bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Voltage, High-Frequency Electrochemical Capacitor
Authors: Miller John R. , Outlaw Ronald A , Butler Sue M.
Published: February 2020

Electric double layer capacitors (EDLCs) with electrical performance like aluminum electrolytic capacitors have been developed.(1) They can be smaller in size and offer higher reliability. Operation of such devices relies on charge stored on vertically oriented graphene nanosheet (VOGN) carbon. Vertically oriented graphene nanosheets are prepared using RF plasma enhanced chemical deposition of a hydrocarbon feed gas.(2) Under proper growth conditions, VOGN are ohmically connected to the metal current collector on which they grow, offer high electronic conductivity, and have an “open” structure totally free of porous electrode behavior. Each of these characteristics is necessary for efficient operation at frequencies of 1 kHz and higher.

EDLC cells, like battery cells, operate at low voltage. Thus cells must be series connected to operate at high-voltage. Figure 1 shows an approach devised for interconnecting the EDLC cells to create a high-voltage, high-frequency EDLC. It involves interconnecting planar EDLC cells using the substrate metallization. As shown, interdigitated gaps are created in the VOGN that has been grown on a thin metal layer covering an insulating substrate, for instance, nickel on alumina. The gap is created using a laser to cut through the VOGN and metal down to the insulating substrate. This then creates multiple electrically-isolated regions (six are shown in the figure). Two adjacent regions become a single EDLC after electrolyte is applied over the gap and the surface of that region. To make a series connection of cells, each gap must be individually covered with an electrolyte, making sure that the electrolyte band does not touch the neighboring bands. This is a “bipolar” design in two dimensions, the substrate metallization serving as the bipolar plate.

Connecting M cells in series each rated at voltage Vo with capacitance Co and series resistance Ro yields a capacitor with a voltage rating M·Vo, capacitance Co/M, and series resistance M·Ro. The frequency response of this high-voltage capacitor is nearly identical to that of one of its cells because the interconnects add minimal resistance. Voltage-balance resistors can be added using, for instance, thick-film printing processes. Details of the fabrication process are described and electrical performance data on these high-voltage, high-frequency electric double layer capacitors is presented.

References

1J.R. Miller el al, “Graphene Double-Layer Capacitor with ac Line-Filtering Performance”, Science 329
, 1637 (2010).

2Cai M, Outlaw RA, Butler SM, and Miller JR, “A High Density of Vertically-Oriented Graphenes for Use in Electric Double Layer Capacitors”, Carbon
50, 5481–5488 (2012).

.
Aqueous Hybrid Supercapacitor Using Protected Pre-Lithiated Carbon Anode
Authors: Sugimoto Wataru , Makino Sho , Shimizu Wataru
Published: February 2020

1. Introduction

Pseudocapacitive oxide electrodes generally perform best in aqueous electrolytes. The use of aqueous electrolytes unfortunately limits the maximum cell voltage to no more than 2 V, which is a disadvantage for energy density (E=0.5 CV2). This disadvantage can be overcome by using a water-stable solid electrolyte [1-3]. The new cell configuration is based on the use of a protected Li anode, which consists of a water stable Li-conducting solid electrolyte, a Li-conducting gel electrolyte buffer layer, and Li foil as the negative electrode. The application of the water stable anode allows the implement of aqueous electrolytes at the pseudocapacitive positive electrode. The cell voltage can reach as high as 4.3 V when MnO2 is used as the positive electrode [1,3]. In this study, we pre-lithiated carbon (LixC6) was adopted as the negative electrode instead of Li.

2. Experimental

Li doping into graphite was conducted with a three-electrode cell at constant current (0.2C) in 1.0 M LiPF6/EC:DEC. After the pre-doping procedure, the cell was disassembled and reassembled into a pouched cell. The multi-layered anode consists of a LISICON-type solid glass ceramic (Li1+x+y(Ti,Ge)2-xAlxSiyP3-yO12 (Ohara Inc., Japan, hereafter denoted as LTAP) as the water-stable solid electrolyte, and a buffer layer consisting of polyethylene oxide with Li(CF3SO2)2N polymer electrolyte (PEO-LiTFSI) between the lithium metal or pre-lithiated carbon and the solid electrolyte. These 3 layers were sealed into a laminated pouched cell leaving a 5 mm x 5 mm window cut out for the solid electrolyte (LTAP) to come into contact with the aqueous electrolyte.

Results and discussion

After Li-doping of graphite in the pre-doping cell, the potential of the negative electrode was 57 mV vs. Li/Li+. The color pf graphite changed from black to gold with Li doping. Taking into consideration the irreversible capacity, it can be assumed that pre-doping at 0.2C is sufficient to achieve close to fully doped state. Figure 1 shows the charge/discharge curves using activated carbon positive electrode (LiC6 | PEO-LiTFSI | LTAP | 1.0 M Li2SO4aq. | AC). Maximum cell voltage of 3.7 V was obtained. The AC positive electrode showed capacitive behavior with the potential varying linearly with time between 0.33 and 1.29 V vs RHE. The potential of the negative electrode was -0.24 V vs RHE, and exhibited typical battery-like behavior. The overall cell performance is similar to lithium-ion capacitors. The specific capacitance of the AC positive electrode was 135 F/g.

1) S. Makino, Y. Shinohara, T. Ban, W. Shimizu, K. Takahashi, N. Imanishi and W. Sugimoto, RSC Adv., 2, 12144 (2012).

2) S. Makino, T. Ban and W. Sugimoto, Electrochemistry, 81, 795 (2013).

3) W. Shimizu, S. Makino, K. Takahashi, N. Imanishi, W. Sugimoto, J. Power Sources, 241, 572-577 (2013).

Figure 1. Galvanostatic charge/discharge curves of aqueous hybrid capacitor (LiC6 | PEO-LiTFSI | LTAP | 1.0 M Li2SO4 aq. | AC) at 0.102 mA cm-2.
Development of a Coupled Electrical, Thermal and Degradation Supercapacitor Model for Automotive Applications
Authors: Sarwar Wasim , Marinescu Monica , Taylor Nigel , Offer Greg
Published: February 2020

Despite the fact that supercapacitors are less complex than lithium ion batteries, they are less well understood. Although supercapacitors do not possess sufficient energy density to make them suitable as the only source of energy storage in the majority of applications, they are ideal as a buffer for the primary energy source. Applied to hybrid and electric cars, supercapacitors can be used to reduce the degradation and power requirements of the primary energy source, typically lithium ion batteries.

To the best of the author’s knowledge, currently, no unified, high fidelity, electrical, thermal and degradation model exists of a supercapacitor that meets automotive requirements. This is because the electrical and thermal models must re-create both short term and long term cell behavior over a large range of temperatures, frequencies, and currents. They must also include degradation models that are valid under complex cycling conditions and not simply under constant current cycling.

The state-of-the-art electrical models of a supercapacitor are equivalent circuit models, which utilize a de-Levie transmission line. The length of the transmission line is analogous to the path length of an ion from its initial location to forming part of the electrical double layer, or pore depth penetration. Thus, the transmission line can be utilised to either model the available electrode surface for ion adsorption, and hence capacitance variation with frequency, or model the charge distribution throughout the porous structure, and hence determine voltage hysteresis as a result of charge re-distribution. The standard de-Levie transmission line cannot be used to characterize both of these effects simultaneously, (which is necessary for automotive requirements) without being adapted.

The majority of supercapacitor thermal models are either lumped models or axi-symmetric models utilizing an assumption of uniform heat generation. Although these models are suitable for determining thermal management strategies, and degradation under steady state conditions, they are unsuitable for determining degradation in highly dynamic systems. They are unable to predict localized hotspots at the electrode/electrolyte interface, which are caused by the entropy effects of the generation or breakdown of the electrical double layer. Furthermore, they are unable to predict the temperature difference between the positive and negative terminals.

This talk will outline the development and validation of a new equivalent circuit model of a supercapacitor for automotive use. The electrical model is capable of reproducing cell behavior, including power limits, variation of capacitance and resistance with operating temperature and frequency, charge re-distribution and self-discharge. The coupled thermal model is capable of predicting reversible and irreversible heat generation and its spatial distribution throughout the cell, and the resultant degradation.
Enabling Sub-10nm Lithography with Atomic Layer Deposition and Block Copolymer Self Assembly
Authors: Ruiz Ricardo , Chapuis Yves-Andre , Wan Lei , Xiong Shisheng , Gao He , Patel Kanayialal , Dobisz Elizabeth , Bogdanov Alexei , Nealey Paul , Albrecht Thomas
Published: February 2020

Block copolymer lithography, an alternative lithographic technique by which self-assembled patterns made from block copolymer thin films are used as lithographic masks, has achieved a high enough level of maturity to be considered for nanofabrication in magnetic recording bit patterned media and in some applications in the semiconductor industry. As the demand for lithographic dimensions squeezes into the single-digit nm scale, pairing block copolymer materials that segregate at these dimensions with adequate pattern transfer techniques is increasingly difficult. For example, PS-b-PMMA, the most mature block copolymer system can only form line/space patterns with pattern transfer above 10 nm. Other promising materials like P2VP-PS-P2VP triblocks, however, lack sufficient etch contrast for reactive ion etching. Here, we present a nanofabrication strategy that integrates atomic layer deposition, ALD, with block copolymer lithography to enable fabrication of sub-10nm features for high density magnetic storage.

The selective, cyclic and self-terminating nature of the materials synthesis within ALD reactors provides powerful nanofabrication tools. In particular, two of these tools stand out as enablers for high density patterning: First, the chemical selectivity of the organometallic precursors has facilitated selective synthesis inside porous polymeric materials. Second, the conformality afforded by the self-terminating nature of the ALD reactions has proven to be ideally suited for feature doubling in self-aligned double patterning, SADP. Integrating these powerful tools with block copolymer lithography opens new possibilities in two fronts: On the one hand, it is possible to generate hybrid nanocomposites with nanometer-scale resolution and high etching contrast. This is particularly useful for high resolution block copolymer materials for which no natural etch contrast exists such as P2VP-PS-P2VP triblocks. On the other hand, it is possible to use the already sub-lithographic features obtained by standard PS-b-PMMA block copolymer lithography as the starting point for an additional density multiplication using spacer lines grown by ALD for SADP.

Be it for selective infiltration synthesis in block copolymer patterns or for the precise conformal growth in nanostructures made from block copolymers, ALD is likely to emerge as an ideal complimentary technique to block copolymer self assembly to enable sub-10nm lithography.
Manganese Precursor Selection and the Thermal Atomic Layer Deposition of Copper/Manganese Alloy Films
Authors: Kalutarage Lakmal C. , Clendenning Scott B. , Winter Charles H.
Published: February 2020

Our laboratory seeks to develop the growth of metallic first row transition metal thin films using atomic layer deposition (ALD). The microelectronics industry is calling for the growth of metallic first row transition metal films by the ALD method for a variety of applications, including copper metallization, seed layers for copper metallization, copper/manganese alloys for self-forming copper diffusion barriers, and magnetic alloys. The ALD growth of noble metal thin films has been explored extensively in the past ten years, due to the positive electrochemical potentials of these metal ions and relative ease of reduction to the metallic state. The low temperature ALD of high purity, low resistivity Cu films has been described, but ALD routes to the other metallic first row transition metal films remain poorly developed, largely because of the negative electrochemical potentials of most of the ions and a corresponding lack of powerful reducing co-reagents that can convert precursors in positive oxidation states to the metals. We will describe the synthesis, structure, and properties of a large series of new first row transition metal ALD precursors that combine high volatilities, high thermal stabilities, and high reactivities toward reducing agents. We will also report borane and other reducing agents that can react with the metal precursors to afford metallic films. Additionally, we will overview the thermal growth of metallic copper, nickel, cobalt, iron, manganese, and chromium thin films from these new precursors. Key advances include development of optimized ALD precursors with very similar ligands and chemistry, and identification of new reducing co-reagents that can rapidly reduce the positive oxidation state precursors to the metals.
RF Power Effect of Post-Deposition Oxygen Plasma Treatment on HfO2 Gate Dielectrics
Authors: Bo Tian-Cih , Cheng Yi-Lung
Published: February 2020

The RF power effect of post-deposition O2 plasma treatment on the physical, electrical characteristics, and reliability performance of high-k HfO2 dielectric films were investigated in this study. Increasing RF power in post-deposition O2 plasma treatment results in a stoichiometric HfO2 film, but leading to a thinner interfacial layer with a new Hf-Si bond. Additionally, the electrical performance and reliability of high-k HfO2 dielectric films were related to the RF power in post-deposition O2 plasma treatment. As RF power is less than 50 W, the leakage current density and time-to-breakdown were improved as compared to those of un-treated samples. However, these properties were continuously degraded with an increase of RF power due to plasma damage induced by oxygen active spices in a O2 plasma environment. Therefore, the post-deposition O2 plasma treatment is benefit in the improvement of HfO2 gate dielectric properties, but the plasma power is needed to be well controlled.
Heteroleptic Precursors for Atomic Layer Deposition
Authors: Niinistö Jaakko , Blanquart Timothee , Seppälä Sanni , Ritala Mikko , Leskelä Markku
Published: February 2020

As the atomic layer deposition (ALD) method is based on sequential, self-limiting surface reactions the precursor chemistry is the key to a successful processing of conformal high quality thin films. ALD precursor chemistry has traditionally been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides and alkoxides. However, these precursors may have drawbacks such as possible halide contamination and low thermal stabilities in the case of the alkylamides and alkoxides. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes.

In the recent years, increasing research effort has been dedicated in development of novel ALD processes focusing especially on transition metals and their oxides using heteroleptic precursors. Interestingly, heteroleptic compounds often show different properties than their homoleptic counterparts. One type of ligand can provide reactivity and another stability, thus widening the process window with comparable film growth rate.

In this presentation heteroleptic precursors for ALD processes of transition metals and their oxides will be reviewed. Special focus is given to oxides of the rare earths and groups 4 and 5. Trends in the properties of heteroleptic precursors are discussed. Several examples of our recent results are shown, including introduction of novel processes based on amidinate-cyclopentadienyl complexes for ALD of rare earth oxides.
Doping Mechanism in Transparent Conductive ZnO Films Grown by Atomic Layer Deposition
Authors: Lee Do-Joong , Kwon Jang-Yeon , Kim Soo-Hyun , Kim Hyun-Mi , Xu Jimmy , Kim Ki-Bum
Published: February 2020

Transparent conducting oxides (TCOs) have been one of the essential elements of various optoelectronic devices, photovoltaics, and photoelectrochemical energy-harvesting cells which require an electrically conducting layer (s ~103-104 S/cm) with high optical transparency (>80%). The TCOs are typically doped with foreign elements, as in the cases of Sn-doped In2O3 (ITO) and Al-doped ZnO (AZO), and become degenerate semiconductors with an extremely high electron concentration of 1020-1021 cm-3. While TCOs have been deposited by various methods including sputtering, pulsed laser deposition, chemical vapor deposition, and spray pyrolysis, recent emergence of nanostructured solar cells and organic light emitting diodes has accelerated necessity of ultrathin TCO coating onto complex or large surface area substrates at a low deposition temperature which are quite challengeable for the conventional deposition methods. In order to meet those emerging requirements, atomic layer deposition (ALD) has gathered great interest. Since ALD uses an alternative supply of source gases, conformal coating of desired films can be readily elucidated onto high-aspect-ratio structures and film thickness can be exactly controlled by repeating discrete ALD cycles. Therefore, there have been increasing demands of integrating ALD-grown TCOs into the emerging applications addressed above.

In this presentation, we report structural and electrical properties of ‘atomic-layer-doped’ ZnO films.[1,2] Firstly, Al-doped ZnO films were deposited by ALD via alternate stacking of a ZnO matrix and AlOx dopant layers. Scanning TEM-HAADF analysis revealed that the ALD-AZO films have a unique layer-by-layer structure as those were grown. Upon correlation of the structural and electrical properties, effects of the layer-by-layer doping manner were interpreted in order to investigate a carrier generation mechanism of the ALD-AZO films. In the latter part, efforts of optimizing electrical properties of ALD-ZnO films will be given by controlling surface coverage of dopant ions incorporated in each atomic-doping layer. These efforts include two approaches; i) control of the amount of Al ions deposited during 1 ALD cycle of AlOx via process-parameter adjustment, and ii) introduction of other dopant oxides (group III: In, B, transition metals: Hf, Zr, Ti) which have different surface coverage. Among the tested dopants, it is remarkable that Ti exhibited the highest electrical conductivity (950 S/cm) and doping efficiency (51%). This finding is extraordinary compared to the conventional homogeneous compounds where Al has long been considered as one of the best dopants for the ZnO.

[1] D.-J. Lee, K.-B. Kim et al., Adv. Funct. Mater. 21, 448 (2011).

[2] D.-J. Lee, K.-B. Kim et al., J. Electrochem. Soc. 158, D277 (2011).
Invited; Stress and Doping Impact on Intrinsic Point Defect Behavior in Growing Single Crystal Silicon
Authors: Sueoka Koji , Kamiyama Eiji , Vanhellemont Jan
Published: February 2020

For the further development of 450 mm-diameter defect-free Si crystals, one has to take into account the impact of thermal stress on intrinsic point defect properties and behavior during single crystal growth from a melt. In this study, we evaluate the impact of thermal stress between -30 MPa (tensile) and 30 MPa (compressive), which probably covers the actual values in mass production for 450 mm-diameter crystals, on the so-called Voronkov criterion of dominant point defects.The dependence of the formation and migration enthalpies of vacancy V and self-interstitial I on the stress is evaluated by density functional theory (DFT). The obtained results are used to more accurately describe the impact of thermal stress on the critical (v/G)0. The impact of compressive thermal stress on (v/G)0 is predicted to shift the growing Si crystal more vacancy-rich, as recently confirmed experimentally by Nakamura et al (ECS Solid State Letters, 3 (2014) N5-N7). Furthermore, the dependence on the thermal stress of the process window for defect-free Si growth is clarified, which is important for the development of the pulling process of future large-diameter defect-free Si crystals.

Also the mechanisms behind the experimentally observed impact of the type and concentration of substitutional dopants on intrinsic point defect behavior and formation of grown-in defects (voids and interstitial clusters) in a Si single crystal growing from a melt, are clarified. DFT calculations with 216-atom supercells are carried out to obtain the formation energies of V and I at all sites within a sphere around the dopant atom with 6 A radius for V and 5 A radius for I. P-type (B and Ga), neutral (C, Ge, and Sn) and n-type (P, As, Sb, and Bi) dopants are considered. The formation energies of V and I around dopant atoms change depending on the types and sizes of dopants. On the basis of the calculated results, an appropriate model of intrinsic point defect behavior in heavily doped Si is proposed. (1) The incorporated total V and I concentrations at the melting point depend on the types and concentrations of dopants. (2) Most of the total V and I concentrations contribute to Frenkel pair recombination during Si crystal growth at temperatures much higher than those to form grown-in intrinsic point defect clusters. The Voronkov model, while taking into account the present improvements, clearly explains all reported experimental results on grown-in defects for heavily doped Si.

The proposed improved Voronkov model uniformly explains point defect behavior for all dopant types and concentrations, taking into account also thermal stress levels.
Deep-Level Defects in High-Dose Proton Implanted and High-Temperature Annealed Silicon
Authors: Jelinek Moriz , Laven Johannes , Rommel Mathias , Schustereder Werner , Schulze Hans-Joachim , Frey Lothar , Job Reinhart
Published: February 2020

Proton-implantations are valued for their ability to modify the properties of semiconductor grade silicon over a wide spatial range spanning four orders of magnitude between a depth of about 100 nm and 1 mm at comparatively low thermal budgets. At moderate proton doses up to about 1×1013 cm-2 and low annealing temperatures at about 300 °C, proton implantations are used to tailor the carrier life-times in bipolar power semiconductor devices. A large number of deep-level defects are known to form in this parameter regime. At higher doses and higher temperatures proton implantations may be used for modifying the doping profile of the silicon substrate by the creation of hydrogen-related thermal donors. While a large number of studies have investigated deep-level defects induced in the parameter regime typical to life-time tailoring, only few are concerned with the deep-level defects remaining in the samples.

In this report we give a brief review of the principal mechanisms of deep-level defect formation after proton irradiation and subsequent annealing of float zone-grown crystalline silicon. Various reaction paths commonly related to vacancy-complexes, interstitial oxygen and hydrogen are discussed. In the experimental part of the study, new DLTS measurements of proton-irradiated pn-diode structures are presented. The study focusses on the regime of elevated doses and annealing temperatures, typically used for proton-implantation doping. The results suggest that for the increased doses used, some of the detected defects show a thermal stability differing from that reported in literature. At least for some of these defects, this may be due to their higher initial concentration. In addition, other defects may appear at higher temperatures as decay products of other, thermally more stable, defects induced by the high-dose implantations.

For the first time, we also report on two defect levels at 300 meV and 418 meV below the conduction band with a metastable behavior. The observed levels and their behavior show a high similarity to a negative-U defect known from samples implanted at 88 K without any further thermal budget above room temperature. To our knowledge, these levels have not been detected in a sample annealed above room temperature before.

The figure depicts possible reaction paths of vacancies in crystalline silicon under the presence of extrinsic hydrogen and oxygen. Many of these defects lead to localized levels in the silicon bandgap and can therefore impact the electrical properties of a device. The actual appearance of a defect is however determined by the activation energy for its formation together with the applied process temperatures. If known from literature, the activation energy for each reaction path is indicated.
Self-Aligned Ni-Germanide Ohmic Contact to n-Type GaAs Substrate for High Mobility III-V Channel Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET)
Authors: Kang Min-Sung , Leem Chang-Hyun , Lee Ye-Ji , Lim Yi-Rang , Shim Kyu-Hwan , Choi Chel-Jong
Published: February 2020

We have investigated the microstructural evolution and electrical property of self-aligned Ni-germanide thin film formed on n-type GaAs (100) substrate as a function of rapid thermal annealing at temperatures in the range of 300 – 600 °C. The heteroepitaxial growth of Ge on GaAs (100) substrates was carried out using rapid thermal chemical vapor deposition (RTCVD) method. The Ge epitaxial layers were formed by the decomposition of GeH4 in a H2 ambient at substrate temperatures of 400 – 500 °C. The specific contact resistivity was extracted using four-point (Kelvin) probe technique. The specific contact resistivity values of the Ni-germanide films varied with variation in annealing temperature and were comparable to those obtained for Ni-germanide. A low specific contact resistivity of the order of 2.1 × 10-6 Ωcm2 was obtained for the Ni-germanide film formed at annealing temperature of 500 °C. The variation in the specific contact resistivity with annealing temperature could be associated with the phase evolution, surface and interface morphologies of Ni-germanide that occur at different annealing temperatures.
Invited; Light Induced Degradation in Compensated B-Doped Czochralski Silicon
Authors: Yang Deren
Published: February 2020

Light induced degradation (LID) in B-doped Czochralski Si solar cells is a universal phenomenon, which reduces the conversion efficiency by 2-5% relatively. It is believed that Boron-Oxygen complexes are formed during light illumination, which are the effective recombination centers. Studies in the exclusively B-doped Si, B/Ga co-doped Si and p-type B/P compensated Si show that the saturated concentration (Nt*) of B-O defect is proportional to the B concentration (NB
) (or the net hole concentration p0
) and the generation rate constant (Rgen
) proportional to p0
2
. Interestingly, the LID has also been found in n-type B/P compensated Si, which was supposed to be unlikely to happen. Hence, it brings out a fundamental question of whether the p- and n-type B-doped Si have the same formation mechanism of LID.

In this presentation, we will report our recent work about LID in B-doped compensated Cz silicon. It is believed that the BO defect density in compensated silicon depends on the B concentration and the net doping concentration. Moreover, High B concentration in the compensated silicon results in very serious cell efficiency loss. Furthermore, The electrical parameters of the reference and compensated cells can get fully recovered by illumination at high temperatures.

Moreover, the LID in n-type B-doped Cz silicon with thermal donors (TDs) compensation is also reported. The advantage of TDs compensation is able to obtain a variation of carrier density but with a constant NB
. We find that the formation of B-O complex also occurs under the light illumination and can be annealed out quickly in the dark at 200 oC. The Nt* exhibits a nonlinear dependence on the majority carrier concentrations n0
, and the Rgen
is independent on the n0
. The formation activation energy is determined to be 0.4 eV, identical to the value in p-type Si. Based on the results, we believe that the nature of LID in p- and n-type silicon should be the same.
Fabrication of Uniform Sized Metal Spheres by Plasma Induced Dewetting
Authors: Han Dong-Hoon , Lee Seung Moo , Lee Jung-Joong , Kim Dohyung , Choi Jinho , Won Jaihyung
Published: February 2020

Sn and InSn metal spheres were fabricated by plasma induced dewetting with various conditions. Dewetting was effective under a hydrogen plasma environment despite the absence of an external heat source. FE-SEM images revealed that hydrogen plasma dewetting of Sn and InSn films proceeded through heterogeneous hole nucleation on the film surface and films changed to spherical with no large aggregation while there were large aggregations under thermal dewetting. Droplet size was controllable by selecting the plasma treatment conditions and initial film thickness. The longer films were plasma-treated, sphere size was decreased and larger spheres were divided to smaller ones. In addition, increasing plasma power yielded increasing sphere size regularity. It was suggested that plasma induced the digestive ripening of the metal spheres which interpreted by charge effect in colloid system.
Nuclear Forensics Using Plasma Source Ion Beams
Authors: Boswell Rod , Smith Noel , Charles Christine , Martin Noel , Tesch Paul
Published: February 2020

Secondary Ion Mass Spectroscopy uses beam of primary ions (typically O-) focused onto a target. Sputtered secondary ions are measured by mass spectrometer which can detect elements and their isotopes in the low parts per billion (10-9 or ng/g) range. Particles as small as a few 100 nanometres can be analysed.

Time of Flight (TOF)SIMS measures the time of arrival of the secondary ions at the detector, which depends on their mass yielding an extremely good high mass resolution.

It can detect: cocaine in urine, benzodiazepines (eg. valium) in hair and gunshot residues in fingerprints even after strenuous washing!

Additionally, TOF-SIMS can simultaneously detect cocaine in the presence of other drugs (i.e. flurazepam (a benzodiazepine hypnotic) and chlorpromazine (used for psychosis and heroin withdrawal) in urine.

It is possible to relate the TOF-SIMS fingerprints to the evidence found at the crime scene, which can be considered as examination of forensic evidence transfer.

Elemental composition of anthrax spores using TOF-SIMS has been carried out by Weber et. al. at LLNL. This is of use in assessing the origin of bio-weapons.

Oregon Physics has developed the HyperionTM system of high brightness plasma ion sources which are now being used on Focused Ion Beams and TOF-SIMS around the world. These plasma sources are ten times brighter than present sources and reduce the time necessary for analysis from days to hours. They are also more reliable and can be focused down to smaller spots.
Plasma Solutions for Life Sciences and Medical Device Manufacturing
Authors: Foote David
Published: February 2020

The medical device industry is highly regulated which demands reliable and reproducible components and manufacturing processing to satisfy said regulators. Regulated devices range from a simple bandage to the most complex implantable heart defibrillator. Developing these devices requires rigorous testing and validation of the materials and processes used to manufacture them. Challenges abound due to issues with bio-compatibility, material mismatch, implant duration, ability to withstand sterilization, wettability, lubricity, and so on. Plasma processes address many of these challenges while enabling more reliable and robust devices. Plasma has been shown to enhance surface wettability, remove surface contamination, improve bondability and maintain the bulk properties of the material treated.

Medical diagnostics are highly dependent on reliable chemical analytic techniques where fluids are contacted with reagents in polymer containers such as microtiter plates or plated used in gene sequencing systems or chemiluminescence detection tools. The reliability of such techniques are dependent upon the repeatable wetting of the containers by the fluids and/or reagents. Plasma processing is an excellent choice for increasing the surface energy of polymers enabling more wettable surfaces.

Because plasma treatment will enhance the surface energy of samples treated it is chosen prior to adhesive bonding, lubricious coating application, polymer coating application, device printing, etc. Plasma is also useful for depositing polymer films via plasma assisted polymerization. Plasma polymer films can be used to enhance adhesion of subsequent bonding steps and in certain cases forms an excellent tack reduction film when deposited on rubber compounds. Plasma is also utilized to remove surface contaminants that can interfere with subsequent bonding steps.

Specific application examples will be presented showing the many uses and benefits of plasma processing for medical devices.
Through Silicon via Filling by Electroplating Using Reduced Graphene Oxide (rGO) as a Conducting Layer
Authors: Chang Shih-Cheng , Dow Wei-Ping
Published: February 2020

Graphene materials, including single layer and multi layer graphene platelet, have recently drawn extensive attention due to their outstanding electrical and thermal properties. Reduction of grapheme oxide (GO) is a method for preparing the graphene film. Since GO has a large amount of oxygen functional groups, it can be well dispersed in several solvents and enable it to be coated on a substrate by using a chemical grafting method[1].

Three-dimensional (3D) chip stacking is a major focus in recent research and development of microelectronics, MEMS, and MOEMS technology. Through silicon vias (TSVs) play a key role in the 3D IC chip stacking connections. A main advantage of TSV is to make the shortest chip-to-chip vertical interconnection, which allows for size reduction of the chip and reducing signal transmission delay[2]. Electrodeposition plays an important role for TSV metallization, especially copper electrodeposition, which is a critical technology and generally used in the 3D chip packaging.

For TSV technology, the thermo-mechanical fatigue may lead to failure in the TSV interconnects[3] because the coefficient of thermal expansion (CTE) of copper is much higher than that of silicon. The package materials with different CTEs will induce large stresses at interfaces. In order to overcome this problem, copper should be substituted by tungsten. However, tungsten cannot be directly plated from an aqueous electrolyte, it can be co-deposited with iron group metals. Alternatively, since the CTE of graphene is much closer to silicon than copper, we choose graphene sheets to substitute copper seed layer.

Traditional process for TSV fabrication is a dry process that includes the following step: (1) formation of vias by reactive ion etching; (2) formation of a SiO2isolation layer; (3) deposition of a TiN barrier layer and a copper seed layer; (4) electrodeposition of copper inside the via. In our research, we reduce the procedure of TSV fabrication using a wet process to substitute barrier and seed layer with graphene, and electrodeposition with Ni-W alloy to make a copper-free TSV. In other words, a copper-free TSV with simplified process steps is fabricated, leading to a low fabrication cost. Moreover, a low-stress TSV filled with low CTE materials (Ni-W and rGO) is also fabricated to improve the thermo-mechanical fatigue of TSV, leading to better package reliability.

References

1. P. Songfeng, and C. Hui-Ming, “The Reduction of Graphene oxide ”, Carbon., 2012, 50, 3210-3228.

2. K. Kondo, T. Yonezawa, D. Mikami, T. Okubo, Y. Taguchi, K. Takahashi, and D. P. Barke, “High Aspect Ratio Copper Via Filling for Three-Dimensional Chip Stacking”, J. Electrochem. Soc., 2005, 152, 658-662.

3. S. H. Choa, C. G. Song, and H. S. Lee, “Investigation of Durability of TSV Interconnect by Numerical Thermal Fatigue Analysis”, Int. J. Pricis. Eng. Man., 2011, 12, 589-596.

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Advances in Wafer Bonding for 3D Integration and Other Applications
Authors: Lu James J-Q
Published: February 2020

Bonding is one of the key technologies that enable the 3D integration. 3D integration has more choices in terms of 3D process flows, such as chip-on-chip (CoC), chip-on-wafer (CoW) or wafer-on-wafer (WoW). Bonding process can be used to glue multiple functional IC chips vertically and provide some combinations of mechanical, thermal, electrical and optical connections between chips or wafers permanently, or to provide temporary mechanical support for wafer thinning and thinned wafer handling. Bonding process also varies with different materials and applications. The choice of bonding technology depends on combinations of the chips and their required process conditions such as temperature limitations. This invited talk focuses on advances in bonding technologies for 3D integration and other applications, including different bonding approaches, requirements for materials and processes, bonding quality characterizations and application-specific bonding technologies.
Numerical Analysis of the Correlation between the Cu+ Ion Concentration and the Current Density
Authors: Hayashi Taro , Kondo Kazuo , Yokoi Masayuki , Saito Takeyasu , Okamoto Naoki
Published: February 2020

Introduction

3D chip stacking realize high-density packaging and high-speed performance. High-aspect-ratio through-silicon via(TSV) allow short interconnects and reduced signal delays. This TSV interconnection will be applied to wide I/O memories of the next generation smart phone. Cu electrodeposition in high-aspect-ratio via is one of the key technologies for 3D packaging. Voids or seams formed in the via may causes serious problems in reliability. The formation of the Cu+ ion is a crucial intermediate and the Cu+ion intermediate is always produced during the electrodeposition process (eq.1 and 2).

We already reported that 4 μm diameter via of aspect ratio of 7.5 is perfectly filled with the increasing Cu+ ion concentration inside the via[1,2]. Additionally, K. Kondo et al. have reported that a large amount of Cu+ ion within the confined area of the trench of the trench bottom electrodes and experimentally verified the relation between the Cu+ ion and acceleration[3]. In this study, we have calculated the Cu+ion concentration shifting at the trench bottom during electrodeposition by using COMSOL Multiphysics.

Numerical Analysis

The simulation model is shown Fig.1. We have assumed that the electrode surface is only trench bottom. And the reaction equations of Cu2+ ion and Cu+ ion at trench bottom are shown eq.3 and 4. The reaction kinetic parameters, k1, k-1, k2 and k-2 have been reported our previous study[2]. The reaction kinetic parameter from Cu2+ ion to Cu+ ion, k1 as 8.4×10-8 m/s, that from Cu+ ion to metallic Cu, k2 as 5.5×10-5 m/s, that from Cu+ ion to metal Cu2+, k-1 as 7.0×10-6 m/s, that from metallic Cu to Cu+ ion, k-2 as 1.6×10-8 m/s. Additionally, the diffusion equations in the electrolyte are shown eq.5 and 6. In this simulation model, the reverse current has been applied from 1 to 13 s, and the off-time has been applied from 0 to 1 s and 13 to20 s.

Results and discussion

We have calculated the Cu+ ion concentration shifting at the trench bottom with various trench widths. The calculation results are shown in Fig. 2. From Fig. 2, we have understood that the Cu+ ion concentration increase with the reverse current(1s to 13 s) and the off-time(13s to 20 s) with narrowing trench widths.

Figure 3 shows the result of LSV measurements by using trench-shaped through mask electrode that reported in reference 3. Before measurements, the trench bottom electrode has been dissolved for 12 s with 10 mA/cm2 in order to produce Cu+ ion at the trench bottom. From Fig. 3, we have understood the current density increase with narrowing trench widths.

Cu(I)Thiolate formation and acceleration effect will be discussed at the meeting.

[1] T. Hayashi et al., J. Electrochem. Soc., 160(6) D256 (2013).

[2] T. Hayashi et al., ECS 224thMeeting (2013).

[3] K. Kondo
et al., ECS Electrochem Lett., 3(4) D3 (2014).
Bottom-up Copper Deposition in Damascene Features Using Alkali Electrolytes
Authors: Josell Daniel , Moffat Thomas P.
Published: February 2020

I will discuss deposition processes in patterned features such that filling starts towards the feature bottoms with deposition then proceeding upward. In particular I will present results for alkaline electrolytes that exhibit critical behavior in the presence of a single deposition-rate suppressing additive and, for deposition under conditions that take advantage of the critical behavior, exhibit localized filling within patterned features and bottom-up filling of those features. I will detail bottom-up filling during copper electrodeposition in submicrometer features. I will point out the electrochemical and feature filling characteristics shared with previously observed bottom-up filling with both copper and gold in TSVs by a mechanism based on the resistively stabilized negative differential resistance evident in the voltammetry for the electrolytes. I will also point out the differences from superfilling of fine features using the curvature enhanced accelerator coverage mechanism.
Barrier Metal Slurry for Low Defect Copper Damascene Chemical Mechanical Polishing
Authors: Kim Hojoong , Seo Kyewon , Moon Jinok , Kim Hyunsoo , Hwang Hasub
Published: February 2020

In the semiconductor process, chemical mechanical polishing/planarization (CMP) is inevitable in copper (Cu) interconnect forming. Cu damascene scheme is achieved by help of CMP to form highly ordered metal lines.

As the CMP process uses a set of partial polishing steps to complete a damascene structure, slurries of each partial step is designed to have different performances to that of other steps. Among the steps, final partial step, so called, barrier metal (BM) CMP is a critical step because it determines the superior flat finish.

In the BM CMP, a structure consists of heterogeneous materials such as Cu, dielectric oxide, and BM should be polished at once. Thus, abrasive suspended in the BM slurry should be optimized to achieve the superior flat finish.

In the present study, 3 kinds of BM slurry were utilized. Abrasive of those slurries are made of colloidal silica in the size of 30 nm to 60 nm. The abrasive surfaces, however, are differently modified to have suitable performance for various polishing environments. The modification involves shape of abrasive, chemical additive to increase suspension stability, coating with polymers, and operation pH. Their effects on the CMP performance not only for blanket wafers but also for pattern wafers having 2x nm pitch were observed experimentally. The results indicated that not only polishing performance but also defect occurrence, which is important in mass fabrication, should be considered equally. Finally, strategy for reducing defect occurrence while maintaining Cu damascene performance will be discussed.
Development of Materials Integration for Laser Gain Media: Single Crystals and Ceramic (Polycrystalline) Materials and Applications
Authors: McKay Jeffrey , Bai Tingyu , Goorsky M. S.
Published: February 2020

A study of the fundamental issues of materials integration for wafer bonding offers new pathways for achieving photonic materials with unique properties.

First, the bonding of single crystal oxide crystals (YAG and yttria, for example) with different compositions and even different orientations is shown to critically depend upon several important parameters. A detectable level of subsurface damage usually accompanies the polishing of these crystals. We studied chemical mechanical polishing (CMP) of these oxide crystals to provide surfaces which exhibit sub-nm roughness, and the absence of subsurface damage. These surfaces are then activated and we use XPS and other surface sensitive techniques to assess the state of the surface after different processes. Next, we demonstrate that we can significantly reduce the bonding time and temperature to attach two single crystal pieces based on these improved polishing techniques. These techniques also apply to polycrystalline (ceramic) materials as well.

Second, we demonstrate wafer bonding for polycrystalline laser gain media. Two issues are important here. First, the grain composition – and hence chemistry – may be different than the bulk composition / chemistry. Under ideal conditions, the grain boundaries may simply be regions of misorientation and be nearly atomically abrupt. The second issue is that the different grain orientations present on a surface may (i) exhibit different hardnesses and / or (ii) different chem-mech polishing rates. Therefore, the issues of chemistry are more important than is the case with single crystal materials. We determined that the best combination of solution chemistry and polishing parameters involves the use of the SUBA 500 (yellow) pad and the same applied force as for the single crystal YAG. For many combinations of force, chemistry, and pad material, a clear delineation of the grain boundaries was revealed. However, we were able to achieve a set of polishing conditions for which the boundaries are not preferentially etched. These surfaces also proved to be damage-free and were able to show a high fraction of bonded interface (>90%) on 50 mm diameter gain media disks.