超薄氧化層CMOS元件中低頻雜訊分析

Abstract

超薄氧化層CMOS元件中低頻雜訊分析 學生:張鴻智 指導教授:汪大暉 博士 國立交通大學 電子工程學系 電子研究所 摘要 在之前的研究顯示低頻雜訊是觀察矽氧介面可靠性不錯的指標,本篇主要是根據Unified Noise Model以及建立Two-Region Model探討氧化層可靠性和低頻雜訊的關係,經由stress產生衰減和低頻雜訊的關係了解雜訊的主要來源,由我們的實驗結果可知熱載子會對1/f雜訊產生及嚴重的增加,這個現象可藉由Two-Region Model來解釋,除此之外,低頻雜訊在經由高壓操作下的變化會根據測量時的閘極偏壓以及電晶體的類型而不同,其原因是不同1/f雜訊的擾動機制所造成,我們發現在n型電晶體中高低閘極偏壓分別由移導率擾動以及數量擾動所主宰,然而在p型電晶體主要由移導率擾動所主宰. 此外,超薄氧化層電晶體會有直接穿燧電流以及,在高閘極偏壓會有軟性崩潰,因此也可用低頻雜訊來觀察其對元件的影響程度,在軟性崩潰前後比較發現p型電晶體和n型電晶體相比有嚴重的低頻雜訊衰變,我們的研究結果顯示是由於軟性崩潰的突穿點正電荷聚集因而產生的不均勻的通道導通電壓所造成.

Analysis of Flicker Noise Degradation Mechanism in Ultra-thin Oxide CMOS Student: Hung-Chih Chang Advisor: Dr. Tahui Wang Institute of Electronics, National Chiao Tung University Hsinchu, Taiwan, R.O.C Abstract Previous research has shown that the drain current flicker noise is a good monitor of the Si-SiO2 interface quality. This thesis will focus on the flicker noise degradation issue after stressing and use a two-region model based on the unified noise theory to study this phenomenon. The flicker noise degradation mechanisms are verified by various kinds of stresses. From our observation, we found that the local oxide charge caused by CHE stress could give rise to serious degradation of flicker noise, which can be understood through the two-region model. Besides, the behavior of flicker noise degradation depends on the measurement gate bias and the type of MOS transistors, which is attributed to different dominant noise process, such as number fluctuation and mobility fluctuation. We found that the number fluctuation dominates at low gate bias in nMOSFETs. As the gate bias increases, the mobility fluctuation mechanism will become more important. In the case of pMOSFETs, the mobility fluctuation dominates the noise behavior in the entire range of applied gate biases. Furthermore, the soft breakdown effects on drain current flicker noise degradation in ultra thin oxide MOSFETs are also investigated. The results show that the soft breakdown effects would induce larger noise degradation in pMOSFETs, when compared to nMOSFETs. Our study reveals that the serious noise degradation in pMOSFETs is attributed to the non-uniform threshold voltage distribution resulting from positive oxide charge creation in the soft breakdown spot.