| |
| 8.1 Motivation |
| As seen in the last lecture as channel length is reduced, departures from long channel behaviour may occur. These departures, which are called Short Channel Effects, arise as results of a two-dimensional potential distribution and high electric fields in the channel region. |
| For a given channel doping concentration, as the channel length is reduced, the depletion layer widths of source and drain junctions become comparable to channel length. The potential distribution in the channel now depends on both the tranverse field Ex(controlled by the gate voltage and back-surface bias) and the longitudinal field Ey(controlled by the drain bias). In other words, the potential distribution becomes two dimensional, and the gradual channel approximation (i.e. Ex >> Ey) is no longer valid. This two dimensional potential results in the degradation of the threshold behaviour, dependence of threshold voltage on the channel length & biasing voltages and failure of the current saturation due to punch through effect. |
| In further sections, we will study various effects due to short channel length in MOSFET. |
|
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
|
