bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) X-Ray Crystallographical Studies on the Intermediates in the Solution Fabrication Process for Highly Efficient Perovskite Solar Cells
Authors: Wakamiya Atsushi 
Published: February 2020

Perovskite solar cells represent cost-effective next generation printable photovoltaics. In a relatively short period, power conversion efficiencies (PCEs) in such cells have been substantially increased, mainly due to improvements of the fabrication protocols for the perovskite layer as well as the development of new materials for buffer layers. In this presentation, the recent progress and perspective on this promising new type of photovoltaics are introduced, including our approaches toward development of high PCE cells in terms of materials science.
Regarding the molecular design for organic semiconductors that are used as p-type buffer layer in perovskite solar cells, we have recently reported that the use of partially oxygen-bridged triarylamines as quasiplanar scaffolds for charge-transporting materials facilitates delocalized pi-conjugation and on-top pi-stacking in the solid state, which ensures high carrier mobilities in the pi-stacking direction. In this study, we designed and synthesized the two-dimensionally expanded system (HND-Azulene) with a sheet-shaped structure, in which four oxygen-bridged triarylamines that contain alkoxy groups to enhance the solubility were attached to an azulene core skeleton. Using HND-Azuleneas a HTM in perovskite solar cells led to high PCEs (16.5%), even compared to Spiro-OMeTAD. By comparison with reference compounds, we were able to determine the key factors that improve the efficiency of HTMs in perovskite solar cells, which ultimately led to an increase in cell performance.
Moreover, we focused on the fabrication of perovskite layer by one-step solution method with solvent engineering, and studied on the mechanism in terms of the elucidation of the key intermediates formed during the process and the roll of solvents. Based on these results, we could develop and optimize the fabrication protocol to obtain dense and planar perovskite layer with 500 nm thickness. Using this protocol, we achieved to prepare the perovskite solar cells with high PCEs over 20%. The details of our recent progress will also be discussed in this presentation.
Investigation of Dynamics of Perovskites using Chemically, Spatially and Temporally Resolved 2D Mapping
Authors: Namkoong Gon , Jeong Hyeon Jun , Mamun M A , Byun Hyeryung , Demuth Derek , Jeong Mun Seok , Baumgart Helmut 
Published: February 2020

Currently, there is an ongoing strong discussion regarding the nature of organometallic CH3NH3PbI3-xClx perovskites for solar cells. In this work, perovskites have been investigated using chemically, spatially, and temporally resolved measurements. To investigate the carrier dynamics of perovskites, perovskite (CH3NH3PbI3-xClx) films were prepared using hot casting technique in which perovskite (CH3NH3PbI3-xClx) solution was prepared by dissolving equimolar ratios of lead iodide (PbI2, Sigma-Aldrich, 99%) and methylamine hydrochloride (MACl, Sigma-Aldrich) in N, N-dimethylformamide (DMF, Sigma-Aldrich, anhydrous, 99.8%) in 11% concentration. A lower hot-casting temperature (100 °C) resulted in smaller grain size, with typical grain sizes of 1~2µm. Hot-casting temperatures higher than 100 °C produced perovskite samples with larger grains of ~ more than tens of micrometers, which was confirmed by high-resolution scanning electron microscopy (SEM). The PL intensity and peak-position mapping image of submicron-scale were performed using confocal micro-spectroscopy. In-plane spatial resolution of ~380nm was indicated by an objective lens with numerical aperture of 0.7 and a solid-state laser with 405nm wavelength for the excitation. The signal collected by the objective lens was detected by a thermoelectrically cooled CCD detector. For the analysis of time resolved PL (TRPL), multifunctional confocal microscopy including a time-correlated single photon counting (TCSPC) system was employed. In addition, 2-D energy-dispersive X-ray (EDS) measurement was performed to elucidate the distribution of chemistries for the surface of perovskites, which were correlated to spatially and temporally resolved PL. Particularly, the carrier dynamics between grain interiors and grain boundaries were systematically investigated.
Fabrication of Non-Vacuum Sns Thin Film for Solar Cell Application
Authors: Eo Young Joo 
Published: February 2020

Tin mono-sulfide (SnS) thin film has been investigated as a photovoltaic absorber material due to not only a high optical absorption coefficient but also non-toxicity and earth abundance. However, the highest photovoltaic conversion efficiency is as low as 4.4%. One of the reasons for the low efficiency is considered to be the poor quality of the SnS layer, such as the formation of secondary phases and a high grain boundary density. Thus, many research groups have dedicated their own effort to obtaining a high quality of SnS thin film.
Nano-particle based approach can be one of the suitable fabrication methods of SnS thin films because the thin film can be prepared by a simple coating process using the nano-particle based ink, and the subsequent thermal annealing. The thermal annealing can transform the nano-particle precursors into the thin film and promote the grain growth. Moreover, it can affect the micro-crystalline structure of the thin film. Thus, we can control the physical properties of the SnS thin films by the modification of the thermal annealing condition.
In this study, we focused on the effect of the thermal annealing condition on the properties of the SnS thin films. We have found that the crystallinity and band gap (Eg) of thin film are highly dependent on the thermal annealing temperature. The partial pressure of hydrogen sulfide (H2S) gas during the thermal annealing affects the valence of Sn atom and the composition of the thin film. Finally, we demonstrate a SnS thin film solar cell and characterize its photovoltaic performance.
Transparent Conducting Oxide Layer By Thermal Evaporation for Cu(In,Ga)Se2 Solar Cell with Chemical Bath Deposited-ZnS Buffer Layer
Authors: Lee Woo-Jung , Cho Dae-Hyung , Wi Jae-Hyung , Han Won Seok , Chung Yong-Duck , Kim Yi Do , Choi Myung-Woon , Choi Jin Chul 
Published: February 2020

Chemical-bath-deposited (CBD) ZnS buffer layer is being steadily studied in Cu(In,Ga)Se2 (CIGS) thin-film solar cell because of their beneficial properties, for examples, good transparency with large direct bandgap, less toxicity and cost effectiveness. CBD-ZnS buffer layer, however, is easily affected during subsequent sputtering process for window layer and the conversion efficiency decreases with sputtering power. The decrease of efficiency in CBD-ZnS/CIGS thin-film solar cells is known to be related to plasma damage originated from high energy negative oxygen ions or neutral particles at the interface. In typical CIGS solar cell, ITO/i-ZnO bilayer deposited by sputtering process has been used as a conventional window layer and then interface properties between window layer and buffer is considered as an important key to determine the cell efficiency.
In this paper, to know actual effects of interface property between window layer and buffer on cell performance, we applied the two types of window layer and fabricated CIGS solar cell with CBD-ZnS buffer; (i) typical structure of ITO/i-ZnO/CBD-ZnS/CIGS, and (ii) thermally grown-IZO/i-ZnO/CBD-ZnS/CIGS. To completely exclude plasma damage from sputtering, two types of CIGS solar cell were also fabricated without i-ZnO layer. As a result, the cell performance interestingly shows the opposite tendency depending on presence or absence of i-ZnO layer; cell efficiency with IZO layer is higher than that with ITO layer in the presence of i-ZnO layer, while the former is lower than the latter in the absence of i-ZnO layer. To understand these phenomena, interfacial properties between window and buffer layer are characterized by various analysis tools.
(Invited) Scaled Magnetic Tunnel Junctions for High-Density Nonvolatile Memories
Authors: Sugii Toshihiro , Yoshida Chikako , Noshiro Hideyuki , Yamazaki Youichi , Iba Yoshihisa 
Published: February 2020

We report scaled magnetic tunnel junction (MTJ) for high-density nonvolatile cache memory. Under the same clock frequency, CPU performance can be improved by increasing its embedded cache memory capacity because the probability of cache misses decreases as cache memory capacity increases. Our motivation is to realize small magnetic tunnel junctions which enable high density embedded STT-MRAM cache. We have already proposed a unique fabrication technique which we call it as “shrink process” for reducing the size of a MTJ and realized MTJs with 20 nm in diameter [2014 Symposium on VLSI Technol. pp.212-213].
In this paper, in order to realize scaled MTJs with an MgO barrier, two major issues have to be solved. One is to realize a very thin barrier to keep moderate MTJ resistance from the point of a 1-transistor and 1-MTJ memory cell configuration. Another is to fabricate small MTJs without increasing their size variation.
In this paper, in order to realize the thin MgO barrier, its leakage mechanism was studied precisely, and proposed its model and possible solutions which will leads to much reduced leakage current and enough write endurance.
The shrink process for small MTJs was also investigated from the point of scalability without increasing MTJ size variation. After the MTJ etching, various plasma treatments were done. During this treatment, the sidewall surface of the MTJ was modified, which resulted in the small electrical MTJ size of around 20 nm. Proposed techniques are scalable and promising for sub-20 nm MTJ generations.
This work was funded by ImPACT Program of Council for Science, Technology and Innovation.
Resistive Switching Effect in BiFeO3 Nano-Islands
Authors: Choi Taekjib 
Published: February 2020

With a revolution in mobile devices and the increasing demand for higher data storage density, non-volatile memory technologies have rapidly developed. Among various non-volatile memories, resistive random access memory (ReRAM) based on metal oxide has been emerging as a promising alternative to flash memory due to its high speed, long retention, good endurance, low operating voltage, and high scalability. However, gaining a high memory performance and overcoming the scaling limitations would still impose a significant challenge and require nanoscale device structure, reliable resistive switching (RS) materials, and cost-effective device architectures. To realize high density resistive random access memory (ReRAM) compatible with cross-point stack structure, highly nonlinear bistable current-voltage (I-V) characteristics is necessary. Here, we report highly nonlinear bistable I-V characteristics in a BiFeO3 (BFO) nano-island arrays. We explored the local charge conduction and ferroelectric polarization in highly-oriented ferroelectric BFO nano-islands by using conductive atomic force microscopy and piezoresponse force microscopy. A mosaic nano-crystalline BFO nano-island grown on a Nb-doped SrTiO3 substrate, which has pinned downward polarization, exhibits both bipolar resistive switching with resistance ratio of 4,420 and nonlinear behavior with nonlinearity factor α of 1,100 in low resistance state. Such high resistance ratio and nonlinearity factor suggest that our BFO nano-islands can be extended to an N × N array of N = 3,740 corresponding to ~107 bits. Therefore, our BFO nano-island showing both high resistance ratio and nonlinearity factor offers a simple and promising building block of high density ReRAM.
TiO2 Based Conductive-Bridge-Random-Access-Memory
Authors: Kim Dong-Won , Song Myung-JIn , Kwon Ki-Hyun , Kim Hye-Jee , Jin Soo-Min , Kim Do-joon , Park Jea-Gun 
Published: February 2020

NAND flash is currently facing physical limitations for 10nm technology because as NAND flash cells have been getting smaller, cell to cell interference significantly increase. To overcome these challenge, new memories have been developed. Conductive Bridge Random Access Memory (CBRAM) is a one of the most promising new memories due to its simple structure, low power consumption, high scaling potential, large on/off margin and high speed. It has been reported that resistivity switching of CBRAM is induced by filament formation and rupture due to metal cation movement in the solid electrolyte. In the previous our research work, we studied CuO based CBRAM using CuTe top electrode. But CuO is not a fab-friendly material. In this work, instead of CuO based material, TiO2 are used for solid electrolyte because TiO2 is fab-friendly material and it has a good compatibility with a conventional CMOS process. TiO2 exist in three phases in atmospheric pressure, i.e. anatase, rutile and brookite, which phase of TiO2 presents different physical properties. In this work, we compared switching characteristics of amorphous with anatase phases TiO2 CBRAM. XRD confirmed amorphous-anatase phase transition at annealing temperature of 400 oC, as shown in Fig.1. Based on the crystallinity of TiO2 thin film, two different samples were prepared, amorphous (W/O annealing) and anatase phase TiO2 CBRAM (400 oC annealing). The CBRAM was fabricated on plug type TiN bottom electrode patterned wafer. The size of the bottom electrode was 34nm to 1921nm. TiO2 layer was deposited by RF magnetron sputter. And CuTe electrode was deposited by DC magnetron sputter. The structure of the device was shown in Fig.2 (a). On/Off ratio of TiO2 based CBRAM with amorphous phase was greater than that with anatase phase TiO2 CBRAM because HRS (High Resistive State) of the amorphous phase TiO2 CBRAM was lower than that of anatase phase TiO2 CBRAM. The amorphous and anatase phase TiO2 based CBRAMs demonstrated the endurance cycles of 105 and 2X106 respectively. We will report the memory characteristic of two phases TiO2based CBRAMs and explained why they showed the different memory characteristic.
* This work was financially supported by the Industrial Strategic Technology Development Program (10039191, The Next Generation MLC PRAM, 3D ReRAM, Device, Materials and Micro Fabrication Technology Development) funded by the Ministry of Trade, Industry and Energy (MOTIE), Republic of Korea and the Brain Korea 21 Plus, Republic of Korea.

Figure 1
Resistance Switching Structures Based on Hydrogen Silsesquioxane (HSQ) Thin Films
Authors: Ng Wing Hung , Mehonic Adnan , Montesi Luca , Buckwell Mark , Kenyon Anthony Joseph 
Published: February 2020

In recent years, resistance switching (ReRAM) devices have attracted a lot of attention due to their properties in low programmable energy and fast switching speed which could lead to potential applications in non-volatile memory. Hydrogen silsesquioxane (HSQ) is commonly used in electronic industry as a flowable dielectric material, and here we present our recent study of using HSQ thin film as an active switching material.
We carried out x-ray photoelectron spectroscopy (XPS) on HSQ thin films; results showed that they are SiO2 like after spin-coating and soft baking. Electrical characterisation results showed our metal-insulator-metal devices required typically -1.2V to switch from a high resistance state (HRS) to low resistance state (LRS). The voltage required to reset the device from LRS to HRS was typically +1.5V. The device was capable of bipolar switching and multiple setting and resetting cycles could be achieved with voltage pulses. Retention studies showed the device had retention properties of up to 105 seconds.
We have also fabricated HSQ nanopillar array and addressed individual nanopillars with a conductive atomic force microscope (CAFM). Results showed we could change the conductivity of individual pillars by applying bias on the sample via the CAFM tip. These encouraging results show HSQ is potentially a very promising material for non-volatile ReRAM applications.
The Application of Advanced Pulsed Plasma in Fin Etch Loading Improvement
Authors: Zhang Haiyang , Xiao Fangyuan , Han Qiuhua 
Published: February 2020

With the background of general integrated circuit (IC) feature size shrinking designers to get high performance transistors, Self-Alignment-Double-Patterning (SADP) FinFETetch was widely used in 14/16 nm technologies node and beyond. Rigorous process loading control (CD, profile, depth) in reactive ion etch (RIE) becomes more critical and challenging to ensure precise patterning and to avoid performance degradation among different features.[1]However, it’s quite hard to tackle such notorious loading for its inherent high Te induced ionization in traditional continuous wave (CW) plasmas.Thus, significant improvements in controlling plasma properties in a dry etching reactor are essential to satisfy such stringent requirement.
Pulsed plasmas have demonstrated several advantages compared to CW plasmas. By varying the pulse frequency and the duty cycle, pulsed plasma provide additional “control knobs” in controlling critical plasma parameters, such as ion and electron densities, electron temperature, flux and energy of the ions and radicals incident on surface. These critical factors affecting overall on-wafer performance during plasma etching processes at both within wafer and within die levels, etching and deposition, vertical and lateral etch rate, profile control, feature sidewall passivation and plasma damage.[2]In view of characters of pulsed plasma noted above, it appears to be a promising approach to improve RIE-lag loading in SADP fin etch.
In this paper, we systematically investigated the influence of both bias pulsed plasma and synchronous pulsed plasma to fin CD, profile (sidewall angle) and depth loading performance among dense and semi-isolated lines. It was found that proper duty cycle and frequency of pulsed power could drastically impact the loading performance. Based on the above learning, we finally delivered the overall solution by introducing synchronous pulsed plasma etch in mandrel and shallow trench isolation (STI) to address the rigorous loading control between dense and isolated patterns.
[1] Y. Wang, et al, CSTIC, “Process Loading Reduction on SADP FinFET Etch”, 2015
[2] S. Banna, et al, JVST A, “Pulsed High-density Plasmas for Advanced Dry Etching Process”, 2012
In-Situ Rare Earth Doping of Silicon-Based Nanostructures By Plasma Enhanced Chemical Vapour Deposition
Authors: Mascher Peter , Wojcik Jacek , Khatami Zahra , Miller Jeremy William , Brown Austin 
Published: February 2020

In order for Si-based materials to be used in solid-state lighting (SSL) schemes it is necessary to have precise control of the optical emission from these materials. This can be accomplished through the use of rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. After a brief review of the latest developments in the field, this talk will focus on several in-situ doping approaches to achieving very high, optically active concentrations of the rare earths. The methodologies include electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD), inductively coupled plasma (ICP) CVD as low thermal budget processes for film deposition, reactive sputtering, as well as the use of a recently installed Circular High Vacuum Magnetron Sputtering source attached to the ECR-PECVD tool. We will describe the salient features of the deposition systems and correlate important process parameters with the observed luminescence. Finally, we will discuss some of the challenges in developing electrically driven lighting cells suitable for SSL and in particular, for the development of widely tuneable Si-based light sources.
This work has been supported by the Natural Sciences and Engineering Research Council (NSERC) under its Discovery Grants Program.
Atmospheric Plasma Jet Oxidation of Solution Based Precursors for Enabling Material Discovery
Authors: Ajayi Babajide , Jaramillo-Cabanzo Daniel Felipe , Kumari Sudesh , Spurgeon Joshua M , Jasinski Jacek B , Sunkara Mahendra Kumar 
Published: February 2020

Paramount to the global action plan on climate change is the renewable energy technology that drives carbon neutrality goal, and vital in this pursuit is the addressing of material challenges currently facing this technology. To properly address this issue, a synthesis technique capable of accelerating the discovery of materials for various energy conversion and storage applications needs to be developed. Here we present a technique that allows rapid and controlled synthesis of mixed metal oxide particles using plasma oxidation of liquid droplets containing mixed metal precursors1. The conventional wet chemical methods for synthesis of multimetal oxide solid solutions often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control. The concept is demonstrated by synthesizing binary and ternary transition metal oxide solid solutions with control over entire composition range using metal precursor solution droplets oxidized using atmospheric oxygen plasma. The results show the selective formation of metastable spinel and the rocksalt solid solution phases with compositions over the entire range by tuning the metal precursor composition. The synthesized manganese doped nickel ferrite nanoparticles, NiMnzFe2−zO4 (0 ≤ z ≤ 1), exhibits considerable electrocatalytic activity toward oxygen evolution reaction, achieving an overpotential of 0.39 V at a benchmarking current density of 10 mA/cm2 for a low manganese content of z = 0.20.

References

1. Ajayi, B. P., S. Kumari, et al. (2016). "A rapid and scalable method for making mixed metal oxide alloys for enabling accelerated materials discovery." Journal of Materials Research, 1-12 doi: http://dx.doi.org/10.1557/jmr.2016.92
Thin and Flexible Nickel Based Current Collectors Developed By Electroless Deposition for Energy Storage Devices
Authors: Wu Haoran , Susanto Amelia , Lian Keryn 
Published: February 2020

The rapid development in portable and wearable consumer electronics for recreation, fitness and medicines requires thin, light weight and flexible solid state energy storage devices to improve the user experience and safety. Among the key components for solid state energy storages, relatively little effort has been made to the development of flexible current collectors. A polyethylene terephthalate (PET) film here was metallized by a simple and inexpensive electroless nickel deposition to form thin and flexible current collector for solid state energy storage devices. The PET was etched in butylamine, followed by surface activation of reduced nickel particles by sodium borohydride. The electroless nickel was then conducted in a commercial available plating bath. The chemical composition of the developed nickel on PET (Ni-PET) current collector was characterized by EDX and XPS, which showed a high P nickel deposition. SEM images suggested an island growth during the film formation.
The electrochemical characterizations showed that the Ni-PET can be used both as current collectors for electrochemical capacitors (EC) and as electrodes for batteries (Fig. 1a) in the respective potential regions. The electrochemical performance of the Ni-PET current collector was similar to that of Ni foil but with less hydrogen evolution at low potential, and the flexibility was also better than that of a metallic Ni foil. The resistance of the Ni-PET current collector almost remained the same under compression but increased under tension. Nonetheless, the shape and conductivity can be recovered when the applied force was released. The carbon nanotube was coated on the Ni-PET to form an electrochemical capacitor electrode and showed high chemical stability in both liquid and solid electrolytes (Fig. 1b), suggesting a promising application in solid energy storage devices.

Figure 1