bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Crystalline Oxide Semiconductor Applicable to Low-Power Consumption Edge AI
Authors: Kunitake Hitoshi , Baba Haruyuki , Okuno Naoki , Ito Yuki , Takahashi Masahiro , Jimbo Yasuhiro , Hodo Ryota , Kurokawa Yoshiyuki , Onuki Tatsuya , Sasagawa Shinya , Yamane Yasumasa , Yamazaki Shunpei
Published: July 2021

Scaling of Si MOSFETs has proceeded based on scaling law reported by R. H. Dennard in 1974[1], and technologies scaled down to 5 nm node are currently incorporated in ICs in production. Meanwhile, according to an IEEE semiconductor roadmap[2], the 5-nm node device has a gate length of 18 nm, suggesting that scaling is reaching its limit.

FETs using crystalline oxide semiconductor (OS), especially, c-axis-aligned crystalline (CAAC)-IGZO, are highly compatible with BEOL process of CMOS because OSFETs can be fabricated at 450°C or lower. Unlike bulk Si, OSFETs can adopt a trench-gate-self-aligned (TGSA) structure[3] enabling isolation from the substrate and accommodating chip bonding technologies. Crystalline oxide semiconductor process contributes to vertical integration required in the future technology.

FETs using CAAC-IGZO is preferred to have a charge accumulation structure such as n-i(n-)-n junction (FIG. 1) in which its channel region, especially the region direct below the gate, has to be adjusted to have an i(n-)-type conductivity. Such a junction structure enables threshold voltage control and a reduction in leakage current of the FET. The leakage current of the CAAC-IGZO FET is extremely low, yA (10-24 A)/mm measured at the transistor level at 85°C, which is lower by 10 digits than that of a CMOS device[3].

A variety of applications using crystalline OS have been studied, including AI accelerators, high-resolution displays, nonvolatile memories and combination with sensors. Among them, an AI accelerator using crystalline OS has attracted attention[4]. Using crystalline OS enables memory to be placed near compute units. It can also be driven with low current; accordingly, improvement in computational efficiency is expected.

Crystalline oxide semiconductor process is a promising technology enabling both high integration and lower power consumption of ICs with CMOS devices.

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Reference
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[1] R. H. Dennard et al., “Design of Ion-Implanted MOSFET’s with Very Small Physical Dimensions,” IEEE Journal of Solid-State Circuits, vol 9, Issue 5, pp.256-268, 1974.

[2] International Roadmap for Devices and Systems (IRDS™) 2020 Edition, 2020.

[3] H. Kunitake et al., “A c -Axis-Aligned Crystalline In-Ga-Zn Oxide FET With a Gate Length of 21 nm Suitable for Memory Applications,” IEEE J-EDS, vol. 7, pp. 495-502, 2019.

Yamazaki et al., “Crystalline IGZO ceramics (crystalline oxide semiconductor)–based devices for artificial intelligence,” Ceramic Engineering & Science, vol. 1, Issue 1, pp.6-20, 2019.

[4] D. Saito et al., “IGZO-Based Compute Cell for Analog In-Memory Computing—DTCO Analysis to Enable Ultralow-Power AI at Edge,” IEEE Transactions on Electron Devices, vol. 67, Issue 11, pp.4616-4620, 2020.

FIG. 1: Electron holography analysis result of sample using crystalline OS.

Figure 1
(Invited) Memristive Devices based on Two-Dimensional Materials
Authors: Lemme Max C.
Published: July 2021

Two-dimensional layered materials are emerging as candidates for neuromorphic switches. So far, several different phenomena have been proposed as device switching mechanisms. These include the lateral movement of ions, either in van der Waals gaps [1] or grain boundary mediated [2], phase changes in 2D materials [3], defect mediated resistive switching [4], or vertical ion movement and subsequent modulation of electronic barriers [5].

In this talk, vertically aligned molybdenum disulfide (MoS2) will be discussed as a memristive material that allows ionic transport along its van der Waals gaps. These ions contribute to the electron transport properties across the vertical device structures [6]. In addition, the motion of ions can be used to tune energy barriers at MoS2/semiconductor Schottky junctions [5]. We have identified hydroxyl (OH-) ions that likely originate from catalytic splitting of water molecules in the devices [7]. In addition, vacancies are present in the 2D films that manifest as absorbers for infrared radiation, i.e. wavelengths beyond what is expected from a semiconductor with a bandgap of approximately 1.2 eV [8], [9].

Acknowledgements

The authors acknowledge funding by the European Commission in the Horizon 2020 grant agreements 881603 (Graphene Flagship) and 829035 (QUEFORMAL), the German BMBF grant NEUROTEC (16ES1134) and the DFG projects MOSTFLEX (407080863) and ULTIMOS2 (412113712).

References

[1] X. Zhu, D. Li, X. Liang, and W. D. Lu, “Ionic modulation and ionic coupling effects in MoS 2 devices for neuromorphic computing,” Nat. Mater., vol. 18, no. 2, Art. no. 2, Feb. 2019.

[2] V. K. Sangwan et al., “Gate-tunable memristive phenomena mediated by grain boundaries in single-layer MoS2,” Nat. Nanotechnol., vol. 10, no. 5, pp. 403–406, May 2015.

[3] F. Zhang et al., “Electric-field induced structural transition in vertical MoTe 2 - and Mo 1–x W x Te 2 -based resistive memories,” Nat. Mater., vol. 18, no. 1, p. 55, Jan. 2019.

[4] S. M. Hus et al., “Observation of single-defect memristor in an MoS 2 atomic sheet,” Nat. Nanotechnol., pp. 1–5, Nov. 2020.

[5] M. Belete et al., “Nonvolatile Resistive Switching in Nanocrystalline Molybdenum Disulfide with Ion-Based Plasticity,” Adv. Electron. Mater., p. 1900892, 2020.

[6] M. Belete et al., “Dielectric Properties and Ion Transport in Layered MoS2 Grown by Vapor-Phase Sulfurization for Potential Applications in Nanoelectronics,” ACS Appl. Nano Mater., vol. 1, no. 11, pp. 6197–6204, Nov. 2018.

[7] S. Li et al., “Edge-Enriched 2D MoS2 Thin Films Grown by Chemical Vapor Deposition for Enhanced Catalytic Performance,” ACS Catal., vol. 7, no. 1, pp. 877–886, Jan. 2017.

[8] A. Bablich et al., “Few-Layer MoS2/a-Si:H Heterojunction Pin-Photodiodes for Extended Infrared Detection,” ACS Photonics, vol. 6, no. 6, pp. 1372–1378, Jun. 2019.

[9] D. S. Schneider et al., “Highly Responsive Flexible Photodetectors Based on MOVPE Grown Uniform Few-Layer MoS2,” ACS Photonics, vol. 7, no. 6, pp. 1388–1395, Jun. 2020.
(Invited) Binary Stochastic Neurons and Compound Synapses from Nano-Magnets
Authors: Appenzeller Joerg
Published: July 2021

In this presentation I will introduce the nCORE center CAPSL’s activities towards a probabilistic spin logic for Boolean and Non-Boolean computing. While magnetic materials in storage devices are part of our electronic world since many decades and are explored more recently by the semiconductor industry for memory applications such as Spin-transfer torque magnetic random-access memory (STT-RAM), spin based devices for logic applications are still in their infancies. Mimicking a CMOS type logic with magnets requires a “Write” and a “Read” unit as well as proper input/output isolation. Based on this, a device concept in which i) charge-to-spin conversion occurs through the Giant Spin Hall Effect (GSHE) [1], ii) dipolar coupling mediates the information transfer from a magnet in the Write unit to another one in the Read unit, and iii) a magnetic tunnel junction (MTJ) is used as the Read unit was proposed in 2012 under the name charge spin logic (CSL) [2]. Next, I will explain in how far the use of low-barrier magnets cannot only help to reduce power consumption of CSL devices but introduces a conceptually new way of computing through the introduction of “tunable randomness”. This idea, that is also known as probabilistic spin logic (PSL), was introduced in 2017 [3] and uses a counterintuitive aspect of magnets, namely their capability of creating a truly random magnetic signal if low-barrier circular nano-magnets are used. In particular, I will connect PSL with activities in the realm of quantum computing as well as neural networks.

[1] L. Liu, C.-F. Pai, Y. Li, H. W. Tseng, D. C. Ralph, and R. a. Buhrman, Science 336, 555 (2012).

[2] S. Datta, S. Salahuddin, and B. Behin-Aein, Applied Physics Letters 101, 252411 (2012).

[3] K. Y. Camsari, R. Faria, B. Sutton and S. Datta. Physical Review X 7, 031014 (2017).
Characterization of InP Surfaces Perturbations after Ar+ Bombardment By Combining Electrochemistry and X-Ray Photoemission Spectroscopy
Authors: Bechu Solene , Aureau Damien , Bouttemy Muriel , Fregnaux Mathieu , Goncalves Anne-Marie , Etcheberry Arnaud
Published: July 2021

Over the past decades, the perturbations induced by ionic bombardment on semi-conductors have been explored, raising questions such as the deepness affected inside the material. Here, we focus on one well-known semi-conductor: InP, under Ar bombardment induced by an ionic sputtering performed directly inside the X-Ray photoemission spectroscopy (XPS) chamber using an ion gun. We already proved that, after a bombardment by Ar ions, InP surfaces suffer from several perturbations, degrading the initial properties of this semi-conductor: chemical ones (oxidation degree, atomic network organization and stoichiometry) [1], but also morphological and optical ones [2]... To get a better insight on the damages induced on the surfaces of InP semi-conductors, we present a study where electrochemistry is coupled to XPS analysis. Electrochemistry is indeed a very efficient probe to detect modification of the electrical and electrochemical properties of the materials but also a quantitative tool to provide information bulk and surface properties of any electrode material.

In our approach, n- & p- type samples were investigated toward their modified electrochemical responses. We observed that, on p-type InP, after bombardment, the surface modification is evidenced by a lower dark open circuit potential compared to the one measured on pristine surface. Moreover, cyclic voltammetry performed at pH 10 shows initial cathodic features on the surface, related to an oxidized metallic In-enriched layer onto InP surface. This feature agrees with XPS analysis. By continuing the cyclic voltammetry, a more pronounced In rich overlayer formation is observed, due to specific oxidation /reduction phenomenon.[3] This behavior is very similar to the one obtained by cathodic decomposition onto InP surface. We will also explore the response of a n-type InP surface under similar conditions.

In conclusion, we will discuss how the XPS and electrochemical characterizations combination is able to provide complete and complementary diagnostic of the stoichiometry loss and its electrochemical reactivity.

[1] Aureau et al., SIA, 2018, 50 (11) 1163-1167 ; D. Aureau et al., ECS Trans., 2019, 89, 9

[2] Béchu et al., JVST B, 2019, 27, 062902

[3] Béchu et al., Electrochem. Comm., 2020, 117, 106766
Resolving Mixed Electrical-Ionic Transport at Nanometer Length Scales in Polymer Electrochemical Cells Using Color Impedance Spectroscopies
Authors: Chen Zhiting , Ratcliff Erin
Published: July 2021

The mechanical flexibility of conductive polymer electrodes coupled with their hybrid electronic-ionic transport properties enables a wide range of technologies from biology to energy conversion, including biosensors, flow batteries, and photo-electrochemical cells. Herein, we focus on a prototypical material to better understand hybrid transport properties - poly(3-hexylthiophene) (P3HT) - which has been widely studied in organic semiconductors and photovoltaics. In solid-state studies, the electronic transport within P3HT is limited by localized states induced by disordered regions and the mechanism is described by the multiple trapping and release (MTR) model. Recent electrochemical impedance spectroscopy (EIS) results have demonstrated anomalous diffusion of ions in regioregular and regiorandom P3HT films, indicative of ionic trapping. However, EIS has been historically equated with ambiguity, as interpretation is limited to equivalent circuit models to extract chemical parameters of interest.

Herein we combine EIS and color impedance spectroscopy (CIS) to further understand the hybrid transport mechanism. Specifically, electrochemical doping of conductive polymers results in the formation of polarons – electronic free carriers that can be observed spectroscopically due to the reorganization of chemical bonds to support the radical cations. Thus, CIS allows us to combine the sensitivity of chemical phenomena attributed to optical signatures with the in operando control afforded by application of electrochemical potential. In particular, this approach allows us to resolve mixed transport properties in subpopulations (i.e. crystallites versus aggregates) that exist at nanometer length scales.
Charge Transfer in Conjugated Polymer Mxene Interface
Authors: Jones Sheenamelia , Ware Alisha , Wright Tia , Keith Danielle , Danilov Evgeny , Han Shubo , Autrey Daniel , Gautam Bhoj
Published: July 2021

Optimization of charge generation and charge transport is crucial for the fabrication of highly efficient polymer solar cells. In the present work, using ultrafast pump-probe spectroscopy and atomic force microscopy, we showed the efficient charge generation and transport at polymer blend MXene interface compared to PEDOT:PSS interface. We observed long charge carrier lifetime, strong photoluminescence of donors and acceptors and higher current on PBDB:ITIC thin film prepared on ITO substrate with MXene. Our study provides the guidelines for the fabrication of inexpensive, flexible, and highly flexible polymer solar cells by interface tuning.
Phase-Field Modeling to Investigate the Influence of Nano-Filler Properties on Composite Breakdown Strength and Discharge Energy Density
Authors: Ansari Talha Q , Huang Haitao
Published: July 2021

Composite materials have wide range of energy storage applications where high energy density is desirable. Inclusion of nano-fillers with low electrical conductivity in the polymers have been associated with the improvement in breakdown strength and hence the discharge energy density. A phase-field model is developed to investigate the influence of nano-filler properties, shape and volume fraction on the breakdown phase evolution, breakdown strength and discharge energy density. The model is validated with the experimental results from literature. The results reveal that the inclusion of nano-filler (nano-sheets) with lower electrical conductivity as compared to polymer, result in the increase of breakdown strength. The results also show that nano-fillers with high dielectric constant would result in high discharge energy density. This increase in discharge energy density comes at the expense of decrease in breakdown strength. This work reports strategies on choosing suitable nano-filler material (and shape) for specific polymer material.
(Invited) Simulation-Driven Optimization of Unconventional Digital Logic Devices
Authors: Kim Chang-Hyun
Published: July 2021

Organic thin-film transistor (OTFT) based electronics has been under extensive investigation over the last three decades. Dramatic improvements have been made during this time in terms of basic device performance and stability, yet a formidable challenge remains as to how to disentangle highly complex interplays between the materials properties, device layouts, and final circuit topologies, knowing that there are simply too may possible choices for synthetically diverse, solution-processable organic electronics. In this presentation, we highlight some of our latest researches on robust simulation-based design and realization of novel organic semiconductor logic systems. We first demonstrate the possibility of guided data-level matching at the organic lateral heterojunction ternary inverters that utilize a charge anti-ambipolarity. Here, it is found that controlling the energetic diffusion barrier and minority carrier mobility is the key to obtain the evenly distributed logic values. We then switch the topic to the recently reported 3-D complementary inverter circuits where the p-type and n-type transistors are vertically integrated with a reduced circuit footprint. We focus on the critical effects of the charge injection barriers into the unintentionally doped organic semiconductors, and reveal that the systematic contact efficiency variation leads to a largely improved signal amplification gain, as well as un unusual development of the multi-valued logic behaviors up to the quaternary level. Such results clearly demonstrate that physically-based device simulation has a strong capability of correlating various influential parameters at relevant focus levels, thus paving the way toward a totally predictive engineering paradigm of new materials-based electronics platforms.
Exploring the Structure-Function-Performance Relationship of Carbon Electrodes Toward Rational Design of High-Performance Redox Flow Cells
Authors: Nourani Mahnaz , Aravamuthan Sundar Rajan , Pezeshki Alan , Goulart James , Gallaway Joshua W , Agar Ertan
Published: July 2021

Redox flow batteries (RFBs) are a promising grid-scale energy storage technology for the integration of intermittent renewable sources, such as wind and solar, into the electrical grid due to their modularity, flexible design, and cost-effectiveness in long-duration storage [1]. Unlike traditional batteries, for RFBs, electrolytes are stored in external tanks and are circulated through the flow cell. In the flow cell, electrical energy is stored via the electrochemical reactions of the redox active species dissolved in liquid electrolytes. While this new archetype provides unique benefits, the flow-assisted nature of RFBs presents many challenging issues, including but not limited to significant transport losses due to the poor electrode and cell design, and the related low power density [2-3]. It can be hypothesized that many of these challenges are primarily related to the concept of electrolyte utilization [4]. In this regard, porous electrode is the key component, which is responsible for multiple critical functions including delivery of liquid electrolytes as well as facilitating ion/charge transfer and providing sites for electrochemical reactions [4]. Despite its importance, the required fundamental knowledge on how to systematically design effective electrodes specifically tailored for RFB applications has not received much attention [5].

In this talk, the recent efforts on establishing the structure-function-performance linkages for commercially available carbon electrodes will be presented. The results of the experiments utilizing an electrochemical protocol that combines symmetric flow cell cycling with electrochemical impedance spectroscopy (EIS) and polarization curve (PC) measurements will be discussed. The impedance data is fitted into a mathematical model, and key physicochemical properties of carbon electrodes and the correlated performance losses are quantified. Additionally, we will share our perspective on manufacturing high-performance carbon electrodes using a high-throughput screening platform.

References:

X. Ke, J. M Prahl, J. I. D. Alexander, J. S. Wainright, T. A. Zawodzisnki, R. F. Savinell, Chem. Soc. Rev., 2018, 47 (23), 8721-8743.

P. A. Garcia-Salaberri, T. C. Gokoglan, S. E. Ibanez, E. Agar, M. Vera. Processes, 2020, 8, 775.

M. Nourani, B. I. Zackin, D. C. Sabarirajan, R. Taspinar, K. Artyushkova, F. Liu, I. V. Zenyuk, E. Agar. J. Electrochem. Soc., 2019, 166 (2), A353-A363.

B. Akuzum, Y. C. Alparslan, N. C. Robinson, E. Agar, E. C. Kumbur, J. Appl. Electrochem., 2019, 49 (6), 551-561.

A. Forner-Cuenca, F. R. Brushett, Curr. Opin. Electrochem., 2019, 18, 113-122.
A Mediated Lithium-Sulfur Flow Battery
Authors: Meyerson Melissa , Small Leo
Published: July 2021

With the growth of intermittent renewable power sources, such as solar and wind energy, there is an increasing need for inexpensive, high capacity, grid-scale energy storage. The high capacity (1675 mAh/g) and low cost (~0.1 $/kg) of sulfur make Li-S batteries an ideal candidate to fill this need. However, sulfur has poor electrical conductivity and Li-S batteries are prone to polysulfide shuttling that decreases the battery life. In an effort to address these problems, we are developing a highly-scalable mediated Li-S flow battery using a lithium metal anode, solid state Li ion conductor separator, sulfur cathode, and a redox mediator. During discharge, the Li metal is oxidized to Li+ and the redox mediator (RM) is reduced. The RM will then react with the S returning to its oxidized form and enabling the formation of Li2S without the need for electrical contact between the S and counter electrode. The oxidized RM is then reduced again, and the process is repeated until all available S has reacted. A second RM with a potential lower than that of the Li-S reaction is used to enable the charge process. Two such mediators are decamethylferrocene (2.86 V vs Li/Li+) and cobaltocene (2.06 V vs. Li/Li+), Figure 1. The flow battery design has multiple benefits. First, the use of a solid state Li ion conductor mitigates polysulfide shuttling, thereby increasing the cycle life. Second, the issue of sulfur conductivity is addressed through use of the redox mediator, where the mediator can easily diffuse through the electrolyte reaching the sulfur and eliminating the need for excess conductive carbon additives. Third, the flow battery design enables physical separation of the anode and cathode, mitigating the potential for short circuiting and thermal runaway even if the Li does puncture the solid state electrolyte. Using this cell design, we examine the role of the solvent, anion, and polysulfide concentration on Li+ transport across the solid electrolyte interphase as well as the role of the mediation potential and interactions between the polysulfide and mediator.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Figure 1
Role of Electrolyte in Stabilizing the Solid Electrolyte Interface of Hard Carbon As an Anode for Sodium-Ion Batteries
Authors: Hirsh Hayley S , Sayahpour Baharak , Shen Ashley , Li Weikang , Zhao Enyue , Meng Shirley
Published: July 2021

Hard carbon (HC) is an attractive anode material for sodium-ion batteries (NIBs) because it can be made from biomass or plastic, has a high capacity of ~300 mAh/g, and an extremely low average voltage near 0V. When fabricated with cathodes free of Li, Ni, and Co, NIBs using HC anodes are a promising approach for grid storage because they are energy-dense, sustainable, and have a low cost of energy. In order for these batteries to become a practical long-life solution, the issues of low first coulombic efficiency and poor rate performance of HC in conventional carbonate electrolytes need to be addressed. Two mechanisms that potentially cause these issues to occur are changes to the HC structure affecting sodium storage and the formation of the solid electrolyte interface (SEI). The proper selection of electrolyte is critical for controlling these mechanisms. To observe and characterize these mechanisms, we compared HC using a conventional carbonate electrolyte, 1M NaPF6 in propylene carbonate (PC), with a high performing glyme based electrolyte, 1M NaBF4 in tetraethylene glycol dimethyl ether (TEGDME). Compared to the poor rate capability of HC in PC electrolyte, HC in TEGDME electrolyte shows an excellent rate capability of ~265 mAh/g at C/20 and ~260 mAh/g at C/3. Titration gas chromatography and Raman spectroscopy were used to show that the HC with either electrolyte had the same sodium storage mechanism with no “stuck” sodium in the HC structure after the first cycle. These observations suggest that SEI formation is responsible for the irreversible capacity differences. The SEI formation was explored with scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). The PC electrolyte’s SEI is found to be thick, fluffy, irregular and composed of polyesters, alkyl carbonates, NaxPFyOz, and NaF. The TEGDME electrolyte’s SEI is found to be thin, conformal, uniform, and composed of polyethers, sodium alkoxides, NaxBFyOz, and NaF. Additionally, the PC electrolyte’s SEI is rate dependent with more unstable products formed at high rates whereas the TEGDME electrolyte’s SEI is not rate dependent. These findings show that HC anode’s rate capability is controlled by the quality of the SEI formed by the electrolyte rather than the HC material structure. This model of rate and electrolyte dependent SEI indicates that SEI engineering is a pathway to improve HC as an anode for long-life grid-level NIBs.

Figure 1
(Invited) III-Nitrides for Vacuum Nanoelectronics
Authors: Pavlidis Dimitris , Bellotti Enrico , Graham Samuel , Mohammadi Saeed , Rajan Siddharth , Redwing Joan
Published: July 2021

Vacuum Field Effect Transistors (VFETs) are explored using wide-bandgap (III-Nitrides), VFETs avoid high power consumption caused by cathode heating in thermionic emission devices and have small turn-on voltage with potential for millimeter-wave operation. Special attention is placed on emitter design, growth of high-quality materials and evaluation of thermal properties

Progress in Si- and III-V-based electronic devices allowed operation at high-frequencies extending well into the millimeter-wave range. Device performance is limited by carrier transport properties and parasitics which have been addressed using different semiconductor materials, shrinking of device dimensions and advanced design approaches, permitting in this way to achieve operation at several hundred GHz. Further performance advances continue to be reported but start reaching a limit. The advances made in nanotechnology together with the possibility of utilizing field- rather than thermionic-emission offer, however, the possibility of revisiting the principle of vacuum tubes. Nanoelectronic devices utilizing such approaches offer the possibility of operating at millimeter-wave frequencies. Materials used for their realization are semiconductors i.e. II-Nitrides that can be processed using well-developed technologies and nanofabrication techniques, providing therefore ways of shrinking dimensions in critical parts of the device such as for example the gap between the emitter and cathode.

The paper addresses device approaches for vacuum nanoelectronics using wide-bandgap i.e. III-Nitride semiconductors. The studies rely on appropriate emitter design, growth of high-quality materials and evaluation of thermal properties that can play a critical role in device performance.
AlGaN/AlN/SiC Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors with Al2O3 Gate-Oxide and Step-Graded AlGaN Channel
Authors: Lee Ching-Sung , Lin Yun-Jung , Hsu Wei-Chou , Huang Yi-Ping , You Cheng-Yang , Lee Kuan-Tin , Lee Jia-Luen , Cheng Chih-Chung , Jian-Hong Ke
Published: July 2021

Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs), grown on a SiC substrate, with step-graded Si-doped (n = 3 × 1018 cm-3) widegap AlxGa1-xN channel and Al2O3 gate-dielectric are investigated. Increased Al-compositions with x = 0.25, 0.5, and 0.75 towards the buffer were devised in the composite widegap channel. The high-k Al2O3 dielectric/passivation layer was grown by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. Experimental comparisons were made with respect to a conventional Schottky-gate HFET.

The epitaxial structure of the studied Al2O3-dielectric Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN MOS-HFET (sample A) and Schottky-gate HFET (sample B). Both devices have the identical epitaxial structure grown on a SiC substrate by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The layer structure includes an undoped AlN buffer, a 20-nm undoped Al0.75Ga0.25N barrier, a 150-nm step-graded Si-doped (n = 3 × 1018 cm-3) AlxGa1-xN channel (x = 0.25, 0.5, and 0.75), and a 20-nm undoped Al0.75Ga0.25N barrier. Standard photolithography and lift-off techniques were used for device processing. For sample B, mesa etching was performed with respect to a 100-nm thick Ni barrier by using an inductively coupled-plasma reactive ion etcher (ICP-RIE). Flow rates were tuned and set at 10 sccm and 20 sccm for the mixed etching gases of BCl3 and Cl2, respectively. The 20-nm undoped Al0.75Ga0.25N barrier was etched away before deposition of source/drain electrodes. Ti (10 nm)/Al (50 nm)/Ni (10 nm)/Au (50 nm) were evaporated. The source/drain ohmic contacts were formed by annealing the sample for 25 seconds at 900°C by using a rapid thermal annealing (RTA) system (ULVAC MILA-5000). Then, 30-nm thick Al2O3 layer was deposited on the Al0.75Ga0.25N barrier by using the USPD technique. Finally, gate electrode of Ni (100 nm)/Au (50 nm) was evaporated after gate photolithography. As for sample A, the gate electrode was formed directly on the surface of Al0.75Ga0.25N barrier without oxide deposition.

Improved device performance of the present MOS-HFET design have been obtained, including maximum drain-source current density (IDS, max
) of 130.1 A/mm at VGS
= 10 V and VDS
= 20 V, IDS
at VGS
= 0 V (IDSS0
) of 83.1 mA/mm, on/off-current ratio (Ion
/Ioff
) of 1.4 × 107, maximum extrinsic transconductance (gm, max
) of 11.8 mS/mm, two-terminal off-state gate-drain breakdown voltage (BVGD
) of -404 V, and three-terminal on-state drain-source breakdown voltage (BVDS
) of 364 V at 300 K. The present MOS-HFET design has also shown high spectral responsivity (SR) of 737 A/W under 250-nm deep-UV radiation at 300 K.
X-Ray Photoemission Investigation of the Beryllium Oxide Band Alignment with Magnesium Oxide and Estimates for Other Insulating and Conducting Oxides
Authors: Koh Donghyi , Hudnall Todd W , Bielawski Chris W , Banerjee Sanjay , Brockman Justin , Kuhn Markus , King Sean W
Published: July 2021

Beryllium oxide (BeO) is a wurtzite structured, large bandgap (E
g > 8 eV) material of significant interest as an alloying agent and cladding dielectric in various wide band gap oxide based optoelectronic devices. The success of such devices is highly reliant on bandgap and band alignment engineering to achieve sufficient charge carrier and optical confinement for device operation. In this regard, we have utilized x-ray photoemission spectroscopy (XPS) to determine the valence band offset (VBO) between atomic layer deposited (ALD) BeO and a magnesium oxide (MgO) substrate with (001) orientation. The BeO VBO with MgO (001) was determined to be 0.1 ± 0.15 eV. Applying the rules of commutativity and transitivity for band alignment, we additionally predict the BeO VBO with other wide bandgap conductive oxides such as ZnO, Ga2O3, and InGaZnO4, to be 1.15 ± 0.3 eV, 0.3 ± 0.2 eV, and 0.9 ± 0.2 eV, respectively. Utilizing the reported bandgaps for ALD BeO and the conductive oxides, we find a Type I band alignment with CBOs > 1 eV in all cases. BeO is therefore a promising dielectric for oxide based optoelectronic and high-frequency, -power, and -temperature device applications
(Invited) Application of Machine Learning for High-Performance Multicrystalline Materials
Authors: Usami Noritaka
Published: July 2021

Many practical materials are multicrystalline to contain complex microstructures and crystal defects. Owing to its complexity, universal guideline regarding ideal microstructures to maximize macroscopic performance has not been fully established. Therefore, we attempt to pioneer “multicrystalline informatics” through collaboration of experiments, theory, computation, and machine learning to show how we can obtain high-performance multicrystalline materials. We employ silicon as a model material, and prepare various useful machine learning tools for efficient materials development.

One example is to predict distribution of crystal orientations in a large sample (e.g. whole 6-inch wafer) from optical images. We started with surface treatment of multicrystalline silicon wafers so that the reflection become sensitive to the crystal orientations. Multiple optical images were captured from each wafer with white-light illumination from different orientations. In addition, orientations of each crystal grain for a couple of wafers were measured by X-ray Laue scanner. The obtained data sets of reflection patterns and crystal orientations were used for training, validation, and test of a long short-term memory recurrent neural network. The trained model was applied to a test wafer to contain ~1,000 crystal grains, and the median of the estimated errors was ~3 degree.

Another example is to predict probability of generation of dislocation clusters. For this purpose, a large quantity of photoluminescence (PL) images was collected from wafers obtained from a same ingot. Three-dimensional reconstruction of PL images after extracting dislocation clusters by image processing successfully visualized distribution of dislocation clusters. Therefore, we can collect many small PL images as positive samples to act as the source of dislocations as well as negative samples. The obtained data sets were used for transfer learning of pre-trained convolutional neural network for image classification. The final output layer was changed to contain two outputs if the input image acts as the source of dislocations or not, and weights for the last edges were determined using the data sets. The network was applied to test wafers so that we can visualize probability distribution of generation of dislocation clusters. A part of sources was used for multiscale structural characterizations to clarify microscopic origins.

In addition, we are working on various machine learning models and statistical analysis for multicrystalline materials. Integration of such models is believed to be beneficial to show how we can maximize macroscopic performance of multicrystalline materials.

This work was supported by JST/CREST, Grant No. JPMJCR17J1 (2017-2023).
New Frontiers in Smart Sensors Based on Printed Organic Electronics
Authors: Fattori Marco , Cantatore Eugenio
Published: July 2021

Organic printed electronics is an attractive platform to develop mechanically flexible and cost-effective solutions for innovative applications such as foldable displays, flexible sensing surfaces, or biomedical instrumentation that can adapt to the shape of the body. Despite the growing interest and the recent advancements of printed electronic technologies, their use in commercial products remains very limited till now. Processing challenges such as limited yield, large transistor variability, and poor electrical performance still prevent printed systems-on-foil from commercial exploitation. The approach proposed in this work aims to tackle several of these limitations at different levels of abstraction, starting from the fabrication process and reaching the system-on-foil design. From the processing side, the major mechanisms leading to defects in a gravure-printed unipolar Organic Thin-Film-Transistor (OTFT) technology have been identified, and a successful approach to improve both device yield and performance has been developed. The availability of a reliable transistor technology is indeed a key requirement to enable complex systems-on-foil with high-yield. Assisted design flows and reliable Process Design Kits (PDKs) are also a fundamental asset to simulate and predict the system performance, further improving yield and significantly reducing design time. For these reasons a complete PDK specifically suited for gravure printed technologies has been developed. Furthermore, a methodology for the design and transistor-level implementation of analog and mixed-signal systems has been proposed: it aims at minimizing the transistor count, thus maximizing the overall yield. Circuit techniques which make use of ratiometric radouts and passive feedback networks have been used to reduce the sensitivity to the parameter variability and decrease the risks of soft failures in circuits. This multidisciplinary approach allowed us to design and successfully fabricate state-of-the-art printed smart sensors. Flexible solutions for large-area proximity and pressure sensing applications have been demonstrated, using lamination of a foil containing sensing functionality to a foil carrying analog fronted readout electronics. Both fully organic and hybrid organic-Si CMOS electronic approaches have been exploited for the readout and signal conditioning of this class of sensors. Finally, an ultra-low cost printed smart temperature sensor on an RFID tag suitable for cold chain temperature monitoring applications has also been designed and built. These results demonstrate that printed electronics can be successfully used today to fabricate inexpensive smart sensing devices for a large number of applications in which sensing over a large area, mechanical flexibility and cost are important requirements.
(Invited) Smart Nanomembranes for Multifunctional Sensors and Reconfigurable Electronics
Authors: Mei Yongfeng
Published: July 2021

Following the path of More than Moore requirements, functionalization and diversification of integrated circuits becomes an urgent topic. Integration of functions in a single chip is also an important issue in wearable and portable electronics. Smart nanomembranes, with thickness ranging from several to hundreds of nanometers, is considered as an ideal candidate in these circumstances for its flexibility. The word “smart” shows that these nanomembranes can perform sensing and actuating tasks by themselves, which largely reduces the complexity of flexible sensors and devices. The talk given here is focused on our recent progress in the development of smart nanomembranes for flexible sensors and reconfigurable electronics. Combined with sensing-type smart nanomembranes as palladium and hydrogel, we designed a multifunctional soft platform to detect different kinds of signals (e.g. gas and humidity), which can be integrated into a smart digital dust device. Furthermore, smart nanomembranes with actuation properties were applied in reconfigurable electronic devices. These nanomembrane-based devices are able to be stabilized in different configurations to provide particular and switchable electronic functions. These investigations highlight the great potential of smart nanomembranes in flexible electronics. And their unique sensing and actuating properties paves the way to intelligent robots in micro and nanoscale.
Hybrid Nanomanufacturing for Wearable Intelligence
Authors: Wu Wenzhuo
Published: July 2021

The seamless and adaptive interactions between functional devices and their environment (e.g., the human body) are critical for advancing emerging technologies, e.g., wearable devices, consumer electronics, and human-machine interface. The state-of-the-art technologies, however, require a complex integration of heterogeneous components to interface the environmental mechanical stimulus, which is ubiquitous and abundant in the above applications. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes.

I will discuss our recent progress in developing self-powered human-integrated nanodevices through the hybrid nanomanufacturing of heterostructured nanodevices with hierarchical architectures. This new class of wearable devices are conformable to human skins and can sustainably perform non-invasive functions, e.g., physiological monitoring and gesture recognition, by harvesting the operation power from the human body. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g., biomedical monitoring, consumer electronics, and intelligent robotics.
High Proton Conductivity in Sc-Doped BaZrO3: Effect of Dopant on Hydration Thermodynamics and Transport Behavior
Authors: Regalado Vera Clarita Yosune , Ding Hanping , Zhou Meng , Luo Hongmei , Ding Dong
Published: July 2021

Proton conducting solid oxide electrolysis cells (SOECs) have great promise in converting renewable energies into hydrogen at intermediate temperatures (400~600 oC). The high efficiency and fast hydrogen production rate benefit from the proton conducting electrolyte with attractive proton conductivity and low activation energy. Transition element doped-BaZrO3 oxides have been widely employed as electrolyte because they show modest conductivity and high chemical stability in the realistic SOEC conditions. Still, the electrolyte development with higher proton conductivity is urgently needed to further reduce hydrogen production costs. In this work, a series of Sc doped BaZrO3 electrolytes are studied to understand the effects of the dopant, gas atmosphere and temperature on the hydration behavior and proton transport. The proton concentration, hydration thermodynamics and relevant characterizations are investigated to understand how the proton incorporation process is affected. The dehydration process can reveal that the protons have different stabilized positions in the lattice. Furthermore, the proton trapping can be also affected by the different dopant, which indicates the selection of the Zr-site doping should be balanced with consideration on proton concentration and migration energy simultaneously. This work will give some helpful insights into the design of proton conducting materials.
Study of Enhanced Conduction from Ceramic/Carbonate Composite Electrolytes
Authors: Fung Kuan-Zong , Tsai Shu-Yi , Tang Jhih Yu , Chang Ting-You
Published: July 2021

Mixed ionic/electronic conduction in many electrochemical devices have received great attention. For instance, oxygen transport membrane (OTM) based on (Ba,Sr)(Co,Fe)O3 perovskite exhibit unique hole/oxygen ion mixed conduction behavior for oxygen separation application. Moreover, composite electrodes/electrolytes consisting of electronic and/or multiple ionic conductors have received great attention for high temperature fuel cell application. For example, enhanced conduction was observed when the oxygen ion conductor, doped ceria was directly mixed with Li/K carbonates. The electrical conduction of composite electrolyte was contributed by the migration of oxygen ions in solid state and carbonate ions in liquid state. It was observed that the two-phase electrolytes exhibit coionic (O=/H+) conductors during fuel cell operation under the H2/ air atmosphere. It is believed that highly mobile ions at the interface between doped ceria and carbonates may contribute to the high conductivity of the composite electrolyte. In other words, the super-ionic phase might exist at the interface between doped ceria and carbonates, where the defect concentrations are high. Similarly, mixed conducting electrodes based on composite electrode (e.g. LSM/SDC, LSM/YSZ) also show improved SOFC performance in comparison to conventional electrode. However, to optimize the mixed conduction, the materials/microstructure designs play an important role. Thus, the objective of this work is to conduct (1) fabrication/design of MIEC and composites (2) microstructure development, (3) characterization of conduction/interfacial kinetics for electrodes/electrolytes in high-temperature fuel cells. High-resolution SEM, XRD, and Electrochemical Impedance Spectroscopy are employed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrode/electrolytes will be rationalized based on the pore size, pore distribution and interface area.
ZrO2-Based Electrocatalysts for Methane Partial Oxidation to Liquid Fuels at Room Temperature
Authors: Xu Nengneng , Coco Cameron A , Zhou Xiao-Dong
Published: July 2021

As the main component of natural gas, methane is a well-established and widely available feedstock for the production of chemicals, particularly small chain organics. Among them, the electrochemical conversion of methane to liquid fuels is of particular interest, because it can scale up directly with surface area and current density (not volume), typically operates at low temperature, and is capable of achieving efficiencies that are not limited by the Carnot cycle efficiency. Also, electrochemical processes provide a unique opportunity to pair with renewable energy sources, such as wind and solar. In this work, a series of ZrO2-based catalysts are investigated, which exhibit catalytic activity attributed to the strong synergetic effect between ZrO2 and metal oxides (TMO, Fe2O3, Co3O4 and NiO). In contrast to ZrO2@Co3O4 and ZrO2@NiO, the ZrO2@Fe2O3 shows the highest catalytic activity with the largest current density difference at 1.3 V (Δj: 13.65 mA cm-2). Furthermore, these samples show a long-term stability over 200 hours. 1-propanol and 2-propanol are the main product of CH4 partial oxidation after 10 hours under ambient conditions. The density functional theory calculations revealed that the high activity of these ZrO2-based catalysts originated from the optimized charge distribution after the ZrO2 cluster grew on the TMO. The study herein offers more possibilities for the synthesis of higher alcohols by CH4 partial oxidation at room temperature.
Bifunctional MnO2/CNTs-Based Oxygen Catalysts with Tailored Catalytic Activity for Rechargeable Zn-Air Batteries
Authors: Xu Nengneng , Zhang Yanxing , Wang Yudong , Wang Min , Su Tianshun , Coco Cameron A , Qiao Jinli , Zhou Xiao-Dong
Published: July 2021

Metal-air batteries, as highly effective clean energy devices, play an important role in current sustainability development. Zn-air batteries are of great interest in future power devices due to eco-friendliness, superior safety, low-cost and high theoretical energy density. Yet, it remains challenging to identify inexpensive, high-efficient and durable bifunctional catalysts to boost various reactions for Zn-air batteries. a-MnO2 exhibits 2×2 tunnels with a unique orthorhombic structure shows a higher oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity than other-phase MnO2. In this work, metal oxide anchored MnO2/CNTs hybrid catalysts (M-MnO2/CNTs) are developed via a facile hydrothermal process. Indeed, M-MnO2/CNTs display better catalytic activity and stability than MnO2/CNTs. The improved performance and stability are originated from (i) the novel hierarchal structure improving the mass transport, (ii) the redistribution of electrons from metal ion to MnO2 activating the Mn catalytic sites, (iii) the coupling effect from the metal oxide and MnO2/CNTs. Particularly, the overpotential (ΔE) of Co-MnO2/CNTs is low to 0.803 V, which highly approaches the referenced Pt/C+IrO2 (ΔE: 0.801 V). Accordingly, the peak power density of the Co-MnO2/CNTs-based Zn-air battery reaches 342.7 mW cm-2. The recharge Zn-air battery also exhibits good charge-discharge stability with a low voltage gap of 0.72 V for 128 hours. This work provides an effective mothed to achieve MnO2/CNTs materials with tailored catalytic activity by anchoring different metal oxides, and reveals great potential in the field of high specific energy batteries for portable electronics, electrical vehicles, and wearable devices.