A simulation study of FET-based nanoelectrodes for active intracellular neural recordings

Active FET-based nanoelectrodes are promising candidates to serve as sensors for neural signal recording. Based on a multiscale-multiphysics TCAD modeling framework, we study the interaction of two representative nanoelectrode architectures in intracellular contact with neurons. The methodology is explained, and DC, AC, and transient simulations are extensively used to compare the main performance metrics of the proposed structures. The lateral coating of the nanoelectrode results to be a key parameter to control the sensor performance

Backscattering and common-base current gain of the Graphene Base Transistor (GBT)

In this paper, we investigate electron transport and electron scattering in the insulators of the Graphene Base Transistor (GBT) by means of a Monte Carlo transport model. We focus on electron backscattering in the base-collector insulator as the possible root cause of the large experimental base current and small measured common-base current gain (\u3b1F) of GBTs. Different GBT structures have been simulated and the impact of the scattering parameters on the base current is analyzed. Simulated backscattering-limited \u3b1F values are found to be much higher than available experimental data, suggesting that state-of-the-art technology is still far from being optimized. However, those simulated \u3b1F values can be low enough to limit the maximum achievable GBT performance

A TCAD-Based Methodology to Model the Site-Binding Charge at ISFET/Electrolyte Interfaces

5noWe propose a new approach to describe in commercial TCAD the chemical reactions that occur at dielectric/electrolyte interface and make the ion sensitive FET (ISFET) sensitive to pH. The accuracy of the proposed method is successfully verified against the available experimental data. We demonstrate the usefulness of the method by performing, for the first time in a commercial TCAD environment, a full 2-D analysis of ISFET operation, and a comparison between threshold voltage and drain current differential sensitivities in the linear and saturation regimes. The method paves the way to accurate and efficient ISFET modeling with standard TCAD tools.partially_openopenBandiziol, A.; Palestri, P.; Pittino, F.; Esseni, D.; Selmi, L.Bandiziol, Andrea; Palestri, Pierpaolo; Pittino, Federico; Esseni, David; Selmi, Luc

The Electron\u2013Hole Bilayer TFET: Dimensionality Effects and Optimization

An extensive parameter analysis is performed on the electron-hole bilayer tunnel field-effect transistor (EHBTFET) using a 1-D effective mass Schr\uf6dinger-Poisson solver with corrections for band non-parabolicity considering thin InAs, In0.53Ga0.47As, Ge, Si0.5Ge0.5, and Si films. It is found that depending on the channel material and channel thickness, the EHBTFET can operate either as a 2-D-2-D or 3-D-3-D tunneling device. InAs offers the highest I ON, whereas for the Si and Si0.5Ge0.5 EHBTFETs, significant current levels cannot be achieved within a reasonable voltage range. The general trends are explained through an analytical model that shows close agreement with the numerical results

Underlap counterdoping as an efficient means to suppress lateral leakage in the electron\u2013hole bilayer tunnel FET

The electron\u2013hole bilayer tunnel (EHBTFET)\uf0a0has been proposed as a density of states (DOS) switch capable of achieving a subthreshold slope lower than 60mV/decade at room temperature; however, one of the main challenges is the control of the lateral band-to-band tunneling (BTBT) leakage in the OFF state. In this work, we show that by using oppositely doped underlap regions; the unwanted penetration of the wavefunction into the underlap region at low gate biases is prevented; thereby drastically reducing the lateral BTBT leakage without any penalty on the ON current. The method is verified using a full-quantum 2D Schr\uf6dinger\u2013Poisson solver under the effective mass approximation. For a channel thickness of 10 nm, an In0.53Ga0.47As EHBTFET with counterdoping can exhibit an ON-current up to 20 mA mm and an average subthreshold swing (SS) of about 30 mV/dec. Compared to previous lateral leakage suppression solutions, the proposed method can be fabricated using template-assisted selective epitaxy

A review of selected topics in physics based modeling for tunnel field-effect transistors

The research field on tunnel-FETs (TFETs) has been rapidly developing in the last ten years, driven by the quest for a new electronic switch operating at a supply voltage well below 1 V and thus delivering substantial improvements in the energy efficiency of integrated circuits. This paper reviews several aspects related to physics based modeling in TFETs, and shows how the description of these transistors implies a remarkable innovation and poses new challenges compared to conventional MOSFETs. A hierarchy of numerical models exist for TFETs covering a wide range of predictive capabilities and computational complexities. We start by reviewing seminal contributions on direct and indirect band-to-band tunneling (BTBT) modeling in semiconductors, from which most TCAD models have been actually derived. Then we move to the features and limitations of TCAD models themselves and to the discussion of what we define non-self-consistent quantum models, where BTBT is computed with rigorous quantum-mechanical models starting from frozen potential profiles and closed-boundary Schr\uf6dinger equation problems. We will then address models that solve the open-boundary Schr\uf6dinger equation problem, based either on the non-equilibrium Green's function NEGF or on the quantum-transmitting-boundary formalism, and show how the computational burden of these models may vary in a wide range depending on the Hamiltonian employed in the calculations. A specific section is devoted to TFETs based on 2D crystals and van der Waals hetero-structures. The main goal of this paper is to provide the reader with an introduction to the most important physics based models for TFETs, and with a possible guidance to the wide and rapidly developing literature in this exciting research field

Mixed Tunnel-FET/MOSFET Level Shifters: A New Proposal to Extend the Tunnel-FET Application Domain

In this paper, we identify the level shifter (LS) for voltage up-conversion from the ultralow-voltage regime as a key application domain of tunnel FETs (TFETs).We propose a mixed TFET\u2013MOSFET LS design methodology, which exploits the complementary characteristics of TFET and MOSFET devices. Simulation results show that the hybrid LS exhibits superior dynamic performance at the same static power consumption compared with the conventional MOSFET and pure TFET solutions. The advantage of the mixed design with respect to the conventional MOSFET approach is emphasized when lower voltage signals have to be up-converted, reaching an improvement of the energy-delay product up to three decades. When compared with the full MOSFET design, the mixed TFET\u2013MOSFET solution appears to be less sensitive toward threshold voltage variations in terms of dynamic figures of merit, at the expense of higher leakage variability. Similar results are obtained for four different LS topologies, thus indicating that the hybrid TFET\u2013MOSFET approach offers intrinsic advantages in the design of LS for voltage up-conversion from the ultralow-voltage regime compared with the conventional MOSFET and pure TFET solutions