A Comprehensive Analytical Study on Dielectric Modulated Drift Regions—Part II: Switching Performances

A comprehensive study on the dielectric modulated (DM) drift region for power devices is presented in this paper. The performance of this drift region structure is theoretically analyzed and compared with other two structures: conventional and superjunction. In this paper, a study is focused on switching performance. The C-V relationships during switching are analytically derived, and the depletion widths predicted by the proposed analytical model agree well with simulation in a wide reverse bias region. The switching energy loss is evaluated based on the analytical model and its accuracy is verified by 2-D simulations. An effective depletion charge Q_D is defined as E_loss/ breakdown voltage (BV), from which a figure of merit (FOM) of R_ON,sp* QD is proposed to compare the performances of these different drift region structures, considering both the conduction and switching losses. The discussions in part I on Si and silicon carbide device structures are extended in part II to include FOMs. It is found that the DM drift region structures show better R_ON,sp-BV tradeoffs compared with the conventional structures, but slighter inferior FOMs. However, DM structures are still attractive for applications, where switching loss is less critical than the conduction loss, such as low frequency or soft switching.

I. Introduction

In part I, the breakdown voltage (BV) and the specific ON-resistance ( of conventional, dielectric modulated (DM), and superjunction (SJ) drift region structures were studied by analytic models and numerical simulations. The optimal BV- tradeoffs and the corresponding structure parameters were obtained from a proposed methodology. It was concluded that the DM structure yields a better BV- tradeoff than the conventional structure if a high- dielectric material is used. Filling deep trenches with a dielectric material for vertical Si MOSFETs has been demonstrated [1], and depositing high- dielectric down in high aspect ratio trenches is a standard process for a modern Dynamic Random Access Memory technology [2]. Therefore, with the advancement of CVD or other thin-film deposition processes, it is possible to realize completely filled or partially filled deep trenches with high- dielectrics.