The Use of a Dual Material Gate (dmg)

Today’s mobile electronics world is driven by the devices which should inherently provide high speed, high performance and low leakage. Such a growing demand of high performance devices catalyzes the aggressive scaling of the transistors below 22 nm. However, the incessant miniaturization of transistor dimensions has resulted in the increased static power dissipation due to the leakage current at an appalling rate.

Moreover, the physical constraints in realizing ultra-scaled dimensions such as abrupt doping profiles, lithography alignment and the increased short channel effects due to inefficient gate control have restricted the realization of the ultra-scaled classical planar transistors. All these factors have outdistanced the conventional single gate planar transistors thereby shifting the focus of the researchers towards the multiple-gate transistors which consume the minimum real-estate on the semiconductor wafer along with better performance by providing efficient gate control. In this current realm, 3D topologies such as Gate-all-around (GAA) nanowires (NW) are considered to be the most promising ultimate short channel device for future technology [1]-[4].

However the effective drive current that may be extracted from a single nanowire is quite low and therefore, needs to be stacked into arrays consuming the valuable chip area thereby countering the advantage of the scaled dimensions [5],[6]. Moreover, this effective gate control leads to a significant overlap of the channel region valence band with the drain conduction band in the OFF-state regime triggering the lateral band to band tunneling (L-BTBT) of electrons from the channel to the drain [4][6-16]. However, the conventional transverse-BTBT (T-BTBT) induced gate induced drain leakage (GIDL) current arises due to the tunneling of the electrons from the valence band to the conduction band in the gate-drain overlap region through the mechanism of band to band tunneling (BTBT) and trap assisted tunneling(TAT) and is dominant at large negative gate bias [4][17],[18].

Therefore, the expedition of FETs with an enhanced output drive current from 3D topologies along with a better ION/IOFF ratio has resulted in the invention of the silicon nanotubes with core shell gate stack [19-27]. Such a nanotube architecture offers the best possible electrostatic gate control which not only provides immunity to the short channel effects but also results in a higher drive current due to the efficient volume inversion compared to the nanowires along with the effective utilization of the real-estate [19-22]. However, this ultimate gate control in the NT architecture results in an enhanced L-BTBT mechanism due to the presence of the core gate [27]. Therefore, the enhanced L-BTBT in nanotube increases their OFF-state current degrading their ION/IOFF ratio Moreover, the L-BTBT is more pronounced at the scaled dimensions hindering their scaling to the future technology nodes and making their usage impractical for high performance computing as well as low power applications. Hence, L-BTBT needs to be mitigated and this problem has been overlooked till date.

Therefore, in this work, we propose the use of a dual material gate (DMG) in both the core as well as outer gate to circumvent the enhanced L-BTBT component in NTFETs to facilitate their scaling for future technology nodes. The DMG has been implemented in the past for conventional lateral channel devices such as planar bulk and SOI MOSFET, TFETs, Junctionless FETs and nanowire architectures [28-37] and had also been experimentally realized[28][31][36][37] for improving the transistor’s performance. However, for such conventional lateral channel devices, the fabrication of a DMG