Browsing by Author "Chen, Cheng-Lung"

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Automatic-Patterned Sapphire Substrate Nanometrology Using Atomic Force Microscope
(2015-03-01)
Hung, Shao-Kang
;
Cheng, Chiao-Hua
;
Chen, Cheng-Lung
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機械工程學系
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Department of Mechanical Engineering
Light emitting diodes become brighter because of the contribution of patterned sapphire substrates (PSS). The dimensions of PSS crucially affect its performance. The most suitable instrument to measure PSS is atomic force microscope, which provides three-dimensional surface profiles. This paper proposes an automatic method to analyze AFM-collected raw data and produce characteristic parameters of PSS, including height, diameters, pitch, and side angles. Experimental results show that this method has good repeatability of 1.2 and 6.3 nm on measuring height and bottom diameter, respectively. This nanometrology method will be extensively applicable for similar nanostructures with periodic patterns.
Enhancing thermoelectric performance by Fermi level tuning and thermal conductivity degradation in (Ge1-xBix)Te crystals
(2019-06-13)
Wei, Pai-Chun
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Cai, Cheng-Xun
;
Hsing, Cheng-Rong
;
Wei, Ching-Ming
;
Yu, Shih-Hsun
In this work, a high thermoelectric figure of merit, zT of 1.9 at 740 K is achieved in Ge1-xBixTe crystals through the concurrent of Seebeck coefficient enhancement and thermal conductivity reduction with Bi dopants. The substitution of Bi for Ge not only compensates the superfluous hole carriers in pristine GeTe but also shifts the Fermi level (E-F) to an eligible region. Experimentally, with moderate 6-10% Bi dopants, the carrier concentration is drastically decreased from 8.7 x 10(20) cm(-3) to 3-5 x 10(20) cm(-3) and the Seebeck coefficient is boosted three times to 75 mu VK-1. In the meantime, based on the density functional theory (DFT) calculation, the Fermi level E-F starts to intersect with the pudding mold band at L point, where the band effective mass is enhanced. The enhanced Seebeck coefficient effectively compensates the decrease of electrical conductivity and thus successfully maintain the power factor as large as or even superior than that of the pristine GeTe. In addition, the Bi doping significantly reduces both thermal conductivities of carriers and lattices to an extremely low limit of 1.57W m(-1)K(-1) at 740 K with 10% Bi dopants, which is an about 63% reduction as compared with that of pristine GeTe. The elevated figure of merit observed in Ge1-xBixTe specimens is therefore realized by synergistically optimizing the power factor and downgrading the thermal conductivity of alloying effect and lattice anharmonicity caused by Bi doping.
[INVITED] Total-internal-reflection-based photomask for large-area photolithography
(2016-05)
Hung, Shao-Kang
;
Lin, Kung-Hsuan
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Chen, Cheng-Lung
;
Chou, Chen-Hsun
;
Lin, You-Chuan
Photolithography has been widely implemented with a photomask in contact or in close proximity to the photoresist layer. The flatness of the substrates is a crucial factor to guarantee the quality of the entire patterned photoresist (PR) layer especially for large-area photolithography. However, some substrates, such as sapphire wafers, do not possess highly uniform thickness as silicon wafer does. In this work, we demonstrate that a flexible polydimethylsiloxane (PDMS) photomask with optical total-internal-reflection structure can effectively circumvent this problem for mass production. Different from conventional photomask that the light is blocked by the patterned reflective/absorbing materials, the distributions of light intensity on the PR is engineered by the geometric structure of the transparent PDMS photomask. We demonstrate that 4 in. patterned sapphire wafers can be successfully fabricated by using this PDMS photomask, which can be easily integrated into the present techniques in industry for mass production of substrates for GaN-based optoelectronic devices. (C) 2015 Elsevier Ltd. All rights reserved.
Visual Servo Control System of a Piezoelectric 2-Degree-of-Freedom Nano-Stepping Motor
(2019-12-01)
Chen, Cheng-Lung
;
Hung, Shao-Kang
;
機械工程學系
;
Department of Mechanical Engineering
A nano-stepping motor can translate or rotate when its piezoelectric element pair is electrically driven in-phase or anti-phase. It offers millimeter-level stroke, sub-micron-level stepping size, and sub-nanometer-level scanning resolution. This article proposes a visual servo system to control the nano-stepping motor, since its stepping size is not consistent due to changing contact friction, using a custom built microscopic instrument and image recognition software. Three kinds of trajectories straight lines, circles, and pentagrams are performed successfully. The smallest straightness and roundness ever tested are 0.291 mu m and 2.380 mu m. Experimental results show that the proposed controller can effectively compensate for the error and precisely navigate the rotor along a desired trajectory.