bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancement of Switching Property of Perpendicular- Magnetic Tunnel Junctions Using Single MgO Based Co2Fe6B2 Double Free Layer Structure
Authors: Kondo Kei , Lee Julie , Lee dong-Gi , Park Jea-Gun 
Published: February 2020

Recently, perpendicular-spin-transfer torque magnetic random access memory (p-STT MRAM) has received considerable attention as the next-generation memory referred from its pre-eminent characteristics. It has high speed writing and reading property like dynamic random access memory (DRAM) with an additional property of non-volatility. Furthermore, it also has stable endurance (> 1014), less electric energy consumption to maintain its data (~1 pJ/bit) and high scalability. Because of these properties, p-STT MRAM has been considered to be the universal memory that can replace other memories in the market. However, it is difficult to be commercialized due to many critical issues of device parameters i.e., the tunneling magnetoresistance (TMR) ratio, thermal stability (Δ), and switching current density (JC). In particular, theses three device parameters should be achieved at 400oC temperature of the back-end of line (BEOL) to be manufactured into the market. To gain a reputation as a non-volatile memory at the market, p-STT MRAM needed low switching current density for low-power operating device.

In our research, we investigated new MTJ structure using single MgO based double Co2Fe6B2free layers separated by a W spacer layer (See Fig.1) for low current switching.
Samples were made by utilizing　12-inch multi-chamber magnetron sputtering system and magnetic vacuum oven. After sputtering process, samples were ex-situ annealed at 350 or 400oC under a perpendicular magnetic field of 3T for 30 minutes.
Figure 2 shows the switching voltage of anti-parallel state to parallel state (AP-P) and parallel state to anti-parallel state (P-AP) on I-V measurement. The switching voltage of AP-P and P-AP at newly double free layer decreased about 3.8 and 5.2% respectively, compared with the conventional free layer. This means that upper Co2Fe6B2 free layer had an influence for the lower Co2Fe6B2 free layer, therefor the lower Co2Fe6B2free-layer easily switched to perpendicular direction by in-plane magnetic anisotropy (IMA) magnetic resonance coupling.
In our presentation, we will present the switching property of Co2Fe6B2 double free layer for p-MTJs and review the switching mechanism for IMA magnetic resonance coupling by using IV measurement. In addition, we review the magnetic properties, atomic composition and TMR ratio, by using vibrating-sampling-magnetometer (VSM), Secondary-Ion-Mass-Spectrometry (SIMS), current-in–plane-tunneling (CIPT) measurement respectively.
* This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2014R1A2A1A01006474) and the Brain Korea 21 PLUS Program in 2014.

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(Invited) Design and Challenging Issues of Core/Shell Quantum Dots for Enhancing Power-Conversion-Efficiency in Si Solar-Cells
Authors: Park Jea-Gun 
Published: February 2020

For last several decade, although intensive researches has been conducted, the maximum power-conversion-efficiency (PCE) of Si solar cells has been economically limited to ~25%. Since Si solar cells absorbed mainly photons in visible wavelength, the silicon solar cells using energy-down-shift (EDS) mechanism has been recently proposed. Un-doped core/shell quantum dots such as CdSe/ZnS or Cd0.5Zn0.5S/ZnS have well demonstrated EDS by the Stokes shift of 52~127 nm and enhances ~1% of the PCE in the Si solar cells by implementing them on the Si solar-cell surface1. In addition, environment-safe InP/ZnS core/shell quantum dots well demonstrated the PCE enhancement of the Si solar cells. However, such small Stokes shift from core/shell quantum dots led the Si solar cell surface to resorb partially the emitting blue light so that the possible PCE enhancement would be limited to ~1%. Recently, the higher than ~200 nm of the Stokes shift from Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots has been demonstrated and enhances ~0.5% of the PCE in Si solar cells. Since Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots basically performs a lower quantum yield (~51%) so that their PCE enhancement would be limited to less than 1%2. Thus, another challenge such as energy-up-conversion through the core/shell quantum dots is necessary to overcome the limit of EDS in enhancing the PCE of Si solar cells. In this presentation, we will discuss these issues.

Reference

1. S.W.Baek, J.H.Shim, H.M.Seung, G.S.Lee, J.P.Hong, K.S.Lee, and J.G.Park, Nanoscale, 6, 12524 (2014).
2. M.Jalalah, Y.H.Ko, F.A.Harraz, M.S.Al-Assiri, and J.G.Park, Nano Energy, 33, 257 (2017)
Experimental Study of PVD Cu/CVD Co Bilayer Dissolution for BEOL Cu Interconnect Applications
Authors: Sun Xiaoxuan , Peethala Brown , Hopstaken Marinus , Hu Chao-kun , Mclaughlin Paul S , van der Straten O. , Demarest James , Motoyama K. , Nogami Takeshi , Lin Xuan , Zhang Xunyuan , Kelly James 
Published: February 2020

CVD Co liners are of interest for back end of the line (BEOL) interconnects due to improved Cu interconnect gapfill, especially at narrow feature widths.1-4 The stability of Co liner during downstream BEOL processing is a concern that has been discussed with respect to chemical mechanical planarization (CMP),5-6but its behavior during Cu plating has received less attention. Since Co is less noble than Cu (and its oxide is unstable at low pH), an optimized BEOL metallization process is important to prevent Co liner loss during plated Cu fill. Insufficient Cu seed coverage could expose Co to oxidation and attack in the Cu electrolyte, compromising yield and reliability.
In this study, we characterize the anodic dissolution behavior of thin PVD Cu/CVD Co bilayer films using linear sweep amperometry. The thin blanket seed layers are intended to mimic the sparse Cu seed coverage that might be present over a Co liner in a narrow dual damascene geometry. An example of this type of analysis is shown in Figure 1. The top figure (1a) shows the anodic polarization behavior of two separate electrode samples (plotted together), one for thick Co, another for thick Cu. The expected potential difference in the stripping peaks is observed, with Co dissolving at less anodic potentials. The middle (1b) and bottom (1c) figures show the behavior of bilayer electrodes having Cu overlayers of varying thickness. The Cu thickness clearly affects the polarization behavior of the underlying Co, with a fairly thick overlayer required to completely suppress early Co dissolution. The impact of these effects and other Cu chemistry aspects on the interconnect yield and reliability will be discussed.
1. T. Nogami, J. Maniscalco, A. Madan, P. Flaitz, P. DeHaven, C. Parks, L. Tai et al., In Interconnect Technology Conference (IITC), 2010 International, pp. 1-3. IEEE, 2010.
2. H. Shimizu, K. Sakoda, T. Momose, Y. Shimogaki, Japanese Journal of Applied Physics, 51, 05EB02-1 (2012).
3. A. H. Simon, T. Bolom, C. Niu, F. H. Baumann, C-K. Hu, C. Parks, J. Nag et al., In Reliability Physics Symposium (IRPS), 2013 IEEE International, pp. 3F-4. IEEE, 2013.
4. M. He, X. Zhang, T. Nogami, X. Lin, J. Kelly, H. Kim, T. Spooner, D. Edelstein, and L. Zhao, J. Electrochem. Soc., 160, (12) (2013): D3040-D3044.
5. N. Heylen, L. Yunlong, K. Kellens, L. Carbonell, H. Volders, G. Santoro, V. Gravey et al. In Interconnect Technology Conference (IITC), 2010 International, pp. 1-3. IEEE, 2010.
6. K. Tanwar, D. Canaperi, M. Lofaro, W. Tseng, R. Patlolla, C. Penny, and C. Waskiewicz, J. Electrochem. Soc., 160, D3247 (2013).

This work was performed by the Research Alliance Teams at various IBM Research and Development facilities.

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(Invited) Nanofabrication of Devices Using Scanning Force Microscopes
Authors: Bouchiat Vincent 
Published: February 2020

Among the most promising nanometer-scale manufacturing methods are lithographies using scanning probe microscopes mainly because they operate in the near field, contrary to all the competing techniques that operate by emitting radiation (light, electrons) in a far-field regime. The local probe microscopes encompasses a large family, the best known of which are the tunneling microscope (STM) and the atomic force microscope (AFM). They are based on a very local interaction between a tip and a given substrate. The scanning of the tip is carried out by piezoelectric ceramics whose movement is controlled to a fraction of angstrom. The measurement of the signal given by the tip/sample interation gives a topographical image of the surface, which can reach atomic resolution. The principles of these nanolithography techniques derived from these microscopes are based on a simple observation: since these techniques make it possible to carry out topographic imaging of a surface on a nanometric or even atomic scale, why not use them to modify surfaces at this same scale?
I will make a review of recent advances in the field of nanofabrication of fully operational quantum devices using Scanning Probe microscopes. In particular I will detail the techniques involving anodization techniques under the voltage biased tip of an Atomic Force Microscope and will conclude on the perspectives of using these techniques for large throuput at the industrial scale.
(Invited) Scalable Growth of Two-Dimensional Materials – a Prerequisite for Process Integration
Authors: Kataria Satender , Wagner Stefan , Lemme Max Christian 
Published: February 2020

Materials have always been at the heart of new inventions and, semiconductor industry is not an exception in this case. Two-dimensional (2D) materials are further enriching the available atlas of such novel materials. After the discovery of graphene in 2004, hundreds of other 2D materials are being explored owing to their distinct structures which lead to exciting properties and applications, unseen in other dimensions. Graphene and transition metal dichalcogenides (TMDs) based on molybdenum and tungsten have shown great promises for future technological applications including Internet of Things. Moreover, intriguing desired properties can be obtained by making hybrids and heterostructures of suitable 2D materials. Chemical vapor deposition (CVD) is the technique with a potential for scaling up the production of good quality 2D materials.
In this talk, I will give a brief introduction to 2D materials like graphene and molybdenum disulphide (MoS2) with emphasis on their large-scale production using CVD method. The open challenges for integrating these materials, especially graphene, into process technology will be discussed.

References:

1. Butler SZ, Hollen SM, Cao L, Gupta JA, Gutierrez HR, Heinz TF et al. Progress, Challenges and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 7 (2013) 2898.
2. Kataria S, Patsha A, Dhara S, Tyagi AK, Barshilia HC. Raman Imaging on High-Quality Graphene Grown by Hot-Filament Chemical Vapor Deposition. J Raman Spectrosc. 43 (2012) 1864.
3. Chang C-K, Kataria S, Kuo C-C, Ganguly A, Wang B-Y, Hwang J-Y, et al. Band Gap Engineering of Chemical Vapor Deposited Graphene by in Situ BN Doping. ACS Nano 7 (2013) 1333.
4. Kataria S, Wagner S, Ruhkopf J, Gahoi A, Pandey H, Bornemann R, et al. Chemical Vapor Deposited Graphene: From Synthesis to Applications. Phys Status Solidi A 211 (2014) 2439.
5. Lupina G, Kitzmann J, Costina I, Lukosius M, Wenger C, Wolff A, Kataria S et al. Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene. ACS Nano 9 (2015) 4776.
6. Bablich A, Kataria S, Lemme MC. Graphene and Two-Dimensional Materials for Optoelectronic Applications. Electronics. 5 (2016) 13.
7. Riazimehr S, Bablich A, Schneider D, Kataria S, Passi V, Yim C et al. Spectral Sensitivity of Graphene/Silicon Heterojunction Photodetectors. Solid-State Electron 115 (2016) 207.
8. Kataria S, Wagner S, Cusati T, Fortunelli A, Iannaccone G, Pandey H, Fiori G, Lemme MC. Growth-Induced Strain in Chemical Vapor Deposited Monolayer MoS2: Experimental and Theoretical Investigation. Adv Mat Inter (2017) DOI: 10.1002/admi.201700031.
(Invited) Exploring Thermoelectric Materials Using Predictive Theoretical Modeling
Authors: Maassen Jesse , Askarpour Vahid 
Published: February 2020

An important challenge facing society involves reducing our energy consumption and shifting away from fossil fuels and towards sustainable, abundant sources of power that do not harm the environment. Waste heat is a tremendous unutilized energy source, accounting for roughly 60% of the energy humans produce, that if we could only partially recover would have a major impact. Thermoelectrics (TE) provide a solution as materials than can convert heat into electrical power. A major goal is to enhance the TE conversion efficiency, characterized by the figure-of-merit ZT, which depends on the material TE properties: Seebeck coefficient, electrical conductivity and electronic/lattice thermal conductivities. Increasing ZT is critical for the advancement of TE technologies, but difficult since the TE properties are interrelated. To discover more high-ZT materials, it is important to explore and design new materials with unique properties tailored for TE conversion. In the past decade, there have been several breakthroughs in this direction, including nanostructured alloys, resonant impurity states, superlattice structures, all-scale defect engineering, and ultra-low thermal conductivity materials. These, like most advances, were experimentally led and based on trial-and-error, which can be expensive and time-consuming. To help guide experimental efforts and expedite discoveries, there is an opportunity to explore emerging materials using predictive theoretical modeling.
In this talk, I will present recent work focused on the development and application of a first principles approach for TE parameter predictions. I will describe our adopted framework, which combines density functional theory (DFT) and the Boltzmann transport equation (BTE). DFT is employed to extract the full electron and phonon dispersions, and to compute the detailed electron-phonon and phonon-phonon lifetimes, the dominant scattering mechanisms for electrons and phonons, respectively. These material properties serve as input for the BTE, which is solved for the TE transport coefficients. With this DFT-based approach, all TE parameters are obtained predictively, including Seebeck coefficient, electrical conductivity and electronic/lattice thermal conductivities, as a function of temperature and carrier concentration. Recent results on select materials, for example SnSe, will be presented to demonstrate the approach and to illustrate how we can gain physical insight. This work will help guide experimental breakthroughs by theoretically exploring and identifying new TE materials with enhanced properties.
(Invited) High Performance and Flexible Nanostructured Thermoelectric Devices By Additive Printing of Colloidal Nanocrystals
Authors: Zhang Yanliang 
Published: February 2020

Thermoelectric generators (TEGs) produce electrical power using thermal energy from various sources, including the waste heat. Thermoelectric materials have undergone tremendous improvement of the figure of merit ZT in recent two decades largely attributed to nanostructuring. Despite these progresses in materials performances, the high cost of manufacturing the nanostructures into functional materials and devices is still a significant barrier to bring these materials into commercial domain.
Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type and p-type films demonstrate peak ZTs of 0.43 and 0.8 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. The printed nanostructured thermoelectric films present ultralow thermal conductivities due to the nanoscale grains and pores, which significantly scatter the phonon transport and reduce phonon mean free path.
A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm2 with 60 ºC temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications.
In-Plane ZT Measurements of PbTe/PbSe Superlattice Layers Deposited by Atomic Layer Deposition
Authors: Chen Xin , Linseis Vincent , Lin Pengtao , Zhang Kai , Baumgart Helmut , Reith Heiko 
Published: February 2020

The conversion efficiency of the thermoelectric (TE) device is determined by the dimensionless figure of merit ZT, which is expressed as ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. The key strategy to enhance ZT involves the reduction in thermal conductivity k
of TE materials. This led to the synthesis of low-dimensional structured materials such as 2-D superlattice structure, 1-D nanowire, and 0-D quantum dots. The phonon transport was suppressed if the dimension of the film approaching the mean free path of the phonons, resulting in a reduction in thermal conductivity and consequently improves ZT. The direction of the measurement, either in-plane or vertical to the surface, plays an important role in determining TE properties of the anisotropic samples, such as superlattices and quantum well structures. It is essential to measure all the parameters in the same direction and simultaneously to obtain accurate ZT value.
In this work, a novel Si-based test chip was utilized to perform in-plane ZT measurements of PbTe/PbSe superlattice films. Figure 1 (a) shows the pre-fabricated circuit on the chip for measuring simultaneously the Seebeck coefficient, electrical conductivity, and thermal conductivity [1]. The thermoelectric film was deposited in the red square area by using a shadow mask. All the parameters were measured in the temperature range of 120 K to 450 K with a 1 T magnet field. In our work, PbTe and PbSe thin films and superlattice layers were synthesized by Atomic Layer Deposition (ALD) technology directly on the pre-structured Si chip. Figure 1 (b) shows an SEM micrograph of the 30 nm thick PbSe film grown on the chip. The PbTe/PbSe superlattice was then deposited on the PbSe buffer layer using ALD by alternatively depositing PbTe and PbSe layers. A thin Al2O3protection and diffusion barrier layer was applied to avoid oxidation and degradation of PbTe/PbSe films. The period of superlattice structure was varied from 2 nm to 10 nm to observe optimized period for achieving highest ZT value.
Reference:
[1]. Linseis, V., Völklein, F., Reith, H., Woias, P., & Nielsch, K. Platform for in-plane ZT measurement and Hall coefficient determination of thin films in a temperature range from 120 K up to 450 K. Journal of Materials Research,
31(20), 3196-3204, (2016).

Figure 1
Pulsed Laser Deposition of BiCl3 Doped Bi2S3/Cu Nanoparticle Composite Films for Thermoelectric Applications
Authors: Chen Tsung-Han , Chou Wei-Yen , Chen Chun-Hua 
Published: February 2020

Thermoelectric (TE) materials capable of directly converting heat into electricity have become a highly potential category in energy materials and are expected to tackle the energy issue of the future. Among a variety of TE materials, lead telluride (PbTe) has been recognized as an outstanding mid-temperature TE material with an applicable TE figure of merit (ZT) of ~1.2. However, due to the toxicity of both Pb and Te, development of alternative mid-temperature TE materials is urgently required. Bismuth sulﬁde (Bi2S3) is specially selected in the present study as the most promising candidate for alternating PbTe mainly because of its potentially high Seebeck coefficient (102−103 μVK-1). Unfortunately, the generally poor electrical conductivity (<102 S/cm) and the resulting low ZT (~0.2) of Bi2S3 severely restrict its applicability. In this work, by controlling the substrate temperature, the volatility of sulfur would lead the compositional deviation from the chemical stoichiometry of Bi2S3 and the electrical conductivity of the sulfur-vacancy introduced Bi2S3-x would thus be improved. Similarly, BiCl3 was also considered and applied as a donor dopant to improve the electrical conductivity. Furthermore, a series of novel BiCl3 doped Bi2S3-Cu nanoparticles layer-by-layer composite films were designed and fabricated through the newly built dual-beam pulsed laser deposition for improving the electric conductivity without seriously sacrificing the Seebeck coefficient.
The prepared highly crystalline intrinsic Bi2S3 films on insulated SiO2/Si substrates exhibit a very high electric conductivity of 638 Scm-1 evidently due to the simultaneously enhanced carrier concentration and mobility, and the Seebeck coefficient of - 453 μVK-1. The resulting power factor is 137 μWcm-1K-1 which is four times higher than the reported highest value (29 μWcm-1K-1) from the chemically prepared Bi2S3 so far. The introduction of BiCl3 into Bi2S3 indeed leads to an enhancement of the electrical conductivity from 170 Scm-1 (before BiCl3 doping) to 450 Scm-1 whereas the Seebeck coefficient decreases from -522 μVK-1 to -221 μVK-1. On the sake of enhancing the electricity conductivity and Seebeck coefficient simultaneously, the Cu nanoparticles were introduced into the BiCl3 doped Bi2S3 film. The heterostructure of Cl doped Bi2S3/Cu played an important role in obtaining the high electrical conductivity of 715 Scm-1, Seebeck coefficient of -413 μVK-1 and the power factor of 122 μWcm-1K-1 which is twice higher than those of the intrinsic Bi2S3 film (49 μWcm-1K-1).