Modeling and performance study of nanoscale double gate junctionless and inversion mode MOSFETs including carrier quantization effects
Introduction
Reasons to focus on emerging device technologies such as the junctionless transistor (JLT) are for instance, the increasing fabrication difficulties of ultra-abrupt pn-junctions at the nanometer scale and the need to keep up with the strong requirements of the ITRS road-map [1]. A complete description of the JLT׳s operation principle and a first performance estimation, using Atlas 3-D simulator, was given in [2], [3]. It was shown that this new device concept, which does not contain pn-junctions, offers reduced short-channel effects (SCEs) compared to their conventional counterparts, an excellent subthreshold slope behavior, very low off leakage currents, high ratios and less variability. In order to support the technology development and optimization and to reduce times and costs, the development of compact models, especially for this new device concept, is an urgent task.
This research study is dedicated to explore the scaling behavior of the JL and IM MOSFET in double gate configuration in the nanometer regime (Fig. 1). The main purpose is to use our predictive compact model, which was presented in [4] and enhanced in [5], and a method to extract the ratios [6], to estimate the performance of the mentioned devices in present- and future-scaled sizes. The performances of both device types are compared and investigated. In addition, our previous modeling approach is extended by the inclusion of QEs. Briefly, the 2-D model is developed using Poisson׳s equation and the conformal mapping technique by Schwarz–Christoffel [7]. The analytical solution includes the dependencies on the transistor׳s geometrical dimensions and doping concentrations. The threshold voltage VT and the subthreshold slope S are calculated and an unified mobile charge density model is derived by applying Lambert׳s W-function. A standard current equation rounds off the model [5]. In this paper we assume n-type devices with a crystal orientation and additional source/drain implants () to avoid high parasitic access resistances, which also eliminates the need to consider incomplete ionization effects [8].
Section snippets
General modifications
This section intends to focus on the enhancements and changes of the model from [5], where we developed a 2-D physics-based, compact model for DG JL MOSFETs. Therefore, only the significant modifications are addressed here. For the complete model description and derivation, the reader is kindly asked to refer to [5]. To make our previous model also valid for DG IM MOSFETs, we neglect the mobile charges below threshold and express 2-D Poisson׳s equation inside the channel region as
Performance analysis and discussions
In this section we present the modeling versus the simulation results and compare the performances of both the DG JL and DG IM MOSFET. Important device parameters such as S, DIBL and the ratios are in focus of the discussion. For the JL device we choose a channel doping concentration (highly doped) and for the IM device we choose (lightly doped). All other parameters (structural and electrical) are identical – in the model and the simulations. As reference data
Conclusions
We presented a 2-D physics-based, predictive compact model for nanoscale DG JL and DG IM MOSFETs, which includes the effect of carrier quantization in ultra-scaled devices. The comparison versus 2-D numerical simulation data from TCAD Sentaurus verified the correctness of the model. A performance study for both device types was carried out, whereby important device metrics such as DIBL, S and the ratios were analyzed and discussed. We found that: QEs have a strong influence on VT in
Acknowledgments
This project was supported by the German Federal Ministry of Education and Research under contract No. 1779X09, by the German Research Foundation (DFG) under Grant KL 1042/3-1, by the European Commission under FP7 Projects ICTSTREP 257111 (“SQWIRE”) and IAPP-218255 (“COMON”), by the Spanish Ministerio de Ciencia y Tecnología under Projects TEC2011-28357-C02-01, by the PGIR/15 Grant from URV and also by the ICREA Academia Prize. We also acknowledge AdMOS GmbH in Frickenhausen (Germany) for
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