VERTICAL TRIGATE METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR IN 4H - SILICON CARBIDE

2020-07-28T18:29:44Z (GMT) by Rahul Padavagodu ramamurthy

Advances in modern technology and recent demand for high power applications have motivated great interest in power electronics. Power semiconductor devices are key components that have enabled significant advances in power electronic systems. Historically, silicon has been the material of choice for power semiconductor devices such as diodes, transistors and thyristors. However, silicon devices are now reaching their fundamental limits, and a transition to wide bandgap semiconductors is critical to make further progress in the field. Among them, SiC (silicon carbide) has attracted increasing attention as a power semiconductor to replace silicon due to its superior properties and technological maturity. In fact, SiC power MOSFETs have been commercially available since 2011, and are actively replacing their silicon counterparts at blocking voltages above 1 kV. At these voltages, the specific on-resistance of SiC MOSFETs is 200-300x lower than that of silicon devices. However, conventional vertical SiC MOSFETs are still far from their theoretical performance at blocking voltages below 2 kV. In this regime, the channel resistance is the dominant limitation due to the relatively low channel mobility at the SiO2/4H-SiC MOS interface.

In this thesis, the first successful demonstration of a novel power device in 4H-SiC called the trigate power DMOSFET (double diffused metal oxide semiconductor field effect transistor) is presented. This device reduces the channel resistance by a factor of 3-5× compared with the state-of-art commercial power DMOSFETs, without requiring an increase in the channel mobility. The trigate structure is applied to a power MOSFET for the first time along with a self-aligned short channel process. This new structure utilizes both the conventional horizontal surface as well as the sidewalls of a trench to increase the effective width of the channel without increasing the device area. Conceptual design, optimization, process development and electrical results are presented. The trigate power MOSFET with a trench depth of 1 μm designed for a blocking voltage of 650 V has a specific on-resistance of 1.98 mΩcm2 and a channel resistance of 0.67 mΩcm2.This corresponds to a ∼2× reduction in the total specific on-resistance, and a 3.3× reduction in the specific channel resistance as compared to a conventional DMOSFET with the same blocking voltage rating. This demonstration is a landmark that could help SiC technology compete successfully in the lower blocking voltage regime below 600 V, and access for the first time a completely new segment in the power electronics application space.