由於矽基互補式金氧半場效電晶體 (Si CMOS) 已經被公認為操作量子位元的最佳候選者之一，矽基互補式金氧半場效電晶體可用於連接低溫量子系統 (~mK)與室溫古典系統 (300K)的介面。為了研究CMOS元件在低溫下的電性表現，本論文涵蓋了奈米尺度下遭遇的量子效應。其中重要的物理效應，一為量子侷限效應，在小尺寸元件可以觀察到，例如鰭式電晶體和奈米片電晶體。該效應會導致載子質心遠離氧化物與通道界面。雖然這個效應可以減少表面粗糙度散射，但它也明顯地降低了閘極的控制能力。能帶結構因為尺寸縮小的原故，將發生改變，導致有效質量和能隙增加，因此，這種效應對於電性表現的影響尚未明朗，尤其是在低溫操作下。第二個效應是源極-汲極穿隧(SDT)效應，當縮小元件尺度，尤其是通道長度時，源極與汲極之間的距離變短，這將引發從源極到汲極的量子穿隧效應與漏電流。
本論文旨在藉由TCAD模擬比較MOSFET和TFET在室溫(300K)至低溫(10 K) 下操作的電性表現。根據我們的TCAD模擬結果，由於SDT效應，短通道MOSFET遭受不可接受的高漏電流。因此，MOSFET的次臨界擺幅(SS)可能在低溫下達到飽和。另一方面，雖然TFET的SS表現出與溫度無關的趨勢，漏電流雖比MOSFET小，但由於帶間穿隧的性質，導通電流明顯小於MOSFET。
根據我們的模擬結果，對於長通道結構(25nm)的MOSFET，降低溫度下的 SS 降低的趨勢遵循波茲曼極限，但當溫度繼續下降至低溫 (10K)時，SDT 電流主導次臨界電流，使SS無法繼續下降，導致SS飽和。對於短通道結構(8 nm)，由於SDT的影響更大，SS 在更高的溫度下就會飽和。

As Si CMOS has been recognized as one of the best candidates for qubit operation agent. Si CMOS can be used as an interface between quantum (~mK) and classic (300 K) systems. In order to study the electrical characteristics of small CMOS devices working at low temperatures, this thesis covers the effects encountered in nanometer scale. One of the crucial physics is the quantum confinement effect, which occurs in devices with small dimensions, such as FinFETs and Nanosheet FETs. The effect will result in carrier centroid located away from the oxide-channel interface in the channel. Though this effect may reduce surface scattering, it also effectively degrades the gate controllability. The band structure might be changed due to quantum confinement, resulting in an increase in effective mass and bandgap. Therefore, the impact of this effect on electrical characteristics are not yet clear, especially at low temperatures. The second effect is the source-drain tunneling (SDT) effect. When scaling down the device dimensions, especially the channel length, the distance between the source and drain becomes shorter, which leads to tunneling from the source to the drain regions quantum mechanically and leakage currents.
This thesis aims to compare the electrical performance of MOSFETs and TFETs working at low temperatures, from 300 to 10 K by carrying out TCAD simulations. According to our TCAD results, short-channel MOSFETs suffer from unacceptably high leakage currents because of the SDT effect., Hence, the subthreshold swing (SS) of a MOSFET may saturate at a low temperature. On the other hand, although the SS of a TFET shows temperature-independent trend, the leakage current is smaller than that of the MOSFETs, but because of the nature of band-to-band tunneling, the conduction current is significantly smaller than that of a MOSFET.
According to our simulation results, with a long channel structure (25nm) of the MOSFETs, the SS reduction effect with lowering the temperature is following the Boltzmann limit, but when the temperature continues to drop to the cryogenic temperature, the SDT current dominates the subthreshold currents so as to saturate the SS reduction. With a short channel structure (8 nm), the SS is saturated at higher temperatures because of the greater SDT influence.

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