Browsing by Author "Yang, Shih-Hsien"

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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.
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.
Intrinsic Carrier Transport of Phase-Pure Homologous 2D Organolead Halide Hybrid Perovskite Single Crystals
(2018-12-27)
Li, Min-Ken
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Chen, Tzu-Pei
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Lin, Yen-Fu
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Raghavan, Chinnambedu Murugesan
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Chen, Wei-Liang
This work reveals the intrinsic carrier transport behavior of 2D organolead halide perovskites based on phase-pure homologous (n = 1, 2, and 3) Ruddelsden-Popper perovskite (RPP) (BA)(2)(MA)(n-1)PbnI3n+1 single crystals. The 2D perovskite field effect transistors with high-quality exfoliated 2D perovskite bulk crystals are fabricated, and characteristic output and transfer curves are measured from individual single-crystal flakes with various n values under different temperatures. Unipolar n-type transport dominated the electrical properties of all these 2D RPP single crystals. The transport behavior of the 2D organolead halide hybrid perovskites exhibits a strong dependence on the n value and the mobility substantially increases as the ratio of the number of inorganic perovskite slabs per organic spacer increases. By extracting the effect of contact resistances, the corrected mobility values for n = 1, 2, and 3 are 2 x 10(-3), 8.3 x 10(-2), and 1.25 cm(2) V-1 s(-1) at 77 K, respectively. Furthermore, by combining temperature-dependent electrical transport and optical measurements, it is found that the origin of the carrier mobility dependence on the phase transition for 2D organolead halide perovskites is very different from that of their 3D counterparts. Our findings offer insight into fundamental carrier transport behavior of 2D organic-inorganic hybrid perovskites based on phase-pure homologous single crystals.
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.
Oxidation-boosted charge trapping in ultra-sensitive van der Waals materials for artificial synaptic features
(2020-06-12)
Yang, Feng-Shou
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Li, Mengjiao
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Lee, Mu-Pai
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Ho, I-Ying
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Chen, Jiann-Yeu
Exploitation of the oxidation behaviour in an environmentally sensitive semiconductor is significant to modulate its electronic properties and develop unique applications. Here, we demonstrate a native oxidation-inspired InSe field-effect transistor as an artificial synapse in device level that benefits from the boosted charge trapping under ambient conditions. A thin InOx layer is confirmed under the InSe channel, which can serve as an effective charge trapping layer for information storage. The dynamic characteristic measurement is further performed to reveal the corresponding uniform charge trapping and releasing process, which coincides with its surface-effect-governed carrier fluctuations. As a result, the oxide-decorated InSe device exhibits nonvolatile memory characteristics with flexible programming/erasing operations. Furthermore, an InSe-based artificial synapse is implemented to emulate the essential synaptic functions. The pattern recognition capability of the designed artificial neural network is believed to provide an excellent paradigm for ultra-sensitive van der Waals materials to develop electric-modulated neuromorphic computation architectures. Developing efficient memory and artificial synaptic systems based on environmentally sensitive van der Waals materials remains a challenge. Here, the authors present a native oxidation-inspired InSe field-effect transistor that benefits from a boosted charge trapping behavior under ambient conditions.
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.
THE INFLUENCE OF PROCESS PARAMETERS ON THE STRUCTURE AND MORPHOLOGY OF PULSED PLASMA-POLYMERIZED OCTAFLUOROTOLUENE FILMS
(2010-11-01)
Jiang, Meng-Dan
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Wang, Ling-Yung
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Lin, Hong-Cheu
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Wei, Ta-Chin
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Yang, Shih-Hsien
This work describes amorphous fluorinated polymer films deposited by pulsed plasma polymerizations of octafluorotoluene (PPP-OFT) monomers on ITO glass as the hole-injection layer of organic electroluminescent (EL) devices, in order to study the influence of sample position and duty cycle on PPP-OFT film characteristics, and also to find a good process to yield a higher retention degree of monomers and lower roughness of PPP-OFT fluorocarbon films. Experimental results revealed that PPP-OFT films deposited at positions far away from the RF coil and close to the monomer inlet showed less roughness than films deposited near the high RF-flux regions. In addition, the retention of the monomers in the PPP-OFT layer will be high if the deposition is conducted near the monomer inlet but some distance away from the RF electrode. Moreover, amorphous fluorinated polymer films can be deposited with higher fluorine to carbon (F/C) ratios and CF(2) contents at proper substrate positions by means of different sticking coefficients of free radicals dissociated by octafluorotoluene monomers.