In this letter, electrical and reliability characteristics of diagonally shaped n-channel MOSFET's have been extensively investigated. Compared with the conventional device structure, diagonal MOSFET's show longer device lifetime under peak I(sub) condition (V(g) = 0.5V(d)). However, in the high gate bias region (V(g) = V(d)), diagonal MOSFET's exhibit a significantly higher degradation rate. From the I(sub) versus gate voltage characteristics, this larger degradation rate under high gate bias is considered to be due mainly to the current-crowding effect at the drain corner. For a cell-transistor operating condition (V(g) > V(d)), this current-crowding effect in the diagonal transistor can be a serious reliability concern.
