Ⅳ有限的反型层电容 效应 在进行MOSFET模拟时,一般假定沟道内流动的电荷是随着阈值以上的栅压偏置线性增加的。只要氧化物的厚度比反型层的厚度大得多,并且电源电压根对地大,情况的确是这样的。用理想的恒定电场按比例缩小时,反型层的厚度基本上保持不变,而氧化物厚度要依据按比例缩小因子进行减小。因此,氧化物电容相对反型层电容来说增加了,C_i=-(Q_n/αφ_s)导致亚线性的沟道电荷变化和跨导降低。 IV. Limited Reversed-Layer Capacitance Effect When performing MOSFET simulations, it is generally assumed that the charge flowing in the channel increases linearly with the gate-voltage bias above the threshold. This is indeed true as long as the thickness of the oxide is much greater than the thickness of the inversion layer and the supply voltage is large. When scaled down with the ideal constant electric field, the thickness of the inversion layer remains essentially unchanged, whereas the thickness of the oxide is reduced according to a scaled-down factor. Therefore, the oxide capacitance increases with respect to the inversion layer capacitance and C_i = - (Q_n / αφ_s) results in sub-linear channel charge variation and transconductance reduction.