Proton Irradiations on SJ HV Power MOSFETs to Realize Fast Diode Devices

This paper studies the effects of proton irradiations on Super Junction High Voltage power MOSFETs to realize transistors with fast diode. Experiments were performed on a sample of 600？V power MOSFETs and achieved results were compared to standard irradiated devices by electrons. 1. Introduction In many modern applications and, in particular, when using full bridge converters, intrinsic diode of HV power MOSFET is even utilized to free wheel the current in the circuit without using any other external component [1–7]. Intrinsic diode of a power MOSFET is implemented by considering the body-drain junction of the same device. In fact, when the device is switched off and the transistor is polarized in reverse mode, the current flows from the source to the drain terminals working in third quadrant configuration. In such operating conditions, intrinsic diode needs to guarantee particular performances and features. In particular, diode needs to be fast in order to reduce switching losses when operating switching frequencies increase. A diode becomes fast when charges moved during rapid variation of against time are quite low as shown in Figure 1. In fact, in the example shown in Figure 1, MOSFET is rapidly switched off. When increases, drain current decreases down to negative values because charges stored in the body-drain junction need to be discharged. Standard devices (red curve) reach the lowest peak of drain current () because the charge stored in the junction () is higher than fast devices (green curve). That turns in a higher time to discharge () and, thus, it makes the devices slower during commutation. To improve the performances of intrinsic diode, special processes need to be implemented. The typical action consists in the irradiation of the body-drain junction by energetic electrons in order to create suitable damage in the reticle. Such damage introduces deep energetic level traps in the silicon band-gap. Such traps capture the carriers lowering the quantity of charges moved during the fast transition from on to off states as described above. Typical irradiation doses are in the range of 5–50？MRad when considering power MOSFETs. Afterwards, a thermal process needs to be implemented in order to activate the traps. However, irradiation by considering electrons can bring issues related, for example, to the quality of gate oxide. In fact, interface traps states can be created increasing drain-source leakage current. Figure 1: Example of commutation of the intrinsic diode and comparison with a fast diode. Recently, a new technique was implemented to