"In this document a theory is proposed that all power MOSFETs will go through three regions of operation during their lifetime with respect to the threshold voltage. Equations are presented for this proposed theory and analytical assumptions are made. The first region that will be examined is when the MOSFET is healthy and all parameters of the MOSFET are kept constant. The second region of operation is when the gate oxide begins to degrade and the threshold voltage begins to dip. The third region of operation is when Fowler-Nordheim tunneling begins to dominate the threshold voltage of the device and the threshold voltage begins to continuously rise. An accelerated aging experiment was conducted to try and prove the proposed theory. Adverse effects were seen in the devices tested and the regions of operation were modified in order to account for the large shift in the threshold voltage. Here the proposed equations were reformulated to account for the different trapped charges in the device throughout its lifetime. The equations formulated differ from the proposed theory and are presented as new findings for the different regions of operation for power MOSFETs. Data was also collected to calculate the turn on resistance and these findings will be published at a later date. A final conclusion is given based on the data collected and the different effects seen that account for the threshold voltage change in power MOSFETs. This new theory may also be applied to insulated-gate bipolar transistors (IGBTs) and various other power MOSFETs."--Page ii.
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