Browsing by Author "Liu, Chien-Min"

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Core-Shell Ni-NiO Nano Arrays for UV Photodetection without an External Bias
(2012)
Liu, Chien-Min
;
Chen, Chih
;
Tseng, Yuan-Chieh
;
材料科學與工程學系
;
Department of Materials Science and Engineering
This work demonstrates a simple method for fabricating a nano-structured device that performs notable photodetecting capabilities. With a template of anodic aluminum oxide, highly ordered Ni-NiO nano core-shell arrays were fabricated by annealing the electroless-deposited Ni arrays at 300 degrees C for 30 minutes. High-resolution transmission electron microscopy (HRTEM) demonstrated that a NiO layer with a thickness of similar to 5 nm was developed on the surface of the Ni arrays. The effects of annealing time and temperature on NiO were probed by HRTEM. Results show that temperature has a greater effect on the development of NiO. The Ni/NiO interface forms naturally a Schottky nanojunction, which covers most of the array surface when patterned with an indium-tin oxide (ITO) electrode. The ITO/Ni-NiO/Si device was found to yield photocurrent when exposed to ultraviolet (UV) light without an external voltage bias. The device takes great advantage of the large junction area and one-dimensional configuration of the core-shell array, displaying rapid photoresponse to UV light and subsequent steady photocurrent. These features make the proposed device a viable alternative to the UV photodetector. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.067204jes] All rights reserved.
Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays
(2011-10-01)
Yang, Chao-Yao
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Huang, Chun-Chao
;
Tseng, Yuan-Chieh
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Liu, Chien-Min
;
Chen, Chih
A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (similar to 6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM -> FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host's electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3647753]
Direct probe of heterojunction effects upon photoconductive properties of TiO(2) nanotubes fabricated by atomic layer deposition
(2010-06-04)
Chang, Yung-Huang
;
Liu, Chien-Min
;
Tseng, Yuan-Chieh
;
Chen, Chih
;
Chen, Chia-Chuan
This study investigated Schottky- and ohmic-contact effects upon the photoresponses of ITO/TiO(2)/Si and Ti/TiO(2)/Si nanotube-based photodiodes. The TiO(2) tube arrays were fabricated by atomic layer deposition (ALD) and shaped by an anodic aluminum oxide (AAO) template on a p-type Si substrate. The contact area between the electrode (Ti or ITO) and the TiO(2)'s tip was varied by tuning the tube's inner wall thickness with ALD, providing a direct and systematic probe of the heterojunction effects upon the photodiodes' responses. Results show that the Ti/TiO(2)/Si diode exhibits a highly thickness-dependent photoresponse. This is because the photocurrent is driven by the p-n junction at TiO(2)/Si alone and it faces no retarding at the ohmic contact of Ti/TiO(2). For the ITO/TiO(2)/Si diode, the Schottky contact at ITO/TiO(2) regulates photocurrent overriding TiO(2)/Si as a result of higher efficiency in photogeneration, leading to the opposite response compared with the Ti/TiO(2)/Si diode. Respective energy band diagrams are provided to support the statements above, and a consistent picture is obtained for both time response and quantum efficiency measurements.
Direct probe of heterojunction effects upon photoconductive properties of TiO2 nanotubes fabricated by atomic layer deposition
(2010-06-04)
Chang, Yung-Huang
;
Liu, Chien-Min
;
Tseng, Yuan-Chieh
;
Chen, Chih
;
Chen, Chia-Chuan
This study investigated Schottky- and ohmic-contact effects upon the photoresponses of ITO/TiO2/Si and Ti/TiO2/Si nanotube-based photodiodes. The TiO2 tube arrays were fabricated by atomic layer deposition (ALD) and shaped by an anodic aluminum oxide (AAO) template on a p-type Si substrate. The contact area between the electrode (Ti or ITO) and the TiO2's tip was varied by tuning the tube's inner wall thickness with ALD, providing a direct and systematic probe of the heterojunction effects upon the photodiodes' responses. Results show that the Ti/TiO2/Si diode exhibits a highly thickness-dependent photoresponse. This is because the photocurrent is driven by the p-n junction at TiO2/Si alone and it faces no retarding at the ohmic contact of Ti/TiO2. For the ITO/TiO2/Si diode, the Schottky contact at ITO/TiO2 regulates photocurrent overriding TiO2/Si as a result of higher efficiency in photogeneration, leading to the opposite response compared with the Ti/TiO2/Si diode. Respective energy band diagrams are provided to support the statements above, and a consistent picture is obtained for both time response and quantum efficiency measurements.
Effect of Geometric Nanostructures on the Absorption Edges of 1-D and 2-D TiO2 Fabricated by Atomic Layer Deposition
(2013-05-08)
Chang, Yung-Huang
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Liu, Chien-Min
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Cheng, Hsyi-En
;
Chen, Chih
;
材料科學與工程學系
2-Dimensional (2-D) TiO2 thin films and 1-dimensional (1-D) TiO2 nanotube arrays were fabricated on Si and quartz substrates using atomic layer deposition (ALD) with an anodic aluminum oxide (AAO) template at 400 degrees C. The film thickness and the tube wall thickness can be precisely controlled using the ALD approach. The intensities of the absorption spectra were enhanced by an increase in the thickness of the TiO2 thin film and tube walls. A blue-shift was observed for a decrease in the 1-D and 2-D TiO2 nanostructure thicknesses, indicating a change in the energy band gap with the change in the size of the TiO2 nanostructures. Indirect and direct interband transitions were used to investigate the change in the energy band gap. The results indicate that both quantum confinement and interband transitions should be considered when the sizes of 1-D and 2-D TiO2 nanostructures are less than 10 nm.
Effect of grain orientations of Cu seed layers on the growth of < 111 >-oriented nanotwinned Cu
(2014-08-19)
Liu, Chien-Min
;
Lin, Han-Wen
;
Lu, Chia-Ling
;
Chen, Chih
;
材料科學與工程學系
We investigate the growth of Cu films on two different Cu seed layers: one with regular < 111 >-oriented grains and the other with very strong < 111 >-preferred orientation. It is found that densely-packed nanotwinned Cu (nt-Cu) can be grown by pulsed electroplating on the strong < 111 >-oriented Cu seed layer without a randomly-oriented transition layer between the nt-Cu and the Cu seed layer. The electroplated nt-Cu grow almost epitaxially on the seed layer and formed < 111 >-oriented columnar structures. However, with the regular < 111 >-oriented Cu seed, there is a randomly-oriented transition layer between the nt-Cu and the regular < 111 >-oriented Cu seed. The results indicate that the seed layer plays a crucial role on the regularity of < 111 >-oriented nanotwinned Cu.
Eliminate Kirkendall voids in solder reactions on nanotwinned copper
(2013-03-01)
Liu, Tao-Chi
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Liu, Chien-Min
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Huang, Yi-Sa
;
Chen, Chih
;
Tu, King-Ning
Electroplating was used to fabricate a high density of nanotwins that exhibited the preferred (111) orientation in Cu. We found no formation of Kirkendall voids in solder reactions on the nanotwinned Cu. This was due to the high density of steps and kinks on the nanotwin boundaries, which serve as vacancy sinks. Thus the vacancy concentration cannot reach supersaturation and nucleate voids. The finding is a significant advance in the problem of solder joint reliability in microelectronic three-dimensional integrated circuit devices. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Extremely anisotropic single-crystal growth in nanotwinned copper
(2014-10-01)
Lu, Chia-Ling
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Lin, Han-Wen
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Liu, Chien-Min
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Huang, Yi-Sa
;
Lu, Tien-Lin
By electroplating of nearly unidirectionally < 111 >-oriented nanotwinned and fine-grained Cu on a Si wafer surface followed by annealing at 400-500 degrees C for up to 1 h, we grew many extremely large < 100 >-oriented single crystals of Cu with sizes ranging from 200 to 400 mu m. By patterning and annealing the nanotwinned Cu films, we grew an array of < 100 >-oriented single crystals of Cu with sizes ranging from 25 to 100 mu m on Si. In comparison, single-crystal nano-wire growth is a one-dimensional anisotropic growth process, in which the growth along the axial direction is much faster than in the radial direction. We report here a bulk-type two-dimensional crystal growth of an array of numerous < 100 >-oriented single crystals of Cu on Si. This growth process has the potential for microbump applications in three-dimensional integrated circuit-packaging technology for hand-held consumer electronic products.
Fabrication and Characteristics of Self-Aligned ZnO Nanotube and Nanorod Arrays on Si Substrates by Atomic Layer Deposition
(2010)
Chang, Yung-Huang
;
Wang, Shun-Min
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Liu, Chien-Min
;
Chen, Chih
;
材料科學與工程學系
Vertically self-aligned ZnO nanorods and nanotubes are fabricated on Si substrates by atomic layer deposition with the assistance of anodic aluminum oxide at 250 degrees C. These nanostructures are equal in height, isolated, and vertical to the Si substrate. With 550 deposition cycles, we can fabricate regular arrays of ZnO nanorods with an average diameter of 70 nm and with a height of 470 nm. In particular, the wall thickness of the nanotubes can be controlled precisely by using the atomic layer deposition approach. The measured wall thickness is 18.5 perpendicular to 1 nm after 250 deposition cycles, which yields a growth rate of 0.075 nm/cycle. A polycrystalline structure for both ZnO nanorods and nanotubes was confirmed by a transmission electron microscope and selected area diffraction pattern. Compared with the ZnO films and nanorods, the fabricated ZnO nanotubes exhibit an excellent performance on photoluminescence characteristics due to their larger surface area. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489953] All rights reserved.
Fabrication and Characterization of (111)-Oriented and Nanotwinned Cu by Dc Electrodeposition
(2012-10-01)
Liu, Tao-Chi
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Liu, Chien-Min
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Hsiao, Hsiang-Yao
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Lu, Jia-Ling
;
Huang, Yi-Sa
We report an approach to fabricating (111)-oriented and nanotwinned Cu (nt-Cu) by dc electroplating. A 200 nm thick Cu with (111) preferred orientation is required as a seed layer. Highly oriented Cu films with densely packed nanotwins can be grown to exceed 20 mu m thick at high current and high stirring speeds. X-ray diffraction indicates that the intensity ratio of (111) to (220) is as high as 506, which is the highest among the reported electroplated Cu films. The spacing of twins ranges from 10 to 100 nm, which reveals a high hardness value of 2.23 GPa. The (111)-oriented nt-Cu will have many potential applications in interconnects and 3D IC packaging.
Fabrication of (111) nanotwinned Cu and its applications in interconnects of microelectronic devices
(2016)
Chen, Chih
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Liu, Chien-Min
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Lu, Tien-Lin
;
Lin, Han-wen
;
Chu, Yi-Cheng
Fabrication of arrays of (100) Cu under-bump-metallization for 3D IC packaging
(2015)
Chiu, Wei-Lan
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Lu, Chia-Ling
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Lin, Han-Wen
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Liu, Chien-Min
;
Huang, Yi-Sa
Due to the thousands of microbumps on a chip for 3D ICs, the precise control of the microstructure of all the material is required. The nearly < 111 >-oriented nanotwinned and fine-grained Cu was electroplated on a Si wafer surface and annealed at 400-500 C for 1 h, many extremely large < 100 > oriented Cu crystals with grain sizes ranging from 200 to 400 um were obtained. The < 111 >-oriented Cu grains were transformed into super-large < 100 >-oriented grains after the annealing. In addition, we patterned the < 111 >-oriented Cu films into pad arrays of 25 to 100 um in diameter and annealed the nanotwinned Cu pads with same conditions. An array of < 100 >-oriented single crystals Cu pads can be obtained. Otherwise, single-crystal nano wire growth displays a process by one-dimensional anisotropic growth, in which the growth along the axial direction is much faster than in the radial direction. This study reported here a bulk-type two-dimensional crystal growth of an array of numerous < 100 >-oriented single crystals of Cu on Si. The growth process in 3D IC has the potential for microbump applications packaging technology.
Formation of nearly void-free Cu3Sn intermetallic joints using nanotwinned Cu metallization
(2014-04-28)
Chiu, Wei-Lan
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Liu, Chien-Min
;
Haung, Yi-Sa
;
Chen, Chih
;
材料科學與工程學系
Cu3Sn intermetallic compounds (IMCs) are more resistant to fracture than solders. In addition, the Cu3Sn IMCs are more conductive than the solders. In this study, we manufactured Cu3Sn IMCs to serve as a joint using electroplated nanotwinned Cu as a metallization layer to react with pure Sn at 260 degrees C and 340 degrees C. The results show that there were almost no Kirkendall voids generated inside the Cu3Sn layer. In addition, the kinetics of the Cu3Sn growth was analyzed to predict the time needed to form the Cu3Sn joint. (C) 2014 AIP Publishing LLC.
Formation of plate-like channels in Cu6Sn5 and Cu3Sn intermetallic compounds during transient liquid reaction of Cu/Sn/Cu structures
(2016-02-01)
Chiu, Wei-Lan
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Liu, Chien-Min
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Haung, Yi-Sa
;
Chen, Chih
;
材料科學與工程學系
Transient liquid reactions in Cu/Sn/Cu sandwich structures during various stages were conducted at 340 degrees C. In the early stages of the reaction, Cu atoms dissolved into the molten Sn through the valleys between the scallop-like Cu6Sn5 intermetallic compounds (IMCs). When the Sn layer was almost consumed, formation of plate-like Sn channels in Cu6Sn5 IMCs was observed at later stages of the reaction. In addition, plate-like Cu6Sn5 channels formed in Cu3Sn IMCs because Cu atoms diffused faster in Cu6Sn5 than in Cu3Sn IMCs. These channels serve as fast diffusion paths for Cu to react with the remaining Sn. Hence, the growth kinetics at later stages are quite different from those at the beginning stages. (C) 2015 Elsevier B.V. All rights reserved.
Grain growth in electroplated (111)-oriented nanotwinned Cu
(2014-10-15)
Huang, Yi-Sa
;
Liu, Chien-Min
;
Chiu, Wei-Lan
;
Chen, Chih
;
材料科學與工程學系
The grain growth of pulse-plated (111)-oriented nanotwinned Cu (nt-Cu) was investigated at 200-350 degrees C. The results indicate that after the annealing, the nt-Cu exhibits good thermal stability, and columnar grains with a (111)-oriented nt-Cu structure are maintained up to 300 degrees C. The columnar grains consume the original fine-grained region at the bottom of the sample. In addition, these fine grains were converted into nanotwinned columnar grains with a (111) orientation. The electroplated Cu film possessed extremely high (111) preferred orientation after the annealing. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Growth Mechanism of TiO(2) Nanotube Arrays in Nanopores of Anodic Aluminum Oxide on Si Substrates by Atomic Layer Deposition
(2011-01-01)
Liu, Chien-Min
;
Chen, Chih
;
Cheng, Hsyi-En
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this study, we combined atomic layer deposition and anodic aluminum oxide (AAO) on a silicon substrate and developed self-aligned TiO(2) nanotube arrays. We studied the growth mechanism of TiO(2) nanotubes on the inner wall of AAO at 100 and 400 degrees C. We found that at 100 degrees C, TiO(2) grew in a layer-by-layer manner. Therefore, it can be grown into TiO(2) nanotube arrays with very thin walls. However, at 400 degrees C, TiO(2) needs to first form a 2.5-nm amorphous layer, before becoming crystalline TiO(2) via a phase transformation, and growing into crystalline TiO(2) nanotube arrays along the preferred plane {101} by means of a space-limited growth mechanism. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528939] All rights reserved.
Growth Mechanism of TiO2 Nanotube Arrays in Nanopores of Anodic Aluminum Oxide on Si Substrates by Atomic Layer Deposition
(2011-01-01)
Liu, Chien-Min
;
Chen, Chih
;
Cheng, Hsyi-En
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this study, we combined atomic layer deposition and anodic aluminum oxide (AAO) on a silicon substrate and developed self-aligned TiO2 nanotube arrays. We studied the growth mechanism of TiO2 nanotubes on the inner wall of AAO at 100 and 400 degrees C. We found that at 100 degrees C, TiO2 grew in a layer-by-layer manner. Therefore, it can be grown into TiO2 nanotube arrays with very thin walls. However, at 400 degrees C, TiO2 needs to first form a 2.5-nm amorphous layer, before becoming crystalline TiO2 via a phase transformation, and growing into crystalline TiO2 nanotube arrays along the preferred plane {101} by means of a space-limited growth mechanism. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528939] All rights reserved.
Low-temperature and low pressure copper-to-copper direct bonding enabled by creep on highly (111)-oriented Cu surfaces
(2015)
Tseng, Chih-Han
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Liu, Chien-Min
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Lin, Han-wen
;
Chu, Yi-Cheng
;
Chen, Chih
Cu-to-Cu microbumps have many advantages, such as better electrical and thermal conductivities. The Cu-to-Cu microbumps may be a potential solution to the heat dissipation problem in 3D IC integration. In addition, for packaging of CMOS image sensors, the bonding temperature is preferred to below 200 degrees C. Therefore, low temperature and low pressure Cu-to-Cu direct is of great interests for packaging industry. However, it is a challenging issue because Cu atoms diffuse slowly below 200 degrees C. In this study, we achieved low temperature and low pressure Cu bonding using highly (111)-orientated Cu films. Because the diffusivity of Cu atoms on the (111) surface diffusivity is the fastest among all the crystallographic planes of Cu. The bonding temperature can be lowered to 150 degrees C at a compressive stress of 114 psi held for 60 min at 10-3 torr. Since the melting points of popular Pb-free solders such as SnAg and SnAgCu are over 230 degrees C. Therefore the present technique can be applied to packaging of CMOS image sensors and 3D IC integration.
LOW-TEMPERATURE AND LOW-PRESSURE DIRECT COPPER-TO-COPPER BONDING BY HIGHLY (111)-ORIENTED NANOTWINNED CU
(2016)
Chen, Chih
;
Liu, Chien-Min
;
Lin, Han-Wen
;
Huang, Yi-Sa
;
Chu, Yi-Cheng
As the size of microbumps continues to shrink, the amount of solder decreases gradually, resulting the brittleness of solder joints due to formation of intermetallic compounds. Low-temperature Cu-to-Cu direct bonding appears to be one of the solutions for fine-pitch microbumps for 3D IC packaging. However, the high bonding temperature and pressure are the main problems of this approach. We achieve low-temperature Cu-to-Cu direct bonding at low pressure and ordinary vacuum. In addition, the cleaning process is simple. To bond the electroplated Cu films, the samples were cut into 3 x 3-mm(2) pieces. Then, the pieces were cleaned in acetone for 5 min, dried with a N-2 purge, cleaned with a mixed solution of HCl and deionized water (DI) water for 30 sec, rinsed with DI water, and purged with N-2 gas again. The bonding temperature can be lowered to 150 degrees C at a compressive stress of 114 psi held for 60 min at 10-3 torr, or at 200 degrees C at for 30 min. The temperature is lower than the reflow temperature of 250 degrees C for most Pb-free solders. We achieve low-temperature bonding using electroplate highly (111)-oriented nanotwinned Cu (nt-Cu) films. Excellent bonding interface can be accomplished by bonding two highly (111)-oriented nt-Cu films. In addition, excellent interface with few voids can be achieved between a highly (111)-oriented nt-Cu film and a randomly-oriented Cu film. Our breakthrough is based on the finding that the (111) orientation of the Cu surface is critical for bonding. The diffusivity of Cu atoms on (111) surfaces is approximately 3-4 orders higher than other major planes. The (111) plane allows for fast surface diffusion, which enables low-temperature creep to occur. The bonded interface between two (111) surfaces forms a twist-type grain boundary (GB). If the GB has a low angle, it has a hexagonal network of screw dislocations. The hexagonal network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface creep will be presented. Our breakthrough provide a potential solution with a huge impact to the interconnect materials in 3D IC. The detail results will be presented in the conference.
Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu
(2015-05-12)
Liu, Chien-Min
;
Lin, Han-Wen
;
Huang, Yi-Sa
;
Chu, Yi-Cheng
;
Chen, Chih
Direct Cu-to-Cu bonding was achieved at temperatures of 150-250 degrees C using a compressive stress of 100 psi (0.69 MPa) held for 10-60 min at 10(-3) torr. The key controlling parameter for direct bonding is rapid surface diffusion on (111) surface of Cu. Instead of using (111) oriented single crystal of Cu, oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nano-twin Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. Such network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface creep is presented; and the calculated and measured time of bonding is in reasonable agreement.