射頻金氧半場效電晶體於熱載子效應及氧化層崩潰時之特性化及模型化分析

Abstract

近年來隨著生活水準提升,無線通訊 ( wireless communication) 市場快速成長,無論是學術界或是工業界皆無不極力地發展無線通訊這高科技 o 而微波元件則是通訊系統中最重要的骨架。又由於以矽為基底的金氧半場效電晶體已經成為射頻元件的主流，所以射頻金氧半場效電晶體的可靠度分析亦變得愈益重要。 本篇論文之重點即是在研究以矽為基底的金氧半場效電晶體受到熱載子效應以及氧化層崩潰時的特性分析，此外我們也提出受到熱載子效應及氧化層崩潰時的金氧半場效電晶體小訊號模型並且討論個別小訊號參數的變化情形。 首先受到熱載子效應後的金氧半場效電晶體其高頻雜訊，功率特性以及截止頻率受到很嚴重的破壞。這主要是因為金氧半場效電晶體的互導下降之故。另外我們可以藉著固定汲極電流來減緩熱載子效應對於金氧半場效電晶體的影響。這可以由金氧半場效電晶體在受到熱載子效應後其臨界電壓，次臨界擺幅，電子遷移率的變化來解釋。 另一方面，由於氧化層在崩潰後會產生一個漏電路徑，所以輸入端的阻抗以及反射係數會有很明顯的變化。值得注意的是金氧半場效電晶體在氧化層崩潰後會在氧化層區產生額外的散粒雜訊, 因此其最小雜訊值會劇烈地增加。 最後，透過小訊號模型的分析，我們發現金氧半場效電晶體的互導，汲極到源極的電阻以及閘極到源極的電容受到熱載子效應以及氧化層崩潰的影響較大。另外我們也確認了在氧化層崩潰後主要的漏電路徑是產生在閘極與源極或通道的重疊區域。

In recent years, with the improvement of living standard, the development of wireless communication has become the most important technology, not only in academic circles but also in the industries. Microwave transistors are the backbone of these modern wireless communication systems. Since the Si-based MOSFETs (metal-oxide-semiconductor field-effect transistors) have become the mainstream of RF transistors in recent years, the reliability of RF MOSFETs is more and more important. The purpose of this thesis is to investigate the characteristics of RF MOSFETs under hot carrier stress and oxide breakdown. In addition, we proposed a small-signal model individually after hot carrier (HC) stress and oxide breakdown (OBD) and discuss the variations of each small-signal parameter. Firstly, we found that the degradations of cut-off frequency, noise and power characteristics are very obvious after HC stress. It can be explained by the decrease of the transconductance. In addition, the degradation of linearity can be softened by biasing the transistor at constant drain currents. This experimental observation can be explained by the change of threshold voltage, transconductance, subthreshold swing, and mobility under HC stress. Secondly, since a new leakage path is generated in the gate oxide after oxide breakdown, the input impedance and optimized input reflection coefficient suffer degradations. It is worthwhile to notice that the minimum noise figure increases dramatically after hard oxide breakdown (HBD). It can be explained by the additional shot noise source in gate oxide after HBD. Finally, from the small-signal model, the transconductance (gm0), drain-to-source resistance (Rds), and gate-to-source capacitance (Cgs) suffer more degradation after HC stress and oxide breakdown. We also confirm that the main leakage path locates at the gate and source/channel overlap region.