bluuebunny/crossref_metadata_2025 huggingface dataset:
Concentrated Electrolytes for High-Energy Metallic Li Batteries
Authors: Hu Yong-Sheng
Published: February 2020

Liquid electrolyte plays a key role in commercial lithium batteries to allow conduction of lithium ion between cathode and anode. Traditionally, taking into account the ionic conductivity, viscosity and dissolubility of lithium salt, the salt concentration in most of liquid electrolytes is typically less than 1.2 mol/L. We propose a new class of “Solvent-in-Salt” (SIS) electrolytes with high salt concentration, in which salt holds a dominant position in the lithium ion transport system. It remarkably enhances cyclic and safety performance of the next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite and shape change of metallic lithium anode. First, when used in lithium-sulfur battery, the power of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of the most challengeable technological hurdles: “polysulphide shuttle phenomenon”. Consequently, a Coulombic efficiency nearing 100% and long cycling stability are achieved. Second, when used in lithium-NCA pouch cell, the ca. 3Ah cell exhibits over 150 cycles.
GaN LED on Quartz Substrate through Wafer Bonding and Layer Transfer Processes
Authors: Lee Kwang Hong , Wang Yue , Zhang Li , Chua Soo Jin , Fitzgerald Eugene A. , Tan Chuan Seng
Published: February 2020

A method to transfer GaN LED layers (which was grown initially on a Si substrate) to a quartz substrate is proposed and demonstrated. Quartz substrate is chosen due to its optical transparency to enhance the light extraction efficiency. The GaN LED-on-Si substrate was temporarily supported on a Si handle wafer. A quartz substrate was then bonded to the GaN LED layers-containing handle wafer. Finally, the handle wafer was released to realize the GaN LED layers on the quartz substrate. All substrates used were 200 mm in diameter. The transferred film demonstrates excellent optical properties. The GaN LED devices were then fabricated on coupon size samples (singulated from the 200 mm GaN LED on quartz substrate) using standard photolithography techniques. The mesas were formed by dry etching processes. The performance of the devices is promising and the details will be presented. Through this method, we can improve the light extraction efficiency and hence, benefit to the integration of Si-CMOS + LED platform for applications such as multi-color microdisplay.
Design and Development of Nitrogen Doped Nano Porous Activated Carbon As Electrode Active Material for Supercapacitors
Authors: Mitravinda Tadepalli , Sharma Chandra Shekhar , Anandan Srinivasan , Rao Tata Narsinga
Published: February 2020

Supercapacitors (SCs), which have been extensively applied in consumer electronics and energy management, are alternative energy storage devices for their high power densities. Electrochemical double layer capacitors (EDLCs) storing charge on the interface between electrode and electrolyte and pseudocapacitors associated with rapid surface redox reaction are the two categories of SCs. The former requires carbon materials with high specific surface area, high conductivity and suitable pore channels to achieve promising specific capacitance and long cycling life. N-doped activated carbon has been synthesized using cork, a biomass waste obtained from the bark of oak trees as carbon source by a two step thermal annealing process. The obtained carbon material possesses honey comb structure with microporous structure, high specific surface area (up to 1172 m2 /g) and large pore volume (0.12 cm3/g). Besides, N-doped carbon (CAC 1:1) with a nitrogen content of 5.17 wt.% exhibits a maximum specific capacitance of 185 F/g at a current density of 1 A/g in 6 M KOH aqueous electrolyte. It also displays a good rate performance, i.e., 176 F/g at 10 A/g and cycle stability, i.e., ~80.3% retention after 1175 charge-discharge cycles. The assembled CAC1:1 symmetric capacitor exhibits a maximum energy density of 20.2 Wh/kg at a power density of 448 W/kg within a voltage range of 0 - 1.8 V in 1M Na2SO4 aqueous electrolyte. The unique porous structure and N-doping characteristic endue the electrode material a potential candidate for high-performance supercapacitors.
Pseudocapacitive Charge Storage in Titanate–Reduced Graphene Oxide Nanocomposites
Authors: Ko Jesse S. , Kim Hyungseok
Published: February 2020

Pseudocapacitance is an emerging charge-storage mechanism that allows materials to achieve both high energy and high power capabilities. One strategy to enable pseudocapacitance is to modulate material morphologies at the nanoscale because the specific surface area and pore structure are strongly related to charge-storage kinetics. In our study, two different sodium titanate (Na2Ti3O7) morphologies, nanotubes and nanosheets, are prepared by efficient synthetic routes to examine the influence of surface nanostructures on both Li+ and Na+ charge storage properties in nonaqueous electrolytes. We confirm that the titanate nanotube structure provides higher surface area and pore volume compared to its nanosheet counterpart by using surface analysis techniques. Moreover, we incorporate reduced graphene oxide (rGO) to further improve the high-rate capability of the titanates. The nanotube-rGO nanocomposite exhibits superior electrochemical performance in terms of capacity (170 and 80 mAh g–1 in a Li+ and Na+ system, respectively) and rate capability, accompanied by a broad voltammetric response and sloping charge-discharge voltage profiles under galvanostatic mode. These electrochemical features resemble pseudocapacitive charge-storage and this mechanism is further verified by electrochemical kinetic analysis using current–scan rate dependence. This analysis allow us to determine that 80% of the stored charge at 1 mV s–1 arises from surface-limited processes for the titanate nanotube-rGO nanocomposite. This study demonstrates the importance of modulating surface structures, thereby enabling facile storage of ions to the electrochemically active sites of the material of interest.

Figure 1
Effect of Electrolyte Cation on the Electrochemical Performance of AC Electrochemical Capacitor
Authors: Forghani Marveh , Donne Scott W
Published: February 2020

The aim of this study is to observe the effects of electrolyte cation on the electrochemical performance of anodic electrode in electrochemical capacitor. In an ideal electrochemical capacitor, the symmetrical anodic and cathodic electrodes have the same contribution to overall cell performances. However, the performance of anodic and cathodic electrodes is dependent on the size of electrolyte cations and anions which are adsorbed at the surface of electrodes. Hence, there would be a deviation in anodic and cathodic potential due to diffusion of ions with different characteristics into the electrode materials.

In this study, each electrochemical cell has been made of two symmetrical activated carbon (AC) electrodes with the same mass of active material on each electrode. The AC electrochemical cells have been tested in organic electrolytes with the same anion and different cations, using cycling voltammetry (CV) at 25 mV/s sweep rate. This was followed by the step potential electrochemical spectroscopy (SPECS) experiment with a 10 mV potential step and 300 s equilibration time. SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window [1]. At the same time, the open circuit potential (OCP) of both electrodes have been measured with respect to Ag/AgNO3 reference electrode during the CV and SPECS experiments. This technique allows us to see how an individual electrode behaves in overall cell performances.

The outcome of this work indicates the shift between the anodic and cathodic potential in all different electrolytes. It was found that, the cathodic potential is more shifted towards the anodic electrode which means that during charging process more anions are adsorbed at the surface of the cathodic electrode so it covers a larger potential window than the anodic electrode.

Additionally, the specific capacitance obtained by the SPECS method was used to obtain the performance of the AC electrochemical cell in non-aqueous electrolytes with different cations in the form of a Ragone diagram.

[1]. Marveh Forghani and Scott W. Donne, Journal of the Electrochemical Society 2018 165: A664-A673.
Prototyping Aqueous Electrochemical Capacitors
Authors: Brown David , Douard Camille , Crosnier Olivier , Athouël Laurence , Ait Hammou Taleb Said , Dillet Jérôme , Mainka Julia , Lottin Olivier , Guillemet Philippe , Brousse Thierry
Published: February 2020

An ever increasing number of electrode materials are nowadays presented as potential candidates for electrochemical capacitor. This includes different forms of carbons (carbon nanotubes, graphene, activated carbon, ...), conducting polymers (PEDOT, PANI, PPy, ...), metal oxides (RuO2, MnO2, FeWO4, ...), or other inorganic materials such as metal nitrides, phosphates, etc... However, most of the reported performance of related electrodes are based on only few mg of active material and/or few mm2 surface area. Such low values definitely do not enable to upscale the performance using simple multiplying factor. Indeed, several studies have shown that experimental up-scaling of electrodes and devices often leads to quite different values, usually much lower than those reported for small scale electrodes.[1-3]

In this manuscript, we will illustrate such discrepancy between small cell and larger cell performance by using commercially available activated carbon in different configurations, including coin-type cells (< 1F) and pouch cells (up to 25 F). The different parameters influencing the electrode preparation (binder, additives, porosity, ...) as well as those related with cell assembly (current collectors, separators, ...) will be detailed as well as their influence on the cell performance. Finally, a practical illustration of symmetrical carbon based EDLC in neutral aqueous electrolyte will be given, namely the internal hybridization of such cell in a PEMFC. Its influence on power capability will be reported and compared with external hybridization using a commercial cylindrical EDLC.

[1] True performance metrics in electrochemical energy storage, Y. Gogotsi and P. Simon, Science, 334, 917 (2011).

[2] Improving the volumetric energy density of supercapacitors, N. Goubard-Bretesché, O. Crosnier, F. Favier, T. Brousse, Electrochimica Acta 206 (2016) 458–463.

[3] A Guideline for Reporting Performance Metrics with Electrochemical Capacitors: From Electrode Materials to Full Devices, A. Balducci, D. Belanger, T. Brousse, J.W. Long, W. Sugimoto, Journal of The Electrochemical Society (2017) 164 (7), A1487-A1488.
Bifunctional Activated Carbon-Lithium Ceramic for Hybrid Asymmetric Capacitor
Authors: Manzano Matias , Mosqueda Hugo A , Vázquez Jorge Gabriel , González Ignacio
Published: February 2020

The industrial world needs energy storage devices rather than lithium batteries or double-layer electrochemical capacitors with a specific power and energy density. One of the challenges is to build a durable and safe hybrid supercapacitor with high energy density and specific power and long life. Compared to lithium batteries, the lower heat emission allows the use of simpler, cheaper and more reliable cooling systems. Compared to the existing supercapacitor, the acceleration can be maintained up to 10 times more, due to the higher energy density. Hybrid trucks and buses with frequent starts / stops are also interesting applications where LIC will offer competitive advantages.

The intermittent nature of renewable energies, wind and solar, blocks the growth of these energies or imposes the need for a powerful system of energy storage to operate the electricity network during this short space. LICs are the most competitive tools for bridging the gap between electricity shortages and the actual start-up of generators.

Our team has analyzed the development of electrodes because they are critical because the electrode development process has a considerable impact on the performance of the final device. The best performance cathode was obtained by combining iron phosphate and lithium (LFP) with activated carbon (AC). The choice of electrolyte components is extremely critical to guarantee the performance of the device and in particular the safety. Organic and aquatic electrolytes have been tested to compare the functionality of devices. The experimental results show a synergistic effect between AC (energy storage in double electric layer) and LFP (energy storage by intercalation processes).

References

[1] B. Wang, Q. Wang, B. Xu, T. Liu, D. Wang, RSC Adv, 3 (2013) 20024-20033.

[2] Y. Lei, Z. Huang, W. Shen, F. Kang, Y. Zheng, Electrochimica Acta, 107 (2013) 413-418.

[3] X. Hu, Y. Huai, Z. Lin, J. Sue, Z. Deng, Journal of Electrochemical Society, 154 (2007) A1026-A1030.

Fig: a)Cyclic voltammograms using AC (YP 80F) and LiFePO4 (0.0 and 20%), reference Li/Li+ electrode, b) Nyquist diagram of AC-LiFePO4 (diferent potentials),

Figure 1
Low Dark Current Ge/Si Photodetector Grown By Selective Epitaxial Growth
Authors: Cheng Buwen , Liu Zhi , Li Xiuli , Yang Fan , Xue Chunlai , Li Chuanbo , Zheng Jun , Zuo Yuhua , Wang Qiming
Published: February 2020

Normal-incidence p-i-n Ge/Si photodetectors were fabricated on SOI substrate by selective epitaxy. Thermal annealing and surface Si passivation were performed in situ to reduce the dark current. Bulk leakage current density and surface leakage density as low as 3.4 mA/cm2 and 0.4 μA/cm are achieved under –1 V, respectively. The responsivity at wavelength of 1550 and 1310 nm are 0.27 and 0.59 A/W under zero-bias, respectively. The photodetector has a 3-dB bandwidth of 48 GHz at –3 V. Clear open eye diagrams at 40 Gbps are observed under zero-bias at a wavelength of 1550 nm.
(Invited) 2D Materials for Electronic and Optoelectronic Applications: Growth and Device Integration
Authors: Bacher Gerd
Published: February 2020

Atomically thin layers represent a novel class of materials with unique properties, like e.g. high electrical conductivity combined with high transparency in graphene or efficient light absorption and emission in transition metal dichalcogenides (TMDCs). Originally prepared by mechanical exfoliation for more basic scientific studies, recent developments in large area CVD growth techniques paved the path towards practical applications.

In this contribution some of our recent efforts on 2D materials for electronic and optoelectronic applications will be presented. This includes CVD growth of graphene on both, metallic and semiconducting substrates, and selected applications, e.g., as transparent electrode or in high frequency transistors. In addition, large area fabrication approaches of TMDCs via MOCVD growth will be demonstrated and the potential of these ultrathin semiconductors for light emitting devices in the red spectral range will be discussed. As powerful tools for nanoscale material and device analysis confocal optics and electrical scanning force microscopy have been applied.
(Invited) Heterogeneous Integration Maintaining the Pace of Progress as Moore’s Law Slows
Authors: Bottoms Bill
Published: February 2020

Germanium was used for the first transistor in 1947 but was displaced by silicon despite its higher conductivity and mobility due to higher operating temperature. Germanium was reintroduced as the end of Moore’s Law approached first in strain engineering to improve performance of silicon transistors. Today SiGe, Ge, SiC, GaN and other materials are used in diverse applications ranging from logic and memory to sensors, power devices and PICs.

Systems integration of these devices into 3D heterogeneous System-in-Package architectures is enabling the pace of progress at the system level to maintain or exceed that of Moore’s Law. This requires new materials for conductors, dielectrics, semiconductors and interface materials. These materials will require new, lower temperature integration processes due to differential CTE and other considerations. This will also require new system architectures to support increased functional and thermal density. The interconnect fabric of these systems will dramatically change due to increasing physical density of bandwidth required that is already limiting the performance of server class computers.

There are many difficult challenges to be overcome for this HI-SiP architecture to realize its potential of maintaining that rate of progress for decades to come. These challenges and potential solutions will be discussed.
Propertities of Modes of Compound Cavity in Quasicrystal Under Low Index-Contrast
Authors: Cai Yuanyuan , Wang Zhi , Chen Xiao , Li Changwei , Feng Shuai , Wang Yiquan
Published: February 2020

Comparing with periodic photonic crystal structures, quasicrystals have more interesting and complex defect modes, so that they are expected to be applied in novel defect-based photoelectronic devices. Modes of compound cavity in octagonal and dodecahedral quasicrystal investigated under the low index contrast. The results show that in the quasicrystal structure with double and several nine-air-hole-missing microcavities, it is observed not only the mode splitting, but also a new mode generation supported by a compound resonator, which covers two microcavities and the scatterers between. The field distribution of the new mode is studied. It is found that the field intensity and transmission of the new mode are much stronger than those of the modes in single defect cavity. These results will lay a theoretical foundation for the research of photonic crystal laser arrays and sensors.
(Invited) Enabling Low Temperature and High Quality Epitaxial Films for Current and Future Nodes
Authors: Hemkar Manish , Sanchez Errol , Mandrekar Tushar , Chowdhury Mohammad , Zhu Zuoming , Olsen Chris , Vellaikal Manoj , Chu Schubert
Published: February 2020

Device scaling and new applications in nanoelectronics present increasing challenges to epitaxy. Reducing thermal budgets, compatibility with novel materials, increasing topology and higher device density require new strategies for both the epitaxial film growth itself and substrate preparation. In this talk we will review specific problems for enabling low temperature epitaxial growth and discuss the impact of non-volatile contaminants beyond oxygen on Si and SiGe epitaxy. We will compare multiple potential solutions and discuss their utility and limitations.
(Invited) Large-Scale DFT Study of Ge/Si 3D Nanoislands and Core-Shell Nanowires
Authors: Miyazaki Tsuyoshi
Published: February 2020

The control of semiconductor nanostructures is increasingly valuable for the next-generation devices. Density functional theory (DFT) calculations have been playing important roles to clarify the structures of semiconductor surfaces at atomic scale. However, conventional DFT methods can usually treat systems containing less than a thousand atoms, and cannot treat the complex nanostructures. To overcome this problem, we have been developing a linear-scaling DFT code CONQUEST, which can perform structure relaxation or molecular dynamics of 100,000+ atom systems.

In this talk, I will present our large scale DFT study on (1) the growth of Ge 3D nanostructure of Si(001) surface and (2) the atomic and electronic structures of Si/Ge or Ge/Si core-shell nanowires. I will show that CONQUEST can calculate the strain distributions in the actual size of the nanostructures created experimentally. I will also report the unique properties of the electronic structure of Si/Ge or Ge/Si core-shell nanowires.

This work was done in collaboration with Prof. D. R. Bowler, Dr. Sergiu Arapan and Dr. J. Lin, and was partly funded by New Energy and Industrial Technology Development Organization of Japan (NEDO) Grant (P16010).
Highly n-Type Doped Ge and Gesn Wires Fabricated By Lateral Liquid-Phase Epitaxy
Authors: Watanabe Heiji , Tomita Takashi , Oka Hiroshi , Inoue Keitaro , Hosoi Takuji , Shimura Takayoshi
Published: February 2020

Germanium is a promising semiconductor material for both electronic and photonic devices owing to its high carrier mobility and pseudo-direct-bandgap properties. Recently, several approaches have been explored to modulate the energy band structure of Ge to direct bandgap, such as introducing tensile strain and Sn alloying. Highly n-type doping was also proven to enhance direct bandgap emission from the Ga-based materials. Moreover, Ge(GeSn)-on-insulator structures have attracted great interest to realize the monolithic integration of Ge-based optoelectronic devices. Although various methods, including solid-phase crystallization and wafer bonding, have been studied to form GOI and GeSnOI structures, these methods have difficulties achieving high-quality Ge and GeSn layers. In this study, we fabricated tensile-trained single-crystalline local GOI and GeSnOI structures by lateral liquid-phase epitaxy (LLPE), in which amorphous Ge and GeSn wires surrounded by SiO2 layers but partly connected to the Si seed regions were melted to induce lateral growth in the micro-crucibles. Biaxial tensile strain (0.3 – 0.4%) was spontaneously induced by the large difference in the thermal expansion coefficients between Ge(GeSn) wires and Si substrates. Moreover, whereas n-type doping of Ge-based materials is generally difficult because of the high diffusivity and low solid solubility of dopant atoms, highly n-type doping can be achieved in the LLPE method by incorporating Sb atoms into the initial amorphous Ge and GeSn layers. Our micro-photoluminescence spectroscopy study revealed that direct gap emission was enhanced more than 30 times than that of reference Ge substrates at room temperature and that the emission intensity increased with the decrease in measurement temperature, indicating a significant increase in electron density at the Brillouin zone center due to high Sb doping. Moreover, Fabry-Pérot resonator made of the highly doped Ge and GeSn wires showed clear resonance peaks even at room temperature.
(Invited) Raman Stress Measurements at the Nanoscale
Authors: Nuytten Thomas , Bogdanowicz Janusz , Witters Liesbeth , Eneman Geert , Hantschel Thomas , Schulze Andreas , Favia Paola , Bender Hugo , De Wolf Ingrid , Vandervorst Wilfried , van der Heide Paul
Published: February 2020

In semiconductor technology, strain can be used as a concept to improve the mobility of the charge carriers in the channel region and boost the performance of the eventual device. Control over the precise strain levels in confined volumes is difficult and non-destructive local stress measurements remain a challenge for the semiconductor industry. Recently however, it was found that a periodic array of semiconductor fins can act as a photonic crystal where the incident light is focused into the channel material and light transmission into the surrounding oxide is forbidden. This confines the excitation light into the region of interest and enhances the Raman scattering over orders of magnitude. At the same time, the coupling of light into the surrounding material is blocked resulting in screening of parasitic signals coming from, for instance, the substrate. The result is that even though the region of interest makes up only a small fraction of the total probed volume, it dominates the Raman spectra. As such, this nanofocusing of light has re-enabled the application of Raman spectroscopy for the purpose of stress and composition measurements in structures far beyond the diffraction limit. Additionally, the reliable Raman characterization of anisotropic stress profiles requires the independent detection of TO and LO phonons, which is achieved through the use of a high-NA objective for the Raman microscope. In this work we show how this approach can be combined with intrinsic enhancement effects to reach quantitative stress metrology without the need for additional sample preparation. As a demonstration, measurements of the anisotropic biaxial stress along and across finFET structures with channel widths down to 20 nm are discussed. These fins have been designed to have uniaxial stress in the direction of the channel in order to enhance the transport properties, but our measurements show that a small but non-zero compressive stress component is also present in the direction across the channel. The results were validated using nano-beam diffraction measurements confirming the trends observed with Raman. This indicates that the combination of high-NA sample excitation and nano-focusing of the light into the sample results in quantitative stress measurements at the nanoscale using a non-destructive optical technique.

FIGURE 1. Raman scan along a 20 nm-wide finFET channel showing anisotropic biaxial stress components along with the scattering intensity.

Figure 1
(Invited) Composition and Strain Engineering of New Group-IV Thermoelectric Materials
Authors: Kurosawa Masashi , Imai Yukihiro , Iwahashi Taisei , Takahashi Kouta , Sakashita Mitsuo , Nakatsuka Osamu , Zaima Shigeaki
Published: February 2020

Sequential integration of thermoelectric generators (TEGs) on a silicon wafer is essential for next-generation electronics such as internet-of-things sensing network as an energy-harvesting device. A guideline of thermoelectric performance is defined as dimensionless figure of merit, zT=S2

σT/κ, which is calculated from Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), and absolute temperature (T). Germanium tin (Ge1
−

x
Sn
x
) binary alloys theoretically possess a low κ [1] and a high σ [2], implying that Ge1
−

x
Sn
x
enables high-performance TEGs. In our previous study on the thermal conductivity of Ge1
−

x
Sn
x
epitaxial layer grown on (001)-oriented Ge [3], it was revealed that a very low κ of 2.0 W/mK was obtained for a Ga-doped Ge0.929Sn0.071 epitaxial layer. The value is at least 77 and 30 times lower than that for bulk-Si (156 W/mK) and bulk-Ge (60 W/mK) [4], respectively, and same order with that for amorphous Si (1−2 W/mK) [5]. However, thermoelectric properties of the epitaxial layers could not be clarified because the underlying substrates were not electrical insulators.

It is therefore, in this study, we aim to reveal thermoelectric properties of Ge1
−

x
Sn
x
epitaxial layers with a wide range of Sn contents grown by low-temperature molecular beam epitaxy. Here, semi-insulating wafers of Si, GaAs, and InP were used as a substrate in order to isolate electrically from the substrates. Combined with the results for the polycrystalline films, we will establish a guideline for enhancing the zT value in narrow band-gap group-IV materials.

Acknowledgments: This work was partially supported by Grants-in-Aid for Scientific Research (S) (Grant No. 26220605) and Young Scientists (A) (Grant No. 17H04919) from JSPS in Japan and PRESTO (Grant No. JPMJPR15R2) from JST in Japan.

References: [1] S. N. Khatami and Z. Aksamiji, Phys. Rev. Appl. 6, 014015 (2016). [2] K. L. Low et al., J. Appl. Phys. 112, 103715 (2012). [3] M. Kurosawa et al., “Thermophysical characterizations of Ge1
−x
Sn
x
epitaxial layers aiming for thermoelectric device,” 9th International Conference on Silicon Epitaxy and Hetero-structures (ICSI-9), Montreal, Canada, 4.4.1, May 21, (2015). [4] C. J. Glassbrenner and G. A. Slack, Phys. Rev. 134, A1058 (1964). [5] D. G. Cahill et al., J. Vac. Sci. Technol. A 7, 1259 (1989).
(Invited) Low-Resistance Ferromagnet/Germanium Schottky-Tunnel Contacts for Spintronic Applications
Authors: Hamaya Kohei , Naito Takahiro , Tsukahara Makoto , Yamada Michihiro , Sawano Kentarou
Published: February 2020

For CMOS-compatible spintronic devices, electrical spin injection and detection in silicon (Si) [1] and germanium (Ge) [2] have been explored. Due to the conductivity mismatch problem [3], the insulator tunnel barriers such as MgO [1,2] were generally used for electrical spin injection from ferromagnets (FM) into Si and Ge, where the resistance area products (RA) values of the tunnel contacts were approximately 104 Ωμm2 (10-4 Ωcm2) [1,2]. However, these contacts with large RA values cannot be utilized as a source and drain for spin-based MOS transistors [4]. If spintronic technologies are integrated with Ge-CMOS and/or Ge-based photonics, novel spin-injection techniques with low- RA contacts should be developed.

In this paper, we have developed high-quality FM/n-Ge heterointerfaces with a delta-doped Ge interlayer for low-RA Schottky-tunnel contacts [5,6]. Because of the tunable doping concentration of the delta-doped layer, we can obtain the contacts with relatively low-RA values of ~102 Ωμm2 (~10-6 Ωcm2) for n-Ge. Using the Schottky-tunnel contacts, we can observe lateral transport of pure spin currents in n-Ge up to room temperature [7]. In addition, by using the low-RA contacts, the two-terminal magnetoresistance effect can be observed even at room temperature [8]. Although we should further reduce the RA value as low as possible, our results with the low-RA Schottky-tunnel contacts will open a road to integrate the spintronic technologies into next generation Ge-based devices on the Si platform.

[1] T. Suzuki et al., Appl. Phys. Exp. 4, 023003 (2011).

[2] Y. Zhou et al., Phys. Rev. B 84, 125323 (2011).

[3] G. Schmidt et al., Phys. Rev. B 62, R4790 (2000).

[4] M.Tanaka and S. Sugahara, IEEE Trans. Electron. Devices 54, 961 (2007).

[5] M. Yamada, KH et al., Mat. Sci. Semicon. Proc. 70, 83 (2017).

[6] Y. Fujita, KH et al., Phys. Rev. Appl. 8, 014007 (2017).

[7] M. Yamada, KH et al., Appl. Phys. Exp. 10, 093001 (2017).

[8] Y. Fujita, KH et al., (submitted).
(Invited) Light Emission from Group IV Semiconductors
Authors: Bakkers Erik P.A.M.
Published: February 2020

Light emission from Si would revolutionize semiconductor industry since it allows integration of electronic and optical functionality in one main technology platform. This has, however, been impossible due to the indirect band gap of Si. In this talk I will discuss 2 different approaches, using unique properties of nanowires, to realize light emission from Si-based compounds.

In the first route, we focus on the fabrication of defect-free GeSn compounds. GeSn has been shown to exhibit a direct band gap at Sn concentrations above 12.5% in the infrared part of the spectrum (around 0.5 eV). In the nanowire geometry, the GeSn/Ge lattice strain can be effectively relieved in the radial direction, which is exploited to grow Ge/GeSn core shell nanowires with high (13%) Sn content. The core/shell nanowires are free of dislocations and therefore show a very high photoluminescene internal quantum yield at room temperature. In this talk the growth mechanism, the structural properties and the temperature dependent optical properties are studied.

In the second route, we concentrate on Si and Ge with the hexagonal (2H) crystal structure, which have been predicted to have a direct band gap with an energy close to the telecom wavelength. Here, we employ crystal structure transfer, in which we use wurtzite GaP as a template to epitaxially grow SiGe compounds with the hexagonal crystal structure. We show that with this method we can grow defect free hexagonal SiGe shells and branches with tunable Ge concentration. The structural and optical properties of these new crystal phases will be discussed. We show room temperature photoluminescence from hexagonal SiGe.
(Invited) Tubular Thermoelectric Generator for Enhanced Power Generation
Authors: Hussain Muhammad Mustafa , Singh Devendra N. , Kutbee Arwa T , Ghoneim Mohamed T. , Hussain Aftab M.
Published: February 2020

Thermoelectric generators are interesting energy harvesting option due to its clean nature, silent operation and it harnesses the power from otherwise wasted heat. While most of the research has been directed toward high thermoelectric performance based material innovation, we have focused on its architecture and how to connect hot and cold ends when they are far apart. From that perspective, we have devised an effective integration strategy to roll-up otherwise ultra-thin layers of thermoelectric materials to form tubular architecture and to integrate them in array for high power thermoelectric generator development. We have used widely used thermoelectric materials such as bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3). We also offer an analytical methodology to deduce the effective mechanics of the strain associated with the thermoelectric materials and the used polymeric materials (as stressor and as support layers). Experimentally we have shown seamless 4 cm (and further expandable) tubular arrays of thermoelectric piles. Such a long length allows us to connect to far apart hot and cold end for higher power generation as we also maintain higher temperature difference for longer time. We also compare its effectiveness with solid slab and wire of the same tube from its performance and cost perspective. At the initial stage we report up to 5 μW (8 pairs of p and n-type thermopiles) through a temperature difference of 60 °C. We also show how this can be improved further and potential integration strategy with 2D material system.
Superconformal Cu Electrodeposition
Authors: Moffat Thomas P. , Liu Guokun , Zou Shouzhong , Ou Yang Liang Yueh , Braun Trevor , Walker Marlon , Wheeler Daniel , Richter Lee , Josell Daniel
Published: February 2020

State of the art manufacturing of semiconductor devices involves electrodeposition of copper for device wiring and chip stacking. The success of the electroplating process depends on electrolyte additives that affect the local deposition rate to yield void-free superconformal, or bottom–up filling of trenches and vias that comprise 3D interconnects. Quantitative chemical process models have been shown to be effective in describing the filling of high aspect ratio features that range from nanometers (on-chip wiring1) to micrometers (through-silicon-vias2) to millimeters (printed circuit boards) in scale. Nevertheless, much remains to be known about the molecular nature of the additives and the competitive, co-adsorption dynamics involved in both suppression and acceleration of metal deposition. Accordingly, a variety of surface science tools, such as scanning tunneling microscopy (STM) and surface-enhanced infrared absorption spectroscopy (SEIRAS) are being used to investigate additive function. This lecture will focus on recent SERIAS experiments that reveal the important role of adsorbate water interactions, i.e. hydrophilicity, in the design and operation of additives used for superconformal film growth.
A Study on the Diamond Wear Mechanism of Conditioner during W CMP in 3D NAND
Authors: Oh Dong Won
Published: February 2020

The memory device fabrication system has already applied a lot of CMP processes for various purposes. As memory device integration increased, more CMP processes are needed. Typically CMP process can be divided into Oxide CMP, W CMP, Cu CMP, etc. These CMP technologies are important solution that can be used as memory mass production technologies develop.

3D NAND devices are being highlighted and developed as a way increase the integration method, due to the nature of its structures, 3D NAND device needs various CMP processes. In particular, the number of W CMP processes has several times multiplied over than 2D devices. In addition, more W CMP processes will be required as the device's generation evolves. However, a period of change pad, in W CMP process, is shorter than other CMP processes. Hence, it will lead to lower productivity and higher costs in fabrication system. Productivity and cost in mass production system are very important competitiveness. Thus, it is necessary to make improvements to the same level as others. There are several reasons why the W CMP process has a shorter pad replacement cycle in the 3D NAND device. One of the causes is that slurry directly or indirectly affects the wear of diamonds on conditioner. As a result, ability of polishing is decrease, pad and conditioner have no choice but to replace.

In this study, we figured out which components of W slurry are being applied by W CMP in the 3D device and how they affect the wear of diamonds. And we have carried out experimental study to improve it and we will discuss the results.
Size Estimation of Copper Plating Additives Using a High-Speed AFM
Authors: Ikuta Ryo , Akita Takanori , Hayase Masanori
Published: February 2020

Filling copper into TSVs (Through Silicon Via) is achieved by copper electroplating in an acid copper sulfate bath with combination of several additives. The additives are generally classified into accelerator, suppressor or leveler. It is assumed that suppressor and leveler cover a plating surface and both additives suppress electrodeposition, while accelerator obstructs suppressor adsorption and prevents the suppression of electrodeposition. However, the filling mechanism is not well understood. For the TSV filling, we consider that leveler has an essential role because extreme bottom-up deposition is available with only leveler addition though significant non-uniformity is observed. We assume that the extreme bottom-up is caused by diffusion-adsorption based mechanism. To achieve more detailed understanding, mathematical modeling and numerical simulation are discussed, but there are many unknown parameters to perform the simulation. Additive size is one of important parameters we want to know, because coverage of suppressing additives adsorbing on the plating surface dominates the electrodeposition rate. Therefore, in this study, sizes of additives were attempted to measure in an aqueous condition using an AFM (Atomic force microscope).

High-speed AFM (Research institute of biomolecule metrology Co., Ltd. , Japan ) is a good tool for measuring soft material in an aqueous solution, and we employed it for the observation of the plating additives. Figure 1 shows an example image. PEG (Polyethylene glycol) of Mw. 3000 was observed on a mica substrate. The high-speed AFM can take one frame image very quickly (maximum 20 frames per sec.), but each image is not that reliable as shown in figure 2 which shows an identical particle observed by the high-speed AFM. Averaging was needed to determine the particle size. Probe tip of the AFM was also problematic. Less than 10nm of tip radius was guaranteed by the manufacturer, but precise shape was unknown. Then, we decided to measure DNAs (deoxyribonucleic acid) as a reference, and the tip radius of the probe was estimated to be typically 5.5nm. With image averaging and probe tip compensation, additive radiuses were calculated assuming hemisphere shape. Radiuses of PEGs of Mw. 3000 and 20,000 were estimated to be 1.8nm and 3.3nm, respectively. Interestingly, radius of PEI (Polyethylene imine) of Mw. 10,000 was estimated to be 1.3nm which was smaller than PEG of Mw. 3000.

Figure 1
Electroless Deposition of Co-W-P on Polyimide Films for Enhancing the Adhesion of Followed Electroplated Copper Film
Authors: Hsieh Yun-Zhen , Dow Wei-Ping
Published: February 2020

Recently, electronic products pursue nanoscale, lightness, thinness, miniaturization and multi-function products, so the demand for flexible printed circuit board (FPCB) and rigid-flex PCB has grown substantially. Polyimide (PI) is dynamic and rollable products, because it has thin and flexible characteristics, also, it has high thermal stability, good mechanical strength. However, the line width and space is about five and five micrometer on FPCB, so FPCB with fine pitch would be manufactured by semi-additive process (SAP) PI-SAP will not use copper foil anymore. Instead, PI will directly be metallized by electroless deposition and then electroplating to form conducting lines. Because the copper line on the PI surface is very thin and micro-scaled, the peeling strength is a very critical target in this metallization. In this study, we used an overall wet process to directly metallize the PI film. Electroless deposition of Co-W-P films was performed on a PI film as seed and barrier layer followed by copper electroplating. The aim of our work was to develop an optimal electroless plating composition and process parameters to increase the adhesion between the Co-W-P layer and the PI film. Scanning electron microscopic (SEM) examination shows that the surface morphologies of Co-W-P films. FE-TEM and XPS confirm that Co-W-P films deposit can serve as a perfect diffusion barrier layer to prevent Cu diffusion from the surface layer into the PI film. SEM with energy dispersive spectroscopy (SEM/EDS) data indicates the composition of Co-W-P film. Tensile strength measurement tool can explain the adhesion between the Co-W-P layer and the PI film.

Keywords:

Electroless deposition, Barrier layer, Co-W-P thin films, Polyimide

Reference:

[1] R. Tarozaitė, Z. Sukackienė, A. Sudavičius, R. Juškė nas, A. Selskis, A. Jagminienė, E. Norkusė, Materials Chemistry and Physics, 117 (2009) 117-124.
Characterizing Thermal Transport to Inform Process Design
Authors: Marconnet Amy
Published: February 2020

Ultimately, as electronic devices shrink, thermal properties become increasingly important to prevent failure. The thermal properties of materials are inextricably linked to the structure and quality of the material, which are governed by the synthesis and processing conditions. In particular thermal conductivity is significantly reduced by grain boundaries and defects, and can be modified by the introduction of impurities and dopants. This talk will focus on evaluation of thermal properties as a metric to inform processing conditions. In particular, measurements of thermal conductivity can provide insight into the quality of the materials synthesized with plasma technologies. In particular, thermoreflectance methods enable optical non-contact measurement of cross-plane thermal conductivity and interface resistances between successive layers of materials, while most measurements of in-plane thermal transport require microfabrication. Non-destructive thermal characterization could provide a new avenue for quality control during depositions.
(Charles W. Tobias Young Investigator Award) Overcoming the Materials Science Challenges to Nanocarbon Electronics
Authors: Arnold Michael S
Published: February 2020

In this presentation, I will present on 2 recent advances in nanocarbon electronics from my laboratory: (1) We have pioneered a scalable approach for assembling parallel arrays of ultrahigh purity (Fig. 1) semiconducting nanotubes. This approach has allowed us to create carbon nanotube field effect transistors (FETs) with current density that exceeds Si and GaAs, for the first time, which has been a goal of the nanoelectronics field for 20+ years. (2) We have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics on the surface of Ge(001) single crystal wafers via CH4 chemical vapor deposition. This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are as narrow as 1.7 nm and are self-orienting, self-defining, and have smooth edges. The ribbons exhibit exceptional transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms.

Both aspects of this work have implications towards extending Moore’s Law, creating ultra-low energy logic circuits, developing higher bandwidth RF communication devices, and realizing next-generation FET based sensors.

[1] Joo et al. Langmuir (2014); Brady et al. APL (2014); Brady et al. ACS Nano (2014); Brady et al. Science Advances (2016); Jinkins et al. Langmuir (2017); Brady et al. J. Appl. Phys. (2017); Jinkins et al. In Preparation (2018).

[2] Jacobberger et al. Nature Comm. (2015); Jacobberger et al. ACS Nano (2017); Way et al. Nano Lett. (2018);

Fig. 1 SEM image of aligned semiconducting carbon nanotube (CNT) array FET.

Figure 1
(Invited) Paper Based Wearable Standalone Wheezing Sensor - Not a Low Dimensional System
Authors: Hussain Muhammad Mustafa , Khan Sherjeel M , Nassar Joanna M , Qaiser Nadeem , Bahri Meznan , Buttenhoff Kristin
Published: February 2020

We present a sensor made from paper using a Do-It-Yourself (DIY) integration strategy that can be attached to the human chest like a stethoscope for real-time asthma symptom monitoring. The sensor is designed such that it resonates around the dominant frequency of wheezing (a common symptom of asthma). This helps the sensor produce large output signals, thus it can be directly integrated with a microprocessor without the need for signal amplification circuits. Matched filtering is used to extract and detect features from the acquired chest sounds for wheeze detection. The sensor successfully detects wheezing from the human chest, even when subjected to background noise and other sounds made to imitate the lungs. The sensor is connected to a smartphone via Bluetooth, enabling signal processing and further integration into digital medical electronic systems based on the Internet of Things (IoT). Bending, cyclic pressure, heat, and sweat tests are performed on the sensor to evaluate its performance under the harsh conditions of real-life scenarios.