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

Validity of the parabolic effective mass approximation in silicon and germanium n-MOSFETs with different crystal orientations

This paper investigates the validity of the parabolic effective mass approximation (EMA), which is almost universally used to describe the size and bias-induced quantization in n-MOSFETs. In particular, we compare the EMA results with a full-band quantization approach based on the linear combination of bulk bands (LCBB) and study the most relevant quantities for the modeling of the mobility and of the on-current of the devices, namely, the minima of the 2-D subbands, the transport masses, and the electron density of states. Our study deals with both silicon and germanium n-MOSFETs with different crystal orientations and shows that, in most cases, the validity of the EMA is quite satisfactory. The LCBB approach is then used to calculate the values of the effective masses that help improve the EMA accuracy. There are crystal orientations, however, where the 2-D energy dispersion obtained by the LCBB method exhibits features that are difficult to reproduce with the EMA model

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

Multiphysics Finite-Element Modeling of the Neuron/Electrode Electrodiffusive Interaction

Understanding the biological-electrical transduction mechanisms is essential for reliable neural signal recording and feature extraction. As an alternative to state-of-the-art lumped-element circuit models, here we adopt a multiscale-multiphysics finite-element modeling framework. The model couples ion transport with the Hodgkin-Huxley model and the readout circuit, and is used to investigate a few relevant case studies. This approach is amenable to explore ion transport in the extracellular medium otherwise invisible to circuit model analysis

Multi-Wire Tri-Gate Silicon Nanowires Reaching Milli-pH Unit Resolution in One Micron Square Footprint

The signal-to-noise ratio of planar ISFET pH sensors deteriorates when reducing the area occupied by the device, thus hampering the scalability of on-chip analytical systems which detect the DNA polymerase through pH measurements. Top-down nano-sized tri-gate transistors, such as silicon nanowires, are designed for high performance solid-state circuits thanks to their superior properties of voltage-to-current transduction, which can be advantageously exploited for pH sensing. A systematic study is carried out on rectangular-shaped nanowires developed in a complementary metal-oxide-semiconductor (CMOS)-compatible technology, showing that reducing the width of the devices below a few hundreds of nanometers leads to higher charge sensitivity. Moreover, devices composed of several wires in parallel further increase the exposed surface per unit footprint area, thus maximizing the signal-to-noise ratio. This technology allows a sub milli-pH unit resolution with a sensor footprint of about 1 \ub5m2, exceeding the performance of previously reported studies on silicon nanowires by two orders of magnitude

Assessment of InAs/AlGaSb Tunnel-FET Virtual Technology Platform for Low-Power Digital Circuits

In this work, a complementary InAs/Al0.05Ga0.95Sb tunnel field-effect-transistor (TFET) virtual technology platform is benchmarked against the projection to the CMOS FinFET 10-nm node, by means of device and basic circuit simulations. The comparison is performed in the ultralow voltage regime (below 500 mV), where the proposed III\u2013V TFETs feature ON-current levels comparable to scaled FinFETs, for the same low-operating-power OFF-current. Due to the asymmetrical n- and p-type I\u2013Vs, trends of noise margins and performances are investigated for different Wp/Wn ratios. Implications of the device threshold voltage variability, which turned out to be dramatic for steep slope TFETs, are also addressed