Emanuele Baravelli

Impact of LER and Random Dopant Fluctuations on FinFET Matching Performance

Parameter variations pose an increasingly challenging threat to the CMOS technology scaling. Among the sources of variability, line-edge-roughness (LER) and random dopant (RD) fluctuations are significant in current technology nodes. In this paper, the impact of the LER and RD on the matching performance of FinFETs is investigated for the LSTP-32 nm node, where these devices represent an attractive alternative to the planar CMOS transistors. Line-edge-roughness contributions from the fin, top-, and side wall-gates of n- and p-channel FinFETs are compared by means of 2-D and 3-D technology computer-aided design (TCAD) simulations, performed with a quantum-corrected hydrodynamic model on large statistical ensembles. Correlations between geometrical roughness and resulting electrical parameters are analyzed to provide further insight into the impact of the LER. A noise analysis approach is adopted to evaluate the impact of RD fluctuations throughout the impurity concentration ranges of interest, providing a direct comparison with the line-edge-roughness contributions. The impact of the extension doping profile specifications on the LER- and RD-induced mismatch is investigated, highlighting the potential drawbacks of junction engineering.

Optimization of n- and p-type TFETs Integrated on the Same

Design of a suitable technology platform is carried out in this paper for co-integration of simultaneously optimized n- and p-type tunnel field-effect transistors (TFETs). InAs/AlxGa1-xSb heterostructures are considered, and a 3-D full-quantum simulation approach is adopted to investigate the combined effect of Al mole fraction x and transverse quantization on band lineups at the heterojunction. Design optimization leads to a TFET pair with similar dimensions and feasible aspect ratios realized on the same InAs/Al0.05Ga0.95Sb platform. These devices exhibit average subthreshold slopes below 60 mV/dec and relatively high ON-currents of 270 (n-TFET) and 120 μA/μm (p-TFET) at a low-supply voltage VDD=0.4 V. Combined ON- and OFF-state performance of the proposed technology platform is expected to be compatible with low operating power applications, while potential candidates for low standby power scenarios are obtained by reducing TFET cross sections from 10 to 7 nm.

{\rm InAs}/{\rm Al}_{x}{\rm Ga}_{1-x}{\rm Sb}

This paper presents a novel time-frequency procedure based on the warped frequency transform (WFT) to process multi-mode and dispersive Lamb waves for structural health monitoring (SHM) applications. The proposed signal processing technique is applied to time waveforms recorded at an array of scan points after waveguide excitation. The WFT is combined with a basis pursuit algorithm to extract the distance traveled by the ultrasonic waves even in the case of multi-modal dispersive propagation associated with broadband excitation of the waveguide. This is obtained through a decomposition of the acquired signals using dictionaries composed by optimized atomic functions which are designed to match the spectro-temporal structure of the various propagating modes. The warped basis pursuit (W-BP) analysis of several acquired waveforms results in distance signals that can be combined through classical beamforming techniques for acoustical source imaging purposes. A masking procedure is also proposed to suppress imaging noise. This approach is tested on experimental data obtained by broadband guided wave excitation in a 1-mm-thick aluminum plate with an artificially introduced through crack and tiny holes, followed by multiple waveguide displacement recording through a scanning laser Doppler vibrometer. Dispersion compensation, high-resolution source, and defect imaging are demonstrated even in domain regions that are not directly accessible for measurement.

Technology Platform

A frequency-steerable acoustic transducer (FSAT) is employed for imaging of damage in plates through guided wave inspection. The FSAT is a shaped array with a spatial distribution that defines a spiral in wavenumber space. Its resulting frequency-dependent directional properties allow beam steering to be performed by a single two-channel device, which can be used for the imaging of a two-dimensional half-plane. Ad hoc signal processing algorithms are developed and applied to the localization of acoustic sources and scatterers when FSAT arrays are used as part of pitch-catch and pulse-echo configurations. Localization schemes rely on the spectrogram analysis of received signals upon dispersion compensation through frequency warping and the application of the frequency-angle map characteristic of FSAT. The effectiveness of FSAT designs and associated imaging schemes are demonstrated through numerical simulations and experiments. Preliminary experimental validation is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The presented results demonstrate the frequency-dependent directionality of the spiral FSAT and suggest its application for frequency-selective acoustic sensors, for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health.

Warped basis pursuit for damage detection using lamb waves

This paper investigates feasible inverter configurations based on co-optimized n- and p-type tunnel field-effect transistors (TFETs) integrated on the same InAs/Al0.05Ga0.95 Sb platform. Based on 3-D full-quantum simulations, the considered devices feature steep subthreshold slopes and relatively high on- currents and are combined into two inverter designs. Benchmarking against aggressively scaled CMOS logic based on multigate architectures highlights potential of the proposed TFET implementations to perform up to 10× and 100× faster in low operating power and low standby power environments, respectively. The comparison is conducted at low supply voltages (VDD=0.25 V) and for equal levels of static power consumption. The proposed TFET-based platform is thus expected to be a good candidate for low-voltage/low-power applications in near-future technology generations.

Double-channel, frequency-steered acoustic transducer with 2-D imaging capabilities

Lamb wave testing for structural health monitoring (SHM) often relies on analysis of wavefields recorded through scanning laser Doppler vibrometers (SLDVs) or ultrasonic scanners. Damage detection and characterization with these techniques requires isolation of defect-induced reflections in the wavefield from the injected wave packet and from scattering events associated with structural features such as boundaries, rivets, joints, etc. This is a challenging task when dealing with complex structures and multimodal, dispersive propagation regimes, whereby various wave contributions in both the time/space and the frequency/wavenumber domain overlap. A new mathematical tool named warped curvelet frames (WCFs) is proposed to effectively decompose the recorded wavefields. The presented technique results from the combination of two operators, i.e., the curvelet transform (CT) and the warped frequency transform (WFT). The CT provides an optimally sparse representation of nondispersive wave propagators. Combining the CT with the WFT allows for a flexible analysis of multimodal wave propagation in dispersive media. Exploiting the spatial and temporal localization of curvelets, as well as the spectro-temporal adaptation of the analysis frame to the characteristics of each propagating mode, provided by frequency warping, a convenient decomposition of guided waves is achieved and relevant contributions can be effectively isolated. The proposed approach is validated through dedicated simulations and further tested experimentally to demonstrate the effectiveness of the method in separating guided wave modes corresponding to acoustic events in close spatial proximity.

TFET Inverters With n-/p-Devices on the Same Technology Platform for Low-Voltage/Low-Power Applications

This paper reports on the fabrication and the experimental characterization of a wavenumber frequency-steerable acoustic transducer (WS-FSAT). Here, the transducer is employed for the localization of broadband acoustic events corresponding to the propagation of guided elastic waves in an isotropic plate. The WS-FSAT records the plate response and defines the source location through a time-frequency analysis of the received signal. This is achieved by exploiting the frequency selective response of the transducer which directly maps the dominant component of the received signal to the direction of arrival of the incoming wave. This feature is the result of the spatial filtering effect produced by the characteristic shape of the sensing surface, which is designed in the wavenumber domain. Experiments are performed on a prototype fabricated on a polyvinylidene fluoride substrate mounted on an aluminum test plate. Tests are conducted for various source locations, and with multiple sources activated simultaneously. The results highlight the robustness of the proposed device, its good sensitivity and angular resolution, as well as the low complexity of hardware and signal processing. This paper suggests the WS-FSAT as an attractive solution for the detection of broadband acoustic events, such as impacts on structural substrates, and its potential use as part of active structural health monitoring systems based on pitch-catch or pulse-echo operations.

Guided wave expansion in warped curvelet frames

Stiffness and damping are conflicting requirements in many material systems. High stiffness is required in a wide range of structural components to provide sufficient robustness under demanding loading conditions. Simultaneously, a structure should be able to effectively mitigate shock and vibrations dynamically transmitted to it by the environment. While most conventional structures currently exhibit limited adaptability and damping capabilities, design strategies to simultaneously endow structural assemblies with high stiffness and high damping performance are proposed in this work. To this aim, a backbone structure suitable to meet stiffness requirements is combined with metamaterial inclusions able to provide fully-passive shock and vibration absorption. Viscoelastic resonant lattices with chiral topology are employed as inclusions, whose aim is to confine vibrational energy, pump it away from the backbone structure, and dissipate it through viscoelastic damping. The lattices are composed by an elastomeric matrix with the desired chiral shape, and stiff resonating inclusions are inserted at nodal locations. Both finite element simulations and experimental tests demonstrate that periodic chiral assemblies give rise to wide frequency bandgaps. Low-frequency tuning of the assembly for effective suppression of the first resonant mode of a backbone structure represented by an aluminum box-beam is demonstrated both numerically and experimentally. The considered lightweight inclusion is a chiral matrix realized with castable rubber, featuring graded cylinder mass insertions. The proposed design methodology can be flexibly tailored to various frequency ranges and is applicable to both existing and novel structural components at different scales.

Fabrication and Characterization of a Wavenumber-Spiral Frequency-Steerable Acoustic Transducer for Source Localization in Plate Structures

A novel time-frequency procedure is presented in this paper for guided wave (GW) propagation analysis in structure health monitoring (SHM) applications.The proposed approach combines the Warped Frequency Transform (WFT) with a Basis Pursuit algorithm to generate a sparse yet accurate time-frequency representation of the acquired signals even in the case of multi-modal dispersive propagation associated to broadband excitation of the waveguide. This is obtained through over complete dictionaries composed by optimized atoms which are designed to match the spectro-temporal structure of the various propagating modes.The Warped Basis Pursuit (W-BP) decomposition of several acquired waveforms results in distance signals that can be combined through classical beamforming techniques for imaging purposes. This approach is tested on experimental data obtained by broadband GW excitation in a 1 mm thick aluminum plate with an artificially introduced through crack, followed by multiple waveguide displacement recording through a scanning laser Doppler vibrometer. Dispersion compensation and high-resolution source as well as defect imaging is demonstrated even in domain regions that are not directly accessible for measurement.

High stiffness, high damping chiral metamaterial assemblies for low-frequency applications

To improve the defect detectability of Lamb wave inspection systems, the application of nonlinear signal processing was investigated. The approach is based on a Warped Frequency Transform (WFT) to compensate the dispersive behavior of ultrasonic guided waves, followed by a Wigner-Ville time-frequency analysis and the Hough Transform to further improve localization accuracy. As a result, an automatic detection procedure to locate defect-induced reflections was demonstrated and successfully tested by analyzing numerically simulated Lamb waves propagating in an aluminum plate. The proposed method is suitable for defect detection and can be easily implemented for real-world structural health monitoring applications.