Thesis Examination Committee

Prof Hongyu YU, MAE/HKUST (Chairperson)
Prof Johnny Kin On SIN, ECE/HKUST (Thesis Supervisor)
Prof T. Paul CHOW, Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute (External Examiner)
Prof Kevin Jing CHEN, ECE/HKUST
Prof Kei May LAU, ECE/HKUST
Prof Lilong CAI, MAE/HKUST
 

Abstract

Edge termination is located at the periphery of the active region in power devices for alleviating junction curvature effect and avoiding premature breakdown. The current density of power devices has been increased a lot during the past decades. However, the edge termination does not change much, leading to increasingly large edge termination area to total chip size ratio. It is necessary to reduce the edge termination length for further reduction of chip cost. In this thesis, novel edge termination structures with deep trenches and sloped field plates are proposed and demonstrated for achieving the ideal planar junction breakdown voltage with record-short edge termination lengths.
 
First, a novel 600 V-class sloped-field-plate edge termination structure is proposed and demonstrated. The structure features a BCB (BenzoCycloButene) dielectric filled trench and a sloped field plate buried inside the trench. Experimental results show that the ideal planar junction breakdown voltage of 755 V can be achieved by the devices with a trench width larger than 20 µm. Second, a new 1200 V-class trench edge termination structure with double-field-plates is proposed and demonstrated. One of the field plates is for achieving the ideal planar junction breakdown voltage, and the other one is for stopping the depletion region extension at the right side of the trench to achieve high dV/dt performance. The fabricated device achieves the ideal planar junction breakdown voltage of 1422 V. Besides, it can handle a high dV/dt value of 73 kV/µs at a bus voltage of 1400 V. Finally, optimization of the trench sidewall of the termination structures for low leakage current is carried out. It was found that the leakage current is highly dependent on the trench sidewall treatment. Smooth trench sidewall and a thin layer of thermal oxide should be applied to the trench for achieving a significantly lower leakage current.