MOSFET Scaling and Short channel effect
Much of the progress in semiconductor integrated circuit technology can be attributed to the ability to shrink or scale the devices. Scaling down MOSFETs has a multitude of benefits.
From Table, we see the benefits of scaling in terms of the improvement of packing density, speed and power dissipation. A key concept in scaling, first due to Dennard at IBM, is that the various structural parameters of the MOSFET should be scaled in concert if the device is to keep functioning properly. In other words, if lateral dimensions such as the channel length and width are reduced by a factor of K, so should the vertical dimensions such as source/drain junction depths (xj) and gate insulator thickness shown in table. Scaling of depletion widths is achieved indirectly by scaling up doping concentrations.
However, if we simply reduced the dimensions of the device and kept the power supply voltages the same, the internal electric fields in the device would increase. For ideal scaling, power supply voltages should also be reduced to keep the internal electric fields reasonably constant from one technology generation to the next. Unfortunately, in practice, power supply voltages are not scaled hand-in-hand with the device dimensions, partly because of other system-related constraints. The longitudinal electric fields in the pinch-off region, and the transverse electric fields across the gate oxide, increase with MOSFET scaling. A variety of problems then arise which are generically known as hot electron effects and short channel effects.
Short Channel effects:
When an electron travels from the source to the drain along the channel, it gains kinetic energy at the expense of electrostatic potential energy in the pinch-off region, and becomes a "hot" electron. At the conduction band edge, the electron has potential energy only; as it gains more kinetic energy, it moves higher up in the conduction band. A few of the electrons can become energetic enough to surmount the 3.1-eV potential barrier between the Si channel and the gate oxide. Some of these injected hot electrons can go through the gate oxide and be collected as gate current, thereby reducing the input impedance. More importantly, some of these electrons can be trapped in the gate oxide as fixed oxide charges.