High Permittivity Dielectric Junction Termination for Vertical High Voltage Devices
T2020-072 A novel edge termination concept using extreme permittivity dielectrics is proposed to effectively manage peak electric fields in vertical power devices
Gallium Nitride (GaN)-based devices are promising for high frequency and power applications because they have a superior combination of the critical electric field, electron mobility, saturation drift velocity, and power density. With the recent interest in solid-state power electronics technologies with operating voltages higher than 1 kV, there is a need to design highly efficient power devices with low resistance and switching losses. The vertical device topology is a preferred one for several applications since it allows for high current injection necessary in such high power systems.
In addition, high voltage planar junctions under reverse bias exhibit significantly lower breakdown voltages than the ideal case due to the effects of field crowding at the junction periphery. Thus, the edge termination technique is considerably important for power devices to achieve closer expected ideal breakdown voltage and specific on-resistance. In order to achieve higher breakdown voltage efficiency, precise and additional processing is necessary. However, patterned p-type doping, which is used to achieve edge termination in other material technologies such as Si and SiC, has been challenging for GaN, Ga2O3 due to the absence of an efficient and reliable patterned doping process. This has prevented the demonstration of guard ring (GR) and junction termination extension structures (JTE) with good field termination efficiency. Previous efforts on vertical GaN power devices used field plate structures (FP) or step-etching processes instead of patterned p-type doping. However, these methods are not optimal to achieve higher field termination efficiency especially at fields greater than 1 kV. In addition, in order to manage the electric field effectively, multiple field plates or etches are needed.
A team of researchers at The Ohio State University led by Dr. Siddharth Rajan has developed a novel edge termination concept using extreme permittivity dielectrics to effectively manage peak electric fields in vertical power devices. This new method is expected to be particularly significant for wide bandgap semiconductors such as GaN, SiC, and Ga2O3, where field termination is a significant challenge due to material and process limitations. This technology has demonstrated that peak electric fields at various points are significantly reduced by using this high dielectric constant field termination layer. Low process complexity and flexibility in the design of power devices with different breakdown voltage can be achieved by this method. The method is capable of increasing junction termination efficiency from 22.7 % (for no junction termination) and 50 % (for conventional field plate-based field termination) to 80 % in the high permittivity-terminated device.
- High voltage devices ( > 1 kV)
- Increases junction efficiency from 22% to 80%.