Prof. Dr. Leo Lorenz
President, ECPE European Center for Power Electronics e.V.
THE FUTURE OF POWER ELECTRONICS Power device development trends – from Silicon to Wide Bandgap?
The megatrends of our modern society such as energy efficiency, E-Mobility, SMART Grid and Digitalization is asking for green power electronic solutions. Power semiconductor devices are enabling technology to meet these requirements.
In this article, I want to show the development trend related to IC technologies and the replacement of Silicon power transistors towards Wide Bandgap (WBG) devices.
Development trends of power devices regarding IC technologies
Power Electronics is the technology associated with the efficient conversion, precise control and conditioning of electric power from the source up to the load. It is the enabling technology for energy saving, distribution and generation out of renewable sources such as wind- or solar power. As a cross-functional technology it´s covering the whole power range from very high “Giga –Watt” power (e.g. energy transmission line, propulsion systems for ships or high-speed trains,etc.) down to the very low “Mili –Watt” power needed to operate a mobile phone or LED lighting. Power conversion technologies drive many market segments such as domestic and office appliances, air conditioning, lighting, computers and ICT, factory automation, e- mobility and renewable energy.
Having a look on the ITRS (International Technology Roadmap for Semiconductors) as shown in Fig.1 it can be seen that since the middle of the 90ties power semiconductors are not any more pure technology-driven devices such as memory products the feature size is having a minor influence on the performance improvement. Figure 1 demonstrates very nice that starting from 2005, power devices do not anymore feature size driven like memory IC´s. The significant increase in electrical performance is coming from the overall silicon utilization (vertical- & horizontal optimization). Based on this idea the technology Roadmap for power devices follows a horizontal chip optimization, e.g. smaller feature size is translated into higher cell densities and new trench gate structures and a vertical optimization to minimize the drift layer and reduce the bulk substrate material significantly. These measures are helping to reduce the overall losses, increase the switching frequency and reliability. This power device mainstream technology development is applied to all device types such as the IGBT, Fast Recovery Diode, Super Junction Transistor, low voltage MOSFET and WBG technologies. However, it has to be considered that the new generation of power chips having a smaller chip volume.
A smaller chip volume translates into high switching speed, higher knowledge for chip design and application engineering to operate these devices in short-circuit or avalanche and to optimize the thermal management.
Next-generation of power devices base on Wide Bandgap material
To break technology limits in terms of ultra-high efficiency ratings and ultra-high power densities on device and system-level at even improved reliability ratings, there is a strong push towards the development of WB-Devices.
As shown in Figure 2, the primary development trend of Silicon and WBG devices is the chip scaling - the red marking indicating Silicon devices (IGBT) and green marking SiC Devices. As power devices in the next generation, Fuji Electric has developed Reverse Conducting IGBTs (RC-IGBT) by introducing a concept of integrating IGBT and FWD (Free Wheeling Diode) in a single chip. This technology realizes further downsizing and increased current ratings of power modules. SiC devices are showing a new milestone in reducing the die size by more than a factor of two. These new type of devices are having extremely low losses (dynamic and static losses), designed for high switching frequency and outstanding ruggedness. As Fuji Electric has demonstrated these devices covering the voltage range from 650V up to 3.3kV in mass production today and higher voltage ratings are in planning for the future. However it has to be considered to utilize these new types of power devices many new challenges are come up such as of how to handle the high switching speed, the thermal management, packaging technologies and dedicated circuit layout.
Will Wide-Bandgap devices replace Silicon transistors
Addressing the wide range of power electronic applications - from “Mili Watt” power needed for the operation of mobile phones up to the “GigaWatt” power for high-speed trains - all looking into power electronic potential for energy efficiency and sustainable reduction of CO2 emission in future power conversion systems. As demonstrated in Figure 3 besides the Si-based devices like IGBT, Super Junction MOSFET the new type of Devices like SiC and GaN transistors are coming up.
While SiC devices and GaN transistors are already qualified in many emerging applications, silicon-based devices are still dominating in most applications. As diagram 3 is showing the replacement of WBG devices will take two or three decades. There are several reasons for this: Si-based devices still have substantial further development potential, the electrical and thermal performance is outstanding; the reliability is proven because of many years in application, and the cost is low. WBG devices are still at the beginning of their production cycle, the learning in material development and device design is ongoing, the benefits on the system level needs to be qualified, long-term reliability issues needs to be proven and cost down programs will come along with high volume production.
Summary and outlook
Power Devices are still the driving technology for energy saving ,system miniaturization and contributing significantly to sustainable improvement of our environment. For ultra-high efficiency and ultra-high power density solutions WBG-devices are being developed. The long-term Roadmap development driven by ECPE will demonstrate and prepare the movement from Si- Devices to WBG technologies. Specialist trainings and workshops organized by ECPE will support the application engineers of how to manage all the challenges by using this new type of devices in system engineering.