Threshold behavior of short-channel LDD MOSFET´s

The threshold behavior of short-channel LDD devices (0.3- 1.35 µm) was studied carefully using a 2-D device simulator developed by the author. We have found that the dependence of the threshold voltage on device parameters such as the drain voltage, the oxide thickness, and the doping for the channel and the n- regions can be adequately described by a simple formula proposed by the author. The discrepancy in very short-channel devices (0.3 µm) was due to punchthrough, which makes the predictions higher than the simulation results. In this work, no noticeable threshold variation was observed for devices with different Spacer lengths. The threshold voltage, however, Was found to have a definite dependence on the gate-drain overlap especially for devices with sufficiently short effective channel length. It exhibits a hump characteristic as the overlap increases and this phenomenon becomes more pronounced as the channel length decreases.