possible to greatly reduce ECU size.

There has been increasing demand for smaller power conversion equipment and better fuel efficiency in eco-friendly vehicles such as hybrid electric vehicles. Accordingly, power MOSFET products are being required to be compact, low loss and low noise. Fuji Electric has developed and launched the “Super J MOS S1A Series,” a product for automotive applications that adopt a superjunction structure characterized by their low on-state resistance and low switching loss. More recently, Fuji Electric has developed the 2nd-Generation SJ-MOSFET for automotive applications “Super J MOS S2A Series,” which reduces conduction loss while improving the trade-off between switching loss and jumping voltage during turn-off switching. The use of this product contributes to size reduction and enhanced efficiency of the power conversion equipment for automotive applications.

For the relatively large capacity switching power supplies for electronic equipment, a power factor correction (PFC) circuit is required to suppress harmonic current, and a LLC current resonant circuit is also widely used due to the effectiveness in low noise applications. Fuji Electric has developed the critical mode PFC control IC “FA1A60N” and LLC current resonant control IC “FA6B20N” adding new functionality while using our conventional technology. Using these ICs in combination allows power supply systems to improve the efficiency during light loads, achieve low standby power, and reduce the system cost by reducing the number of power supply components. Furthermore, as an enhancement over previous products, these ICs can be used in power supply adapters.

In order to make efficient use of energy, there has been increasing demand for enhanced efficiency in power conversion equipment, and as such, the power MOSFET mounted on this equipment are required to be compact, low loss and low noise. Fuji Electric has been developing and manufacturing products that have reduced on-state resistance and improved trade-off between turn-off switching loss and surge voltage. We have recently developed the 2nd-generation low loss SJ-MOSFET “Super J MOS S2FD Series,” which features user-friendliness and low loss, by improving its reverse recovery withstand capability through a built-in fast diode. The use of this product is expected to improve the efficiency of power conversion equipment and facilitate product miniaturization.