Snappy Recovery Research Articles

Investigation of SiC MOSFET Body Diode Reverse Recovery and Snappy Recovery Conditions

This paper investigates the behavior of SiC MOSFETs body diode reverse recovery as a function of different operating conditions. The knowledge of their effects is crucial to properly designing and driving power converters based on SiC devices, in order to optimize the MOSFETs commutations aiming at improving efficiency. Indeed, reverse recovery is a part of the switching transient, but it has a significant role due to its impact on recovery energy and charge. The set of different operating conditions has been properly chosen to prevent or force the snappy recovery of the device under testing. The experimental results and specific software simulations have revealed phenomena unknown in the literature. More specifically, the analysis of the reverse recovery charge, Qrr, revealed two unexpected phenomena at high temperatures: it decreased with increasing gate voltage; the higher the device threshold, the higher the Qrr. TCAD-Silvaco (ATLAS v. 5.29.0.C) simulations have shown that this is due to a displacement current flowing in the drift region due to the output capacitance voltage variation during commutation. From the analysis of the snappy recovery, it has emerged that there is a minimum forward current slope, below which the reverse recovery cannot be snappy, even for a high current level. Once this current slope is reached, Qrr varies with the forward current only.

Physical Modeling of Fast p-i-n Diodes With Carrier Lifetime Zoning, Part I: Device Model

This paper presents the development and implementation of a physics-based diode model which can simulate aspects of high-voltage diodes such as snappy recovery during punch-through and the modified carrier density profile due to local lifetime control. It uses a Fourier series solution for the ambipolar diffusion equation in the lightly doped base region. The model is compared with finite-element device simulations. A parameter extraction procedure for the diode with lifetime control is proposed in Part II.

Freewheeling diode reverse-recovery failure modes in IGBT applications

In this paper, reverse-recovery failure modes in modern fast power diodes are investigated. By the aid of semiconductor device simulation tools, a better view is obtained for the physical process, and operating conditions at which both diode snappy recovery and dynamic avalanching occur during the recovery period in modern high-frequency power electronic applications. The work presented here confirms that the reverse-recovery process can by expressed by means of diode capacitance effects which influence the reverse-recovery characteristics. The paper also shows that the control of the carrier gradient and the remaining stored charge in the drift region during the recovery phase influence both failure modes and determine if the diode exhibits soft, snappy, or dynamic avalanche recovery characteristics.

Design considerations of the diode effective area with regard to the reverse recovery performance

Previous work has shown that the reverse recovery performance of fast power diodes at low currents becomes more critical because of snappy recovery. At low current densities, the shallower stored charge in the base region leads to a lower reverse recovery charge, and under high commutating di/dts it can lead to snappy recovery and total device failure. In this article, the effect of the current density on the reverse recovery performance is investigated by means of varying the diode effective area rather than the forward current. Simulation and experimental results have shown that at a given forward current and commutating d i/d t, snappy recovery occurs for larger device areas with an increase in the reverse recovery charge. The outcome of this work will aid device and circuit designers in reducing the possibilities of device failures by choosing the correct size of diode or the optimum number of diodes in parallel for a certain application and rated current.