Abstract
For nanometer MOSFETs, charging and discharging a single trap induces random telegraph noise (RTN). When there are more than a few traps, RTN signal becomes complex and appears as within a device fluctuation (WDF). RTN/WDF causes jitters in switch timing and is a major challenge to low power circuits. In addition to RTN/WDF, devices also age. The interaction between RTN/WDF and aging is of importance and not fully understood. Some researchers reported aging increasing RTN/WDF, while others showed RTN/WDF being hardly affected by aging. The objective of this paper is to investigate the impact of hot carrier aging (HCA) on the RTN/WDF of nMOSFETs. For devices of average RTN/WDF, it is found that the effect of HCA is generally modest. For devices of abnormally high RTN/WDF, however, for the first time, we report HCA reducing RTN/WDF substantially (>50%). This reduction originates from either a change of current distribution or defect losses.
Highlights
As device area scales down, the impact of a single charge in gate dielectric scales up [1,2,3,4,5,6,7,8]
The objective of this work is to investigate the relation between the amplitude of random telegraph noise (RTN)/WDF and hot carrier aging (HCA) for nMOSFETs
This agrees with the early works [10, 19] and the verdict that RTN/WDF is dominated by as-grown defects [4, 21]
Summary
As device area scales down, the impact of a single charge in gate dielectric scales up [1,2,3,4,5,6,7,8]. For current and future CMOS nodes, charging and discharging a single trap induces a random telegraph noise (RTN) in Id under a given Vg. When there are more than a few (e.g. 4) of traps, it becomes difficult to separate them and the complex RTN signals appear in the form of within-a-device-fluctuation (WDF) [5, 9]. The low (Vg-Vth) used in low power circuits has less headroom to tolerate a given Vth shift, ΔVth, since ΔVth/(Vg-Vth) is higher and the impact of ΔVth on the driving current is relatively stronger. It has been reported that a single charge can cause a Vth shift of ~30 mV [4], while a shift of only several mV can cause errors in circuits like successive approximation analogue-to-digital converters [11]
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