The inability to scale supply voltage and hence reduce power consumption remains a serious challenge in modern nanotransistors. This arises primarily because the Sub-threshold Swing (SS) of the thermionic MOSFET, a measure of its switching efficiency, is restricted by the Boltzmann limit (kBT/q = 60 mV/dec at 300 K). Tunneling FETs, the most promising candidates to circumvent this limit, employ band-to-band tunneling, yielding very low OFF currents and steep SS but at the expense of severely degraded ON currents. In a completely different approach, by introducing concurrent tuning of thermionic and tunneling components through metal/semiconductor Schottky junctions, we achieve an amalgamation of steep SS and high ON currents in the same device. We demonstrate sub-thermionic transport sustained up to 4 decades with SSmin ∼ 8.3 mV/dec and SSavg ∼ 37.5(25) mV/dec for 4(3) dec in few layer MoS2 dual gated FETs (planar and CMOS compatible) using tunnel injected Schottky contacts for a highly scaled drain voltage of 10 mV, the lowest for any sub-thermionic devices. Furthermore, the same devices can be tuned to operate in the thermionic regime with a field effect mobility of ∼84.3 cm2 V−1 s−1. A detailed mechanism involving the independent control of the Schottky barrier height and width through efficient device architecture and material processing elucidates the functioning of these devices. The Gate Tunable Thermionic Tunnel FET can function at a supply voltage of as low as 0.5 V, reducing power consumption dramatically.
The ultrathin channel in 2D semiconductors, although playing host to several interesting properties, also renders strong interactions (scattering) of charge carriers with the surrounding medium. The over‐arching dominance of surface (interfacial) optical phonons in 2D charge transport and engineering ideal nitride‐based dielectric environments for large performance gains is reported. Charge transport in MoS2 field effect transistors (FETs) fabricated on three conventional substrates, SiO2, Al2O3, and HfO2, is contrasted with a newly introduced, CMOS‐compatible nitride‐based dielectric: aluminum nitride (AlN) by employing semi‐classical models which account for charged impurity, surface optical phonon, and intrinsic phonon scattering. Unlike previous reports focused on charge impurity scattering, this work presents a new paradigm of utilizing high optical phonon energies intrinsic to “stiff” nitride bonds. This results in substantially lower surface optical phonon scattering in 2D FETs which directly influences peak field effect (FE) mobility, high field mobility degradation, and temperature‐dependent mobility. Leveraging on these insights, high‐performance sulfur‐passivated MoS2 FETs with an optimum all‐nitride environment (hexagonal boron nitride/MoS2/AlN) are demonstrated with FE mobility up to 72.8 cm2 V−1 s−1. This work is envisioned to address important issues in design of dielectric environments for a host of applications based on 2D materials.
The prognosis after evacuation of a chronic subdural hematoma is generally good, yet occasionally post-operative complications do occur. Intracerebral hematoma following such evacuation is rare and two cases are reported. It is suggested that this complication could be due to the disturbances of intracerebral vascular homeostasis occurring after rapid evacuation of subdural hematomas where there has been a large shift of the brain stem.
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