Browsing by Author "Lee, Ko-Chun"

Now showing 1 - 7 of 7

A Triode Device with a Gate Controllable Schottky Barrier: Germanium Nanowire Transistors and Their Applications
(1970-01-01)
Lin, Che-Yi
;
Chen, Chao-Fu
;
Chang, Yuan-Ming
;
Yang, Shih-Hsien
;
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
;
Yang, Shih-Hsien
;
Sung, Yung-Shang
;
Chang, Yuan-Ming
;
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.
Investigation and comparison of analog figures-of-merit for TFET and FinFET considering work-function variation
(2015-02-01)
Lee, Ko-Chun
;
Fan, Ming-Long
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper investigates and compares the impacts of metal-gate work-function variation on important analog figures-of-merit (FOMs) for TFET and FinFET devices using 3-D atomistic TCAD simulations. Our study indicates that, at 0.6 V supply voltage and 0.2 V gate-voltage overdrive, TFET exhibits superior variation immunity regarding transconductance to drain-current ratio (g(m)/I-DS), output resistance (R-out) and intrinsic gain, and comparable variability in g(m) and cutoff frequency (f(T)) as compared with the FinFET counterparts. In addition, how the correlations between pertinent parameters (e.g., g(m) and R-out) impact the variation immunity of important analog FOMs are analyzed. Our study may provide insights for low-voltage analog design using TFET/FinFET technologies. (C) 2014 Elsevier Ltd. All rights reserved.
Multifunctional full-visible-spectrum optoelectronics based on a van der Waals heterostructure
(2019-12-01)
Yang, Shih-Hsien
;
Lee, Ko-Chun
;
Tsai, Meng-Yu
;
Chang, Yuan-Ming
;
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.
Oxidation-boosted charge trapping in ultra-sensitive van der Waals materials for artificial synaptic features
(2020-06-12)
Yang, Feng-Shou
;
Li, Mengjiao
;
Lee, Mu-Pai
;
Ho, I-Ying
;
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
;
Lin, Che-Yi
;
Chang, Yuan-Ming
;
Li, Mengjiao
;
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.
Room-Temperature Ferroelectricity in Hexagonally Layered alpha-In2Se3 Nanoflakes down to the Monolayer Limit
(2018-12-12)
Xue, Fei
;
Hu, Weijin
;
Lee, Ko-Chun
;
Lu, Li-Syuan
;
Zhang, Junwei
2D ferroelectric material has emerged as an attractive building block for high density data storage nanodevices. Although monolayer van der Waals ferroelectrics have been theoretically predicted, a key experimental breakthrough for such calculations is still not realized. Here, hexagonally stacking alpha-In2Se3 nanoflake, a rarely studied van der Waals polymorph, is reported to exhibit out-of-plane (OOP) and in-plane (IP) ferroelectricity at room temperature. Ferroelectric multidomain states in a hexagonal alpha-In2Se3 nanoflake with uniform thickness can survive to 6 nm. Most strikingly, the electric-field-induced polarization switching and hysteresis loop are, respectively, observed down to the bilayer and monolayer (approximate to 1.2 nm) thicknesses, which designates it as the thinnest layered ferroelectric and verifies the corresponding theoretical calculation. In addition, two types of ferroelectric nanodevices employing the OOP and IP polarizations in 2H alpha-In2Se3 are developed, which are applicable for nonvolatile memories and heterostructure-based nanoelectronics/optoelectronics.