Browsing by Author "Lin, Che-Yi"

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A Triode Device with a Gate Controllable Schottky Barrier: Germanium Nanowire Transistors and Their Applications
(1970-01-01)
Lin, Che-Yi
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Chen, Chao-Fu
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Chang, Yuan-Ming
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Yang, Shih-Hsien
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Lee, Ko-Chun
Electrical contacts often dominate charge transport properties at the nanoscale because of considerable differences in nanoelectronic device interfaces arising from unique geometric and electrostatic features. Transistors with a tunable Schottky barrier between the metal and semiconductor interface might simplify circuit design. Here, germanium nanowire (Ge NW) transistors with Cu3Ge as source/drain contacts formed by both buffered oxide etching treatments and rapid thermal annealing are reported. The transistors based on this Cu3Ge/Ge/Cu3Ge heterostructure show ambipolar transistor behavior with a large on/off current ratio of more than 10(5) and 10(3) for the hole and electron regimes at room temperature, respectively. Investigations of temperature-dependent transport properties and low-frequency current fluctuations reveal that the tunable effective Schottky barriers of the Ge NW transistors accounted for the ambipolar behaviors. It is further shown that this ambipolarity can be used to realize binary-signal and data-storage functions, which greatly simplify circuit design compared with conventional technologies.
Analog Circuit Applications Based on All-2D Ambipolar ReSe2 Field-Effect Transistors
(2019-05-01)
Lee, Ko-Chun
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Yang, Shih-Hsien
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Sung, Yung-Shang
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Chang, Yuan-Ming
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Lin, Che-Yi
Complementary circuits based on 2D materials show great promise for next-generation electronics. An ambipolar all-2D ReSe2 field-effect transistor (FET) with a hexagonal boron nitride gate dielectric is fabricated and its electronic characteristics are comprehensively studied by temperature dependence and noise measurements. Ambipolar transfer characteristics are achieved owing to the tunable Fermi level of the graphene contact and negligible and 30 meV Schottky barrier heights for the n- and p-channel regimes, respectively. An inverter is also fabricated to demonstrate ambipolar ReSe2 FET operation in a logic circuit. Furthermore, a p/n switchable unipolar FET is designed and shows potential for building complimentary circuits from a signal device. This work demonstrates the potential of all-2D ReSe2 FETs and makes available new approaches for designing next-generation devices.
Atomically thin van der Waals tunnel field-effect transistors and its potential for applications
(2019-03-08)
Yang, Shih-Hsien
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Yao, You-Teng
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Xu, Yong
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Lin, Che-Yi
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Chang, Yuan-Ming
Power dissipation is a crucial problem as the packing density of transistors increases in modern integrated circuits. Tunnel field-effect transistors (TFETs), which have high energy filtering provided by band-to-band tunneling (BTBT), have been proposed as an alternative electronics architecture to decrease the energy loss in bias operation and to achieve steep switching at room temperature. Very recently, the BTBT behavior has been demonstrated in van der Waals heterostructures by using unintentionally doped semiconductors. The reason of the BTBT formation is attributed to a significant band bending near the heterointerface, resulting in carrier accumulations. In this work, to investigate charge transport in type-III transistors, we adopted the same band-bending concept to fabricate van der Waals BP/MoS2 heterostructures. Through analyzing the temperature dependence of their electrical properties, we carefully ruled out the contribution of metal-semiconductor contact resistances and improved our understanding of carrier injection in 2D type-III transistors. The BP/MoS2 heterostructures showed both negative differential resistance and 1/f(2) current fluctuations, strongly demonstrating the BTBT operation. Finally, we also designed a TFET based on this heterostructure with an ionic liquid gate, and this TFET demonstrated an subthreshold slope can successfully surmount the thermal limit of 60 mV/decade. This work improves our understanding of charge transport in such layered heterostructures and helps to improve the energy efficiency of next-generation nanoscale electronics.
Effect of Temperature and Extrusion Pass on the Consolidation of Magnesium Powders Using Equal Channel Angular Extrusion
(2013-05-01)
Lee, Hsiao-Chien
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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Lin, Che-Yi
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Wang, Hsiao-Chung
The microstructure and characteristics of bulk magnesium consolidated from Mg powder by equal channel angular extrusion (ECAE) were investigated. Cu cans filled with Mg powder, of about 74 mu m in diameter, were ECAE processed for one, two and four passes via the Bc route at 473, 523 and 573 K. The microstructure of ECAE-processed samples was observed by OM and SEM. The density of each sample was determined using Archimedes' principle. Microhardness and compression tests were conducted to investigate the mechanical properties of each ECAE-processed sample. The best consolidated condition between powders was achieved after four passes of ECAE at 573 K. Density at 98.4% of the ideal density of bulk Mg was achieved, microhardness was about 49 Hv, and compressive yield stress was about 100 MPa.
Effects of equal channel angular extrusion on the microstructure and high-temperature mechanical properties of ZA85 magnesium alloy
(2012-07-01)
Lin, Che-Yi
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Tsai, Hao-Jan
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
This study examined the microstructure and high-temperature tensile properties of the Mg-8wt.%Zn-5 wt.%Al (ZA85) alloy that was subjected to equal channel angular extrusion (ECAE) with various passes at 180-250 degrees C. The original grain size and precipitate size of the as-cast specimen were 150 and 100 mu m, respectively. The average grain size was reduced to 4 mu m by dynamic recrystallization and the precipitate size was reduced to 1 mu m after six ECAE passes at 180 degrees C. However, the average grain size of the ECAE-processed specimens at 250 degrees C increased from 14 mu m after two passes to 20 mu m after four passes owing to the grain growth effect. In tensile tests at 200 degrees C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimens processed with six ECAE passes at 180 degrees C improved to 249 MPa and 162 MPa, respectively, compared with 105 MPa (UTS) and 74 MPa (YS) for the as-cast specimens. Furthermore, elongation increased from 5.1% to 28.5%. This significant improvement in the high-temperature tensile properties of the ZA85 alloy was attributed to the refined grains and the well-distributed fine Mg-32(Al, Zn)(49) (tau-phase) precipitates. (C) 2012 Elsevier B.V. All rights reserved.
Enhanced ductility of the ZA85 magnesium alloy fabricated by equal-channel angular pressing
(2013-04-15)
Lin, Che-Yi
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Bor, Hui-Yum
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
Equal-channel angular pressing (ECAP) was applied to the as-cast Mg-8 wt.% Zn-5 wt.% Al (ZA85) alloy to produce a fine-grained structure with fine and uniformly distributed Mg-32 (Al, Zn)(49) (tau-phase) particles. Experiments showed that the ZA85 alloy had an initial grain size of similar to 150 mu m after casting and was significantly reduced to 4 mu m after six ECAP passes at 180 degrees C. After annealing at 300 degrees C for 1 h, the average grain size merely increased to 7.1 mu m. This thermal stability of the fine-grained structure at temperatures at or below 325 degrees C is attributed to the presence of the fine and well distributed tau-phase. It was demonstrated that ECAP processing greatly enhances ductility of the experimental alloy. By testing over a range of temperatures and strain rates, a maximum elongation to failure of 400% was obtained in the ECAP ZA85 alloy tested at 300 degrees C (0.53 T-m) with the initial strain rate of 1.0 x 10 (4) s (1). The dominant deformation mechanism for the specimens tested at 300 and 350 degrees C with the initial strain rates ranging from 1.0 x 10 (4) s (1) to 1.0 x 10 (3) s (1) is GBS controlled by grain boundary diffusion. At the higher testing temperature of 400 degrees C, the deformation mechanism for the experimental alloy is dislocation creep. (C) 2012 Elsevier B. V. All rights reserved.
High Mobilities in Layered InSe Transistors with Indium-Encapsulation-Induced Surface Charge Doping
(2018-11-02)
Li, Mengjiao
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Lin, Che-Yi
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Yang, Shih-Hsien
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Chang, Yuan-Ming
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Chang, Jen-Kuei
Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm(2) V-1 s(-1) at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices.
Low-Voltage Operational, Low-Power Consuming, and High Sensitive Tactile Switch Based on 2D Layered InSe Tribotronics
(2019-05-09)
Li, Mengjiao
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Yang, Feng-Shou
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Hsiao, Yung-Chi
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Lin, Che-Yi
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Wu, Hsing-Mei
Electronics based on layered indium selenide (InSe) channels exhibit promising carrier mobility and switching characteristics. Here, an InSe tribotronic transistor (denoted as w/In InSe T-FET) obtained through the vertical combination of an In-doped InSe transistor and triboelectric nanogenerator is demonstrated. The w/In InSe T-FET can be operated by adjusting the distance between two triboelectrification layers, which generates a negative electrostatic potential that serves as a gate voltage to tune the charge carrier transport behavior of the InSe channel. Benefiting from the surface charging doping of the In layer, the w/In InSe T-FET exhibits high reliability and sensitivity with a large on/off current modulation of 10(6) under a low drain-source voltage of 0.1 V and external frictional force. To demonstrate its function as a power-saving tactile sensor, the w/In InSe T-FET is used to sense INSE in Morse code and power on a light-emitting diode. This work reveals the promise of 2D material-based tribotronics for use in nanosensors with low power consumption as well as in intelligent systems.
Multifunctional full-visible-spectrum optoelectronics based on a van der Waals heterostructure
(2019-12-01)
Yang, Shih-Hsien
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Lee, Ko-Chun
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Tsai, Meng-Yu
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Chang, Yuan-Ming
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Lin, Che-Yi
Multifunctional devices are expected to allow development of low-cost, highly integrated, and energy-efficient electronics for the internet of things (IoT) era. Here, we demonstrate an all-two-dimensional ReSe2/h-BN/graphene heterostructure (ReSe2 HS) consisting of a vertically coupled ReSe2 field-effect transistor and charge storage component, which possesses multifunctional characteristics for use in electronics and optoelectronics. As an electrically controlled non-volatile memory (NVM), the ReSe2 HS delivers high-performance multilevel data storage with a readout on/off current ratio exceeding 10(5) and excellent durability (> 10(4) s) at an ultralow V-ds of 50 mV, which benefits to the development of power saving devices. The ReSe2 HS design and high-photoresponsivity ReSe2 channel also achieve an energy efficient optical NVM with full-visible-spectrum distinction. Besides, the ReSe2 HS displays unique ambipolarity to operate as either an inverter or frequency doubler. We further propose a power-free ReSe2 HS optical memory matrix to simplify imaging systems. The ReSe2 HS shows promise for use in light-programmable information storage systems and neuromorphic computation with low power consumption.
Negative-Differential-Resistance Devices Achieved by Band-Structure Engineering in Silicene under Periodic Potentials
(2018-10-18)
Chen, Chang-Hung
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Li, Wen-Wu
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Chang, Yuan-Ming
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Lin, Che-Yi
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Yang, Shih-Hsien
An important development in modern electronics is the realization of band-structure engineering for the design of novel materials and devices. One possible way to realize band-structure engineering is by addition of periodic potentials to two-dimensional (2D) materials, such as graphene, to form a superstructure, known as a "superlattice.' Unlike the band gap of graphene, the band gap of silicene can be tuned by an out-of-plane electric field owing to its unusual buckled structure. In this work, we use the designable band gap of silicene and the band structure of superlattices, together with the spin and valley degrees of freedom, to propose a design principle for optimizing the performance of spin-and valley-dependent negative-differential-resistance (NDR) devices using silicene superlattices. On the basis of the effective Hamiltonian formalism, we predict that the peak-to-valley current ratio could be larger than most recently reported results achieved by 2D materials, suggesting that the silicene superlattice is a good candidate for realizing NDR devices. The design principle proposed in this work could also be extended to other layered materials with tunable band gaps. This could pave the way for advanced material and device designs based on band-gap engineering of 2D materials.
Oxygen-Sensitive Layered MoTe2 Channels for Environmental Detection
(2019-12-18)
Yang, Shih-Hsien
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Lin, Che-Yi
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Chang, Yuan-Ming
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Li, Mengjiao
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Lee, Ko-Chun
The oxygen (O-2)-dependent resistance change of multilayered molybdenum ditelluride (MoTe2) channels was characterized. A variation of the channel resistance could reproducibly determine relative O-2 content (denoted as the O-2 index). We found that Joule heating in a layered MoTe2 field-effect transistor caused the O-2 index to decrease drastically from 100 to 12.1% in back gate modulation. Furthermore, Joule heating caused effective O-2 desorption from the MoTe2 surface and repeatable O-2 detection by multilayered MoTe2 channels was realized. This work not only explored the influence of O-2 on the electrical properties of multilayered MoTe2 channels but also revealed that MoTe2 channels are promising for sensing O-2 in an environmental condition.
Reversible and Precisely Controllable p/n-Type Doping of MoTe2 Transistors through Electrothermal Doping
(2018-03-27)
Chang, Yuan-Ming
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Yang, Shih-Hsien
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Lin, Che-Yi
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Chen, Chang-Hung
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Lien, Chen-Hsin
Precisely controllable and reversible p/n-type electronic doping of molybdenum ditelluride (MoTe2) transistors is achieved by electrothermal doping (E-doping) processes. E-doping includes electrothermal annealing induced by an electric field in a vacuum chamber, which results in electron (n-type) doping and exposure to air, which induces hole (p-type) doping. The doping arises from the interaction between oxygen molecules or water vapor and defects of tellurium at the MoTe2 surface, and allows the accurate manipulation of p/n-type electrical doping of MoTe2 transistors. Because no dopant or special gas is used in the E-doping processes of MoTe2, E-doping is a simple and efficient method. Moreover, through exact manipulation of p/n-type doping of MoTe2 transistors, quasi-complementary metal oxide semiconductor adaptive logic circuits, such as an inverter, not or gate, and not and gate, are successfully fabricated. The simple method, E-doping, adopted in obtaining p/n-type doping of MoTe2 transistors undoubtedly has provided an approach to create the electronic devices with desired performance.
Two-dimensional MoTe2 materials: From synthesis, identification, and charge transport to electronics applications
(2016-11-01)
Chang, Yuan-Ming
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Lin, Che-Yi
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Lin, Yen-Fu
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Tsukagoshi, Kazuhito
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電子物理學系
We present a review of recent developments in the synthesis, thickness identification, electronic properties, and possible applications of layered MoTe2 flakes. Special emphasis is made on two-dimensional (2D) MoTe2 semiconductors and the extensive research in recent years on their applications in electronics. Layered MoTe2 flakes have been the focus of substantial interest in the research community because of their fascinating characteristics, including an appropriate band gap and a simple fabrication method (exfoliation) to form layered nanomaterials. Our aim is to provide the readers an overview of layered MoTe2 flakes and to understand their properties, which may lead to their applications in micro- and nanoelectronics. (C) 2016 The Japan Society of Applied Physics