In this work, a compact transport model has been developed for monolayer transition metal dichalcogenide (TMDC) channel MOSFET. The analytical model solves the Poisson's equation for the inversion charge density to get the electrostatic potential in the channel. Current is then calculated by solving the drift-diffusion equation. The model makes gradual channel approximation to simplify the solution procedure. The appropriate density of states obtained from the first principle density functional theory simulation has been considered to keep the model physically accurate for monolayer TMDC channel FET. The outcome of the model has been benchmarked against both experimental and numerical quantum simulation results with the help of a few fitting parameters. Using the compact model, detailed output and transfer characteristics of monolayer WSe FET have been studied, and various performance parameters have been determined. The study confirms excellent ON and OFF state performances of monolayer WSe FET which could be viable for the next generation high-speed, low power applications. Also, the proposed model has been extended to study the operation of a biosensor. A monolayer MoS channel based dielectric modulated FET is investigated using the compact model for detection of a biomolecule in a dry environment.
Two dimensional materials such as Transition Metal Dichalcogenides (TMDC) and their bi-layer/trilayer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M=Mo or, W and X=S or, Se) Metal Oxide SemiconductorField Effect Transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device 'on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate Field Effect Transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.
A previous theoretical study has shown that spin-polarized current can excite ultra-high frequency spin precessions in collinear antiferromagnetic (AF) films due to the strong antiferromagnetic coupling with the frequency spanning over a wide spectrum from giga-hertz to tera-hertz. In this paper, we present a design to incorporate the AF-based spin torque oscillator into a conventional spin transfer torque magnetic random-access memory. The AF-based oscillator consists of a perpendicular spin polarization layer and an AF layer, separated by a normal metallic interlayer. The AF layer is then exchange-coupled to the free layer on the side that is opposite to the tunnel barrier of the magnetic tunnel junction. Magnetization of the perpendicular spin polarization layer always orients in the opposite direction to that of the reference layer on the other side of the tunnel barrier. When the AF layer thickness and materials are adequately designed, the lateral spin precession in the AF layer excited by the write current provides significant assistance to the magnetization switching of the free layer, resulting in substantial reduction of the switching current threshold and the switching time.
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