用能带展宽描述FD-SOI MOSFET的低温亚阈值摆幅饱和
Cryogenic Subthreshold Swing Saturation in FD-SOI MOSFETs described with Band Broadening
摘要：
在作为施加的栅极电压$V_{GS}$的函数的漏极电流$I_{D}$的标准MOSFET描述中，亚阈值摆幅$SS(T)\equiv dV_{GS}/d\log I_{D}$具有由$SS(T) = \ln10~k_BT/e$给出的作为温度$T$的函数的基本下限。然而，最近对不同先进CMOS技术的低温研究报告了至少大一个数量级的$SS$（4K或更低）值。在这里，我们提出并分析了$SS(T)$在28 nm全耗尽绝缘体上硅（FD-SOI）器件的饱和度为n型和p型MOSFET的不同栅极氧化层厚度和栅极长度下降到4K。到目前为止，已经提出了随着温度降低，靠近带边的界面陷阱密度增加来理解饱和。在这里，一个原始的解释的现象是通过考虑在导（价）带边的状态密度的无序诱导的尾巴的MOS沟道输运的计算，通过应用费米-狄拉克统计。这导致具有饱和值$SS(T<T_0) = \ln 10~k_BT_0/e$的$T_0=35$ K的亚阈值$I_{D}\sim e^{eV_{GS}/k_BT_0}$。所提出的模型充分地描述了从300到4 K的实验数据，使用$k_BT_0 \simeq 3$ meV的指数尾的宽度，也可以准确地描述$SS(I_{D})$在整个亚阈值区域内。我们的分析可以直接确定的技术依赖的带尾延伸形成一个关键因素，在未来紧凑的建模和设计的低温电路。
英文摘要：
In the standard MOSFET description of the drain current $I_{D}$ as a function of applied gate voltage $V_{GS}$, the subthreshold swing $SS(T)\equiv dV_{GS}/d\log I_{D}$ has a fundamental lower limit as a function of temperature $T$ given by $SS(T) = \ln10~k_BT/e$. However, recent low-temperature studies of different advanced CMOS technologies have reported $SS$(4K or lower) values that are at least an order of magnitude larger. Here, we present and analyze the saturation of $SS(T)$ in 28nm fully-depleted silicon-on-insulator (FD-SOI) devices for both n- and p-type MOSFETs of different gate oxide thicknesses and gate lengths down to 4K. Until now, the increase of interface-trap density close to the band edge as temperature decreases has been put forward to understand the saturation. Here, an original explanation of the phenomenon is presented by considering a disorder-induced tail in the density of states at the conduction (valence) band edge for the calculation of the MOS channel transport by applying Fermi-Dirac statistics. This results in a subthreshold $I_{D}\sim e^{eV_{GS}/k_BT_0}$ for $T_0=35$K with saturation value $SS(T<T_0) = \ln 10~k_BT_0/e$. The proposed model adequately describes the experimental data of $SS(T)$ from 300 down to 4K using $k_BT_0 \simeq 3$meV for the width of the exponential tail and can also accurately describe $SS(I_{D})$ within the whole subthreshold region. Our analysis allows a direct determination of the technology-dependent band-tail extension forming a crucial element in future compact modeling and design of cryogenic circuits.
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