bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Challenges and Solutions in Metrology for Complex, Confined Systems
Authors: Vandervorst Wilfried 
Published: February 2020

Probing composition, doping , strain and defectivity in confined heterostructures (fins, nanowires, etc) represents a challenge in terms of 3D-spatial resolution, sensitivity as well as in localization and heterogeneity. We will discuss progress and limitations of two approaches. The first approach is linked to methods such as Atomprobe tomography or SPM imaging which provide ultra-high resolution inherently. Unfortunately when reducing the analysed volume to the atomic scale, signal intensity becomes very low limiting the achievable sensitivity. Moreover their application (for instance Atomprobe tomography on embedded FIN, STM on trenches embedded in STI) becomes very complex and prone to many distorting artifacts which one needs to overcome. Speed of the analysis and time to data becomes then another limitation. In the opposite approach one abandons the idea of achieving the resolution to probe inside one single device but rather exploits broad beams (>1-20 mm) to investigate an ensemble of many, small identical structures. In cases like self-focusing SIMS, the physics of cluster ion formation is exploited to confine the information to the very small regions of interest whereby the averaging over many features enhances the signal substantially and enables good sensitivity. Examples demonstrate composition analysis in trenches as narrow as 20 nm. The spatial selectivity even allows to determine the composition of two mixed phases (i.e. InGaAs and InAlAs). Similarly strain and composition can be measured with (Edge-enhanced) Raman in similar trenches, as the confined volume provides a 100x increase in sensitivity. Channeling RBS on ensemble structures has been exploited to probe the early stages of III-V in narrow trenches. The important relevance of this approach is that it provides the opportunity to study the material as it grows in such a confined volume which frequently is very different from blanket experiments while all conventional (broad) methods can still be used.
On the Challenges of SiGe HBTs in Advanced BiCMOS Technology Toward Half THz fMAX
Authors: Liu Qizhi , Jain Vibhor , Camillo-Castillo Renata A , Pekarik John J , Adkisson James W. , Joseph Alvin , Harame David L. 
Published: February 2020

Advanced BiCMOS technology is a cost-effective candidate for wide-range of applications, including Radar (automotive radars, high-speed industrial sensors), high-speed wireless and wireline communication, high-speed instrumentation, and mmWave THz imaging and sensing that require high performance SiGe HBTs with high cut-off frequencies fT and high maximum frequencies fMAX.
Development of SiGe HBTs in BiCMOS technology with both high fT and fMAX faces significant challenges. Vertical scaling is employed to increase fT in advanced SiGe HBTs including reduction in base and collector thickness or by increasing the collector doping. All these approaches reduce the carrier transit times, but result in an increase in the base resistance and the collector-base capacitance, which degrade fMAX. To overcome these limits, lateral scaling is necessary to reduce the base resistance and the collector-base capacitance. Reduction in emitter width reduces the intrinsic base resistance and Ccb, self-aligned emitter-base integration schemes reduce the extrinsic base link resistance, and raised extrinsic base helps with lower Rb and Ccb. In short, these scaling rules and approaches would need to reduce both base resistance and collector-base capacitance simultaneously for improved fMAX and fT

In this paper, results from two experimental studies are presented in a 90nm SiGe BiCMOS technology. Compared with the baseline, one experiment shows more reduction in collector-base capacitance, while the other shows more reduction in base resistance. Both experiments achieved 300GHz fT and met or exceeded the 360GHz fMAX goal of the technology.
In addition to straight vertical and lateral scaling, a series of experiments employing other process techniques and structure innovation have also been studied and are reviewed in this paper, including millisecond anneal techniques, low temperature silicide and low temperature contact processes, and secondary trench isolation, achieving fT around 300GHz and fMAX toward half THz.
Very High-Resolution Mobility, Resistaivity and Activation for High-Mobility Materials
Authors: Joshi Abhijeet 
Published: February 2020

Advanced high-mobility material based devices require knowledge of carrier concentration, mobility and resistivity profiles as well as the effects of strain. Active Layer Parametrics, Inc.’s ALPro system represents a technique to directly measure these parameters as well as the effects of strain from high dopant concentrations in high mobility materials like SiGe, Ge, and III-V high-mobility materials.
Current standard electrical metrology techniques such as Scannning Spreading Resistance Microscopy (SSRM) cannot provide complete mobility and activation data on these high-mobility materials. Furthermore resolutions currently achieved by the ALPro System (>0.5nm in Si, SiGe and Ge) cannot be achieved by SSRM or Spreading Resistance Profiling (SRP). Sample preparation of relatively fragile high-mobilty materials like Ge and GaAs is difficult to standardize, is known to have resulted in widely varying resistivity data values. The continual making and breaking of contacts in both SSRM and SRP, though reasonlably well-understood for Silicon, has not been adequately understood in the case of Ge requiring modeling to account for bandgap changes due to applied pressure that vary with probe dimensions and properties.
The ALPro System overcomes all the above deficiencies while providing a high-resolution, high-throughput system that may be safely deployed in a fabrication environment.
This paper discusses some of the data extracted using the ALPro System for high and low-doped Gematerials.
Role of High-k Interlayer in ZrO2/High-k/ZrO2 Insulating Multilayer on Electrical Properties for DRAM Capacitor
Authors: Onaya Takashi , Nabatame Toshihide , Sawada Tomomi , Kurishima Kazunori , Sawamoto Naomi , Ohi Akihiko , Chikyow Toyohiro , Ogura Atsushi 
Published: February 2020

For < 25 nm DRAM capacitors, large cell capacitance (20 fF/cell), low leakage current density (J ≤ 1.6×10-7 A/cm2) at the operation voltage (0.6 V), maximum process temperature < 650 oC and conformal films on a three-dimensional structure (pedestal structure) with a large aspect ratio over 30 are required. Recently, the ZrO2/Al2O3/ZrO2 (ZAZ) multilayer was widely used as insulator of DRAM.[1] Al2O3 has advantages of large band gap and amorphous structure, and disadvantage of low k-value. However, it is still not clear how amorphous structure and band gap of interlayer affect to leakage current property. Here, we pay attention to (Ta/Nb)Ox (TN) because of its high k-value (~29), amorphous structure and low band gap (4.3 eV).[2] In this paper, we studied role of various interlayer between ZrO2 layers on leakage current property for DRAM capacitors with TiN electrode.
We fabricated four TiN capacitors with ZrO2/ZrO2 (ZZ), ZAZ, ZrO2/(Ta/Nb)Ox/ZrO2 (ZTNZ), and ZrO2/(Ta/Nb)Ox-Al2O3/ZrO2 (ZTNAZ) multilayer by atomic layer deposition (ALD) and post-deposition annealing (PDA) processes. The ZrO2, Al2O3, and TN layers were deposited by ALD using (C5H5)Zr[N(CH3)2]3, Al(CH3)3, and (Ta/Nb = 1/1)(NtAm)(NMe2)3 precursor, respectively, and H2O gas. The TNA nano-laminate layers were fabricated by alternately depositing every 1 cycle using TN and Al2O3. After multilayer fabrication, PDA was performed at 600 °C. Finally, TiN top electrode was fabricated by photo-litho. process.
Fig. 1 shows relationship between CET and J at 0.6 V for all capacitors. The J values of the ZTNAZ and ZAZ capacitors decrease significantly by 10-7 ~ 10-8 A/cm2 order of magnitude while ZTNZ exhibits large J of ~ 10-5 A/cm2. Moreover, the J value of the ZTNAZ (CET = 1.2 nm) is lower than that of the ZAZ (CET = 1.3 nm). AFM images and RMS roughness of ZZ (CET = 1.1 nm), ZTNZ (CET = 1.2 nm), ZAZ (CET = 1.3 nm), and ZTNAZ (CET = 1.2 nm) are shown in Fig. 2. The RMS roughness of all samples exhibit almost the same value of around 1 nm. Based on these experimental data, we found that the leakage current property of capacitor is influenced by band gap width (conduction band offset of TiN) rather than amorphous structure. We conclude that the TNA is one of candidate material as interlayer for future DRAM. A part of this research is supported by CREST, JST.
[1] D. Martin et al., J. Appl. Phys. 113, 194103 (2013).
[2] T. Nabatame et al., J. Vac. Sci. Technol. A 33, 01A118 (2015).

Figure 1
(Invited) The Effect of Germanium/Silicon Interface on Germanium Photonics
Authors: Kim Daeik , Bao Shuyu , Tan Chuan Seng , Nam Ju Hyung , Saraswat K. C. , Nam Donguk 
Published: February 2020

Obtaining a high-quality germanium layer on silicon has recently garnered much attention for photonic-integrated circuits. Epitaxial growth of germanium on silicon has made significant progress toward suppressing the propagation of threading dislocations that are inevitably created at the germanium/silicon interface due to a large lattice mismatch. Recently, there have been numerous reports on successful demonstration of high-performance MOSFETs fabricated on this improved germanium layer. However, unlike MOSFETs in which charge carriers are transported primarily at the defect-free top interface, the performance of optical devices may be significantly hampered by the defects at the germanium/silicon interface.
In this talk, I will present our research works on the effect of the germanium/silicon interface on germanium-based optical devices. We demonstrate methods to improve structural and optical properties of germanium by effectively reducing the defective interface. By using various characterization techniques including TEM, time-resolved photoluminescence and Raman spectroscopy, we show that the minority carrier lifetime and internal quantum efficiency can be significantly improved. We also show improved performances from devices integrated on our germanium platform.
(Invited) Periodically Oriented Gallium Nitride for Frequency Conversion
Authors: Hite Jennifer K , Freitas Jaime A. , Mastro Michael A , Vurgaftman Igor , Meyer Jerry R. , Brown Christopher G. , Leach Jacob , Udwary Kevin , Bowman Steven R. , Eddy Charles R. , Kub Francis J 
Published: February 2020

Gallium nitride is a semiconductor widely used in both optical and electronic devices. The polarity of GaN (+/- c-direction) influences many properties of the resultant material, including chemical reactivity and electric field in these ‘spontaneously polarized’ materials. By engineering inversion layers, we have demonstrated control of GaN polarity on both polar faces of GaN. By employing a selective growth method to deposit the IL, the lateral polarity of the GaN can be alternated, thus enabling structures referred to as periodically oriented (PO) GaN. We have shown such structures on both N-polar and Ga-polar native substrates by changing the IL material.
On N-polar substrates, we demonstrated that optimization of the MOCVD growth rates resulted in sharp, vertical interfaces and smooth surfaces. This work has moved the technology substantially closer to practical non-linear optic emitters by using HVPE to extend the PO GaN templates on N-polar substrates to total thicknesses of up to 500 μm, while faithfully maintaining the pattern of alternating polarity. Additionally, cross-sectional cathode-luminescence (CL) imaging of such an extension shows that the large initial dislocation densities occurring in the original inversion layers greatly decreased after about 25 μm of regrowth. The results of phase matching experiments with these structures will be presented, with discussion on fabrication issues.
These methods of GaN polarity inversion offer the promise of engineered materials with custom lateral and vertical polarity variations for applications in novel electronic and optoelectronic devices, a subset of which are expected to be suitable for non-linear optics.
Effect of Flow Field Configuration on Oxygen Transport Resistances in Proton Exchange Membrane Fuel Cell Cathode
Authors: Karani Jash , Shrivastava Udit N , Tajiri Kazuya 
Published: February 2020

Land-channel geometry is necessary for proton exchange membrane fuel cells to transport electron and at the same time to transport reactants/products. However, this configuration causes the difference in transport distance between the flow channel to the catalyst layer, and results in the non-uniform distribution of various factors, such as species concentration, current generation, and rate of degradation. In order to investigate the distributions of various parameters in the land-channel direction, a small-scale segmented cell with about 300-micron resolution was developed by the authors’ group, and successfully measured the current and high-frequency resistance distribution in the land-channel direction. Distribution of oxygen transport resistance from the flow channel to the catalyst layer was also measured using limiting current technique.
The oxygen transport mechanism is completely different in the conventional flow field and in the interdigitated flow field. In the conventional flow field, the oxygen transport is mostly driven by the duffusion due to the concentration gradient. In the interdigitated flow field, on the other hand, the convective flow through gas diffusion layer (GDL) makes the diffusion distance shorter than the conventional flow field case, and therefore the lower oxygen transport resistance is expected.
In this study the oxygen transport resistance distribution in land-channel direction is measured in two different flow field configurations, that is, conventional flow field and interdigitated flow field. The comparison of the results from these two flow fields reveals the impact of the convective transport through GDL on the oxygen transport resistance and on the distribution.
Advanced Characterization of Electrocatalyst Interfaces
Authors: Shao Yuyan , Luo Langli , Cheng Yingwen , Engelhard Mark H , Liu Jun , Wang Chongmin 
Published: February 2020

In PEM fuel cells, electrocatalyst interfaces including Pt-C, Pt-ionomer, C-ionomer interfaces, play a critical role for both performance and durability.1-3 Pt-C interface influences the stability and activity of Pt dramatically; electrocatalyst/ionomer interfaces4 in fuel cell catalyst layers determine the electrochemical surface area (ECSA), local transport, and structural stability of catalyst layer. Delineating the structure evolution of the interfaces in response to PEM fuel cell operating environment will provide the science foundation for new electrocatalyst/catalyst layer design therefore improve the performance and durability of PEM fuel cells.
We have developed an aberration corrected environmental transmission electron microscopy (ETEM), which allows unprecedented spatial and temporal resolution in the relevant gas environment, such as O2, H2, H2O, CO, CH4, and CO2. With customized intelligent gas delivery system, the gas environment relevant to PEM fuel cell anode and cathode (H2/H2O, O2/H2O) can be simulated and precisely controlled through the residual gas analyzer (RGA). The ETEM opens new avenue to study the dynamic changes of electrocatalyst interfaces.
In order to study the surface chemistry of catalysts under different environment, a specially-designed pre-treatment system is integrated into X-ray photoelectron spectroscopy (XPS), which allows us to move catalysts seamlessly between the pre-treatment system and XPS chamber so that surface contamination from external environment will be eliminated.
In this talk, we will present our recent progress on identifying both structure and surface chemistry evolution and their correlation in electrocatalysts under PEM fuel cell relevant environment through the combination of ETEM and XPS capabilities.
1. Y. Y. Shao, G. P. Yin and Y. Z. Gao, J. Power Sources, 2007, 171, 558-566.
2. S. Park, Y. Y. Shao, H. Y. Wan, V. V. Viswanathan, S. A. Towne, P. C. Rieke, J. Liu and Y. Wang, J. Phys. Chem. C, 2011, 115, 22633-22639.
3. R. Kou, Y. Y. Shao, D. H. Mei, Z. M. Nie, D. H. Wang, C. M. Wang, V. V. Viswanathan, S. Park, I. A. Aksay, Y. H. Lin, Y. Wang and J. Liu, J. Am. Chem. Soc., 2011, 133, 2541-2547.
4. A. Z. Weber and A. Kusoglu, J. Mater. Chem. A, 2014, 2, 17207-17211.
Cobalt Phosphide Based Nanostructures as Bifunctional Electrocatalysts for Low Temperature Alkaline Water Splitting
Authors: Lambert Timothy N. , Vigil Julian A. , Christensen Ben 
Published: February 2020

Hydrogen is regarded as a valuable high energy density, zero-emission fuel for the future, with the potential to reduce or eliminate fossil fuels. H2 also has potential as an energy carrier or storage molecule: i.e. being generated, stored, and consumed to bridge the gap of high and low production cycles of renewable energy sources, such as solar cells and wind turbines. Because molecular hydrogen is not naturally available, the complications of generation, storage and transportation must be addressed. On Earth, hydrogen (H) mainly occurs in combination with oxygen, i.e. in water. One possible technology option for clean H2 generation is low temperature water electrolysis, with the two half-reactions being the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). These reactions, particularly the OER, are mechanistically complex and dependent on the surface energy of multiple intermediate species, leading to high overpotentials and low efficiency. Precious metal-based catalyst materials are ultimately not viable, due to rarity and cost, and typically provide high catalytic activity for the OER or HER, but not both. More effective catalysts with the ability to catalyze both the OER and HER (i.e. OER/HER bi-functional behavior) could improve current electrolyzers and enable future technologies. Thus, there is a desire to design electrocatalysts based on earth- abundant, low-cost materials for overall water splitting.
In this talk we will present on the synthesis and electrochemical characterization cobalt phosphide-based materials. CoP-based electrocatalysts in both thin film and nanoparticle form have been prepared from their respective Co3O4 spinel precursors using phosphine gas, generated in situ from the thermal decomposition of sodium hypophosphite. These electrocatalysts were found to have performance comparable to that of the commercial precious metal benchmarks when examined in alkaline electrolyte. For example, ΔE(OER–HER) values were calculated by adding the overpotentials at which j
geo = 10 mA cm-2 and j
geo = -10 mA cm-2were attained for the OER and HER, respectively, to the thermodynamic OER–HER potential difference of 1.23 V. Values of ΔE(OER–HER) = 1.77 V for cobalt phosphide catalysts are within 70 mV of the idealized water electrolysis with 20% Ir/C (anode):20% Pt/C (cathode) where ΔE(OER–HER) = 1.70 V. Various aspects of this work will be presented.
This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Hydrogen Evolution Reaction on Pt/RuO2-TiO2 Electrocatalyst in Alkaline Media
Authors: He Cheng , Wang Guanxiong , Parrondo Javier , Ramani Vijay K 
Published: February 2020

Hydrogen is poised to be a key energy carrier in a sustainable energy economy (1). Among the different approaches to produce hydrogen, water electrolysis has received special attention due to its unique advantages including reactant availability, safety, stable output and product purity (2). Alkaline water electrolysis offers additional advantages, including the possibility of using stainless steel flow fields and endplates (with the subsequent reduction in costs) and the possibility of using cheaper non-platinum-group-metal electrocatalysts for the oxygen evolution reaction. However, the slow kinetics for the hydrogen evolution reaction (HER) in alkaline media is currently a key drawback.
In this work we evaluated a mixed-metal-oxide composed of titanium dioxide and ruthenium dioxide as a support for Pt and measured the catalytic activity of this supported electrocatalys for the HER. The mixed-metal-oxide (TiO2-RuO2, RTO) was synthesized using a wet chemical synthesis procedure, and the Pt/RTO was synthesized by reduction of Pt precursor onto the support using an impregnation-reduction method. These materials were characterized by XRD, TEM and BET. The activity of Pt/RTO towards HER the was compared with a benchmark Pt/C catalyst (46%Pt; Tanaka, K. K.). Rotating disk electrode (RDE) measurements showed Pt/RTO outperforming (under all the conditions) the benchmark catalyst (Pt/C). The specific exchange current density for Pt/RTO was 2.51mA/cm2
Pt (295 K, 1600rpm, H2-saturated 0.1M KOH), more than five times that of Pt/C. The catalysts were also evaluated in a solid-state water electrolyzer operated with ultrapure water at 50°C, wherein MEAs were prepared with IrO2 as a common anode electrocatalyst. The MEAs fabricated with Pt/RTO as the cathode catalyst outperformed the benchmark catalyst by 0.1-0.2 V across relevant current densities (see Figure 1).
1. M. S. Dresselhaus and I. L. Thomas, Nature, 414, 332 (2001).
2. H. Yin, S. Zhao, K. Zhao, A. Muqsit, H. Tang, L. Chang, H. Zhao, Y. Gao and Z. Tang, Nat Commun, 6, 6430 (2015).

Figure 1