Browsing by Author "Cheng, CM"

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Development behaviours and microstructure quality of downward-development in deep x-ray lithography
(2001-11-01)
Cheng, CM
;
Chen, RH
;
機械工程學系
;
Department of Mechanical Engineering
This paper presents a novel development method for fabricating high aspect ratio microstructures in deep x-ray lithography. In this method, microstructures are developed downward to utilize the difference of the specific weight between the development products and the developer to efficiently remove the development products. The development behaviours of the proposed method (downward-development) are investigated and compared with the conventional method (upward-development). Experimental results indicate that the developing rate of downward-development is approximately twice that obtained by upward-development. Additionally, the development products are easily removed and a satisfactory microstructure quality is achieved via this process. The proposed method also yields accurate predictability to estimate the necessary developing time. Moreover, the elevated temperature increases the developing rate of downward-development more sensitively than for upward-development.
Distortion analysis of single V-groove butt welding on heat treatable aluminum alloys
(2005-09-01)
Cheng, CM
;
Chou, CP
;
Lee, IK
;
Lin, HY
;
機械工程學系
In this study we conducted single V-groove butt welding (GTAW) on three types of heat treatable aluminum alloys 2024-T351, 6061-T6 and 7075-T6 and compared the angular distortion levels of the three aluminum alloys at different Vee preparation angles with or without restraint. Experimental results demonstrated that when the Vee preparation angle was 0 degrees (l-shaped groove), the angular distortion level of the restrained weldment can exceed that of the unrestrained weldments. Moreover, when. the Vee preparation angle was 45 degrees, 60 degrees or 90 degrees, the restrained weldment had lower angular distortion than the unrestrained weldments. The single Vee preparation angle (amount of filler metal) in butt welding affected the angular distortion of the weldment. Without restraint, the angular distortion tended to increase with the single Vee preparation angle. Meanwhile, the angular distortion tended to decrease when the single Vee preparation angle was 60 degrees. Additionally, a restrained weldment had high angular distortion when the single Vee preparation angle was 0 degrees. Notably, the angular distortion tended to reduce with increasing single Vee preparation angle. The angular distortion of the weldment was minimized at an angle of 60 degrees. However, the angular distortion increased when the Vee preparation angle exceeded 60 degrees. The high-temperature yield strength of a material also affected its angular distortion. Angular distortion increased with high-temperature yield strength. Experimental results also showed that, from the strongest to the weakest, the high-temperature yield strength of the three types of aluminum alloys followed the order 6061-T6 and 2024-T351 > 7075-T6.
Effect of aging treatment on the mechanical properties of C-250 maraging steel by flow forming
(2003-02-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long, thin walled tube made of C-250 maraging steel. The forward flow forming can save raw material, increase strength, and reduce the production process time. Because the work hardening effect on solution-treated C-250 using flow forming is minimal, the flow-formed tube requires an additional heat treatment to obtain higher hardness and strength. With the direct aging treatment, low elongation values are obtained, making this treatment unsuitable for the engineering design. It was found that the 540 degreesC/6 h/AC over-aging treatment results in better strength and elongation values. The strengthening phase of the flow-formed C-250 maraging steel was found to be the intermetallic compound of Fe3Mo.
Effect of heat treatment on microstructures of flow formed C-250 maraging steel
(2003-11-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long thin walled tube of C-250 maraging steel. Forward flow forming can conserve material, increase strength and reduce production process time. Since the hardness of solution treated C-250, using flow forming, can be increased by approximately 16.2%, flow formed tube must be given an additional aging treatment to increase hardness and strength. Direct aging treatment yields low elongation, which is not suited to design requirements. Using a homogenisation treatment, the microstructure of C-250 was of coarse grained lath type on aging and of needle type after solution treatment and aging. These treatments resulted in low tensile strength, and tensile fracture showed a tendency to brittleness. A 'solution + aging' treatment yielded greater strength and elongation.
Effect of stress relief on microstructure and mechanical properties of flow formed maraging steel weldment by electron beam welding
(2003-06-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long and thin wall tube of C-250 maraging steel. The work hardening effect of solution treated C-250 by flow forming is small. Therefore aging treatment after flow forming is required to increase hardness and strength. Final formed C-250 tubes are usually manufactured by combining aging treatment and electron beam welding (EBW). The hardness and tensile strength of aged C-250 maraging steel weldment decreased to the corresponding values obtained in the solution annealed state. Thus, the formed tube by EBW requires stress relieving treatment (and similarly for the aged condition) to increase hardness and strength and thus meet the required specification. The strength requirement was successfully achieved but the elongation of the aged, EBW, and stress relieved specimen was 88.5% lower than that of the unwelded specimen. (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.
Experimental investigation of fabrication properties of electroformed Ni-based micro mould inserts
(2004-11-01)
Cheng, CM
;
Chen, RH
;
機械工程學系
;
Department of Mechanical Engineering
In this work, Ni and Ni-Fe micro mould inserts with high aspect ratios are fabricated by Si-LIGA. Many analyses were performed to elucidate the material properties of Ni-based micro mould inserts. The surface properties were examined using a scanning probe microscope (SPM). Nanoindentation was used to measure the elastic modulus and hardness of Ni-Fe microstructures. When the iron content of Ni-Fe micro mould inserts exceeded 12%, the grain size of the Ni-Fe alloy was under 15 nm. Additionally, the mechanical properties of Ni-based microstructures obtained by electroformng are superior to those obtained by casting or powder metallurgy. Satisfactory electroforming current densities for obtaining a mould insert with a fine surface profile ranged from 4 ASD to 6 ASD. (C) 2004 Elsevier B.V. All rights reserved.
Fabricating a micromould insert using a novel process
(2005)
Chen, RH
;
Chang, CC
;
Cheng, CM
;
機械工程學系
;
Department of Mechanical Engineering
A new method of fabricating micromould inserts that is compatible with semiconductor manufacturing is proposed. Diffusion of phosphorous at a high temperature is first used to increase the electric conductivity of the surface of the silicon wafer to generate a silicon-based seed layer for electroforming. If the process temperature and the duration of doping with phosphorous are controlled, then the electric conductivity of this novel silicon-based seed layer can be expected to equal that of a metal seed layer. Then, a structure layer of amorphous silicon is successfully formed onto the silicon-based seed layer, by plasma enhanced chemical vapor deposition (PECVD). The structure layer has none of the defects that would be present if a metal seed layer were used to replace the silicon-based seed layer. Finally, a silicon-based master microstructure was created by using ICPRIE to etch the structure layer. The silicon-based master has been demonstrated to be useable in successfully fabricating, by electroforming, a metal micromould insert with a large area and high aspect ratio.
High quality interpoly dielectrics deposited on the nitrided-polysilicon for nonvolatile memory devices
(2001-07-01)
Yang, WL
;
Chao, TS
;
Cheng, CM
;
Pan, TM
;
Lei, TF
High quality interpoly dielectrics have been fabricated by using NH3 and N2O nitridation on polysilicon and deposition of tetra-ethyl-ortho-silitate (TEOS) oxide with N2O annealing. The surface roughness of polysilicon is improved and the value of weak bonds is reduced due to nitrogen incorporation at the interface, which improves the integrity of interpoly dielectrics, The improvements include a higher barrier height, breakdown strength, and charge-to-breakdown, and a lower leakage current and charge trapping rate than counterparts. It is found that this method can simutaneously improve both charge-to-breakdown (up to 20 C/cm(2)) and electric breakdown field (up to 17 MV/cm).
High quality interpoly-oxynitride grown by NH3 nitridation and N2O RTA treatment
(2001-02-01)
Pan, TM
;
Lei, TF
;
Yang, WL
;
Cheng, CM
;
Chao, TS
In this letter, a method to grow high quality interpolysilicon-oxynitride (interpoly-oxynitride) film is proposed. Samples, nitridized by NH3 with additional N2O annealing and CVD TEOS deposited on poly-oxynitride (poly-I) with RTA NaO oxidation, show excellent electrical properties in terms of very high electric breakdown field, ion; leakage current, high charge to breakdown, and low electron trapping rate. This novel film is a good candidate for an interpoly dielectric of future high density EEPROM and flash memory devices.
Hot cracking of welds on heat treatable aluminium alloys
(2005-06-01)
Cheng, CM
;
Chou, CP
;
Lee, IK
;
Lin, HY
;
機械工程學系
The Spot Varestraint test was used to evaluate the hot cracking susceptibility of several aluminium alloys namely 6061-T6, 6061-T6 ( H), 7075-T6, 7075-T6 ( H). The effects of augment strain, the number of thermal cycles and cold working ( rolling) on the cracking susceptibility were investigated, and the total crack length was used to evaluate the hot cracking susceptibility. The results indicate that the number of thermal cycles is irrelevant to the hot cracking susceptibility in the weld fusion zone, but does affect this susceptibility in the heat affected zone (HAZ). More thermal cycles correspond to larger hot cracks in the HAZ, especially in the weld metal HAZ. The hot cracking susceptibility of materials increased with augment strain in both the fusion zone and the HAZ. Cold working of the materials can reduce their hot cracking susceptibility. The hot cracking susceptibility of 7075-T6 aluminium alloys is higher than that of 6061-T6. There was significant Cu segregation in the HAZ of 7075-T6 aluminium alloy, resulting in a higher susceptibility to hot cracking in this zone.
ICA-based spatiotemporal approach for single-trial analysis of postmovement MEG beta synchronization
(2003-12-01)
Lee, PL
;
Wu, YT
;
Chen, LF
;
Chen, YS
;
Cheng, CM
The extraction of event-related oscillatory neuromagnetic activities from single-trial measurement is challenging due to the non-phase-locked nature and variability from trial to trial. The present study presents a method based on independent component analysis (ICA) and the use of a template-based correlation approach to extract Rolandic beta rhythm from magnetoencephalographic (MEG) measurements of right finger lifting. A single trial recording was decomposed into a set of coupled temporal independent components and corresponding spatial maps using ICA and the reactive beta frequency band for each trial identified using a two-spectrum comparison between the postmovement interval and a reference period. Task-related components survived dual criteria of high correlation with both the temporal and the spatial templates with an acceptance rate of about 80%. Phase and amplitude information for noise-free MEG beta activities were preserved not only for optimal calculation of beta rebound (event-related synchronization) but also for profound penetration into subtle dynamics across trials. Given the high signal-to-noise ratio (SNR) of this method, various methods of source estimation were used on reconstructed single-trial data and the source loci coherently anchored in the vicinity of the primary motor area. This method promises the possibility of a window into the intricate brain dynamics of motor control mechanisms and the cortical pathophysiology of movement disorder on a trial-by-trial basis. (C) 2003 Elsevier Inc. All rights reserved.
Improving spin-coating process using altered cover design
(2004-12-01)
Cheng, CM
;
Chen, RH
;
機械工程學系
;
Department of Mechanical Engineering
A novel work chamber cover design for a spin coater that can reduce the effect of airflow on spin coating is presented. The experimental results reveal that superior uniformity and film area can be obtained by utilizing the modified design instead of the conventional design.
Key issues in fabricating microstructures with high aspect ratios by using deep X-ray lithography
(2004-05-01)
Cheng, CM
;
Chen, RH
;
機械工程學系
;
Department of Mechanical Engineering
High aspect ratio microstructures are frequently made with the Lithographie, Galvanoformung, Abformung (LIGA) process. The success of this process depends critically on "deep" X-ray lithography (DXRL). This paper presents a variety of experimentally and analytically determined techniques for optimizing DXRL. These include methods for designing and fabricating high-quality X-ray masks. Methods for optimizing the exposure dosage and developing cycle are described. New methods for promoting resist adhesion and for avoiding resist film cracking are discussed. The influence of developer surface tension on the resist solvation process is quantified and new methods for controlling this surface tension are described. (C) 2004 Elsevier B.V. All rights reserved.
Sintering BaTi4O9/Ba2Ti9O20-based ceramics by glass addition
(2000-07-01)
Cheng, CM
;
Yang, CF
;
Lo, SH
;
Tseng, TY
;
電子工程學系及電子研究所
After calcining BaCO3 + 4TiO(2) mixed powder at 1150 degrees C for 2 h, BaTi4O9 is the major phase, Ba4Ti13O30 and BaTi5O11 are minor phases. After calcining 2BaCO(3) + 9TiO(2) mixed powder at 1200 degrees C for 10 h, Ba2Ti9O20 is the major phase, BaTi4O9 and BaTi5O11 are the minor phases. The calcining powders are used as the BaTi4O9 and Ba2Ti9O20 precursors. MgO-CaO-SiO2-Al2O3 (MCAS) composite glass powder, fabricated by sol-gel method, is used as the low melting addition to lower the sintering temperatures of BaTi4O9 and Ba2Ti9O20 dielectric. The addition of MCAS glass does not inhibit the residual satellite phases to transform into BaTi4O9 and Ba2Ti9O20. For MCAS-doped BaTi4O9 and Ba2Ti9O20 ceramics the major phases are BaTi4O9 and Ba2Ti9O20, cordierite is observed as minor phase. The temperatures needed to densify the BaTi4O9 and Ba2Ti9O20 ceramics are lowered down with the increase amount of MCAS glass addition. For BaTi4O9 and Ba2Ti9O20 ceramics, both the densities and the dielectric constants (at 1 MHz) increase with the sintering temperature and decrease with the amount of MCAS glass addition. (C) 2000 Elsevier Science Ltd. All rights reserved.
Study of linear and nonlinear optical properties of distorted Ti-O-6 perovskite structure in BaxSr1-xTiO3
(2000-06-01)
Chen, WK
;
Cheng, CM
;
Huang, JY
;
Hsieh, WF
;
Tseng, TY
We report the linear and nonlinear optical properties of sol-gel prepared BaxSr1-xTiO3 (BST) crystalline powders. The results from powder X-ray diffraction, birefringence, and second-order optical nonlinearity measurements indicate that the paraelectric-ferroelectric phase transition of Ba0.75Sr0.25TiO3 occurs near room temperature. The second-order optical nonlinearity of the ferroelectric BST is about 7.9 pm/V. The index of refraction, n = 2.2, and birefringence, Delta n(B) similar to 0.05, are also appropriate for practical nonlinear optical applications. (C) 2000 Elsevier Science Ltd. All rights reserved.
Study of spin coating properties of SU-8 thick-layer photoresist
(2001)
Chen, RH
;
Cheng, CM
;
機械工程學系
;
Department of Mechanical Engineering
In this paper the coating properties including film thickness, thickness uniformity and variation of viscosity of SU8 photoresist were investigated by using a spin coater and rheometer. Experimental results indicate that the coating qualities of SU8 are affected by several factors including the spinning speed, the photoresist viscosity, the initial acceleration and the duration. Some recommendations are presented for increasing the quality of SU8 spin coating in thick-film processing.