Yogesh Singh Chauhan

Bio: Yogesh Singh Chauhan is an academic researcher from Indian Institute of Technology Kanpur. The author has contributed to research in topics: Transistor & MOSFET. The author has an hindex of 30, co-authored 265 publications receiving 3355 citations. Previous affiliations of Yogesh Singh Chauhan include École Normale Supérieure & Indian Institutes of Technology.

Analysis and Compact Modeling of Negative Capacitance Transistor with High ON-Current and Negative Output Differential Resistance—Part I: Model Description

Abstract: We present an accurate and computationally efficient physics-based compact model to quantitatively analyze negative capacitance FET (NCFET) for real circuit design applications. Our model is based on the Landau–Khalatnikov equation coupled to the standard BSIM6 MOSFET model and implemented in Verilog-A. It includes transient and temperature effects, and accurately captures different aspects of NCFET. A comprehensive quasi-static analysis of NCFET in its different regions of operation is also performed using a simpler loadline approach. We also analyze the impact of ferroelectric and gate oxide thicknesses on the performance gain of NCFET over MOSFET.

Analytical Modeling of Surface-Potential and Intrinsic Charges in AlGaN/GaN HEMT Devices

Abstract: A surface potential (SP)-based analytical model for intrinsic charges in AlGaN/GaN high electron mobility transistor devices is presented. We have developed a precise analytical method to calculate the Fermi-level position Ef from a consistent solution of Schrodinger's and Poisson's equations in the quantum well, considering the two important energy levels. The accuracy of our Ef calculation is on the order of femto-volts for the full range of bias voltage. The SP calculated from Ef is used to derive an analytical model for intrinsic charges in these devices. The model is in excellent agreement with experimental data.

Numerical Investigation of Short-Channel Effects in Negative Capacitance MFIS and MFMIS Transistors: Above-Threshold Behavior

Abstract: In this paper, we analyze the impact of length scaling on the ON-state operation of the two classes of double-gate negative capacitance transistors: metal–ferroelectric–metal–insulator–semiconductor (MFMIS) and metal–ferroelectric–insulator–semiconductor (MFIS). We show that for long-channel structures, MFMIS configuration shows a higher ON current than the MFIS due to a lower drain saturation voltage of the latter. For short-channel cases, we compare these negative capacitance field effect transistors (NCFETs) under two scenarios: equal flat band voltages (iso- ${V}_{\textsf {FB}}$ ) and equal OFF currents (iso- ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ ). In iso- ${V}_{\textsf {FB}}$ condition, a higher negative differential conductance (NDC) effect in the MFMIS suppresses its ON current below that of the MFIS. However, the MFMIS provides a higher ON current than the MFIS for all the channel lengths under iso- ${I}_{ \mathrm{\scriptscriptstyle OFF}}$ condition. We further investigate the influence of quantum mechanical effects and velocity saturation of carriers on the electrical characteristics of short-channel NCFETs. We also explore the impact of inner and outer spacer fringings in NCFETs. We find that the ferroelectric voltage gain in NCFETs with spacers increases with the channel length scaling, which provides a further improvement in the ON current contrary to those without spacers. Moreover, increase in the spacer permittivity also boosts both the ON current and the NDC.

BSIM—SPICE Models Enable FinFET and UTB IC Designs

Abstract: Two turn-key surface potential-based compact models are developed to simulate multigate transistors for integrated circuit (IC) designs. The BSIM-CMG (common-multigate) model is developed to simulate double-, triple-, and all-around-gate FinFETs and it is selected as the world's first industry-standard compact model for the FinFET. The BSIM-IMG (independent-multigate) model is developed for independent double-gate, ultrathin body (UTB) transistors, capturing the dynamic threshold voltage adjustment with back gate bias. Starting from long-channel devices, the basic models are first obtained using a Poisson-carrier transport approach. The basic models agree with the results of numerical two-dimensional device simulators. The real-device effects then augment the basic models. All the important real-device effects, such as short-channel effects (SCEs), quantum mechanical confinement effects, mobility degradation, and parasitics are included in the models. BSIM-CMG and BSIM-IMG have been validated with hardware silicon-based data from multiple technologies. The developed models also meet the stringent quality assurance tests expected of production level models.

BSIM6: Analog and RF Compact Model for Bulk MOSFET

Abstract: BSIM6 is the latest industry-standard bulk MOSFET model from the BSIM group developed specially for accurate analog and RF circuit designs. The popular real-device effects have been brought from BSIM4. The model shows excellent source-drain symmetry during both dc and small signal analysis, thus giving excellent results during analog and RF circuit simulations, e.g., harmonic balance simulation. The model is fully scalable with geometry, biases, and temperature. The model has a physical charge-based capacitance model including polydepletion and quantum-mechanical effect thereby giving accurate results in small signal and transient simulations. The BSIM6 model has been extensively validated with industry data from 40-nm technology node.

Electronic Transport In Mesoscopic Systems

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Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk

Abstract: Hexagonal boron nitride (h-BN) and semiconducting transition metal dichalcogenides (TMDs) promise greatly improved electrostatic control in future scaled electronic devices. To quantify the prospects of these materials in devices, we calculate the out-of-plane and in-plane dielectric constant from first principles for TMDs in trigonal prismatic and octahedral coordination, as well as for h-BN, with a thickness ranging from monolayer and bilayer to bulk. Both the ionic and electronic contribution to the dielectric response are computed. Our calculations show that the out-of-plane dielectric response for the transition-metal dichalcogenides is dominated by its electronic component and that the dielectric constant increases with increasing chalcogen atomic number. Overall, the out-of-plane dielectric constant of the TMDs and h-BN increases by less than 15% as the number of layers is increased from monolayer to bulk, while the in-plane component remains unchanged. Our computations also reveal that for octahedrally coordinated TMDs the ionic (static) contribution to the dielectric response is very high (4.5 times the electronic contribution) in the in-plane direction. This indicates that semiconducting TMDs in the tetragonal phase will suffer from excessive polar-optical scattering thereby deteriorating their electronic transport properties. The out-of-plane dielectric constant of transition metal dichalcogenides and h-BN is thickness-dependent, unlike their in-plane counterpart. A team led by William Vandenberghe at the University of Texas at Dallas performed calculations of the optical and static relative permittivity of free-standing monolayer, bilayer, and bulk transition metal dichalcogenides, in the in-plane and out-of-plane directions. In h-BN, the in-plane contribution was found to be larger than its out-of-plane counterpart, and independent on the number of h-BN layers. Conversely, the out-of-plane h-BN dielectric constant showed an increase when going from monolayer to bulk. In transition metal dichalcogenides, the dielectric constant components displayed similar trends to those observed in h-BN with regards to their thickness evolution. The calculations also indicated that the electronic component dominates the overall dielectric response for most of the analyzed 2D materials.

Advent of 2D Rhenium Disulfide (ReS2): Fundamentals to Applications

Abstract: Rhenium disulfide (ReS2) is a two-dimensional (2D) group VII transition metal dichalcogenide (TMD). It is attributed with structural and vibrational anisotropy, layer-independent electrical and optical properties, and metal-free magnetism properties. These properties are unusual compared with more widely used group VI-TMDs, e.g., MoS2, MoSe2, WS2 and WSe2. Consequently, it has attracted significant interest in recent years and is now being used for a variety of applications including solid state electronics, catalysis, and, energy harvesting and energy storage. It is anticipated that ReS2 has the potential to be equally used in parallel with isotropic TMDs from group VI for all known applications and beyond. Therefore, a review on ReS2 is very timely. In this first review on ReS2, we critically analyze the available synthesis procedures and their pros/cons, atomic structure and lattice symmetry, crystal structure, and growth mechanisms with an insight into the orientation and architecture of domain and grain boundaries, decoupling of structural and vibrational properties, anisotropic electrical, optical, and magnetic properties impacted by crystal imperfections, doping and adatoms adsorptions, and contemporary applications in different areas.