金氧半場效應電晶體在次臨界區的不匹配效應

Abstract

本論文研究隨機摻雜物以及電路的不匹配效應對於臨界電壓擾動的影響與其物理模型。首先，我們量測各種不同尺寸的電晶體，並觀察到在次臨界區存在比過臨界區更大的電特性誤差。接著我們萃取出許不同的製程參數，並且建立一個有關通道摻雜濃度變異的新模型來解釋臨界電壓隨著閘極長度的縮短而上升。同時我們發現到萃取出的臨界電壓變動值會與元件面積平方根的倒數成正比，這與前人所提出的理論符合。我們也發現背閘順向偏壓可以減少製程參數變動值並可用來補償小尺寸電晶體較大的參數變動值。 接著我們特別著重在進一步探討臨界電壓的擾動特性。過程中我們觀察到在不同的汲極電壓下，所造成的臨界電壓的差異，此時因電子的能階產生變化，而會導致元件的控制力有所升降。再來我們利用Takeuchi的模型做比對，並考慮到隨機摻雜以及硼簇合族對於臨界電壓擾動的影響。從我們分析的結果看來，隨機摻雜對於臨界電壓擾動的影響會因為硼簇合族的原子個數上升而更加明顯。在最後，我們推導出一個在次臨界區中，與汲極電流誤差相關的新的臨界電壓擾動模型，並且此模型能經由電流誤差成功的估計臨界電壓的擾動值。

The physical model of the threshold voltage fluctuation from random dopant, as well as current mismatch, is investigated in the thesis. At first we have extensively characterize MOSFETs with different gate widths and lengths, especially in subthreshold region of operation. We observe that the mismatch exhibits a larger mismatch while operating in subthreshold region than in above-threshold region. We extract various process parameters and hence construct a new model due to varying of channel doping to explain the threshold voltage increase with gate length decrease. The threshold voltage variations are shown to follow the inverse square rule. Simultaneously, the back-gate forward bias is found to be able to reduce the mismatch and compensate for larger variations for smaller devices. Further, we pay more attention to the threshold voltage fluctuation, and observe that the drain voltage might cause the DIBL. Then we discuss the threshold voltage fluctuation by a Takeuchi plot, and the effect of random dopant and the boron clusters are taken into account. From our analysis, the random dopant induced threshold voltage fluctuation has more significant effect on threshold variation while the number of boron atoms per cluster increases. Finally, we also statistically derive a new model that can estimate the threshold voltage fluctuation from drain current mismatch in subthreshold region. The validity of the model is verified.