The role of velocity saturation in the switching delay of an R-C loaded inverter

Abstract

Exact analytical expressions for the switching delay of an inverter driving an RC load, taking into account the velocity saturation, are obtained. Modified expressions to include theeffectofsource resistance arethen presented.Owing to the limitation on switching current imposed by the velocity saturation mechanism, the switching delay is substantially increased for identical width-io-length ratios of the MOSFET in a complementary MOS logic circuit. Obviously, it is important to increase the saturation velocity by miniband engineering or otherwise to improve the performance. However, it is found that the improvements in the time delay are marginal after a saturation velocity of 2.4 x lO'cm s-' is reached. The effect of technologies aimed at circumventing the hot-electron and other deleterious effects is a longer delay time of the circuit due to increased series resistance. However, the effect of increased series resistance is substantially damped due to velocity safuration. These results are particularly important in designing CMOS circuits with submicrometre MOSFET dimensions

ENHANCEMENT OF NANO-RC SWITCHING DELAY DUE TO THE RESISTANCE BLOW-UP IN InGaAs

“…Similar delay analysis study on series-connected MOSFET circuits was done by Sakurai and Newton. 5 Samudra et al 6 obtained exact analytical expressions for the switching delay of a CMOS inverter driving an RC load, taking into account the velocity saturation of the channel, but not that of the load resistor. Sakurai 7 attained closed form expressions for interconnect delay, coupling, and crosstalk in VLSI circuits, not including the breakdown of Ohm's law.…”