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如图1所示,在增强型MOS晶体管中,把源和漏接在一起并反偏置(V_R<0),当未加栅脉冲时,I_B只是结的反偏电流。当栅上加负脉冲时,I_B就反过来变成正向电流。这个电流随栅脉冲频率f增加而线性增大,并大致正比于栅面积。由于结是反偏置的,而I_B是正向流动,这就意味着功率从栅脉冲源转换到电池。这种现象就是MOS器件中的电荷泵效应。这个“泵电流”(“pumped current”)现象与每个周期存储在栅电极下面的电荷有关,其中部分电荷在周期结束时与衬底的多数载流子复合形成泵电流I_B。为解释电流的产生,讨论一下反型层的建立与消失过程就清楚了。
As shown in Figure 1, in an enhancement mode MOS transistor, the source and drain are connected together and reverse biased (V_R <0). When no gate pulse is applied, I_B is only the junction reverse bias current. When a negative pulse is applied to the gate, I_B, in turn, becomes a positive current. This current increases linearly with the gate pulse frequency f and is roughly proportional to the gate area. Since the junction is anti-biased and I_B is flowing in the forward direction, this means that power is being transferred from the gate pulse source to the battery. This phenomenon is the charge pump effect in MOS devices. This “pumped current” phenomenon is related to the charge stored under the gate electrode for each cycle, with part of the charge recombining with the majority carriers of the substrate at the end of the cycle to form a pump current I_B. To explain the current generation, it is clear that the inversion layer build-up and disappearance process is discussed.