Using Anisotropic Insulators to Engineer the Electrostatics of Conventional and Tunnel Field-Effect Transistors

Materials scientists have developed a wide variety of anisotropic insulators that could offer avenues to separately manipulate lateral and perpendicular electric fields if implemented as the gate insulators or spacers in field-effect transistors (FETs). However, there have been no works that have studied how the electrostatics of an FET can be engineered by using anisotropic insulators. We address this gap in knowledge by simulating metal–oxide–semiconductor FETs (MOSFETs) and tunnel FETs (TFETs) while separately varying the in-plane and out-of-plane permittivities of their insulators. Our results show that MOSFETs should have gate insulators and spacers with small in-plane and large out-of-plane permittivities to maximize their performance, and we demonstrate that an FET with a single anisotropic insulator that covers both the gate dielectric and spacers can outperform a similar structure that uses hafnium dioxide for the gate dielectric and air for the spacers. We also demonstrate that anisotropic gate insulators can greatly improve the subthreshold swing and ON-currents of TFETs, and we introduce a new type of heterogate dielectric for TFETs by manipulating the gate insulator’s in-plane permittivity. We anticipate that the results of this study will motivate experimental research toward developing FETs with anisotropic insulators.