bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Improved Thin Film Transistor Model Predicts TFT Operation in the THz Range
Authors: Shur Michael , Liu Xueqing , Ytterdal Trond
Published: November 2022

Novel Thin-film-transistor (TFT) TFT materials such as ZnO, InGaZnO, AMO-CNT, and organic materials dramatically improved the achieved and projected TFT performance. The low field mobility of oxide materials has reached values comparable to those for short-channel Si CMOS. The effects related to electron inertia and electron density oscillations in field effect transistors channels (FETs) diminish the role of the low field mobility as a figure of merit in short channel devices making the performance gap between TFTs and Si CMOS smaller enabling high frequency TFT applications even reaching sub-THz and THz frequencies (for the operating regimes using the rectification of the plasma oscillations. We report on an improved compact model based on the RPI TFT model [1] and using the Unified Charge Control Model (UCCM). [2, 3] This model accounts for a non-exponential slope in the subthreshold regime by introducing a varying subthreshold slope and accounts for non-trivial capacitance dependence on the gate bias. It also accommodates the inclusion of the parasitics related to the gate impedance. These new features allowed us to obtain an excellent agreement with the measured I-V/C-V characteristics for both long and short n-channel and p-channel TFTs. The application of this new TFT model to the analysis of the TFT response requires accounting for non-local potential distribution in the device channel. This is achieved by using a multi-segment nonlinear transmission line model of the TFT channel reproducing the approach that has been previously used for the THz SPICE/ADS Si CMOS model implementation. As a possible application example, we simulated a TFT complementary inverter. Our simulations showed that using the phase-matched THz signal feeding should yield a very sensitive detection of THz radiation impinging on a short channel TFT. These results show that the TFT RFID and other applications could be extended into the THz range of frequencies.
(Invited, Digital Presentation) Nondegenerate Hydrogen-Doped Polycrystalline Indium Oxide (InOx:H) Thin Films for High-Mobility Thin Film Transistors
Authors: Furuta Mamoru , Magari Yusaku
Published: November 2022

Transparent metal oxide semiconductors (OSs) have been extensively investigated for use as the active channel layer of thin film transistors (TFTs) for next-generation flat-panel displays, nonvolatile memories, image sensors, and pH sensors, to name a few. Among OSs, the amorphous In–Ga–Zn–O (IGZO) has attracted particular attention for TFT applications owing to its high field effect mobility (μFE) of more than 10 cm2V−1s−1, steep subthreshold swing (S.S.), extremely low off-state current, large-area uniformity, and good bias stress stability. Although the μFE of an IGZO TFT is approximately one order of magnitude higher than that of an amorphous Si TFT, further improvement of the μFE of OS TFTs is required to expand their range of applications as an alternative to polycrystalline Si TFT.

Single-crystalline In2O3 has a Hall mobility as high as 160 cm2V−1s−1, which makes amorphous (a-) or polycrystalline (poly-) InOx a potential material for enhancing the μFE of OS TFTs. However, undoped InOx thin films is known as a degenerate semiconductor with high background electron density of over 1020 cm-3, which is attributed to the presence of native defects, such as oxygen vacancies, making them unsuitable for a channel material of OS TFTs.

In this presentation, nondegenerate hydrogen-doped polycrystalline InOx (poly-InOx:H) thin films were successfully prepared by low-temperature solid phase crystallization (SPC). A degenerate amorphous InOx:H thin film was deposited by sputtering in Ar, O2, and H2 gases, and an amorphous to polycrystalline phase transition (SPC) of the film was achieved after PDA at more than 175 °C. By PDA at 250 °C in air, a nondegenerate poly-InOx:H film could be obtained with a carrier density as low as 2.4 × 1017 cm−3, which is approximately three orders of magnitude lower than that of the initial a-InOx:H film. The TFTs with a 50 nm thick nondegenerate poly-InOx:H channel could be fully depleted by a gate electric field. A maximum μFE of 125.7 cm2V−1s−1 was exhibited by the TFT with the poly-InOx:H channel. The use of a nondegenerate poly-InOx:H film is a promising approach to boost the μFE of OS TFTs.
UV/Ozone Based Facile Surface Modulation Technique for Efficient Organic Thin Film Transistor
Authors: Shaharukh Sk , Dhar Achintya
Published: November 2022

The capacity to actualize a comprehensive range of electronic functions based on organic devices is important to the development of fully functional organic electronic circuits. Specifically low voltage, quick switching transistors, in particular, have previously been demonstrated but a critical function, i.e. dependable data storage, is currently lacking. Organic thin-film transistors (OTFTs) have received a lot of interest for possible use in memory, flexible electronics such as sensors, and light-emitting diodes because of their inexpensive production costs, lightweight, mechanical flexibility, and other advantages.

The most often utilised active ingredient in organic TFTs is pentacene (C22H14). The electrical properties of organic TFTs based upon pentacene, such as field-effect mobility, are equivalent to those of amorphous silicon thin film transistors (a-Si TFTs), which are typically employed for the backplane of liquid crystal displays (LCDs), but far inferior to those of generic inorganic TFTs. As a result, electrical properties for high-performance flexible electronics must be improved. The interfacial properties of active layer and gate insulator layer plays a very crucial role in determining the electrical properties of organic TFTs. Therefore in this work we report an UV/ozone treatment on the surface of gate dielectric layer so as to improve the interfacial properties.

At first the glass substrate was cleaned in an ultrasonic cleaner with acetone, ethanol, isopropyl alcohol and DI water. Then by using thermal evaporation technique a gate electrode with thickness of approximately 80 nm was deposited on the substrate. Later a solution of Poly 4-vinylphenol (PVP) was spin coated with a thickness of 140 nm, this organic layer was deposited as the bottom insulator layer. Now an ozone treatment (wavelength = 253nm) for 5,10 and 20 min was done over the PVP layer. Subsequently a layer of PMMA was coated over the UV treated layer. Finally with a coating of 70nm thick pentacene active layer 100 nm thick silver drain/source electrodes with channel length of 50µm were also deposited using thermal deposition.

Further the morphology and topography was studied using AFM images and element analysis was done from XPS spectra. The device performance (output and transfer characteristics) was characterized using Kiethley 4200 SCS semiconductor parameter analyser. The changes in performance of transistor devices before and after UV/ozone treatment could be explained using XPS spectra, AFM images and water contact angle measurement. It is evident from the AFM images that the grain size of pentacene on UV/Ozone treated dielectric surface are larger than the untreated surface, thus reducing the boundary scattering and enhancing the field effect mobility. Thus surface treatment with UV/Ozone could acts as simple, low cost method to enhance the performance of a organic thin film transistors.
(Invited) Nanospike Electrode Thin-Film Transistors: A New Design for Improved Nanoscale Tfts
Authors: Dodabalapur Ananth , Liang Kelly , McCulley Calla , Zhou Yuchen , Wang Xiao , Xu Xin
Published: November 2022

A new design for short channel length thin-film transistors (TFTs) is proposed and demonstrated with indium gallium zinc oxide (IGZO) and organic semiconductor active layers. The principal advantages of the new design arise from two distinct effects: (i) Nanospike array electrodes produce field-emission enhanced charge injection from the source/drain contacts to the semiconductor and lead to higher currents, current densities, and carrier velocities. (ii) Quasi-three-dimensional gate control at low gate voltages leading to improved turn-off characteristics, better sub-threshold swing and reduced drain voltage dependence of sub-threshold behavior. These advantages are very beneficial for back-end-of-the-line (BEOL) TFTs and will also apply to most other semiconductor material TFTs with Schottky contacts. Multi-nanospike TFTs with channel lengths as small as 50 nm, and single nanospike TFTs with channel lengths of ~ 10 nm have been fabricated.
(Invited) Vertical Transparent ZnO TFT Based on a Stack of Thin-Films Deposited in Solution
Authors: Mohammed-Brahim Tayeb , Hussain Sajid , Wei Lei
Published: November 2022

A lot of works are devoted now to integrate driving TFT with OLED, minimizing the area of the pixel. In other part, people try to fabricate devices using low cost technologies as deposition in solution avoiding any photolithography step in the process. Finally, it can be better if the full driving TFT-OLED device is transparent.

The present work try to answer simultaneously to these 3 desires. Particularly, the present paper focus on the TFT.

Vertical TFT will answer to the first desire to minimize the area of the device. It is based here on a stack of the gate, the insulator, the source, the semiconducting active layer and the drain; meaning 5 films all solution deposited.

Thanks to the present available insulator solutions for the deposition, different insulators can be chosen. High k HFO2 insulator is chosen in this work. It is is spincoated and then annealed at 300C during 1 hour. Figure 1 shows the current-voltage curves of ITO/HFO2/AgNWs stack. After rapid increase, the current stabilizes at 10 pAmp at least still a voltage of 10V, meaning a field of 7.7x105 V/cm2 with a thickness of 130 nm. Present HFO2 film is then a good insulator.

ZnO is chosen as active layer. It is spin-coated and then annealed at 180C. This temperature was found enough high to lower the conductivity (Figure 2)

The source and drain layers are spin-coated using Ag nanowires (AgNWs) solution. As source AgNWs layer is deposited before ZnO layer, it will be annealed at the same temperature 180C. Figure 3 shows that AgNWs film stays enough conducting after such annealing temperature. It can be used as conducting source and drain.

Finally, the full stack of 5 films is characterized as a TFT.

Figure 4 shows the transfer characteristic of this TFT plotted at a drain voltage of 2.6V. The drain current is modulated by 4 orders from off to on regime.

Very simple and low cost fully in solution process is presented in this work. Working transparent TFT is demonstrated. The process shows its high potential in the development of integrated TFT-OLED in small area. It is very promising.

Its shows also the need of future hard work in this way to demonstrate fully integrated driving TFT-OLED

Figure 1
(Digital Presentation) Power Efficient Transistors with Low Subthreshold Swing Using Abrupt Switching Devices
Authors: Aziz Jamal , Kim Honggyun , Kim Deok-Kee
Published: November 2022

With the rapid development of transparent integrated circuits, transistors with extremely low subthreshold swing (SS) is becoming a necessary requirement. Here, we fabricated three transparent device structures that show abrupt electrical switching and make their series connection to the source terminal of the conventional field effect transistors (FET) to lower the SS value. Firstly, we demonstrate an environment friendly, disposable, and transparent conductive bridge random access memory (CBRAM) device composed of a cellulose nanocrystals active layer. Our CBRAM consists of a silver (Ag) electrochemically active top electrode and a cellulose nanocrystals-based switching layer on the FTO coated glass substrate. Devices with CBRAM can enable FET with an ultra-steep slope that is SS < 0.24 mV/dec and has a significantly high on/off ratio (~105) by switching the Ag metallic filament between on and off. Niobium oxide (NbO2) based threshold switching devices and zinc oxide (ZnO) based flexible Schottky diodes that show electrical breakdown were also stacked with FET, which gave SS values < 0.74 mV/dec and < 5.20 mV/dec, respectively. Comparatively, a nano-watt transistor called filament transistor (FET + CBRAM stack) can significantly improve the SS slope value with the lowest leakage current (~nA) and a record low turn on-voltage (~0.2 V) with a set power of only ~197 nW compared to the other series stack, which thereby attracts the attention of low power operations.

Keywords:
filament transistor, threshold switching, Schottky diode, subthreshold swing, on/off ratio

Figure 1
Self-Powered Water Disinfection System Acheving a Novel Oxidation-Assisted Electroporation Mechansim with Rotational Triboelectric Nanogenerator
Authors: Suh In-Yong , Lee Dong-Min , Kim Sang-Woo
Published: November 2022

In world, one of three people lack reliable access to clean water and water-borne diseases resulting from pathogenic microbescontaminated water remain a great threat to public health. Disinfection is an effective drinking water purification method; however, the most commonly used water disinfection method, chlorination, is limited by carcinogenic disinfection byproducts formation. Alternative methods such as ultraviolet (UV) radiation and membrane filtration suffer from drawbacks such as pathogen regrowth, low throughput, and intensive energy/chemical consumption. In addition, the methods have a limited disinfecting capacity and may be inadequate during a crisis like in cases of a severe epidemic outbreak, such as coronavirus disease 2019. Here, we report a rapid, self-powered water disinfection system for both bacterial and viral inactivation based on a novel oxidation-assisted electroporation mechanism powered by a supercoiling-mediated rotational TENG (S-TENG) that converts the periodic hand stretching/releasing into high-speed rotation. Owing to a rational design of the S-TENG that yields an ultrafast rotation (≈7500 rpm), we successfully overcame the insufficient output limitations of TENG caused by the low-frequency stimuli ambient energy harvesting. The S-TENG with sufficient voltage and current output can generate an NW-enhanced localized electric field and oxidative species simultaneously, and therefore achieving high disinfection efficiency. More than 99.9999% of bacteria and viruses were inactivated at a high flux of 15 m3 h–1 m–2. Our work presented an efficient enlarged demonstrator wherein 1 L of natural water can flow through the whole system within 1 min solely driven by gravity, and achieve complete disinfection, confirming the feasibility of this method for water disinfection in areas with an inadequate power supply.

Figure 1
Ambient Humidity-Induced Phase Separation for Electrospun Fiber Morphology Engineering Toward Piezoelectric Self-Powered Sensing
Authors: Kim Dabin , Lee Sooun , Lee Sangryun , Kim Yong-Il , Kum Sihyeon , Kim Sang-Woo , Kim Yunseok , Ryu Seunghwa , Kim Miso
Published: November 2022

Electrospun polymeric piezoelectric fibers have a considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent-induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher β phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape-adaptive energy harvesting and self-powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self-powered motion sensing.
(Invited) Metallic Transport Behaviors in Monolayer and Multi-Layer MoS2 By Surface-Charge Transfer Interaction with Redox-Active Molecules
Authors: Kiriya Daisuke
Published: November 2022

In the last decade, transition metal chalcogenides (TMDCs), e.g., MoS2 and WSe2, have gathered attention as semiconducting 2D materials. Modulation of carrier concentrations in TMDCs is a crucial matter for applying to semiconductor devices. So far, we have developed a method to gain the carrier concentrations of MoS2 by a junction with organic molecules and achieved obtaining a degenerately doped state in the MoS2. The mechanism of the doping is a surface-charge transfer interaction at the interface. Although the transfer characteristic behaviors show the degenerately doped state (small ON/OFF ratio), the details of the transport behavior have not been well understood. In this presentation, I will discuss the details of the device characteristics of the monolayer and multilayer MoS2 metal-oxide-semiconductor field-effect-transistors (MOSFETs) with a junction of redox-active molecules in a manner of the surface-charge transfer interaction. The devices were fabricated via standard lithography (e-beam and photolithography) techniques to prepare each monolayer and multilayer MoS2 MOSFETs. Transport properties in the MoS2 MOSFETs were measured in the as-prepared device and the device after the molecular doping. The dopant molecule is benzyl viologen (BV) molecule which is known as a redox-active molecule with high-reduction potential. After the doping with BV molecules, the MoS2 MOSFET showed a small ON/OFF ratio in the transfer characteristic curves, indicating a degenerately doped state. The identical device further showed the metallic behavior in the temperature dependence (the conductivity increases with decreasing the temperature). Both monolayer and multilayer MoS2 MOSFETs showed similar metallic behavior. This metallic transport behavior changes to an insulative regime when applying gate-voltage to reduce the carrier concentrations in the channel MoS2. Therefore, the gate-electrostatic induced metal-insulator-transition was suggested. At the conference, I will discuss the details of the transport behaviors, gate-potential and temperature dependence of the contact resistance. In addition, I will also discuss potential candidates of other molecules for obtaining doping to TMDCs for going forward the 2D materials-based electronics.

REF: Matsuyama, et al., "Metallic transport in monolayer and multilayer molybdenum disulfides by molecular surface-charge transfer doping", ACS Appl. Mater. Interfaces, 2022, 14, 8163-8170.
(Invited) Large Carrier Mobility in Graphene with Enhanced Shubnikov–De Haas Quantum Oscillations
Authors: Xiang Bin , Zhang Ying
Published: November 2022

Graphene devices are susceptible to the surrounding environment1-4. For example, the substrate in contact with graphene influences the device performance because the carriers are confined in two-dimensional (2D) atomic thickness. However, 2D van der Waals dielectric materials used as an interface modifier can provide a path to improve the device quality. In this paper, we report an enhanced mobility of 35000 cm2 V-1 s-1 in a CrOCl-coated monolayer graphene on the SiO2/Si substrate through a dielectric shielding effect. When monolayer graphene is sandwiched between two layers of 2D CrOCl insulator, the enhanced mobility can be 70000 cm2 V-1 s-1. Because of the enhanced mobility, the Shubnikov-de Haas (SdH) quantum oscillation is also observed with the amplitude linearly decreasing with increasing temperature, consistent with the standard Lifshitz-Kosevich theory, and the effect persists at temperatures up to 100 K. Our work paves a way to improve graphene mobility and realize nontrivial quantum states at high temperature for the exploration of potential applications in electronics.
(Invited, Digital Presentation) Heterogeneous Integration of Ultrahigh-Κ Single-Crystalline SrTiO3 Membranes for Two-Dimensional Electronics
Authors: Huang Jing-Kai , Wan Yi , Shi Junjie , Zhang Ji , Chiu Ya-Ping , Li Sean , Li Lain-Jong
Published: November 2022

Even though competitive 2D field-effect transistors (FETs) with the scaled channel dimensions have been demonstrated, it still is a challenge to integrate 2D semiconductors and high-κ dielectrics without deteriorating their interfaces, while decreasing capacitance equivalent thickness (CET) of dielectrics to maintain the gate controllability. In particular, the dielectric/channel interface is one of the predominant factors to affect device performance, including carrier mobility, switching behavior, and drifts of device parameters. This is often caused by the nature of dielectrics used, and the integrating methodologies applied.

Typically, high-κ dielectrics used in silicon technology (i.e., Al2O3 and HfO2) are inherited by 2D FETs. The amorphous nature of these oxides makes the elimination of charge scattering and trapping sites at the dielectric/channel interfaces extremely difficult, not to mention that the direct deposition of dielectrics usually damages the 2D channel and results in poor uniformity in sheer thickness. Some interfacial passivation layers and processes have been developed, but they lead to thickening overall CET instead. Alternative approaches with the crystalline dielectric materials such as multilayer hBN and epitaxial calcium fluoride (CaF2), whose surfaces are well-constructed and atomic-flat, have demonstrated the competitive advantages of crystalline dielectric over the conventional amorphous oxides in spite of relatively lower κ values.

Here, we demonstrate ultra-scaled 2D FETs with desirable sub-1 nm CET through heterogeneous integration of monolayer CVD MoS2 and quasi-2D single-crystalline SrTiO3 membranes, where the optimized SrTiO3 gate dielectrics exhibit a low gate leakage (J
leak < 10-2 A/cm2 at 2.5 MV/cm). Typical transistors manifest good reliability and competitive performance characteristics, including steep subthreshold swings (SS) down to ~70 mV dec-1 and ON/OFF current ratios up to 107, matching low-power specifications suggested by the latest International Roadmap for Devices and Systems (IRDS). In addition, the van der Waals (vdW) interface between quasi-2D dielectrics and 2D semiconductors moderates the unfavorable fringing-induced barrier lowering (FIBL) effect occurring in ultra-scaled Si transistors with very high-κ dielectrics, which broadens the dielectric selection in 2D electronics for future technology node.
Nano-Pattern Oxidation of WSe2
Via Block Copolymer Self-Assembly for Highly Responsive Homojunction Phototransistors
Authors: Kang Miae , Kim Kihyun , Bang Joona , Kim Jihyun
Published: November 2022

Tungsten diselenide (WSe2), one of the two-dimensional (2D) materials, has emerged as a promising optoelectric candidate because of its thickness dependent bandgap, large optical absorption coefficient, good air stability and high carrier mobility. In addition, the electrical properties of the ambipolar WSe2 could be tuned through the electrostatic doping by the gate modulation. However, the low photo responsivity is a critical problem of WSe2-based optoelectric devices. To overcome this limitation, several approaches have been suggested such as stacking different 2D materials and coating with quantum dots. But these conventional methods were focused on the formation of heterojunctions, which requires complicated alignment process and leads to unavoidable defects and residues. Thus, the novel ways to build homojuction should be investigated for fabricating devices with a clean interface in a simple process.

In this work, block copolymer (BCP) was used to prepare hexagonally packed cylinder nano-template as an oxidation mask for UV/ozone treatment, which resulted in numerous nanoscale homojunctions on WSe2. To fabricate the mask with hexagonally packed cylinders, asymmetric poly (styrene-block-methyl methacrylate) (PS-b-PMMA) was spin-coated. After thermal annealing for self-assembly, PMMA was selectively removed by reactive ion etching. UV/ozone treatment, one of the oxidation methods of the WSe2, leads to the formation of the the tungsten oxide (WOX) with high electron affinity and induces a p-doping effect. By using BCP as an oxidation mask, the only region of the WSe2 under the removed PMMA blocks could be converted into WOX.

The responsivity of the nano-pattern oxidized WSe2 phototransistor manifests a dramatic change depending on the applied gate bias. The device exhibited a responsivity (532 nm, 8.515 mW/cm2) of 27.5 mA/W under applied gate bias of 0 V. However, under the gate bias of +60 V, the device showed an enhanced responsivity of 155.2 mA/W, as strong p-n junctions were induced. In conclusion, the nano-pattern oxidized WSe2 phototransistor presents increased responsivity (155.2 mA/W), external quantum efficiency (36.3%) and faster response time than the pristine WSe2.

This work demonstrates that the responsivity of the WSe2 phototransistor can be improved though well-established perpendicular BCP and optimized by effective modulation of gate bias. By implementing homojunctions on the WSe2
via the nano-pattern oxidation method, this work greatly expands the potential applications of 2D TMDs materials for next-generation nanoscale optoelectronic devices.
(Invited) Rare Earth Doped Nanoparticles
Authors: Vetrone Fiorenzo
Published: November 2022

Luminescent nanomaterials that can be excited, as well as emit, in the near-infrared (NIR) have been investigated for use in a plethora of applications including nanomedicine, nanoelectronics, biosensing, bioimaging, photovoltaics, photocatalysis, etc. The use of NIR light for excitation mitigates some of the drawbacks associated with high-energy (UV or blue) excitation, for example, little to no background autofluorescence from the specimen under investigation as well as no incurred photodamage. Moreover, one of the biggest limitations is of course, that of penetration. As such, NIR light can penetrate tissues much better than high-energy light especially when these wavelengths lie within the three biological windows (BW-I: 700-950, BW-II: 1000-1350, BW-III: 1550-1870 nm) where tissues are optically transparent. At the forefront of NIR excited nanomaterials are rare earth doped nanoparticles, which due to their 4f electronic energy states can undergo conventional (Stokes) luminescence and emit in the three NIR biological windows. However, unlike other classes of nanoparticles, they can also undergo a multiphoton process (known as upconversion) where the NIR excitation light is converted to higher energies resulting in anti-Stokes luminescence spanning the UV-visible-NIR regions. Perhaps the biggest impact of such materials would be in the field of disease diagnostics and therapeutics, now commonly referred to as theranostics. Due to the versatility of their optical properties, it now becomes possible to generate high-energy light (UV or blue) in situ to trigger other light activated therapeutic modalities (i.e. drug release) while using the NIR emission for diagnostics (i.e. bioimaging, nanothermometry). Here, we present the synthesis of various NIR excited (and emitting) rare earth doped core/shell (and multishell) nanoparticles and demonstrate how their luminescence properties can be exploited for potential use in diverse biomedical applications.
(Invited) Wireless Healthcare Flexible Sensor System with Comfortable and Precise Monitoring
Authors: Takei Kuniharu
Published: November 2022

Daily continuous health condition monitoring is now of great interests using multi-functional flexible sensors. In particular, vital signals from skin are the most convenient way to measure continuously data collections during daily life. For this purpose, flexible sensor sheets allow it to detect multiple information from skin precisely due to conformable covering over skin surface. To realize this platform, multiple developments including flexible sensors, wireless system, and potential application are required. In this talk, I introduce a wireless multiple sensor sheet system with multiple printed flexible sensors such as skin perspiration, respiration, electrocardiogram etc. The system makes a feedback alarm if abnormal human condition signals are detected. Furthermore, to monitor the vital signals precisely and comfortably even under activity such as walking and running, device architecture is also discussed.

Although a lot of researches and developments are still required for practical application, these studies may help to open a door for the next step of flexible electronics.
(Excellent Student Presentation Award) Triboelectrification Induced Self-Powered Microbial Inactivation with Nanowire-Enhanced Localized Electric Field
Authors: Kim Young-Jun , Kim Sang-Woo
Published: November 2022

Air-transmitted pathogens may lead to severe epidemics (e.g., COVID-19) showing huge threats to public health. Inactivation of the pathogenic microbes in the air is an essential process, whereas the feasibility of existing air disinfection technologies has encountered obstacles including only achieving physical separation but no inactivation, obvious pressure drops, and energy intensiveness. Here we report a rapid disinfection method for inactivating air-transmitted bacteria and viruses using the nanowire-enhanced localized electric field to damage the outer structures of microbes.[1] This air disinfection system is driven by a triboelectric nanogenerator that converts mechanical vibration to electricity effectively and achieves self-powered. Assisted by a rational design for the accelerated charging and trapping of microbes, this self-powered air disinfection system promotes the microbial transport and achieves high performance: >99.99% microbial inactivation within 0.025s in a fast airflow (2 m/s) while only causing low pressure drops (<24 Pa). This rapid, self-powered air disinfection method may fill the urgent need for the air-transmitted microbial inactivation to protect public health.

References

Liu, X. Xie, W. Zhao, N. Liu, P. A. Maraccini, L. M. Sassoubre, A. B. Boehm, Y. Cui, Nano Letters 13, 4288-4293 (2013)
Researches and Applications of Nanostructured 2D Materials growth By Continuous Wavelength Laser Process
Authors: Yang Tzu Yi , Chueh Yu-Lun
Published: November 2022

Two-dimensional (2D) nanomaterials, such as graphene and hexagonal boron nitride (hBN), have recently attracted increasing attention of researchers due to their unique phonon and electronic structures. These nanomaterials have been widely used in applications, such as sensors, catalysts, and optoelectronic devices, due to the lack of interlayer bonds and the quantum confinement of electrons. There have been several well studied methods to synthesis 2D materials including chemical vapor deposition(CVD), physical vapor deposition(PVD), liquid exfoliation, Li-intercalation exfoliation,wet chemistry,ultrasonic-ball milling, Among them, CVD is the most famous method to fabricate electronic device with high quality materials characteristic. However, CVD processes will cause extremely harsh heat budget to substrate during high temperature process. Recently, researchers have established transfer method fabricating device on other undamaged substrate. It is the trickiest problem make it cannot apply to industry.

In this research, we built an indirect laser projection transfer method. First, we sputter requiring material on Si wafer as donor chip. Followed, placed the donor chip upside down on acceptor substrate, and radiated by laser on the donor chip backside. The deposited component on donor substrate would evaporate, and the vapor would fill between two substrates interspacing. Then, the vapor will recrystallize on the cooler acceptor surface. We have successfully transferred low melting temperature 2D materials such as SnSex, NiSex, SbSex on different acceptor substrate, even on flexible and flammable paper. By controlling laser intensity and irradiation time, we can control the amount of Se scattering, finally manipulate SnSe/SnSe2 phase ratio successfully. The mechanism has been demonstrated by SEM, RAMAN, TEM, XPS, XRD. Owing to indirection irradation, it can transfer materials on several fragile substrates without any heat budget, which reveals the great potential of this method for electronics applications. In this report we successfully demonstrate transferred SnSe/SnSe2 have good feasibility in energy storage system and sensor device.
(Digital Presentation) Enhanced Streaming Vibration Potential By Silane-Modificated Mxene/PVA Hydrogel for High-Performance Flexible Triboelectric Nanogenerator
Authors: Lai Bo Yu , Wu Jyh-Ming
Published: November 2022

Triboelectric nanogenerators (TENGs) play a vital role in self-powered electronics, based on their superior energy harvesting ability and simple construction. In this work, polyvinyl alcohol (PVA) hydrogel is fabricated, exhibiting a three-dimensional (3D) network structure that allows PVA chains to be covered by a large amount of water. Combining MXene nanosheets with the hydrogel TENG, the composite improves the ion transport of the hydrogel and provides the streaming vibration potential (SVP) mechanism. This composite effectively enhances the output performance of hydrogel TENG. Furthermore, this work adopts different functional groups of silane (APTES, CPTMS, FOTS) to modify the surface work function of MXene nanosheets. The surface modification increases the charge density at the interface between MXene and water inside the hydrogel, improving the electrical output performance and mechanical sensitivity of MXene hydrogel TENG (MH-TENG). The result demonstrates that the electrical output performance of MH-TENGs modified by 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (FOTS) is approximately two times larger (output-voltage~85 V/output-current~240 nA) than pristine hydrogel TENG (output-voltage~40 V/output-current~100 nA). The MH-TENG behaves unlimited potential in the use of flexible electronics, such as movement monitoring electronics, strength sensors on the paddle, and wearable energy harvesting devices in the future.
Dual Threshold and Memory Switching Induced By Conducting Filament Morphology in Ag/WSe2 Based ECM Cell
Authors: Chaudhary Mayur , Chueh Yu-Lun
Published: November 2022

In recent years, two-dimensional (2D) materials-based RRAMs have gained high importance because of their thermal and mechanical stability, and better potentiation-depression controllability. 2D materials based conductive bridge random access memory (CBRAM) has been considered as promising approach for neuromorphic and image processing technology [1]. Despite much progress in CMOS technology, the growth and deposition technology of 2D materials for semiconductor integrated circuit are much complex and is generally available at wafer scale [2]. In addition, high growth temperature for high quality of 2D materials complicates direct wafer growth and makes transfer process desirable. At the device level, challenges are linked to controlled and uniform growth of 2D material for high density electronic structure.

Recently, discreet 2D based memristor have been used in crossbar structure as synapse for neuromorphic computing. However, the plasma-assisted chemical vapor reaction (PACVR) based memristor for neuromorphic application are rarely demonstrated. Here, we report the co-integration of plasma-assisted chemical vapor reaction (PACVR) with silicon CMOS technology to provide brain-inspired computing device. PACVR offers compatibility with temperature limited 3D integration process and also provides much better thickness control over a large area. Furthermore, it an easy platform for direct and controlled synthesis of TMDs compared to conventional CVD approach. The PACVR grown WSe2 layer (~2 nm) on silicon substrate is realized, which exhibits both threshold and bipolar switching. The threshold and bipolar switching emulate integrate-fire neuron function and is obtained by modulating the compliance current in the device. The dynamics of the switching is closely related to the diffusive dynamics of the active metal (Ag or Cu) which can be controlled by device current. As a result, the WSe2/Si memristor shows synaptic behavior for neuromorphic system with learning accuracy of 96%.

References:

Wang, C.-Y. et al. 2D layered materials for memristive and neuromorphic applications. Electron. Mater. 6, 1901107 (2020)

Zhang, X. et al. Two-dimensional MoS2-enabled flexible rectenna for Wi-Fi-band wireless energy harvesting. Nature
566, 368–372 (2019).

Figure 1
First-Principles Study on the Origin of Tribo-Negative Nature of Polytetrafluoroethylene
Authors: Jeon Sera , Kim Dabin , Kim Sang-Woo
Published: November 2022

Triboelectric nanogenerator (TENG) is an energy harvesting device that converts mechanical energy into electricity based on the coupling of contact electrification and electrostatic induction. Fluorocarbon polymers, such as polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkane (PFA) are the widely used polymeric triboelectric materials, however, their tribo-negative nature has been poorly understood. Here, using first-principles calculations, we have systematically investigated the electronic structure of PTFE and PFA. It is revealed that the defects associated with carbon dangling bonds act as charge trapping centers during contact electrification. Furthermore, the simulation on the contact model of PTFE and nylon confirms that the charge transfer occurs when the distance between them is as near as the atomic orbitals overlap. In addition, the calculated work functions of polymeric materials are consistent with the triboelectric series, giving a powerful method to predict the triboelectric property of materials. We expect our study provides fundamental understandings on the origin of the triboelectric property of materials and the atomistic phenomena during contact electrification. Our results also give insight into triboelectric material designs with a strong electron-withdrawing property.
(Excellent Student Presentation Award) Activated Biomass Converted Carbon in High-Efficient Water Desalination By Capacitive Deionization
Authors: He Rui , Dong Pei , Yang Yingchao
Published: November 2022

Porous carbon materials, utilized as electrodes in capacitive deionization (CDI), play an important role in water desalination. Currently, benefiting from the abundance, cheap, environmental-friendly, biomass converted carbon was selected as the carbon electrode. We study the salt adsorption properties of carbon materials prepared by biomass precursor such as wood, eggplant, etc. The as obtained biomass converted carbon was further processed with activation. Potassium hydroxide, as a chemical activation agent, was selected and reacted with biomass converted carbon at high temperature. The influence of activating agent-carbon ratio and activating temperature was investigated. Due to the natural porous morphology, the biomass converted carbon materials usually exhibit a large surface area and high electrical specific capacitance after carbonization. Taking advantage of these properties, biomass converted carbon materials own a good water desalination performance. Additionally, the salt adsorption property of activated biomass converted carbon usually has an obvious enhancement, which benefit from the creation of extra porous structure. Based on our experiment, the activated biomass converted carbon materials are excellent candidates to be utilized in further industrial water purification.
Binder-Free Wood Converted Carbon in Water Desalination By Capacitive Deionization
Authors: He Rui , Dong Pei , Yang Yingchao
Published: November 2022

In recent years, the clean water crisis has become a significant environmental challenge. Thus, water desalination has intensified over the past decades. As an energy-efficient, environmentally friendly, economical, and easy-operate technique, capacitive deionization (CDI) has attracted enthusiasm, in which carbon materials play an important role in salt ion removal. Benefiting from the abundance and easy preparation properties, biomass converted carbon has obtained attention in water desalination by CDI. Because of natural porous structure, wood is chosen as the biomass carbon precursor and to study the water desalination performance: Binder-free wood converted carbon sheets were successfully converted from several species of natural wood, and further chemical activation was processed to enlarge the porous structure. We found the pine and balsa converted carbon have a comparable salt adsorption capacity with commercial activated carbon, and activated balsa exhibits an extraordinary improved adsorption performance. The promising results indicate that activated balsa is an excellent material for water desalination.
Electrocatalytic Reduction of Nitrogen to Ammonia By Janus Wsse Nanowalls
Authors: Peng Yu-Ren , Tang Shin-Yi , Yang Tzu-Yi , Wu Shu-Chi , Chueh Yu-Lun
Published: November 2022

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been made in improving the NRR for the significant effort in catalytic activity due to its unique crystal structures, electronic properties, and promising nonprecious catalysts. However, many studies have provided solutions to activate the inert basal plane with low improvement. With highly asymmetric configuration, Janus monolayer with intrinsic strain and electric field can enable a way to tune the activity in TMDs-based catalysts. Although the first successful experimental synthesis of Janus structure (MoSSe) has gained significant interest and become a fast-growing TMDs-based material, the structure remains limited in the low dimensional and hard to expose the edges site to enhance the catalytic activity. Besides the common benefits of 2D TMDs, such as high surface area, short carrier migration distance, and tunable electronic structure. In this regard, the inherent structural asymmetry of Janus WSSe nanowalls as a new means to enhance the NRR activity was investigated. Janus TMDs nanowalls as the catalyst by taking advantage of its introduction of in-gap states with a shift in the Fermi level in nitrogen adsorbed system because of Janus asymmetry from the origin of stimulating NRR activity. Raman spectra showthe related main modes for WSSe Janus structure as shown in Fig. 1a, for which peaks at 271 and 333 nm can be found, respectively. The linear sweep voltammetric (LSV) curves of the catalysts as shown in Fig. 1b confirm the onset potential of the NRR, which increases with the different materials. Janus WSSe Janus nanowalls exhibit outstanding NRR performance over its parent materials (WS2 and WSe2). The results should propose a new path to design high performance and a novel structure for Janus TMD-based catalysts.

Fig1. (a) Evolution of Raman spectra in the WSSe nanowalls as a function of chemical composition (b) LSV curves for WS2, WSe2, WS2-XSe2-2X alloy, and WSSe Janus nanowalls

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(Digital Presentation) Scalable Growth of Transition Metal Dichalcogenides for Next-Generation Nanoelectronics
Authors: Tong Shi Wun , Ng Man-Fai
Published: November 2022

Alternative channel materials for future ultra-scaled electronic devices have been intensively pursued nowadays since the feature size of silicon-based transistors has been scaled down to their physical limit. Atomically-thin semiconducting transitional metal dichalcogenides (TMDCs) including WS2, MoS2, WSe2, MoSe2, e. have shown a lot of unique properties compared to their bulk crystals, such as indirect-to-direct bandgap transitions, strong spin-orbit coupling and valley polarization. In particular, monolayer WS2 has shown the highest theoretical room temperature electron mobility among other semiconducting TMDCs as a result of its low effective mass. Combined with the large exciton/trion binding energy with high photoluminescence quantum yield, monolayer WS2 is a strong candidate as a potential channel material for high-efficiency optoelectronic applications.

However, it is still challenging to grow wafer-sized, highly uniform and strictly monolayer TMDCs continuous film through the conventional chemical vapor deposition (CVD) due to the uncontrollable growth kinetics. The evaporation rates and amounts of the heated precursors are uncontrollable because the saturation vapor pressure of the precursor is exponentially dependent on the temperature inside the furnace. The sulfurized film is thus consisted of a mixture of monolayer, bilayer and multiple layers of TMDCs. The film with such unreproducible quality is not applicable for real industrial applications.

In this work, we provide a self-limiting growth strategy based on modified CVD process to prepare the wafer-sized monolayer TMDCs. Theoretical simulations were performed to understand the fundamental thermodynamically mechanism of the strictly monolayer growth. The property-variation in TMDCs due to difference in electronic structure between different layers of TMDCs can be significantly reduced based on this new approach. The following figure indicates that the PL spectra detected from different spots (spot 1 to 5) of the WS2 film. All spectra measured from the 4'' wafer-sized sample show characteristics unique to monolayer WS2. This poses a reliable route for the growth of large-area monolayer TMDCs, which is essential for their reliable and robust applications in nanoelectronic devices.

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(Invited) Recent Progress in Wide-Bandgap Semiconductor Devices for a More Electric Future
Authors: Kizilyalli Isik C , Blum Spahn Olga , Carlson Eric P
Published: November 2022

Wide-bandgap (WBG) semiconductors, with their excellent electrical properties, offer breakthrough performance in power electronics enabling low losses, high switching frequencies, and high temperature operation. WBG semiconductors are likely candidates to replace silicon-based semiconductors in the near future seeing as Silicon is fast approaching its performance limits for high power requirements. Wide-bandgap power semiconductor devices offer breakthrough circuit performance enabling low losses, high switching frequencies, and high temperature operation which will allow for enormous energy efficiency gains in a wide range of potential applications. In the past ten years, the U.S. Department of Energy’s Advanced Research Project Agency - Energy (ARPA-E), which was established to fund creative, out-of-the-box, transformational energy technologies that are too early for private-sector investment, has invested in WBG semiconductors including material and device-centric programs along with application specific programs targeting the barriers to widespread adoption in power electronics. Under these ARPA-E programs, medium voltage (10-20kV) WBG device development has commenced to push the voltage boundaries of the devices including the development of WBG super-junction devices. Light triggered photoconductive WBG devices are also being investigated for MV applications. The WBG MV devices will enable MVDC grid distribution applicable to markets including electrified transportation, renewable interconnections, and offshore oil, gas, and wind production. Other WBG device ideas are also being explored under ARPA-E programs including WBG integrated circuits and neutron detectors. The progress and challenges of the WBG devices being developed under ARPA-E programs will be reviewed along with thoughts on the future trends of WBG device development.