Intentional Distortion of Transistor Shape to Improve Circuit Performance

A mixed-mode 3-D simulation study has been performed for ring oscillators made of 30-nm planar CMOS transistors with nonrectangular channel shapes. Nonrectangular shapes happen unintentionally due to optical proximity effects and can also be introduced intentionally. Transistors with large drains are shown to degrade ring-oscillator performance, whereas transistors with large sources are shown to simultaneously increase the ring-oscillator frequency by 25% and reduce the leakage current by a factor of three.