Impact of Process Imperfection of CNFET on Circuit-level Performance and Proposal to Improve Using Approximate Circuits

Despite tremendous potential shown by emerging low dimensional materials including carbon nanotube field effect transistor (CNFET) technology for sub-10 nm transistors, the current processes for their fabrication still lack precise control and material quality; resulting in transistors suffering from process imperfections. With likely degradation in circuit performance due to poor process quality, the current CNFET technology will be more suitable for error resilient applications involving approximate circuits. A methodology is first provided considering the effect of imperfect CNFET process on circuit performance. Secondly, a systematic methodology is provided for generating approximate circuits to reduce the effect of process induced degradation due to imperfect process. With example of 16-bit CNFET adder, the two approximate adders at PCNT_open = 5%, achieved circuit-level pass rate of 62.7% and 71.8% respectively in comparison to only 8.4% for the precise adder; with relative logic error of 3.3% and 24.0% respectively.