By keeping the same electric fields in the scaled devices, the reliability is not compromised. However, in actual technology evolution, voltages have not been reduced with the same scaling factor. There has been lack of enthusiasm, for example to change standardized power supply levels that have been used in preceding circuits. In addition, other non-scaled factors such as threshold voltages and sub threshold currents have made reduction in applied voltages less desirable. Consequently, electric fields in MOS devices have increased as the device dimensions shrink. Whatever clever techniques one build to make one more step towards smaller devices, there are some ultimate limits. Figure 4.1(a) shows the cross section of original NMOS transistor and Figure 4.1(b) shows the scaled NMOS transistor. Scaling laws and their effect on device and circuit parameters are shown in Table 4.1.