Browsing by Author "Chung, Yun-Yan"

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Demonstration of 40-nm Channel Length Top-Gate p-MOSFET of WS2 Channel Directly Grown on SiOx/Si Substrates Using Area-Selective CVD Technology
(2019-12-01)
Chung, Yun-Yan
;
Lu, Kuan-Cheng
;
Cheng, Chao-Ching
;
Li, Ming-Yang
;
Lin, Chao-Ting
For high-volume manufacturing of 2-D transistors, area-selective chemical reaction deposition (CVD) growth is able to provide good-quality 2-D layers and may be more effective than exfoliation from bulk crystals or wet/dry transfer of large-area as-grown 2-D layers. We have successfully grown continuous and uniform WS2 film comprising around seven layers by area-selective CVD approach using patterned tungsten source/drain metals as the seeds. The growth mechanism is inferred and supported by the transmission electron microscope (TEM) images, as well. The first top-gate MOSFETs of CVD-WS2 channels on SiOx/Si substrates are demonstrated to have good short channel electrical characteristics: ON-/OFF-ratio of 10(6), a subthreshold swing of 97 mV/decade, and nearly zero drain-induced barrier lowering (DIBL).
Demonstration of HfO2-Based Gate Dielectric With Low Interface State Density and Sub-nm EOT on Ge by Incorporating Ti Into Interfacial Layer
(2019-02-01)
Tsai, Yi-He
;
Chou, Chen-Han
;
Chung, Yun-Yan
;
Yeh, Wen-Kuan
;
Lin, Yu-Hsien
HfO2-based gate stacks with titanium (Ti) incorporated into a GeOx interfacial layer (IL) were fabricated on p-Ge substrates. X-ray photoelectron spectroscopy results, incorporating Ti, can efficiently suppress the GeO volatilization. This contributed to achievement of an equivalent oxide thickness of approximately 0.8 nm, a low interface states density D-it of approximately 2.5 x 10(11) eV(-1)cm(-2), and a smaller D-it increment of approximately 1 x 10(11) eV(-1)cm(-2) after constant negative voltage stress at a field of 8 MV/cm. Therefore, Ti is appropriate for improving the quality of GeOx through high temperature annealing.
Experimentally Determining the Top and Edge Contact Resistivities of Two-Step Sulfurization Nb-Doped MoS2 Films Using the Transmission Line Measurement
(2019-10-01)
Chung, Yun-Yan
;
Li, Chi-Feng
;
Lin, Chao-Ting
;
Ho, Yen-Teng
;
Chien, Chao-Hsin
This study determined the top (vertical) and edge (horizontal) resistivities of metal-MoS2 contact based on the experimental results obtained using the transmission line measurement structure. A novel two-step sulfurization scheme was conducted for forming Nb-doped MoS2 films on a sapphire substrate. The edge contact resistivity, rho(C_edge), was almost two orders of magnitude lower than the top contact resistivity, rho(C_top). Our findings highlight a simple and effective method to accurately determine the edge and top contact resistances of a metal-two-dimensional material contact.
First demonstration of 40-nm channel length top-gate WS2 pFET using channel area-selective CVD growth directly on SiOx/Si substrate
(2019-01-01)
Cheng, Chao-Ching
;
Chung, Yun-Yan
;
Li, Ming-Yang
;
Lin, Chao-Ting
;
Li, Chi-Feng
Area-selective channel material growth for 2D transistors is more desirable for volume manufacturing than exfoliation or wet/dry transfer after large area growth. We demonstrate the first top-gate WS(2)p-channel field-effect transistors (p-FETs) fabricated on SiOx/Si substrate using channel area-selective CVD growth. Smooth and uniform WS2 comprising approximately 6 layers was formed by area-selective CVD growth in which a patterned tungsten-source/drain served as the seed for WS2 growth. For a 40 nm gate length transistor, the device has impressive electrical characteristics: on/off ratio of similar to 10(6), a S.S. of similar to 97 mV/dec.. and nearly zero DIBL.
Study of the Band Alignment between Atomic-Layer-Deposited High-kappa Dielectrics and MoS2 Film
(2018-01-01)
Chung, Yun-Yan
;
Tsai, Ming-Li
;
Ho, Yen-Teng
;
Tseng, Yuan-Chieh
;
Chien, Chao-Hsin
In this study, we determined the energy-band alignment of various amorphous high-kappa dielectrics (Al2O3, HfO2, ZrO2, and TiO2) that were deposited on amolybdenum disulfide (MoS2) film through atomic layer deposition by using high-resolutionX-ray photoelectron spectroscopy. The uniformity and continuity of the MoS2 films were inspected by physical characterizations. The roughness of MoS2 film deposited by chemical vapor deposition was evaluated using atomic force microscopy. Moreover, cross-sectional transmission electron microscopy images confirmed that all high-kappa dielectrics were uniformly and continuously deposited on the MoS2 film, leading to superior high-kappa dielectric-MoS2 stacks. An abrupt interface between the high-kappa dielectrics and MoS2 film was also observed. Finally, the valance and conduction band offsets between the Al2O3, HfO2, ZrO2, and TiO2 and the MoS2 film interface were measured to be 3.14, 1.81, 1.56, and 0.18 eV and 2.36, 1.77, 1.88, and 1.68 eV, respectively. Our study demonstrated the direct deposition of numerous commonly used high-kappa dielectrics on top of a MoS2 film. This top-down scheme is very useful for applying two-dimensional materials to complementary metal-oxide-semiconductor field-effect-transistor circuits. (C) 2018 The Electrochemical Society.