bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stretched-Exponential Trends in a-Igzo Tfts
Authors: Zhou Fan , Chiang Tsung Han , Wager John F 
Published: February 2020

A bias temperature stress (BTS) investigation of amorphous InGaZnO thin-film transistors (a-IGZO TFTs) is undertaken using the stretched-exponential (SE) relation to model the threshold voltage shift (ΔVTH) as a function of time, temperature, and applied gate voltage. Explicitly, the SE equation employed herein is described as ΔVTH (t, T, VG) = (VG-VTH0) (1-exp(-(t/τ)β)), where VTH0 is the initial unstressed TFT threshold voltage, τ is a trapping time, τ = τ0exp(Eτ/kBT), where τ0 is a trapping time prefactor, Eτ is an energy barrier, and β is an energy barrier parameter [1, 2]. Simulation indicates that a larger τ and/or β results in less ΔVTH, i.e., a more stable a-IGZO TFT. An alternate form of the SE voltage prefactor (VG-VTH0) involves the use of V0, which is identified as a saturation voltage [3, 4]. Either prefactor formulation can be used to accurately fit ΔVTH trends for stress times less than ~3 hours. However, as shown in Fig. 1, fitting of a sample data set restricted to stress times less than 3 hours leads to dramatically different saturated threshold voltage shifts, even though both prefactors precisely fit the initial 2 hours of data (see insert of Fig. 1). Physically, this is associated with the fact that the (VG-VTH0) prefactor corresponds to the applied overvoltage which explicitly depends on VG, while V0 is independent of VG. Simulation is useful for revealing various kinds of ΔVTH (t, T, VG) trends. For example, Fig. 2(a) shows that the relevant energy barrier, Eτ, associated with ΔVTH (10-5 s, 300 K, VG = 30 V) is very narrow for β = 1 and broadens dramatically as β → 0. The Eτ-β relationship is better represented by taking the derivative of ΔVTH with respect to Eτ, as shown in Fig. 2(b), where the magnitude of the peak increases and the distribution of Eτ narrows as β increases. As a larger β is indicative of a more stable TFT, it is reasonable to theorize that a narrow Eτ distribution is meaningful in predicting stable long-term TFT reliability.
[1] M. Mativenga, et al., “High stable amorphous indium-gallium-zinc-oxide thin-film transistor using an etch-stopper and a via-hole structure,” Journal of Information Display, Vol. 12, No. 1, 47-50 (2011)
[2] T. Y. Hsieh, et al., “Investigating degradation behavior of InGaZnO thin-film transistors induced by charge-trapping effect under DC and AC gate bias stress,” Thin Solid Films, 528, 53-56 (2013)
[3] J. M. Lee, et al., “Bias-stress-induced stretched-exponential time dependence of threshold voltage shift in InGaZnO thin film transistors,” Applied Physics Letters, 93, 093304 (2008)
[4] S. Park, et al., “Threshold voltage shift prediction for gate bias stress on amorphous InGaZnO thin film transistors,” Microelectronics Reliability, 52, 2215-2219 (2012)

Figure 1
Comprehensive Depletion-Mode Model for TFT Assessment
Authors: Zhou Fan , Chiang Tsung Han , Wager John F 
Published: February 2020

A comprehensive depletion-mode model is developed to describe depletion-mode thin-film transistor (TFT) behavior [1]. This model is distinctly different than the square-law model, which accurately describes enhancement-mode TFT behavior and establishes the equations normally employed for carrier mobility extraction. In the comprehensive depletion-mode model, bulk mobility (μBULK) and interface mobility (μINT) are distinguished based on the assumption that carrier transport can occur within an accumulation layer and/or within the ‘bulk’ of the channel. In this work, the comprehensive depletion-mode model is used to estimate the mobility of p-channel TFTs and solution-processed n-channel TFTs, and also to estimate the free carrier concentration of within the ‘bulk’ of the channel when a TFT exhibits depletion-mode behavior. Simulation reveals that the estimated interface mobility of a depletion-mode TFT is often overestimated when mobility is improperly extracted using the square-law model.
[1] F. Zhou et al., “Mobility assessment of depletion-mode oxide thin-film transistors using the comprehensive depletion-mode model,” ECS Journal of Solid State Science and Technology, 3(9), Q3027-Q3031 (2014)
Enhancement of Field-Effect Mobility By Controlling the Surface Potential of PVP Insulator in Pentacene-Based Thin Film Transistors
Authors: Jang Yunseok , Kim Kwang-Young 
Published: February 2020

In recent years, the surface potential at insulator/semiconductor interface has received considerable attention for improving the electrical performance of various electronic and optoelectronic device. Many studies of the effect of a surface potential at insulator/semiconductor interface have been carried out. Most of these studies have focused on achieving efficient hole or electron injection at the inorganic insulator (i.e., such as SiO2)/ semiconductor interface. But the surface potential effects at the polymer insulator/semiconductor interface of organic thin-film transistors have not been sufficiently studied. In this presentation, we focus in particular on the effects of varying the surface potential on the polymer insulator/semiconductor interface.
We demonstrated a method of reducing the surface energy in a polymer insulator for use in high-performance OTFTs. The surface energy of a poly(4-vinyl phenol) insulator was reduced from 45 mJ/m2 to 32 mJ/m2 through treatment with UV/ozone and ODTS. These treatments facilitated the deposition of the pentacene film onto the ODTS-treated poly(4-vinyl phenol) insulator to prepare a single phase that showed better π-orbital overlap among the pentacene molecules. As a result, the field-effect mobility in the insulator increased by 209 %. These results demonstrated that adjusting the surface energy of a polymer insulator provided a suitable approach to enhancing the performances of OTFTs.
Acknowledgments
This study was supported by the R&D program of the Korea Research Council for Industrial Science and Technology of Republic of Korea (Grant 2015K000217/ 10052802/ KM3710/ NK186C/ SC1130/ MO5970/ NM8270).
Solution-Processed Nanoscale Carbon Nanotube Thin-Film Transistors Fabricated By Electromigration
Authors: Jeon Jun-Young , Ha Tae-Jun 
Published: February 2020

Solution-processed carbon nanotube thin-film transistors (CNT-TFTs) have been of great scientific and technological attention due to the merits of fabrication processes and structual integration. Significant improvements in material design and process optimization have resulted in high performance CNT-TFTs which are comparable to or better than conventional ones. However, it is still difficult to realize sub-nano-scaled solution-processed CNT-TFTs suitable for integrated circuits and systems. In order to fabricate a sub-nm gap between source and drain electrodes in the channel region of the solution-processed CNT-TFTs, the DC breakjunction method by applying the electric field to trap Au nanoparticles and to form a short bridge was investigated through electromigration. A gradually ramping electric bias was imposed on the contact junctions, thereby breaking the bridge into a sub-nm gap in TFTs. The combination of surface treatment and vacuum thermal annealing increased the density of the nanotubes in the channel region and improved charge injection between the channel and the source electrode. In this presentation, we will demonstrate the process optimization to realize high-performance solution-processed CNT-TFTs with a channel length of ~20 nm and discuss the effect of surface treatment and vacuum thermal annealing on device performance.
(Invited) Growth of Transfer-Free 2D Materials: From Controllable Growth to Material Characterizations and Device Applications
Authors: Chueh Yu-Lun 
Published: February 2020

Novel condensed matter systems can be understood as new compositions of elements or old materials in new forms. According to the definition, various new condensed matter systems have been developed or are under development in the recent years. 2D layered materials, including graphene, transition metal dichalcogenides (TMDs) allow the scaling down to atomically thin thicknesses and possess unique physical properties under dimensionality confinement. Chemical vapor deposition (CVD) process is the most popular approach for all kind of 2D materials due to its high yield and quality. Nevertheless, the need of high temperature and the relative long process time within each cycle hinders for commercial development in terms of production cost. However, the transfer procedure has become one of the major limitations of the overall performance.
In the first part of my talk, I will present several approaches, including ultra-fast microwave heating, plasma selective reaction, controlled segregation process by laser irradiation and metal vapers-assisted growth processes developed in my lab these years to directly grow graphene with controllable thicknesses on arbitrary substrates without any extra transfer process. In the 2nd part of my talk, I will also introduce development of various methods, including laser irradiation assisted-selenization (LIAS) process, fast microwave annealing and plasms enhance selenization processes on different two dimensional transition metal dichalcogenides materials in my lab. The detailed formation mechanisms, microstructures and physical performances as well as its applications on field emission and gas sensors based on these two 2D materials were reported and investigated.
Fluorescence Microscopy Characterization of Patterned Nano-Crystalline Quantum Dot Films
Authors: Sabeeh Ala , Price Jared , Ruzyllo Jerzy 
Published: February 2020

This experiment is a continuation of the study concerned with the lift-off based patterning of nanocrystaline quantum dot (NQD) films [1]. The ultra-thin films formed using colloidal solutions of nanocrystalline quantum dots show good promise in display/LED, as well as nano-labeling applications between others. Regardless of application, to become a part of the functional device the NQD film must be patterned accordingly.
Following on the experiments demonstrating effectiveness of the lift-off process in patterning NQD films with resolution down to 1 µm [1] further investigation of the performance of the proposed patterning scheme needed to be carried out. The goal of this contribution is to study uniformity of surface coverage with lift-off patterned NQD films by means of fluorescence microscopy.
When exposed to UV light the NQDs feature high photoluminescence with intensity depending on the dots size. The fluorescence microscopy allows capturing the intensity to obtain information about the NQD film uniformity. As a result, using images obtained by means of fluorescence microscopy and employing dedicated image processing tools information regarding film uniformity, pattern definition accuracy, and average intensity can be derived. Also, the fluorescence image can be transferred into grey scale to study its histogram plot and get information about intensity distribution across the NQD patterns.
In this study silicon wafers used as substrates are first covered by spin coating with a layer of positive 1805 photoresist to the thickness of about 420 nm and then cured at 100oC. The resist covered wafers were subsequently exposed through the standard Cr-photomask in an aligner/exposure and developed in photoresist developer (351) to create the required patterns [1]. After that, NQDs were blanked deposited using mist deposition technique. The NQD deposited were CdSe/ZnS core/shell featuring average diameter of 6.5 nm and corresponding red (620 nm) emission wavelength. Then, the photoresist removal performed using either dry or wet lift-off. The dry lift-off applied using O2 plasma system and the wet lift-off used acetone dissolution [2].
Figure 1 demonstrates the fluorescence image for NQD patterned film and its intensity distribution. The intensity analysis of the patterns after the lift-off process is considered in terms of an average intensity. The results obtained in this study give further insights into the process of lift-off patterning of nano-crytalline quantum dot films and demonstrate feasibility of the proposed approach.
In the full account of this work a complete set of experimental results obtained in the course of this investigation is presented and more detailed analysis of fluorescence images provided.

References [1] A. Sabeeh, Y.Thakur, and J. Ruzyllo, ECS Transactions 69.12 (2015): 53-57. [2] J. C. Chao, A. Kshirsagar, and J. Ruzyllo, ECS Trans., 58(6), 311 (2013).

Figure 1
(Invited) High Density Individually Addressable Nanowire Arrays for Intracellular Mapping of Neuronal Activity
Authors: Dayeh Shadi 
Published: February 2020

Critical to the large scale mapping of neuronal activity is the ability to develop neurotechnologies that can interface with neurons at nanometer scales and that can measure the smallest potential fluctuations of each cell in a neuronal network and the response of these cells to added chemicals and drugs. We developed a robust and scalable fabrication process for ultra-high density neuronal probes on insulating substrates. Arrays at an electrode density of 10 million/cm2 enabled recording of single unit and subthreshold activity in both intracellular and extracellular configurations from rat, human induced pluripotent stem cells and cortical neurons. We validated by transmission electron microscopy that positively measured potentials corresponded to intracellular penetrating nanowires and that the cells survived the natural nanowire penetration for 6 weeks. This exhibits the longest ever intracellular recording with subthreshold sensitivity from neuronal cultures and have implications for highly predictive drug screening applications.
(Invited) Layered (III-Se) Photodetectors
Authors: Wang Kaiyou 
Published: February 2020

Due to the unique properties of the 2D materials, the photodetectors based on two dimensional (2D) materials have attracted considerable attentions.
For both the bottom and top Ti/Au contacted metal-semiconductor-metal (MSM) photodetectors in using layered GaSe and InSe devices, we systematically investigate the dependence of the photoresponsivity on the spacing distance. Through spatially resolved photocurrent measurements, we find the photocurrent active region is always close to the Schottky barrier with higher electrical potential. A theoretical model has also been developed to well explain for the underlying physics for the photoresponse [1]. The response time can be further reduced down to a few hundreds of microseconds for the devices with single layer graphene as metallic electrodes [2].

References

(1) Y. F. Cao, K. M Cai, P. A. HU, L. X. Zhao, T. F. Yan, W. G. Luo, X. H. Zhang, X. G. Wu, K. Y. Wang and H. Z. Zheng, Scientific Reports, 5, 8130 (2015).
(2) W. G. Luo, Y. F. Cao, P. A. Hu, K. M. Cai, Q. Feng, F. G. Yan, T. F. Yan, X. H. Zhang and K. Y. Wang, Adv. Opt. Mater., 3,(2015)1418.
Chemical Vapor Deposition Growth of High Density Perovskite Nanowire Arrays and Their Applications in Optoelectronic Devices
Authors: Zhang Daquan , Gu Leilei , Tavakoli Mohammad Mahdi , Fan Zhiyong 
Published: February 2020

Organic-inorganic halide perovskite materials have emerged as one kind of promising optoelectronic materials with greatly attractive performance in corresponding devices because of their unique and excellent optoelectronic properties. In this work, we developed a novel chemical vapor deposition (CVD) method using the metal nanoclusters to grow three-dimensional (3-D) arrays of single crystalline perovskite nanowires (NWs) with well-defined geometry. By utilizing different anodic aluminum oxide (AAO) templates, we can precisely control the diameter, pitch, and depth of NWs. The as-obtained NWs are well-embedded in the optically transparent and mechanically robust templates, and thus can significantly improve the stability of materials. The NW arrays have been fabricated into optoelectronic devices including photodetectors and solar cells and their device performance has been systematically investigated. Finally, combining the intriguing electrical and optical properties of perovskite materials, such 3-D nanowire arrays may find a broad spectrum of applications for high performance electronics and optoelectronics.
Flexible High Performance Hybrid Azo/Ag-Nanowire/Azo Sandwich Structured Transparent Conductors for Flexible Cu(In,Ga)Se2 Solar Cell Applications
Authors: Thomas Stuart Richard , Chueh Yu-Lun , Tsai Wen-Chi , Wang Zhiming 
Published: February 2020

Transparent conducting oxides (TCOs) are an important class of materials used in a wide range of optoelectronic technologies, including solar cells, flat-panel displays and organic light emitting diodes, and presently there is a strong drive toward the development of solar cell technologies on flexible platforms that are robust, portable and flexible enough to conform to unusual shapes, particularly building structures. Tin-doped indium oxide (ITO) is currently the commonly chosen TCO for use in non-flexible applications; however, its brittleness limits its application on flexible substrates, whilst the scarcity of indium maintains an undesirably high cost for use in solar cell applications. As such, it is important that ITO alternatives are developed with suitably flexible mechanical and electronic properties, which can also be fabricated at reasonable costs. The chalcopyrite absorber, copper indium gallium selenide, Cu(In,Ga)Se2, has a very high absorption coefficient (~104 cm-1), requiring only thin-films (~1 μm) for efficient solar cell fabrication, making it thin enough for flexible applications. However the lack of a high quality flexible TCO has, to date, limited its use in such applications.
In this work, we present a new approach for the fabrication of high performance transparent electrodes suitable for flexible CIGS solar cell applications, using a stacked Al-doped ZnO/Ag-nanowire/Al-doped ZnO (AAA) sandwich structure.1 In our AAA electrode the Al-doped ZnO (AZO) layers act as a broad area charge carrier collector and protective encapsulant for the Ag-nanowire network. Concurrently, the Ag-nanowires provide low-resistance, long-range pathways that aid the extraction of charge carriers, but more importantly, they aid in maintaining a low resistivity for our total electrode structure, by maintaining charge transport pathways across cracks that develop in the AZO during repeated strenuous bending. By optimising of our Ag-nanowire network density, AZO deposition and AAA stack structure we are able produce a transparent electrode with comparable resistivity and transparency performance to that of ITO. These combined benefits enable us to fabricate CIGS solar cells that are able to maintain 95% of their initial power conversion efficiency, following 1000 bending cycles. In comparison, devices fabricated using equivalent thickness AZO and ITO electrodes are only able to maintain 57 and 5%, respectively, due to crack formation and delamination of the films. This AAA sandwich structure electrode could therefore serve as a high-performance electrode for numerous flexible optoelectronic applications.
1. W.-C. Tsai, S. R. Thomas, C.-H. Hsu, Y.-C. Huang, J.-Y. Tseng, T.-T. Wu, C.-h. Chang, Z. M. Wang, J.-M. Shieh, C.-H. Shen and Y.-L. Chueh, Journal of Materials Chemistry A, 2016.
(Invited) Nanoscale Morphology Control in Halide Perovskite/Polymer Composites for Printed LEDs and Beyond
Authors: Yu Zhibin 
Published: February 2020

Recently, astounding optoelectronic properties have been discovered in halide perovskites (perovskites). Such materials have a general ABX3 chemical formula, in which A is a cesium (Cs+) or an aliphatic ammonium (RNH3
+) cation, B is a divalent Pb2+ or Sn2+ cation and X is an anion such as Cl-, Br- or I-. Their crystal structures resemble the one commonly found in BaTiO3. The halide perovskites can be processed like polymeric semiconductor materials using solution based processes; and may be coated into large area thin films on arbitrary substrates; they may also be crystallized into three-dimensional periodic structures and behavior like conventional inorganic semiconductors including the superior charge transportation properties.
In this talk, our recent work of developing perovskite/polymer composites towards the realization of fully printable LEDs will be presented. The perovskite/polymer composites possesses all the remarkable optoelectronic characteristics of pure perovskites. For instance, we have demonstrated their use for blue, green and red LEDs. In addition the device efficiencies exceeded those of pure perovskite LEDs. The perovskite/polymer composites have shown advantages in improving the processability and quality of the perovskite thin films; and enhancing the structural stability of the perovskites especially at high humid fabrication and service environments. By embedding the perovskite crystals inside a polymer matrix, the perovskites can be less toxic and more environmentally benign compared to pure perovskite. At the end of the talk, other potential applications of perovskite/polymer composites will be briefly discussed.
(Invited) Thermally-Enhanced Photo-Electrochemical Water Splitting
Authors: Chueh William C 
Published: February 2020

Transition-metal-oxide semiconductors are promising photoanodes for solar water splitting due to their excellent chemical stability and appropriate bandgaps. However, in absorbers such as BiVO4, TiO2, α-Fe2O3, and WO3, charge carriers localize as small polarons or become trapped, leading to low minority carrier mobilities. This limits the minority carrier collection efficiency in the quasi-neutral region of the light absorber, and lowers the overall photoactivity. In this work, we demonstrate that modestly elevating the temperature activates minority carrier hopping in monoclinic BiVO4, significantly enhancing the saturation photocurrent without a substantial anodic shift of the onset potential, and is an attractive alternative to employing complex passivation layers and nanostructured templates towards achieving the theoretical photocurrent density. Specifically, using a Mo:BiVO4/SnO2/Si tandem photoanode/photovoltaic, increasing the absolute temperature by 11% from 10 to 42 °C elevates the saturation photocurrent from 1.8 to 4.0 mA cm−2. This strong temperature enhancement, 3.8% K−1, is 5 times greater than that in α-Fe2O3. Concurrently, the onset potential shifts slightly from 0.02 V to 0.08 V versus the reversible hydrogen electrode (or equivalently, from −1.22 V to −1.13 V versus the equilibrium potential of oxygen evolution). Our observation contrasts with the prevailing understanding that the energy conversion efficiency generally decreases with temperature as a result of reduced photovoltage. Thermally-activating minority carrier transport represents a general pathway towards enhancing the photoactivity of light absorbers where hopping conduction limits the minority carrier collection in the quasi-neutral region.