bluuebunny/crossref_metadata_2025 huggingface dataset:
Decoupling the Role of Anion and Solvent on Mg Electrodeposition Efficiency through Interfacial Speciation Determination
Authors: Zavadil Kevin R , Hahn Nathan T , Feng Xuefei , Anquillare Emma , Guo Jinghua , Seguin Trevor , Persson Kristin A
Published: February 2020

Chemistries based on divalent working cations, such as Mg, are one class where significant effort is required to develop reductively and oxidatively stable electrolytes to support high efficiency metal deposition and cation insertion for practical energy storage systems beyond Li ion batteries. A growing body of literature exists describing bulk Mg(II) speciation over a range of electrolyte types providing insight into the origin of parasitic reactions that limit cell efficiency and overall performance. Bulk Mg(II) speciation can be argued to be an approximate descriptor of electrolyte stability at best, as the interfacial cation-anion-solvent coordination complex is what actually determines the consequences and efficiency of electron transfer. Limited knowledge is reported for interfacial Mg(II) coordination complexes, in part, due to limited available operando probes capable of discriminating between the coordination complexes at the electrode surface and within the bulk of the electrolyte. In this paper, we demonstrate the use of fluorescent and electron yield modes of operando x-ray absorption spectroscopy (XAS) to determine interfacial composition as a function of potential for select Mg(II)-anion-ether systems. We further conduct systematic variation in the coordination strength (e.g., donicity) and coordination diversity (e.g., mono- vs multi-dentate) of anions and ethers with respect to the divalent cation as a means of decoupling the role of anion and solvent in defining stability. Comparison of spectroscopic responses of Mg(II) with Zn(II) allow for additional modulation in anion/solvent coordination enthalpy further clarifying the roles of anion and solvent. The ability of XAS to discriminate early stage interphase formation at the anode providing chemical signatures of parasitic reaction will also be discussed. The methodology presented is equally applicable to electrolyte oxidative stability at the cathode, laying the foundation for design of electrolytes with suitable stability for practical, high energy density Mg ion batteries.

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia National Laboratories is a multimission 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-NA-0003525.
Mechanistic Investigations of Interfacial Stochasticticity in Lithium Metal Anodes
Authors: Verma Ankit , Mukherjee Partha P.
Published: February 2020

Development of next generation batteries with enhanced energy and power density is predicated on utilization of lithium metal anodes in conjunction with liquid electrolytes that inhibit dendritic growth. Lithium metal-liquid electrolyte systems exhibit severe dendritic growth coupled with solid electrolyte interphase (SEI) fracture and formation of dead Li zones under repeated plating-stripping cycles resulting in exacerbated capacity fade and propensity for internal short circuit. Morphological evolution of the interface (liquid electrolyte-SEI-Li metal) impacts the transport-electrochemistry-mechanics interactions and dictates the performance of Li metal anodes. In this work, we elucidate the complexations arising at the interface through a holistic modeling approach cognizant of the aforementioned mechanisms and delineate strategies for improved performance through dendrite suppression.
Highly Reversible Reactions in Neutral Aqueous Zinc Battery Systems
Authors: Pan Huilin , Jin Yan , Shao Yuyan , Liu Jun , Reed David , Sprenkle Vincent
Published: February 2020

Along with the rapid development of renewable energy storage such as wind and solar, the large-scale energy storage technologies are highly desired. Among different energy storage solutions, the rechargeable aqueous Zn-MnO2 batteries are very promising due to their low cost, high environmental benignity and high energy, potentially two times high of the lead-acid batteries. However, the widely investigated rechargeable alkaline Zn-MnO2 batteries suffer from limited depth of discharge (DOD), Zn anode passivation and dendrite, and limited cycle life. In this talk, we will introduce the use of mild aqueous-based electrolytes to address the above issues based on the greatly improved rechargeability of both MnO2 cathode and Zn anode in such systems.[1,2] We will also discuss our recent understanding on how to realize and maintain the highly reversible reactions for both zinc metal and cathodes by optimizing the electrolyte and electrode structures in optimal neutral aqueous electrolyte systems to realize the long-term cycling stability for their future practical applications in large-scale energy storage.
Magnesium Chromium Oxide Nanocrystals: Synthesis and Electrochemistry
Authors: Hu Linhua , Johnson Ian , Kim Soojeong , Nolis Gene M , Freeland John W , Yoo Hyun , Fister Timothy T , Ploszajski Anna , McCafferty Liam , Ashton Thomas , Darr Jawwad , Cabana Jordi
Published: February 2020

Chromium oxides with the spinel structure have been predicted to be promising high voltage cathode materials in magnesium batteries. Perennial challenges involving the mobility of Mg2+ and reaction kinetics can be circumvented by nano-sizing the materials in order to reduce diffusion distances, and by using elevated temperatures to overcome activation energy barriers. Herein, ordered 7 nm crystals of spinel-type MgCr2O4 were synthesized by a conventional batch hydrothermal method. In comparison, the relatively underexplored Continuous Hydrothermal Flow Synthesis (CHFS) method was used to make highly defective sub-5 nm MgCr2O4 crystals. When these materials were made into electrodes, they were shown to possess markedly different electrochemical behavior in a Mg2+ ionic liquid electrolyte, at moderate temperature (110 °C). The anodic activity of the ordered nanocrystals was attributed to surface reactions, most likely involving the electrolyte. In contrast, evidence was gathered regarding the reversible bulk deintercalation of Mg2+ from the nanocrystals made by CHFS. This work highlights the impact on electrochemical behavior of a precise control of size and crystal structure of MgCr2O4. It advances the understanding and design of new cathode materials for Mg-based batteries.
Climate-Immune Extreme Fast Charging of High Energy Li-Ion Batteries
Authors: Yang Xiao-Guang , Liu Teng , Ge Shanhai , Wang Chao-Yang
Published: February 2020

Fast charging is the enabler of mainstream adoption of electric vehicles (EVs). There is a race worldwide for building fast charging stations with the power up to 350kW, which are able to charge a 200-mile-range EV at 6C (10 minutes). State-of-the-art EV batteries (cell-level energy density >200 Wh/kg) could only withstand 2C (30 minutes) charging due to the issue of lithium plating. Even worse, the charge rate must be dramatically reduced at low temperatures to prevent lithium plating.

Most recently, our group presented a controllable cell structure that enables lithium plating free (LPF) fast charging at all temperatures. [1] The key is to charge a cell always above a temperature that can prevent lithium plating. A rapid heating step will be performed before charging if the cell temperature is low. It is demonstrated that a 9.5Ah pouch cell with an energy density of 170 Wh/kg could be charged by 80% state of charge in 15 minutes even at -50oC, an extremely low temperature at which all conventional Li-ion cells would cease to work. Furthermore, the LPF cell sustained 4500 cycles of 15-min fast charging at 0oC with <20% capacity loss, which is equivalent to >12 years and >280,000 miles of EV lifetime, whereas a baseline conventional cell at the same condition only survived 50 cycles.

Based on the LPF cell structure, we proposed an approach to enable 10-min extreme fast charging (XFC) of high energy EV cells. By numerical analysis, we revealed that the optimal temperature for Li-ion battery charging increases with the increase of charge rate and energy density. [2] Thus, we are now partnering with the U.S. Department of Energy (DOE) to develop an XFC battery that is charged at high temperatures (>60oC). The target is to achieve 6C charging of >225 Wh/kg cells with a life of >1000 cycles at <20% capacity loss.

In this talk, we will give a comprehensive discussion of the LPF cell structure and operating strategy. We will also share our latest progress on the development of XFC cells.

References

[1] X.G. Yang, G. Zhang, S. Ge, C.Y. Wang, Proc. Natl. Acad. Sci. U.S.A. 115 (2018) 7266-7271.

[2] X.G. Yang, C.Y. Wang, J. Power Sources 402 (2018) 489-498.
Influence of Additives on Formation of through-Si Via in Si Substrate Using Metal Assisted Chemical Etching
Authors: Shimizu Tomohiro , Hanatani Syunsuke , Yorioka Takuya , Niwa Ryosuke , Ito Takeshi , Shingubara Shoso
Published: February 2020

Recently, metal assisted chemical etching (MacEtch) attracts attention to fabricate a nano/microscale structures in Si substrate, such as nanowire and nanohole arrays. In this method, using a noble metal as a catalyst, only Si under the catalyst is selectively etched in the etching solution. Several papers have been already reported on the formation of microscale patterning using MacEtch. However, it is difficult to obtain high aspect vertical holes using MacEtch process because of its instability of etching direction for prolonged process as shown in figure (a). In this study, we present a new approach using surfactant agents as an additive in MacEtch solution to obtain vertical Si holes in Si substrates. Microscale holes were prepared in Si (100) substrates using the MacEtch process with a disc-shape patterned Au catalyst. The patterned Au discs ( 10 μm in diameter), which were deposited on a Ti / Si substrate using a photolithography lift-off process. For the MacEtch process, a mixture of hydrofluoric acid (HF), hydrogen peroxide (H2O2) and deionized water was used as the base etching solution. The PEG was added to the etching solution as an additive. The MacEtch of the Si substrate with patterned Au were performed for 120 min at 40 oC in the etching solution. Figure (a) shows cross-sectional SEM images of typical morphology of etched Si using MacEtch process without PEG in the etching solution. The etching direction of Si were changed during MacEtch as indicated with dashed arrow in Fig. (a), and these phenomena were observed in more than 60 % Si holes etched with MacEtch without PEG. Adding PEG in the etching solution, drastic improvement in verticality of etched Si holes were observed. Almost all holes were vertically etched to the Si substrate in PEG samples, and typical cross-sectional image of the etched holes is shown in Fig. (b). Fig. (c) and (d) shows enlarged image of Au catalyst films after MacEtch process. The catalyst in the bended hole prepared without PEG was deformed and partially detached from Si substrate, shown in Fig. (c). In contrast, in the case of straight holes etched with PEG shown in Fig. (d), the catalyst tightly contacted to the substrate, and showed relatively less defamation. Thus, there is a strong correlation between defamation of catalyst and formation of bended hole.

The detailed mechanism of PEG additive in etching solution during Macetch process and the MacEtch results using other surfactants as additives will be presented.

Figure 1
Characterization of Silicon Nanowires Reflectance By Effective Index Due to Air-Silicon Ratio
Authors: Koech Philemon Kipsang , Ogini Martins , Mohan Susmitha , Alice Francis Aneeta , Deo Makarand , Albin Sacharia , Sundaram Kalpathy B.
Published: February 2020

Light collection efficiency plays a key role in the performance of many optical and optoelectronic devices. A high reflectivity of the semiconductor surfaces and interfaces in these devices could hinder efficient light collection. To minimize unwanted reflection, several methods have been employed, including anti-reflection coatings, which may increase the process complexity and cost. In this research, we fabricated silicon nanowires (SiNWs) by metal assisted chemical etching (MACE) with hydrogen peroxide (H2O2) as an oxidizing agent. Etching time was varied between 30 and 45 minutes to investigate its effect on the SiNW lengths, air to silicon (Air:Si) ratio and surface reflectance of the processed Si substrates. The Air:Si ratios were determined by analyzing SEM images of substrate surface (Fig. 1a) using image thresholding technique in MATLAB (Fig. 1b). The optical measurements show a significant reflectance change with varying Air:Si ratio. For normal incidence, a minimum reflectance of around 0.2% was achieved for about 2µm long SiNW samples on Si produced by 30 minutes etching. Further increase in etching time resulted in slight increase in the reflectivity. Fresnel’s equations at minimum reflectance provided an estimated effective refractive index (ERI) of 1.04. The Air:Si ratio decreased from 0.70 to 0.62 when the etching time was increased from 30 to 45 minutes which corresponded to an increase in the estimated ERI from 1.04 to 1.07. Hence it is reasonable to conclude that beyond the etching time for minimum reflectance, the increase in reflectance is due to increase in the ERI caused by the decreased Air:Si ratio. This result can be used in optimizing the chemical processes to achieve a near-zero-reflectance in SiNW samples.

Figure 1
(Invited) Analysis of Charge Transfer Reactions with Semiconductor Ultramicroelectrodes
Authors: Maldonado Stephen
Published: February 2020

This presentation will detail our latest advancements utilizing semiconductor ultramicroelectrodes (SUMEs) as platforms to study semiconductor/liquid interfaces. Specifically, we will show the accurate, quantitative measurement of heterogeneous charge transfer rate constants with n-Si, n-GaP, and n-GaN SUMEs immersed in non-aqueous electrolytes. The intent is to develop methodologies that test the extent that classical Marcus theory describes charge transfer at semiconductor/liquid interfaces. The presented data will show that SUMEs offer the unique possibility of making measurements either in depletion or in accumulation conditions. Additional data will be presented that highlighted the response characteristics of SUME arrays under illumination, highlighting an alternative design motif for PEC photoelectrodes.
(Invited) Role of Domain Purity in Non-Fullerene Acceptor Based Organic Solar Cells
Authors: Mukherjee Subhrangsu , DeLongchamp Dean M
Published: February 2020

The field of non-fullerene organic solar cells (OSC) has experienced rapid development during the past few years, mainly driven by the development of novel non-fullerene acceptors and matching donor semiconductors with device efficiencies approaching 15%. However, organic solar cell material development has progressed via a trial-and-error approach with limited understanding of the materials’ structure–property relationships and the underlying device physics of non-fullerene devices. In addition, the availability of hundreds of donor and acceptor semiconductors creates a large pool of possible donor–acceptor combinations, which poses a daunting challenge for rationally screening material combinations. Resonant soft X-ray scattering (RSoXS) has proven to be a powerful technique to measure domain purity in OSC active layer blends. In polymer-fullerene systems, RSoXS has shown that higher average domain purity is generally correlated to device performance. A simple interpretation of RSoXS purity measurements is complicated by the consideration that real morphologies may be composed of three or more phases, with mixed amorphous regions in addition to relatively pure, aggregated donor and acceptor domains. Whilst charges are understood to migrate to the aggregated domains due to a favorable electronic landscape, these charges might be effectively trapped in aggregates if there is insufficient number of percolating pathways in the amorphous mixed regions. Conversely, if the mixed regions have a composition much beyond the percolation threshold or if the volume faction of the mixed regions is large, then recombination is enhanced. Therefore, understanding the role of domain purity over different length scales and controlling the mixed amorphous phase for maximum charge creation and minimum recombination remains a principal challenge for non-fullerene OSCs.

We will summarize several of our RSoXS studies that compare non-fullerene acceptor based organic solar cells having different primary chemical structures of the constituents and with significant processing variations. Our analysis suggests that mixed regions are often detrimental to good performance in these systems, typically having a pronounced negative impact on FF. Optimizing performance continues to be a delicate balance of possibly competing factors and the volume fraction of the ideal morphology remains to be determined. However, the miscibility of blend components, which might be probed using near-edge X-ray absorption spectroscopy as a screening tool, can guide expectations of achievable phase purity and ultimately the achievable performance of the active layer.
Improved Electron Injection and Transport in Semiconducting Polymers By Doping with Guanidino-Functionalized Aromatic Compounds
Authors: Schneider Severin , Lorenz Roxana , Himmel Hans-Joerg , Zaumseil Jana
Published: February 2020

Efficient and stable n-dopants are still rare but highly desired for organic electronics and thermoelectrics. Many high mobility, n-type semiconducting polymers still show some hole transport, which is unwanted for applications in complementary inverters, as it gives rise to increased power dissipation. The use of n-type contact dopants that block the injection of holes is thus beneficial. We successfully applied 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb), a guanidino-functionalized aromatic (GFA) compound, as a strong two-electron donor to networks of single-walled carbon nanotube field-effect transistors to create purely n-type devices with high electron mobilities and high on/off current ratios [1]. Here, we demonstrate the versatility of this dopant by applying it to the well-known n-type (but still slightly ambipolar) polymer semiconductor P(NDI2OD-T2).The dopant ttmgb can be processed directly from solution, which leads to significantly improved device characteristics. Additionally, we show that vapor deposition of ttmgb is another pathway to high-performance injection layers. In all cases, the injection of electrons and their mobility is significantly improved compared to the untreated reference samples. In addition, the injection of holes is blocked by ttmgb2+ on the electrode surface, which enables the fabrication of solely n-type FETs. Contact doping with ttmgb and other GFAs could potentially also be used on other semiconducting materials, e.g. for two-dimensional transition metal dichalcogenides, and may find widespread application in high performance thin film electronics.

[1] Schneider et al., ACS Nano
2018, 12 (6), 5895-5902

Figure 1
(Invited) Seebeck Coefficient Model Based on Hopping Transport
Authors: Li Ling , Lu Nianduan
Published: February 2020

Seebeck coefficient is applied to promote an accurate transport process in organic semiconductors. In this talk, I will present a general analytical model to describe the seebeck effect for organic semiconductors based on hopping transport and percolation theory. The proposed model can well interpret the seebeck feature of the polymers with approaching disorder-free transport, as well as that of organic semiconductors with general disorder.

Figure 1
(Invited) Design and Fabrication of Organic Thin Film Transistors Using Solution-Processable Liquid Crystalline Phthalocyanine Derivatives
Authors: Ray Asim Kumar
Published: February 2020

Phthalocyanines (Pcs) are an extremely non-toxic organic chromophores with a range of versatile range applications from industrial pigments to photodynamic agents in cancer therapy and photosensitizers in photocopiers and compact discs. The central atom is coordinated with four pyrrolic nitrogen atoms. The conjugated π-systems of eighteen electrons in the macrocyclic ring gives rise to unique semiconducting properties which can be tuned by substituents of alkyl, alkoxy, or alkoxymethyl chains at sixteen sites on the benzenoid rings and axial ligation sites at the central metal or metalloid. Unsubstituted Pcs are generally both thermally and chemically stable but ring substituents such as SO3H and aliphatic chains confer solubility in water and organic solvents, respectively. They can form liquid crystalline phases. The present talk will highlight the achievements in application of phthalocyanine layers in different electronic devices such as field effect transistors (OFET) and memory devices taking into account literature data and our experimental results. Special attention will be focused to liquid crystalline phthalocyanines. Disk-like molecules, typically comprising a flat rigid aromatic core and flexible peripheral substituents, self-organizes into one-dimensional "supramolecular wires". Due to high charge carrier mobility along the columns, discotic mesogens are considered as realistic candidates for application in organic electronic devices. The well-ordered films with controllable molecule alignment can be obtained by slow cooling from isotropic liquid temperature.
(Invited) A Simple and Efficient Solution-Based Technique to Electrically Dope Organic Semiconductors
Authors: Larrain Felipe A. , Fuentes-Hernandez Canek , Chou Wen-Fang , Rodriguez-Toro Victor A. , Kippelen Bernard
Published: February 2020

The printed electronics industry offers a paradigm change in manufacturing, cost and environmental impact when compared to the conventional semiconductor industry. Printed electronic devices are expected to be mass-produced from less-energy-demanding processes over large areas and on flexible substrates, with techniques that closely resemble the well-known mass production of printed media on paper.

Still, critical to the widespread of these devices is the ability to convert lab produced “champion” figures into reliable industrial-scale products. The well-established strategies for the design and fabrication of efficient lab-scale printed electronics are not always compatible with large-area manufacturing, where several additional requirements must be met.

Solution-based electrical doping of organic semiconductors has received increased attention as a technique with the potential to comply with some of these additional requirements. Stable ink-type formulations of dopant, semiconductor and solvents have been reported, some of which may be compatible with roll-to-roll coating. Yet, the ability to fabricate vertical doping gradients, critical to maintain optimal optoelectronic performance at reduced cost, has proven challenging. Vertical doping gradients would reduce the amount of coating steps without a loss in optoelectronic device functionality, simplifying manufacturing and preventing defects to propagate.

In 2017 we reported a simple technique to fabricate vertical electrical p-type doping gradients in organic semiconductor films by dipping them in solutions. Still, the initial approach, which involved 12-molybdophosphoric acid (‘PMA’ dopant) and nitromethane (processing solvent), was highly solvent selective, and the use of nitromethane was found limiting. Thus, in 2018, our team replaced nitromethane with acetonitrile and showed that the PMA-acetonitrile solution became stable in air without losing its doping ability. Furthermore, organic solar cells fabricated using the updated approach showed longer air stability.

In this talk we will start by discussing the basics of the solution-based technique to electrically p-type organic semiconductors using PMA, and compare it against similar, well-studied approaches. Then, we will emphasize on our latest insights on the path to unravel, from a molecular perspective, how organic semiconductors are doped down to a limited depth from solution, using PMA molecules. That is, what is the interplay between the organic film and PMA molecules in solution that leads to p-type electrical doping of the semiconducting layer? Additionally, what are the key parameters that determine the efficiency and extent of the process?
(Invited) Printing Transistors Circuits: Interest of Organic Materials and Challenges
Authors: Charbonneau Micael , Locatelli Denis , Lombard Stephanie , Laugier Christelle , Tournon Laurent , Romanjek Krunoslav , Gaitis Alexandre , Coppard Romain , Serbutoviez Christophe
Published: February 2020

This paper will present the recent work done at CEA-LITEN for the development of Printed Transistor circuits. In particular, through Collaborative Project and internal Development, CEA-LITEN and partners have been working on the transfer and scale-up of OTFT Circuits from Lab to Printing Pilot Line (GEN1). The paper will discuss the challenges and requirements for the materials at the different technological level from process to device as well as for circuits design and integration into hybrid system. The material strategy and inks developed for robust printing capability and the engraving technologies engineered for the downscaling of printed pattern down to 150 µm and beyond will be introduced. Electrical performances and electrical bias stress stability of the OTFT fabricated on GEN1 pilot line will be presented and discussed (µFE > 2cm²/V/s; Vt~ -3..-4.5 V). Finally, in the last section the paper will present the current capability of technology for smart sensor applications and discuss the current limitation and track of improvement through innovative materials.

Figure 1
(Invited) High-Frequency Operation of Vertical Organic Field-Effect Transistors
Authors: Kleemann Hans
Published: February 2020

Organic thin-film transistors (OTFT) are attracting great interest in view of flexible electronics enabling future revolutionizing applications such as flexible displays or wearable electronics. Due to the poor intrinsic charge carrier transport in organic semiconductor thin-films, the main target of development in the last two decades was to find suited semiconductor materials offering a higher charge carrier mobility. However, although record values of clear beyond 10cm²/Vs have been demonstrated, key transistor parameters such as the transconductance or transition frequency have not been improved substantially. In consequence, the performance of today's OTFTs is still too low for many demanding electronic applications.

In the last couple of years we have develop various architectures for vertical organic transistor offering superior current driving capabilities compared to state-of-the-art horizontal organic TFTs. Within this 3-dimensional VOFET geometry, the channel length is not defined by the applied patterning technique but rather by the thickness of the organic layers, typically <300nm, separating the vertically stacked source and drain electrodes. This ultra-short channel configuration allows for superior current driving, however, it is usually accompanied by undesired short-channel effects such as loss of saturation and an increased off-current level.

In my presentation I introduce the VOFET concept and highlight the development of optimized transistor geometries leading to superior performance with an on/off ratio>10⁷, transition frequency approaching 100MHz and excellent operational stability.

In the second part of the contribution I focus on the potential of VOFETs for active matrix OLED (AMOLED) display driving. Comparing typical TFT design guidelines for vertical and horizontal TFTs, it can be deduced that the VOFET design leads to a considerable reduction of area consumption within a pixel which ultimately enables a higher display resolution and a lower power consumption.

The concept of vertical transistors is not restricted to organic semiconductors. Hence, I discuss in the third part of my presentation the potential of high mobility metal-oxide semiconductors for vertical thin-film transistors for GHz operation.
(Invited) Recent Developments in Contact-Controlled Transistors
Authors: Sporea Radu Alexandru
Published: February 2020

An effective route to achieving high gain and low saturation voltage in thin-film transistors is by controlling the current by modulating the conductivity of the source contact area [1-3], potentially at the expense of operating speed. Such devices, called source-gated transistors (SGTs) are easily made using the usual techniques, in a variety of organic and inorganic semiconductor technologies, with the requirement that a potential barrier is reliably engineered at the source electrode. Most often, this barrier results from the presence of a Schottky contact [4], which has been proven beneficial in similar devices [5]. As this type of TFT gains popularity, novel ideas which leverage both the device physics and the specifics of the fabrication process are emerging [6].

In this paper we will discuss recent advances in device architecture and highlight important design decisions specific to the envisaged application. Since the contact injection area plays an important part in this type of devices, it is an essential design parameter. Traditionally, contact overlap should be minimized to reduce capacitance, but in SGTs it may be advantageous to purposely increase gate-to-source overlap. Interesting circuit behaviour results from the sizing of this parameter [7] and could be useful in designing circuit blocks which take advantage of this factor, in contrast with conventional TFT circuit design. This reasoning is especially relevant to pixel circuits where a storage capacitor is required in the circuit between these two electrical nodes: circuit optimization necessarily includes electrical characteristics and layout area.

In many applications, the versatility and robustness of these contact-controlled devices outweighs their reduced operating frequency, and their ease of fabrication recommends them for high-gain circuits where uniformity of performance is critical.

[1] S. D. Brotherton, Introduction to Thin Film Transistors: Physics and Technology of TFTs, Springer, 453–480, Cham (2013).

[2] A. Valletta et al., J. Appl. Phys. 114 064501 (2013).

[3] R. A. Sporea et al., Scientific Reports
4 4295 (2014).

[4] N. Papadopoulos et al., Proc CICC 2017 (2017).

[5] Lee, S. and A. Nathan, Science
354, 302 (2016).

[6] L. Wang et al., Appl. Phys. Lett.
110, 152105 (2017).

[7] J. M. Shannon et al., IEEE Trans. Electron Devices, 60, 2444–2449 (2013).

[8] R. Drury et al., Proc. CAD-TFT 2018, Shenzhen, China (2018).
Effects of Doping States of Polyaniline Thin Films on Their Photo-Responsive Properties
Authors: Choi Jongwan
Published: February 2020

Polyaniline (PANI) has been of great interest in development of conducting polymers because of easy bulk-scale polymerization and relatively high electrical conductivity. The physical and electrical characteristics of PANI largely depend on its protonation-induced doping states. The protonation of imine sites upon acid doping leads to the formation of a conductive polaron lattice along the backbone. The effects of acid dopants on dielectric, optoelectronic, and thermoelectric properties of PANI have recently been investigated.

In this study, we investigate the effects of doping/dedoping states of PANI thin films on their photo-responses under laser irradiation in visible and near-infrared regions. The doping levels were controlled by treating as-prepared, acid-doped PANI with aqueous ammonia solutions. Spectroscopic analyses confirmed the changes in the doping states by evolution or decrease of characteristic peaks. The electrical and photo-responsive properties were significantly affected by the doping states of the PANI thin films. The photocurrent and photovoltage under irradiation of controlled wavelengths from various laser sources were measured. While the photocurrent followed the trends of electrical conductivity upon dedoping, the photovoltage was related to the absorption and photocharge generation of the PANI samples.
(Invited) Hexagonal Boron Nitride Epilayers
Authors: Jiang Hongxing , Lin Jingyu
Published: February 2020

As a member of the III-nitride wide bandgap semiconductor family, BN has received much less attention in comparison with other nitride semiconductors. The stable phase of BN synthesized at any temperature under ambient pressure is hexagonal. Due to its wide bandgap (> 6 eV) and layered structure, hexagonal BN (h-BN) is an ideal platform for probing fundamental 2D properties of wide bandgap semiconductors. In this talk, a brief overview of the synthesis and electrical and optical properties of wafer-scale h-BN epilayers will be presented [1-7]. It was shown that the unique 2D structure of h-BN induces exceptionally high density of states, large exciton binding energy and high optical absorption and emission intensity. By growing h-BN under high V/III ratios, epilayers exhibiting pure free exciton emission have been obtained [4]. Photocurrent excitation spectroscopy results directly provided a room temperature bandgap value for h-BN in between 6.4 and 6.5 eV and the free exciton binding energy (Ex) of 0.73 eV [5]. Layer-structured B-rich BGaN alloys, heterostructures, and quantum wells have also been successfully grown and their properties will be discussed. Thermal neutron detectors fabricated from 100% B-10 enriched h-BN epilayers of thicknesses exceeding 50 mm have attained the highest detection efficiency to date among solid-state detectors at about 58% [6, 7]. These solid-state neutron detectors have become increasingly desirable for a wide range of applications from fissile materials sensing to well logging, because 3He gas detectors are inherently bulky, require high pressurization and high voltage application, slow response time, and expensive. It is our belief that h-BN will lead to many potential applications from deep UV optoelectronics, radiation detectors, to novel layered-structured photonic and electronic devices.

[1] R. Dahal, J. Li, S. Majety, B.N. Pantha, X. K. Cao, J. Y. Lin, and H.X. Jiang, Appl. Phys. Lett. 98, 211110 (2011).

[2] S. Majety, J. Li, X. K. Cao, R. Dahal, B. N. Pantha, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 100, 061121 (2012).

[3] H. X. Jiang, and J. Y. Lin, Semicon. Sci. Technol. 29, 084003 (2014).

[4] X. Z. Du, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 106, 021110 (2015); 108, 052106 (2016).

[5] T. C. Doan, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 109, 122101 (2016).

[6] A. Maity, T. C. Doan, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 109, 072101 (2016).

[7] A. Maity, S. J. Grenadier, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 111, 033507 (2017) and J. Appl. Phys. 123, 044501 (2018).
Magnetic III-N Semiconductors Based on Rare Earth Doping
Authors: Zavada John M
Published: February 2020

This paper focuses on the magnetic properties of wide bandgap III-N semiconductors doped with rare earth elements. Such materials form a novel class of dilute magnetic semiconductors that have an important potential impact on future information processing devices [1]. In particular, rare earth doped III-N thin films may lead to integration of electronic, optical, and magnetic functionality for sensing and communication applications. The two main thrusts of this paper are the efficient incorporation of rare earth ions in III-N thin films and the demonstration of magnetic effects at room temperature. While early studies were based on ion implantation and solid-state diffusion, major advances have been achieved through molecular beam epitaxy and metal-organic chemical vapor deposition. [2, 3]. Measurements of room temperature magnetic effects from III-N films doped with rare earth elements, including neodymium, europium, gadolinium, erbium, and thullium, will be presented. The dependence of the magnetic properties on the synthesis method and co-doping will be addressed.

[1] Rare Earth and Transiton Metal Doping of Semiconductor Materials: Synthesis, Magnetic Properties and Room Temperature Spintronics, Ed. V. Dierolf, I.T. Ferguson and J.M. Zavada (Elsevier Woodhead Publishing, 2016).

[2] “Er Doping of AlN During Growth by Metalorganic Molecular Beam Epitaxy,” J.D. MacKenzie, C.R. Abernathy, S.J. Pearton, U. Hömmerich, X. Wu, R.G. Wilson, J.M. Zavada, and R.N. Schwartz, Appl. Phys. Lett.692083 (1996).

[3] “Erbium-doped GaN epilayers synthesized by metal-organic chemical vapor deposition,” C. Ugolini, N.Nepal, J. Y. Lin, H. X. Jiang, and J. M. Zavada, Appl. Phys. Lett. 89151903 (2006).
(Invited) Enabling 5nm and Beyond Device Fabrication with New Etch Technologies
Authors: Ranjan Alok , Ventzek Peter
Published: February 2020

All logic device roadmaps predict significant change in the form and nature of logic at 5 nm. III-V’s, SiGe, Ge, nanowires and nano-sheets, while attractive as device options, bring pause to process and integration teams that need to integrate new materials or new material forms. Research grade devices are certainly possible today but high volume manufacturing of new devices in whatever form they may take requires change to unit processes available in today’s fabrication facilities. The question is whether something entirely new is needed or it is a matter of enhancing the capabilities of process and equipment that exists today. A key of those responsible for next generation logic is damage in one form or another by the (plasma) etch unit process. III-V’s, SiGe and Ge devices are particularly sensitive to damage. This has motivated calls for a complete move to thermal etch processes potentially upending available integration approaches. Unfortunately, thermal processes are themselves not damage free in that it is impossible not to leave interfaces and the immediate sub-surfaces unaltered. Fortunately, advances in plasma etch technology allow plasma etch to meet and exceed thermal process performance. Pulsing technology went a long way to mitigating damage caused during silicon device fabrication more than a decade ago. Now, advanced pulse technology applied to advanced plasma sources delivers performance equivalent to thermal processes by precise control of surface passivation, surface volatilization and surface reaction by-products. Concurrent advances in applying novel process chemistries (plasma based self-limited material removal and deposition processes) are also ready for new logic materials. Key is the availability of advanced materials chemistry simulations for use in process development. The research opportunities for new etch technology for “selective area etching” in advanced logic manufacturing will be the next frontier of R&D activities.
(Invited) Graphene Based Devices for in Vitro and In Vivo Electrophysiology
Authors: Offenhäusser Andreas , Kireev Dmitry
Published: February 2020

In the field of electrophysiology, graphene has just recently gained impact in cellular interfacing. Compared to silicon-based transistors, they are more sensitive, hence more favorable. Moreover, intrinsic flexibility and biocompatibility of graphene has a promising future for this research, pointing out in the direction of fully flexible, soft and implantable neuroprosthetic applications. There, graphene can be used either actively as a transistor's active area or passively as an electrode material. In the first case, the device requires at least two electrodes (source and drain), complicated electrochemical gating, and read-out schematics while in the second case there is just one feedline required to feed and record from a graphene electrode. Moreover, such graphene-based electrodes are comparably easy to fabricate, characterize and use.

In this presentation, we will describe a method to fabricate arrays of graphene-based probes, requiring minimal number of fabrication steps, while maintaining overall device functionality. These devices are either fabricated on rigid or flexible substrates. Devices, such as graphene field effect transistors (GFETs) and graphene multielectrode arrays (GMEAs) have been designed, fabricated and tested for their performance. The flexible GFETs exhibit an order of magnitude larger sensitivity compared to silicon transistors with similar geometry. Multiple probe per wafer design allows us to fabricate different kinds of devices on one 4-inch wafer, consequently increasing a possible range of applications from e.g. retinal to cortical neuroprosthetics.
(Invited) Electron Transport and Spin Selectivity in Nucleic Acids and Peptides
Authors: Waldeck David H. , Beall Edward , Clever Caleb
Published: February 2020

We discuss how the properties of nucleic acids and peptides affect their electron transmission and electron spin filtering properties. We present experimental results on the single molecule conductance through nucleic acid duplexes as a function of the length, the sequence, and the duplex flexibility. The experiments address the influence of the flexibility of nucleic acid duplexes on the single molecule conductance by changing the nature of the backbone which positions the Watson-Crick base pairs and by introducing a single nick in the backbone of the duplex. Also, the sequence and length dependence of a duplexes conductance is used to examine how the flexibility of the molecules impacts the electronic delocalization over the duplex. We present experimental results on a new type of electrode measurement that probes the spin polarization of chiral molecules by the magnetization that they generate on an electrode surface. These studies quantify the magnitude of the polarization for peptides, which display secondary structure, as well as amino acids, which display only primary structure.
Design Considerations of Liquid Gated High Field Modulated FET Biosensor for Enhanced Sensing Characteristics
Authors: Sarangadharan Indu , Pulikkathodi Anil Kumar , Chen Po-Hsuan , Wang Shin-Li , Kuo Wen-Che , Wang Yu-Lin
Published: February 2020

Medical diagnostics are rapidly evolving to meet the requirements of personalized medicine and home-care based in-vitro diagnostics are in very high demand. Translating the clinical blood based assays into home-care tests pose several challenges. Primarily, we need to develop a compact, portable system that can enable the end user to perform the assay with minimal protocols that can be carried out without prior training, cost-effective and quick response time. More importantly, the home-care tests should retain the sensitivity and selectivity of the laboratory based assays. We previously developed high field modulated field effect transistor (FET) biosensors for the direct detection of protein biomarkers in whole blood. In this work, we investigate the sensor structure in detail to assess the parameters that govern the sensing characteristics. The basic sensor structure includes a functionalized reference electrode to which gate voltage is applied, placed at a narrow gap from the extended gate metal, which is connected to the FET’s gate terminal. The test solution containing the target analyte is placed across the gap such that it is sandwiched between the reference electrode and extended gate metal, together forming the sensing region. It was revealed from our previous studies that there are two ways in which the field generated across the test solution can be modulated: by applying higher amplitude of gate voltage and by decreasing the gap between the electrodes. It was found that at smaller gap distances, the potential drop in the solution is linearly dependent on the gap between the electrodes, and hence higher sensitivity can be observed for smaller gap configurations. In this work we initially explore the gap dependence of sensor response for micron scale and nano scale gap distances. The results indicate that noise characteristics and sensitivity are improved when the gap between the reference electrode and extended gate metal is decreased. The geometry of the sensing areas are also studied to evaluate the optimal electric field distribution across the test solution to generate enhanced sensing characteristics. Finally the surface functionalization is investigated to analyse the effect of surface coverage and number of receptor binding sites on the sensor performance. Through the integration of sensor design, geometry and optimal surface functionalization, we can improve the sensing characteristics, while satisfying the practical considerations of implementation of a home-care whole blood assay.
An Ionic Polymer Actuator Capable of Simultaneously Improving Bandwidth and Blocking Force for Efficient Haptic Feedback
Authors: Choi Hanbin , Kim So Young , Kim Yongchan , Cho Changhyeon , Lee Hojin , Kim Do Hwan
Published: February 2020

Recently, an ionic electroactive polymer (i-EAP) actuators are spotlighted in various fields because they provide a lot of advantages such as lightweight, flexibility, simple process, and low driving power. However, they suffer from low blocking force, displacement, and wide bandwidth that can be implemented under electric field for apply to various applications. In order to apply these i-EAP actuators to various applications, it is important to provide the optimum characteristics of the i-EAP actuator adaptive to the target application. Particularly, it is required to achieve high blocking force and displacement as well as wide actuation bandwidth for haptic feedback among the various applications.

In this talk, we propose an ionic polymer actuator (IPA) with wide bandwidth of over 100Hz and high blocking force based on PEDOT:PSS electrode with additives and ionic polymer with fibrillary nanostructures for effective haptic feedback. In particular, we developed an actuator that improves the interfacial properties between electrodes and an ionic polymer as well as electrical conductivity of electrodes by simple and effective way through spray-coating of PEDOT: PSS solution with additives. As a result, the IPA was successfully operated with a large displacement up to 2.5mm at an operating frequency of 20mHz under an applied voltage of 2V. Further, the IPA shows large blocking force of 0.4mN at operating frequency of 1Hz. These our actuator is capable of driving up to a high frequency of 200Hz and shows an improved blocking force up to 0.4mN. We potentially believe our IPA will provide a rational guide to future haptic feedback.