Anomalous Bulk Current Effects in Trench-Based Integrated Power Transistors

This letter reports on anomalous bulk current effects in vertically integrated power transistors. The transistors use trench processing to make a vertical stack of gate oxide and drift oxide, the latter being used to completely deplete the drift region. The bulk current - a direct measure for the maximum impact ionization in the device - is shown to reach a maximum at intermediate drain voltage, and decreases for increasing drain voltage. The latter has important consequences for the hot carrier reliability evaluation of the transistors. A comparison between a standard lateral DMOS and a trench-based MOS is made.