超薄氧化層n-MOSFET元件之低頻雜訊分析

Abstract

本文探討了閘極氧化層厚度在直接穿遂範圍的n-MOSFET之低頻1/f雜訊。對14Å氧化層厚度而言，我們觀察到額外增加的低頻雜訊是電子和電洞藉由介面的缺陷結合所導致的。在如此薄的氧化層，價電層電子會發生穿遂而導致電子和電洞的費米能階分裂。這額外的低頻雜訊被歸因於電子和電洞佔據準費米能階之間的介面缺陷。 本文也探討了有著浮動體極的超薄氧化層n-MOSFET上，軟性崩潰位置對於低頻1/f雜訊會有所衝擊。在通道崩潰的元件，過量的雜訊現象可以在歐姆操作區域內被看到。這額外雜訊密度的量比較背景的1/f雜訊可大上十倍。這雜訊的來源被相信是和因軟性崩潰而加強電子穿遂價電帶所導致的浮動體極效應有關。作者指出，通道的軟性崩潰會增加汲極電流的雜訊，在部分空乏的類比SOI電路上，會是一個可靠度的問題。

Low-frequency flicker noise in n-MOSFETs with gate oxide thickness in direct tunneling regime is investigated. For a 14Å oxide, excess low frequency noise arising from interface trap assisted electron and hole recombination is observed. In such thin oxide devices, valence-band electron tunneling takes place and results in the splitting of electron and hole quasi Fermi-levels. The excess low-frequency noise is attributed to electron and hole capture at interface traps between the quasi Fermi-levels. The impact of soft breakdown location on low-frequency noise in ultra-thin oxide n-MOSFETs with floating body is also investigated. In a channel breakdown device, a noise overshoot phenomenon is observed in the ohmic regime. This excess noise spectral density is about one order of magnitude higher than the background 1/f noise. The origin of this excess noise is believed due to soft breakdown (SBD) enhanced valance-band electron tunneling and thus induced floating body effect. Our findings indicate that channel SBD enhanced drain current noise degradation can be a reliability issue in partially depleted analog SOI CMOS circuit.