In this work we discuss limitations of the split-CV method when it is used for extracting carrier mobilities in devices with thin silicon channels like FinFETs, ultra thin body silicon-on-insulator (UTB-SOI) transistors and nanowire MOSFETs. We show that the high series resistance may cause frequency dispersion during the split-CV measurements, which leads to underestimating the inversion charge density and hence overestimating mobility. We demonstrate this effect by comparing UTB-SOI transistors with both recessed-gate UTB-SOI devices and thicker conventional SOI MOSFETs. In addition, the intrinsic high series access resistance in UTB-SOI MOSFETs can potentially lead to an overestimation of the effective internal source/drain voltage, which in turn results in a severe underestimation of the carrier mobility. A specific MOSFET test structure that includes additional 4-point probe channel contacts is demonstrated to circumvent this problem, Finally, we accurately extract mobility in UTB-SOI transistors down to 0.9 nm silicon film thickness (four atomic layers) by utilizing the 4-point probe method and carefully choosing adequate frequencies for the split-CV measurements. It is found that in Such thin silicon film thicknesses quantum mechanical effects shift the threshold voltage and degrade mobility. (C) 2009 Elsevier Ltd. All rights reserved.
Mobility extraction in SOI MOSFETs with sub 1 nm body thickness / Schmidt, M; Lemme, Mc; Gottlob, Hdb; Driussi, Francesco; Selmi, Luca; Kurz, H.. - In: SOLID-STATE ELECTRONICS. - ISSN 0038-1101. - 53:12(2009), pp. 1246-1251. [10.1016/j.sse.2009.09.017]
Mobility extraction in SOI MOSFETs with sub 1 nm body thickness
SELMI, Luca;
2009
Abstract
In this work we discuss limitations of the split-CV method when it is used for extracting carrier mobilities in devices with thin silicon channels like FinFETs, ultra thin body silicon-on-insulator (UTB-SOI) transistors and nanowire MOSFETs. We show that the high series resistance may cause frequency dispersion during the split-CV measurements, which leads to underestimating the inversion charge density and hence overestimating mobility. We demonstrate this effect by comparing UTB-SOI transistors with both recessed-gate UTB-SOI devices and thicker conventional SOI MOSFETs. In addition, the intrinsic high series access resistance in UTB-SOI MOSFETs can potentially lead to an overestimation of the effective internal source/drain voltage, which in turn results in a severe underestimation of the carrier mobility. A specific MOSFET test structure that includes additional 4-point probe channel contacts is demonstrated to circumvent this problem, Finally, we accurately extract mobility in UTB-SOI transistors down to 0.9 nm silicon film thickness (four atomic layers) by utilizing the 4-point probe method and carefully choosing adequate frequencies for the split-CV measurements. It is found that in Such thin silicon film thicknesses quantum mechanical effects shift the threshold voltage and degrade mobility. (C) 2009 Elsevier Ltd. All rights reserved.File | Dimensione | Formato | |
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