bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of ALD Tungsten Trioxide Thin Films from W(CO)6 and H2O Precursors
Authors: Zhang Kai , McCleese Christopher , Lin Pengtao , Chen Xin , Morales Monica , Cao Wei , Seo Felix J. , Burda Clemens , Baumgart Helmut
Published: February 2020

Tungsten trioxide (WO3) thin films are extensively investigated for their remarkable semiconducting properties in electrochromics, microelectrics, selective catalysts, solar cells, gas-sensors and environmental engineering. In addition, WO3 has been particularly developed for electrochromic applications, such as smart windows for green buildings and airplanes, rear mirrors in automobiles, displays, and electro-devices.WO3 thin films have been fabricated  by various methods, including physical vapor depostion (PVD), pulsed vapor deposition (PLD), RF magnetron sputtering deposition, and electrodeposition [1, 2].

Atomic layer deposition (ALD) is a novel  process  to synthesize   variaous  thin films, where the sequential alternating vapor pulses of chemical precursors are introduced into the  ALD reaction chamber, one at a time. Each precursor pulse was separated by inert gas, such as Ar or N2. The excess precursors and reaction by-products were evacuated by vacuum pump from the ALD reaction chamber. The precursor is fully reacted with only one monoatomic layer on the reacting surface through a surface saturating self-terminationg process. Therefore, the ALD technique produces extremely uniform and conformal films in  atomic level thickness. In general ALD has been shown to be able to generate reproducible and well-defined thin films of binary oxides, nitrides, and sulfides.  In recent years  ALD has been used to deposit pure elemental metals, new types of ternary and quarternary materials.

Presently only a few processes have been reported on the synthesis of WO3 films by atomic layer deposition (ALD) so far. ALD WO3 thin films have been deposited using WF6 and H2O as precursors. WO3 films have also been deposited by ALD using  tungsten hexacarbonyl (W(CO)6) and ozone as reactant precursors for tungsten and oxygen.

In this work, we report on the synthesis of WO3 thin films on Si and quartz substrates by thermal ALD using a cross-flow reactor, with W(CO)6 and DI water as the chemical ALD precursors for tungsten and oxygen, respectively. This was followed by 600 oC furnace annealing in regular  atmosphere. Characterization of WO3 thin films has been performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), UV-VIS-NIR spectrometer, Raman spectroscopy (RS).

 Figure 1 shows the XRD pattern of the ALD WO3 samples obtained after furnace annealing at 600 oC   under atmospheric conditions. All the diffraction peaks can be indexed into the monoclinic structure of the WO3 phase [space group: P21/n (14)], which is consistent with PDF 83-0950.

References:

 J.  Malm, T. Sajavaara, and M. Karppinen, Chem. Vap. Deposition 18, 245 (2012).

P. Tägtström, P. Mårtensson, U. Jansson, and J.-O. Carlsson, J. Electrochem. Soc. 146, 3139 (1999).

Figure 1
(Invited) Atomic Layer Deposition of Nanophase Materials for Electrical Energy Storage
Authors: Meng Xiangbo , Elam Jeffrey W
Published: February 2020

Batteries, as one of the most successful electrochemical electrical energy storage (EES) devices, hold great promise to boost widely implementation of renewable clean energies such as wind and solar power in three major domains: portable electronics, transport, and smart grids. To date, state-of-the-art lithium-ion batteries (LIBs) are dominant in consumer electronics, but still not applicable for electrical vehicles and smart grids in terms of energy density, cost, safety, and stability. In this context, huge research effort has been undergoing in pursuing cost-effective, high-energy, and robust batteries as next-generation EES devices.

In the past few years, atomic layer deposition (ALD), a traditional thin film technique in semiconductor industries, has been identified as a new thrust for advanced EES and demonstrated powerful capabilities in addressing existing difficulties with various advanced battery technologies. Benefited from its unique mechanism, ALD now has become a versatile and irreplaceable tool for developing a large range of novel nanophase materials. The resultant nanoscale materials are playing more and more important roles in seeking new clean energy solutions. In the first place, ALD enables to provide a large variety of high-efficient electrodes (anodes and cathodes) by nanoarchitecturing energy-related materials. Secondly, ALD is particularly capable of finely tailoring battery interfaces for improved battery safety and stability, distinguishing its unrivalled quality from other methods in accurately controlling sub-nano to nanoscale ultrathin films with the most desired properties. In addition, ALD shows notable potential in constructing superionic lithium conductors as solid-state electrolytes for reliable battery safety, featuring its exceptional ability in tuning materials composition and crystallinity of complex compounds. In this invited talk, we will summarize and illustrate the various demonstrable strategies of ALD for next-generation LIBs and beyond Li-ion technologies (e.g., lithium-sulfur, lithium-oxygen, and sodium-based batteries), and highlight the most successful accomplishments of ALD in batteries. We will also give some outlooks on ALD future research trends and its opportunities in helping accomplish our energy missions.
(Invited) Opportunities in Atomic Layer Deposition for Electronic Textile and Hydrophobic Coating Applications
Authors: Lee Han-Bo-Ram
Published: February 2020

Atomic layer deposition (ALD) has been widely applied for high technology applications from semiconductor industry to energy devices since it has several superior properties in nanoscale device fabrications, such as excellent conformality, large area uniformity, and process compatibility, over the conventional thin film deposition methods. In this work, we extended ALD researches to two novel applications, electronic textile (e-textile) and hydrophobic coating applications. We developed a Pt ALD process capable of low temperature deposition down to 80 °C using a new Pt precursor and O2 counter reactant. Pt was deposited on organic textile substrates, such as cotton and Nylon. The ALD-Pt-coated textiles showed high electrical conductivity and high mechanical durability even after mechanical wrinkling test. Fabrications of pressure sensor arrays using ALD-Pt-coated textile were demonstrated. For the hydrophobic coating, we developed rear earth oxides (REOs) ALD including Y2O3, La2O3, CeO2, Dy2O3 and Er2O3 by using new rare earth precursors All the ALD REOs showed hydrophobic property over 100 ° of water contact angles. In addition, the hydrophobicity of ALD REOs showed high durability even after high temperature process over 500 °C. A superhydrophobic surface was fabricated by using ALD REOs and nanostructured Si surface. The nanostructured Si coated by ALD REOs showed very high water contact angle as high as 158 °.
Atomic Layer Deposition and in-Situ Characterization of Yttrium Oxide and Yttria-Stabilized Zirconia
Authors: Lecordier Laurent
Published: February 2020

Y2O3 is an attractive rear-earth oxide due to its large permittivity (~14-18), high refractive index above 1.9, optical transparency over a wide spectral range (0.2-8µm), large bandgap of 5.8eV and excellent thermodynamic stability. Additionally, when co-deposited with ZrO2, it leads  to yttria-stabilized zirconia (YSZ), a dense ionic conductor widely used as an SOFC electrolyte. The depositions of Y2O3and YSZ by thermal ALD are therefore important in the context of achieving dense pinhole-free thin films (<50nm) that can potentially be applied with excellent conformallity over high aspect ratio 3D nanostructures either for electronic, optical or energy applications.

In this paper, Y2O3 and YSZ thin films are thermally deposited by ALD in a commercial Ultratech Savannah reactor. Tris(ethylcyclopentadienyl)yttrium -Y(EtCp)3  - heated at 120˚C (0.15 Torr vapor pressure) - is used as a precursor with  N2 carrier bubbled through via  a Low Vapor Pressure Delivery system. Additionally, tetrakis(dimethylamido)zirconium TDMAZr is selected for ZrO2 deposition while H2O is the co-reactant. A quartz crystal microbalance has been implemented in order to rapidly characterize the ALD process space from 150 to 300˚C as a function of Y(EtCp)3 and H2O doses.  In-situ spectroscopic ellipsometry data are also collected in order to measure the evolution of the optical film properties with temperature. 

 In the case of Y2O3, a soft saturation of the growth per cycle vs. Y(EtCp)3 bubbling time is observed with a GPC of 1.6Å/cycle at 250˚C. The non-uniformity across 150 mm wafers decreases to ~2% at an optimal Y(EtCp)3 dose.   The GPC increases monotonically with temperature with no apparent plateau between 150 to 300˚C. The optical index remains stable at 1.92 above 200˚C. The Y2O3film stoichiometry is confirmed by RBS while SIMS measurements indicate a carbon content below 0.1%.

Uniform YSZ thin films were deposited and the yttria to zirconia composition is accurately controlled by adjusting the ratio of TDMAZr to Y(EtCp)3 cycles. In-situ measurements confirm the growth of Y2O3 on ZrO2, and vice-versa, without evidence of nucleation retardation when alternating the chemistries. The Y:Zr mass ratio monitored by QCM appears consistent with the Y2O3 to ZrO2 ALD cycle ratio and is verified with ex-situ XPS. XRD measurements were done on Y2O3 and YSZ samples to characterize the film crystallinity.

Overall both Y2O3 and YSZ ALD processes prove robust and reproducible with negligible contamination and no apparent sign of thermal decomposition of the precursor.
(Invited) Ru-Based Binary or Ternary Thin Films By Atomic Layer Deposition for a Seedless Cu Interconnects
Authors: Kim Soo-Hyun
Published: February 2020

Ru has been suggested as a diffusion barrier that is compatible with the direct plating of Cu. However, previous studies showed that Ru itself is not a suitable diffusion barrier for Cu metallization due mainly to its poor microstructure with polycrystalline columnar grains. This study developed several Ru-based multi-component thin films, RuMn, RuSiN, and RuAlO using atomic layer deposition (ALD) process, which are compatible with the direct plating of Cu as well as show better diffusion barrier performance against Cu than Ru. Mn, SiNx, AlOx were incorporated into the Ru by combining the Ru and corresponding ALD cycles, and Ru-based binary alloy, RuMn, ternary thin films, RuSiN and RuAlO, were fabricated at 225 oC. As a typical example, the results on ALD-RuAlO were shortly described. The step coverage of ALD-RuAlO was perfect at contact holes with an aspect ratio of ~ 25 (top-opening diameter: ~ 85 nm). XRD and TEM results indicate that ALD-Ru film prepared without AlOx ALD cycle forms a polycrystalline structure with columnar grains. But, with incorporating the AlOx cycles, RuAlO films were formed with non-columnar grains and nano-crystalline microstructure consisting of Ru nano-crystals separated by amorphous AlOx matrix. XRD analysis showed that the structure of Cu/ALD-RuAlO (8 nm)/Si was stable after annealing at 600 oC for 30 minute while Cu/Ru (15 nm)/Si structure was failed after annealing at 450 oC. It was also shown that the electroplating of Cu was directly achieved on a very thin (~8-nm-thick) RuAlO film at blanket and pattern wafer. In the case of binary ALD-RuMn film, it should be noted that after annealing ALD-RuMn film at 500 oC, the self-formation of Mn silicate barrier between Ru(Mn) film and SiO2 was confirmed based on XRD and TEM analysis, which was due to the diffusion of Mn into underlying SiO2, resulting in better diffusion barrier performance than Ru counterpart.

 Acknowledgements

This work was supported by the Technology Innovation Program (Industrial Strategic technology development program, 10035430, Development of reliable fine-pitch metallization technologies) funded by the Ministry of Knowledge Economy (MKE, Korea) and also partially supported by Tanaka Precious Metals, Japan.
(Invited) Understanding and Controlling Electrochemical Effects in Wet Processing
Authors: Raghavan Srini , Chiang Chieh-Chun
Published: February 2020

Electrochemical  and redox effects permeate  many aspects of wet processing in the fabrication of integrated circuits.  This presentation will highlight  areas where electrochemical effects are detrimental to wet processing as well as areas that can be benefited by electrochemical effects. For example, recent work has shown that megasonic  cleaning of conductive surfaces can be enhanced using electrochemically generated hydrogen bubbles. Well known areas that suffer from electrochemical effects are cleaning of silicon and copper in dilute hydrofluoric acid. Challenges encountered in the processing of stack structures that have electrochemical activity will be discussed.Electrochemical  and redox effects permeate  many aspects of wet processing in the fabrication of integrated circuits.  This presentation will highlight  areas where electrochemical effects are detrimental to wet processing as well as areas that can be benefited by electrochemical effects. For example, recent work has shown that megasonic cleaning of conductive surfaces can be enhanced using electrochemically generated hydrogen bubbles. Well known areas that suffer from electrochemical effects are cleaning of silicon and copper in dilute hydrofluoric acid. After a discussion of these areas, challenges encountered in the processing of stack structures that have electrochemical activity will be discussed.
Effect of Particle Contamination on Extreme Ultraviolet (EUV) Mask and Megasonic Cleaning Process for Its Removal
Authors: Kim Min-Su , Ji Hye-Rim , Choi In-Chan , Kim Hyun-Tae , Jang Sung-Hae , Lee Jun , Kim In-Seon , Kim Jung-Hwan , Oh Hye-Keun , Ahn Jin-Ho , Park Jin-Goo
Published: February 2020

Extreme ultraviolet lithography (EUVL) is the most promising lithography technique for the 22 nm half-pitch and beyond. The EUV patterned masks work in a reflective mode and it has 40 to 50 pairs of MoSi multilayer to reflect EUV radiation. This multilayer is capped by a 2.5 nm Ru thin film to protect the MoSi multilayer. Since EUV mask does not have a pellicle which protects mask surface from the contaminants. Therefore, EUV mask is more vulnerable to particle contamination during lithography processing which is a major yield loss in device fabrication. No study has been reported on the effect of particle size on CD variation if they exist on EUV mask. The critical defect size, which can cause 10 % CD error, has to be removed from the mask surface. When the defect is located between line and space patterns on the mask, the reflectivity will be reduced due to defect absorption. Simulation predicted that 30 nm sized silica particles can cause 10 % CD error on 16 nm line and space pattern. Thus, these contaminant particles have to be removed from EUV mask surface for preventing CD variation. In order to evaluate the 30 nm sized silica particle removal test, we adopted 30 nm standard spherical silica particles. Actually, it is a challenge to evaluate 30 nm particles removal test without inspection tools. So, we used atomic micro scope (AFM) for the evaluation of these particles. The silica particles were intentionally deposited on Ru surface using spinning method. Cleaning test was performed with twin type megasnoic. 30 nm silica particles removal efficiency was drastically decreased as compared with 137 nm silica particles at 1 MHz megasonic cleaning. Because the megasonic cleaning force was reduced to ultra-fine particles due to boundary layer thickness. Therefore, higher megasonic cleaning force is required to remove ultra-fine particles to overcome boundary layer thickness. It is well known that the large cleaning force is induced, not only particle removal efficiency but also pattern damage will be increased. Thus, megasonic cleaning process without causing pattern damage has to be optimized.

In this study, we shall discuss the effect of megasonic frequency on the removal of ultra-fine particles and pattern damage. Also, gas dissolved water and dilute alkali cleaning solution are adopted to high frequency megasonic cleaning process to achieve ultra-fine particles removal without pattern damage effectively.

Figure 1
Advanced Wet-Etch-Only Process for Complete Tri-Layer Rework
Authors: Steinke Philipp , Calvo Jesús , Uhlig Benjamin
Published: February 2020

A tri-layer patterning is used for high numerical aperture immersion lithography at 28 nm node. The tri-layer consists of a photoresist (PR) deposited on silicon containing anti-reflective coating (SiARC) above an organic planarization layer (OPL). Defective PR layer (e.g. overlay, over-exposure, residues) are repeatedly being reworked in high volume manufactories. Since selective PR removal has some disadvantages for the remaining SiARC (residues, roughness increase, thickness loss, optical properties modification) commonly, the complete tri-layer stack is removed and reprocessed. Due to the different chemical composition of the three layers, multiple etch processes (e.g. dry-wet-dry) are necessary.

In this work we investigate a wet-etch-only tri layer rework approach that takes advantage of a lower material damage, cost reduction and an increased throughput possibility. A complete removal and low defect levels on patterned 300 mm wafers have been required.

The screening of various ULSI chemicals according to their removal ability and selectivity to functional layers (TiN hardmask and TEOS cap) enabled a wet-etch-only process on an industry standard single wafer tool. Ellipsometric spectroscopy, cross-section scanning electron microscopy (X SEM), Transmission Electron Microscopy (TEM) and defect scans confirm these results.

Figure 1
Post Salicidation Clean: Removal of Unreacted Pt from High Pt Content NiPt Silicide
Authors: Sehgal Akshey , Derderian Garo , Muralidhar Pranesh
Published: February 2020

Introduction

            Silicides have been used in self-aligned processes for several generations of CMOS devices, with the aim of reducing the sheet resistance and providing stable Ohmic contacts with low contact resistance on gate, source and drain areas.1  To avoid bridging at the spacers and the isolation areas, after salicide formation, unreacted NiPt needs to be removed; simplified process flow is shown in Figure 1.  Theoretically, strongly oxidizing wet clean chemistries should be able to remove Ni and/or Pt in the Ni Pt salicide.  Xu et al.2 used a HF and HNO3 acid mix to remove unreacted NiPt (for 5% and 10% Pt content) at high etch rates with high selectivity to other materials exposed at the wafer surface.

        However, for higher Pt contents in Ni Pt salicide, the HF and HNO3 acid mix was unable to remove all the unreacted Pt (Figure 2).  Other strongly oxidizing wet cleans like SPM (sulfuric peroxide mix) and aqua regia were used and found to be inconsistent; Ni Pt residues were found on the wafer surface intermittently.  Therefore, we needed to find a stable high volume manufacturing (HVM) process for removing Ni high Pt residues.

Approach

        The unreacted Ni high Pt residue was analyzed.  Unlike previous generations of Ni-Pt, this residue was almost pure Pt.  That meant that Ni was being preferentially dissolved from the Ni high Pt surface eventually resulting in a pure Pt layer.  So to prevent the preferential dissolution of Ni in Ni high Pt binary alloys, wafer spin changes were used to add a physical component to the chemical dissolution.  The intent was to use centrifugal force to remove the unreacted Ni Pt stringers from the wafer surface.  Unfortunately, this approach did not work and pure Pt residues were still found on the wafer surface.

        Extending the duration of the current wet clean steps was found to increase the attack of the NiPt salicide while the unreacted Ni Pt residue was not eliminated.

        So a new wet clean chemistry was developed to completely removing all the unreacted Ni Pt consistently making the HVM ready process.

Results

Figure 3 shows the effect of using the new wet clean at the Ni Pt Strip 1 step.  Complete removal of Ni high Pt residues was found.  The experiment was found to be repeatable and verified on lots staggered in the production line by 2 weeks.

Additional details and results will be provided in the complete presentation.

References

[1] T. Schram et al., Microelectronic Engineering, 120 (25), pp. 157–162, (2014).

[2] K. Xu et al., ECS Transactions, 11 (2), pp. 327-334, (2007)

Figure 1
(Invited) Reaction Mechanisms on Binary III-V Semiconductor Surfaces during Etching, Passivation, and Deposition
Authors: Muscat Anthony J.
Published: February 2020

Reactions on III-V semiconductors are complicated by virtue of having atoms from different chemical groups on the surface. Which atom dominates the chemistry, group III or group V? Does it depend on the type of chemistry—etching, passivation, deposition? Does the exposed crystal plane play a role? This talk will review recent data that both validates and challenges old assumptions about how these surfaces react with oxidizing liquid and neutral gas phase chemistries.
(Invited) Colloidal Nanocrystal Composites with High and Low Thermal Conductivity
Authors: Wang Robert
Published: February 2020

We present our work on thermal transport in colloidal nanocrystal composites within the context of thermoelectrics and thermal energy management. Colloidal nanocrystals consist of an inorganic crystalline core with short ligand molecules bound to the surface. These nanocrystals can be made with excellent control over size, shape, and composition, thereby enabling microstructural control over thermal energy transport.

Our first two topics focus on low thermal conductivity materials for thermoelectricity: semiconductor nanocrystal thin films and semiconductor matrix – semiconductor nanoparticle composites. Our last topic focuses on metal matrix – metal nanoparticle composites with high thermal conductivity, which can be used to thermally manage transient power spikes in high power electronics.

For the first topic, we systematically study the effect of nanocrystal diameter and surface chemistry on thermal transport in lead chalcogenide nanocrystal thin films. These samples exhibit very low thermal conductivities ranging from 0.1 to 0.5 W/m-K and we find that larger nanocrystals and shorter ligands generally lead to higher thermal conductivities. Our measurements also show that the effect of surface chemistry on thermal transport becomes more pronounced as nanocrystal diameter decreases.

For the second topic, we focus on polycrystalline In2Se3 matrices with embedded CdSe nanocrystals ranging from 0 to ~100 vol%. We find that the thermal conductivities of these composites are very low over the entire nanocrystal volume fraction range and vary from 0.3 to 0.5 W/m-K. We also find that the presence of CdSe nanocrystals strongly effects the formation of the In2Se3 matrix (i.e. grain orientation and size as well as ternary phase formation).

Lastly, we present our work on phase change Bi nanocrystals embedded in a solid Ag-matrix. The latent heat of the phase change Bi nanocrystals can absorb large quantities of transient heat generated during power spikes in power electronics operation. In addition, fast thermal energy transport is facilitated by the Ag-matrix, which leads to high composite thermal conductivities ranging from 101 to 102 W/m-K. We also use size-dependent melting of the phase change nanocrystals as a design variable for the thermal energy absorption temperature.
Ultrafine Manganese Oxide As Sodium-Ion Battery Anode Involving Charge-Transfer Between Mn(III) and Mn(II) Oxides
Authors: Weng Yu-Ting , Huang Tzu-Yang , Lim Chek-Hai , Shao Pei-Sian , Hy Sunny , Kuo Chao-Yen , Cheng Ju-Hsiang , Hwang Bing-Joe , Lee Jyh-Fu , Wu Nae-Lih
Published: February 2020

Our investigation on manganese dioxide (MnO2) as an anode material for sodium (Na)-ion batteries (NIBs) reveals a remarkable size effect within the nanometer range on the electrochemical sodiation activity of the oxide. Space-confined ultrafine (UF)-MnO2, with an average crystal size of 4 nm, synthesized using a porous silicon dioxide templated hydrothermal process exhibits a high reversible sodiation capacity of 392 mAh g−1 compared with the negligible activity shown by the aggregates of larger (14 nm) MnO2 nanocrystallites. To our knowledge, the present study is the first to show that MnO2 is electrochemically active as an NIB anode. The UF-MnO2 anode exhibits exceptional rate and cycle performance, including a reversible sodiation capacity of >100 mAh g−1 at a current density of 7500 mA g−1 and >70% capacity retention after 500 cycles at 150 mA g−1. The enhanced cycle stability may be attributable to the solid-embedding architecture that enables the reduction of the dimensional variations in the active material. In operando synchrotron X-ray absorption near-edge structure analysis reveals combined charge–storage mechanisms involving a unique two-oxide conversion reaction between Mn(III) and Mn(II) oxides, Mn(III)–O1.5 + Na+ + e

-
« 1/2 Na2O + Mn(II)–O, and non-Mn-centered redox reactions. 

Figure 1
Solvothermal Route Based in Situ Carbonization to Metal-Oxide/Carbon Composite As Anode Material for Lithium Ion Battery
Authors: Chen Gen , Yan Litao , Zhou Meng , Luo Hongmei
Published: February 2020

Magnetite (Fe3O4) is a very promising candidate as anode material in rechargeable lithium ion battery (LIBs) because of its ability to store up to eight Li per formula unit via reversible reactions, resulting in a high theoretical capacity of 924 mAh g-1. Moreover, advantages such as low cost, ease of synthesis and environmental friendliness make it a promising candidate for large scale commercial applications for LIBs. However, Fe3O4 suffers from poor conductivity, large volume change and voltage hysteresis during the electrochemical reaction, which strongly limits its practical application. For the fact that carbon in its own feature exhibits several interesting properties, including electronic conductivity, high surface area, tunable porous structure, etc., the combination of Fe3O4 nanostructures and different forms of carbon materials show promising potential in the preparation of composite anode materials.

In this work, a high pressure and temperature based solvothermal route was developed for the synthesis of Fe3O4 with carbon as a composite anode for lithium-ion batteries (LIBs). The carbon in products was a result of the in situ carbonization of organic components under high pressure (24.0 MPa) and temperature (350 °C). Composites with different amounts of carbon were prepared by annealing the solvothermal products at different temperature. Taking advantage of the high theoretical capacity of Fe3O4 and favorable characteristics of carbon, a capacity of about 610 mAh g-1 after 100 cycles was achieved for the composite with 54.6% carbon. The carbon amount depended electrochemical performance was also investigated. The Fe3O4@C composite can be used as an alternative anode material and the introduced synthetic strategy may provide further insights into the preparation of inorganic oxides coupled with carbon via in situ carbonization of organic components.

Figure 1
Solvation and Desolvation Phenomenon and in-Situ NMR Studies on Stripping/Plating of Magnesium Metal in Magnesium Batteries
Authors: Wang Hao , Sa Niya , Burrell Anthony K. , Vaughey John T. , Key Baris
Published: February 2020

Multivalent batteries are promising technologies that can potentially outperform lithium ion batteries in term of energy density, power density and unit cost.1 Among which magnesium batteries have attracted much attention over the last a few years. However, scientific challenges continue primarily due to the lack of understanding of the intercalation mechanism of multivalent ions.2 Our recent study is devoted to the understanding of the solvation and desolvation effect with 1H and 2D solid-state NMR spectroscopy by probing the movement of the water molecules and  solvent molecules in the system (Bis(trifluoromethan sulfonyl)Imide dissolved in diglyme based magnesium batteries) at various charge states. It is suggested that the water and diglyme molecules play a crucial role in facilitating the intercalation of the magnesium ions in the cathode lattice upon charging and discharging. 3

In addition, the effective stripping and plating effect on the magnesium metal is also investigated. By taking advantage of in situ NMR spectroscopy, we investigate metal vs metal pseudo cells while the cells are polarized. No significant changes in the NMR spectra  between the pristine and cycled pseudo cell for Grignard electrolytes, which is in agreements with reversible smooth stripping and plating.

1              D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature
2000, 407, 724-727 10.1038/35037553.

2              H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy & Environmental Science
2013, 6, 2265-2279 10.1039/c3ee40871j.

3              S. H. Lapidus, N. N. Rajput, X. Qu, K. W. Chapman, K. A. Persson, P. J. Chupas, Physical Chemistry Chemical Physics
2014, 16, 21941-21945 10.1039/c4cp03015j.
Direct Determination of Burgers Vectors of Threading Mixed Dislocations in 4H-SiC c-Plane Wafers Grown by PVT Method
Authors: Guo Jianqiu , Yang Yu , Wu Fangzhen , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael
Published: February 2020

Threading Screw Dislocations (TSDs) have long been observed in 4H-SiC crystals grown by the Physical Vapor Transport (PVT) method. Recent studies [1] show that a significant proportion of these threading dislocations are actually mixed type dislocations with a Burgers vectors nc+ma (where n and m are integers). With the help of Synchrotron White Beam X-ray Topography, it is straightforward to distinguish these mixed type threading dislocations from pure screw dislocations simply by recording different reflections from an axially cut sample (cut parallel to growth direction) and applying the 
g.b
=0and
g.bxl
=0 invisibility criteria (g – diffraction vector;  b – Burgers vector). However, axial wafers are only cut from the boules slated for research purposes and are usually unavailable for boules from which commercially preferred c-plane oriented wafers are sliced. In this study, Synchrotron Monochromatic X-ray topography was carried out on a 100mm 4H-SiC c-cut commercial wafer and contrast variation was observed for each single threading screw or mixed dislocation image on six different types of 11-28 reflections. The way the contrast varied in the different reflections was also found to be different and actually depends on the nature of the dislocation itself. Ray Tracing Simulation was then carried out to confirm this observation. This simulation method is capable of simulating dislocation contrast in various geometries and it is based on the fact that orientation contrast is the predominant contributor to contrast from threading dislocations in the grazing incidence and back reflection geometries. According to the simulation results and their comparison to the observed contrast, it is in principle possible to determine the Burgers vector of any single threading dislocation using this methodology.

[1] F. Wu, H. Wang, S. Byrappa, B. Raghothamachar, M. Dudley, E. K. Sanchez, D. Hansen, R. Drachev, S. G. Mueller, and M. J. Loboda, Mater. Sci. Forum 717-720, 343(2011).

[2] X. R. Huang, M. Dudley, W. M. Vetter, W. Huang, W. Si, and C. H. Carter, Jr., J. Appl. Cryst. 32, 516 (1999).

Figure 1
Avalanche Energy of High-Voltage Silicon and SiC Power Diodes
Authors: Shenai Krishna
Published: February 2020

Unlike silicon Merged PiN Schottky (MPS) power diodes, commercial 4H-SiC Junction Barrier-controlled Schottky (JBS) power diodes contain an abundance of threading screw dislocations (TSDs) and threading edge dislocations (TEDs). It is not clear exactly how these crystal defects manifest on the performance and reliability of high-voltage power devices. In this paper, extensive avalanche energy measurements will be used to develop a deeper understanding of the role that crystal defects play on device reliability when switching high currents under high-voltage stress conditions.
(Invited) Threshold Voltage Stability Comparison of Commercial SiC Mosfets and Related Issues
Authors: Green Ron , Lelis Aivars , Habersat Dan
Published: February 2020

Silicon-Carbide (SiC) MOSFETs are beginning to gain wide acceptance for power electronics applications requiring high efficiency and high operational temperatures. There is a growing number of commercial offerings at 1200 V from different manufacturers that may have very distinctive processes that need to be evaluated in a consistent manner to make valid comparisons. As SiC MOSFET technology continues to mature, device performance and reliability should also improve. In recent years, a diverse number of publications in the literature have addressed the poor quality of the MOS gate dielectric layer, and the challenges related to charging of both interface defects and near-interfacial oxide defects during electrical and thermal stressing. A significant number of intrinsic defects in the gate oxide result from growth of the dielectric layer itself. Subsequent process steps can activate a number of these defects which can trap charge during electrical gate-stress, thereby altering the device threshold voltage. During bias temperature stressing, activation of additional oxide defects can occur, which gives rise to larger threshold voltage instabilities. The stability of the MOS threshold voltage under electrical gate-stress at high temperature is an important reliability phenomenon with potential application relevance. A large positive shift reduces on-state conduction, increases power losses, and may reduce efficiency in switch-mode converter applications. A large negative shift in the threshold voltage is a more serious reliability concern because of excessive drain leakage current in the MOS-channel during the off-state. This effect will limit blocking capability and possibly lead to device failure.

This work will provide an overview of threshold voltage stability issues in commercially-available SiC MOSFETs subject to both positive and negative gate-stress at high temperature. Figure 1 is a plot of the subthreshold-voltage shift as a function of unipolar (positive) bias stress time for commercial devices purchased between 2012 and 2015. Recent devices show significant improvement in threshold voltage shift for a +25 V gate-bias stress at 175 °C. The older commercial devices shift considerably more, with the onset of degradation occurring much earlier in time. We have also observed differences in the responses of devices from different manufactures for similar stress and test conditions.  It is expected that process differences among device manufacturers would in turn, result in differences in the bias-temperature-stress responses. A fuller discussion of these test results and related issues will be presented in the final paper.

Figure 1
Study on the Relaxation Process in 4H-SiC Homoepitaxy Growth
Authors: Guo Jianqiu , Yang Yu , Wu Fangzhen , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael
Published: February 2020

BPD half loops arrays (HLAs) present in the homoepitaxial layers of 4H-SiC are responsible for introducing an increase in the forward voltage drop via the electron-hole Recombination Enhanced Dislocation Glide (REDG) and therefore are harmful to the device operation. Different sources are observed to form HLAs and interfacial dislocations (IDs) including surface, scratch, micropipe, 3C inclusion. Recent observation was made in a 100mm 4H-SiC wafer where a short edge-oriented BPD segment in the substrate was drawn towards the interface during the epitaxy growth producing screw-oriented segments intersecting the growth surface. These screw segments of BPDs subsequently glide under the mismatch stress when the critical thickness is reached. HLAs and IDs are subsequently formed. We believe that the formation of HLAs and IDs is driven by the mismatch stress brought by the doping concentration difference between the substrate and the epilayer. To verify this, we first estimate the amount of mismatch strain caused by the epi/substrate doping concentration difference according to Sasaki’s work [1]. Then Matthews-Blakeslee’s model [2, 3] is used to predict the value for critical thickness corresponded to such amount of mismatch strain. The predict value is then compared to the critical thickness that we measured via Synchrotron X-ray study and they are found to have a good agreement with each other. This indicates that mismatch strain brought by the doping concentration is sufficient for relaxation process to occur.

[1] S. Sasaki, J. Suda, and T. Kimoto, Materials Science Forum 717-720, 481 (2012).

[2] J. W. Matthews, Journal of Vacuum Science and Technology 12(1), 126 (1975).

[3] J. Matthews and A. Blakeslee, Journal of Crystal Growth 27, 118 (1974).
Leakage Current Mechanisms in Reverse Biased High-Voltage 4H-SiC Power Diodes
Authors: Shenai Krishna , Raghothamachar Balaji , Dudley Michael
Published: February 2020

Today’s commercial 4H-SiC power diodes contain an abundance of threading screw dislocations (TSDs) and threading edge dislocations (TEDs). It is not clear exactly how these crystal defects manifest on the performance and reliability of high-voltage power devices. In this paper, extensive current-voltage (I-V) and capacitance-voltage (C-V) measurements of 600V, 1200V and 1700V commercial SiC power diodes at temperatures ranging from 22ºC to 250ºC will be reported. Detailed analysis of leakage current mechanisms is performed and it is shown that space charge limited current (SCLC) is a significant contributor to diode leakage current especially at increased electric fields. The static I-V data will be correlated with defect delineation using in-situ hard X-rays and it is shown that TSDs get excited first under high field stress conditions.
(Invited) Surfactant-Assisted Chemical Vapor Deposition of High-Performance Small-Diameter Gasb Nanowires
Authors: Ho Johnny C
Published: February 2020

Due to the intriguing physical properties, III-Sb nanowires such as GaSb have attracted extensive interest as promising channel materials for future electronics, optoelectronics and others. Although various device structures based on GaSb nanowires have been realized, further performance enhancement is still suffering from the notorious uncontrolled radial growth during the nanowire synthesis, resulting in the non-uniform and tapered nanowires with diameters much larger than few tens of nanometers. In this work, for the first time, we report the use of sulfur surfactant in the chemical vapor deposition to achieve high-performance and uniform GaSb nanowires with the diameter down to 20 nm. In contrast to the surfactant effect typically employed in the liquid phase or thin film technologies, the sulfur atoms, commonly used for the surface passivation of III-V semiconductors, are contributed to form stable S-Sb bonds on the as-grown nanowire surface, effectively stabilizing the sidewalls and thus minimizing the unintentional radial vapor-solid nanowire growth. More importantly, when configured into field-effect transistors, these nanowire devices exhibit impressive electrical properties with the peak field-effect hole mobility of ~200 cm2 V-1 s-1, which is the best mobility value reported for any GaSb nanowire devices till now, owing to the improved gate-coupling efficiency and reduced surface carrier scattering in these thin nanowire geometry. All these results evidently indicate the effectiveness of this surfactant-assisted growth for high-performance small-diameter GaSb nanowires, significantly enhancing various device properties for practical applications.
(Invited) Oxide Interface Is the Device: Properties of Two-Dimensional Electron Gas
Authors: Wu Tao
Published: February 2020

Transition metal oxides exhibit rich phase diagrams and exotic physical properties as a result of strong correlations between charge, spin, orbital and lattice. The recent advances of thin film technology allow the synthesis of high-quality epitaxial oxide heterostructures with control at the unit cell level, which enables exploring rich physics and opportunities for future technologies. As a notable example, interesting transport phenomena like 2D electron conduction and orbital reconstruction were discovered at the polar-nonpolar LaAlO3/SrTiO3 (LAO/STO)interface. In this talk, I will first discuss our results of Kondo effect and two-dimensional insulator-to-metal transition obtained on interface-based field effect device with double layer ionic electrolyte as the top gate. Then I will introduce an interface-based nonvolatile resistive switching device, where the ionic drift and alteration of electronic configuration underpin the memory operation. Finally, I will discuss the possible routes to achieving higher electron mobility in such oxide interfaces and the perspective of constructing interface-based photodetectors.
Micropatterned P(VDF-TrFE) Film Based Piezoelectric Nanogenerators for Highly Sensitive Self-Powered Pressure Sensing System
Authors: Yoon Hong-Joon , Lee Ju-Hyuck , Kim Sang-Woo
Published: February 2020

Here we demonstrate micro-patterned poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) films-based piezoelectric nanogenerators (PNGs) with high power-generating performance for highly sensitive self-powered pressure sensors. The micro-patterened P(VDF-TrFE)-based PNGs revealed nearly five times larger power output compared to a typical flat film-based PNG. The micro patterning of P(VDF-TrFE) polymer made itself ultra-sensitive in response to mechanical deformation and stress. We successfully demonstrate their application as self-powered pressure sensors in which mechanical energy comes from water droplet and wind. The mechanism of the high performance is intensively discussed and illustrated in terms of strain developed in the flat and micro-patterned P(VDF-TrFE) films. The impact derived from the patterning on the output performance is studied in term of effective pressure using computational simulation, COMSOL.
(Invited) The Next Generation Biochip
Authors: Yang Yuh-Shyong
Published: February 2020

Biochip in the form of microarray is an ingenious way to collect large amount of biological information from complex biochemical processes in an organism. This method is especially suited for the current genomic and proteomic era when many biological and medical questions can be answered from analyzing big molecular data. We are facing issues such as aging, chronical diseases and personal medicine, all of which require efficient collection and analysis of biochemical information. However, applications of traditional biochip array are facing some major limitations, such as labeling requirement, specificity and sensitivity issues. We propose the development of a Next Generation bioChip (NGC) that fulfills the unmet needs of current biochip to face the growing demand in health care. The proposed NGC takes full advantage of modern electronics and can easily integrate with current development in biochip and other progress in molecular diagnostics. In this presentation, we use polysilicon nanowire field effect transistor base biosensor as an example to demonstrate that the NGC can be achieved with current technologies. Key techniques and its experimental details will be presented to show that the commercial NGC can be built in the near future.
(Invited) Electrical Sensing with a Tube-in-a-Tube Semiconductor
Authors: Wang YuHuang , Ng Allen , Piao Yanmei , Chen Chien-Fu , Kwon Hyejin , Lee Cheng
Published: February 2020

The fundamental idea of field-effect transistors has fueled the development of innovative electrical sensing technologies for the detection of biological and chemical species. However, it is generally challenging to attain simultaneous ultrahigh sensitivity and selectivity as required for chemical sensing. In this talk, we will discuss progress from our lab toward the demonstration of a tube-in-a-tube (Tube^2) semiconductor for the electrical detection of small molecules and biological molecules. A Tube^2 is equivalent to a single-walled carbon nanotube nested within a chemically tailored, impermeable, and atomically-thick functional shell. This structure is created from double-walled carbon nanotubes through outer wall-selective covalent chemistry. Compared with single-walled carbon nanotubes and graphene, electrical sensors created using Tube^2 can be readily tailored with robust covalent chemistries to high functional densities for enabling chemical selectivity while maintaining exceptional sensitivity. We show that 4-carboxylbenzene groups can be covalently attached to the outer wall to the exclusion of the inner tube using diazonium chemistry. Preliminary thin-film transistor sensors based on this novel semiconductor show an ammonia sensitivity of 60 nM (or ~1 ppb) with ~6,000 fold higher chemical selectivity towards amine-containing analytes over other small molecules. Implication of these findings towards biosensing with Tube^2 will be discussed.
(Invited) Triboelectric Nanogenerators Harvesting (Bio)Mechanical Energy for Self-Powered Systems
Authors: Wang Sihong
Published: February 2020

The fundamental science and applicable technologies for harvesting environmental energy are not only essential in realizing the self-powered systems, but also tremendously helpful in meeting the rapid-growing world-wide energy consumptions. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. The triboelectric effect is a universal phenomenon that can generate electrostatic charges from mechanical contact. Here, a new type of technology—triboelectric nanogenerators (TENGs)—has been developed to efficiently convert mechanical energy into electricity, based on the coupling of triboelectrification and electrostatic induction. In order to develop TENGs of different structural designs for harvesting various types of mechanical energies existing in the natural environment, we established three basic modes/mechanisms of TENGs that serve as the basis for most of the TENG structures: (1) vertical contact-separation mode [1]; (2) lateral sliding mode [2]; (3) freestanding-triboelectric-layer based mode [3]. All of the three modes of TENGs are shown to be effective electrical sources that are capable of generating a voltage over hundreds of volts and a power density larger than 10 W/m2, and also instantaneously driving hundreds of electronic devices (such as LEDs).  Based on these fundamental modes, a number of different structural designs for harvesting different types of mechanical energy have been developed. For the storage of the electricity generated by triboelectric nanogenerators, we further developed the self-charging power unit (SCPU) by hybridizing a TENG with a flexible Li-ion-battery into as a single device, which allows a battery to be charged directly by ambient mechanical motion. This physical hybridization enables a new operation mode: the “sustainable mode”, in which the environmental mechanical energy is scavenged to charge the battery while the battery keeps driving an external load. In this mode, the demonstrated SCPU can provide a continuous and sustainable DC current at a stable voltage for as long as there is mechanical motion/agitation. It can be used to continuously drive a UV sensor for extended period of time. Thus, the SCPU can serve as an independent and sustainable power unit, which will meet the general requirement of almost any electronic device. [4] This technology has shown the potential to utilize (bio)mechanical energy to realized self-powered systems.

[1] Wang, S. H.; Lin, L.; Wang, Z. L. Nano Lett. 2012, 12, 6339-6346.

[2] Wang, S. H.; Wang, Z. L. et al.
Nano Lett. 2013, 13, 2226-2233.

[3] Wang, S. H.; Wang, Z. L. et al.
Adv. Mater. 2014, 26, 2818-2824.

[4] Wang, S. H.; Wang, Z. L. et al.
ACS Nano 2013, 7, 11263-11271.