Deep Subthreshold TFT Operation and Design Window for Analog Gain Stages

The intrinsic gain (Ai), transconductance efficiency (gm/IDS) and cut-off frequency (fT) are analysed for thin film transistors (TFTs) operating in the deep subthreshold region to assess the impact of device variations on the design window for analogue circuits. Results suggest that subthreshold operation could improve the Ai and gm/IDS at the cost of reduced fT and increased sensitivity to bias and process variations. Interestingly, a less steep subthreshold slope (SS) could, to some extent, compensate for these shortcomings, which is in contrast to the general thinking of pursuing a steeper SS in TFT fabrication.