Short Channel MOSFET l-V Characteristics
MOSFET l-V Characteristics:
- In short channel devices, the analysis has to be somewhat modified. As mentioned the effective channel mobility decreases with increasing transverse electric field perpendicular to the gate oxide (i.e., the gate bias).
- Furthermore, for very high longitudinal electric fields in the pinchoff region, the carrier velocity saturates in shown in figure given below.
- For short channel lengths, the carriers travel at the saturation velocity over most of the channel
- In that case, the drain current is given by the width times the channel charge per unit area times the saturation velocity:
- As a result, the saturation drain current does not increase quadratically with (VG - VT) as shown in Eq. given below
- But rather shows a linear dependence (note the equal spacing of curves in shown in fig). Due to the advances in Si device processing, particularly photolithography, MOSFETs used in modern integrated circuits tend to have short channels, and are commonly described by the above equ.