Speed enhancement at V_dd = 0.4V and random Τ_pd variability reduction and analyisis of Τ_pd variability of silicon on thin buried oxide circuits

Ring oscillator characteristics of silicon on thin buried oxide (SOTB) were investigated at V_dd down to 0.4V. It was demonstrated that both the propagation delay (τ_pd) and energy-delay (ED) product of SOTB were smaller than those of bulk devices due to its steeper subthreshold swing. It was found that the τ_pd variability of SOTB is dominated by global variability because local variability is small due to the intrinsic channel. The origin of τ_pd variability was analyzed by taking the transistor dc characteristics into account. It was found that the τ_pd variability of SOTB is caused by the global drive current variability because the effect of resistance (or effective drain current I _eff ) is much larger than that of capacitance with V_dd reduction. The τ_pd variability is mainly caused by the global drive-current variability and thus can be easily reduced by die-to-die substrate bias voltage control.