key: cord-0055471-o7pyaybk
authors: nan
title: MRS Communications 2021, Volume 10, Issue 4
date: 2021-01-22
journal: MRS Bull
DOI: 10.1557/s43577-020-00013-z
sha: 86cc0d56792e10ebac67c6af3526a9a524f133c7
doc_id: 55471
cord_uid: o7pyaybk

nan

Richard Haight, IBM T.J. Watson Research Center, USA From thin-film solar cells to metal-oxide-semiconductor (MOS) devices in leading-edge integrated circuits, the electronic structure at and near the interfaces between component materials determines the most important fundamental operating characteristics of those devices, such as turn-on voltage, power dissipation, and off-state current leakage. Fermi-level location at buried interfaces, semiconductor (SC) band bending, charge transfer, oxide defects, and work functions of the constituent materials all contribute to device performance. This paper describes how these important parameters can be determined by employing femtosecond photovoltage spectroscopy, an extension of ultraviolet photoelectron spectroscopy (UPS) using ultrafast lasers. While standard UPS is fundamentally a surface-sensitive spectroscopy, pump/probe techniques add a new dimension to this venerable spectroscopy, permitting the accurate extraction of the underlying band bending in SCs. When combined with the valence-band-edge location of the SC and oxide, and determination of the system Fermi level, full characterization of the electronic structure of a MOS stack can be obtained providing key insights on device operating properties. This approach can be extended to study key device materials in emerging areas of artificial intelligence and quantum computing. In each case, surprising new details are uncovered that lead to performance optimization of these technologically important devices. https :// doi.org/10.1557/mrc.2020.63

Panni Wang, Shimeng Yu, Georgia Institute of Technology, USA Recent discovery of ferroelectricity in doped HfO 2 has reignited research interest in the ferroelectric field-effect transistor (FeFET) as emerging embedded nonvolatile memory with the potential for neuroinspired computing. The authors review two major aspects for its application in neuroinspired computing: ferroelectric devices as multilevel synaptic devices, and the circuit primitive design with FeFET for in-memory computing. First, the authors survey representative FeFET-based synaptic devices. Then they introduce 2T-1FeFET synaptic cell design that improves its in situ training accuracy to approach software baseline, followed by introduction of the FeFET drain-erase scheme for array-level operations, which makes the in situ training feasible for FeFET-based hardware accelerator. Finally, they give an outlook on the future 3D integrated 2T-1FeFET design. Recent applications require vertical chip stacking to increase the performance of many devices without the need of advanced node components. Image sensors and vision systems will embed more and more smart functions, for instance, image processing, object recognition, and movement detection. In this perspective, the combination of Cu-to-Cu direct hybrid bonding technology with Through-Silicon-Via (TSV) will allow 3D interconnection between pixels and the associated computing and memory structures, each function fabricated on a separate wafer. Wafer-to-wafer hybrid bonding was achieved with multipitch design-1-4 μm-of single levels of Cu damascene patterned on 300-mm silicon substrates. Defect-free bonding, as far as the extreme edge of the wafer, was demonstrated on a stack with three wafers. Middle wafers thinning was done with grinding only and with a thickness uniformity (total thickness variation) <2 μm to an ultimate thinning as low as 3 μm. Alignment performance was characterized by post-bonding for two superposed hybrid bonding interfaces. In the set of wafers, modeling the alignment with translation, rotation, and scaling components enables optimization of the residuals down to 3σ < 100 nm. A process flow of thin TSV with a fine pitch of 2 μm for high-density vertical interconnect through a three-wafer stack was developed. Via-last TSV architecture was adopted with 1-μm TSV diameter and 10-μm thickness. Lithography, etching solutions, Ti/TiN barrier deposition, and void-free Cu filling solutions were demonstrated. TSV cross sections after CMP and connections with top and bottom Cu damascene lines show good profile control. Process developments are matured and can be reliably used in the fabrication of an electrical test vehicle, including vertical interconnects associating multiwafers stacking with a hybrid bonding process and high-density thin TSV applicable to low pitches (<5 μm). https ://doi.org/10.1557/mrc.2020.77

Tanveer A. Tabish, University College London, UK; Roger J. Narayan, University of North Carolina and North Carolina State University, USA; Mohan Edirisinghe, University College London, UK From the 1918 influenza pandemic (H1N1) until the recent 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, no efficient diagnostic tools have been developed for sensitive identification of viral pathogens. Rigorous, early, and accurate detection of viral pathogens is not only linked to preventing transmission, but also to timely treatment and monitoring of drug resistance. Reverse transcription-polymerase chain reaction, the gold standard method for microbiology and virology testing, suffers from both false-negative and false-positive results arising from the detection limit, contamination of samples/templates, exponential DNA amplification, and variation of viral ribonucleic acid sequences within a single individual during the course of the infection. Rapid, sensitive, and label-free detection of SARS-CoV-2 can provide a first line of defense against the current pandemic. A promising technique is nonlinear coherent anti-Stokes Raman scattering (CARS) microscopy, which has the ability to capture rich spatiotemporal structural and functional information at a high acquisition speed in a label-free manner from a biological system. Raman scattering is a process in which the distinctive spectral signatures associated with light-sample interaction provide information on the chemical composition of the sample. In this prospective, we briefly discuss the development and future prospects of CARS for real-time multiplexed label-free detection of SARS-CoV-2 pathogens. https ://doi.org/10.1557/mrc.2020.81

Daniel Brito, Guadalupe Quirarte, Joshua Morgan, Eleanor Rackoff, Michael Fernandez, Dithi Ganjam, Albert Dato, Harvey Mudd College, USA; Todd Monson, Sandia National Laboratories, USA Barium titanate (BTO) is a ferroelectric perovskite with potential in energy-storage applications. Previous research suggests that BTO dielectric constant increases as nanoparticle diameter decreases. The authors recount an investigation of this relationship. Injection-molded nanocomposites of 5 vol% BTO nanoparticles incorporated in a lowdensity polyethylene matrix were fabricated and measured. Finite-element analysis was used to model nanocomposites of all BTO sizes, and the results were compared with experimental data. Both indicated a negligible relationship between BTO diameter and dielectric constant at 5 vol%. However, a path for fabricating and testing composites of 30 vol% and higher is presented here. https ://doi.org/10.1557/mrc.2020.69 The authors investigate the photophysical pathways for light absorption, charge generation, and charge separation in donor-acceptor nanoparticle blends of poly(3-hexylthiophene) and indene-C 60 -bisadduct. Optical modeling combined with steady-state and time-resolved optoelectronic characterization reveal that the nanoparticle blends experience a photocurrent limited to 60% of a bulk solution mixture. This discrepancy results from imperfect free charge generation inside the nanoparticles. High-resolution transmission electron microscopy and chemically resolved x-ray mapping show that enhanced miscibility of materials improve the donor-acceptor blending at the center of the nanoparticles; however, a residual shell of almost pure donor still restricts energy generation from these nanoparticles. https ://doi.org/10. 1557/mrc.2020.76 Insensitivity of the extent of surface reduction of ceria on termination: Comparison of (001), (110), and (111) faces Weizi Yuan, Sossina M. Haile, Northwestern University, USA

The enhanced reducibility of the surface of ceria relative to the bulk has long been established. Several studies also show that ceria nanoparticles with different facets exhibit different catalytic activities. Despite consensus that the activity is correlated with the surface Ce 3+ concentration, experimental measurements of this concentration as a function of termination are lacking. Here, x-ray absorption near-edge spectroscopy is used to quantify the Ce 3+ concentration in films with (001), (110), and (111) surface terminations under reaction-relevant conditions. While an enhanced Ce 3+ concentration is found at the surfaces, it is surprisingly insensitive to film orientation. https ://doi.org/10.1557/mrc.2020.73

Stable near-infrared photoluminescence from silicon quantum dot-bovine serum albumin composites isolated from blood samples and two control strains using a quantitative plaque assay method. Regardless of the precursors and plasma parameters, biofilm formation was inhibited for all plasmamodified microplate wells. The most significant anti-biofilm effect was observed on PS modified by DEP at 90 W plasma power with the inhibition of all Candida species' biofilm formation. https ://doi. org/10. 1557/mrc.2020.79 Electrocardiogram measurements in water using poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) nanosheets waterproofed by polyurethane film Sho Mihara, Waseda University, Japan; Hui-Lin Lee, Singapore Polytechnic, Singapore; Shinji Takeoka, Waseda University, Japan

Waterproof bioelectrodes enable long-term biological monitoring and the assessment of performances of athletes in water. Existing gel electrodes change their electrical properties even when covered with a waterproof film. Here, the authors present the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(styrene-butadiene-styrene) (SBS) bi-layer nanosheet and waterproof film for a comfortable waterproof bioelectrode. PEDOT:PSS/SBS is fully foldable with a conductivity loss of only 5%. This foldable nanosheet electrode provides a reliable electrical connection between the skin and the wire. The waterproof film-covered bioelectrode enables continuous monitoring of electrocardiograms in water, showing a signal-to-noise ratio of 21.5 dB for the R wave and 17.5 dB for the T wave, comparable to atmospheric measurements, and sensing a change in heart rate from 79 to 131 bpm during bathing. https ://doi.org/10. 1557/ mrc.2020.72 Biofunctionalized nanodot zirconia-based efficient biosensing platform for noninvasive oral cancer detection

Boston Children's Hospital

India The authors report results of the studies relating to the synthesis of nanodot zirconia that has been utilized for the fabrication of electrochemical biosensing platform for the detection of a CYFRA-21-1 biomarker, secreted in saliva samples of oral cancer patients. For the synthesis of nanodot zirconia (ndZrO 2 ), the hydrothermal process was used and further functionalized with 3-aminopropyl triethoxysilane (APTES)