Characterization of channel width dependence of gate delay in 0.18-μm CMOS technology

The channel width dependence of gate delay in 0.18-μm CMOSFET has been characterized. Substantial increase of gate delay observed in the narrow channel width region is found due to channel width independent capacitance components, which is inherent to transistors. An expression for gate delay considering the channel width independent capacitance components and gate sheet resistance is derived and compared with experimental data. The minimum gate delay is shown to result from the compromise between delay components proportional to channel width and proportional to inverse of channel width. Although the channel width independent capacitance is negligible in the wide channel width region, the gate delay of the 1-μm channel width ring oscillator increased more than 20% compared with the 5-μm channel width ring oscillator.