Confinement orientation effects in S/D tunneling

The most extensive research of scaled electronic devices involves the inclusion of quantum effects in the transport direction as transistor dimensions approach nanometer scales. Moreover, it is necessary to study how these mechanisms affect different transistor architectures to determine which one can be the best candidate to implement future nodes. This work implements Source-to-Drain Tunneling mechanism (S/D tunneling) in a Multi-Subband Ensemble Monte Carlo (MS-EMC) simulator showing the modification in the distribution of the electrons in the subbands, and, consequently, in the potential profile due to different confinement direction between DGSOIs and FinFETs.Spanish Ministry of Science and Innovation (TEC2014-59730-R), H2020 - REMINDER (687931), and H2020 - WAYTOGO-FAST (662175

Impact of non uniform strain configuration on transport properties for FD14+ devices

As device dimensions are scaled down, the use of non-geometrical performance boosters becomes of special relevance. In this sense, strained channels are proposed for the 14 nm FDSOI node. However this option may introduce a new source of variability since strain distribution inside the channel is not uniform at such scales. In this work, a MS-EMC study of different strain configurations including non-uniformities is presented showing drain current degradation because of the increase of intervalley phonon scattering and the subsequent variations of transport effective mass and drift velocity. This effect, which has an intrinsic statistical origin, will make necessary further optimizations to keep the expected boosting capabilities of strained channels

A Novel Analysis of Periodic Structures Based on Loaded Transmission Lines

Periodically loaded transmission lines are characterized by a frequency response with regular pass and stopbands. Interestingly, each of the passbands exhibits a peculiar comb-alike behavior, in which again, nested (or internal) pass and stopbands can be identified. In this work, we focus our attention on the effect that changing the characteristics of the periodic load (which is a varactor capacitance in our case) has in this peculiar response of the structure, providing a novel and detailed analysis of such bands. The control of the response of the structure when changing the properties of the load allows to adjust the transmission characteristics of the circuit once it is fabricated. To this purpose, we derive the design equations of the periodically loaded structures, obtaining the expressions which govern the position and number of the transmission peaks, i.e., the points where |S21| = 1 for both cases, the frequency sweep and the capacitance sweep. We experimentally validate our analysis by fabricating a periodic structure with five unit cells and compare the measurements against both theoretical results and circuit simulations to an excellent agreement. The present analysis paves the way towards further exploitation of these kind of structures for the design of different microwave applications such as tunable filters or phase shiftersMCIN/AEI/PTA grantPTA2020-018250-IPAIDI 2020European Social Fund Operational Programme 2014-2020 under Grant 20804Ministerio de Universidades under Grant CAS21/00483FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades under Grants A-TIC-646-UGR20, B-RNM-375-UGR18P20_00633MCIN/AEI/10.13039/501100011033European Union “NextGenerationEU”/PRTRPID2020-116518GB-I00TED2021-129769B-I00TED2021-129938B-I0

Simulation of the phonon-limited electron mobility in multi-layer MoS 2 field-effect transistors

We study the electron mobility in Metal-Insulator-Semiconductor Field-Effect-Transistors which use multi-layer MoS 2 as channel. The electrostatic behavior is calculated by self-consistently solving the 1D Poisson and Schrödinger equations under the effective mass approximation. Phonon-limited electron mobility is then calculated solving the Boltzmann Transport Equation under the Momentum Relaxation Time approximation for different device sizes and bias conditions

Charge model of four-terminal 2D semiconductor FETs

A charge model for four-terminal two-dimensional (2D) semiconductor based field-effect transistors (FETs) is proposed. The model is suitable for describing the dynamic response of these devices under time-varying terminal voltage excitations.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No GrapheneCore2 785219, and from Ministerio de Economía y Competitividad under GrantsTEC2015-67462-C2-1-Rand TEC2017-89955-R(MINECO/FEDER)

Large-signal model of 2DFETs: compact modeling of terminal charges and intrinsic capacitances

We present a physics-based circuit-compatible model for double-gated two-dimensional semiconductor-based field-effect transistors, which provides explicit expressions for the drain current, terminal charges, and intrinsic capacitances. The drain current model is based on the drift-diffusion mechanism for the carrier transport and considers Fermi–Dirac statistics coupled with an appropriate field-effect approach. The terminal charge and intrinsic capacitance models are calculated adopting a Ward–Dutton linear charge partition scheme that guarantees charge conservation. It has been implemented in Verilog-A to make it compatible with standard circuit simulators. In order to benchmark the proposed modeling framework we also present experimental DC and high-frequency measurements of a purposely fabricated monolayer MoS2-FET showing excellent agreement between the model and the experiment and thus demonstrating the capabilities of the combined approach to predict the performance of 2DFETs.The authors would like to thank the financial support of Spanish Government under projects TEC2017-89955-P (MINECO/AEI/FEDER, UE), TEC2015-67462-C2-1-R (MINECO), and RTI2018-097876-B-C21 (MCIU/AEI/FEDER, UE). F.P. and D.J. also acknowledge the support from the European Union’s Horizon 2020 Research and Innovation Program under Grant Agreement No. 785219 GrapheneCore2. A.G. acknowledges the funding by the Consejería de Economía, Conocimiento, Empresas y Universidad de la Junta de Andalucía and European Regional Development Fund (ERDF), ref. SOMM17/6109/UGR. E.G.M. gratefully acknowledges Juan de la Cierva Incorporación IJCI-2017-32297 (MINECO/AEI). A.T.-L. acknowledges the FPU program (FPU16/04043). D.A. acknowledges the Army Research Office for partial support of this work, and the NSF NASCENT ERC and NNCI programs

GFET Asymmetric Transfer Response Analysis through Access Region Resistances

Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene field-effect transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, little attention has been paid, so far, to the role of the access regions in these devices. Here, we analyse in detail, via numerical simulations, how the GFET transfer response is severely impacted by these regions, showing that they play a significant role in the asymmetric saturated behaviour commonly observed in GFETs. We also investigate how the modulation of the access region conductivity (i.e., by the influence of a back gate) and the presence of imperfections in the graphene layer (e.g., charge puddles) affects the transfer response. The analysis is extended to assess the application of GFETs for RF applications, by evaluating their cut-off frequency.This research was founded by Spanish government grant numbers TEC2017-89955-P (MINECO/AEI/FEDER, UE), TEC2015-67462-C2-1-R (MINECO), IJCI-2017-32297 (MINECO/AEI), FPU16/04043 and FPU14/02579, and the European Union’s Horizon 2020 Research and Innovation Program under Grant GrapheneCore2 785219

A thorough study of Si nanowire FETs with 3D Multi-Subband Ensemble Monte Carlo simulations

We thoroughly compare the DC electrical behavior of n-MOS transistors based on Si nanowires with 〈 1 0 0 〉 and 〈 1 1 0 〉 channel orientations by means of Multi-Subband Ensemble Monte Carlo simulations. We find that the drain current depends on the nanowire diameter and it is slightly, but consistently, larger for 〈 1 0 0 〉 than for 〈 1 1 0 〉 nanowires. The observed differences in mobility, velocity and spatial charge distribution are interpreted in terms of the effective masses and populations of the different Si conduction band valleys, whose sixfold degeneracy is lifted by quantum confinement in narrow nanowires. Finally, we study the scaling behavior for channel lengths down to 8 nm, concluding that the differences observed between orientations are minimal

Multi-Subband Ensemble Monte Carlo simulations of scaled GAA MOSFETs

We developed a Multi-Subband Ensemble Monte Carlo simulator for non-planar devices, taking into account two-dimensional quantum confinement. It couples self-consistently the solution of the 3D Poisson equation, the 2D Schrödinger equation, and the 1D Boltzmann transport equation with the Ensemble Monte Carlo method. This simulator was employed to study MOS devices based on ultra-scaled Gate-All-Around Si nanowires with diameters in the range from 4 nm to 8 nm with gate length from 8 nm to 14 nm. We studied the output and transfer characteristics, interpreting the behavior in the sub-threshold region and in the ON state in terms of the spatial charge distribution and the mobility computed with the same simulator. We analyzed the results, highlighting the contribution of different valleys and subbands and the effect of the gate bias on the energy and velocity profiles. Finally the scaling behavior was studied, showing that only the devices with D = 4 nm maintain a good control of the short channel effects down to the gate length of 8 nm

Variability Assessment of the Performance of MoS2-Based BioFETs

Two-dimensional material (2DM)-based Field-Effect Transistors (FETs) have been postulated as a solid alternative for biosensing applications thanks to: (i) the possibility to enable chemical sensitivity by functionalization, (ii) an atomically thin active area which guarantees optimal electrostatic coupling between the sensing layer and the electronic active region, and (iii) their compatibility with large scale fabrication techniques. Although 2DM-based BioFETs have demonstrated notable sensing capabilities, other relevant aspects, such as the yield or device-to-device variability, will demand further evaluation in order to move them from lab-to-fab applications. Here, we focus on the latter aspect by analyzing the performance of MoS2-based BioFETs for the detection of DNA molecules. In particular, we explore the impact of the randomized location and activation of the receptor molecules at the sensing interface on the device response. Several sensing interface configurations are implemented, so as to evaluate the sensitivity dependence on device-to-device variabilitySpanish Government PID2020-116518GB-I00 TED2021-129769B-I00FEDER/Junta de Andalucia A-TIC-646-UGR20 P20-00633European Commission European Commission Joint Research Centre 825213PAIDI 2020 grant 20804PTA grant PTA2020-018250-ISpanish Government FPU019/05132Plan Propio of Universidad de Granad