  Two-dimensional (2D) semiconductors offer a promising prospect for
high-performance and energy-efficient devices especially in the sub-10 nm
regime. Inspired by the successful fabrication of 2D $\beta$-TeO$_2$ and the
high on/off ratio and high air-stability of fabricated field effect transistors
(FETs) [Nat. Electron. 2021, 4, 277], we provide a comprehensive investigation
of the electronic structure of monolayer $\beta$-TeO$_2$ and the device
performance of sub-10 nm metal oxide semiconductors FETs (MOSFETs) based on
this material. The anisotropic electronic structure of monolayer
$\beta$-TeO$_2$ plays a critical role in the anisotropy of transport properties
for MOSFETs. We show that the 5.2-nm gate-length n-type MOSFET holds an
ultra-high on-state current exceeding 3700 {\mu}A/{\mu}m according to
International Roadmap for Devices and Systems (IRDS) 2020 goals for
high-performance devices, which is benefited by the highly anisotropic electron
effective mass. Moreover, monolayer $\beta$-TeO$_2$ MOSFETs can fulfill the
IRDS 2020 goals for both high-performance and low-power devices in terms of
on-state current, sub-threshold swing, delay time, and power-delay product.
This study unveils monolayer $\beta$-TeO$_2$ as a promising candidate for
ultra-scaled devices in future nanoelectronics.
