Effect of charge coupling on breakdown voltage of high voltage trench-gate-type super barrier rectifier

Abstract

With the rapidly increasing demands pertaining to high voltage applications in modern power electronic systems, power devices have become widely used in today’s power applications. As a major carrier device without unreliable metal-semiconductor Schottky contact, super barrier rectifier (SBR) has been one of promising substitutions for traditional diodes since it was first introduced, owing to its excellent performance and reliability. The main principle behind SBR approach is to create an adjustable potential barrier in the MOS channel. The height of this barrier can be easily adjusted by the doping concentration in the channel and by the oxide thickness. Trench-gate-type SBR (TSBR) with a trench gate is so designed that the junction-type field-effect transistor effect of planar gate structure enables TSBR to be eliminated to have ultralow forward voltages and a good tradeoff between the forward voltages and reverse leakage currents. However, the charge coupling effect under reverse bias, which is usually neglected and not intensively studied, plays an important role in determining the breakdown voltage of TSBR for high voltage applications (above 200 V). In this paper, the two-dimensional electric field distribution influenced by the charge coupling effect is explained and verified by the analytical model and device simulations with TCAD software Sentaurus. Adjusting the key parameters including the trench depth, oxide thickness and mesa width can improve the tradeoff between the forward voltage drops and breakdown voltages. The optimization of key parameters can provide the significant guidance for designing the device structure. Furthermore, some considerations for designing the TSBRs are discussed in this paper. In addition, a novel TSBR with the stepped oxide structure (SO-TSBR) is proposed and demonstrated. Similar to, yet different from, the stepped oxide structure for dual trench MOSFET, the stepped oxide design equipped with this new rectifier possesses the ability to enhance the forward conduction. As indicated by the simulation results, the SO-TSBR reduces the forward voltage drop by 51.49% at a forward current density of 2.5 A/cm<sup>2</sup> compared with the normal structure of TSBR, with almost the same breakdown voltage of 270 V. The optimized TSBRs and SO-TSBRs are very promising rectifiers that can be used in high power electronic systems, because their breakdown voltages are both greater than 250 V.