A schematic cross section of Panasonic’s GaN-based gate injection transistor (GIT) and its band diagram. This year at the 62nd International Electron Devices Meeting (IEDM), a special focus session on the system-level impact of wide bandgap (WBG) power devices presented recent advances in silicon carbide (SiC) and gallium nitride (GaN) power devices. Besides showing how they are transforming power delivery systems and expanding applications to higher voltages, temperatures and power levels, the five papers in this special session also debated improvements in reliability of these devices with future directions.
The first paper, by Professor Alex Huang of North Carolina State University, titled “WBG Power Devices and Their Impacts on Power Delivery Systems,” reviewed progress in WBG devices and their potential transformative impacts on low-voltage, medium-voltage and high-voltage power delivery systems. With regard to high-voltage devices, the paper showed that SiC-based power devices can enable higher voltages (up to 15 kV) and faster switching frequencies (40 kHz) than silicon-based alternatives.
The second paper, “Si, SiC and GaN power devices: an unbiased view on key performance indicators,” was a joint paper between Infineon Technologies Austria and Power Electronic Systems Laboratory of ETH Zurich, Switzerland. Presented by Infineon’s Gerald Deboy, the paper examined key parameters—such as capacitance and switching losses—for silicon, SiC and GaN power devices with respect to applications in switched-mode power supplies. Based on these characteristics, along with very low on-resistance, the paper indicated that silicon-based, super-junction MOSFETs will prevail in classic hard-switching applications at moderate switching frequencies, while the benefits of SiC- and GaN-based power devices will be exploited in resonant topologies at moderate to high switching frequencies.
According to Efficient Power Conversion Corporation’s CEO Alex Lidow, GaN ICs and discretes have given power system engineers new devices to improve efficiency, cost and power density of server and telecom systems. As a result, it is enabling power designers to build DC/DC converters that can convert directly from 48 V input to 1 V output required at the point-of-load (POL) in a single stage with efficiency and density that is better than silicon-based solutions. In fact, EPC’s paper, titled “System-Level Impact of GaN Power Devices in Server Architectures,” investigates four GaN-based DC/DC architectures to deliver 1 V output from 48 V input with various tradeoffs using four parameters—efficiency, power density, transient response and cost.
In the fourth paper, titled “GaN-based Semiconductor Devices for Future Power Switching Systems,” Panasonic Corporation’s Hidetoshi Ishida, along with a team of engineers, demonstrated a GaN-based gate injection transistor (GIT) with p-type gate on AlGaN/GaN heterostructure as a promising new device with lower on-resistance and higher breakdown voltage. The Panasonic paper reviewed the effects of integrated high-side and low-side GaN- based GITs with gate driver on DC/DC converter modules. As per this paper, the fabricated GaN IC achieves the peak efficiency of 88.2% and 84.9% for a 12 V to 1.8 V DC/DC conversion at 2 MHz and 3 MHz, respectively. The researchers said that the 3 MHz operation can reduce the system size of the DC/DC converter by about 60%, as compared to the 1 MHz operation.
The last paper, “Application Reliability Validation of GaN Power Devices,” by Sandeep R. Bahl and others at Texas Instruments (TI), showed that hard switching with the popular double-pulse tester is predictive of device performance under system-level testing. This simplifies the problem of product reliability testing to one of a device and a tester, according to TI’s paper. Consequently it enables TI to detect devices that pass quality inspection but perform poorly in application. As a result, said TI researchers, “our devices pass qual and perform well in application.”
