Modeling and Simulation of Charge-Pumping Characteristics for LDD-MOSFET Devices With LOCOS Isolation

摘要

We propose a model for the so-called constant-amplitude charge-pumping (CP) characteristics, giving the Elliot Gaussian-like CP current curve ($I_{rm CP}$– $V_{L}$) of lightly doped drain (LDD) MOSFET with local oxidation of silicon (LOCOS). This method is based on modulation of the contributing active-channel area $(A_{G})$ to the $I_{rm CP}$ –$V_{L}$ curve, depending on the position of the high and low levels of the gate signal voltage. In addition, it allows to separate and clarify the contribution of all MOSFET regions (such as the effective channel, LDD, LOCOS, and LDD subdiffusion under the LOCOS) to the amount of $I_{rm CP}$– $V_{L}$ curves. We have simulated this model and compared with experimental CP data. The model shows a very good correlation with experimental $I_{rm CP}$ –$V_{L}$ curves, particularly for transistors with short channel gate lengths $(L_{G} leq hbox{1} muhbox{m})$. However, as the channel gate length increases, the model matches only for rising and falling $I_{rm CP}$–$V_{L}$ curve edges, corresponding to the contribution of LDD and LOCOS regions, respectively. Moreover, we have demonstrated that the deviation,-n-n which was observed between the CP model and experimental data at the maximum plateau of $I_{rm CP}$– $V_{L}$ characteristics, depends on the gate pulse fall time and vanishes for large fall time. This difference has been found to behave like a geometric component, since it depends on gate length and fall time and disappears for both short gate lengths and long fall times.