Radiation effects on power MOSFETs

Power MOSFETs are the most widely used semiconductor power device due to their large current handling capability, low on-resistance and large blocking voltage. These devices are known to present several failure modes associated with their operation in radiation environments such as device performance degradation due to accumulated total dose effects, to transient disruptions or even to catastrophic burnout failures resulting from cosmic rays or man made ionizing radiation pulses. The understanding of the processes leading to device failure is of critical importance in the case of space based systems which must meet the highest reliability requirements of any equipment. This thesis describes radiation experiments performed on the IRF-450 power MOSFET using the electron beam from the Gaerttner LINAC Laboratory at Rensselaer Polytechnic Institute. A correlation between burnout processes and the shape of the radiation pulse for the case of long pulses (1$m$s) has been established. The uniformity of the pulse strongly influences the burnout process, an experimental observation, confirmed by device simulation. The leading section of a pulse is postulated to turn on the parasitic bipolar transistor, whereas the trailing section of the same pulse takes the device into avalanche injection and subsequent second breakdown. A consequence of this mode of failure is that space simulations using long irradiation pulses, which tend to concentrate the electron flux towards the trailing section of the pulse, can overestimate the dose rate at which burnout occurs by as much as 100% with respect to a uniform pulse. A result of practical importance is that the hardening of power MOSFETs must consider the effect of a train of pulses, specially important in the case of stochastic cosmic rays fluxes in which an ion can turn-on the parasitic transistor whereas a second ion or pulse can burnout the device. New radiation hardening techniques based on modifying the standard VDMOS implementation, mainly extension of the p-well sidewall depth and active redistribution of the potential around the source are shown to partially mitigate radiation induced burnout processes. An analytical framework and code was used to extract device model parameters using only electrical characteristic of packaged devices and other information provided in manufacturer data sheets.