bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of in-Situ Methods for Solution ALD
Authors: Barr Maissa K. S. , Koch Vanessa , Bachmann Julien , Ding Fei , Tavera Mendez Cindy Ly , Grass Jan-Paul , Wisser Dorothea , Brummel Olaf , Libuda Jörg , Götz Klaus , Unruh Tobias , Liao Pei-Chun , Crisp Ryan
Published: February 2024

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid.1,2 'Solution ALD'(sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as oxides and sulfides deposition. However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors, offering the possibility to grow materials that cannot be obtained by gALD and using mild conditions which allow the growth on sensitive substrates. Recently we extended the understanding of the nucleation of selected materials grown by sALD such as CuSCN, TiO2 and SnSx. The study of the nucleation process relies on, first the identification of the absorbed chemical species at the surface by in-situ infra-red spectroscopy, second the ability to determine the type of interaction of the precursor with the surface by ex-situ solid state nuclear magnetic resonance (NMR) and third the evolution of nuclei formation with in-situ x-ray reflectometry (XRR) and atomic force microscopy. We developed the necessary instrumentation to obtain measurement compatible in liquid environment for each in-situ method. Form IR we can identify the phase preferential phase that is obtained as well as the defects formation for extremely thin films and NMR shows the chemical bonding of precursors at an early stage. Additionally, the AFM and XRR investigations are needed to follow the evolution of the nuclei size and their distribution of a surface as well as the nuclei density of each half cycle.

The extension of the knowledge on the reaction mechanism in sALD process appears to be crucial to design next reactions and to understand later on the properties of the layers obtained with sALD.

Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett.
2015, 15, 6379

Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol.
2017,6, N171
Chemical Vapor Functionalization of Polymer Membranes for Water Treatment
Authors: Elam Jeffrey W. , Mane Anil U. , Pathak Rajesh , Rozyyev Vepa , Shevate Rahul
Published: February 2024

Polymer membranes are used extensively in water purification to filter and remove particulate and molecular contaminants. Ideally, these membranes should exhibit high permeance, selectivity, and fouling resistance, but these attributes are rarely achieved simultaneously. One approach to improve membrane performance is to modify the polymer using reactive chemical vapors to impart the desired physiochemical properties. In this presentation, I will describe recent work at Argonne using atomic layer deposition (ALD), sequential infiltration synthesis (SIS), and vapor-phase grafting to modify polymer membranes used for ultra- and nano-filtration in water treatment. These techniques rely on self-limiting chemical reactions between gaseous precursors and a solid surface to grow material in an atomically controlled fashion. We have used ALD to produce ultrathin and conformal inorganic layers allowing the membrane pore size and pore wall composition to be precisely tuned, SIS for the bulk modification of polymers by creating an organic-inorganic hybrid material, and vapor-phase grafting of small molecules to achieve additional control over the membrane surface properties. Our studies employ a suite of in-situ and in-operando measurements to elucidate the surface chemistry for these processes and extensive ex-situ characterization and testing to understand the effects of chemical vapor treatment on polymers and how they impact membrane performance.
Modeling the Atomic Layer Deposition of Metal Thin Films: Studying the Surface Reaction Mechanism By Density Functional Theory Simulations
Authors: Liu Ji , Nolan Michael
Published: February 2024

Atomic layer deposition (ALD) is widely used in microelectronics and semiconductor industry to deposit thin films as part of device fabrication in nano- or subnano-dimensions. The key advantages of ALD are the conformality and precise thickness control at the atomic scale, which are difficult for physical or traditional chemical vapor deposition methods. The atomic scale understanding of ALD is vital and essential to design and optimize the deposition process, where density functional theory (DFT) calculations play an important role in providing detailed reaction mechanism, theoretical screening of suitable precursors and estimated growth-per-cycle (GPC).

In this study, we show our recent works on DFT calculations of the growth mechanism study of Cobalt (Co) thin film by plasma-enhanced ALD1,2. We first addressed the surface reaction mechanism at the metal precursor pulse and plasma half-cycle on NHx-terminated Co surfaces, which corresponds to the steady growth for the PE-ALD. The adsorption and reactions of metal precursors (CoCp2) on NHx terminated metal surfaces were investigated with the inclusion of van der Waals corrections. The plausible reaction pathways include: precursor adsorption, hydrogen transfer, CpH formation and CpH desorption. The direct Cp dissociation mechanism is not considered on these NHx-terminated metal surfaces due to experimentally observed minimal C impurities at the deposited metal thin films, which indicates that most of the Cp ligand is removed completely. The barrier for proton transfer was calculated using climbing image nudged elastic band (CI-NEB) method.

The reactions at the initial stages on typical H:Si(100) surface are investigated to gain atomic insight on the effect of different substrates on the elimination of Cp ligands. Our work is important to reveal the mechanism and feasibility of atomic layer deposition of metals using N-plasma.

In addition, we present our recent works3,
4 on the thermal ALD of Co using reducing agent Zn(DMP)2 and thermal ALD of Fe4Zn9 thin film with diethyl zinc (DEZ). Our DFT results show that by selecting suitable reducing agent, we can control the deposited thin films to be Zn-free high quality Co thin film or desired intermetallic thin film with high Zn content.

These DFT results are important to understand the reaction mechanism for ALD and provides new knowledge in depositing the thin films by adjusting the reducing agents.

References

[1] Liu, Ji, et al., J. Phys. Chem. C 2019, 123, 4, 25166-25175.

[2] Liu, Ji, et al.,
J. Phys. Chem. C 2020, 124, 22, 11990–12000

[3] Zanders, David, et al,
Chem. Mater. 2021, 33, 13, 5045–5057

[4] Ghiyasi, Ramin, et al.
Chem. Mater. 2022, 34, 11, 5241-5248.
Nucleation Behavior and Growth Characteristics of Atomic-Layer Deposited Iridium Thin Films with Ticp and Oxygen
Authors: Chung Hong Keun , Kim Han , Park Tae Joo , Kim Seong Keun
Published: February 2024

Platinum group elements (Pt, Ru, Pd, Rh, Ag, Au, and Ir) have excellent properties of high thermal and chemical stability, and low electrical resistivity. Due to the attractive characteristics, these materials are also expected for applications in the semiconductor industries. In particular, iridium (Ir) has attracted interests as a potential electrode for memory devices because of its high work function and low resistivity (bulk: 4.7 μΩ cm).

Despite the advantages of Ir, the deposition of Ir thin films for the next-generation memory applications faces critical challenges. Since metal has a high surface energy, it is difficult to adsorb on a surface with a lower surface energy. So, formation of metal nuclei is delayed in the initial growth of atomic layer deposition (ALD), and island growth is preferred. During the ALD, sparsely grown nuclei cause an increase in surface roughness which deteriorates the leakage current properties of capacitors.

In this study, we attempted ALD of Ir films from newly synthesized tricarbonyl (1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl iridium and oxygen. The growth behavior and film properties of impurity contents and bulk resistivity were investigated in terms of the growth temperature. Also, we examined the changes in the surface morphology of the iridium film with the film thickness. Consequently, we achieved the growth of continuous and smooth Ir films even below 4 nm by forming nucleation-promoting layer at high temperature and followed by ALD of Ir at low temperature. In addition, the capacitor device characteristics were also investigated using Ir as a bottom electrode.
ALD-Based IrOx/Ir Supported Electrocatalysts for Water Electrolysis Technology
Authors: Platel Romain , Dufour Fabien , Thuilliez Julien , Cavaliere Sara , Jones Deborah J. , Rozière Jacques
Published: February 2024

Hydrogen (H2) is an alternative energy vector to replace fossil fuels, with potential applications like hydrogen fuel cell-powered vehicles and in the chemical industry. H2 production through polymer electrolyte membrane (PEM) water electrolysis (WE) appears to be a highly promising technology. While iridium oxide is the most commonly used anode oxygen evolution reaction (OER) catalyst for PEMWE, its scarcity makes it an extremely critical raw material. In order to obtain active and stable anodes with an ultra-low iridium loading, we are developing a strategy based on doped metal oxides as conductive supports, on which iridium-based thin films and/or nanostructures are deposited using atomic layer deposition (ALD). ALD can indeed allow the control of the amount of deposited species at sub-nanometric scale by changing the number of ALD cycles, thus ensuring a minimal iridium loading for efficient OER catalysis. In this study, the influence of the temperature of deposition was investigated to obtain either IrOx ultrathin films or Ir nanoparticles. The morphology and composition of these deposits were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The nature and crystallinity of these electrocatalysts will indeed have a huge impact on their catalytic activity and the subsequent electrode’s efficiency as well as in their long-term durability. In brief, we will present the production of nano-structured OER electrocatalysts, in which the bulk consists of a sufficiently conductive metal oxide support with the surface uniformly coated with an ultra-low loading of iridium deposited via conformal ALD.
Atomic Layer Deposition of Ru Nanoparticles on Low Surface Energy Carbon Supports for Alkaline Hydrogen Evolution Reaction
Authors: Thalluri Sitaramanjaneya M. , Zazpe Raul , Rodriguez Pereira Jhonatan , Sopha Hanna , Macak Jan M.
Published: February 2024

Platinum group metals such as Pt, Ru, Pd, Ir, etc., have superior performance for various catalytic applications.[1] Due to their scarcity, efforts were being made to reduce or replace these noble metals. Atomic Layer Deposition (ALD) is one among the best technique to facilitate lowering of loading mass on a support of interest.[2],[3] Furthermore, ALD is the most suitable technology that can decorate high aspect ratio and high surface area substrate architectures by noble metal nanoparticles.[4] Due to the governing surface energy variations between noble metals and support surfaces, the growth initiates as nanoparticles (NP) and with a further increase in ALD cycles the agglomeration among NP’s dominates over the individual NP size increase, thus developing thin films of relatively higher thickness. The surface energy variations are also known to increase the nucleation delay of noble metals especially for Ru considerably. In this regard our efforts were laid to improve the functionality with pretreatments on carbonaceous supports which were shown promising to reduce the nucleation delay of ALD deposited Ru.

For electrocatalytic applications, it is important to choose the right substrates. Among available substrates, carbon papers (CP) and titania nanotube (TNT) layers are best choices considering their physio-chemical properties, availability, vast literature, and low costs incurred using these as support substrates in electrocatalysis and photocatalysis. Several surface modifications for CP’s and variations on morphological aspects of TNT layers had received a great attention form applied fields due to their improved surface area, conductivity and stability.[5]–[8] Uniformly decorating these CP’s and TNT layers by NPs or thin films of catalysts proved to be highly efficient with no boundaries on applications.[9]

The presentation will introduce and describe the synthesis of different noble metal NPs by our ALD tool (Beneq TFS 200) on various aspect ratio TNT layers and CP substrates. It will also include the corresponding physical and electrochemical characterization and encouraging results obtained with alkaline hydrogen evolution reaction.

References:

Huang, Z. F. et al.
Advanced Energy Materials 7 (2017) 1700544.

Yoo, J. E. et al.
Electrochem. commun. 86, (2018) 6.

Anitha, V. C. et al.
J. Catal. 365, (2018) 86.

Zazpe, R. et al.
Langmuir 32, (2016) 10551.

Sopha, H. et al.
Appl. Mater. Today 9, (2017) 104.

Macak, J. M., Zlamal, M., Krysa, J. & Schmuki, P. Small 3, (2007) 300.

Liu, C., Sun, C., Gao, Y., Lan, W. & Chen, S. ACS Omega 6, (2021) 19153.

Thalluri, S. M. et al.
Small (2023) 2300974.

Dvorak, F. et al.
Appl. Mater. Today 14, (2019) 1.
(Invited) Simulations of Ultra-Scaled Electronic Devices with a Novel Flexible Nano-TCAD Nano-Electronic Simulation Software (NESS) Environment
Authors: Georgiev Vihar Petkov
Published: February 2024

Simulation of conventional and emerging electronic devices using Technology Computer Aided Design (TCAD) tools has been an essential part of the semiconductor industry as well as academic research. Computational efficiency and accuracy of the numerical modeling are the key criteria on which quality and utility of a TCAD tool is ascertained. Further, the ability of the tool to incorporate different modeling paradigms and to be applicable to a wide range of device architectures and operating conditions is essential.

In this talk, I will provide an overview of the new device simulator NESS (Nano-Electronic Software Simulator) developed at Device Modelling Group at University of Glasgow. NESS is a fast, modular software with its own structure and mesh generators, and contains different modules for classical, semi-classical, and quantum transport solvers, mobility calculation, kinetic Monte-Carlo etc. NESS can simulate numerous device architectures such as nanowire and bulk transistors, tunnelling field effect transistors (TFET) and resonant tunnelling diodes. Moreover, NESS accounts for various sources of statistical variability in nano-size electronic devices and it can perform statistical simulations for thousands microscopically different devices.
(Invited) Photo-Assisted Electron Emission from Silicon-Based Electron Emission Devices
Authors: Shimawaki Hidetaka , Nagao Masayoshi , Murakami Katsuhisa
Published: February 2024

Ultrafast pulsed electron sources with spatial coherence have attracted significant interest in emerging applications such as scientific instruments of ultrafast electron microscopy [1-3] and electron beam lithography [4], and also as sources of X-ray [5] and micro- and THz-waves [6-9]. In particular, high-frequency electron bunch trains generated directly from the cathode surface can not only dramatically reduce dimensions and weight through the elimination of the pre-modulation circuit, but can also provide extremely high efficiency and improve the power in the electron beam devices due to coherence effects.

One solution is employing photoemission from electron sources driven by ultrashort laser pulses for such emerging applications. Metallic flat photocathodes and recently metallic nanotips have been employed. However, a low quantum efficiency (QE), typically of approximately 0.01 %, and a large work function require a high-power UV laser to generate an intense electron beam. Negative electron affinity (NEA) semiconductor photocathodes such as NEA GaAs can provide QE as high as ~ 10 % [10], operating using visible laser light irradiation. However, the NEA surface is fragile and easily damaged by residual gas adsorption or beam extraction.

In this presentation, we introduce the research and development of gated Si-FEAs with a volcano structure and planar-type electron emission devices based on a MOS diode structure and discuss the potential of the devices as a photocathode of the devices operating without NEA surface treatment. We investigate the optical properties of emitted electrons from the devices under visible laser light irradiation. The results indicate that Si-based electron emission devices with a fully optimized structure hold promise as a photocathode with a high QE and a high-speed response for generating a train of ultrashort electron bunches, operating without NEA surface treatment.

References

[1] H. Dömer, and O. Bostanjoglo, Rev. Sci. Instrum. 74, 4369 (2003).

[2] W. E. King, G. H. Campbell, A. Frank, and B. Reed, J. Appl. Phys. 97, 111101 (2005).

[3] K. Bücker, M. Picher, O. Crégut, T. LaGrange, B. W. Reed, S. T. Park, D. J. Masiel, and F. Banharta, Ultramicroscopy 117, 8 (2016).

[4] J. E. Schneider, J. Vac. Sci. Technol. B 16, 3192 (1998).

[5] X. J. Wang, X. Qiu, and I. Ben-Zvi, Phys. Rev. E 54, R3121 (1996).

[6] C. A. Spindt, C. E. Holland, P. R. Schwoebel, and I. Brodie, J. Vac. Sci. Technol. B 14, 1986 (1996).

[7] K. L. Jensen, R. H. Abrams, and R. K. Paker, J. Vac. Sci. Technol. B 16, 749 (1998).

[8] H. Ishizuka, Y. Kawamura, K. Yokoo, H. Mimura, H. Shimawaki and A. Hosono, Nucl. Instr. Meth. Phys. Res. A 445, 276 (2000).

[9] Y. Neo, H. Shimawaki, T. Matsumoto and H. Mimura, J. Vac. Sci. Technol. B 23, 840 (2005).

[10] W. Liu, S. Zhang, M. Stutzman, and M. Poelker, Phys. Rev. Accel. Beams 19, 103402 (2016).
Controlling Diameter and Morphology of Colloidal-Silica-Abrasives Via Designing Surfactant Functional Group
Authors: Kim Pilsu , Jeon Min-Uk , Jin Hyeong-Ju , Ahn Ho-Jun , Kim Ju-Yeon , Park Jin-Hyung , Park Jea-gun
Published: February 2024

As the design rule of logic semiconductor has been scaled down toward 5, 3, 2.1, 1.5, and 1.0 nm, the line width of Cu-film as interconnect line of logic semiconductor has been rapidly scaled down toward 36, 32, 24, 20 and 16 nm. The CMP of the Cu-lines is essential fabrication process, challenging an achievement of dishing and erosion during Cu-film CMP. In particular, the dishing and erosion of the Cu-film CMP has been principally affected by the diameter and morphology of colloidal-silica-abrasives in a CMP slurry. In a conventional synthesis method synthesis of colloidal-silica-abrasives, ethoxysilanol was formed via the hydrolysis reaction by Tetraethyl orthosilicate(TEOS) and H2O producing ethoxysilanol, following the condensation reaction between two ethoxysilanol. The diameter of colloidal-silica-abrasives could be obtained by adjusting the concentrations of TEOS, alcohol, and alkali catalyst, but the solid loading of colloidal-silica-abrasives could be varied.

Thus, in our study, a novel synthesis method of the colloidal-silica-abrasives was designed by adding a charged functional group surfactant during the conventional colloidal-silica-abrasives synthesis method. The effect of the surfactant having negative charged carboxyl functional group (i.e. Ethylenediaminetetraacetic acid: EDTA) on the diameter and morphology of the colloidal-silica-abrasives were investigated as function of the EDTA concentration; i.e. when the concentration of EDTA increased from 0 to 0.03 wt%, the diameter of colloidal-silica-abrasives increased from 47.0 to 103.8 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.36 wt%, as shown in Fig. 1. In addition, when the ETDA concentration increased above 0.0025 wt%, the morphology of colloidal-silica-abrasives was transformed from cocoon shape to spherical shape. Furthermore, the effect of the surfactant having the positive charged amine functional group (i.e. Triethanolamine: Tri-ETA, Ethylenediamine: EDA, Diethylenetriamine: DETA, Triethylenetetramine: TETA) were estimated as function of the number of amine functional group in the surfactant, as shown in Fig. 2. When the number of positive charged amine functional groups increased 0 to 4, the diameter of colloidal-silica-abrasives increased from 67.2 to 143.86 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.2 wt%. In addition, the synthesis with positive charged amine functional group was transformed from cocoon shape to spherical shape. The synthesis mechanism, the enhanced polishing rate of Cu-film surface, dishing and erosion after Cu-film will be presented in detail.

Acknowledgement

This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (1415180388) and KSRC(Korea Semiconductor Research Consortium) (20019474) support program for the development of the future semiconductor device.

Figure 1
Effect of Ferric Catalyst on Chemical Decomposition of Polyimide-Film-Surface for Enhancing Chemical–Mechanical-Planarization Polishing-Rate
Authors: Kim Seongin , Kang Seon-Hwa , Cho Jin-Woong , Park Jin-Hyung , Park Jea-gun
Published: February 2024

In semiconductor devices, flexible displays and microelectromechanical systems (MEMS), polyimide has been utilized as a protecting layer, interlayer dielectric polymer for thin-film metallization and low-stress polymer for wafer-level packaging. Since, it has low stress, low thermal coefficient of expansion, low moisture, high modulus, good ductility, thermal stability, high glass transition temperature, and low process cost. However, the applications of polyimide required estentially chemical-mechanical-planarization (CMP) of the polyimide-film-surface. that can be challenging to enhance the polishing rate of the polyimide-film-surface because of the hard and covalently bonded nature of the polyimide-film surface.

In this study, to enhance chemical dominant CMP, the chemical decomposition of the polyimide-film-surface was performed by hydrolysis reaction between ferric ions and oxygen atoms covalently bonded with pyromellitimide on the polyimide-film-surface during CMP, as shown in Fig. 1. The polyimide-film polishing rate was estimated as a function of ferric catanylst concentration in the CMP slurry;surprisingly, the polyimide film polishing rate(i.e., 1465A/min) peaked at a specific(i.e., 0.05wt%) ferric catalyst concentration, as shown in Fig. 2. This result indicates that the degree of chemical decomposition during CMP could be principally determined by ferric nitrate concentration. The details of both chemical and mechanical dominant polishing mechanisms will be presented. In addition, the evidence of the chemical composition of the polyimide-film-surface will be demonstrated, depending on the ferric catalyst concentation in the CMP slurry.

Figure 1
Hierarchical Networks Composed of Silver Micromeshes and Silver Nanowires for Optoelectronic Devices
Authors: Kang Seoin , Chung Choong-Heui
Published: February 2024

Metal based networks are expected to be promising candidates to replace transparent conducting oxides such as indium tin oxide and doped zinc oxide in many kinds of optoelectronic devices such as displays and thin-film solar cells because they have lower sheet resistance, higher optical transmittance, and better mechanical flexibility than transparent conducting oxides. However, carrier transport in the empty spaces present in the metal networks has to be considered for the metal networks to be successfully integrated to real electronic devices. Therefore, it is still questionable for them to be appropriately implemented in real optoelectronic devices even though they have such advantages over transparent conducting oxides. Here, hierarchical networks composed of silver micromeshes and silver nanowires are presented. The hierarchical networks are successfully integrated to thin-film solar cells as transparent conducting electrodes by replacing transparent conducting oxides while they show low sheet resistance of ~2 ohm/sq, high optical transmittance of 88%. The silver micromeshes provides such low sheet resistance and high optical transmittance and the silver nanowires have role of ensuring carrier transport between empty spaces in the hierarchical network. In addition, they have excellent mechanical flexibility of no degradation of optoelectronic properties at a mechanical bending of radius of curvature of 5 mm.
Synthesis of Dielectric Al-Doped HfO2 Thin Film by Polymer-Assisted Deposition
Authors: Park Gyeongbae
Published: February 2024

As transistors scale down, demands for high-k dielectric materials increase. Among various dielectric materials, HfO2 have drawn attention because of its large band gap, high dielectric constant, and excellent physical/chemical stability. Although several solution-based synthesis have been developed, their dielectric properties are inferior to those obtained by conventional vacuum processes (e.g., atomic layer deposition, sputtering). This study demonstrates a solution-based polymer-assisted deposition (PAD) of high-k Al-doped HfO2 thin films exhibiting excellent dielectric properties comparable to the conventional deposition methods. The PAD process enables the control of film thickness (≥3 nm) and the homogenous Al doping in the entire thin film. The key to the success is HCl-mediated coordination of metal ions and polymer. Systematic analysis on the structure and chemical composition of the dielectric layer is carried out. It is found that the phase transition from monoclinic phase to a mixture of tetragonal and amorphous phases results in excellent dielectric properties. The 7.8 nm thick thin film doped with 4.1 at% of Al exhibits a high dielectric constant of 30.2 with a high areal capacitance (674 nF cm−2 at 1.0 kHz), a low leakage current (3.3 × 10−9 A cm−2 at 2.0 MV cm−1), and a high breakdown voltage (7.7 V).
Study of Nb2O5 High-k Dielectric Material Deposited By Atomic Layer Deposition for Metal-Insulator-Metal Capacitor
Authors: Ihara Kou , Labbé Christophe , Cardin Julien , Frilay Cédric , Lemenager Maxime
Published: February 2024

Metal-Insulator-Metal (MIM) capacitors are important components in many electronic devices, including memory devices, filters, and oscillators. The performance of these devices depends strongly on the electrical properties of the dielectric layer. The application of new high-k materials can improve the properties of modern capacitors such as leakage current and capacitance density. However, it is necessary to understand the deposition conditions of both electrode and dielectric materials in order to master the dielectric properties in future MIM capacitors.

One potentially interesting high-k material is niobium pentoxide (Nb2O5) with a wide band gap (3.6 eV) and high refractive index (n=2.3 @633 nm) deposited by Atomic Layer Deposition (ALD) using niobium (V) ethoxide as niobium precursor at 180°C and H2O as reaction agent and oxygen source. Nb2O5 films were deposited directly on a silicon (Si 100) substrate or on a 10nm of titanium nitride (deposited by ALD on Si substrate, n=1.4@633 nm). The Nb2O5 films were deposited with a good film thickness uniformity on the 6-inches of the wafers with a thickness ranging from 20 to 60 nm on each sample. The deposition was done under a suitable ALD temperature of 200-300 °C. In order to investigate the film growth, structure, morphology and optical properties, the samples were characterized by spectroscopic ellipsometry (SE), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and atomic force microscopy (AFM). The as-deposited films were then annealed in a furnace at temperature ranging from 500 to 650°C under N2 atmosphere.

Subsequently, a MIM structure (Al/Nb2O5/TiN) was produced by adding a second aluminum layer deposited at 250°C on a Nb2O5/TiN/Si stack by the sputtering method. The surface of the second electrodes was aimed to have 0.1-1.0 mm2 to confirm the surface dependency of the capacitance value. The electrical properties of Nb2O5 dielectric layer such as dielectric constant, breakdown voltage and leakage current at possible user voltage were measured on this last structure. The low leakage current density is desirable for MIM capacitors as it helps to minimize energy loss and increase the energy storage capabilities of the capacitors. The obtained J-E curve was compared to some electrical conduction mechanisms to identify its electrical conduction behaviors. The barrier height of the F-N tunneling mechanism was determined by fitting the experimental data to the F-N equation. These measurements indicate that the electrical properties of the Nb2O5 material produced by ALD with specific settings are promising for the application in capacitors. These results provide new insight into our understanding of the application of Nb2O5 realized by ALD for the MIM capacitor.
Threshold Switching of ALD-NbOx Films for Neuromorphic Applications
Authors: Moon Jaehyun , Lee Ju-Hun , Kim Kitae , Kim Junho , Park Soohyung , Yi Yeonjin , Kang Seung-Youl
Published: February 2024

Neuromorphic architecture has been suggested as an alternative to the existing von Neumann counterpart. The neuromorphic approach allows massively parallel processing and asynchronous timing schemes with low power consumption. This work presents ALD- NbOx thin films as a potential material for neuromorphic computation. NbO2 shows metal-insulator transition which is the desired property for threshold switching (TS). However, direct forming of NbO2 is rather difficult and deposited NbOx tends predominantly to result in Nb2O5. To obtain NbO2 we used an oxygen scavenger layer of Ti to alter Nb2O5 to NbO2. After a proper electroforming process, the device with a Ti insert showed metal-insulator transition above a specific voltage, i.e., a threshold voltage, and a stable threshold switching characteristics with wide operation range, characteristics not observed in the absence of a Ti insert. The well-defined TS characteristics clearly indicated the Ti role in controlling the oxidation state of NbOx.To verify the oxidation state of NbOx, XPS depth profile analyses were used. The presence of a Ti insertion layer resulted in an increase of 10~30% in Nb4+ states, depending on the total thickness of the NbOx films, while Nb5+ states decreased. Bearing in mind practical applications, we used only CMOS-compatible materials and processes to fabricate TS devices. Our approach suggests a reliable method to fabricate NbO2 neurons.

Acknowledgment: This work was supported by Electronics and Telecommunications Research Institute (ETRI) grant funded by the Korean government under grant " Non-CMOS Neuromorphic Device Basic Technology." (22BB1110).
Natural Organic Carbohydrate Materials Based Resistive Random Access Memory for Sustainable Neuromorphic Computing Systems
Authors: Zhao Feng
Published: February 2024

Current computing systems are facing two essential challenges: (1) tremendous energy consumption due to the conventional Von Neumann architecture with low energy efficiency; and (2) environmental sustainability by depletion of nonrenewable materials, production of electronic waste, etc. One potential solution to simultaneously address these two issues is by “brain-like” and “green” neuromorphic computing with energy-efficient operation, sustainable material resources, and environmentally friendly disposals. Such neuromorphic computing systems require hardware components not only capable of mimicking human neuron and synapse - the basic building block of biological neural networks, but also made from natural organic materials such as polypeptides (proteins) and polysaccharides (carbohydrates) which are renewable, abundant in nature, and biodegradable. In this paper, we report resistive random access memory (ReRAM) made from encouraging natural organic carbohydrate materials, honey and fructose, for emerging neuromorphic computing systems and neural networks. Honey or fructose resistive films were formed by a low cost solution-based process and sandwiched between bottom and top electrode, a simple metal-insulator-metal structure analogous to a biological synapse with presynaptic neuron (top electrode), postsynaptic neuron (bottom electrode), and synaptic cleft (fructose film). The nonvolatile memory behaviors were demonstrated by modulating the conductance by voltage stimuli applied on the memory device, with excitatory current flow in the device being monitored. Nonvolatile memory characteristics including bipolar resistive switching, retention, endurance cycles, long-term potentiation and depression, etc. were reported. All these results testify that carbohydrate-ReRAM devices are promising for energy-efficient and sustainable neuromorphic systems.

Figure 1
Multi-Bit Self-Rectifying Synaptic Memristor Having Tri-Layer Structure for Quantization Aware Training of Quantized Neural Network
Authors: Woo Dae-Seong , Choi Hyun-Do , Jin Hong-Uk , Kim Jae-Kyeong , Shim Tae-Hun , Park Jea-Gun
Published: February 2024

Recently, a cross-point synaptic memristor arrays have been employed to implement synaptic cores of various ANNs, i.e., deep neural networks (DNNs), spiking neural networks (SNNs), and convolutional neural networks (CNNs). The most of reported studies conducted training and inference of ANNs using analog synaptic weight modulation of memristors such as resistive random access memory (ReRAM), phase change random access memory (PCRAM), and ferroelectric random access memory (FeRAM). In other words, no case has been reported so far in which a synaptic memristor with quantized multi-bit is utilized onto a synaptic core of a quantized neural network (QNN).

In this study, for the first time, we introduced the multi-bit self-rectifying synaptic memristor having tri-layer structure being composed of oxygen-rich AlOx rectifying layer, oxygen-deficient HfOx top switching layer, and oxygen-rich HfOy bottom switching layer for quantization aware training of QNN. The resistive switching and self-rectifying mechanism of the multi-bit self-rectifying synaptic memristor was evidently proven by precisely investigating migration of oxygen ions and vacancies in resistive switching layers via ToF-SIMS and XPS depth profiles depending on the resistance states (i.e., pristine, set, and reset). The designed multi-bit self-rectifying synaptic memristor presented linear, discrete, and quantized 4-bit (i.e., 16-level) conductance level depending on incremental write pulse number, which was 4-bit self-rectifying synaptic memristor for the first time. In addtion, the quantization aware training (QAT) was conducted using 4-bit quantized conductance level of the desgiend multi-bit self-rectifying synaptic memristor via stright through estimator (STE). Finally, three different iris datasets were successfully classified using a quantized neural network designed via SPICE circuit simulation. The conductance mechanism of the self-rectifying synaptic memristor and its application of QNN will be presented in detail.

Acknowledgement

This research was supported by National R&D Program through the National Research Foundation of Korea(NRF) funded by Ministry of Science and ICT(2021M3F3A2A01037733)

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(Digital Presentation) Improving Field-Effect Transistor Performance through Pulsed Laser Irradiation-Mediated MoS2-Metal Contact Engineering
Authors: Wani Sumayah Shakil , Kuo Yao-Zen , Kimbulapitiya K.M.M.D.K , Chueh Yu-Lun
Published: February 2024

Two-dimensional (2D) layered materials, such as MoS2, with their atomically thin characteristics, offer promising novel solutions for the field of nanoelectronics. MoS2 has been identified as a prospective building block for flexible and transparent nanoelectronics in the future, and has the potential to contribute to the continuation of Moore's law by enabling high integration levels with low power consumption. Although the use of 2D semiconductor materials as contact interfaces presents advantages over conventional Si-based metal-semiconductor contacts practical applications still face several obstacles. One of the biggest concerns being is the presence of the large contact resistance which can caps the available field effect carrier mobility making intrinsic quantum transport phenomena in the material inaccessible. In this work, we demonstrate the use of 1064 nm pulsed-laser to selectively anneal the metal contacts of the CVD synthesized MoS2 based back gated FET. The improved metal–semiconductor interface after laser annealing resulted in higher mobility and improved On-Off ratio (10^6~10^7). This selective contact annealing enhanced back gated MoS2 FET overall performance metrics by increasing peak field effect mobility, improving current saturation due to decreased contact resistance.

Our findings suggest that Pulsed laser annealing of metal contacts in TMD-based FETs can significantly reduce contact resistivity without causing channel or substrate distortion, which is not possible with conventional thermal annealing. This approach can provide most promising application in the field of high-performance two-dimensional semiconductor in flexible/ wearable electronics.

Keywords: TMDCs, CVD, MoS2 FET, laser annealing, contact resistance.
(Invited) Applications of Electrochemistry Toward Blue/Green and SWIR-Wavelength VCSELs
Authors: Li Bingjun , Mi Chenziyi , Elafandy Rami , Kang Jin-ho , Han Jung
Published: February 2024

Unlike the more established edge-emitting lasers (EELs) with a horizontal Fabry-Perot (FB) cavity, VCSELs have a vertical cavity with highly reflective top and bottom mirrors sandwiching the active region. This design enables wafer-level testing, one- and two-dimensional arrayed integration, and scalability for low- and high-power applications. VCSELs are poised to surpass EELs as a more versatile and intelligent option for semiconductor lasers in the future.

Currently commercially available VCSELs only cover the red to near-infrared (NIR) range of 700-1100nm, whereas EELs offer products across a wide spectral range. The optimal active regions for blue and short-wavelength infrared (SWIR) spectra are only supported on GaN and InP substrates, respectively. Lattice-matched, epitaxial mirrors compatible with these two substrates remain major challenges. As a solution, we propose the use of electrochemistry to engineer the refractive index of the material. The innovation is based on the recognition that nanoporous (NP) semiconductor layers can be considered a nanocomposite with nanoscale voids of air uniformly dispersed in a single-crystalline semiconductor, thus rendering a unique way to control the effective optical index with a tunability that is typically un-attainable through epitaxy.

We have studied the electrochemistry of semiconductors for applications in photonics, beginning with GaN and most recently with InP. In both material systems, we have discovered a selective porosification process based on the doping concentration. Due to the doping selectivity in EC etching, layers with high doping concentration will be converted to low index nanoporous material with an unprecedented tunability in the refractive index depending on the porosity. Meanwhile, the lightly doped layers remain intact. As a result, highly reflective mirrors were fabricated on GaN and InP substrates with wide stopbands. In this talk, we will provide latest updates in the VCSEL performances in the blue/green and long-wavelength region.
(Invited) Towards GaN-on-GaN High-Power Electronic Devices
Authors: Bockowski Michal
Published: February 2024

Application of gallium nitride (GaN) substrates in electronic and optoelectronic industries is constantly increasing. In order to fabricate wafers, GaN crystals of the highest structural quality and desired electrical (and sometimes optical) properties must be grown. Today, there are three main GaN crystallization methods: i/ halide vapor phase epitaxy (HVPE) with its derivatives: halide-free VPE and oxide VPE; ii/ sodium-flux; and iii/ ammonothermal. The last approach can be basic or acidic depending on what mineralizer is used to increase the solubility of GaN in the feedstock zone. In this paper we will focus on HVPE and basic ammonothermal growth of GaN [1]. Not only bulk growth will be presented. The HVPE method will also be discussed as the best method to crystallize the drift layers necessary for high-power vertical electronic devices (FET transistors, Schottky diodes).

One of the best methods for introducing dopants into semiconductors is ion implantation. The introduced structural damage can be removed by a proper annealing process. The high-temperature treatment enables also electrical and/or optical activation of the implanted dopants. In the case of GaN, annealing at high temperature (~1300°C - 1400°C) seems difficult. This compound loses its thermodynamic stability slightly above 800°C at atmospheric pressure. At higher temperature the crystal will decompose. One of the solutions is to anneal GaN at high nitrogen (N2) pressure. Such technology is called ultra-high-pressure annealing (UHPA) [2]. In this paper, application of UHPA for GaN crystals and layers implanted by different ions (acceptors and donors) will be presented. The latest results of the implantation with magnesium (Mg), beryllium (Be), zinc (Zn), and calcium (Ca) ions into GaN in order to obtain p-type conductivity will be discussed [3,4]. Silicon (Si) implantation into GaN for n-type doping will also be analyzed. Structural, electrical and optical properties of implanted GaN after UHPA will be discussed in terms of application for GaN-based devices.

A kV class, low ON-resistance, vertical GaN junction barrier Schottky (JBS) diode with selective-area p-regions formed via Mg implantation followed by high-temperature, ultra-high pressure post-implantation activation anneal without a capping layer was already demonstrated [5]. The forward characteristics of the JBS diode showed ideality factor (n) 1.03, turn-on voltage (VON) 0.75 V, current ON/OFF ratio (at ±3 V) ~1011, and specific differential ON-resistance (RON) 0.6 mΩ·cm2. The breakdown voltage of the JBS diode was 915 V.
(Invited) Ferroelectric Nitride Semiconductors: Epitaxy, Properties, and Emerging Device Applications
Authors: Mi Zetian
Published: February 2024

The incorporation of rare-earth elements such as scandium (Sc) can transform conventional III-nitride semiconductors to be ferroelectric. In this talk I will present recent advances of ferroelectric Sc-III-nitride heterostructures and nanostructures, including epitaxy, properties and emerging device applications. Molecular beam epitaxy and properties of ScAlN and ScGaN with a wide range of Sc compositions will be discussed. Special attention will be paid to the unique ferroelectric properties of these ultrawide bandgap semiconductors. The realization of ultrathin ferroelectric nitride heterostructures and the underlying physics and properties will be discussed, together with their applications in quantum photonics and electronics.
Delamination Behavior Characterization during Bond Strength Measurement
Authors: Iwata Tomoya , Fuse Junya , Sano Marie , Tanaka Fabiana Lie , Inoue Fumihiro
Published: February 2024

Direct bonding is a key enabler for future node 3D semiconductor devices [1]. It is crucial to have sufficient bonding strength to withstand thinning and subsequent processes. However, there is no standardized method for bonding strength measurement. The most frequently used bonding strength measurement technique is the double cantilever beam (DCB) method. However, it is known that delamination length propagates with time by water stress corrosion. Nevertheless, the reported bonding strength is not considered these phenomena. Therefore, interfacial reactions occurred by blade insertion have been deeply investigated in this study. We unveiled the influence of annealing and plasma conditions on the bonding strength measurement using the DCB method in a controlled environment. In addition, we discuss the behavior of delamination during blade insertion.

Our DCB system is compatible with 300 mm wafers and the insertion of the blade is fully controlled by actuator. The blade is inserted at the bonding interface as shown in Fig.a, and the delamination length is measured from a captured IR image.

Fig.b shows the results of bonding strength measurements on 300 mm bonded wafers with different annealing conditions. It can be seen that the bonding strength increases with the annealing temperature. When the annealing temperature is lower than 150℃, the delamination length is propagated by the time even when the measurement is performed in anhydrous environments. Therefore, the calculated results of bonding energy decrease due to this phenomenon.

Fig.c shows the bonding energy reduction rate for each annealing temperature with time. These values are calculated based on the value immediately after insertion and after 180 seconds. The results show that water stress corrosion significantly affects the delamination length when annealed at 150℃, however, the samples annealed above 250℃ show almost no propagation of delamination length with time and the values are almost saturated.

In this paper, we present the experimental results on the effects of annealing temperatures on bond strength as well as the propagation of delamination length caused by water stress corrosion. Additionally, we will discuss other factors that can affect bond strength measurements during the presentation.

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A Comprehensive Study on Chemical Bonding and Open Spaces with Silicon Carbon Nitride Films for Direct Bonding
Authors: Ebiko Sodai , Onishi Koki , Uedono Akira , Iacovo Serena , Inoue Fumihiro
Published: February 2024

Wafer-to-wafer (W2W) direct bonding has been extensively developed as a key unit process for BS-PDN, CFET and advanced chiplet. As a bonding dielectric layer, CVD-SiO2 has been comprehensively studied for direct/hybrid bonding. SiCN is emerging dielectric bonding layer due to its unique properties such as high bonding strength at low annealing temperatures, suppressing void formation after Post Bond Annealing (PBA) and barrier properties against Cu diffusion [1][2]. However, the bonding mechanism for SiCN has not yet been clearly described. In this study, we investigated the mechanism from several kinds of perspectives by analyzing the properties of different films under various conditions. From those results, SiCN is characterized and compared to SiO2.

SiO2 and SiCN films were deposited on 300mm Si wafers using plasma-enhanced chemical vapor deposition (PECVD). Subsequently, the wafers were polished and bonded.

Atomic level open spaces in dielectric films were analyzed by positron annihilation spectroscopy (PAS). For the SiO2 samples after plasma activation, the S parameter did not show significant changes. This indicates the open spaces in SiO2 were not significantly influenced by plasma. On the contrary, the S parameter of SiCN samples increased after post deposition annealing (PDA) and decreased after plasma activation. This atomic level open spaces might be contributed the unique properties of SiCN for direct bonding.

Since the analysis by PAS is one of the examples, we will report the overall results of the analysis on SiCN, e.g. TDS, XPS, AFM, and so on, then discuss the bonding mechanism for SiCN-SiCN.

[1] F. Inoue, et. al., ECS Journal of Solid State Science and Technology 8(6), P346(2019)

[2] F. Nagano, et. al., ECS Journal of Solid State Science and Technology 9 123011(2020)

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