[paper] Performance limits of hBN as an insulator for scaled CMOS

Theresia Knobloch¹, Yury Yu. Illarionov^1,2, Fabian Ducry³, Christian Schleich⁴, Stefan Wachter⁵, Kenji Watanabe⁶, Takashi Taniguchi⁷, Thomas Mueller⁵, Michael Waltl⁴, Mario Lanza⁸, Mikhail I. Vexler², Mathieu Luisier³ and Tibor Grasser¹

The performance limits of hexagonal boron nitride as an insulator for scaled CMOS devices based on two-dimensional materials

Nature Electronics; Vol 4; Feb.2021; pp.98–108;

DOI: 10.1038/s41928-020-00529-x

1. Institute for Microelectronics, TU Wien, Vienna, Austria.
2. Ioffe Institute, St Petersburg, Russia.
3. Integrated Systems Laboratory, ETH Zürich, Zurich, Switzerland.
4. Christian Doppler Laboratory for Single-Defect Spectroscopy in Semiconductor Devices at the Institute for Microelectronics, TU Wien, Vienna, Austria.
5. Institute for Photonics, TU Wien, Vienna, Austria.
6. Research Center for Functional Materials, National Institute for Matierals Science, Tsukuba, Japan.
7. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
8. Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia.

Abstract: Complementary metal–oxide–semiconductor (CMOS) logic circuits at their ultimate scaling limits place extreme demands on the properties of all materials involved. The requirements for semiconductors are well explored and could possibly be satisfied by a number of layered two-dimensional (2D) materials, such as transition metal dichalcogenides or black phosphorus. The requirements for gate insulators are arguably even more challenging. At present, hexagonal boron nitride (hBN) is the most common 2D insulator and is widely considered to be the most promising gate insulator in 2D material-based transistors. Here we assess the material parameters and performance limits of hBN. We compare experimental and theoretical tunnel currents through ultrathin layers (equivalent oxide thickness of less than 1 nm) of hBN and other 2D gate insulators, including the ideal case of defect-free hBN. Though its properties make hBN a candidate for many applications in 2D nanoelectronics, excessive leakage currents lead us to conclude that hBN is unlikely to be suitable for use as a gate insulator in ultrascaled CMOS devices.

Fig: Comparison of gate insulators for ultrascaled CMOS devices based on 2D materials. a.) Currents at constant EOT for 3D oxides and layered insulators. The leakage currents as calculated with the Tsu–Esaki model are given for 3D amorphous oxide and 2D layered insulators at a constant thickness of EOT=0.76nm. If no tunnel masses were known, the free-electron mass was used. The filled circles indicate the results of ab initio calculations and the dotted line connecting the circles is a guide to the eye. b.) Currents at constant EOT for native oxides and fluorides. The leakage currents are given for native oxides and ionic fluorides at a constant thickness of EOT=0.76nm.

Acknowledgements: T.K., Y.Y.I. and T.G. acknowledge the financial support through FWF grant numbers I2606-N30, I4123-N30 and P29119-N35. Y.Y.I. and M.I.V. acknowledge financial support by the Ministry of Science and Higher Education of the Russian Federation under project number 075-15-2020-790. F.D. and M. Luisier thank CSCS for giving them access to the Piz Daint supercomputer under project number s876. C.S. and M.W. gratefully acknowledge financial support by the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development and the Christian Doppler Research Association. The computational results presented have been achieved in part using the Vienna Scientific Cluster (VSC). S.W. and T.M. acknowledge financial support through the Graphene Flagship number 785219 and number 881603. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, number JPMXP0112101001, JSPS KAKENHI grant number JP20H00354 and the CREST(JPMJCR15F3), JST. M. Lanza acknowledges support from the Ministry of Science and Technology of China (grant numbers 2018YFE0100800, 2019YFE0124200) and the National Natural Science Foundation of China (grant number 61874075).