bluuebunny/crossref_metadata_2025 huggingface dataset:
Engineering the Magnetic Anisotropy of Electrodeposited Multilayers
Authors: Shirtcliffe James , Schwarzacher Walther
Published: February 2020

Induced magnetic anisotropy is important in numerous technical applications. An in-plane easy axis may be induced in an electrodeposited alloy film by deposition in an applied field. The origin of this anisotropy is thought to be preferential alignment of pairs of atoms of the same species, and the effect is generally small compared to magnetocrystalline anisotropy or surface anisotropy. Despite the phenomenon being well established, many open questions remain, including what happens to the induced anisotropy as the film thickness is reduced, or what the minimum applied field required to induce anisotropy is. We have studied the induced anisotropy in electrodeposited Fe-Co-Ni(Cu)/Cu multilayers, and find that induced anisotropy is still observed for layer thicknesses down to 2nm. We have also shown that the field required to induce anisotropy in this system is extremely low. Furthermore, it is possible to engineer the anisotropy of the film as a whole by changing the direction of the applied field during growth.
Utilization of Hard X-Ray Photoelectron Spectroscopy for Silicon-Based Negative Electrodes Buried within Solid Electrolyte Interphase
Authors: Masuda Takuya , Aoki Nana , Iwai Hideo , Yoshikawa Hideki , Kondo Toshihiro , Uosaki Kohei
Published: February 2020

Silicon is one of the alternative materials for currently used negative electrodes in Li-ion batteries because of its high lithium insertion capability. However, volume expansion of silicon-based active materials accompanied with the lithium insertion is a severe problem towards their practical application since this volume expansion can destroy both the silicon-based material itself and electrical connection composed of binders, current collectors and the silicon-based materials. Hence, understanding of the lithium insertion is essential to design the silicon-based negative electrode with a high tolerance to the volume expansion. However, these negative electrodes are buried with a thin film, so-called, a solid electrolyte interphase (SEI), which often prohibits the characterization of electrode surfaces.

X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique which can analyze the composition and oxidation states of elements within the sample surfaces, and often combined together with destructive ion-sputtering methods to obtain their depth profile. XPS utilizing hard x-rays, so-called HAXPES (Hard X-ray Photoelectron Spectroscopy), can be a complementary non-destructive technique to analyze a deeper region from the surface. Recently, we constructed an in-house HAXPES equipped with a Cr Kα (5415 eV) source for electrode materials buried within the SEI. Here, we compared “destructive” Ar ion sputtering-XPS and “non-destructive” HAXPES to characterize the depth profile of the SEI-covered Si(111) negative electrodes with and without lithium insertion.
(Invited) Control of Internal Plasma Parameters Toward Atomic Level Processing
Authors: Sekine Makoto , Tsutsumi T , Fukunaga Y , Takeda K , Kondo H , Ishikawa K , Hori M
Published: February 2020

Plasma processes have been indispensable core technologies to manufacture ultra-large integrated circuits (ULSIs) and variety of devices, including MEMS and bio sensors. In order to develop the next generation devices, advancing of the plasma processes should be needed. However, the plasma processes have been developed based on the trial-and-error tuning of external parameters, such as electric power, gas pressure and gas flow ratio. Towards the surface processing with atomic level accuracy with extremely low damage, the precise control of internal parameters that actually define the surface reaction has become more important. Particularly, it is necessary to control the energies of species and eventually their chemical reactions on the surface directly. Furthermore, the spatiotemporally control of chemical species in gas phase in the processing is the key issue to obtain the high performance as well as establishment of the plasma science for manufacturing.

We have developed an autonomous plasma manufacturing system, which is able to measure radical densities with a compact monitoring system and control them at optimum values in real time. The spatiotemporal fluctuation of species in the plasma affects much on the surface reactions, which is fatal to fabricate nano-size, atomic level structures. Then, we can make nano-scale etching with an ultrahigh precision by employing the autonomous plasma system. [1] The plasma induced damages on the organic material and the method to realize the precise etching were clarified.

On the other hand, the wafer temperature has influenced considerably the process performances for the precise control of surface reactions. However, it was not dynamically controlled because the wafer temperature rises abruptly from the plasma ignition. Interactions between the plasma and the material surface at the beginning and the end of processing need to be considered as entirely different conditions. The temperature change should be minimized and kept in a specific range throughout the processing. We developed a feedback control system based on actual temperature monitoring in a real time by dynamical changes in plasma discharge on-off intervals. [2]

This presentation will emphasize the importance of the internal parameter control of species together with a wafer temperature in the plasma processing for the atomic level control and discuss the advanced plasma processes for ULSIs and GaN semiconductors. [3]

[1] H. Yamamoto, et al., J. Appl. Phys. 51 (2012) 016202.

[2] T. Tsutsumi, et al., Appl. Phys. Lett. 103 (2013) 182102.

[3] Z. Liu, et al., Jpn. J. Appl. Phys. 54 (2015) 06GB04.
Low Temperature Atomic Layer Deposited TiO2 Compact Layers for Planar Perovskite Solar Cells
Authors: Kim In Soo , Haasch Richard , Cao Duyen , Farha Omar K. , Hupp Joseph T. , Kanatzidis Mercouri , Martinson Alex B. F.
Published: February 2020

Titanium dioxide (TiO2) thin films have been utilized in a wide range of applications in optoelectronics and solar energy conversion. In particular, TiO2 has been exclusively used in photovoltaic (PV) devices and photoelectrochemical (PEC) cells owing to its ability to efficiently transport electrons and passivate photoactive materials against aqueous media. However, TiO2 exhibits optimal transport properties in the crystalline anatase phase, and thus requires a high temperature annealing step at 500 °C, which significantly limits its application in temperature sensitive substrates (e.g. PET) or active materials (e.g. organic-inorganic hybrid perovskites). Moreover, while high resistance of TiO2 films necessitates the need for ultrathin films to reduce series resistance in PV devices, the synthesis of ultrathin pinhole-free TiO2 films remains a challenge through conventional deposition methods. To address these issues, TiO2 compact layers for planar perovskite PV devices were deposited via atomic layer deposition (ALD) – a chemically diverse vapor phase deposition technique with the capability to synthesize ultrathin pinhole-free films.

We have investigated the influence of low temperature atomic layer deposited (ALD) compact TiO2 layers as a function of post-treatment (i.e. O3, UV-O3, 500 °C) on the performance of planar perovskite PV cells. The performance of devices indicated variations primarily in open circuit voltage (VOC) and fill factor (FF) upon various forms of post-treatment. Changes in the VOC was mainly associated with the density of states within the bandgap of TiO2 as confirmed by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Also, low temperature post-treatment (O3 and UV-O3) resulted in reduced FF compared to the conventional high temperature annealing treatment as a consequence of decreased shunt resistance. We attribute this phenomena to the amorphous nature of the low temperature post-treated compact TiO2 layers providing channels for hole conduction. However, the devices fabricated with UV-O3 treated TiO2 compact layers resulted in a comparable overall performance compared to those fabricated with the conventional post-annealing process at 500 °C, opening possibilities for its application in temperature sensitive substrates as well as active materials.
The Origin of the Oxygen Redox Activity in Layered and Cation-Disordered Li-Excess Cathode Materials
Authors: Seo Dong-Hwa , Lee Jinhyuk , Urban Alexander , Ceder Gerbrand
Published: February 2020

With increasing complexity of technology comes a demand for higher-energy density Li-ion batteries, which requires high-energy density cathode materials. Reversible oxygen redox in Li-excess materials can substantially expand the search space of high capacity and energy density cathodes, because it can deliver excess capacity beyond the theoretical transition metal (TM) redox capacity, reducing the necessity of heavy and expensive TM ions.[1-4] Nevertheless, the structural and electronic origin of the oxygen redox process is not understood, preventing the rational design of better cathode materials with oxygen redox.

In this talk, we explain how specific chemical and structural features in layered and cation-disordered Li-excess cathode materials introduce labile oxygen electrons that can be easily extracted and participate in the practical capacity of these materials. Our ab initio calculations demonstrate that Li excess and cation disorder create unhybridized oxygen 2p states in lithium-metal-oxide cathodes that promote oxygen redox, which can create extra capacity beyond the TM redox capacity and lead to peroxo-like species when local distortion in the chemical bond is allowed (Figure 1).[5] Furthermore, we explain how this specific oxygen redox process competes with the TM redox, providing clear guidelines for the design of high-capacity cathodes with optimized TM or O redox.

References

[1] H. Koga, L. Croguennec, M. Ménétrier, K. Douhil, S. Belin, L. Bourgeois, E. Suard, F. Weill, C. Delmas, J. Electrochem. Soc.
160: A786-A792 (2013).

[2] M. Sathiya, G. Rousse, K. Ramesha, C.P. Laisa, H. Vezin, M.T. Sougrati, M.L. Doublet, D. Foix, D. Gonbeau, W. Walker, A.S. Prakash, M. Ben Hassine, L. Dupont, J.M. Tarascon, Nature Mater.
12: 827-835 (2013).

[3] N. Yabuuchi, M. Takeuchi, M. Nakayama, H. Shiiba, M. Ogawa, K. Nakayama, T. Ohta, D. Endo, T. Ozaki, T. Inamasu, K. Sato, S. Komaba, Proc. Natl. Acad. Sci.
112: 7650-7655 (2015).

[4] J. Lee, D.-H. Seo, M. Balasubramanian, N. Twu, X. Li, G. Ceder, Energy Environ. Sci.
8: 3255-3265 (2015).

[5] D.-H. Seo, J. Lee, A. Urban, R. Malik, SY. Kang, G. Ceder, Nature Chem. in press (2016).

Figure 1
Synthesis of Layered MoS2 with Enlarged d-Spacing and Its Carbon Composite By Substrate-Induced-Coagulation Coating Method As Anode Materials for Lithium-Ion Batteries
Authors: Han Joong-Hee , Kahr Jürgen , Hamid Raad , Han Sung-Hwan , Ahn Do-Young , Trifonova Atanaska
Published: February 2020

2D layer structured molybdenum disulfide (MoS2) has been considered as an alternative next generation anode material over graphite, hard carbon and metal alloys, because MoS2 is structurally analogous to graphite (0.335nm) and has the interlayer d-spacing of 0.615nm while exhibiting two or three times the specific capacity of graphite.

We will show how electrochemically active molybdenum disulfide (MoS2) with extended interlayer d-spacing was successfully prepared by the solvothermal synthesis method in an ethylene glycol-based mixed solvent at 200oC for 24h under an inert gas atmosphere. Then the prepared MoS2 samples were thermally annealed at various temperatures (300oC, 500oC, 800oC) to remove ethylene glycol from between the MoS2 nanosheets and to tune the d-spacing distance. The main redox reaction is described as Li2S ↔ 2Li+ + S + 2e-, and it suggests that the electrical conductivity of the MoS2 electrode must be enhanced by impregnation with carbonaceous materials to counteract the insulating properties of the sulfur. Therefore, the as-prepared MoS2 powders were surface- modified with nano-carbons (e.g. graphite and graphene) by the substrate-induced coagulation coating process and subsequent annealing at 600oC for 5h under the argon gas environment. The surface-modified carbon-MoS2 composite had a lithium diffusion coefficient (DLi: 1.08x10-6 cm2/s) during charging and discharging as compared to the as-prepared MoS2 (DLi: 4.14x10-7 cm2/s); the cell with the modified MoS2also exhibited higher capacity with a good capacity retention.

The carbon-modified MoS2 electrode showed an initial capacity of 1150mAh/g and an average specific capacity of around 900 mAh/g, comparing favorably to the as-prepared MoS2 (700mAh/g). The carbon-MoS2 composite showed a higher capacity with good capacity retention and higher rate capability. The cells were electrochemically characterized by cyclic voltammetry, rate capability measurements, electrochemical impedance spectroscopy, lithium ion diffusion coefficient (DLi) measurement, differential capacity measurements, and in-situ electrochemical XRD measurement.

In particular, the volumetric dilatation of the electrode materials during repeated cycles was monitored by in-situ electrochemical dilatometry. It was observed that the dilatations occur during charging /discharging, which corresponds to lithium inter-/deintercalation reactions at redox potentials of reduction at 1.1 V and oxidation at 1.6 V, 2.2V, respectively. The improved electrochemical properties of MoS2 tuned by the enlargement of the d-spacing and by the surface modification make it possible for MoS2to be used as a promising anode material for lithium-ion batteries.
Critical Parameters Governing Energy Density of Li-Storage Cathode Materials Unraveled By Confirmatory Factor Analysis
Authors: Han Su Cheol , Jeong Jae Hyang , Park Chun Guk , Pyo Myoungho
Published: February 2020

Up to date, a devotion to high energy density (ED) Li ion batteries (LIBs) has been carried out via rather one-by-one confirmation of a relationship between electrochemical properties and materials traits without a general, reliable, and comprehensive model. Therefore, although such a scrutinized investigation on a specific cathode material has elicited significant scientific findings, the sensitive dependence of electrochemical properties on crystallographic and elemental properties made the generalization of such findings difficult. Density functional theory (DFT) calculation could compensate for these shortcomings to some extent. However, DFT is also far from complete in understanding the overall trend of reported experimental data, indicating a necessity of a new systematic approach that can prospect a whole experimental data a quantum-leap innovation in material designs. In this work, we data-mine the cathode materials of LIBs through confirmatory factor analysis (CFA). Both layered and spinel structures are data-mined separately. By collecting accurate structural and electrochemical data of the both types, we prepared a systematic data set and utilized it in the CFA through principal component analysis (PCA) and a simple linear regression. The data sets that we adopt for CFA are huge in size, i.e., 19 X 40 for layered structure and 16 X 33 for spinel. The CFA reveals that, while the control of a few crystallographic parameters is critical for layered cathodes of high ED, some of intrinsic properties of constituent elements govern the ED in spinel structures. The CFA also disclose that the cyclability of the both is irrelevant to the parameters we selected, implying that the electrochemical conditions during C-D are crucial factors for the least capacity (Q) fading. The acquisition of these conceptual understandings with human cognition capability is practically impossible without a smart statistical approach like CFA.
Electrochemical Characteristics of Coal Tar Pitch Prepared By Chemical Activation for Lithium Ion Battery
Authors: Lee Jong Dae , Hwang Jin Ung
Published: February 2020

In recent years, carbon-based materials have been extensively investigated as an anode material for Li-ion battery (LIB). Because of their low material cost, abundance, nontoxicity and good capacity, carbon materials have been considered promising materials for LIB anodes in portable electronic devices and electric/hybrid vehicles. Despite these advantages, the practical application of carbon-based materials in many electronic device and electric/hybrid vehicles is still limited by its poor
electrochemical performances
. 
To enhance these electrochemical performances, we have performed the surface modification of coal tar pitch (CTP) by the
chemical activation with KOH and K2CO3

. Coa
l tar pitch (CTP) as an industrial by-product, composed of cyclical hydrocarbons of various molecular weights and configurations.
The preparation method has been optimized through the analysis of diverse experimental variables. The results obtained confirm the importance of the activating chemical agents to CTP ratio and the flow rate of gas during carbonization on the development of porosity. In addition, it shows that chemical activation with
KOH and
K2CO3

can be successfully used to develop CTP with high surface area and mean pore size.

 
In this study, the effect of
activating chemical agent
/CTP weight ratio, CTP particle size and vinylene carbonate (VC) as an electrolyte additive on electrochemical performances was investigated. The prepared modified CTP was analyzed by BET, XRD, FE-SEM and XPS. Also the electrochemical performances of modified CTP as the anode were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests in the electrolyte of LiPF6 dissolved in organic solvents(EC:DMC=1:1 vol%). 
The coin cell using modified CTP(
KOH
/CTP =
1
:
5
in weight) has better initial capacity (421 mAh/g) than that of other composition coin cells. Also, modified CTP anode appeared a high capacity of 4
11
mAh/g on the second cycle and the retention rate capability of 2C/0.1C was
83
% after 30 cycle. It is found that prepared CTP anode showed improved cycling and rate capacity performance.
Microstructure and Electrochemical Properties of the Si-M(M : Cr, Ni) Anode for Lib According to the Si Amount
Authors: Lee SeongHyeun , Kim Sung-soo
Published: February 2020

To enhance the cyclic performance of silicon binary alloy used in LIB as anode material, we used active/inactive nanocomposite. Active/inactive composite method is one of the methods to suppress silicon’s volume expansion. In this method active-Si particles are embedded in Inactive-matrix. Our previous results obtained using this method showed that Cr-Si alloy had better cyclic performance and fine microstructure than Ni-Si alloy which had dendritic structure. In this work we compared cyclic performance and microstructures of these alloys depending on the amount of Silicon. We design each alloy’s capacity using phase diagram and lever rule (356, 600, 900, 1,200 mAh/g). Silicon-Chromium (Cr-Si) and Silicon-Nickel(Ni-Si) nanocomposites were prepared using a melt-spinning method. Through the melt-spinning method, we can make alloy sample which has fine microstructure (structure size, < 100nm). Powder samples(D50 : ~20㎛) were prepared by Paint Shaker. Electrodes were prepared using Ketjen black carbon and PAI binder which is suitable for silicon alloy anode because of its good adhesive strength. So, it is able to bear stress caused from silicon volume expansion. We used PSA, ex-situ SEM, XRD to characterize samples and Coin cell test for electrochemical characteristic. Ex-situ SEM showed that each microstructure of Cr-Si (active-Si size : ~10nm) and Ni-Si has different behavior as the amount of silicon increases. These alloys were confirmed to have Active-Si and Inactive-Matrix (CrSi2 ,NiSi2) phases by ex-situ XRD measurement. Any other phases weren’t detected except these phase. Electrochemical tests show such characteristic features as all Cr-Si alloy has good Coulombic efficiency of more than 98% after 1st cycle. However, we couldn’t control the Ni-Si alloy’s electrochemical characteristic by the amount of Si.
Si-SiOx nanoparticles Synthesis for Lithium-Ion Battery Anode Material By Atmospheric Pressure Microwave Plasma
Authors: KIM Joon-soo , Jang Bo-yun
Published: February 2020

Si-SiOx nanoparticles with core-shell structure were synthesized by atmospheric microwave plasma using tetrachloride silicon. Crystalline Si core and amorphous SiOx shell could be controlled by various process conditions. In order to determine the Si-SiOx core-shell ratio for application to anode materials in lithium-ion battery, microstructures and electrochemical properties of synthesized Si-SiOx nanoparticles with various core-shell ratios were investigated. From a result of HR-TEM analysis, there are Si nanoparticles with thickness of 1~3 nm SiOx shell which are only native oxide layer on crystalline Si core. Typical electrochemical behaviour of Si such as high initial reversible capacity and poor retention was observed in those nanoparticles. The shell thickness of Si-SiOx nanoparticles affects the electrochemical properties such as first reversible capacity, retention. For example, nanoparticles with shell thickness of 10 nm exhibited the first reversible capacity of about 1,274 mAh/g and retention at 50th cycle of about 94.8 %. As a result, electrochemical properties could be controlled by the core-shell ratios of Si-SiOx nanoparticles.
Graphene Modified Feof Nano-Structured Hybrid As Cathode Materials for Li-Ion Battery
Authors: Liu Yadong , Yang Fan , Xin Le , Ren Yang , Sun Chengjun , Liu Yuzi , Xie Jian
Published: February 2020

Lithium-ion batteries (LIBs) are the major power sources for electronic and transportation applications due to their high specific energy, good cyclability and environmental friendliness. Intercalation compounds were commercially employed as the positive (cathode) electrode material. However, they have a limited capacity, which are not likely to meet the growing demand on specific energy and energy/power density. Transition-metal oxides, fluorides and oxyfluorides have attracted a lot of interest due to their ability to deliver high electrochemical specific energy arising from 2-3 electrons transferred. FeOF was proposed as a promising candidate1 because it has a high theoretical specific capacity, 885 mAh/g (3-electron process) and 590 mAh/g (2-electron process), leading to an exceptionally high specific energy of 1328 Wh/kg. However, the electrochemical performance of FeOF is drastically different in practice due to its low electronic conductivity and poor structure stability during charge/discharge cycling process.

To overcome these obstacles, conducting carbon matrices have been introduced to absorb the volume changes and to improve the structural stability of the electrodes. Graphene, a single−layer of sp2 carbon lattices, has been considered as one of the most attractive carbon materials for its excellent charge carrier mobility, mechanical robustness and thermal and chemical stability2. Our approach is to prepare a mixture of precursor of FeOF and graphene oxide in solution and to ensure a better bonding between FeOF and GO through a hydrothermal procedure. The resulted hybrid material showed much improved initial columbic efficiency and cyclability compared with the blank FeOF material. The initial specific capacity reached 621 mAh/g (Fig. 1) and the capacity retention was 78.9% (specific capacity 493 mAh/g) after 100 cycles at 0.1 C rate. It has been demonstrated that the performance improvement could be attributed to introduction of graphene which improved the electric conductivity and provide a substrate to stablize the FeOF particles by morphology observation and structure characterization. SEM (Fig. 2) and TEM were employed to observe the morphology change after introducing graphene. The structure evolution during charge/discharge process were also characterized by in situ XAS and high resolution XRD. The results showed that the graphene nano-sheets serve as substrates to stabilize the structure of FeOF and form a framework to stabilize the Fe clusters through bonding them to their original sites without migration. Thus, the FeOF/Graphene composite can keep the (de)lithiation reaction reversible during discharge and charge process.

Figure 1
Superior Li-Storage Performances of Liquid-Phase Exfoliated Two-Dimensional Gallium Sulfide Nanosheets/Single-Walled Carbon Nanotubes Flexible Composite
Authors: Zhang Chuanfang , Park Sang Hoon , Ronan Oskar , Harvey Andrew , Coleman Jonathan N , Nicolosi Valeria
Published: February 2020

we have demonstrated the facile production of porous, binder-free gallium sulfide (GaS) NS/SWCNT flexible composite films via a liquid-phase exfoliation/vacuum filtration approach. As a LiB anode material, the composite film exhibits excellent rate capability, high specific capacity (838 mAh g-1) and a remarkably high utilization of GaS NS (1161 mAh g-1), demonstrating electrochemical performances competitive with those of other reported 2D MC-based electrode systems. This work opens up vast opportunities for other families of MC NS to be scalably processed into porous, binder-free, flexible conductive thin films and composites with a broad range of applications such as flexible electronics and optoelectronics, energy storage systems, sensors and fuel cells.
(Invited) Graphene for Biosensor Applications
Authors: Matsumoto Kazuhiko
Published: February 2020

By using the feature of high mobility and two dimensionality of graphene, the bio molecules are detected electrically with high sensitivity at the surface of the graphene channel FET. The bare graphene FET can only detect the charge of the molecule and has no selectivity of the molecule detection. Therefor, to get the selectivity, the surface of the grapehene should be modified by the receptor such as antibody, sugar chain, etc. depending on the target. Furthermore, in the measurement in the electrolyte solution, the Debye length should be took into account. For this purpose, the fragment antibody which is the head pert of the antibody and its size is less than Debye length was used for the detection of the heat shock protein. By optimizing the density of the fragment antibody, the highest sensitivity of 7pM was attained. Using the same process, the surface of the garaphene was modified by the two kinds of sugar chains. One sugar chain fits the bird influenza virus, and the other human influenza virus. Using this sugar chain modified graphene FET, the human and bird influenza viruses are selectively detected electrically for the first time.
GaN Based Ethanol Sensor
Authors: Jung Sunwoo , Baik Kwang Hyeon , Bai Seoung Jai , Jang Soohwan
Published: February 2020

Ethanol is one of most common aliphatic alcohol, which is used in chemical, biomedical, and food industry including alcoholic beverage. In recent, there are growing demands for the ethanol gas sensor to detect early spoilage of carbohydrate food, and this kind of sensors are to be employed in consumer electronics including refrigerators and mobile devices. Electrochemical, optical, potentiometric, polymer, and semiconductor sensors have been developed for fast and accurate detection of ethanol. Among the various detection methods, semiconductor based sensor can be operated at low power consumption in compact size. So far now, metal oxide semiconductors such as SnO2, Fe2O3, CuO, and ZnO are researched mostly.

GaN based material is very suitable for gas sensors, and has many superior material properties to oxide semiconductors. Wide bandgap of GaN enable devices to be operated at high temperature and harsh radiative environment, and mechanical and chemical robustness of GaN ensures reliability and durability of the device. Many types of GaN based gas sensing devices including Schottky diodes, metal oxide semiconductor (MOS) diodes, GaN nanowires and AlGaN/GaN high electron mobility transistors (HEMTs) which employ specific sensing material as a catalytic active layer have been developed for prompt and sensitive detection of target gas. Specially, AlGaN/GaN HEMT structure with 2 dimensional electron gas (2-DEG) channel induced by piezoelectric and spontaneous polarization at the interface between the AlGaN and GaN layers shows highly sensitive current changes to surface charges created by catalytic reaction of target gas on the specific active sensing layer. Typically, field effect transistors with higher drain current exhibit better responsivity of gas detection. With 30 % Al concentration in AlGaN layer, 5~10 times higher channel sheet electron densities are obtained compared to GaAs or InP HEMTs.

In this study, AlGaN/GaN HEMT based Schottky diode ethanol sensor using silver as a sensing material was fabricated, and the response of the device to ethanol gas was investigated. The diode showed current reduction in ethanol ambient due to the increase of Shottky barrier height at 250oC, and fast reliable repeatability to cyclic exposures of various concentrations of ethanol gas.
Low-Temperature Aluminum-Aluminum Wafer Bonding
Authors: Rebhan Bernhard , Hinterreiter Andreas , Malik Nishant , Schjølberg-Henriksen Kari , Dragoi Viorel , Hingerl Kurt
Published: February 2020

Thermo-compression wafer bonding is a key technology for the wafer-level production of hermetically sealed cavities, which are essential for the functioning of many microelectromechanical systems (MEMS). Aluminum, with its low material price, high thermal and electrical conductivities and its complementary metal oxide semiconductor (CMOS) compatibility, is a promising candidate for the fabrication of CMOS-MEMS, in which the sensor/actuator part is bonded to the electrical circuit. The chemically highly stable oxide layer on the Al surface cannot be removed by conventional methods. It acts as a thin diffusion barrier layer between the two aluminum metallization layers, and therefore inhibits successful low temperature Al-Al wafer bonding. So far, effective Al-Al wafer bonding has required extreme processing temperatures of >300°C and high contact pressures. Typically, 450°C-550°C led to bonded Al-Al wafers with incorporated alumina (Al2O2) precipitates and reasonable bonding quality. By using the EVG®580 ComBond®system, in which the aluminum oxide is first removed physically, followed by bonding of the two metallization layers – both performed in a high vacuum cluster – for the first time successful Al-Al wafer bonding was feasible at a temperature of 100°C.

In the present work, the microstructure of structured and unstructured aluminum films on silicon substrates was characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). C-mode scanning acoustic microscopy (C-SAM), TEM and energy dispersive x-ray spectroscopy (EDXS) interface studies of Al-Al wafer pairs bonded with this novel method revealed oxide-free, atomic contact and grain growth across the original interface. Further, the bond strength was characterized based on dicing yield and pull tests.
Surface Preparation and Eutectic Wafer Bonding
Authors: Heller Martin , Zoberbier Margarete , Fujita Toma , Eichler Marko
Published: February 2020

Bond surface preparation is an integral part of all eutectic wafer bond processes currently used in high volume production. It is not unusual to have a requirement conflict between the bond surfaces and the device itself, especially in case of MEMS inertial sensors. A typical example of the issue at hand is the need of an anti-stiction coating material for the device and the interference of the material with the eutectic bond process. This paper reports on the novel usage of localized plasma in conjunction with an improved permanent wafer bonder to reconcile the conflicting needs in case of eutectic Aluminum-Germanium wafer bonding.
(Invited) MEMS Capping By Anodic Bonding of Evaporated Glass Thin Films
Authors: Hansen Ulli , Maus Simon , Gyenge Oliver , Hu Xiaodong
Published: February 2020

Anodic bonding is a widely used MEMS process to join silicon and glass wafers. It has been utilized for many years in a large variety of devices and is valued for its possibility to create highly reliable and strong bonds at rather robust process parameters – e.g. not demanding extremely perfect surface conditions as in fusion bonding. However, the limitation in the choice of bond partners (typically borosilicate glass like Pyrex or Borofloat33 to silicon) and the rather harsh processing conditions (temperatures around 400°C and typical voltages of 600-1000V) has restricted the use of this process.

 Extensive research has been done over the years to adapt the process conditions in order to enable anodic bonding at lower temperatures and voltages and reach a higher compatibility of the process. The quality of the anodic bond is characterized by the charge (alkaline ion content) moved in the glass substrate and the ability of the glass to form covalent bonds with the silicon wafer. It can be observed that the bonding result is mainly an interaction on three process parameters: temperature, voltage, and process time with a clear dependence on the surface roughness of the bond partners. In bulk anodic wafer bonding it is not p ossible to reduce all three of these parameters and receive a satisfactory result. In order to enhance the compatibility of the anodic bonding process, the limitation of bulk silicon glass bonding needs to be overcome. Work has been reported on replacing the bulk glass wafers by thinner glass structures e.g. formed on a silicon wafer by polishing a previously anodically bonded glass substrate to a thickness of 20-50µm to achieve a kind of glass film. Other approaches include sputtering of borosilicate glass and the evaporation of this glass type, which is the focus of this contribution. On part of the silicon wafer, anodic bonding has be verified to work with different metalization layers, esp. aluminum coatings. Our contribution gives an overview on the possibilities of bonding with evaporated glass thin films to silicon and aluminum structures, and it applications in e.g. MEMS capping or pressure sensors. We investigate the influence of the process parameters of the glass deposition on the bonding result and present concepts for enhancing the compatibility of the anodic bonding process using evaporated glass thin films.
(Invited) Self-Assembly Based Multichip-to-Wafer Bonding Technologies for 3D/Hetero Integration
Authors: Fukushima Takafumi , Lee Kangwook , Tanaka Tetsu , Koyanagi Mitsumasa
Published: February 2020

3D chip stacking approaches with TSV (thorough-silicon vias) are mainly classified into three categories: chip-to-chip, wafer-to-wafer, and chip-to-wafer 3D integration. The chip-to-chip technologies are widely used for traditional microelectronic packaging in which KGDs (known good dies) are assembled using one-by-one pick-and-place techniques. Although the assembly yield is high due to the use of KGDs, the assembly throughput is not sufficiently high, compared with wafer-to-wafer approaches. However, wafer-to-wafer technologies have a serious issue in total production yield that is exponentially decreased with the number of stacked layers because the failure dies cannot be removed from the wafers to be stacked. Therefore, chip-to-wafer 3D integration is thought to be a promising candidate to satisfy both the throughput and yield issues. However, chip-to-wafer 3D integration potentially has a trade-off between assembly throughput and alignment accuracies in the conventional robotic pick-and-place techniques. In order to address the problems, we have proposed and developed multichip-to-wafer 3D integration using liquid surface tension. From the technical point of view of chip-to-wafer bonding, we talk about the basic concept and recent studies of the self-assembly based 3D integration. These approaches using surface tension-driven multichip assembly are divided into two methodologies: one is non-transfer stacking without carrier wafers and the other one is transfer stacking with them. These carrier wafers are typically used for temporary wafer bonding in standard 3D integration processes. Here, we also introduce temporary multichip bonding technologies applicable to 3D integration with multichip transfer stacking in which an inorganic temporary adhesive and a debonding layer sensitive to near UV lasers are utilized. In this presentation, we introduce our multichip-to-wafer 3D integration studies with non-transfer and transfer stacking particularly focused on solder microbump bonding (indium/gold and tin/cupper), CVD (chemical vapor deposition)-oxide/CVD-oxide direct bonding, and hybrid bonding through a new material of Cu nano-pillars that have been most recently reported toward upcoming IoT (internet of things) and trillion sensor societies.
Cooling Rate Dependent High Substitutional Sn Concentration (>10%) in GeSn Crystals on Insulator by Pulsed Laser-Annealing
Authors: Moto Kenta , Matsumura Ryo , Sadoh Taizoh , Ikenoue Hiroshi , Miyao Masanobu
Published: February 2020

Introduction

Crystalline GeSn thin-films on insulator with high substitutional Sn concentration (>10%) are deseired to realize high-speed thin film transistors. However, thermal equilibrium solid-solubility of Sn in Ge is only 1%. To solve this problem, we examined non-thermal equilibrium crystallization of amorphous-GeSn (a-GeSn) by pulsed laser-annealing (PLA). In the present study, we focus on the influence of pulse number on crystallization of a-GeSn by PLA.

Experimental Procedure

In the experiment, a-Ge1-xSnx (0≦x≦0.2) films (thickness: 100 nm) were prepared on quartz substrates by a molecular beam deposition technique. These samples were irradiated with a pulsed laser (wavelength: 248 nm, pulse duration: 80 ns, repetition rate: 100 Hz, fluence: ~140 mJ/cm2, pulse number: 1-200 shot). The laser-annealed regions were analyzed by Nomarski microscopy, Raman scattering spectroscopy, and transmission electron microscopy (TEM). Cooling rate after PLA was estimated by in-situ optical reflectivity measurements.

Results and Discussion

　Figure 1(a) shows Raman spectra of Ge0.95Sn0.05 samples after PLA (laser flunence: 140 mJ/cm2) with various pulse numbers. In all spectra, sharp peaks due to Ge-Ge bonding in crystalline GeSn are observed. Thus, GeSn has been crystallized for all pulse numbers, which was confirmed by TEM observation. Substitutional Sn concentration in the grown layers is investigated from the difference of Ge-Ge Raman peak positions between GeSn samples and a crystalline Ge substrate [1]. Pulse number dependence of substitutional Sn concentration is shown in Fig. 1(b). Substitutional Sn concentration increases with decreasing pulse number, and GeSn crystals with very high substitutional Sn concentration (~13%) has been realized for the sample (initial Sn concentration: 20%) with a single shot. These results suggest that non-thermal equilibrium conditions are enhanced by lower pulse number. To explore non-thermal equilibrium growth by modulating pulse number, cooling rate after PLA is estimated by in-situ optical reflectivity measurements, as shown in Fig. 2(a). Reflectivity at 10th and 100th shots as a function of time is shown in the inset of Fig. 2(b). From the decreasing curve of reflectivity, time constants of cooling processes are estimated, which are summarized in Fig. 2(b). Interestingly, substitutional Sn concentration increases with decreasing time constant. The detailed physics will be discussed in the presentation.

References

[1] V. R. D’Costa, J. Tolle, R. Roucka, C.D. Poweleit, J. Kouvetakis, J. Menendez: Solid State Communications 144, 240 (2007).

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(Invited) Vertical Channel Amorphous Indium Gallium Zinc Oxide Thin Film Transistors
Authors: Shieh Han-Ping D. , Chauhan Ram Narayan , Chuang Kang-Ju , Tiwari Nidhi
Published: February 2020

Vertical channel thin film transistors (VTFTs) are proposed as an effective approach to reduce driving voltage and power consumption for achieving high speed and high resolution displays. VTFTs with amorphous silicon (a-Si) technology have severe problems related to low on/off current ratio (Ion/off), high drain-leakage current, and absence of saturation behavior at high drain voltages. In this concern, thin gate insulator plays a key role to result well behaved a-Si VTFT characteristics such as clear saturation behavior at high drain voltage, low leakage current and good device performance with high Ion/off. However, poor mobility and contact resistance due to space charge limited current a-Si VTFT become increasingly noticeable, when the channel length is scaled down to nanometer dimensions. In contrast, the oxide semiconductor can be scaled to a very short channel without deteriorating the device performances. Considering that oxide semiconductors have large-area compatible processes, it will be better to find a method for achieving low driving voltages with conventional optical lithography machines used for large area display panels. In this talk, we will review the state of art of the vertical TFTs and explore the major fabrication issues. In addition, we will examine amorphous indium gallium zinc oxide (a-IGZO) vertical channel TFT fabricated at low temperature to evaluate the impact of gate dielectric on electric characteristics of the vertical vis-à-vis planar TFTs. VTFTs employing vertical amorphous a-IGZO channel of 500 nm have been fabricated without additional photolithography process. The various issues related to the improved device performance will be addressed.

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Optimization of Poly(3,4-ethylenedioxythiophene):Poly(4-styrenesulfonate) Electrodes Using Electrohydrodynamic Printing Process
Authors: Jung Eun Mi , Lee Seung Woo , Kim Se Hyun , Park So Hyun
Published: February 2020

An electrohydrodynamic(EHD) printing process was optimized for the printing of a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) conductive polymer by manipulating the surface tension of a PEDOT:PSS solution. A stable cone-jet mode was confirmed by adjusting the process parameters of the EHD printing process, such as applied voltage, flow rate, and working distance. The addition of a nonionic surfactant, Triton X-100, enabled both printing of PEDOT:PSS conductive lines with widths ranging from 335 µm to 90 µm in a low-power operation (0.5 kV), as well as a 100-fold increase in conductivity of the PEDOT:PSS film compared with that of the pristine one. To utilize printed PEDOT:PSS lines for high functional applications, a multi-deposition technique was carried out, which results in a decrease in line resistance from 1.3 x 104 Ω mm-1 to 0.2 x 103 Ω mm -1.
Low Temperature Synthesis of High Quality a Few PtSe2 Monolayers By Plasma Assisted Selenization Process
Authors: Su Teng-Yu , Medina Henry , Chen Chia-Wei , Wu Bo-Wei , Chueh Yu-Lun
Published: February 2020

Transition metal dichalcogenides (TMDs) receive a significant attention due to its intriguing properties for fundamental research and potential for application in electronics, catalysis, optoelectronics, and so on. In this work, we focus on growth of PtSe2 because of its chemical activity, small band gap and low resistivity. Recently, Yeliang Wang et al.

1
demonstrate single layer of PtSe2 by single crystal Pt substrate and selenization with 270 ºC. Despite in this case, the electrical properties of PtSe2 monolayer cannot be exploited due to the underneath Pt. It should be pointed that the synthesis temperature of PtSe2 is much lower compared with other TMDs such as MoS2 and WSe2. Besides, the electrical performance of PtSe2 is different from the other TMDs. Theoretical calculations of the band structure of PtSe2 shows large changes in the bandgap going from 1.3eV at the monolayer to 0.3 eV on bilayer and is expected a semi-metallic behavior at multiple PtSe2 monolayers. However, no experimental demonstration of the electrical properties has been explored so far. In our work, we try to grow PtSe2 by the plasma assisted selenization process. First, we deposit Pt metal on Si substrate by DC sputtering process within 5 nm thickness. After Pt deposition, we apply plasma assisted selenization to form a few PtSe2 monolayers at a temperature below 200 oC. Material characterization based on TEM, XPS and Raman analysis was applied to investigate the quality and the plasma effect on the resulting PtSe2 film. Moreover, we experimentally demonstrate the semiconducting properties of PtSe2and demonstrate the potential as a channel material for MOSFET applications.

References

1. Wang Y., et al. Monolayer PtSe(2), a New Semiconducting Transition-Metal-Dichalcogenide, Epitaxially Grown by Direct Selenization of Pt. Nano Lett
15, 4013-4018 (2015).
Direct Current-Induced Oxidization of Metallic Nanowires and Their Resistive Switching Properties
Authors: Shih Yu-Chuan , Liang Kai-De , Chen Yu-Ze , Tsai Hung-Wei , Chueh Yu-Lun
Published: February 2020

Memristors have recently attracted a significant interest due to their potential application in nanoscale logic and memory devices. Memristors are two-terminal memory resistors that retain internal resistance state according to the history of applied voltage and current. The memristive behavior was obtained in metal/oxide/metal ultra-thin-film structure. Devices based on transition metal oxide have been reported in the previous works. However, none of researches demonstrate the simple synthesis of memristors from metallic nanowires by taking advantage of Joule Heating. In our research, direct current-induced oxidation of Cu nanowires by high current density in atmospheric air at room temperature was investigated. Subsequently, reversible switching up to 100 cycles with large ON/OFF ratio (> 103) and low threshold voltages (>0.5V) was demonstrated. From TEM analysis of the manipulated nanowire devices, core-shell (Cu2O/Cu) nanowire structure was observed which provided an evidence of current-induced oxidation.
(Invited) Nanoscale III-Vs on Oxides and Metals - a Route Towards Low-Cost, High-Performance Electronic and Photonic Devices on Non-Traditional Substrates
Authors: Kapadia Rehan
Published: February 2020

Pushing the boundaries of electron devices—from transistors to photovoltaics—demands complete control over device architectures and material systems. However, traditional growth and fabrication techniques often fall short when optimal design calls for non-planar geometries or integration of non-epitaxial material systems. Thus, in the past decade, a variety of techniques for X-on-Y growth/integration have been explored. In particular, nanostructures grown via the vapor-liquid-solid (VLS) technique have been studied heavily, demonstrating excellent device performance with the possibility of integrating single crystalline materials with non-epitaxial substrates. However, the stringent restrictions on growth geometry due to the traditional VLS growth mode limits the devices architectures that may be grown and fabricated. Here, a novel method for substrate-agnostic growth of arbitrary geometry III-V materials will be presented as a route towards high performance optoelectronic devices.

The direct growth of optoelectronic quality III-V semiconductors on non-epitaxial substrates will be discussed. Structures with geometries varying from the micro/nanoscale single crystalline islands to ultra-large grain polycrystalline thin films may be grown via a thin-film vapor-liquid-solid (TF-VLS) technique. By careful control over nucleation position and shape of III-V semiconductors, arbitrarily shaped single-crystalline islands may be grown on non-epitaxial substrates. First, the general method for this growth will be discussed, illustrating how different structures and geometries may be obtained. Next electronic and optoelectronic characterization of the grown materials will be presented, showing that films display excellent optoelectronic characteristics. Finally, devices fabricated from the grown material will be shown, illustrating that high-performance devices may be obtained without utilizing costly lattice matched substrates.